THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC...
Transcript of THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC...
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THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC LIQUIDS FOR
CARBON DIOXIDE CAPTURE
A Thesis
Submitted to the Faculty of Graduate Studies and Research
In Partial Fulfillment of the Requirements
For the Degree of
Master of Applied Science
In
Industrial Systems Engineering
University of Regina
By
Mohamed Farag Zoubeik
Regina, Saskatchewan
July, 2013
Copyright 2013: M. Zoubeik
UNIVERSITY OF REGINA
FACULTY OF GRADUATE STUDIES AND RESEARCH
SUPERVISORY AND EXAMINING COMMITTEE
Mr. Mohamed Farag Zoubeik, candidate for the degree of Mater of Applied Science in Industrial Systems Engineering, has presented a thesis titled, Thermodynamic and Experimental Studies of ionic Liquids for Carbon Dioxide Capture, in an oral examination held on July 25, 2013. The following committee members have found the thesis acceptable in form and content, and that the candidate demonstrated satisfactory knowledge of the subject material. External Examiner: Dr. David deMontigny, Process Systems Engineering
Supervisor: Dr. Amr Henni, Industrial Systems Engineering
Committee Member: Dr. Mohamed Ismail, Industrial Systems Engineering
Committee Member: Dr. Mohamed El-Darieby, Software Systems Engineering
Chair of Defense: Dr. Lisa Watson, Faculty of Business Administration
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Abstract
One of the biggest environmental challenges of our generation is global warming.
Emission of carbon dioxide (CO2) is possibly the most significant greenhouse gas activity
implicated in climate change. As a result, the development of environmentally friendly,
energy efficient and economic capture technologies for CO2 from flue gas is becoming a
hot topic. There have been an evolution of ideas surrounding capture modalities for CO2;
however, none without drawbacks. Ionic Liquids (ILs) offer the potential for a cleaner
capture technology compared to current chemical solvents.
There is a gap in the industrial applied knowledge and data regarding
thermodynamic and physical properties of ionic liquids. The objective of this research
study is to investigate ionic liquids and their potential for CO2 capture at different
concentrations and temperatures. CO2 solubility was obtained using an Intelligent
Gravimetric Analyzer (IGA 003, Hiden Analytical) for the following seven ionic liquids:
1,2,3-Tris(diethylamino) cyclopropenylium dicyanamide, 1-Ethyl-3-methylimidazolium
L-(+)- lactate, 3-Methyl-1-propylpyridinium bis [(trifluoromethyl) sulfonyl]imide,
Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide, 1,2,3-
Tris(diethylamino)cyclopropenylium bis(trifluoromethanesulfonyl)imide, 1-(4-
Sulfobutyl) -3-methylimidazolium Bis(trifluoromethanesulfonyl)imide, 1-(4-Sulfobutyl)-
3-methylimidazolium hydrogen sulfate. Carbon dioxide solubility was obtained at
temperatures of 313.15, 323.15 and 333.15K over a pressure range from 100 mbar to
20,000 mbar. The thermodynamic models used to correlate the experimental CO2
solubility included equations of state, such as the Peng-Robinson (PR-EoS), Sove-
Redlich-Kwong (SRK) with quadratic mixing rules, and Non-Random Two-Liquid
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(NRTL) activity coefficient model. Binary interaction parameters were obtained for the
correlations. All models produced low values for their average absolute deviations,
implying they can satisfactorily describe the solubility of CO2 in ionic liquids. The
solubility of CO2 in all the ionic liquids under study, decreased with increasing
temperature and increased with increasing pressure. Carbon dioxide solubility decreased
in the following order: [TCD][TF2N] > [PMPY][TF2N] > [EMMP][TF2N] >
[emim][LACTATE] > [TCD][DCN] > [(CH2)4SO3HMIm][TF2N] >
[(CH2)4SO3HMIm] [HSO4]. The three ionic liquids, [TCD][TF2N], [PMPY][TF2N]
and [EMMP][TF2N], show promise with respect to CO2 absorption as they have a similar
solubility pattern to some ionic liquids published in the literature that are noted for their
high solubility, such as [hmim][TF2N], which are comparable in terms of their physical
absorption. Furthermore, Henry’s Law constants for CO2 were determined from the ionic
liquids. The enthalpies and entropies of absorption were also calculated.
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Acknowledgments
First and foremost, I would like to give thanks to the Al-mighty Allah for giving me the
opportunity to study in Canada and for providing my health and many blessings. Without
the blessings from Allah none of this would have been possible.
I would like to thank my supervisor, Dr. Amr Henni, for accepting me as a graduate
student and providing the opportunity to come to Saskatchewan. I would also like to
thank him for his support and guidance throughout my studies. My grateful thanks are
extended to Dr. David deMontigny, Dr. Mohamed Ismail, and Dr. Mohamed El-Darieby,
my thesis committee.
I would like to thank my colleagues, Thanawat Nonthanasin and Kazi Zamshad Sumon,
for their support and training throughout my whole research experience, their expertise
was invaluable.
Additionally, I would like to thank the support of the CBIE (Canadian Bureau of
International Education) and the Libyan government for their support and funding of my
studies.
In addition, I would like to thank my parents, my brothers and my sisters, for their
continued support and prayers throughout my studies abroad. I would also like to thank
Dr. Fauzi and Nazmia Ramadan, my in-laws, for their unwavering support and
continuous prayers for my success. I would also like to thank Ahmed Ramadan, my
brother, who helped me settle and make Regina my home.
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Dedication
Dedicated to my mum, Keria Abd Aslam and my wife, Dr. Eman Ramadan for their
support and love.
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Table of Content
ABSTRACT ··························································································· I
ACKNOWLEDGMENTS······································································· III
DEDICATION ···················································································· IV
TABLE OF CONTENT ········································································· III
TABLE OF FIGURES ········································································· VIII
TABLE OF TABLES ········································································· XVII
LIST OF SYMBOLS AND ABBREVIATIONS ······································· XXVI
1 CHAPTER ONE: INTRODUCTION AND BACKGROUND THEORY ··· 1
1.1 INTRODUCTION ············································································· 1
1.2 OBJECTIVE OF THIS RESEARCH UNDERTAKING ······································· 1
1.3 BACKGROUND ·············································································· 2
1.3.1 Sources Of CO2 Emissions ···························································· 2
1.4 CAPTURE OF CO2 ·········································································· 2
1.4.1 Capture Systems For CO2: Pre, Oxy, And Post-Combustion ···················· 2
1.5 IONIC LIQUID CAPTURE TECHNOLOGY ·················································· 4
1.5.1 What Are Ionic Liquids? ······························································ 4
1.5.2 Synthesis Of Ionic Liquids ···························································· 5
1.5.3 What Are The Categories Of Ionic Liquids? ······································· 6
1.6 HISTORY OF IONIC LIQUID USE FOR CO2 CAPTURE AND THE DEVELOPMENT OF
IONIC LIQUIDS ······················································································ 8
1.6.1 Before The Development Of Ionic Liquids ········································· 8
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1.6.2 History And New Developments Of Ionic Liquids ································ 8
1.7 THERMOPHYSICAL PROPERTIES OF IONIC LIQUIDS ··································· 10
1.7.1 Physical Properties Of Ionic Liquids ··············································· 10
1.8 CO2 SOLUBILITY IN IONIC LIQUIDS AND FACTORS THAT AFFECT SOLUBILITY ·· 13
1.9 NEW DEVELOPMENTS IN THE PURSUIT OF THE PERFECT IONIC LIQUID:
LITERATURE REVIEW ············································································· 19
1.10 OUTLINE OF THE CHAPTERS ···························································· 26
2 CHAPTER TWO: GENERAL METHODOLOGY, THEORY AND
EXPERIMENTAL DETAILS ·································································· 27
2.1 METHODS FOR GAS SOLUBILITY MEASUREMENTS ··································· 27
2.1.1 Pressure Drop Technique For Measuring CO2 Solubility ······················· 27
2.1.2 Stoichiometric Technique For Measuring CO2 Solubility ······················· 28
2.1.3 Gravimetric Method For Measuring CO2 Solubility ····························· 29
2.1.4 Gravimetric Method: Buoyancy Correction Factor ······························ 31
2.1.5 Calculation Of Buoyancy Correction Factor ······································ 32
2.2 THERMODYNAMIC PROPERTIES ························································· 34
2.2.1 Derivation For Henry’s Law Constants ············································ 34
2.2.2 Derivation For Enthalpy And Entropy Of Absorption ··························· 35
2.3 MATERIALS ················································································ 37
2.3.1 Ionic Liquids ··········································································· 37
2.3.2 Ionic Liquid Treatment And Equilibrium Time ··································· 39
2.3.3 Selection Of Ionic Liquids ··························································· 41
2.3.4 Gases ···················································································· 42
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2.4 GRAVIMETRIC MICROBALANCE ························································· 42
2.5 EXPERIMENTAL PROCEDURE ···························································· 44
2.6 SUMMARY OF EXPERIMENTAL PROCEDURES ········································· 45
2.7 ACCOUNTING FOR BUOYANCY ·························································· 48
2.8 ENSURING EQUILIBRIUM ································································· 48
2.9 ERROR ANALYSIS ········································································· 49
3 CHAPTER THREE: RESULTS AND DISSCUSION ·························· 50
3.1 DENSITY OF PURE IONIC LIQUIDS ······················································ 50
3.2 SOLUBILITY OF CARBON DIOXIDE ····················································· 53
3.2.1 Verification Of Measurements ······················································ 53
3.2.2 Experimental Isotherm CO2 Solubility ············································· 54
3.3 SOLUBILITY ISOTHERMS GRAPHS ······················································· 58
3.3.1 Solubility Of CO2 In [EMMP][TF2N] ············································· 58
3.3.2 Solubility Of CO2 In [TDC] [TF2N] ··············································· 59
3.3.3 Solubility Of Co2 In [PMPY] [TF2N] ·············································· 60
3.3.4 Solubility Of CO2 In [TDC] [DCN] ················································ 61
3.3.5 Solubility Of CO2 In [EMIM] [LACTATE] ······································· 62
3.3.6 Solubility Of CO2 In [(CH2)4SO3HMIm][TF2N] And
[(CH2)4SO3HMIm][HSO4] ································································· 63
3.4 RESULTS: EFFECTS OF CATION WITH [TF2N] ANION ······························· 64
3.4.1 Discussion: Effects Of Cation With [TF2N] Anion ······························ 65
3.5 RESULTS: EFFECTS OF ANION WITH [TDC] CATION ································ 66
3.5.1 Discussion Results: Effects Of Anion With [TDC] Cation ····················· 67
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3.6 RESULTS: COMPARISON OF THE [DCN] ANION WITH DIFFERENT CATIONS ····· 68
3.6.1 Discussion: Comparison Of The [DCN] Anion With Different Cations ······ 69
3.7 COMPARISON OF ALL THE IONIC LIQUIDS STUDIED ································· 70
3.8 COMPARISONS OF CURRENT WORK WITH PREVIOUSLY PUBLISHED WORK ······ 72
3.8.1 Effect Of Changing The Cation ····················································· 73
3.8.2 Effect Of Changing The Anion With An [Emim] Cation ······················· 79
3.9 COMPARING THE LITERATURE WITH [BMIM][AC] ··································· 80
3.10 COMPARISON OF AMMONIUM BASED IONIC LIQUID FROM THE LITERATURE AND
CURRENT WORK ·················································································· 81
3.11 COMPARING THE CURRENT WORK WITH RECENT RESULTS FROM AN AFFILIATED
GROUP ······························································································ 84
4 CHAPTER FOUR: MODELING ··················································· 96
4.1 THEORY OF THERMODYNAMIC PROPERTIES AND MODELING ······················ 96
4.1.1 Peng Robinson Eos ···································································· 97
4.1.2 Soave-Redlich-Kwong (The SRK With Quadratic Mixing Rules) ············· 98
4.1.3 NRTL Activity Coefficient Method ·············································· 100
4.2 THERMODYNAMIC MODELING ························································ 101
4.2.1 Critical Property Estimation ······················································· 101
4.2.2 Modified Lydersen‐Joback‐Reid Method ········································ 101
4.2.3 Calculated Density And Deviation %Δp From Experimental Density ······ 103
4.3 EQUATION OF STATE ·································································· 107
4.3.1 The Standard Peng-Robinson (PR-Eos) ·········································· 107
4.3.2 Modeling Graphs Using PR-Eos For All Ils ····································· 109
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4.3.3 The Soave-Redlich-Kwong (SRK) With Quadratic Mixing Rules ··········· 116
4.3.4 Modeling Graphs Using SRK -Eos For All Ils ·································· 117
4.3.5 Non-Random Two Liquid Segment Activity Coefficient (NRTL) ··········· 122
4.3.6 Modeling Graphs Using NRTL For All Ils ······································ 124
4.4 HENRY’S LAW CONSTANTS ··························································· 131
4.5 ENTHALPIES AND ENTROPIES OF ABSORPTION ····································· 133
5 CHAPTER FIVE: CONCLUSION ··············································· 134
REFERENCES ··················································································· 137
6 APPENDIX ············································································ 143
6.1 RAW DATA FOR GAS SOLUBILITY MEASUREMENTS USING THE GRAVIMETRIC
MICROBALANCE ················································································· 143
6.2 MODELING RESULTS ··································································· 158
6.3 HENRY’S LAW CONSTANTS AND ENTHALPIES AND ENTROPIES OF ABSORPTION
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Table of Figures
Figure 1.1: Block diagrams illustrating post-combustion, pre-combustion, and oxy-
combustion systems (Figueroa et al., 2007)........................................................................ 3
Figure 1.2: Common routes for the preparation of ionic liquids (Arshad, 2009). .............. 5
Figure 1.3: Common anions and cations that make up ionic liquids (Ramdin et al., 2012).
............................................................................................................................................. 7
Figure 1.4: The effect of an anion on viscosity for a common [bmim] cation (Ramdin et
al., 2012). .......................................................................................................................... 12
Figure 1.5: the effect of alkyl chain length on viscosity for all IL classes (Ramdin et al.,
2012). ................................................................................................................................ 12
Figure 1.6: The effect of changing the cation on CO2 solubility (Ramdin et al., 2012). .. 15
Figure 1.7: CO2 solubility in [bmim][PF6] at 283.15, 298.15, and 273.15 K (10, 25 and 50
C) (Anthony et al., 2002). ............................................................................................... 16
Figure 1.8: Effect of fluorination on CO2 solubility (Ramdin et al., 2012). ..................... 17
Figure 1.9: The effect of the alkyl chain length on CO2 solubility (Ramdin et al., 2012).19
Figure 1.10: Comparison of the solubility of CO2 in different ionic liquids at 313 K: (■)
THEAL; (●) [bmim][PF6]; (▲) [omim][PF6]; (▼) [Nbupy][BF4]; (♦) [emim][EtSO4]
(Yuan et al., 2007). ........................................................................................................... 24
Figure 2.1: Pressure drop technique for measuring CO2 solubility (Brennecke et al, 2008).
........................................................................................................................................... 28
Figure 2.2: Stoichiometric gas solubility apparatus (Brennecke et al., 2008). ................. 29
Figure 2.3: Schematic diagram of IGA003 gravimetric microbalance. Symbols: arrow B
indicates direction due to buoyancy on the sample side of the balance, arrow Wg
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indicates direction of weight due to gravity on the sample side of the balance, additional
symbols described in Table 1 (Shiflett and Yokozeki, 2005). .......................................... 30
Figure 2.4: IGA apparatus (http://www.zpph.com/userfiles/file/iga_series_brochure.pdf)
........................................................................................................................................... 31
Figure 2.5:[TDC] [DCN] equilibrium under 1000 millibars and 40
°C............................ 39
Figure 2.6: [EMIM] [LACTATE] equilibrium under 1000 millibars pressure at 40
°C. . 40
Figure 2.7: Gravimetric microbalance .............................................................................. 43
Figure 2.8: Schematic of the gravimetric microbalance ................................................... 44
Figure 2.9: Experimental procedure followed when using IGA ....................................... 45
Figure 2.10: [TDC] [TF2N] equilibrium providing at high pressure................................ 48
Figure 3.1: Liquid density of the studied ionic liquids at temperatures ranging from
278.15 K to 353.15 K. ....................................................................................................... 52
Figure 3.2: Solubility of CO2 in [bmim][PF6] at 323.15 K compared to the solubility data
result this work with previously published results : ● [bmim][PF6],green this work; ■
[bmim][PF6],red, (Shiflett, 2005); ▼[bmim][PF6],blue, (Anthony et al., 2002). ........... 53
Figure 3.3: Comparison of measured isothermal solubility data of CO2 in
[EMMP][TF2N] at 313.15, 323.15 and 333.15 K. ........................................................... 58
Figure 3.4: Comparison of measured isothermal solubility data of CO2 in [TDC][TF2N]
at 313.15, 323.15 and 333.15 K. ....................................................................................... 59
Figure 3.5: Comparison of measured isothermal solubility data of CO2 in [PMPY][TF2N]
at 313.15, 323.15 and 333.15 K. ....................................................................................... 60
Figure 3.6: Comparison of measured isothermal solubility data of CO2 in [TDC][DCN] at
313.15, 323.15 and 333.15 K. ........................................................................................... 61
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Figure 3.7: Comparison of measured isothermal solubility data of CO2 in
[EMIM][LACTATE] at 313.15, 323.15 and 333.15 K. .................................................... 62
Figure 3.8: Comparison of measured isothermal solubility data of CO2 in
[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and
333.15 K. ........................................................................................................................... 63
Figure 3.9: Comparison of three ionic liquids with the same anion to illustrate the effect
of the cation at 313 K. ....................................................................................................... 64
Figure 3.10: Comparison of CO2 solubility of [TDC] with [TF2N] and [DCN] at 313.15
K ........................................................................................................................................ 67
Figure 3.11: Comparison of CO2 solubility of [TDC] with [bmim] cations with same
anion at 313.15 K. ............................................................................................................. 69
Figure 3.12: Comparison of measured isothermal solubility data of CO2 in different ionic
liquids at 313.15 K ............................................................................................................ 70
Figure 3.13: Comparison of [emim][Ac] and [emim][LACTATE] at 50°C. ................... 72
Figure 3.14: Comparison of CO2 solubility at 333.15 K with different cations paired with
the [TF2N] anion............................................................................................................... 74
Figure 3.15: Comparison of CO2 solubility at 60°C with different cations paired with the
[TF2N] anion at 333.15 K and about 12 to 14.97 bar. ...................................................... 75
Figure 3.16: Comparison of CO2 solubility in different ILs with the same anion at 323.15
K ........................................................................................................................................ 77
Figure 3.17: Comparison of changing the anion with limidazoloium cation ................... 79
Figure 3.18: Comparison between the solubility of CO2 in the studied ionic liquids and
published results in the literature at 323.15 K .................................................................. 81
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Figure 3.19: Comparison between the solubility of CO2 in the studied ionic liquids and
the published results in the literature at 323.15 K and high pressure from 1 to 120 bar. . 82
Figure 3.20: Comparison of CO2 solubility at 323.15 K .................................................. 86
Figure 3.21: Comparison of CO2 solubility at 323.15 K ................................................... 87
Figure 3.22: CO2 solubility comparing the ionic liquids used in this work with that of
Nonthanasin (2013) ........................................................................................................... 88
Figure 3.23: Comparison of the solubility of CO2 in the studied ionic liquids and the one
in the present research at 313.15 K. .................................................................................. 89
Figure 3.24: Comparison of the solubility of CO2 in the studied ionic liquids and Uygur,
2013 at 323.15 K. .............................................................................................................. 90
Figure 3.25: Comparison of the solubility of CO2 in the studied ionic liquids and the ones
in our group at 323.15 K. .................................................................................................. 91
Figure 3.26: CO2 solubility of different best ionic liquid in this work, (Ugyur, 2013) and
(Nonthanasin, 2013) at 323.15 K. ..................................................................................... 92
Figure 3.27: Summary of the CO2 solubilities in decreasing order from this work, (Ugyur,
2013) and (Nonthanasin, 2013) at 323.15 K at same pressure 19 bar. ............................. 94
Figure 4.1: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green. .......................................................... 109
Figure 4.2: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
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333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15K; green. ........................................................... 110
Figure 4.3: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green. .......................................................... 111
Figure 4.4: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green. .......................................................... 112
Figure 4.5: P-x diagram of the system [EMIM][LACTATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at
313.15 K; blue, at 323.15 K; red and at 333.15K; green. ............................................... 113
Figure 4.6: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]] and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the standard PR-EoS: at 313.15 K;
blue, at 323.15 K; red. ..................................................................................................... 114
Figure 4.7: P-x diagram of the system [(CH2)4SO3HMIm][HSO4] and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the standard PR-EoS: at 313.15 K;
blue, at 323.15 K; red. ..................................................................................................... 115
xiii
Figure 4.8: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. ................................ 117
Figure 4.9: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K, green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. ................................ 118
Figure 4.10: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. ................................ 119
Figure 4.11: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. ................................ 120
Figure 4.12: P-x diagram of the system [EMIM][LCATATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by the SRK with quadratic
mixing rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. .................... 121
Figure 4.13: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
xiv
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green. ............................................................................ 124
Figure 4.14: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green. ............................................................................ 125
Figure 4.15: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green. ............................................................................ 126
Figure 4.16: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green. ............................................................................ 127
Figure 4.17: P-x diagram of the system [EMIM][LACTATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by NRTL: at 313.15 K;
blue, at 323.15 K; red and at 333.15 K; green. ............................................................... 128
Figure 4.18: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red. ................................................................................................................. 129
xv
Figure 4.19: P-x diagram of the system [(CH2)4SO3HMIm][HSO4]and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red. ................................................................................................................. 130
Figure 4.20: Henry’s law constants for CO2 in [EMMP][TF2N], [PMPY][TF2N],
[TDC][TF2N], [TDC][DCN], [EMIM][LACTATE], [(CH2)4SO3HMIm][TF2N] and
[(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and 333.15 K ....................................... 132
Figure 6.1: Determining the Henry’s law constant for CO2 in [bmim][PF6] ................. 185
Figure 6.2: Determining the enthalpy of absorption for CO2 in [bmim][PF6] ............... 185
Figure 6.3: Determining the entropy of absorption for CO2 in [bmim][PF6] ................. 186
Figure 6.4: Determining the Henry’s law constant for CO2 in [Emmp][TF2N] ............. 188
Figure 6.5: Determining the entropy of absorption for CO2 in [Emmp][TF2N] ............ 189
Figure 6.6: Determining the entropy of absorption for CO2 in [Emmp][TF2N] ............ 190
Figure 6.7: Determining the Henry’s law constant for CO2 in [PMPY][TF2N] ............ 192
Figure 6.8: Determining the enthalpy of absorption for CO2 in [PMPY][TF2N] .......... 193
Figure 6.9: Determining the entropy of absorption for CO2 in [PMPY][TF2N] ............ 194
Figure 6.10: Determining the Henry’s law constant for CO2 in [TDC][TF2N] ............. 196
Figure 6.11: Determining the enthalpy of absorption for CO2 in [TDC][TF2N] ........... 197
Figure 6.12: Determining the entropy of absorption for CO2 in [TDC][TF2N] ............. 197
Figure 6.13: Determining the Henry’s law constant for CO2 in [TDC][DCN] .............. 199
Figure 6.14: Determining the enthalpy of absorption for CO2 in [TDC][DCN] ............ 200
Figure 6.15: Determining the entropy of absorption for CO2 in [TDC][DCN] .............. 201
Figure 6.16: Determining the Henry’s law constant for CO2 in [EMIM][LACTATE] .. 203
xvi
Figure 6.17: Determining the enthalpy of absorption for CO2 in [EMIM][LACTATE] 203
Figure 6.18: Determining the entropy of absorption for CO2 in [EMIM][LACTATE] . 204
Figure 6.19: Determining the Henry’s law constant for CO2 in [(CH2)4SO3HMIm]
[HSO4] ............................................................................................................................ 206
Figure 6.20: Determining the enthalpy of absorption for CO2 in [(CH2)4SO3HMIm]
[HSO4] ............................................................................................................................ 207
Figure 6.21: Determining the entropy of absorption for CO2 in [(CH2)4SO3HMIm]
[HSO4] ............................................................................................................................ 208
Figure 6.22: Determining the Henry’s law constant for CO2 in
[(CH2)4SO3HMIm][TF2N] ........................................................................................... 210
Figure 6.23: Determining the enthalpy of absorption for CO2 in
[(CH2)4SO3HMIm][TF2N] ........................................................................................... 211
Figure 6.24: Determining the entropy of absorption for CO2 in
[(CH2)4SO3HMIm][TF2N] ........................................................................................... 212
xvii
Table of Tables
Table 2-1: Microbalance components for buoyancy correction ....................................... 33
Table 2-2: Ionic liquids studied with their short hand notation and structure. ................. 37
Table 2-3: Ionic liquids used and their specifications: ..................................................... 38
Table 2-4: Calculation of weight lost for each ionic liquid at 313.15K and the percent
impurity lost ...................................................................................................................... 46
Table 3-1: Experimental densities of pure ionic liquids measured at 1.01325 bar ........... 51
Table 3-2: Temperature-dependent density correlations for the ionic liquids .................. 52
Table 3-3: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [TDC][DCN] (1) + CO2 at 313.15, 323.15 and 333.15 K. ......................................... 54
Table 3-4: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [PMPY][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ..................................... 55
Table 3-5: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [EMMP][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ..................................... 55
Table 3-6: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [TDC][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ......................................... 56
Table 3-7: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [EMIM][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ...................................... 56
Table 3-8: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [[(CH2)4SO3HMIm][TF2N]] (1) + CO2 at 313.15, 323.15 and 333.15 K. ................ 57
Table 3-9: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [(CH2)4SO3HMIm][HSO4] (1) + CO2 at 313.15, 323.15 and 333.15 K. .................. 57
Table 3-10: Numerical representation summary of the IL seen in Figure 3.14 ................ 75
xviii
Table 3-11: Comparison of [emim] cation with different anions. .................................... 80
Table 3-12: Summary of the CO2 solubilities in decreasing order from this work, Ugyur
(2013) and Nonthanasin (2013) at 323.15 K and same pressure 19 bar. .......................... 93
Table 4-1: Molecular weights, normal boiling temperatures, critical properties, and
acentric factors of ionic liquids ....................................................................................... 103
Table 4-2: Regressed and Experimental Density Data of [EMMP] [TF2N] by using
Modified Group Contribution Method............................................................................ 103
Table 4-3: Regressed and Experimental Density Data of [PMPY] [TF2N] by using
Modified Group Contribution Method............................................................................ 104
Table 4-4: Regressed and Experimental Density Data of [TDC] [TF2N] by using
Modified Group Contribution Method............................................................................ 104
Table 4-5: Regressed and Experimental Density Data of [EMIM] [LACTATE] by using
Modified Group Contribution Method............................................................................ 105
Table 4-6: Regressed and Experimental Density Data of [TDC] [DCN] by using Modified
Group Contribution Method ........................................................................................... 105
Table 4-7: Regressed and Experimental Density Data [(CH2)4SO3HMIm][TF2N] by
using Modified Group Contribution Method .................................................................. 106
Table 4-8: Regressed and Experimental Density Data [(CH2)4SO3HMIm][HSO4] ..... 106
Table 4-9: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the standard PR-EoS for the ionic liquids + CO2 system ............. 108
Table 4-10: Binary interaction parameters of the standard PR-EoS for the ionic liquids (1)
+ CO2 (2) system. ............................................................................................................ 108
xix
Table 4-11: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the SRK with quadratic mixing rules for the ionic liquids + CO2
system ............................................................................................................................. 116
Table 4-12: Binary interaction parameters of the SRK with quadratic mixing rules for the
ionic liquids (1) + CO2 (2) system .................................................................................. 117
Table 4-13: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the NRTL for the ionic liquids + CO2 system .............................. 122
Table 4-14: Binary interaction parameters of the NRTL for the ionic liquids (1) + CO2 (2)
system (α = 0.3) .............................................................................................................. 123
Table 4-15: Henry’s law constants and enthalpies and entropies of absorption for CO2 in
the studied ionic liquids .................................................................................................. 132
Table 6-1: Carbon dioxide in [Emmp][TF2N] at 313.15 K ........................................... 143
Table 6-2: Carbon dioxide in [Emmp][TF2N] at 323.15 K ............................................ 144
Table 6-3: Carbon dioxide in [Emmp][TF2N] at 333.15 K ............................................ 145
Table 6-4: Carbon dioxide in [Pmpy][TF2N] at 313.15 K ............................................. 146
Table 6-5: Carbon dioxide in [Pmpy][TF2N] at 323.15 K ............................................. 147
Table 6-6: Carbon dioxide in [Pmpy][TF2N] at 333.15 K ............................................. 148
Table 6-7: Carbon dioxide in [TDC][TF2N] at 313.15 K .............................................. 149
Table 6-8: Carbon dioxide in [TDC][TF2N] at 323.15 K .............................................. 150
Table 6-9: Carbon dioxide in [TDC][TF2N] at 333.15 K .............................................. 151
Table 6-10: Carbon dioxide in [EMIM][LACTATE] at 313.15 K ................................. 152
Table 6-11: Carbon dioxide in [EMIM][LACTATE] at 323.15 K ................................. 153
Table 6-12: Carbon dioxide in [EMIM][LACTATE] at 333.15 K ................................. 153
xx
Table 6-13: Carbon dioxide in [TDC][DCN] at 313.15 K.............................................. 154
Table 6-14: Carbon dioxide in [TDC][DCN] at 323.15 K.............................................. 155
Table 6-15: Carbon dioxide in [(CH2)4SO3HMIm][TF2N]at 313.15 K ....................... 155
Table 6-16: Carbon dioxide in [(CH2)4SO3HMIm][TF2N] at 323.15 K ...................... 156
Table 6-17: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K ....................... 156
Table 6-18: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K ....................... 157
Table 6-19: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 313.15 K........................................................ 158
Table 6-20: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 323.15 K........................................................ 158
Table 6-21: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 333.15 K........................................................ 159
Table 6-22: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K ........................................................ 159
Table 6-23: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 323.15 K ........................................................ 160
Table 6-24: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 333.15 K ......................................................... 160
Table 6-25: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 313.15 K. .................................................................................. 161
Table 6-26: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 323.15 K ................................................................................... 161
xxi
Table 6-27: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 333.15 K ................................................................................... 162
Table 6-28: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN
(1) + CO2 (2) system at 313.15 K ................................................................................... 163
Table 6-29: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN]
(1) + CO2 (2) system at 323.15 K. .................................................................................. 163
Table 6-30: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN]
(1) + CO2 (2) system at 333.15 K ................................................................................... 164
Table 6-31: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 313.15 K ................................................ 164
Table 6-32: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 323.15 K ................................................ 165
Table 6-33: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 333.15 K ................................................ 165
Table 6-34: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 313.15 K .................................... 165
Table 6-35: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 323.15 K .................................... 166
Table 6-36: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 313.15 K .................................... 166
Table 6-37: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 323.15 K .................................... 167
xxii
Table 6-38: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K ........................................................ 167
Table 6-39: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 323.15 K ........................................................ 168
Table 6-40: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 333.15 K ........................................................ 168
Table 6-41: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 313.15 K ........................................................... 169
Table 6-42: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 323.15 K ........................................................... 169
Table 6-43: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 333.15 K ........................................................... 170
Table 6-44: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 313.15 K ............................................................ 170
Table 6-45: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 323.15 K. ........................................................... 171
Table 6-46: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 333.15 K. ........................................................... 171
Table 6-47: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMIM][LACTATE] (1) + CO2 (2) system at 313.15 K. ............................................... 172
Table 6-48: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMIM][LACTATE] (1) + CO2 (2) system at 323.15 K. ............................................... 172
xxiii
Table 6-49: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMMP][LACTATE] (1) + CO2 (2) system at 333.15 K. .............................................. 173
Table 6-50: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 313.15 K. ................................................................................................... 173
Table 6-51: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 323.15 K. ................................................................................................... 174
Table 6-52: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 333.15 K. ................................................................................................... 174
Table 6-53: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 313.15 K. ................................................................................................... 175
Table 6-54: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 323.15 K. ................................................................................................... 175
Table 6-55: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 333.15 K. ................................................................................................... 176
Table 6-56: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 313.15 K. ......................................................................................................... 176
Table 6-57: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 323.15 K. ......................................................................................................... 177
Table 6-58: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 333.15 K. ......................................................................................................... 178
Table 6-59: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 313.15 K. ......................................................................................................... 178
xxiv
Table 6-60: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 323.15 K. ......................................................................................................... 179
Table 6-61: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 333.15 K. ......................................................................................................... 179
Table 6-62: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 313.15 K. ........................................................................................... 180
Table 6-63: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 323.15 K. ........................................................................................... 180
Table 6-64: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 333.15 K. ........................................................................................... 181
Table 6-65: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][HSO4]
(1) + CO2 (2) system at 313.15 K. .................................................................................. 181
Table 6-66: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][HSO4]
(1) + CO2 (2) system at 323.15 K. .................................................................................. 182
Table 6-67: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][TF2N]]
(1) + CO2 (2) system at 313.15 K. .................................................................................. 182
Table 6-68: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][TF2N]]
(1) + CO2 (2) system at 323.15 K. .................................................................................. 183
Table 6-69: Experimental fugacity of CO2 in [bmim][PF6] (Shiflett, 2005) at 283.15 K
......................................................................................................................................... 184
Table 6-70: Experimental fugacity of CO2 in [bmim][PF6] (Shiflett, 2005) at 323.15 K
......................................................................................................................................... 184
Table 6-71: Experimental fugacity of CO2 in [Emmp][TF2N] at 313.15 And 323.15 K 187
xxv
Table 6-72: Experimental fugacity of CO2 in [Emmp][TF2N] at 333.15 K ................... 188
Table 6-73: Experimental fugacity of CO2 in [PMPY][TF2N] at 313.15 And 323.15 K191
Table 6-74: Experimental fugacity of CO2 in [PMPY][TF2N] at 333.15 K. ................. 192
Table 6-75: Experimental fugacity of CO2 in [TDC][TF2N] at 313.15 And 323.15 K .. 195
Table 6-76: Experimental fugacity of CO2 in [TDC][TF2N] at 333.15 K ..................... 196
Table 6-77: Experimental fugacity of CO2 in [TDC][DCN] at 313.15 And 323.15 K ... 198
Table 6-78: Experimental fugacity of CO2 in [TDC][DCN] at 333.15 K ...................... 199
Table 6-79: Experimental fugacity of CO2 in [EMIM][LACTATE] at 313.15 ,323.15 and
333.15 K .......................................................................................................................... 202
Table 6-80: Experimental fugacity of CO2 in [(CH2)4SO3HMIm] [HSO4] at 313.15 And
323.15 K .......................................................................................................................... 205
Table 6-81: Experimental fugacity of CO2 in [(CH2)4SO3HMIm][TF2N] at 313.15 And
323.15 K .......................................................................................................................... 209
xxvi
List of Symbols And Abbreviations
Abbreviations:
RTILs Room temperature ionic liquids
VLE Vapour-liquid equilibrium
LLE Liquid liquid Equilibrium
SRK Sove-Redlich-Kwong
PR Peng-Robinson
AAD Average absolute deviation
EoS Equation of state
NRTL Non-random two-liquid models
DMA Digital density meter
IGA Intelligent gravimetric analyzer
Greek symbols:
γi Activity coefficient
ρ Density (kg/m3)
∆ represents a change
ω Acentric factor
Subscripts:
1 Component 1
2 Component 2
i i-th component
j j-th component
xxvii
Symbols:
F Fugacity (bar)
H Henry’s constant (bar)
K Kelvin
M Molar mass (g/mole)
Pc Critical pressure (bar)
Zc Critical compressibility factor
Tc Critical temperature (K)
Vc Critical volume (cm3/mol)
Tb Boiling point temperature
R Universal gas constant (cm3.bar/mole .K)
x Mole fraction in liquid phase
∆h Enthalpies
∆s Entropies
Cb Buoyancy
1
1 Chapter One: Introduction And Background Theory
1.1 Introduction
One of the biggest environmental challenges of our generation is global warming.
Emission of carbon dioxide (CO2) is possibly the most significant greenhouse gas activity
implicated in climate change. As a result, the development of environmentally friendly,
energy efficient and economic capture technologies for CO2 is becoming a hot topic.
There has been an evolution of ideas surrounding capture modalities for CO2; however,
none without drawbacks. In the midst of the advances in promising technologies for CO2
capture, ionic liquids (IL) have been given much attention and are regarded as
prospective candidates (MacDowell et al., 2010; Blanchard et al., 1999; Wappel et al.,
2010).
1.2 Objective of This Research Undertaking
There is a gap in the industrial applied knowledge and data regarding the
thermodynamic and physical properties of ionic liquids. There is a need for translation of
this knowledge into large scale industrial applications using simulation models to predict
the behaviors of ionic liquids in industrial applications. The objective of this research
study is to investigate different ionic liquids and their potential capacity for CO2 capture
at different temperatures and pressures. In addition, we hope to find some features and
physical characteristics that would allow us to contribute some knowledge towards the
industrial application of ionic liquids for CO2 capture.
2
1.3 Background
1.3.1 Sources of CO2 Emissions
Human activities, especially activities aimed at energy production, are the principal
sources of CO2 emission, of which fossil fuel combustion comprises the vast majority.
Carbon dioxide is the main greenhouse gas with emissions increasing by 80% from 1970
to 2004 (Pachauri and Reisinger, 2007).
Other than fossil fuels, deforestation produces about 17% of the global emissions
which places it in third place as the largest source of greenhouse gas emissions (Eliasch,
2008). Other sources include the transportation industry and residential and commercial
buildings (Pachauri and Reisinger, 2007).
1.4 Capture of CO2
1.4.1 Capture systems for CO2: Pre, Oxy, and Post-combustion
There are various stages where CO2 can be captured. The research interest of this
project will focus mainly on natural gas sweetening but also, to a lesser extent, post-
combustion CO2 capture from flue gases. Industrial power plants use atmospheric air
which contains about 80% nitrogen from combustion which generates a flue gas at
atmospheric pressure with about 15% CO2 concentration (Figueroa et al., 2007). The
flue gas has a CO2 partial pressure of about 0.15 atm or less, making it technically
challenging to design an effective capture medium (Figueroa et al., 2007). However,
as previously stated, ionic liquids are showing great promise as an effective capture
medium. Their physical properties allow for good CO2 solubility even at low
pressures and the fact that they are stable at high temperatures removes the need to
3
cool the flue gas before CO2 recovery, decreasing operating expenses and energy
expenditures.
Figure 1.1: Block diagrams illustrating post-combustion, pre-combustion, and oxy-
combustion systems (Figueroa et al., 2007).
4
1.5 Ionic Liquid Capture Technology
1.5.1 What Are Ionic Liquids?
Ionic liquids are liquids which are made up of ions. The ions are of two types:
cations and anions. Ionic liquids are different than ionic solutions which are just solutions
of salts in a molecular solvent (Arshad, 2009). Ionic liquids which are liquid at room
temperature are called room temperature ionic liquids (RTIL) (Arshad, 2009). Ionic
liquids are sometimes called liquid organic salts, fused salts or molten salts which are
mainly found in older literature (Arshad, 2009).
The main feature defining the essence of ionic liquids is a melting point of 100ºC
which is made possible by the asymmetry of the cation used in the ionic liquid (Dzyuba
and Bartsch, 2002). On the other hand, the anion is responsible for many of the ionic
liquids’ key physical properties (Dzyuba and Bartsch, 2002). The physical properties of
ionic liquids (melting point, viscosity, density, solubility) can be altered with a specific
task in mind by mixing which cation, anion or substituent is used. Hence the name
“designer solvent” came about (Freemantle, 1998). Ionic liquids have many advantages
over molecular solvents such as very low vapor pressure and thermal stability over a wide
range of temperatures (Arshad, 2009). Ionic liquids are also non-flammable (Arshad,
2009). Ionic liquid fluids are an alternative to volatile conventional solvents and this
leads to a major decrease in the atmospheric release of volatile organic compounds which
are a major source of air pollution (Arshad, 2009). Thus, ionic liquids are a green
beacon of hope for environmentally clean industrial processing of natural and flue gases.
5
1.5.2 Synthesis of Ionic Liquids
The following figure outlines a summary of how a sample ionic liquid is
synthesized.
Figure 1.2: Common routes for the preparation of ionic liquids (Arshad, 2009).
6
1.5.3 What Are The Categories Of Ionic Liquids?
Ionic liquids, previously defined as stable molten salts, can be categorized into
three groups: First generation, second generation, and third generation ionic liquids
(Holbrey and Seddon, 1999).
First Generation: This group encompasses the original ionic liquids that were
pyridinium- and imidazolium-based chloroaluminate ionic liquids (Wilkes, 2002).
They react with water to form HCL and thus are not water stable. They have many
drawbacks which include their reactivity with water which leads to a loss of the ionic
liquid and the production of corrosive byproducts.
Second Generation: This group of ionic liquids was developed as moisture stable
ionic liquids which allowed for easier use and wider applications. It also solved the
issue of corrosive byproducts and loss of ionic liquid. This group includes the first
moisture stable imidazolium salts paired with BF4 and PF6 anions (Wilkes, 1992).
Third Generation: This group is the task specific group of ionic liquids. This new
emerging group of ionic liquids features a special ability, to be tailored based on the
attached functionalities for a specific function or task. This idea of designing ionic
liquids was first proposed by Bates et al. in 2001 (Bates et al., 2001).
The following figure is an example of commonly used anions and cations that
make up ionic liquids (Ramdin et al., 2012).
7
Figure 1.3: Common anions and cations that make up ionic liquids (Ramdin et al.,
2012).
8
1.6 History of Ionic Liquid Use for CO2 Capture And The Development Of Ionic
Liquids
1.6.1 Before The Development of Ionic Liquids
Chemical absorption of CO2 by a weakly basic solution of monoethanolamine
(MEA) is, historically, one of the most popular industrial process for CO2 capture
(Sánchez, 2008). MEA was developed over seventy years ago as a non-specific
solvent to remove acidic gases such as CO2 and H2S from natural gas streams
(Herzog, 1999). However, MEA use had some drawbacks. During the capture
process, the amine group in MEA is broken down (Strazisar et al., 2003). The
byproducts of MEA degradation decrease the efficiency of CO2 capture, leading to
corrosion of machinery and the loss of solvent (Strazisar et al., 2003). When
comparing ionic liquid use with MEA, the use of IL can reduce the energy losses by
16% and provide a 12% reduction in the equipment footprint (Zhang et al., 2012).
The industry sought out a better alternative to MEA that would not increase material
and waste disposal costs (Strazisar et al., 2003). An alternative method to MEA is the
use of chilled ammonia (Wang et al., 2010). Ammonia also has its own set of
drawbacks. The low temperatures needed to minimize solvent losses lead to increased
energy expenditures and higher operating costs (Wang et al., 2010). Hence, there was
a large need by industry to revolutionize CO2 capture modalities.
1.6.2 History and New Developments of Ionic Liquids
Carbon dioxide capture took on a new life with the development of ionic liquids
as a solvent medium for absorption. The extremely low vapor pressure of ionic
liquids makes them non-volatile which is a major advantage (Sánchez, 2008). The
9
new development this kind of solvent allows for decreased solvent losses and thus
lower operating costs and a cleaner gaseous product (Sánchez, 2008). There were
issues with reactivity with water when ionic liquids first came about. The pyridinium-
and imidazolium-based chloroaluminate ionic liquids predated the moisture stable
salts. The ILs reacted with water (Wilkes, 2002) and produced a corrosive byproduct
(HCL). Zaworotko first proposed the idea of developing water stable ionic liquids in
1990 (Wilkes, 2002). He wanted to develop ionic liquids with dialkylimidazolium
cations and water-stable anions (Wilkes, 2002). They were able to produce moisture
stable imidazolium salts paired with BF4 and PF6 anions (Wilkes, 1992).
A research group used room temperature ionic liquids (RTILs) for CO2 capture in
1999 (Blanchard et al., 1999). They determined CO2 is highly soluble in 1-butyl-3-
methylimidazolium hexafluorophosphate ([bmim][PF6]) ILwhich triggered the
potential for CO2 separation (Blanchard et al., 1999; Baltus et al., 2005). Another
research team created a model that would predict the thermodynamic interactions
between a gas and ionic liquid (Shiflett and Yokozeki, 2005). They wanted to develop
a thermodynamic model that would allow testing of gas solubility under a wider
range of pressures, temperatures and different ionic liquid compositions (Shiflett and
Yokozeki, 2005). Shiflett and Yokozeki examined CO2 solubility with l-n-butyl-3-
methylimidazolium hexafluorophosphate ([bmim][PF6]) and l-n-butyl-3-
methylimidazolium tetrafluoroborate ([bmim]-[BF4]) (Shiflett and Yokozeki, 2005).
They tested the solubility of CO2 from 283.15 to 348.15 K and for pressures up to 2.0
MPa (Shiflett and Yokozeki, 2005). Their proposed thermodynamic model was an
equation of state (EoS) (Shiflett and Yokozeki, 2005). Since then, the use of ionic
10
liquids has been spreading and research into this potentially lucrative idea has
skyrocketed.
1.7 Thermophysical Properties of Ionic Liquids
1.7.1 Physical Properties of Ionic Liquids
Melting Point: One of the notable features of ionic liquids is that they have
melting points below 100°C and most of them are liquid at room temperature
(Arshad, 2009). Cations and anions play a role in creating this low melting point
property (Arshad, 2009). The increase in anion size leads to a decrease in melting
point (Wasserscheid & Keim, 2000). Other features of the ionic liquid such as the
length of the alkyl chain length can have an effect on the melting point (Gordon et
al., 1998). The melting point of salts increased to some extent with increasing
alkyl chain length (Gordon et al., 1998). The type of cation base can also affect
the melting point where the pyridinium cation produces higher melting points
than imidazolium salts of equivalent alkyl chain length cations (Gordon et al.,
1998).
Density: Ionic liquids are denser than water with density readings ranging from 1 to
1.6 g/cm3 (Arshad, 2009). Their densities decrease with an increase in the length of
the alkyl chain attached to the cation (Arshad, 2009). Density also decreases with an
increase in temperature (Meindersma et al., 2007). The relationship between density
and temperature was further demonstrated by Kim et al. who examined the density of
the following ionic liquids and calculated the densities using the group contribution
equation of state: [bmim][PF6], [C6mim][PF6], [emim][BF4], [C6mim][BF4],
11
[emim][TF2N] and [C6mim][TF2N] (Kim et al., 2005). They examined the density
over a range of temperatures from 293 to 343 K (Kim et al., 2005). Their findings
show that an increase in the temperature and alkyl chain length of an ionic liquid
leads to a decrease in density (Kim et al., 2005).
Viscosity: One of the drawbacks of ionic liquids is an increase in viscosity when
exposed to carbon dioxide (Gutowski and Maginn, 2008). Extensive research has
focused exclusively on finding a solution to this problem. Ionic liquids, when
compared to other molecular solvents, are naturally more viscous (Arshad, 2009). The
viscosity of ionic liquids is measured by van der Waals forces and hydrogen bonding
which leads to the formation of salt bridges (Gurkan et al., 2010). Thus, attempts have
been made to limit the available hydrogen bonds in a given ionic liquid in order to
limit the rise in viscosity once it reacts with CO2 (Gutowski and Maginn, 2008). For
example, the viscosity of ionic liquids containing imidazolium-based cations is
determined by the alkyl chain length of the cation, as well as the nature of the anion
used (Arshad, 2009). Viscosity is also affected by the type of anion used in the ionic
liquid (Ramdin et al., 2012). The viscosity increases with the anion in the following
order: [DCN] < [TF2N] < [SCN] < [TfA] < [TfO] < [BF4] < [BETI] < [NO3] <
[MeSO4] < [PF6] < [Ac] (Ramdin et al., 2012). Thus, the research world has many
options for fine-tuning ionic liquids in order to minimize the rise in viscosity with
CO2 fixation. The following graph shows the effect of an anion on viscosity for a
common [bmim] cation (Ramdin et al., 2012).
12
Figure 1.4: The effect of an anion on viscosity for a common [bmim] cation (Ramdin et
al., 2012).
The following graph shows the effect of the alkyl chain length on viscosity for different
ionic liquids with a common bis[(trifluoromethyl)sulfonyl]imide [TF2N] anion (Ramdin
et al., 2012). Viscosity increases with increasing alkyl chain length for all IL classes
(Ramdin et al., 2012).
Figure 1.5: the effect of alkyl chain length on viscosity for all IL classes (Ramdin et al.,
2012).
13
Vapour Pressure: One of the key features that make the use of ionic liquids green is
their almost non-existent vapour pressure. They do not evaporate and thus no solvent
is lost from the reaction vessels and separation equipment, minimizing operational
costs (Bates et al., 2001). This is a refreshing contrast to the traditional volatile
compounds used by industry. It also decreases worker exposure thus it is also better
from an occupational health point of view.
Thermal Stability: Another key identifier of ionic liquids is the fact they remain
thermally stable at temperatures above 300°C (Bates et al., 2001).
1.8 CO2 Solubility in Ionic Liquids and Factors That Affect Solubility
As ionic liquids are becoming a viable option for CO2 capture from natural and
flue gases, improving the efficiency of CO2 solubility in the ionic liquid is vital. There
are many different factors that influence the solubility of CO2 in ionic liquids and a good
understanding of these parameters is necessary in order to design an ionic liquid that is
optimized for the function of CO2 separation. The factors playing a role in the solubility
of CO2 in ionic liquids include the type of anion and cation, the amount of fluorination of
the anion, the alkyl chain length, the molecular weight of the ionic liquid and much more.
The anion effect on CO2 solubility: When it comes to CO2 solubility, the anion plays
a primary role and the cation takes a “back seat”. Many attempts and experiments
have been performed to understand the exact mechanism explaining why some ionic
liquids have a higher solubility than others. For example, Cadena et al. examined CO2
solubility in imidazolium ionic liquids: 1-butyl-3-methylimidazolium
hexafluorophosphate ([bmim][PF6]), 1-butyl-2,3- dimethylimidazolium
14
hexafluorophosphate ([bmmim][PF6]), 1-butyl-3-methylimidazolium
tetrafluoroborate ([bmim][BF4]), 1-butyl-2,3-dimethyl imidazolium tetrafluoroborate
([bmmim][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([emim][TF2N]) and 1-ethyl-2,3-dimethylimidazolium
bis(trifluoromethylsulfonyl)imide ([emmim][TF2N]) (Cadena et al., 2004). They
studied the CO2 solubility at 283.15, 298.15, and 273.15 K and pressures up to about
13 bar (Cadena et al., 2004). The anion had the greatest impact on the solubility of
CO2 and the cation played a secondary role (Cadena et al., 2004). They specifically
noted that the [TF2N] anion had the highest affinity for CO2, whereas the [BF4] or
[PF6] anions had a minor effect on CO2 solubility (Cadena et al., 2004). Ramdin et
al. observed the effect of many different anions when paired with a [bmim] cation at
333K where CO2 solubilities increase in the order of the following anions: [NO3] <
[SCN] < [MeSO4] < [BF4] < [DCN] < [PF6] < [TF2N] < [Methide] < [C7F15CO2]
(Ramdin et al., 2012). This trend was reproduced using the COSMO-RS model by
Maiti (Maiti, 2009) and Sistla and Khanna (2011).
The cation effect on CO2 solubility: It has been accepted that the cation plays a
secondary role in the solubility of CO2. Nonetheless, it still plays a role. Adding fluro
groups to the cation also improves CO2 solubility but to a lesser extent than if it were
added to the anion. The effect of changing the cation group is shown in the following
graph where cholinium, ammonium, imidazolium, pyridinium, pyrrolidinium, and
phosphonium cations were paired with the [TF2N] anion (Ramdin et al., 2012).
15
Figure 1.6: The effect of changing the cation on CO2 solubility (Ramdin et al., 2012).
Temperature effect on CO2 solubility: The general trend in the literature is that CO2
solubility ionic liquids decreases with increasing temperature. This is a problem when
considering the high temperatures of flue gases (Muldoon et al., 2007). The effect of
temperature on CO2 solubility is clearly seen by the following graph (Figure 1.8)
from Anthony et al. where the solubility of CO2 in [bmim][PF6], at three
temperatures of 283.15, 298.15, and 273.15 K with pressures of up to 13 bar,
decreased with increasing temperature (Anthony et al., 2002). This trend was also
seen by Aki et al. who examined the effect of temperature on the solubility of CO2 in
[bmim][TF2N] (Aki et al., 2004).
16
Figure 1.7: CO2 solubility in [bmim][PF6] at 283.15, 298.15, and 273.15 K (10, 25 and 50
C) (Anthony et al., 2002).
Pressure effect on CO2 solubility: A general trend seen in most ionic liquids is that
CO2 solubility increases with increasing pressure (Muldoon et al., 2007). This was
shown by Aki et al. who investigated CO2 solubility in [bmim][TF2N] with CO2
solubility increasing with increasing pressure, reaching over 0.7 mole fraction at 60
bar (Aki et al., 2004).
Fluorination effect on CO2 solubility: The general trend found by Muldoon et al.
was an increase in CO2 solubility with increased fluorination. They also found that
fluorination of the anion had a greater effect on the solubility than the fluorination of
the cation (Muldoon et al., 2007). Yunus et al. showed the effect of fluorination by
looking at the solubility of CO2 in [C4py][TF2N],[C4py][TfAc] and [C4py][Dca] at
298.15 K and pressures of up to 10 bar (Yunus et al., 2012). The solubility of CO2
increased as follows: [C4py][Dca] < [C4py][TfAc] < [C4py][TF2N] (Yunus et al.,
2012). From the results, the order of CO2 solubility follows the order of fluorination
17
in the anion (Yunus et al., 2012). This was also observed by Aki et al. when they
examined seven different ionic liquids which all had the same cation (1-butyl-3-
methylimidazolium ([bmim])) (Aki et al., 2004). They used seven different anions to
see what effect the anion would have on solubility. The anions were dicyanamide
([DCN]), nitrate ([NO3]), tetrafluoroborate ([BF4]), hexafluorophosphate ([PF6]),
bis(trifluoromethylsulfonyl)imide ([TF2N]), trifuoromethanesulfonate ([TfO]) and
tris(trifluoromethylsulfonyl)methide ([methide]) (Aki et al., 2004). Carbon dioxide
solubility increases as the number of fluoro groups in the anion increases, as seen in
the graph below. The solubility increases in the following anion order: [BF4] < [TfO]
< [TfA] < [PF6] < [TF2N] < [methide] < [C7F15CO2] < [eFAP] < [bFAP] (Ramdin
et al., 2012).
Figure 1.8: Effect of fluorination on CO2 solubility (Ramdin et al., 2012).
18
Thus, one can conclude [bFAP] would achieve the maximum rate of CO2 capture
among the seven ionic liquids.
Alkyl Chain lengths and the effect of CO2 solubility: For any given cation, CO2
solubility increases with increasing alkyl chain length on the cation (Muldoon et al.,
2007). Ramdin et al. examined the effect of alkyl chain lengths on CO2 solubility
(Ramdin et al., 2012). The following graph (Figure 1.10) shows the effect of
increasing alkyl chain length. All the ionic liquids are matched with a common
bis(trifluoromethylsulfonyl)amide [TF2N] anion (Ramdin et al., 2012), while the
alkyl chain length on the imidazolium cation is varied. As the alkyl chain becomes
longer the solubility increases in the following order: [omim] < [hmim] < [pmim] <
[bmim] < [emim] (Ramdin et al., 2012). Aki et al. also examined the role of alkyl
chain length on CO2 solubility while working with [bmim][TF2N],
[hmim][TF2N],and [omim][TF2N] (Aki et al., 2004). They found similar results
where the solubility increased with increasing alkyl chain length (Aki et al., 2004).
For example, at a pressure of 83.7 bar, the solubility increased from 0.72 mole
fraction for [hmim][TF2N] to 0.763 mole fraction for [omim][TF2N] (Aki et al.,
2004). Yunus et al. also examined the effect of the alkyl chain length by looking at
solubility in [C4py][TF2N], [C8py][TF2N] and [C12py][TF2N] at 298.15 K, 313.15
K and 333.15 K (Yunus et al., 2012). The CO2 solubility increased with increasing
alkyl chain length, for example, from 0.200 mol fraction of CO2 to 0.233 mol fraction
of CO2 at 298.15 K and 8 bar in the case of butyl (n = 4) and dodecyl (n =12) (Yunus
et al., 2012).
19
Figure 1.9: The effect of the alkyl chain length on CO2 solubility (Ramdin et al., 2012).
Molecular weight and the effect of CO2 solubility: Another factor that strongly
affects CO2 solubility is the molecular weight of the ionic liquid where CO2 solubility
increases with increasing molecular weight (Ramdin et al., 2012). Carbon dioxide
solubility increases with increasing IL molecular weight, molar volume, and free
volume (Ramdin et al., 2012).
1.9 New Developments in the Pursuit of the Perfect Ionic Liquid: Literature
Review
A main issue or factor that is usually a drawback for ionic liquid use in CO2 capture is the
increase in viscosity of the ionic liquid once it reacts with CO2. Thus, it has become a
race to find solutions or new ILs whose viscosity can be minimized. In addition, certain
modifications of the IL can be done to decrease the reactionary increase in viscosity such
20
as the addition of water. The addition of water to the IL is known to decrease the
solubility, slightly, however the decrease in viscosity is a tradeoff. For example, when
water is added to the IL [P66614][Pro] it showed a significant drop in viscosity which
decreased from 625 cP (0.1 wt% water) to 360 cP (4 wt% water) at 278 K with a small
change in CO2 capacity (Zhang et al., 2012). The slight decrease in CO2 solubility by
[P66614][Pro] appears at lower pressures, and even decreases to a smaller extent at high
pressures (Zhang et al., 2012).
A new approach in the pursuit of an IL with high a CO2 capture rate is the idea of
ring-opened heterocycles which are promising ionic liquids for gas separation and
capture. Mahurin et al. studied the following three ILs: [(N11)2CH][TF2N],
[(N111)2N][TF2N], [(N111)2N][C(CN)3] (Mahurin et al., 2012). The CO2 solubilities
for all three RTILs were nearly equivalent with values of 0.090, 0.099, and 0.095
mol/L∙atm (Mahurin et al., 2012). They are also comparable to the CO2 solubility of
[emim][TF2N] which has been reported to be 0.103 mol/L∙atm. However, only
[(N111)2N][C(CN)3] had a lower viscosity than [emim][TF2N] (Mahurin et al., 2012).
Another new ionic liquid, developed by Martinez et al, examined a new low-viscosity
and non-fluorinated ionic liquid, 1-hexyl-3-methylimidazolium tetracyanoborate
([hmim][TCB]) (Martinez et al., 2012). They were able to demonstrate the new ionic
liquid [hmim][TCB] harbors potential as it shows high CO2 solubility when compared to
the usual ionic liquids that are highly fluorinated. They studied the solubility of CO2 in
[hmim][TCB] within a range of 283.56 to 364.04 K and pressures up to 12.34 MPa. In
addition, it also shows great promise as it has a lower viscosity as well (Martinez et al.,
2012). They compared the solubilities of CO2 in [hmim][TCB] at 333 K to the
21
solubilities of CO2 at the same temperature in other ionic liquids sharing the same cation
i.e., 1-hexyl-3-methylimidazolium hexafluoroborate ([hmim][PF6]), 1-hexyl-3-
methylimidazolium tetrafluoroborate ([hmim][BF4]), 1-hexyl-3- methylimidazolium
bis(trifluoromethylsulfonyl)amide ([hmim][TF2N]), and 1-hexyl-3-methylimidazolium
tris(pentafluoroethyl)trifluorophosphate ([hmim][eFAP]) (Martinez et al., 2012). They
concluded that the new ionic liquid [hmim][TCB] had higher solubilties than expected
from the highly fluorinated ([hmim][eFAP]). The disadvantage of this high solubility and
high fluorination is high viscosity, where the viscosity of [hmim][TCB] is almost half of
[hmim][eFAP] which has a major implication with respect to commercial applicability
(Martinez et al., 2012). Another issue is the health implication of using fluorinated ionic
liquids. Iconic liquids, in general, are starting to lose their environmentally green title, as
more and more evidence reveals that ILs have some problems when it comes to
persistence in the environment due to their low degradation and high water solubility
features (Pham et al., 2010).
Lei et al. came up with the idea of mixing ILs as another approach to increase CO2
solubility (Lei et al., 2012). They examined the solubility of CO2 in pure ILs, i.e.,
[emim][BF4], [bmim][BF4], and [omim][TF2N], and in their binary mixtures, i.e.,
[emim][BF4],[omim][TF2N] and [bmim][BF4], [omim][TF2N] at 313.2 and 333.2 K and
pressures up to 6 MPa (Lei et al., 2012). In this experiment, the IL [omim][TF2N] was
selected because its CO2 solubility is higher in ILs with an anion such as [TF2N] which
contains a fluoroalkyl group, and an increase in the alkyl chain length on the cation also
increases the CO2 solubility. The ILs [emim][BF4] and [bmim][BF4] were selected
because they exhibit higher selectivity but lower solubility (Lei et al., 2012). The
22
solubility of CO2 in mixed ILs increases with increasing pressure at all temperatures, but
decreases with increasing temperature. The solubility of CO2 in mixed ILs increases with
increasing [omim][TF2N] content under the same temperature and pressure, and the
solubility of CO2 in the [emim][BF4],[omim][TF2N] mixed ILs is lower than in the
[bmim][BF4], [omim][TF2N] mixed ILs under the same [omim][TF2N] content,
temperature and pressure (Lei et al., 2012). Thus, experimentation with binary mixtures
of ionic liquids has the potential for improving CO2 capture.
In another paper, Manica et al. tested the solubility of seven different ionic liquids in
a range of pressures from 8 to 22 MPa at two different temperatures (Manica et al.,
2012). They explored the effect and role of cations while using the same anion for all
their ionic liquids. The anion they used was bis(trifluoromethylsulfonyl)imide,[TF2N].
They then paired the anion up with different cations such as 1-butyl-3-
methylimidazolium, [C4mim], 1-decyl-3-methyl imidazolium, [C10mim], 1-butyl-1-
methylpyrrolidinium, [Pyrr4,1], butyltrimethyl ammonium,[N4,1,1,1],
methyltrioctylammonium, [N1,8,8,8] and trihexyltetradecylphosphonium, [P6,6,6,14]
cations. Their results echoed the findings of almost all previous studies which are that the
solubility of CO2 in ILs might be improved by increasing the pressure, increasing alkyl
chain length in the cation, adding fluorination in ILs or by decreasing the temperature.
Althuluth et al. experimented with CO2 solubility in the following ionic liquid 1-
ethyl-3- methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([emim][FAP])
(Althuluth et al., 2012). They examined different solubilites across a range of
temperatures from 283.75 to 364.13 K and at pressures up to 10.4MPa (Althuluth et al.,
2012). The solubility of CO2 was determined by examining different bubble point
23
pressures with different concentrations of CO2 in the ionic liquid. The solubility of CO2
in [emim][FAP] decreases with increasing temperature (Althuluth et al., 2012). This is a
general trend found in the literature for many types of ionic liquids. Therefore, as
temperature increases there is a need to increase pressure to dissolve the same amount of
CO2 in the ionic liquid. They compared the solubility of CO2 in [emim][FAP] and found
it to be higher than all other ILs having the same cation having the following trend:
[emim][FAP] > [emim][TF2N] > [emim][EtSO4] = [emim][PF6] >[emim][BF4]
(Althuluth et al., 2012). This is most likely due to the presence of a large amount of
fluorine atoms in the anion, which result in an increase in CO2 solubility in the IL and it
has a higher stability to moisture and air compared to other fluorinated ionic liquids.
Therefore, it has potential for use as a solvent for gas separation and CO2 capture.
Studies published in the literature are in general agreement that CO2 solubility increases
as fluorination increases in the anion. Thus, fluorination content would be an important
factor to consider in the search for an ionic liquid.
Another new category of ionic liquids being explored are hydroxyl ammonium
ionic liquids (Yuan et al., 2007). Yuan et al. studied eight ionic liquids: 2-hydroxy
ethylammonium formate (HEF), 2-hydroxy ethylammonium acetate (HEA), 2-hydroxy
ethylammonium lactate (HEL), tri-(2-hydroxy ethyl)-ammonium acetate (THEAA), tri-
(2-hydroxy ethyl)-ammonium lactate (THEAL), 2-(2-hydroxy ethoxy)-ammonium
formate (HEAF), 2-(2-hydroxy ethoxy)-ammonium acetate (HEAA) and 2-(2-hydroxy
ethoxy)- ammonium lactate (HEAL) (Yuan et al., 2007). They examined their CO2
solubility at temperatures of 303 to 323K and pressures ranging from 0 to 11MPa (Yuan
et al., 2007). Carbon dioxide solubility in the eight hydroxyl ammonium ionic liquids
24
decreased in the following sequence: THEAL >HEAA>HEA> HEF > HEAL
>THEAA≈HEL > HEAF (Yuan et al., 2007). They also reported all eight ionic liquids
had a lower CO2 solubility than [bmim][PF6] (Yuan et al., 2007). The following graph
compares the eight ionic liquids investigated by Yuan et al. with others from the
literature.
Figure 1.10: Comparison of the solubility of CO2 in different ionic liquids at 313 K: (■)
THEAL; (●) [bmim][PF6]; (▲) [omim][PF6]; (▼) [Nbupy][BF4]; (♦) [emim][EtSO4]
(Yuan et al., 2007).
In another report Jalili et al. examined 1-Octyl-3-methylimidazolium
bis(trifluoromethyl) sulfonylimide ([C8mim][TF2N]) (Jalili et al., 2012). They
experimented with temperatures of 303.15, 313.15, 323.15, 333.15, 343.15, and 353.15 K
and pressures of up to 2MPa. Carbon dioxide solubility was increased by increasing the
number of carbons in the alkyl substituent of the methylimidazolium cation ring (Jalili et
al., 2012).
25
Another group examined pyridinium based ionic liquids and CO2 solubility.
Yunus et al. examined six different pyridinium based ionic liquids, 1-butylpyridinium
bis(trifluoromethyl sulfonyl)imide [C4py][TF2N], 1-octylpyridinium
bis(trifluoromethylsulfonyl) imide [C8py][TF2N], 1-decylpyridinium
bis(trifluoromethylsulfonyl)imide [C10py][TF2N], 1-dodecylpyridinium
bis(trifluoromethylsulfonyl)imide [C12py][TF2N], 1-butylpyridinium trifluoroacetate
[C4py][TfAc] and 1-butylpyridinium dicyanamide [C4py][Dca], at temperatures of
298.12, 313.12, and 333.15K (Yunus et al., 2012). There is little difference in solubility
when compared to the more expensive imidazolium cation. They also arrived at the same
conclusion as all other papers that solubility increases by increasing the alkyl chain of the
anion. They concluded the solubility of CO2 in this series of ionic liquids increases in the
following sequence: [C4py][TfAc] < [bmim][TFA] < [emim][TF2N] < [C4py][TF2N]
≈[bmim] [TF2N] < [hmim][TF2N] < [C8py][TF2N] < [C12py][TF2N] < [bmim][Ac]
(Yunus et al., 2012).
Based on reports in the literature, a good choice for an ionic liquid should contain
an imidazolium cation with a long alkyl chain such as [emim] and an anion with fluro
groups such as [bFAP]. Other groups of ionic liquids that should be considered are those
that are less expensive such as the ionic liquids with the pyridinium cation. The creation
of an ionic liquid with the aforementioned features and maximum molecular weight
should yield an IL with a high CO2 solubility. This was taken into consideration when
selecting the ionic liquids. The selection was based on attempting to provide novel work
and finding ionic liquids that were uncommon in the literature.
26
1.10 Outline of the Chapters
Chapter 2 will provide the steps taken for measuring gas solubilities and the theory
behind calculation of Henry’s law constants, enthalpies and entropies of absorption. It
will also cover the experimental details and the methodology used to obtain the CO2
solubility in the ionic liquids. It will also include a description of all the chemicals, gases
and apparatus used in this experimental study.
Chapter 3 will present the results obtained from CO2 solubility measurements in the
different ionic liquids investigated in this work. The chapter will include the solubility of
carbon dioxide in five ionic liquids and will perform a comparison of the ionic liquids to
research published in the literature and research performed by the Acid Gas Research Lab
(AGRL) affiliated with this research.
Chapter 4 will discuss the theory behind thermodynamic modeling and include a
description of the density calculations for the ionic liquids. It contains details on the
thermodynamic models used to correlate the experimental CO2 solubility including
equations of state, such as the (PR-EoS), Peng-Robinson, Soave-Redlich-Kwong (SRK),
and the Non-Random Two-Liquid (NRTL) activity coefficient model. Henry’s law
constants and enthalpies and entropies of absorption for CO2 in the ionic liquids are
discussed in this chapter.
27
2 Chapter Two: General Methodology, Theory And Experimental Details
This chapter will include the steps taken for measuring gas solubilities and
calculating Henry’s law constants, enthalpies and entropies of absorption. It will explore
the various methods used to measure gas solubilites including the gravimetric method
used in this study.
This chapter will also cover details of the various experiments conducted, and will
also include a description of all the chemicals, gases, and apparatus used for the solubility
measurements.
2.1 Methods for Gas Solubility Measurements
Gas solubility is influenced by many factors as is the accurate measurement of
solubility (Clever and Battino, 1975). The purity of the liquid sample will affect the gas
solubility measurements. The diligent control of the important parameters such as
temperature, pressure, volume and mass are all important for accurate gas solubility
measurements (Clever and Battino, 1975). There are different methods for gas solubility
measurements which include volumetric and pressure drop methods, the stoichiometric
technique and gravimetric method (Clever and Battino, 1975). The following section will
provide a brief description of the different gas solubility measurements.
2.1.1 Pressure Drop Technique for Measuring CO2 Solubility
The pressure drop method measures the pressure change when a known mass of
gas dissolves into a known mass of ionic liquid (Brennecke et al., 2008). Once the system
has reached equilibrium, the pressure change is used to reflect the amount of gas
28
dissolved into the liquid, from which the gas solubility can be extrapolated (Brennecke et
al., 2008).
Figure 2.1: Pressure drop technique for measuring CO2 solubility (Brennecke et al, 2008).
2.1.2 Stoichiometric Technique for Measuring CO2 Solubility
This method determines the solubility of a gas by determining the volume of a
cell, which contains the gas, and the volume of the vapour and liquid phases as they mix
and dissolve (Brennecke et al., 2008). This information is used to measure the number of
moles of gas remaining in the gas phase and thus the number of moles of gas dissolved in
29
the liquid are extrapolated, leading to the solubility measurement (Brennecke et al.,
2008).
Figure 2.2: Stoichiometric gas solubility apparatus (Brennecke et al., 2008).
2.1.3 Gravimetric Method for Measuring CO2 Solubility
The gravimetric method uses the concept of change in the weight of the sample
after absorption to assess the solubility. Due to the non-volatile nature of ionic liquids
30
and the lack of loss of ionic liquid due to evaporation, the weight of the sample is not
affected, and thus this method is commonly used.
This experiment utilized an IGA (Intelligent Gravimetric Analyzer) which utilizes
the gravimetric technique. It combines the computer control and measurements of weight
change, pressure and temperature to allow automatic configuration of gas adsorption-
desorption isotherms. The microbalance is made of an electrobalance with sample and
counterweight parts inside a stainless steel pressure-vessel as shown in the figure below
(Shiflett and Yokozeki, 2005).
Figure 2.3: Schematic diagram of IGA003 gravimetric microbalance. Symbols: arrow B
indicates direction due to buoyancy on the sample side of the balance, arrow Wg
indicates direction of weight due to gravity on the sample side of the balance, additional
symbols described in Table 1 (Shiflett and Yokozeki, 2005).
31
Figure 2.4: IGA apparatus (http://www.zpph.com/userfiles/file/iga_series_brochure.pdf)
2.1.4 Gravimetric Method: Buoyancy Correction Factor
The gravimetric method for gas solubility must be carefully corrected for a
number of forces. These include the buoyant forces, the aerodynamic drag forces due to
the flow of gases, the change in balance sensitivity due to changes in temperature and
pressure and volumetric changes due to sample expansion (Shiflett and Yokozeki, 2005).
The buoyancy effect on the absorbed mass was minimized by using a sample pan
and a counterweight container that were symmetrically configured with the exact same
stainless steel bucket. The buoyancy correction factor follows one of Archimedes’
principals which states there is an upward force placed on an object equivalent to the
mass of the fluid displaced (Shiflett and Yokozeki, 2005). The upward force (Cb) due to
buoyancy is calculated using equation 2.1 where the mass of displaced carbon dioxide is
equivalent to the volume of the submersed object 𝑉𝑖 multiplied by the carbon dioxide
32
density (𝑝𝑔) at a measured temperature and pressure and the local gravitational
acceleration (g) (Shiflett and Yokozeki, 2005).
2.1.5 Calculation of Buoyancy Correction Factor
Cb = Buoyancy = gVipg(T, P) = gmi
pipg(T, P) (2.1)
many important components for weighing the sample are needed in order to use
the IGA to determine the buoyancy correction. The difference between the weight of the
sample side (i) and that of the counterweight side (j) represents the weight measured by
the balance. The microbalance components, their weights and densities can be found in
Table 2.1. Also refer to Figure 1 for the schematic representation of the IGA apparatus.
The mass balance, shown in Figure 1, is mathematically represented by equation 2.2:
Reading =∑ 𝑚𝐼𝐿𝑆𝑖=1 − ∑ 𝑚𝑐𝑤𝑗𝑐𝑤𝑗− ∑
𝑚𝐼𝐿
𝑝𝑠𝑠𝑖=1 𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) +
∑𝑚𝑐𝑤
𝑝𝑐𝑤𝑐𝑤𝑗=1 𝑝𝑔𝑎𝑠 (𝑇𝐶𝑤𝑗
, 𝑃) + 𝑚𝐼𝐿 + 𝑚𝑎𝑏−𝑔𝑎𝑠-𝑚𝐼𝐿
𝑝𝐼𝐿(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿, 𝑃) −
𝑚𝑎𝑏−𝑔𝑎𝑠
𝑝𝑎𝑏−𝑔𝑎𝑠(𝑇𝐼𝐿)
−
𝐶𝑓(𝑇𝐼𝐿𝑃) (2.2)
The IGA is used to measure the mass difference between the sample side and
counterweight which includes the summation of all components as seen in equation 2.2.
The following symbols are defined for the aforementioned equation: The mass of
absorbed gas (mIL) and a correction factor (Cf) due to the sensitivity of the balance, s
and a represent the density of ionic liquids and gas at a sample temperature (Ts) and mIL
is the weight of the dry IL sample (Shiflett and Yokozeki, 2005). The density of the IL
33
sample must be accurately known in order to determine the aforementioned buoyancy
correction and was measured with the DMA 4500 density meter.
Table 2-1: Microbalance components for buoyancy correction
Object Description
Weight
(g)
Density
(g/cm3)
Temperature
(C)
S Dry sample: ionic liquid used 𝑚𝐼𝐿 s -
A Interacted gas: CO2 gas 𝑚𝑎𝑏−𝑔𝑎𝑠 a -
i1 Sample container 0.63275 7.393103 -
i2 Wire 0.06524 21 -
i3 Chain 0.3055 19.8 35
j1 Counterweight 0.81219 7.9 -
j2 Hook 0.00582 2.71 25
j3 Chain 0.239 19.8 35
In addition to accounting for buoyancy, a possible volume expansion can occur at high
temperatures which may be large enough to affect the buoyancy correlation (Shiflett and
Yokozeki, 2005). Therefore, the solubility calculation may be inaccurate if the buoyancy
due to sample expansivity is not taken into account. The volume of the ionic liquid and
the CO2 was ascertained with their weight and density using the following equations
(Shiflett and Yokozeki, 2005):
𝑉𝑚𝐼𝐿=
𝑀𝑊𝐼𝐿
𝑝𝐼𝐿 (2.3)
34
𝑉𝑚𝐺𝑎𝑠=
𝑀𝑊𝑔𝑎𝑠
𝑝𝑔𝑎𝑠 (2.4)
The average molar volume is obtained using the following equation:
𝑉𝑚𝑎𝑣(𝑇, 𝑃) = 𝑉𝑚𝐼𝐿
(1 − 𝑥) + 𝑉𝑚𝑔𝑎𝑠𝑥 (2.5)
The volume of the ionic liquid could be calculated using the average liquid volume, the
moles of ionic liquid, and moles of absorbed gas using the following equations:
V (T, P) =𝑉𝑚𝑎𝑣(𝑇, 𝑃)[(
𝑚𝐼𝐿
𝑀𝑊𝐼𝐿) + (
𝑚𝑎𝑏−𝑔𝑎𝑠
𝑀𝑊𝑔𝑎𝑠)] (2.6)
V(T, P)𝑝𝑔𝑎𝑠(𝑇, 𝑃) =𝑚𝐼𝐿
𝑝𝐼𝐿(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) +
𝑚𝑎𝑏−𝑔𝑎𝑠
𝑝𝑎𝑏−𝑔𝑎𝑠(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) (2.7)
2.2 Thermodynamic Properties
Once the gas solubilites are measured and calculated, some thermodynamic
properties can be derived such as Henry’s law constants and enthalpies and entropies of
absorption.
2.2.1 Derivation for Henry’s Law Constants
Henry’s law constants are proportionality constants that are used to relate the
partial pressure of a gas to the gas solubility in a liquid state at infinitely dilute conditions
(Prausnitz et al., 1999).
The Henry’s law constant is defined as:
𝐻𝑖(𝑇, 𝑃) = lim𝑥𝑖→0
𝑓𝑖𝐿
𝑥𝑖 (2.8)
where fi
L
is the fugacity of the gas dissolved in the liquid phase. Since the fugacity of the
gas in the liquid phase must be equal to the fugacity in the gas phase and approximate the
35
gas phase fugacity at the gas phase pressure, the following form of Henry’s law can be
obtained:
𝑃𝑖 = 𝐻𝑖(𝑇)𝑥𝑖 (2.9)
where Pi is the partial pressure of the gas. H
i(T) will have units of pressure and is
inversely proportional to the mole fraction of gas in the liquid.
The fugacity of the gas is the method used in this experiment to calculate Henry’s
law constant. The fugacity was estimated from the experimental solubility data, pressure
and appropriate mode in AspenPlus. Henry’s law constant is found by fitting the data to a
first or second order polynomial obtain a correlation coefficient of R2 > 0.999. The
limitation of the mole fraction of CO2, as it approaches zero, was used to obtain the
Henry’s law constant at each temperature.
Henry’s constant can also be obtained in a different manner as it is also directly
related to the infinite dilution activity coefficient and the vapor pressure of the gas. The
activity coefficient of the gas in the IL phase, γ1, can be determined directly by measuring
the mole fraction of gas dissolved in the IL as a function of the pressure of gas above the
IL solution.
2.2.2 Derivation for Enthalpy And Entropy Of Absorption
The examination of temperature effects on gas solubilities allows for the
derivation of the enthalpies and entropies of absorption. The bonds between the liquid
and dissolved gas reflect the enthalpy, whereas the entropy indicates the level of ordering
that takes place in the liquid/gas mixture (Hildebrand and Scott, 1962).
36
∆ℎ2 = ℎ2 − ℎ2𝑖𝑔
= 𝑅𝑇 (𝜕𝑙𝑛𝑥2
𝜕𝑙𝑛𝑇)
𝑃(
𝜕𝑙𝑛𝑎2
𝜕𝑙𝑛𝑥2)
𝑃,𝑇 (2.10)
∆𝑠2 = ��2 − 𝑠2𝑖𝑔
= 𝑅 (𝜕𝑙𝑛𝑥2
𝜕𝑙𝑛𝑇)
𝑃(
𝜕𝑙𝑛𝑎2
𝜕𝑙𝑛𝑥2)
𝑃,𝑇 (2.11)
where h1 and s1 are the partial molar enthalpy and entropy of the gas in solution, h1
ig
and
s1
ig
are the enthalpy and entropy of the pure gas in the ideal gas phase, and a1
is the
activity of the gas in the solution:
𝑎2 = 𝛾2 ∙ 𝑥2 (2.12)
The above equations can be rewritten as follows:
∆ℎ2 = 𝑅 (𝜕𝑙𝑛𝑃
𝜕(1/𝑇))
𝑥2
(2.13)
∆𝑠2 = −𝑅 (𝜕𝑙𝑛𝑃
𝜕𝑙𝑛𝑇)
𝑥2
(2.14)
The equations provide ∆h2 and ∆s2 at a specific mole fraction of CO2 in the ionic liquid
(x2). The equations can be simplified to:
∆ℎ2 = −𝑅 (𝜕𝑙𝑛𝑥2
𝜕(1/𝑇))
𝑃= 𝑅 (
𝜕𝑙𝑛𝐻2,1
𝜕(1/𝑇))
𝑃 (2.15)
∆𝑠2 = 𝑅 (𝜕𝑙𝑛𝑥2
𝜕𝑙𝑛𝑇)
𝑃= −𝑅 (
𝜕𝑙𝑛𝐻2,1
𝜕𝑙𝑛𝑇)
𝑃 (2.16)
The above equations provide ∆h2 and ∆s2 at infinite dilution. The equations will also give
the same ∆h2 and ∆s2 as the x2 becomes adequately small to exist in the infinite dilution
range.
37
2.3 Materials
2.3.1 Ionic Liquids
The seven different ionic liquids are listed in the following table.
Table 2-2: Ionic liquids studied with their short hand notation and structure.
Ionic liquid Shorthand Name Structures
1,2,3-
Tris(diethylamino)cyclopropenylium
dicyanamide
[TDC] [DCN]
1-Ethyl-3-methylimidazolium L-(+)-
lactate
[EMIM] [LACTATE]
3-methyl-1-propylpyridinium
bis[(trifluoromethyl)sulfonyl]imide
[PMPY] [TF2N]
Ethyldimethylpropylammonium
bis(trifluoromethylsulfonyl)imide
[EMMP] [TF2N]
1,2,3-
Tris(diethylamino)cyclopropenylium
bis(trifluoromethanesulfonyl)imide
[TDC] [TF2N]
1-(4-sulfobutyl)-3-
methylimidazolium
Bis(trifluoromethanesulfonyl)imide
[(CH2)4SO3HMIm][TF2N]
1-(4-sulfobutyl)-3-
methylimidazolium hydrogen sulfate
[(CH2)4SO3HMIm][HSO4]
The ionic liquids were purchased from Sigma Aldrich. The exception is
[PMPY][TF2N] which was obtained from ionic liquid Technology (io-li-tec , USA) and
38
[(CH2)4SO3HMIm][HSO4] and [(CH2)4SO3HMIm][TF2N] were obtained from
solvionic.
Table 2-3: Ionic liquids used and their specifications:
Ionic liquid Source Molecular weight
1,2,3-Tris(diethylamino) cyclo
propenylium dicyanamide
Sigma Aldrich (purity of
97%)
3g purchased
Product #: 744018
Color: yellow
318.46
1-Ethyl-3-methylimidazolium L-(+)-
lactate
Sigma Aldrich (purity of
>95%)
5g purchased
Product #: 669512
CAS #: 878132-19-5
Color: light brown
200.23
3-Methyl-1-propylpyridinium
bis[(trifluoromethyl)sulfonyl]imide
io-li-tec: ionic liquid
technologies (purity of
99%)
3g purchased
416.40
Ethyldimethylpropylammonium
bis(trifluoromethylsulfonyl)imide
Sigma Aldrich (purity of
99%)
3g purchased
Impurities: ≤1.0%
water
Product #: 727989
CAS#: 258273-77-7
Color: colorless
396.37
1,2,3-Tris(diethylamino)cyclo
propenylium bis(trifluoromethane
sulfonyl)imide
Sigma Aldrich (purity of
97%)
3g purchased
532.56
1-(4-Sulfobutyl)-3-methylimidazolium
Bis(trifluoromethanesulfonyl)imide
Solvionic (purity of
98%)
10g purchased
Impurities: H2O <0.2%
Catalog#: ImSF1808c
Color: colorless
499.43
1-(4-Sulfobutyl)-3-methylimidazolium
hydrogen sulfate
Solvionic (purity of
98%)
10g purchased
Impurities: H20 <1%, Br
<0.3%, Cl <0.3%
Catalog #: ImSF1213c
Color: colorless
316.35
39
2.3.2 Ionic Liquid Treatment and Equilibrium Time
1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) with an assay
of ≥ 97.0% (HPLC) was measured at 82 g. This ionic liquid was used to validate the
results obtained from the system and machine.
1,2,3-Tris(diethylamino)cyclopropenylium dicyanamide ([TDC] [DCN]) was
used in gas solubility measurements and purchased from Sigma-Aldrich. It was dried
under vacuum at 75°C for more than 14 hours in all three experiments before carbon
dioxide was sent to the sample chamber. It took less than 120 minutes to reach
equilibrium under 1000 millibars pressure at 40
°C.
Figure 2.5:[TDC] [DCN] equilibrium under 1000 millibars and 40
°C
1-Ethyl-3-methylimidazolium L-(+)-lactate ([EMIM] [LACTATE]) was used in
gas solubility measurements and purchased from Sigma-Aldrich. It was dried under
vacuum at 75°C for more than 14 hours in all three experiments before carbon dioxide
40
was sent to the sample chamber. It took more than 350 minutes to reach equilibrium
under 1000 millibars pressure at 40
°C.
Figure 2.6: [EMIM] [LACTATE] equilibrium under 1000 millibars pressure at 40
°C.
3-methyl-1-propylpyridinium bis[(trifluoromethyl)sulfonyl]imide ([PMPY]
[TF2N]) was used in gas solubility measurements and purchased from io-li-tec: ionic
liquid technologies. It was dried under vacuum at 75°C for more than 14 hours in all
three experiments before carbon dioxide was sent to the sample chamber. It took less than
120 minutes to reach equilibrium under 1000 millibars pressure at 40
°C.
Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide ([EMMP]
[TF2N]) was used in gas solubility measurements and purchased from Sigma-Aldrich. It
was dried under vacuum at 75°C for more than 14 hours in all three experiments before
carbon dioxide was sent to the sample chamber. For each run, the temperature was set for
41
the isotherm. It took less than 120 minutes to reach equilibrium under 1000 millibars
pressure at 40
°C.
1,2,3-Tris(diethylamino)cyclopropenylium bis(trifluoromethanesulfonyl) imide
([TDC] [TF2N]) was used in gas solubility measurements and purchased from Sigma-
Aldrich. It was dried under vacuum at 75°C for more than 14 hours in all three
experiments before carbon dioxide was sent to the sample chamber. It took less than 120
minutes to reach equilibrium under 1000 millibars pressure at 40
°C.
1-(4-sulfobutyl)-3-methylimidazolium Bis(trifluoromethane sulfonyl)imide
([(CH2)4SO3HMIm] [TF2N]) was used in gas solubility measurements and purchased
from solvionic. It was dried under vacuum at 70°C for more than 14 hours in all three
experiments before carbon dioxide was sent to the sample chamber. It took less more
than 350 minutes to reach equilibrium under 1000 millibars pressure at 40
°C.
1-(4-Sulfobutyl)-3-methylimidazolium hydrogen sulfate
([(CH2)4SO3HMIm][HSO4]) was used in gas solubility measurements and purchased
from solvionic. It was dried under vacuum at 75°C for more than 14 hours in all three
experiments before carbon dioxide was sent to the sample chamber. It took less more
than 350 minutes to reach equilibrium under 1000 millibars pressure at 40
°C.
2.3.3 Selection of Ionic Liquids
Seven ionic liquids were chosen to investigate the CO2 solubility. After an
extensive literature review was performed, certain qualities and characteristics were
chosen as being important for maximizing solubility. Ionic liquids, which have not been
42
extensively published, were identified in order to contribute something new to the field of
CO2 capture with ionic liquids.
A search was performed for anions that were known to have high CO2 solubility
and, of course, bis(trifluoromethylsulfonyl) imide is well known in the literature for
having high CO2 solubility. Thus four of the ionic liquids chosen had this anion. [TF2N]
is known for its high CO2 solubility due to the high fluorination content of the anion.
[emim][LACTATE] was chosen due to the long alkyl chain of the cation when
compared to other imidazolium based cations such as [omim], [hmim], [pmim] or
[bmim]. The anion lactate was chosen as it was thought to be interesting to see the effect
of having an organic anion and to see its effect on CO2 capture.
A good variety of ionic liquids were needs and, thus, different cation bases were
chosen where [TDC] is a propenylium based cation, [PMPY] is a pyridinium based
cation, [EMMP] is an ammonium based cation, [emim] and [(CH2)4SO3HMIm] are
imidazolium based cations. This enables the study of the effect and role of the cation base
on CO2 solubility especially since the anion was identical for most of the ionic liquids.
2.3.4 Gases
Carbon dioxide was purchased from Praxair Inc. (Regina) with a mass purity of
99.99%.
2.4 Gravimetric Microbalance
Solubility was calculated using the Intelligent Gravimetric Analyzer (IGA 003)
from Hiden Analytical. This machine has been used by many researchers and a detailed
description of the apparatus can be found elsewhere (Moore, 2000).
43
Figure 2.7: Gravimetric microbalance
44
2.5 Experimental Procedure
A detailed schematic of the apparatus and its individual components is shown in the
figure below.
Figure 2.8: Schematic of the gravimetric microbalance
45
2.6 Summary of Experimental Procedures
Figure 2.9: Experimental procedure followed when using IGA
46
The microbalance consists of a weighing mechanism with a sample pan and
counterweight which have been symmetrically configured to minimize buoyancy effects.
The sample buckets are attached to the weighing mechanism by chains. The sample
buckets used in the experiments were stainless steel buckets.
The sample is loaded onto the sample bucket which is hung onto the chains and
then placed within the reactor vessel where it is tightly sealed. The sample weight varied
for each ionic liquid used in a range of 60-83 mg. With the aid of a coarse vacuum, the
sample was degassed with the help of a diaphragm pump where the reactor vessel
reached about 200 milibars. The sample is then heated up to about 75°C for a specified
period of time during which the sample weight decreases slowly. The drop in weight is
attributed to the removal of impurities such as water from the loading sample. The
percent weight drop was calculated for each treatment as percentage impurity lost for
each ionic liquid. See the table below:
Table 2-4: Calculation of weight lost for each ionic liquid at 313.15K and the percent
impurity lost
Ionic liquid Initial weight (mg) Dry weight (mg) % impurity lost
[TDC] [DCN]
63.003 62.845 0.25078
[EMIM] [LACTATE]
74.551 70.658 5.22125
[PMPY] [TF2N]
79.935 79.827 0.13498
[EMMP] [TF2N]
79.158 78.962 0.24761
[TDC] [TF2N]
86.735 86.591 0.16729
[(CH2)4SO3HMIm][TF2N] 83.247 64.028 23.0867
[(CH2)4SO3HMIm][HSO4] 74.015 67.627 8.62961
47
All ionic liquids had an acceptable percent impurity loss except
[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4]. These two hydrophobic
ionic liquids had more than the expected weight loss which might be due to their
absorption of water when exposed to ambient atmosphere and some acid evaporation
loss.
The sample temperature is set to the desired experimental temperature once the
weight of the sample reaches a stabilized state, the sample is deemed purified. The
absorption measurements are initiated by allowing the flow of carbon dioxide into the
chamber once the experimental temperature is stabilized.
The temperature of the reactor chamber was controlled during the experiment at
the desired experimental temperature using a water jacket and a constant-temperature
water bath. The sample temperature was monitored with a type K platinum thermocouple
placed inside the sample chamber and automatically maintained within 0.1 °C of the set
point. Once the desired temperature of the sample was reached, gas or vapor was
introduced into the sample chamber through a leak valve until a predetermined pressure
was reached. A pressure maximum of 19 bar was used in this experiment.
As the gas entered the chamber, the change in mass of the ionic liquid was
monitored by the computer program and increased with increasing gas absorption. When
the change in weight stabilized, the sample reached equilibrium providing the absorption
isotherm. This was repeated for the different pressures until the maximum pressure was
reached.
48
Figure 2.10: [TDC] [TF2N] equilibrium providing at high pressure.
2.7 Accounting for Buoyancy
When performing this type of experiments it is important to carefully account for
buoyancy effects in the system, even when a symmetric balance is used. An accurate
calculation of the buoyancy effect is especially important as the buoyancy is a large
percentage of the measured weight change. As mentioned earlier in the chapter, accurate
buoyancy calculations require knowledge of the volume of the balance components
(sample and counterweight buckets, counterweight, and hang-down chains), the volume
of the sample, and the density of the bulk gas phase. The volume of the balance
components is constant. The volume of the sample is calculated from the density.
The volume of the ionic liquid sample is found from its density, therefore, the
density of the IL sample must be accurately known. The density of each ionic liquid was
obtained using a digital density meter DMA 4500 (Anton Par).
2.8 Ensuring Equilibrium
Another important step in the experimental procedure is to allow adequate time
for the system to reach equilibrium. Depending on the viscosity of the ionic liquid,
equilibrium can vary and be a long process requiring patience. The weight change can be
49
monitored as a function of time using a microbalance for the measurements. One is able
to ascertain how much time is required to reach equilibrium when there is no longer a
significant change in mass. The equilibrium time for all samples in this work ranged from
120 to 240 min per point, depending on the ionic liquid, gas or vapor, and the sample
temperature.
2.9 Error Analysis
There are several sources of uncertainty in the microbalance experiments. The
uncertainties in measuring the pressure and mass are extremely small, about 0.06% and
0.0013%, respectively. Most of the source of error comes from the uncertainty
surrounding equilibrium. The uncertainty in the IL density measurements can also affect
the uncertainty in the solubility measurements.
50
3 CHAPTER THREE: RESULTS AND DISSCUSION
This chapter will look at the results obtained for CO2 solubility in the
experimental ionic liquids. The first section looks at the measured experimental density
for seven pure ionic liquids at different temperatures. The second section focuses on the
solubility of carbon dioxide in the seven ionic liquids. The following section will
compare the ionic liquids from this work to others published in the literature. Finally, it
will compare the solubility of CO2 to other ionic liquids recently studied by an affiliated
research group.
3.1 Density of Pure Ionic Liquids
The density of the seven ionic liquids was experimentally obtained using a digital
density meter DMA 4500 (Anton Par) at atmospheric pressure over a range of
temperatures from 278.15 to 353.15K. The results of the experimental density are shown
in Table 1. The graphical representation of the densities illustrate that the density
decreases with increasing temperature in a linear fashion with a correlation coefficient R2
> 0.999. The calculated (AADs) average absolute deviations between the experimental
data of [PMPY] Tf2N] , [EMMP][TF2N]
,[TDC][TF2N],[emim][LACTATE],[TDC][DCN], [(CH2)4SO3HMIm] [TF2N] and
[(CH2)4SO3HMIm][HSO4] are 0.06%, 0.06%, 0.17%, 0.029% and 0.059% ,0.09% and
0.14%, respectively.
In summary, the trend in the experimental density of decreasing order in the ionic
liquids are as follows: [(CH2)4SO3HMIm][TF2N] >[PMPY] Tf2N]
>[(CH2)4SO3HMIm][HSO4]> [EMMP][TF2N]
>[TDC][TF2N]>[emim][LACTATE]>[TDC][DCN]. This is shown in Figure 3.1 below.
51
Table 3-1: Experimental densities of pure ionic liquids measured at 1.01325 bar T (K) (g/cm3)
[TCD][CN] [PMPY ][TF2N] [EMMP][TF2N] [TCD][TF2N] [EMIM][LACTATE]
278.15 1.01638 1.46723 1.42002 -- 1.15745
283.15 1.01327 1.46243 1.41526 -- 1.15347
288.15 1.01014 1.45762 1.41060 -- 1.14977
293.15 1.00701 1.45281 1.40596 -- 1.14611
298.15 1.00391 1.44800 1.40126 1.27341 1.14246
303.15 1.00079 1.44328 1.39646 1.26905 1.13889
308.15 0.99770 1.43854 1.39181 1.26470 1.13543
313.15 0.99462 1.43381 1.38791 1.26036 1.13195
318.15 0.99155 1.42911 1.38336 1.25604 1.12851
323.15 0.98850 1.42443 1.37982 1.25173 1.12507
328.15 0.98546 1.41979 1.37540 1.24743 1.12167
333.15 0.98243 1.41516 1.37097 1.24316 1.11851
338.15 0.97941 1.40980 1.36649 1.23889 1.11798
343.15 0.97641 1.40596 1.36168 1.23464 1.11166
348.15 0.97340 1.40140 1.35766 1.23042 1.10839
353.15 0.97042 1.39685 1.35330 1.22619 1.10514
T (K) (g/cm3)
278.15 [(CH2)4SO3HMIm][TF2N]
[(CH2)4SO3HMIm][HSO4]
283.15 1.59792 1.45030
288.15 1.59296 1.44702
293.15 1.58785 -
298.15 1.58258 1.43708
303.15 1.57787 1.43368
308.15 1.57318 -
313.15 1.56852 1.42676
318.15 1.56387 -
323.15 1.55923 1.42051
328.15 1.55460 -
333.15 1.55001 1.41428
338.15 1.54556 -
343.15 1.54112 1.40807
348.15 1.53668 -
353.15 1.53223 1.40180
52
T(K)
280 300 320 340 360
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4 [TDC ][DCN]
[PMPY] [TF2N]
[EMMP] [TF2N]
[TDC] [TF2N]
[EMIM][LACATATE]
[(CH2)4SO3HMIm][TF2N]
[(CH2)4SO3HMIm][HSO4]
Figure 3.1: Liquid density of the studied ionic liquids at temperatures ranging from
278.15 K to 353.15 K.
Table 3-2: Temperature-dependent density correlations for the ionic liquids
Ionic liquids Density (g/cm3) AAD (%)
[TCD][CN] (g/cm3) =1.10193-0.0006[T(C)] 0.05
[EMIM] [LATATE] (g/cm3) = 1.1601-0.0007[T(C)] 0.02
[TCD][ Tf2N] (g/cm3) = 1.2947-0.0009[T(C)] 0.17
[EMMP][TF2N] (g/cm3) = 1.4236-0.0009[T(C)] 0.06
[PMPY ][TF2N] (g/cm3) = 1.1416-0.0009* [T(C)] 0.06
[(CH2)4SO3HMIm][TF2N] (g/cm3) = 1.6016-0.0009* [T(C)] 0.09
[(CH2)4SO3HMIm][HSO4] (g/cm3) = 1.4533-0.0006* [T(C)] 0.14
53
3.2 Solubility of Carbon Dioxide
3.2.1 Verification of Measurements
The solubility of CO2 was corroborated with [bmim][PF6] at 323.15 K and
compared with previously published results in the literature as published by (Shiflett and
Yokozeki, 2005) and (Anthony et al., 2002) where the AADs of the measured and
reported solubilities at 323.15 K are 4 and 12 %, respectively. The results are shown in
Figure 2. The comparison shows better agreement with data published by Shiflett and
Yokozeki.
Mole fraction of co2 in [Bmim][PF6] (%)
0 5 10 15 20 25
Pre
ssure
(b
ar)
0
5
10
15
20
25
This work
Anthony et al. (2002)
Shiflett and Yokozeki (2005)
Figure 3.2: Solubility of CO2 in [bmim][PF6] at 323.15 K compared to the solubility data
result this work with previously published results : ● [bmim][PF6],green this work; ■
[bmim][PF6],red, (Shiflett, 2005); ▼[bmim][PF6],blue, (Anthony et al., 2002).
54
3.2.2 Experimental Isotherm CO2 Solubility
Previous investigations in the literature have shown that carbon dioxide is highly
soluble in imidazolium-based ionic liquids (Blanchard et al., 2001). In this work, carbon
dioxide was dissolved in a variety of ionic liquids with different cations and anions to
explain the factors governing the solubility in the ILs. Three ionic liquids with the same
anion (bis(trifluoromethylsulfonyl)imide) were used where the effect of the cation on
solubility was investigated. Two ionic liquids with the same cation (1,2,3-
Tris(diethylamino) cyclopropenylium) were investigated to explore the effects of
changing the anion. Two other ionic liquids with the same cation were investigated
[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4]. The following table shows
the solubility of CO2 in all the ionic liquids studied in this work at three temperatures.
Table 3-3: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [TDC][DCN] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[TCD][DCN]
At 313.15 K At 323.15 K At 333.15 K
Pressure
(mbar)
Mole
Fraction of
CO2 (%)
Pressure
(mbar)
Mole
Fraction
of CO2
(%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
101.01 0.178 102.34 0.187 99.81 0.175
500.17 0.854 500.17 0.754 499.63 0.609
1001.02 1.65 997.41 1.45 999.15 1.25
2002.05 3.39 1998.31 2.99 2000.05 2.55
4000.11 6.74 4001.58 5.87 3998.11 5.02
7000.13 11.24 6996.13 9.77 6997.87 8.35
8998.73 14.11 9001.39 12.31 8999.13 10.52
9998.15 15.49 9997.49 13.57 10000.16 11.63
10998.79 16.87 11002.93 14.78 11000.52 12.65
12997.65 19.59 12996.72 17.27 12999.25 14.75
14992.51 22.17 14997.18 19.57 14997.31 16.78
17001.38 24.79 16998.04 21.85 17007.12 18.59
19006.65 27.20 19006.11 24.03
55
Table 3-4: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [PMPY][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[PMPY][TF2N]
At 313.15 K At 323.15 K At 333.15 K
Pressure
(mbar)
Mole
Fraction of
CO2 (%)
Pressure
(mbar)
Mole
Fraction of
CO2 (%)
Pressure (mbar) Mole
Fraction of
CO2 (%)
99.01 0.238 96.34 0.229 99.67 0.219
500.03 1.09 499.49 0.928 499.89 0.744
1001.28 2.12 998.21 1.868 999.01 1.539
1999.24 4.31 1999.37 3.787 1999.78 3.204
3998.51 8.35 3998.51 7.249 3999.04 6.062
7000.13 13.73 7000.93 11.85 6996.93 10.04
8998.99 17.15 9000.33 14.70 9001.53 12.57
9999.76 18.77 9996.42 16.06 9999.62 13.75
10998.79 20.36 10999.06 17.48 10999.06 14.90
12997.92 23.46 13002.45 20.24 12997.25 17.25
14998.65 26.34 14997.71 22.82 15000.25 19.35
16998.18 29.03 17007.38 25.26 16995.37 21.43
18996.91 31.67 19008.11 27.66 18996.51 23.23
Table 3-5: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [EMMP][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[EMMP][TF2N]
At 313.15 K At 323.15 K At 333.15 K
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
97.67 1.60 99.93 0.209 100.87 0.182
499.63 2.29 499.76 0.876 500.16 0.682
998.61 3.35 998.47 1.74 1000.48 1.44
1999.37 5.48 2000.71 3.63 1999.11 3.17
3998.51 9.41 4000.77 7.01 3998.24 6.00
6997.99 14.62 6997.73 11.44 7000.81 9.942
8998.32 17.79 8998.86 14.32 8999.66 12.32
9998.02 19.33 10003.51 15.70 9997.75 13.46
10999.59 20.86 11000.26 17.11 10998.79 14.59
12997.65 23.82 12997.78 19.69 12997.65 16.83
14999.31 26.57 15002.12 22.12 14998.78 18.98
16999.24 29.21 16995.77 24.48 16990.03 20.94
19000.11 31.66 18996.24 26.73 18997.04 22.80
56
Table 3-6: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [TDC][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[TCD][TF2N]
At 313.15 K At 323.15 K At 333.15 K
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
97.54 0.28 101.41 0.25 101.27 0.23
498.96 1.30 500.83 1.05 500.03 0.91
998.88 2.50 998.88 2.09 997.41 1.88
2000.31 5.03 2000.44 4.37 1999.51 3.91
4001.57 9.74 3998.37 8.37 3998.23 7.41
6999.06 15.90 6998.67 13.73 6999.06 12.19
8999.26 19.70 8998.46 17.04 8998.19 15.19
9998.56 21.51 9998.69 18.66 9997.09 16.68
11000.79 23.31 10999.32 20.18 10999.73 18.10
12999.12 26.73 12999.25 23.17 12998.72 20.78
15000.52 30.00 14997.71 26.14 14998.78 23.38
16997.51 33.18 17005.38 28.81 16999.51 25.78
18996.77 36.01 18996.64 31.27 18997.84 28.17
Table 3-7: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [EMIM][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[EMIM][LACTATE]
At 313.15 K At 323.15 K At 333.15 K
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
Pressure
(mbar)
Mole Fraction
of CO2 (%)
998.88 8.70 999.01 7.14 499.63 4.30
2001.51 11.63 3997.83 13.00 998.48 5.97
3998.64 15.25 4998.73 14.29 1999.65 8.29
6999.46 18.90 6998.93 16.39 3996.24 11.24
8997.92 20.90 9997.75 19.07 6999.61 14.27
9998.29 21.84 9997.75 19.07 9000.73 15.95
10999.73 22.70 18998.37 24.99 9998.29 16.74
12997.12 24.23
14998.91 25.59
17000.58 27.08
18998.10 28.31
57
Table 3-8: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [[(CH2)4SO3HMIm][TF2N]] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[(CH2)4SO3HMIm][TF2N]]
313.15K 323.15K
Pressure
(mbar)
Mole Fraction of CO2
(%)
Pressure
(mbar)
Mole Fraction of CO2
(%)
97.67 0.13 98.21 0.16
499.63 0.13 500.29 0.62
998.61 0.73 999.68 1.22
8998.33 13.49 3998.37 5.57
9998.02 14.55 7000.53 9.09
10999.59 15.96 8999.13 11.59
12997.65 18.29 10001.09 12.58
14999.31 20.82 15002.38 18.26
16999.24 22.96
19000.11 25.38
Table 3-9: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data
for [(CH2)4SO3HMIm][HSO4] (1) + CO2 at 313.15, 323.15 and 333.15 K.
[(CH2)4SO3HMIm][HSO4]
313.15K 323.15K
Pressure
(mbar)
Mole Fraction of
CO2 (%)
Pressure (mbar) Mole Fraction of CO2
(%)
99.27 0.076 101.01 0.056
498.43 0.17 499.77 0.12
998.88 0.30 9000.59 3.19
6999.33 2.53 9997.89 3.65
10999.73 4.82 10998.79 4.08
12997.12 5.52 12997.65 4.73
14999.98 5.48
16999.51 6.14
58
3.3 Solubility Isotherms Graphs
The following graphs will illustrate the CO2 solubility of the seven ionic liquids at
three different temperatures.
3.3.1 Solubility of CO2 in [EMMP][TF2N]
The following is a graphical representation of the CO2 solublities in
[EMMP][TF2N] at 313.15, 323.15 and 333.15K.
Mole fraction OF CO2 in [EMMP][Tf2N ](%)
0 5 10 15 20 25 30 35
Pre
ssure
(M
ba
r)
0
5000
10000
15000
20000
313.15 k
323.15 k
333.15 k
Figure 3.3: Comparison of measured isothermal solubility data of CO2 in
[EMMP][TF2N] at 313.15, 323.15 and 333.15 K.
59
3.3.2 Solubility of CO2 in [TDC] [TF2N]
The following is a graphical representation of the CO2 solublities in
[TDC][TF2N] at 313.15, 323.15 and 333.15K.
Mole Fraction of CO2 in [TDC][Tf2N] (%)
0 5 10 15 20 25 30 35 40
Pre
ssure
(M
ba
r)
0
5000
10000
15000
20000
313.15 K
323.15 K
333.15 K
Figure 3.4: Comparison of measured isothermal solubility data of CO2 in [TDC][TF2N]
at 313.15, 323.15 and 333.15 K.
60
3.3.3 Solubility of Co2 in [PMPY] [TF2N]
The following is a graphical representation of the CO2 solublities in
[PMPY][TF2N] at 313.15, 323.15 and 333.15K.
Mole fraction of CO2 in [pmpy ][Tf2N](%)
0 5 10 15 20 25 30 35
Pre
ssure
(M
ba
r)
0
5000
10000
15000
20000
313.5 k
323.15 k
333.15 k
Figure 3.5: Comparison of measured isothermal solubility data of CO2 in [PMPY][TF2N]
at 313.15, 323.15 and 333.15 K.
61
3.3.4 Solubility of CO2 in [TDC] [DCN]
The following is a graphical representation of the CO2 solublities in [TDC][DCN]
at 313.15, 323.15 and 333.15K.
Mole fraction of CO2 in [TDC] [DCN] (%)
0 5 10 15 20 25 30
Pre
ssure
(M
ba
r)
0
5000
10000
15000
20000
313.15 k
323.15 k
333.15 k
Figure 3.6: Comparison of measured isothermal solubility data of CO2 in [TDC][DCN] at
313.15, 323.15 and 333.15 K.
62
3.3.5 Solubility of CO2 in [EMIM] [LACTATE]
The following is a graphical representation of the CO2 solublities in
[EMIM][LACTATE] at 313.15, 323.15 and 333.15K.
Mole fraction of CO2 in [Emim][LACTATE] (%)
0 5 10 15 20 25 30
Pre
ssure
(M b
ar)
5000
10000
15000
20000
313.15 K
323.15 K
333.15 K
Figure 3.7: Comparison of measured isothermal solubility data of CO2 in
[EMIM][LACTATE] at 313.15, 323.15 and 333.15 K.
63
3.3.6 Solubility of CO2 in [(CH2)4SO3HMIm][TF2N] And
[(CH2)4SO3HMIm][HSO4]
The following is a graphical representation of CO2 solublities in
[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15 and 323.15K.
Mole fraction of CO2 (%)
0 5 10 15 20 25 30
Pre
ssure
(M
ba
r)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[(CH2)4SO3HMIm][TF2N] at 313.15k
[(CH2)4SO3HMIm][TF2N] at 323.15k
[(CH2)4SO3HMIm][HSO4] at 313.15 k
[(CH2)4SO3HMIm][HSO4] at 323.15 k
Figure 3.8: Comparison of measured isothermal solubility data of CO2 in
[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and
333.15 K.
64
3.4 Results: Effects of Cation With [TF2N] Anion
The effect of changing the cation on CO2 solubility was investigated using three
cations: 3-Methyl-1-propylpyridinium, ethyldimethylpropylammonium and 1,2,3-
tris(diethylamino)cyclopropenylium, all with the bis(trifluoromethylsulfonyl)imide anion.
The following graph illustrates the CO2 solubility of the four ionic liquids at
313.15 K.
Mole fraction of CO2 in ionic liquids (%)
0 10 20 30 40
Pre
ssu
re (
M b
ar)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000[[PMPY ][Tf2N]
[EMMP][Tf2N]
[TCD][Tf2N]
[(CH2)4SO3HMIm][TF2N]]
Figure 3.9: Comparison of three ionic liquids with the same anion to illustrate the effect
of the cation at 313 K.
65
3.4.1 Discussion: Effects of Cation With [TF2N] Anion
By examining the results of the aforementioned graphs, there are a few trends that can
be identified when comparing the same anion a changing cation. The first trend, as shown
in Figures 3.3-3.5 and 3.8 and in numerous previous findings, shows that the solubility of
CO2 in ionic liquids decreases with increasing temperature and increases with increasing
pressure. The second trend is the effect of changing the cation, as seen in Figure 3.9. In
this case, changing the cation on the IL has a significant effect on the CO2 solubility. It is
clear that the cation [TDC] provides a higher solubility when compared to the other three
cations. The solubility in decreasing order is as follows:
[TDC][TF2N]>[PMPY][TF2N]>=[EMMP][TF2N]> [(CH2)4SO3HMIm][TF2N]].
[TDC] cation contains multiple methyl groups distributed around the ring structure of the
cation which could be providing better free volume dynamics for CO2 to interact with this
ionic liquid as a whole. If the cation structure is examined closely, [TDC] has six methyl
groups hanging off the cation, [PMPY] has three methyl groups, [EMMP] has two methyl
groups and [(CH2)4SO3HMIm][TF2N] has three methyl groups. However, in [TDC] and
[PMPY], the methyl groups are organized around a core ring structure of the cation
perhaps enhancing their interaction with CO2 and providing a larger free volume unlike
[EMMP] which does not contain a ring structure. This may be similar to how the effect of
the alkyl chain length affects CO2 solubility where the increase in alkyl chain length leads
to decreased density of the ILs, and increased free volume within the longer chain of IL
(Muldoon et al., 2007).
66
This is further supported by the fact that [TDC] has the lowest density when
compared to [PMPY], [EMMP] and [(CH2)4SO3HMIm][TF2N]. Thus, it has the most
free volume among the three ILs giving it the highest solubility. Each of the cations has a
different base. For example, [TDC] is a propenylium based cation, [PMPY] is a
pyridinium based cation, [EMMP] is an ammonium based cation and
[(CH2)4SO3HMIm][TF2N] is an imidazolium based cation. The differences in cation
base can also be responsible for the differences in CO2 solubility. According to Sumon
and Henni (2011), cation alterations that decrease CO2 solubility include the addition of
the following groups: hydroxyl ([bmim][TF2N] > [OC2mim][TF2N]), phenyl
([hmim][TF2N] > [bnmim][TF2N]), and ether ([bepyrr]][TF2N] > [EtOEtpyrr]][TF2N])
(Sumon and Henni, 2011). Thus, one can see that modification of the cation can play a
minor role in effecting CO2 solubility. However, substantial changes are seen with anion
modification as seen in the next section.
3.5 Results: Effects of Anion With [TDC] Cation
The effect from changing the anion on CO2 solubility was investigated using two
different anions: bis(trifluoromethanesulfonyl)imide and dicyanamide, each with the
1,2,3-tris (diethyl amino) cyclopropenylium cation.
67
Mole fraction of CO2 in ionic liquids (%)
0 10 20 30 40
Pre
ssure
( M
ba
r)
0
5000
10000
15000
20000
[TDC][DCN]
[TDC][TF2N]
Figure 3.10: Comparison of CO2 solubility of [TDC] with [TF2N] and [DCN] at 313.15
K
3.5.1 Discussion Results: Effects of Anion With [TDC] Cation
In this section, the effects of changing the anion are explored. The
previous graph shows the CO2 solubility of two ionic liquids with the same cation [TDC]
but with two different anions, [TF2N] and [DCN]. The ionic liquid with the higher CO2
solubility possesses the fluorinated anion. [TDC] [TF2N] CO2 solubility is 0.3127 at
323.15K and 19 bar whereas [TDC][DCN] CO2 solubility is 0.2403 at 323.15 K and 19
bar. Thus, the fluorinated anion leads to about a 30% increase in solubility when
compared to the non-fluorinated anion. From the literature (Cadena et al., 2004), it is has
68
been shown time and time again that the nature of the anion has the greatest influence on
the solubility of CO2 and the bis(trifluoromethylsulfonyl)-imide anion [TF2N] has the
greatest affinity for CO2 (Cadena et al., 2004). This increase in CO2 solubility is, in part,
explained by the strong coulombic interactions responsible for the organization of the
liquid (Zhang et al., 2012). The high CO2 solubility, especially with the [TF2N] anion, is
attributable to the fluoroalkyl groups in [TF2N] which are known to be CO2-philic (Aki
et al., 2004). This may be the result of the favorable interactions between the negative
fluorine atoms of the anions and the positive charge on the carbon of carbon dioxide (Aki
et al., 2004; Schilderman et al., 2007). These are similar findings to Aki et al., when they
compared anions and found that [TF2N] has a higher CO2 solubility than the inorganic
anion of [DCN] (Aki et al., 2004). Hence, the anion has an influential role in determining
the CO2 solubility of an ionic liquid and [TDC][TF2N] has a higher solubility than
[TDC][DCN].
3.6 Results: Comparison of The [DCN] Anion With Different Cations
In this next section the ionic liquid [TDC][DCN] is compared with the experimental
results by Aki et al. on [bmim][DCN] and the effect of changing the cation with the same
anion (dicyanamide) is examined. A graphical comparison can be seen in the figure
below.
69
Mole Fraction of CO2 in ILs
0.0 0.1 0.2 0.3 0.4 0.5 0.6
Pre
ssure
(ba
r)
0
20
40
60
80
100
[BMIM][DCN] (Aki et al. 2004)
[TDC][DCN](this work)
Figure 3.11: Comparison of CO2 solubility of [TDC] with [bmim] cations with same
anion at 313.15 K.
3.6.1 Discussion: Comparison of The [DCN] Anion With Different Cations
From the graph, [TDC] [DCN] has a better or comparable CO2 solubility to
[bmim][DCN] at low pressures. This trend could be due to the fact that [TDC] has more
methyl groups hanging off the cation compared to [bmim]. However, [bmim] has a
longer alkyl chain, perhaps giving it the higher solubility at higher pressures. When
comparing the two cations, one is a propenylium based cation and the other is a
imidazolium based cation. This too has a role in the reaction as imidazolium based ionic
liquids can have a higher solubility.
70
3.7 Comparison of All the Ionic liquids Studied
Mole fraction of CO2 in ionic liquids (%)
0 10 20 30 40 50
Pre
ssure
(M
ba
r)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[[PMPY][Tf2N]
[EMMP][Tf2N]
[TCD][Tf2N]
[(CH2)4SO3HMIm][TF2N]
[TCD][DCN]
[EMIM][LACTATE]
[(CH2)4SO3HMIm][HSO4]
Figure 3.12: Comparison of measured isothermal solubility data of CO2 in different ionic
liquids at 313.15 K
The ionic liquids are compared in the previous graph where the CO2 solubility
increases in all ILs with increasing pressure and decreases with increasing temperature.
The CO2 solubility in decreasing order is as follows:
[TCD][TF2N]>[PMPY][TF2N]>[EMMP][TF2N]>[emim][LACTATE]>[TCD][DCN]>
[(CH2)4SO3HMIm][TF2N]>[(CH2)4SO3HMIm][HSO4]. The following are the
solubilities obtained at 323.15K and 19 bar: [TCD][TF2N] =0.3127, [PMPY][TF2N] =
0.2765, [EMMP][TF2N]= 0.2672, [emim][LACTATE]= 0.2499, [TCD][DCN]= 0.2402.
The following are the solubilities obtained at 323.15K and 15 bar:
71
[(CH2)4SO3HMIm][TF2N]= 0.182 and [(CH2)4SO3HMIm][HSO4] =0.0548. As
expected, the ionic liquids with fluorinated anions have the highest solubility among the
studied ionic liquids. In addition to fluorination, the combined effect of fluorination and
the presence of S=O groups on the TF2N anion act synergistically to increase the CO2
solubility (Muldoon et al., 2007). It is suggested that the S=O group can increase CO2-
philicity of molecules due to Lewis base-Lewis acid interactions with the carbon atom of
CO2 (Muldoon et al., 2007). The effect of the TF2N anion on CO2 solubility is seen most
dramatically when comparing [(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm]
[HSO4], where the addition of the fluorinated anion increases the solubility of CO2 by
more than three times that of the hydrogen sulfate anion. The hydrogen sulfate anions
also face another issue beyond low solubility, which is high viscosity. This has also been
reported by Riberio who found imidazolium ionic liquids with HSO4 have a high
viscosity which may be due to the anion-anion interactions (Ribeiro, 2012).
An interesting point to note is that at low pressures, of less than 10 bar, [emim]
[LACTATE] seems to have a higher CO2 solubility. For example, at about 323.15K and 7
bar [emim][LACTATE] has a solubility of 0.1639 whereas [TCD][TF2N] has a solubility
of 0.1373. This trend is seen until about 10 bar. This is similar to Shiflett’s ionic liquid
[emim][Ac] as seen in the graph below, which demonstrates high solubility at low
pressures and thus, [emim][LACTATE] has elements of a physical and chemical reaction
with CO2. As shown by Blath et al. IL with carboxylic anions such as [emim]
[pivalate],[emim][OAc] and [emim][benzoate] show chemoabsorption (Blath et al.,
2012). [LACTATE] contains a carbonyl group which is known to increase CO2 solubility
72
by providing the free electrons to the oxygen and allowing them to interact with the
Lewis acidic carbon of the CO2 (Muldoon et al., 2007).
Mole fraction of CO2
0.1 0.2 0.3 0.4 0.5
Pre
ssure
(b
ar)
0
2
4
6
8
10
12
14
16
18
20
[Emim][LACTATE] (this work)
[Emim][Ac] (Shiflett et al.2008)
Figure 3.13: Comparison of [emim][Ac] and [emim][LACTATE] at 50°C.
3.8 Comparisons of Current Work With Previously Published Work
A great deal of work has been spent on developing CO2 friendly ionic liquids to
increase the solubility of polar molecules in CO2. Some have used fluorination, others
have used nonfluorous methods to increase the CO2-philicity. Other methods used to
increase CO2 solubility are the addition of carbonyl groups and the branching of the alkyl
chain to allow for more free volume for CO2 interactions. These are more
environmentally friendly ways to increase CO2 solubility.
73
There are endless published papers exploring CO2 solubility in many different ionic
liquids. This section will explore a sample of what is currently in the literature and
compare it with the results obtained from this work. Some of the highlights from the
literature include the work by Shiflett et al. and their work with
[hmim][TF2N],[bmim][BF4] ,[bmim][PF6] and [bmim][Ac] (Shiflett and Yokozeki
2007; Shiflett and Yokozeki 2005). Others include the study of [emim][FAP] by
Althuluth et al. (Althuluth et al., 2012), the study of [emim][TF2N] from Schildermana et
al. (Schilderman et al., 2007) and many others.
3.8.1 Effect of Changing The Cation
Among this vast pool of CO2 solubility in different ionic liquids the effect
of the cation alkyl chain length for the imidazolium-based ionic liquids paired with the
[TF2N] anion ([omim][TF2N], [bmim][TF2N] from Aki et al. (Aki et al., 2004) and
[hmim][TF2N]) will be examined and compared with ionic liquids with the same anion:
[PMPY] [TF2N], [TDC] [TF2N], [EMMP][TF2N] and [(CH2)4SO3HMIm][TF2N] and
others such as [hmpy][TF2N],[C6H4F9mim][TF2N], [C8H4F13mim][TF2N] and
[Choline][TF2N] from Muldoon et al (Muldoon et al., 2007).
74
Mole fraction CO2 in ionic liquids
0.0 0.2 0.4 0.6 0.8
Pre
ssure
( b
ar)
0
20
40
60
80
100
[Choline][Tf2N] (Muldoon et al., 2007)
[[C8H4F13mim][Tf2N]( Muldoon et al.,2007)
[bmim][Tf2N] (Aki et al., 2004)
[Omim][Tf2N] (Aki et al .,2004)
[TDC][TF2N] (this work).
[EMMP][TF2N](this work).
[Pmpy][TF2N](this work).
[[C6H4F9mim][Tf2N] (Muldoon et al., (2007)).
[hmmim][Tf2N] (Aki et al.,(2004)).
Figure 3.14: Comparison of CO2 solubility at 333.15 K with different cations paired with
the [TF2N] anion.
75
Table 3-10: Numerical representation summary of the IL seen in Figure 3.14
Ionic liquid at 60 oC Highest Pressure Solubility
[Choline][TF2N] Muldoon et al. (2007) 12 bar 0.156
[bmim][TF2N] Aki et al. (2004) 13.6 bar 0.170
[hmmim][TF2N] Aki et al. (2004) 14.79 bar 0.199
[EMMP][TF2N](this work) 13 bar 0.201
[PMPY][TF2N] (this work) 13 bar 0.205
[C6H4F9mim][TF2N] Muldoon et al.
(2007) 13bar 0.221
[C8H4F13mim][TF2N] Muldoon et al.
(2007) 13 bar 0.232
[TDC][TF2N] (this work) 13 bar 0.235
[omim][TF2N] Aki et al. (2004) 16.23 bar 0.2467
Figure 3.15: Comparison of CO2 solubility at 60°C with different cations paired with the
[TF2N] anion at 333.15 K and about 12 to 14.97 bar.
76
The cation can have an effect on CO2 solubility. There are many variations of
cations causing significant changes to CO2 solubility. The IL showing some promise
when it comes to CO2 solubility from this group of IL is [TDC][TF2N] which has the
highest solubility. [omim][TF2N] from Aki et al. (2004) comes very close in terms of
solubility where [omim][TF2N] has a solubility of 0.2467 at about 16 bar and
[TDC][TF2N] has a solubility of 0.2614 at about 15 bar. By changing the cation from
[omim] to [TDC] the CO2 solubility can increase by about 10%.
Some of other trends that can clearly be seen from the graphs are that cations with
more fluro groups have a higher solubility as seen when comparing
[C6H4F9mim][TF2N] with [C8H4F13mim][TF2N] and [hmim][TF2N].
[C8H4F13mim][TF2N] has a higher solubility than [C6H4F9mim][TF2N] for two
reasons. First, it has more fluro groups and has a longer alkyl chain, both of which have
been shown in the literature to increase CO2 solubility (Muldoon et al., 2007). The ILs
also have comparable CO2 solubility when compared to the three ILs.
[EMMP][TF2N],[PMPY][TF2N] and [TDC][TF2N] all had a slightly lower solubility at
high pressure but very comparable solubility to [C6H4F9mim][TF2N]. The structure of
the cations used in [EMMP][TF2N],[PMPY][TF2N] and [TDC][TF2N] perhaps cause
crowding of the anion and may minimize the free volume of the ionic liquid and interfere
with how CO2 reacts with the anion. Thus, one can conclude that fluorination of the
cation leads to increased CO2 solubility.
77
Mole fraction CO2 in ionc liquids
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
pres
sure
(bar
)
0
5
10
15
20[hmim][Tf2N] (Shiflett and Yokozki. 2007)
[hmpy][Tf2N] (Muldoon et al. 2007)
[bmim][Tf2N] (Anthony et al. 2005)
[TDC] [Tf2N] (this Work)
[Pmpy] [Tf2N] (this work)
[EMMP][Tf2N] (this Work)
Figure 3.16: Comparison of CO2 solubility in different ILs with the same anion at 323.15
K
Similar trends exist for CO2 solubility which increases with increasing pressure. In
Figure 3.16, the comparison of the benchmark that most IL will be compared to,
Shiflett’s [hmim][TF2N], is compared to other ionic liquids with the same anion but
different cations highlighting the effect of cation change. The [hmim][TF2N] CO2
solubility is comparable to [TDC][TF2N]. The effect of the alkyl chain can be seen when
comparing [bmim], [omim] and [hmim] from Figures 3.14 and 3.16, where the trend in
decreasing solubility is as follows: [hmim]>[omim]>[bmim]. Thus, reiterating what is
published in the literature, the increase in alkyl chain length of the cation leads to
increased CO2 solubility.
78
Comparing [TCD] [TF2N] with [hmim] [TF2N] from Figure 3.16, [hmim][TF2N]
does have a slightly lower molecular weight, but the alkyl chain is longer and perhaps
organized in a more linear fashion making it more effective for solubility. The effect of
the alkyl chain length in [hmim] [TF2N] is related to the hydrogen atom located at the C2
position on the imidazolium ring which has a large positive charge (Ramdin et al., 2012).
If this carbon is replaced by a methyl group it decreases the solubility (Ramdin et al.,
2012). Therefore, the position of this acidic hydrogen gives Shiflett’s IL the higher
solubility as also seen in another imidazolium cation such as bmim which has a longer
alkyl chain and is known for higher CO2 solubility. Also, when comparing the cations
paired with [TF2N], at low pressures there is very little difference between the
imidazolium and pyridinium cations as seen between [hmim] and[hmpy] when paired
with [TF2N] (Muldoon et al., 2007). Therefore, depending on the modifications
employed and used on the cation, CO2 solubility can be improved or decreased.
By examining Figures 3.14 and 3.16, some general trends can be seen. Other
comparisons with [hmim][TF2N] can be made with the change of the cation when
examining the [choline] cation. The [choline] cation lowered CO2 solubility compared to
the [hmim] cation, hydrogen bonding of the [TF2N] anion with the [choline] cation may
make the anion less available for interaction with CO2 (Muldoon et al., 2007). Also, when
comparing [choline] with the [TDC] cation from the current experiment, the CO2
solubility is higher in [TDC][TF2N] than in [choline][TF2N] for similar reasons.
The general conclusion from the aforementioned figures is that the cation in an ionic
liquid can play an important role in determining the CO2 solubility capabilities of an ionic
liquid where [TDC][TF2N] has good potential for CO2 solubility.
79
3.8.2 Effect of Changing The Anion With An [Emim] Cation
One of the imidazolium based cations used in the experimental measurements is
[emim] in the ionic liquid [emim][LACTATE]. This section will compare the effects of
changing the anion with research published in the literature such as [emim][TF2N]
(Schilderman et al., 2007) and [emim][FAP] (Althuluth et al., 2012).
Mole fraction of CO2 ionic liquid
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Pre
ssure
(bar)
0
20
40
60
80
[emim][FAP] (Althuluth et al. 2012)
[emim][TF2N] (Schilderman et al. 2007)
[Emim][LACTATE ](this work)
Figure 3.17: Comparison of changing the anion with limidazoloium cation
The solubility of CO2 in [emim][FAP] is higher than in the other ILs with the same
cation following the trend: [emim][FAP]> [emim][TF2N] > [emim][LACTATE]. The
trend seen above is most likely due to the presence of a large amount of fluorine atoms in
the anion, which results in an increase in CO2 solubility of the IL (Althuluth et al., 2012).
The above trend holds true when examining CO2 solubility at high pressures.
However, for low pressure trends, CO2 solubility changes where [emim][LACTATE] has
higher solubility than [emim][FAP] and[emim][TF2N] as seen in the table below.
80
[emim][LACTATE] has a higher solubility than the popular anion of [TF2N] and is more
environmentally friendly due to the lack of fluoro groups.
Table 3-11: Comparison of [emim] cation with different anions.
Ionic liquid Pressure/ bar Mole fraction of CO2 in ILs
[emim][FAP] 5.80 0.1003
[emim][LACTATE] 6.99 0.1427
[emim][TF2N] 8.52 0.1230
3.9 Comparing The Literature With [Bmim][Ac]
The following is a graphical representation of Shiflett’s [bmim][Ac] which
is known for its very high CO2 solubility and a comparison with other measurements of
IL from the literature.
81
Mole fraction of CO2 (%)
0 5 10 15 20 25 30 35 40
Pre
ssure
(M b
ar)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[bmim][Ac] (Shiflett et al., 2008).
[bmim] [PF6] (Shiflett and Yokozeki 2005)
[(CH2)4SO3HMIm][TF2N] (this work)
[(CH2)4SO3HMIm][HSO4](this work)
[TCD][DCN] (this work )
[PMPY][Tf2N] (this work)
[EMMP][Tf2N] (this work)
[TCD][Tf2N] (this work)
[EMIM][LACTATE] (this work)
Figure 3.18: Comparison between the solubility of CO2 in the studied ionic liquids and
published results in the literature at 323.15 K
3.10 Comparison of Ammonium Based Ionic Liquid from the Literature and
Current Work
82
Figure 3.19: Comparison between the solubility of CO2 in the studied ionic liquids and
the published results in the literature at 323.15 K and high pressure from 1 to 120 bar.
The previous graph compares the ionic liquid which is an ammonium
based Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide and compares it
with 2-hydroxy ethylammonium formate (HEF), 2-hydroxy ethylammonium acetate
83
(HEA), 2-hydroxy ethylammonium LACTATE (HEL), tri-(2-hydroxy ethyl)-ammonium
acetate (THEAA), tri-(2-hydroxy ethyl)-ammonium LACTATE (THEAL), 2-(2-hydroxy
ethoxy)-ammonium formate (HEAF), 2-(2-hydroxy ethoxy)-ammonium acetate (HEAA)
and 2-(2-hydroxy ethoxy)- ammonium LACTATE (HEAL) from Yuan et al. (2007). The
eight ionic liquids by Yuan et al. have a much lower CO2 solubility than [EMMP] [TF2N]
at low pressure which can be due to the fact the ionic liquid has a fluorinated anion.
However, two of the Yuan et al. ionic liquids HEAA and THEAL show high CO2
solubility at high pressure.
Most of the contributions have provided information regarding the physical
absorption of CO2 in ionic liquids. Despite the high physical CO2 absorption of the seven
investigated ionic liquids, the solubilities of CO2 in the studied ionic liquids are less than
in [bmim][Ac] as seen in Figure 3.18, which demonstrates unusual behavior in
comparison to other ionic liquids and it possesses the highest CO2 solubility. However,
there is a tradeoff. According to Shiflett et al., when examining [bmim][Ac] which is
known for its high CO2 solubility at low pressure it becomes clear that it must be reacting
with a different mechanism. The high solubility of CO2 in [bmim][Ac] is explained by a
chemical reaction that occurs between the two reactants that leads to the formation of an
intermediary product produced which is 1-butyl-3-methylimidazolium-2-carboxylate
(Cabaco et al., 2012). This carboxylation reaction is irreversible even at very high
temperatures (Cabaco et al., 2012). The carboxylation of the imidazolium ring is
followed by acetic acid formation (Cabaco et al., 2012). The reactions occur as the CO2
solubility approaches 0.35 mole fraction. At this point, a physical reaction occurs
resulting from the interaction of acetic acid molecules with acetate anions (Cabaco et al.,
84
2012). During this second phase, the CO2 reacts with the carboxylate molecule and the
aceteic acids that resulted from the initial chemical reaction. Thus, the chemical reaction
creates a unique environment for the second physical reactions that explain the unique
behavior and high solubility of CO2 in [bmim][Ac].
Figure 3.19 compares Shifflet’s [bmim][PF6] and the seven ionic liquids investigated
in this work. All the ionic liquids had a higher solubility than [bmim][PF6] except for
[(CH2)4SO3HMIm][HSO4]. This is most likely due to the fact
[(CH2)4SO3HMIm][HSO4] lacks a fluorinated anion. When compared to most of the
ionic liquids studied in this work, the anion [PF6] is a weaker CO2 absorbent when
compared to the popular [TF2N] anion which is known for its higher CO2 solubility
(Muldoon et al., 2007).
3.11 Comparing the Current Work With Recent Results From An Affiliated Group
The next section will look at comparing the results from Ugyur, 2013 and
Nonthanasin, 2013 and this work. The ionic liquids used by Ugyur are 1-butyl-3-
methylimidazolium trifluoromethanesulfonate ([bmim OTF]), 1-butyl-3-
methylimidazolium dibutyl phosphate [bmim DPH], 1,3-dimethoxyimidazolium
bis(trifluoromethyl-sulfonyl)imide ([(OMe)2Im-NTF2]), 1-butyl-1-methylpiperidinium
bis(trifluoromethylsulfonyl)imide ([1b1mp NTF2]), and 1,3-diethoxyimidazolium
bis(trifluoromethylsulfonyl)imide ([(OEt)2Im-NTF2]) .
The ionic liquids used by Nonthanasin were triethylsulfonium bis(trifluoromethyl
sulfonyl)imide ([S222][TF2N]), diethylmethyl(2-methoxyethyl)ammonium
bis(trifluoromethyl sulfonyl)imide ([deme][TF2N]), 1-propyl-3-methylimidazolium
85
bis(trifluoromethyl sulfonyl)imide ([pmim][TF2N]), 1-allyl-3-methylimidazolium
bis(trifluoromethyl sulfonyl)imide ([amim][TF2N]), and 1-butyl-4-methylpyridinium
tetrafluoroborate ([4mbp][BF4]). The measurements from the two groups provide
evidence that the ammonium-based ionic liquid [deme][TF2N] achieved the highest CO2
absorption among all the ionic liquids. However, when comparing the current work to the
results, the trend for CO2 solubility in decreasing order is as follows: [TDC] [TF2N] <
[deme][TF2N]< [(OEt)2Im-NTF2]< [PMPY] [TF2N]< [pmim][TF2N]< [1b1mp NTF2]
<[EMMP][TF2N]< [S222][TF2N] < [emim][LACTATE] < [(OMe)2Im-NTf2]<
[TDC][DCN] < [bmim DPH] < [bmim OTF] < [4mbp][BF4]. The following graph
illustrates all the ionic liquids used in this work and their solubilites at different pressures
and at 323.15 K.
86
Mole fraction CO2 in ionic liquid (%)
0 5 10 15 20 25 30 35
Pre
ssure
(M b
ar)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[(OMe)2Im-NTf2](Uygur 2013)
[bmim OTF](Uygur 2013)
[bmim OTF](Uygur 2013)
[(OEt)2Im-NTF2](Uygur 2013)
[bmim DPH](Uygur 2013)
[TCD][DCN] (this work)
[PMPY ][Tf2N] (this work)
[EMMP ][Tf2N] (this work)
[TCD][Tf2N] (this work)
[EMIM][LACTATE] (this work)
[deme][Tf2N] (Nonthanasin 2013)
[pmim][Tf2N] (Nonthanasin 2013)
[S222][Tf2N] (Nonthanasin 2013)
[amim][Tf2N] (Nonthanasin 2013)
[4mbp][BF4] ( Nonthanasin 2013)
Figure 3.20: Comparison of CO2 solubility at 323.15 K
87
Figure 3.21: Comparison of CO2 solubility at 323.15 K
88
0 10 20 30 40
Pre
ssure
(M
ba
r)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[S222][Tf2N](Nonthanasin 2013)
[deme][Tf2N](Nonthanasin 2013)
[pmim][Tf2N](Nonthanasin 2013)
[amim][Tf2N](Nonthanasin 2013)
[4mbp][BF4](Nonthanasin 2013)
[TCD][DCN](this work)
[Pmpy ][Tf2N](this work)
[EMMP][Tf2N](this work)
[TCD][Tf2N](this work)
[(CH2)4SO3HMIm][HSO4](this work)
[(CH2)4SO3HMIm][TFSI](this work)
[EMIM][LACTATE](this work)
(%) liquids ionicin CO ofFraction Mole 2
Figure 3.22: CO2 solubility comparing the ionic liquids used in this work with that of
Nonthanasin (2013)
89
0 10 20 30 40
Pre
ssure
( M
ba
r)
5000
10000
15000
20000
[Deme][Tf2N](Nonthanasin 2013)
[TDC][Tf2N] (this work)
(%) liquids ionicin CO ofFraction Mole 2
Figure 3.23: Comparison of the solubility of CO2 in the studied ionic liquids and the one
in the present research at 313.15 K.
Two ionic liquids are compared with the same anion but different cation,
thus, allowing an examination of the cation effect as seen in Figure 3.23. It compares the
cation [deme] as reported by Nonthanasin (Nothanasin, 2013) and [TDC] as explored in
this current work. The solubility of CO2 in [TDC][TF2N] is higher than [deme][TF2N]
by about 12.5%.
90
0 5 10 15 20 25 30 35
Pre
ssure
(M
ba
r)
5000
10000
15000
20000
(OEt)2Im-NTF2] (Uygur (2013)
[TDC][Tf2N] (this work)
(%) liquids ionicin CO ofFraction Mole 2
Figure 3.24: Comparison of the solubility of CO2 in the studied ionic liquids and Uygur,
2013 at 323.15 K.
In the previous graph, the effect of the cation is seen when comparing Uygur’s best
(Uygur, 2013) ionic liquid to [TCD][TF2N] from this work. It can be seen that for every
pressure [TCD][TF2N] has a higher CO2 solubility than [OEt)2lm-NTF2]. The solubility
of [TCD][TF2N] solubility is higher by 12% .
91
0 5 10 15 20 25 30
Pre
ssure
(M
ba
r)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
[deme][Tf2N] (Nonthanasin 2013)
[emmp][Tf2N] (this work)
(%) liquids ionicin CO ofFraction Mole 2
Figure 3.25: Comparison of the solubility of CO2 in the studied ionic liquids and the ones
in our group at 323.15 K.
A comparison between Nothanasin’s best ionic liquid of [deme][TF2N] and
[Emmp][TF2N] is presented in the previous graph. There is a minor difference in the
composition of the ionic liquids where [deme][TF2N] has an extra methylene group
which has given the solubility a slight increase.
92
0 5 10 15 20 25 30 35
Pre
ssure
(M
ba
r)
5000
10000
15000
20000
[1b1mp NTF2] (Uygur 2013)
[(OEt)2Im-NTF2](Uygur 2013)
[PMPY ][Tf2N] (this work)
[TDC][Tf2N] (this work))
[deme][Tf2N](Nonthanasin 2013)
[pmim][Tf2N](Nonthanasin 2013)
(%) liquids ionicin CO ofFraction Mole 2
Figure 3.26: CO2 solubility of different best ionic liquid in this work, (Ugyur, 2013) and
(Nonthanasin, 2013) at 323.15 K.
93
Table 3-12: Summary of the CO2 solubilities in decreasing order from this work, Ugyur
(2013) and Nonthanasin (2013) at 323.15 K and same pressure 19 bar.
Ionic liquid Bar Solubility
[TDC] [TF2N] (this work) 19 0.3127
[deme][TF2N] (Nonthanasin 2013) 19 0.2805
[(OEt)2Im][TF2N](Ugyur 2013) 19 0.2779
[PMPY] [TF2N] (this work) 19 0.2765
[pmim][TF2N] (Nonthanasin 2013) 19 0.2724
[1b1mp][TF2N](Ugyur 2013) 19 0.2719
[EMMP][TF2N] (this work) 19 0.2673
[S222][TF2N]( Nonthanasin 2013) 19 0.2637
[emim][LACTATE] (this work) 19 0.2499
[(OMe)2Im][TF2N] (Ugyur 2013) 19 0.2405
[TDC][DCN] (this work) 19 0.2403
[bmim ][DPH]( Ugyu 2013) 19 0.2395
[bmim][TfO] (Ugyur 2013) 19 0.2085
[4mbp][BF4] (Nonthanasin 2013) 19 0.1706
94
[TDC] [Tf2N] (this Work)
[deme][Tf2N] (Nonthanasin (2013))
[(OEt)2Im][Tf2N](Ugyur (2013))
[PMPY] [Tf2N] (this Work)
[pmim][Tf2N] (Nonthanasin (2013))
[1b1mp][Tf2N](Ugyur (2013))
[EMMP][Tf2N] (this Work)
[S222][Tf2N]( Nonthanasin (2013))
[emim][LACTATE] (this Work)
[(OMe)2Im][Tf2N] (Ugyur(2013))
[TDC][DCA] (this Work)
[bmim ][DPH]( Ugyu (2013))
[bmim][TfO] (Ugyur (2013))
[4mbp][BF4] Nonthanasin(2013)
Mo
le fra
ctio
n o
f co
2
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
P= 19 bar
Figure 3.27: Summary of the CO2 solubilities in decreasing order from this work, (Ugyur,
2013) and (Nonthanasin, 2013) at 323.15 K at same pressure 19 bar.
When comparing the work of the two groups with the results obtained from the
current study, the propenylium based cation (1,2,3-Tris(diethylamino)cyclopropenylium
bis(trifluoromethanesulfonyl)imide) reigned supreme with respect to CO2 solubility.
When comparing the best ionic liquids from Ugyur and Nonthanasin, all three
[deme][TF2N], [(OEt)2Im-NTF2] and [TDC][TF2N] have the same fluorinated anion,
thus the discrepancy in their solubility must be attributable to their cation. Ugyur’s best
ionic liquid [(OEt)2Im-NTF2] cation only has two methyl groups attached to their cation,
95
perhaps contributing to its low solubility. When examining other factors responsible for
increasing solubility, such as the molecular weight and alkyl chain length, the IL with the
higher molecular weight is [TDC] [TF2N] and it has multiple long alkyl chains on the
cation which are perhaps responsible for its higher solubility.
96
4 CHAPTER FOUR: MODELING
This chapter contains three sections. The first section will describe the theory
behind the thermodynamic modeling. The second section will describe the density
calculations of the ionic liquids and details on the thermodynamic models used to
correlate the experimental CO2 solubility including equations of state, such as the Peng-
Robinson (PR-EoS), the Redlich Kwong (SRK), and the Non-Random Two-Liquid
(NRTL) activity coefficient model. Henry’s law constants, enthalpies and entropies of
absorption for CO2 in different ionic liquids are discussed in the last section.
4.1 Theory of Thermodynamic Properties and Modeling
The estimation of physical properties of gases and liquids is an important component
in research and in attempts to advance the field of ionic liquid research. Just like a
structural engineer needs to know the properties of concrete and steel to design a
structurally sound bridge, a chemical engineer needs to know the properties of gases and
liquids in order to develop their desired or targeted liquid or gas for a specific function
such as CO2 capture. This need or ability to estimate the physical properties was
addressed with the development of equations of state. There are many different
estimation methods or models that one could use. Depending on the effects studied
(Liquid Liquid Equilibrium (LLE), Vapour Liquid Equilibrium (VLE) or both), a
particular model is used (González, 2011). Empirical methods such as NRTL are used in
order to correlate LLE in mixtures of ionic liquids (González, 2011). On the other hand,
to correlate VLE systems, more sophisticated equation-of-state models are employed.
The different methods explored in this section deal with the equation of state method
97
which includes the Peng Robinson (PR-EoS) and Soave-Redlich-Kwong (SRK with
Quadratic Mixing Rules) and the activity coefficient method which includes the NRTL.
4.1.1 Peng Robinson EoS
The first method that the data could be correlated with is the Peng-Robinson
equation of state (EoS). The equation was developed in 1976 (Peng and Robinson, 1976).
It is a cubic thermodynamic equation that aims to describe the state of a given substance
under a specific set of physical conditions (Anthony et al., 2002). It provides a
relationship between temperature, pressure and volume.
The equation for the Peng-Robinson model is (Peng and Robinson, 1976):
)()( bVbbVV
a
bV
RTP
mmmm
(4.1)
The mixture parameters in the ionic liquid phase are calculated from following
four mixing rules (Song et al., 2010):
bVbbVV
a
bV
RTP
ˆˆˆˆ
(4.2)
c
c
P
RTa
2
45724.0
(4.3)
c
c
P
RTb 07780.0
(4.4)
2/11 cTTm (4.5)
226992.054226.137464.0 m (4.6)
The Peng-Robinson equation of state was used to calculate the fugacity
coefficient of carbon dioxide:
98
(4.7)
Some advantages of this equation are the simplicity of its application. However,
one of the drawbacks of this EoS is the limited accuracy that it can provide the user. To
calculate the parameters of the PR-EoS, the critical temperature (Tc), critical pressure
(Pc), and the acentric factor (ω) of both components, and CO2 and ionic liquids are
needed. The values are obtained by estimation using the modified Lydersen-Joback-Reid
method which is explained later in this chapter.
4.1.2 Soave-Redlich-Kwong (The SRK with Quadratic Mixing Rules)
The second method used to correlate the data is the SRK method with quadratic
mixing rules. It’s another equation of state method which provides results that are
comparable to the Peng-Robinson equation. The SRK equation of state is based on the
Redlich-Kwong-Soave (RKS) equation. The SRK equation originated from the Redlich-
Kwong (RK) equation of state (Redlich and Kwong, 1949) and was further modified by
Soave (Soave, 1972).
The Soave-Redlick-Kwon equation is as follows:
𝑃 =𝑅𝑇
𝑉−𝑏−
𝑎(𝑇)
𝑉(𝑉+𝑏) (4.8)
Where the parameters for the SRK-Equation of state are found using:
ci
cii
ci
ciii
P
RTb
P
TRa 08664.0,42747.0
22
(4.9)
The equations are obtained by applying the critical constraint to the EoS under the
following conditions:
m
V
nVTi
i ZdVV
RT
n
P
RTj
ln1
ln
,,
99
𝛼𝑖(𝑇𝑐𝑖) = 1.0 (4.10)
The parameter αi is a temperature function developed by Soave (Soave, 1972) in the RK-
EoS to improve the correlation of the vapor pressure:
𝛼𝑖(𝑇) = [1 + 𝑚𝑖(1 − 𝑇𝑟𝑖0.5)]
2 (4.11)
The parameter mi is uses the concept of correlation with the acentric factor:
𝑚𝑖 = 0.48508 + 1.55171𝜔𝑖 − 0.15613𝜔𝑖2 (4.12)
For multicomponent equilibria, mixing rules and combining rules which relate the
properties of the pure components to the properties of the mixtures are applied. The
mixture parameters in the liquid phase are calculated from the quadratic mixing rules:
𝑎 = ∑ ∑ 𝑥𝑖𝑗𝑖 𝑥𝑗𝑎𝑖𝑗 (4.13)
𝑎𝑖𝑗 = (𝑎𝑖𝑎𝑗)0.5
(1 − 𝑘𝑖𝑗) (4.14)
𝑏 = ∑ ∑ 𝑥𝑖𝑗𝑖 𝑥𝑗𝑏𝑖𝑗 (4.15)
𝑏𝑖𝑗 =(𝑏𝑖+𝑏𝑗)
2(1 − 𝑙𝑖𝑗) (4.16)
where bii = bi and bjj = bj. kij and lij are binary interaction parameters.
The interaction parameters in SRK EoS, has a linear relationship with temperature:
𝑘𝑖𝑗 = 𝑘𝑖𝑗0 + 𝑘𝑖𝑗
1 𝑇
1000 (4.17)
𝑙𝑖𝑗 = 𝑙𝑖𝑗0 + 𝑙𝑖𝑗
1 𝑇
1000 (4.18)
where kij0, kij
1, lij0 and lij
1 are constant.
100
4.1.3 NRTL Activity Coefficient Method
The third method used to correlate the data is the activity coefficient method of
NRTL. The general nonrandom two-liquid (NRTL) equation can be used to correlate the
vapor-liquid equilibrium of IL containing systems. Using AspenPlus, NRTL generates
the liquid activity coefficients. The idea behind NRTL is based on the premise that each
liquid is made of two types of molecules surrounded by each other in a binary mixture
(Walas, 1985). The theory looks at the concentration around each type of molecule which
is different from the overall concentration and this difference is related to the difference
in interaction energy between molecules of the same type (Walas, 1985). It is this energy
difference that introduces the concept of non-randomness at the molecular level in NRTL
(Walas, 1985).
The activity coefficients, γi, were correlated by the following equations based on
the NRTL model (Wang et al., 2010):
𝑙𝑛𝛾1 = 𝑥22 [𝜏21 (
𝐺21
𝑥1+𝑥2𝐺21)
2
+ (𝜏12𝐺12
(𝑥2+𝑥1𝐺12)2)] (4.19)
𝑙𝑛𝛾2 = 𝑥12 [𝜏12 (
𝐺12
𝑥2+𝑥1𝐺12)
2
+ (𝜏21𝐺21
(𝑥1+𝑥2𝐺21)2)] (4.20)
where,
𝐺12 = exp (−∝12 𝜏12)
𝐺21 = exp (−∝12 𝜏21)
12 = (𝑔12 − 𝑔22)/𝑅𝑇
21 = (𝑔21 − 𝑔11)/𝑅𝑇
101
The parameters g12 and g21, are equivalent (g12 = g21). 12, 21 and α12 are three binary
parameters adjusted to the experimental solubility data of ionic liquids.
4.2 Thermodynamic Modeling
4.2.1 Critical Property Estimation
The critical data for the ionic liquid used in this experiment was obtained by the
group contribution using the Modified Lydersen-Joback-Reid method (Valderrama and
Sanga, 2008). It is believed that ionic liquids begin to decompose at low temperatures or
temperatures approaching the natural boiling point and, as a result, the critical values
can’t actually be measured (Valderrama and Sanga, 2008). Therefore, the Modified
Lydersen-Joback-Reid method is used to estimate the values of the critical properties. A
group contribution method is used to find the critical properties (Tc, Pc and Vc), the
normal boiling point temperature (Tb), the critical compressibility factor (Zc), the density
(ρ) and the acentric factor (ω) of ionic liquids (Valderrama and Sanga, 2008).
4.2.2 Modified Lydersen‐Joback‐Reid Method
This method provides a way to estimate the critical properties of ionic liquids by
Valderrama et al. This method combines the equation for critical pressure and volume
which is based on Lydersen’s work and the equations of Joback-Reid for the normal
boiling temperature and the critical temperature (Valderrama and Sanga, 2008). One of
the advantages of this method is that it provides more accuracy for estimating the critical
properties of molecules with high molecular mass (Valderrama and Sanga, 2008).
The following correlations for estimating critical properties and acentric factors
are used (Valderrama and Sanga, 2008):
102
Modified Group Contribution Method: (Valderrama and Sanga, 2008).
𝑇𝑏(𝐾) = 198.2 + ∑ 𝑛∆𝑇𝑏 (4.21)
𝑇𝑐(𝐾) =𝑇𝑏
𝐴+𝐵 ∑ 𝑛∆𝑇𝐶−(∑ 𝑛∆𝑇𝐶)2 (4.22)
𝑃𝑐(𝑏𝑎𝑟) =𝑀
𝐶+(∑ 𝑛∆𝑃𝐶)2 (4.23)
𝑉𝐶(𝑐𝑚3𝑚𝑜𝑙−1) = 𝐷 + ∑ 𝑛∆𝑉𝐶 (4.24)
ω=(𝑇𝑏−43)(𝑇𝑐−43)
(𝑇𝑐−𝑇𝑏)(0.7𝑇𝑐−43)log (
𝑃𝑐
𝑃𝑏) −
(𝑇𝑐−43)
(𝑇𝑐−𝑇𝑏)log (
𝑃𝑐
𝑃𝑏) + log (
𝑃𝑐
𝑃𝑏) − 1 (4.25)
zc =PCVC
RTC (4.26)
Constants:
A=0.5703, B=1.0121, C=0.2573, D=6.75,
A=a+(BM / Vc ), B=(c/Vc )+d/M)Vc1.0470 where a=0.34111, b=2.0773, c=0.5386,
d=0.0393, R =84.31 (bar cm3 /mole k), Pp.=1.01325
In the equations above, M is in g/mol, Tb and Tc are in K, Pc is in bar and Vc is in
(cm3/mol). Where the contributions are indicated as ∆𝑇𝑏, ∆𝑇𝑐 , ∆𝑃𝑐, and ∆𝑉𝑐. M is the
molecular weight of the component. The boiling point Tb also needs to be estimated first
for 𝑇𝑐.
The calculated critical properties, normal boiling temperatures, and acentric
factors of the ionic liquids are listed in the table below. The experimental densities were
compared with the calculated densities obtained using the modified group contribution
method. The predicted densities are within an acceptable range of error.
103
Table 4-1: Molecular weights, normal boiling temperatures, critical properties, and
acentric factors of ionic liquids
Ionic liquids MW
(g/mol) Tb (K) Tc (K)
Pc
(bar)
Vc
(cm3/mol)
ZC
[EMMP][TF2N] 396.37
715.4
1038.7
25.88
955.5
0.3334
0.2863
[PMPY][TF2N] 416.36
839.8
1234.2
27.55
964.7
0.3070
0.2591
[TDC][TF2N] 532.56
938.1
1255.7
18.03
1394.0
0.5876
0.2407
[TDC][DCN] 318.5
858.6
1073.7
16.15
1115.9
1.0726
0.2019
[EMIM][LACTATE] 200.23
693.4
912.7
28.24
620.1
0.9702
0.2260
[(CH2)4SO3HMIm][TF2N]]
499.43 1097.6 1612.8 32.7 1070.1 0.377
0.2615
[(CH2)4SO3HMIm][HSO4]
316.4 1017.6 1433.0 25.88 744.8 0.8437
0.3602
4.2.3 Calculated Density and Deviation %Δp From Experimental Density
Table 4-2: Regressed and Experimental Density Data of [EMMP] [TF2N] by using
Modified Group Contribution Method
T(K) ρ(g/cm3)EXP ρ calc %Δρ
278.15 1.42002 1.38396 2.53953
AAD (%) = 1.18
283.15 1.41526 1.38362 2.23565
288.15 1.41060 1.38329 1.93667
293.15 1.40596 1.38295 1.63710
298.15 1.40126 1.38261 1.33109
303.15 1.39645 1.38227 1.01594
308.15 1.39181 1.38193 0.70978
313.15 1.38791 1.38159 0.45540
318.15 1.38336 1.38125 0.15221
323.15 1.37982 1.38092 0.07944
328.15 1.37540 1.38058 0.37645
333.15 1.37097 1.38024 0.67611
338.15 1.36649 1.37990 0.98142
343.15 1.36167 1.37956 1.31352
348.15 1.35766 1.37922 1.58834
353.15 1.35329 1.37889 1.89088
104
Table 4-3: Regressed and Experimental Density Data of [PMPY] [TF2N] by using
Modified Group Contribution Method
T(K) ρ(g/cm3)EXP ρcalc %Δρ
278.15 1.46723 1.43590 2.13552
AAD (% ) =1.23
283.15 1.46243 1.43560 1.83473
288.15 1.45762 1.43530 1.53107
293.15 1.45281 1.43500 1.22561
298.15 1.44803 1.43471 0.92017
303.15 1.44328 1.43441 0.61478
308.15 1.43854 1.43411 0.30806
313.15 1.43381 1.43381 0.00021
318.15 1.42911 1.43351 0.30777
323.15 1.42442 1.43321 0.61680
328.15 1.41979 1.43291 0.92438
333.15 1.41516 1.43262 1.23348
338.15 1.40980 1.43232 1.59719
343.15 1.40596 1.43202 1.85322
348.15 1.40140 1.43172 2.16355
353.15 1.39685 1.43142 2.47474
Table 4-4: Regressed and Experimental Density Data of [TDC] [TF2N] by using
Modified Group Contribution Method
T(K) ρ(g/cm3)EXP ρcalc %Δρ
298.15 1.27341 1.27021 0.25123
AAD (%) = 1.59
303.15 1.26905 1.26997 0.07251
308.15 1.26470 1.26973 0.39769
313.15 1.26036 1.26949 0.72405
318.15 1.25604 1.26925 1.05159
323.15 1.25173 1.26901 1.38031
328.15 1.24743 1.26877 1.71049
333.15 1.24316 1.26853 2.04048
338.15 1.23889 1.26829 2.37276
343.15 1.23464 1.26805 2.70567
348.15 1.23042 1.26780 3.03836
353.15 1.22619 1.26756 3.37419
105
Table 4-5: Regressed and Experimental Density Data of [EMIM] [LACTATE] by using
Modified Group Contribution Method
T(k) ρ(g/cm3)EXP Ρcalc %Δρ
278.15 1.15745 1.14355 1.20113
AAD (%)=1.5
283.15 1.15347 1.14355 0.86023
288.15 1.14977 1.14355 0.54120
293.15 1.14611 1.14355 0.22358
298.15 1.14246 1.14355 0.09519
303.15 1.13889 1.14355 0.40895
308.15 1.13543 1.14355 0.71493
313.15 1.13195 1.14355 1.02456
318.15 1.12851 1.14355 1.33251
323.15 1.12507 1.14355 1.64234
328.15 1.12167 1.14355 1.95044
333.15 1.11831 1.14355 2.25675
338.15 1.11498 1.14355 2.56215
343.15 1.11166 1.14355 2.86846
348.15 1.10839 1.14355 3.17194
353.15 1.10514 1.14355 3.47535
Table 4-6: Regressed and Experimental Density Data of [TDC] [DCN] by using Modified
Group Contribution Method
T(K) ρ(g/cm3)EXP ρcalc %Δρ
278.15 1.01638 0.99699 1.90802
AAD (%) = 1.26
283.15 1.01327 0.99698 1.60695
288.15 1.01014 0.99699 1.30207
293.15 1.00700 0.99699 0.99431
298.15 1.00391 0.99699 0.68958
303.15 1.00079 0.99699 0.37997
308.15 0.99770 0.99699 0.07144
313.15 0.99462 0.99699 0.23801
318.15 0.99155 0.99699 0.54836
323.15 0.98850 0.99699 0.85860
328.15 0.98546 0.99699 1.16973
333.15 0.98243 0.99699 1.48176
338.15 0.97941 0.99699 1.79468
343.15 0.97641 0.99699 2.10744
348.15 0.97340 0.99699 2.42318
353.15 0.97042 0.99699 2.73771
106
Table 4-7: Regressed and Experimental Density Data [(CH2)4SO3HMIm][TF2N] by
using Modified Group Contribution Method
T(k) ρ(g/cm3)EXP ρcalc %Δρ
278.15 1.59792 1.53372 4.01790
AAD (%)= 1.9
283.15 1.59296 1.53346 3.73500
288.15 1.58785 1.53321 3.44121
293.15 1.58258 1.53295 3.13573
298.15 1.57787 1.53270 2.86270
303.15 1.57318 1.53245 2.58927
308.15 1.56852 1.53219 2.31608
313.15 1.56387 1.53194 2.04188
318.15 1.55923 1.53168 1.76668
323.15 1.55460 1.53143 1.49047
328.15 1.55001 1.53117 1.21516
333.15 1.54556 1.53092 0.94718
338.15 1.54112 1.53067 0.67830
343.15 1.53668 1.53041 0.40787
348.15 1.53223 1.53016 0.13522
353.15 1.52782 1.52990 0.13640
Table 4-8: Regressed and Experimental Density Data [(CH2)4SO3HMIm][HSO4]
by Using Modified Group Contribution Method
T(k) ρ(g/cm3)EXP ρcalc %Δρ
278.15 1.45030 1.44305 0.50014
AAD (%)= 1.3
283.15 1.44702 1.44305 0.27460
298.15 1.43708 1.44305 0.41518
303.15 1.43368 1.44305 0.65332
313.15 1.42676 1.44305 1.14150
323.15 1.42051 1.44305 1.58651
333.15 1.41428 1.44305 2.03400
343.15 1.40807 1.44305 2.48400
353.15 1.40180 1.44305 2.94240
107
4.3 Equation of State
Many thermodynamic models have been proposed for modeling the phase behavior of
ionic liquids and CO2 systems. In this work, the data has been correlated with different
thermodynamic models. The experimental CO2 solubility data were correlated using the
equations of state including the standard Peng-Robinson (PR), SRK and NRTL.
4.3.1 The Standard Peng-Robinson (PR-EoS)
The Peng–Robinson EoS has been applied to model the solubilities of CO2 in
ionic liquids. Using the correlation with the standard PR-EoS, the binary interaction
parameters (k12) from 313.15 to 333.15 K for each system are given in table 4-10. The P-
x diagrams for each system are graphically presented for the experimental results and the
calculated results from the PR-EoS, as depicted in Figures 4.1-4.7. The results show an
absolute average deviation (AAD) between the model correlations and experimental data
which are between 0.07 and 3.3% for the ionic liquids as shown in Table 4-9 below and it
is concluded Peng–Robinson can satisfactorily describe the solubility of CO2 in the ionic
liquids.
The absolute average deviation is calculated using the following equation:
𝐴𝐴𝐷% =∑[𝐴𝐵𝑆(
𝐸𝑥𝑝−𝑅𝑒𝑔
𝐸𝑥𝑝)]
𝑁𝑃∗ 100% (4.27)
where, Exp and Reg are the experimental and regressed values for the partial pressures of
carbon dioxide above ionic liquids, and NP is the number of experimental data points.
Note the different behaviour of [EMIM][LACATE] and its high binary interaction
parameters. Even though the EoS could correlate the data well, using an EoS in this case
108
is not recommended as the interaction is more that just physical interaction as will be
discussed later.
Table 4-9: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the standard PR-EoS for the ionic liquids + CO2 system
Ionic liquids T (K)
313.15 323.15 333.15 Average
[EMMP][TF2N] 2.5 1.9 2.3 2.2
[PMPY][TF2N] 2.2 2.4 2.3 2.3
[TDC][TF2N] 3.3 3.1 3.1 3.1
[TDC][DCN] 1.9 1.9 2.4 2.0
[EMIM][LACTATE] 0.7 0.3 0.6 0.5
[(CH2)4SO3HMIm][TF2N]] 0.8 2.7 - 1.2
[(CH2)4SO3HMIm][HSO4] 2.3 0.7 - 1.4
Table 4-10: Binary interaction parameters of the standard PR-EoS for the ionic liquids (1)
+ CO2 (2) system.
Ionic liquids Binary interaction parameter T (K)
313.15 323.15 333.15
[EMMP][TF2N] k12 = -3.290+[0.009995T(K)] -0.180 -0.083 0.016
[PMPY][TF2N] k12=-0.3368+ [0.0008T(K)] -0.091 -0.077 -0.069
[TDC][TF2N] K12 = 0.01127]+[-0.0004 T(K) -0.120 -0.126 -0.130
[TDC][DCN] k12 = -0.0552+ [0.0000897T(K)] -0.081 -0.084 -0.085
[EMIM][LACATE] k12 = 29.8502+[-0.0908T(K)] 1.422 0.511 -0.396
[(CH2)4SO3HMIm][TF2N]] k12 = 1.65+[-0.005T(K)] -0.440 -0.096 -
[(CH2)4SO3HMIm][HSO4] k12 = -4.5+[0.12T(K)] -0.770 -0.644 -
109
4.3.2 Modeling Graphs Using PR-EoS for All ILs
The following section outlines the graphical representation for the modeling using
PR-EoS for all seven ionic liquids used in this study.
Figure 4.1: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [EMMP][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
110
Figure 4.2: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [PMPY][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
111
Figure 4.3: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
112
Figure 4.4: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15
K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][DCN]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
113
Figure 4.5: P-x diagram of the system [EMIM][LACTATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at
313.15 K; blue, at 323.15 K; red and at 333.15K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [emim][LACTATE]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
114
Figure 4.6: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]] and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the standard PR-EoS: at 313.15 K;
blue, at 323.15 K; red.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [(CH2)4SO3HMIm][TF2N]]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
115
Figure 4.7: P-x diagram of the system [(CH2)4SO3HMIm][HSO4] and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the standard PR-EoS: at 313.15 K;
blue, at 323.15 K; red.
0
2
4
6
8
10
12
14
16
18
20
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [(CH2)4SO3HMIm][HSO4]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
116
4.3.3 The Soave-Redlich-Kwong (SRK) with Quadratic Mixing Rules
The SRK has also been applied to model the solubilities of CO2 in ionic liquids.
The two binary interaction parameters (k12 and l12) in the mixing rules are optimized
using the experimental CO2 solubility data. Table 4-12 summarizes the binary interaction
parameters of the SRK with the quadratic mixing rules at three different temperatures for
each system. k12 and l12 are linear temperature-dependent functions. The P-x diagrams of
each system are graphically presented for the experimental results and the calculated
results from the standard SRK-EoS are depicted in Figures 4.8-4.12. Joback’s group
contribution method was used to estimate the critical temperature and pressure for the
ionic liquids, as well as the normal boiling temperature. The results show an absolute
average deviation (AADs) between the model correlations and experimental data between
0.6-2.9% for the ionic liquids as shown in the table below and it is concluded that SRK
can satisfactorily describe the solubility of CO2 in the ionic liquids.
Table 4-11: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the SRK with quadratic mixing rules for the ionic liquids + CO2
system
Ionic liquids T (K)
313.15 323.15 333.15 Average
[EMMP][TF2N] 1 0.8 0.7 0.8
[PMPY][TF2N] 0.7 0.7 1.2 0.8
[TDC][TF2N] 0.5 1.2 1.5 1.0
[TDC][DCN] 0.6 1.3 2.9 1.6
[EMIM][LACTATE] 0.8 0.7 1.3 0.9
117
Table 4-12: Binary interaction parameters of the SRK with quadratic mixing rules for the
ionic liquids (1) + CO2 (2) system
Ionic liquids Binary interaction parameters T (K)
313.15 323.15 333.15
[EMMP][TF2N] k12 = -0.1166+[-10.776×T(K)/1000] 0.224 0.138 0.031
l12 = 1.610+[-4.7689×T(K)/1000] 0.117 0.069 0.021
[PMPY][TF2N] k12 =-0.296499+[0.970593×T(K)/1000] 0.007 0.017 0.026
l12 =0.01745+[0.025733×T(K)/1000] 0.025 0.025 0.026
[TDC][TF2N] k12 = -0.2366+[0.3965×T(K)/1000] 0.025 0.025 0.026
l12 =-0.007571+[0.060035×T(K)/1000] 0.011 0.011 0.012
[TDC][DCN] k12 = -0.36817+[0.80691×T(K)/1000] -0.115 -0.107 -0.099
l12 = -0.07954+[0.0795201×T(K)/1000] 0.004 0.001 0.005
[EMIM][LACTATE] k12 = -4.749+[15×T(K)/1000] 0.052 0.097 0.214
l12 = -0.2919+[0.9775×T(K)/1000] 0.070 0.107 0.145
4.3.4 Modeling Graphs Using SRK -Eos for All Ils
The following section outlines the graphical representation of the models using
SRK-EoS for all seven ionic liquids used in this study.
Figure 4.8: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [EMMP][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
118
Figure 4.9: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K, green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [PMPY][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
119
Figure 4.10: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
120
Figure 4.11: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing
rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][DCN]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
121
Figure 4.12: P-x diagram of the system [EMIM][LCATATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by the SRK with quadratic
mixing rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [emim] [LACTATE]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
122
4.3.5 Non-Random Two Liquid Segment Activity Coefficient (NRTL)
The NRTL has also been applied to the solubilities of CO2 in ionic liquids. Table
4-14 shows the binary interaction parameters adjusted to the experimental solubility data
of the ionic liquids, which are (g12-g22)/R and (g21-g11)/R. The binary parameters are
related to 12 and 21, respectively. The parameter is assumed to be a constant unique
value of 0.3 in order to obtain accurate results (Al-Rashed et al., 2012). The binary
interaction parameters for the NRTL model, which are (g12-g22)/R and (g21-g11)/R, can be
linearly correlated as a function of temperature. The P-x diagrams of each system are
graphically presented for the experimental results and the calculated results from the
NRTL model, as depicted in Figures 4-13 – 4.19. The results show an absolute average
deviation (AAD) between the model correlations and experimental data between 0.6-
0.93% for the ionic liquids as shown in a table below and it is concluded that NRTL can
satisfactorily describe the solubility of CO2 in the ionic liquids.
Table 4-13: Average absolute deviation (AAD %) between experimental and estimated
values of pressure by the NRTL for the ionic liquids + CO2 system
ionic liquids T (K)
313.15 323.15 333.15 Average
[EMMP][TF2N] 1 0.9 0.9 0.9
[PMPY][TF2N] 0.5 1 1.2 0.9
[TDC][TF2N] 0.5 0.6 1 0.7
[TDC][DCN] 0.4 0.4 1.1 0.6
[EMIM][LACTATE] 1.4 0.4 1.0 0.9
[(CH2)4SO3HMIm][TF2N]] 1.4 0.8 1.1
[(CH2)4SO3HMIm][HSO4] 1.2 1.1 1.1
123
Table 4-14: Binary interaction parameters of the NRTL for the ionic liquids (1) + CO2 (2)
system (α = 0.3)
Ionic liquids
Binary
interaction
parameters
T (K) Linear function
313.150 323.150 333.150
[EMMP] [TF2N] (g12-g22)/R 180.241 578.011 975.782
(g12-g22)/R = [39.77×T(K)]-
12275.9
(g21-g11)/R -350.066 -500.736 -651.407
(g21-g11)/R =
[-15.067×T(K)]+4368.18
[PMPY][TF2N] (g12-g22)/R -186.869 -152.945 -119.020
(g12-g22)/R =
[3.3424×T(K)]-1299.221
(g21-g11)/R -23.244 -73.629 -124.013
(g21-g11)/R =
[-5.03844×T(K)]+1554.54
[TDC][TF2N] (g12-g22)/R -585.138 -593.922 -602.707
(g12-g22)/R =
[-0.8785×T(K)]-310.05
(g21-g11)/R 579.540 522.560 465.580
(g21-g11)/R = [-5.698´T(K)]-
2363.86
[TDC][DCN] (g12-g22)/R -19.353 -24.221 -29.090
(g12-g22)/R =
[-0.4868×T(K)]+422.72
(g21-g11)/R -108.584 -120.303 -132.021
(g21-g11)/R =
[-1.1719×T(K)]+258.384
[EMIM]
[LACTATE]
(g12-g22)/R 498.377 500.793 503.209
(g12-g22)/R =
[0.2415×T(K)]+305.191
(g21-g11)/R -629.930 -578.333 -526.737
(g21-g11)/R =
[5.15963×T(K)]+3690.01
[(CH2)4SO3HMIm]
[TF2N]
(g12-g22)/R 1435.801 523.701 -
(g12-g22)/R =
[-91.2×T(K)]+3000
(g21-g11)/R -496.940 -629.901 -
(g21-g11)/R =
[-13.3×T(K)]+3690
[(CH2)4SO3HMIm]
[HSO4]
(g12-g22)/R -32.830 72.030
(g12-g22)/R = [68.66×T(K)]-
21534.8
(g21-g11)/R 653.800 -246.701
(g21-g11)/R =
[-31.88×T(K)]+10056.81
124
4.3.6 Modeling Graphs Using NRTL for All ILs
The following section outlines the graphical representation for the modeling using
NRTL for all seven ionic liquids.
Figure 4.13: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [EMMP][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
125
Figure 4.14: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [Pmpy][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
126
Figure 4.15: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
127
Figure 4.16: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.
Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at
333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [TDC][DCN]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
128
Figure 4.17: P-x diagram of the system [EMIM][LACTATE] and CO2 with isothermal
data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red
and, at 333.15 K; green. Solid lines represent the estimations by NRTL: at 313.15 K;
blue, at 323.15 K; red and at 333.15 K; green.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [Emim][LACTATE]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
Experiment (333.15 K)
Estimation (333.15 K)
129
Figure 4.18: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red.
0
2
4
6
8
10
12
14
16
18
20
0 0.05 0.1 0.15 0.2 0.25
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [(CH2)4SO3HMIm][TF2N]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
130
Figure 4.19: P-x diagram of the system [(CH2)4SO3HMIm][HSO4]and CO2 with
isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at
323.15 K; red. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at
323.15 K; red.
0
2
4
6
8
10
12
14
16
18
20
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Pre
ssu
re (
bar
)
Mole fraction of CO2 in [(CH2)4SO3HMIm][HSO4]
Experiment (313.15 K)
Estimation (313.15 K)
Experiment (323.15 K)
Estimation (323.15 K)
131
4.4 Henry’s Law Constants
It is well understood that Henry’s law constant reflects the linear relationship
between concentration and pressure, which can be calculated from the slope of the
experimental solubility data of a gas at low solute concentrations. In most cases,
isotherms are not linear over the range of pressures. Based on this theory, the
experimental CO2 solubility data was fitted with a second order polynomial and the
limiting slope was calculated as the pressure (or solubility) approached zero (Anthony,
2004). [emim][LACTATE] was an exception, where a first order polynomial using three
data points was used to obtain the slope and, thus, Henry’s Law constant. Aspen plus was
used to estimate the fugacity coefficients from the experimental solubility data of the
systems of the ionic liquids and CO2. The fugacity was obtained by multiplying the
experimental pressure, mole fraction of CO2 and fugacity coefficient. The graph of the
fugacity of CO2 versus the mole fraction of CO2 at each temperature is reported in the
Appendix.
Henry’s law constants for CO2 in the ionic liquids are listed in Table 4-15 for three
different temperatures. Henry’s Law constants are graphically represented for all
temperatures in Figure 4-20. From Table 4-15, the Henry’s Law Constant at 313.15 K is
lower than at 333.15 K which is true for all ionic liquids studied in this work. This
relationship reflects how solubility changes with temperature indicating an inverse
relationship between Henry’s Law constant and CO2 solubility for each ionic liquid. For
example, the ionic liquid with the lowest Henry’s law constant is [TDC][TF2N] which is
already shown to be the ionic liquid with the highest CO2 solubility in the results section.
132
Table 4-15: Henry’s law constants and enthalpies and entropies of absorption for CO2 in
the studied ionic liquids
[Emm
p][Tf2N]
[PMPY][Tf2N]
[TDC][Tf2N]
[TDC][DCN]
[EMIM ][LACTATE]
[(CH2)4SO3HMIm][TF2N]]
[(CH2)4SO3HMIm][HSO4]
H (
ba
r)
0
50
100
150
200
250
300
350
313.15 k
323.15 k
333.15 k
Figure 4.20: Henry’s law constants for CO2 in [EMMP][TF2N], [PMPY][TF2N],
[TDC][TF2N], [TDC][DCN], [EMIM][LACTATE], [(CH2)4SO3HMIm][TF2N] and
[(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and 333.15 K
Ionic liquids H (bar)
∆h
(kJ/mol)
∆s (J/mol
K) 313.15
K
323.15
K
333.15
K
[Emmp][TF2N] 36.1 53.0 61.0 -22.8 -69.4
[PMPY][TF2N] 43.7 52.1 60.1 -13.8 -42.9
[TDC][TF2N] 37.2 43.4 49.3 -12.2 -37.8
[TDC][DCN] 57.2 66.3 77.3 -13.0 -40.4
[EMIM ][LACTATE] 46.2 54.4 64.8 -14.6 -45.7
[(CH2)4SO3HMIm][TF2N] 58.8 70.9 -15.7 -49.5
[(CH2)4SO3HMIm] [HSO4] 274 301.4 -8 -25.2
133
4.5 Enthalpies and Entropies of Absorption
The CO2 solubility in ionic liquids depends on many thermodynamic properties
including the enthalpies (∆h) and entropies (∆s) of absorption. The enthalpy represents
the strength of interaction between the liquid and gas, while the entropy represents the
level of ordering occurring in the ionic liquid/gas mixture (Anthony et al., 2005). The
enthalpy of absorption is derived from the slope of the plot between the natural logarithm
of the calculated Henry’s law constant and the reciprocal inverse temperature (1/T)
multiplied by the universal gas constant (8.314 J/mol K) (Anthony et al., 2005).
Whereas, the entropy of absorption is derived from the product of the universal gas
constant and the slope of the graph between the natural logarithm of the Henry’s law
constant and the natural logarithm of the temperature (Anthony et al., 2005). The
enthalpy and entropy values for CO2 in the studied ionic liquids are reported in Table 4-
15. The negative enthalpy values show that CO2 has a strong interaction with most of the
ionic liquids and perhaps the strongest interaction is seen with [emmp][TF2N] (Kurnia et
al., 2009). The negative values for entropy indicate a higher ordering degree as CO2
dissolves in the ionic liquids (Kurnia et al., 2009).
134
5 CHAPTER FIVE: CONCLUSION AND FUTURE WORK
In this research work, CO2 solubility was measured in seven different ionic
liquids. The seven ionic liquids studied were 1,2,3-Tris(diethylamino)cyclopropenylium
dicyanamide, 1-Ethyl-3-methylimidazolium L-(+)-lactate, 3-methyl-1-propylpyridinium
bis[(trifluoromethyl) sulfonyl]imide, Ethyldimethylpropylammonium bis(trifluoromethyl
sulfonyl)imide, 1,2,3-Tris(diethylamino)cyclopropenylium bis(trifluoromethane
sulfonyl)imide, 1-(4-Sulfobutyl)-3-methylimidazolium Bis(trifluoromethane
sulfonyl)imide, and 1-(4-Sulfobutyl)-3-methylimidazolium hydrogen sulfate.
The density of the seven ionic liquids was experimentally measured, using a
DMA 4500, at atmospheric pressure over a range of temperatures from 278.15 to 353.15
K. For all the ionic liquids studied in this work, the density decreases with increasing
temperature, and increases with decreasing temperature as a linear function. The trend in
the experimental density in decreasing order in the ionic liquids are as follows:
[(CH2)4SO3HMIm][TF2N] > [PMPY] Tf2N] > [(CH2)4SO3HMIm][HSO4] >
[EMMP][TF2N] > [TDC][TF2N] > [emim][LACTATE] >[TDC][DCN].
The solubility of the ionic liquids was calculated using the Intelligent Gravimetric
Analyzer (IGA 003) from Hiden Analytical at 313.15, 323.15 and 333.15 K and at
different pressures under 20 bar. The solubility of CO2 in ionic liquids decreases with
increasing temperature and increases with increasing pressure for all ionic liquids studied.
CO2 solubility decreased in the following order: [TCD][TF2N] > [PMPY][TF2N] >
[EMMP][TF2N] > [emim][LACTATE] > [TCD][DCN] > [(CH2)4SO3HMIm][TF2N] >
[(CH2)4SO3HMIm] [HSO4]. Three ionic liquids ([TCD][TF2N], [PMPY][TF2N],
135
[EMMP][TF2N]) show promise with respect to CO2 absorption as they have similar
solubility patterns to some of the ionic liquids published in the literature that are well
known for their higher CO2 solubility, such as [hmim][TF2N]. The physical solubility of
CO2 is comparable due to their high fluorination content. However, lower solubilties
were obtained in [TCD][TF2N], [PMPY][TF2N], [EMMP][TF2N] when compared with
[bmim][Ac]. [bmim][Ac]-CO2 displays strong chemical interaction and the formation of
chemical intermediary product responsible for its high CO2 solubility.
The most promising ionic liquid from the current research is [TCD][TF2N] which
is a propenylium based ionic liquid paired with an anion well-known for its high CO2
solubility. The effect of fluorination and presence of S=O groups on the TF2N anion act
synergistically to increase the CO2 solubility (Muldoon et al., 2007). The S=O group may
increase the CO2-philicity of molecules due to Lewis base-Lewis acid interactions with
the carbon atom from CO2 (Muldoon et al., 2007). However, the use of fluorinated ionic
liquids is not without its environmental and health drawbacks when used in high
concentrations.
[EMIM][LACATE] showed high capacity for CO2 but both the solubility curve
shape and the EoS modeling show that the interaction with CO2 is much more than just
simple absorption.
In addition to obtaining CO2 solubility, modeling was used to correlate the
experimental data for the binary systems of CO2 + ionic liquids. The thermodynamic
models used to correlate the experimental CO2 solubility included equations of state, such
as the Peng-Robinson (PR-EoS), SRK with quadratic mixing rules, and the Non-Random
136
Two-Liquid (NRTL) activity coefficient model. All models resulted in low percentages
of AAD reflecting that they can satisfactorily correlate the solubility of CO2 in the ionic
liquids. Furthermore, Henry’s Law constants for CO2 in the ionic liquids at the three
different temperatures, 313.15, 323.15 and 333.15 K, were determined. As the
temperature increased, the Henry’s Law constants decreased for all the investigated ionic
liquids.
Future Work
Further investigations of the seven ionic liquids studied at higher pressures would
be beneficial as it would have more industrial applicability in natural gas processing.
Future work might involve the investigation of other gases such as methane,
ethane, propane, sulfur dioxide, carbon monoxide and hydrogen. Furthermore,
modifications to the seven ionic liquids by the addition of functional groups or the
modification of alkyl chain lengths to allow them to become more biodegradable and thus
more environmentally friendly will be an important aspect of industrial application. There
is a need to reconcile the demand for high solubility and the maintenance of the “green”
solvent reputation that ionic liquids initially possessed.
137
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6 APPENDIX
6.1 Raw Data for Gas Solubility Measurements Using the Gravimetric
Microbalance
Table 6-1: Carbon dioxide in [Emmp][TF2N] at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[EMMP][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.18103 97.67 39.95 0.0041 0.2522 1.604
0.2597 499.63 39.96 0.0059 0.2522 2.286
0.3852 998.61 39.98 0.0087 0.2522 3.353
0.64326 1999.38 39.98 0.0146 0.2522 5.476
1.15361 3998.51 39.98 0.0262 0.2522 9.412
1.90065 6997.99 39.98 0.0432 0.2522 14.62
2.40342 8998.32 39.98 0.0546 0.2522 17.79
2.65967 9998.02 39.96 0.0604 0.2522 19.32
2.92619 10999.59 39.97 0.0664 0.2522 20.86
3.47239 12997.65 39.99 0.0789 0.2522 23.82
4.01696 14999.31 39.96 0.0912 0.2522 26.57
4.58222 16999.24 39.96 0.1041 0.2522 29.21
5.14261 19000.11 39.95 0.1169 0.2522 31.65
144
Table 6-2: Carbon dioxide in [Emmp][TF2N] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[EMMP][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0234 99.94 49.95 0.00053 0.2523 0.210
0.0981 499.77 49.95 0.00223 0.2523 0.880
0.1973 998.48 49.96 0.00448 0.2523 1.750
0.4179 2000.71 49.97 0.00949 0.2523 3.630
0.8369 4000.77 49.97 0.01902 0.2523 7.010
1.4348 6997.73 49.96 0.03261 0.2523 11.44
1.8553 8998.86 49.97 0.04216 0.2523 14.32
2.0673 10003.51 49.97 0.04697 0.2523 15.70
2.2926 11000.26 49.96 0.05209 0.2523 17.11
2.7229 12997.78 49.95 0.06187 0.2523 19.69
3.1538 15002.12 49.98 0.07166 0.2523 22.12
3.5990 16995.77 49.96 0.08177 0.2523 24.48
4.0505 18996.24 49.98 0.09203 0.2523 26.73
145
Table 6-3: Carbon dioxide in [Emmp][TF2N] at 333.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[EMMP][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0201 100.87 59.98 0.00046 0.2523 0.180
0.0762 500.17 59.93 0.00173 0.2523 0.680
0.1627 1000.48 59.98 0.00369 0.2523 1.440
0.3631 1999.11 59.98 0.00825 0.2523 3.170
0.7091 3998.24 59.98 0.01611 0.2523 6.000
1.2251 7000.81 59.99 0.02785 0.2523 9.940
1.5600 8999.66 59.99 0.03544 0.2523 12.32
1.7271 9997.76 59.97 0.03924 0.2523 13.46
1.8968 10998.79 59.98 0.04311 0.2523 14.59
2.2464 12997.65 59.97 0.05104 0.2523 16.83
2.6017 14998.78 59.99 0.05911 0.2523 18.98
2.9406 16990.03 60.00 0.06681 0.2523 20.94
3.2791 18997.04 60.02 0.07451 0.2523 22.80
146
Table 6-4: Carbon dioxide in [PMPY][TF2N] at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[PMPY][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0252 99.01 39.97 0.00057 0.2402 0.240
0.1169 500.03 39.97 0.00266 0.2402 1.090
0.2289 1001.28 39.96 0.00520 0.2402 2.120
0.4763 1999.24 39.97 0.01080 0.2402 4.310
0.9629 3998.51 39.96 0.02190 0.2402 8.350
1.6826 7000.13 39.97 0.03820 0.2402 13.73
2.1876 8998.99 39.97 0.04970 0.2402 17.15
2.4419 9999.76 39.97 0.05540 0.2402 18.77
2.7025 10998.79 39.96 0.06140 0.2402 20.36
3.2392 12997.92 39.97 0.07360 0.2402 23.46
3.7789 14998.65 39.98 0.08590 0.2402 26.34
4.3237 16998.18 39.97 0.09820 0.2402 29.03
4.8991 18996.9 39.98 0.11130 0.2402 31.67
147
Table 6-5: Carbon dioxide in [PMPY][TF2N] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[PMPY][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.000001 1.58 49.96 2.27E-8 0.2402 0.001
0.024223 96.33 49.97 0.00055 0.2402 0.230
0.099011 499.49 49.96 0.00225 0.2402 0.931
0.201272 998.21 49.97 0.00457 0.2402 1.871
0.416054 1999.37 49.95 0.00945 0.2402 3.791
0.82614 3998.51 49.96 0.01877 0.2402 7.251
1.420329 7000.93 49.96 0.03227 0.2402 11.85
1.821213 9000.33 49.97 0.04138 0.2402 14.70
2.02189 9996.42 49.97 0.04594 0.2402 16.06
2.239413 10999.06 49.98 0.05088 0.2402 17.48
2.682775 13002.45 50.01 0.06096 0.2402 20.24
3.125906 14997.71 49.97 0.07103 0.2402 22.82
3.571628 17007.38 49.99 0.08115 0.2402 25.26
4.04087 19008.11 49.97 0.09182 0.2402 27.66
148
Table 6-6: Carbon dioxide in [PMPY][TF2N] at 333.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[PMPY][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0232 99.67 59.99 0.00053 0.2402 0.221
0.0791 499.89 59.99 0.00180 0.2402 0.741
0.1652 999.01 59.99 0.00376 0.2402 1.540
0.3498 1999.78 59.99 0.00795 0.2402 3.201
0.6821 3999.04 60.01 0.01550 0.2402 6.060
1.1799 6996.93 59.97 0.02681 0.2402 10.04
1.5199 9001.53 60.01 0.03454 0.2402 12.57
1.6853 9999.63 59.99 0.03829 0.2402 13.75
1.8508 10999.06 59.96 0.04206 0.2402 14.90
2.2031 12997.25 60.02 0.05006 0.2402 17.25
2.5366 15000.25 60.01 0.05764 0.2402 19.35
2.8837 16995.37 59.96 0.06552 0.2402 21.43
3.1991 18996.5 60.02 0.07269 0.2402 23.23
149
Table 6-7: Carbon dioxide in [TDC][TF2N] at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[TDC][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0235 97.53 39.96 0.00053 0.1878 0.280
0.1085 498.96 39.96 0.00247 0.1878 1.301
0.2118 998.88 39.97 0.00481 0.1878 2.501
0.4379 2000.31 39.97 0.00995 0.1878 5.030
0.8917 4001.57 39.98 0.02026 0.1878 9.740
1.5626 6999.06 39.97 0.03551 0.1878 15.90
2.0276 8999.26 39.98 0.04607 0.1878 19.70
2.2639 9998.56 39.98 0.05144 0.1878 21.50
2.5118 11000.79 39.98 0.05707 0.1878 23.31
3.0142 12999.12 39.98 0.06849 0.1878 26.73
3.5424 15000.52 39.98 0.08049 0.1878 30.00
4.1041 16997.51 39.95 0.09325 0.1878 33.18
4.6494 18996.77 39.98 0.10564 0.1878 36.01
150
Table 6-8: Carbon dioxide in [TDC][TF2N] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[TDC][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.02103 101.407 49.96 0.00048 0.1878 0.250
0.087862 500.833 49.96 0.00199 0.1878 1.050
0.176067 998.88 49.95 0.00401 0.1878 2.090
0.377358 2000.445 49.97 0.00857 0.1878 4.371
0.754707 3998.372 49.96 0.01715 0.1878 8.370
1.315197 6998.665 49.95 0.02988 0.1878 13.73
1.697512 8998.46 49.94 0.03857 0.1878 17.04
1.896281 9998.691 49.97 0.04309 0.1878 18.66
2.089385 10999.32 49.94 0.04747 0.1878 20.18
2.49237 12999.25 49.96 0.05663 0.1878 23.17
2.925119 14997.71 49.94 0.06646 0.1878 26.14
3.344412 17005.38 50.02 0.07599 0.1878 28.81
3.760257 18996.64 49.97 0.08544 0.1878 31.27
151
Table 6-9: Carbon dioxide in [TDC][TF2N] at 333.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[TDC][TF2N]
XCO2 (Mole
Fraction of CO2
%)
0.0191 101.27 59.98 0.00043 0.1878 0.230
0.0752 500.03 59.98 0.00171 0.1878 0.901
0.1587 997.41 59.99 0.00361 0.1878 1.880
0.3365 1999.51 59.99 0.00764 0.1878 3.911
0.6611 3998.24 59.98 0.01502 0.1878 7.410
1.1467 6999.07 59.98 0.02605 0.1878 12.18
1.4798 8998.19 59.99 0.03362 0.1878 15.19
1.6546 9997.09 60.01 0.03759 0.1878 16.68
1.8258 10999.71 60.01 0.04148 0.1878 18.10
2.1678 12998.71 59.99 0.04925 0.1878 20.78
2.5216 14998.88 59.99 0.05729 0.1878 23.38
2.8702 16999.51 59.94 0.06521 0.1878 25.78
3.2407 18997.84 60.03 0.07363 0.1878 28.17
152
Table 6-10: Carbon dioxide in [EMIM][LACTATE] at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[EMIM][LACTATE]
XCO2 (Mole
Fraction of
CO2 %)
2.095 998.88 39.97 0.04760 0.4994 8.701
2.893 2001.51 39.97 0.06570 0.4994 11.63
3.954 3998.64 39.97 0.08980 0.4994 15.25
5.122 6999.47 39.96 0.11630 0.4994 18.90
5.806 8997.93 39.99 0.13190 0.4994 20.90
6.141 9998.29 39.98 0.13950 0.4994 21.84
6.45 10999.7 39.96 0.14670 0.4994 22.70
7.029 12997.1 39.95 0.15970 0.4994 24.23
7.557 14998.91 39.97 0.17170 0.4994 25.59
8.161 17000.58 39.98 0.18540 0.4994 27.08
8.681 18998.1 39.97 0.19720 0.4994 28.31
153
Table 6-11: Carbon dioxide in [EMIM][LACTATE] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[EMIM][LACTATE]
XCO2 (Mole
Fraction of
CO2 %)
1.6891 999.01 49.96 0.03830 0.4994 7.141
3.2837 3997.84 49.96 0.07460 0.4994 13.00
3.6651 4998.74 49.95 0.08320 0.4994 14.29
4.3075 6998.93 49.96 0.09780 0.4994 16.39
5.1784 9997.76 49.96 0.11760 0.4994 19.07
7.3238 18998.37 49.95 0.16640 0.4994 24.99
Table 6-12: Carbon dioxide in [EMIM][LACTATE] at 333.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[EMIM][LACTATE]
XCO2 (Mole
Fraction of
CO2 %)
0.9867 499.63 59.99 0.02242 0.4994 4.301
1.3969 998.48 59.99 0.03174 0.4994 5.980
1.9871 1999.65 59.99 0.04515 0.4994 8.290
2.7824 3996.24 59.99 0.06322 0.4994 11.24
3.6581 6999.6 59.98 0.08312 0.4994 14.27
4.1699 9000.73 60.01 0.09475 0.4994 15.95
4.4184 9998.29 59.97 0.10040 0.4994 16.74
154
Table 6-13: Carbon dioxide in [TDC][DCN] at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[TDC][DCN]
XCO2 (Mole
Fraction of CO2
%)
0.0247 101.01 39.97 0.00056 0.3139 0.181
0.1191 500.16 39.97 0.00271 0.3139 0.850
0.2313 1001.01 39.97 0.00526 0.3139 1.650
0.4856 2002.04 39.96 0.01103 0.3139 3.391
0.9987 4000.11 39.97 0.02269 0.3139 6.740
1.7497 7000.13 39.96 0.03976 0.3139 11.24
2.2701 8998.73 39.97 0.05158 0.3139 14.11
2.5331 9998.15 39.96 0.05756 0.3139 15.49
2.8033 10998.79 39.97 0.06369 0.3139 16.87
3.3666 12997.65 39.97 0.07649 0.3139 19.59
3.9351 14992.51 39.96 0.08942 0.3139 22.17
4.5553 17001.38 39.97 0.10350 0.3139 24.79
5.1638 19006.65 39.96 0.11733 0.3139 27.20
155
Table 6-14: Carbon dioxide in [TDC][DCN] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF CO2 Mole of
[TDC][DCN]
XCO2 (Mole
Fraction of CO2
%)
0.0258 102.342 49.96 0.00059 0.3139 0.190
0.1051 500.165 49.95 0.00239 0.3139 0.750
0.2028 997.412 49.96 0.00461 0.3139 1.451
0.4261 1998.31 49.95 0.00969 0.3139 2.991
0.8615 4001.575 49.96 0.01958 0.3139 5.870
1.4967 6996.13 49.95 0.03401 0.3139 9.771
1.9394 9001.396 49.96 0.04407 0.3139 12.31
2.1686 9997.49 49.97 0.04928 0.3139 13.57
2.3958 11002.93 49.98 0.05444 0.3139 14.78
2.8849 12996.72 49.94 0.06555 0.3139 17.27
3.3630 14997.18 49.95 0.07642 0.3139 19.57
3.8636 16998.04 49.98 0.08779 0.3139 21.85
4.3705 19006.11 49.97 0.09931 0.3139 24.03
Table 6-15: Carbon dioxide in [(CH2)4SO3HMIm][TF2N]at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[(CH2)4SO3HMIm][TF2N
]
XCO2 (Mole
Fraction of
CO2 %)
0.0116 97.67 39.96 0.00026 0.2002 0.138
0.0116 499.63 39.96 0.00026 0.2002 0.138
0.0652 998.61 39.98 0.00148 0.2002 0.731
1.3739 8998.33 39.98 0.03122 0.2002 13.49
1.5006 9998.02 39.97 0.03410 0.2002 14.55
1.6729 10999.59 39.97 0.03801 0.2002 15.96
1.9731 12997.65 39.99 0.04483 0.2002 18.29
2.3172 14999.31 39.96 0.05265 0.2002 20.82
2.6264 16999.24 39.96 0.05968 0.2002 22.96
2.9968 19000.11 39.95 0.06809 0.2002 25.38
156
Table 6-16: Carbon dioxide in [(CH2)4SO3HMIm][TF2N] at 323.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole OF
CO2
Mole of
[(CH2)4SO3HMIm][TF2N]
XCO2 (Mole
Fraction of
CO2 %)
0.0139 98.21 49.96 0.00032 0.2002 0.159
0.0551 500.29 49.96 0.00125 0.2002 0.621
0.1091 999.68 49.96 0.00248 0.2002 1.222
0.5198 3998.37 49.97 0.01181 0.2002 5.570
0.8809 7000.53 49.9 0.02002 0.2002 9.091
1.1557 8999.13 49.94 0.02626 0.2002 11.59
1.2679 10001.09 49.95 0.02881 0.2002 12.58
1.9681 15002.38 49.92 0.04472 0.2002 18.26
Table 6-17: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole
OF CO2
Mole of
[(CH2)4SO3HMIm][HSO4]
XCO2 (Mole
Fraction of
CO2 %)
0.0106 99.27 39.96 0.00024 0.3161 0.076
0.0244 498.43 39.96 0.00055 0.3161 0.175
0.0413 998.88 39.98 0.00094 0.3161 0.296
0.3611 6999.33 39.98 0.00821 0.3161 2.530
0.7044 10999.73 39.96 0.01601 0.3161 4.819
0.8127 12997.12 39.97 0.01847 0.3161 5.519
157
Table 6-18: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K
%Mass = Asymptotic mass uptake as percentage of dry mass
P = Average pressure reading for isotherm point (millibars)
Sample T = Average sample temperature reading for isotherm point (°C)
%Mass Pressure
(M bar)
Sample-
T(°C)
Mole
OF CO2
Mole of
[(CH2)4SO3HMIm][HSO4]
XCO2 (Mole
Fraction of
CO2 %)
0.0078 101.01 49.96 0.00017 0.3161 0.056
0.0161 499.77 49.95 0.00036 0.3161 0.116
0.4588 9000.60 49.94 0.01042 0.3161 3.192
0.5267 9997.89 49.95 0.01196 0.3161 3.648
0.5911 10998.79 49.97 0.01343 0.3161 4.076
0.6907 12997.65 49.96 0.01569 0.3161 4.730
0.8068 14999.98 49.96 0.01833 0.3161 5.482
0.9095 16999.51 49.95 0.02066 0.3161 6.137
158
6.2 Modeling Results
Table 6-19: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09767 0.09958 0.016 0.016
0.49963 0.50056 0.023 0.023
0.99861 0.99498 0.034 0.034
1.99938 1.98415 0.055 0.055
3.99851 3.95448 0.094 0.095
6.99800 6.89461 0.146 0.149
8.99833 8.84299 0.178 0.182
9.99802 9.81225 0.193 0.197
10.99959 10.78082 0.209 0.213
12.99765 12.70273 0.238 0.245
14.99931 14.60915 0.266 0.274
16.99924 16.49649 0.292 0.302
19.00011 18.36211 0.317 0.328
Table 6-20: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed XCO2
0.09994 0.10011 0.002 0.002
0.49977 0.49877 0.009 0.009
0.99848 0.99663 0.017 0.017
2.00071 1.99927 0.036 0.036
4.00077 3.99616 0.070 0.070
6.99773 6.97690 0.114 0.115
8.99886 8.96106 0.143 0.144
10.00350 9.95390 0.157 0.158
11.00026 10.93746 0.171 0.172
12.99778 12.89749 0.197 0.199
15.00212 14.85165 0.221 0.224
16.99577 16.77958 0.245 0.248
18.99624 18.69769 0.267 0.272
159
Table 6-21: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[EMMP][TF2N] (1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10087 0.10233 0.002 0.002
0.50017 0.50442 0.007 0.007
1.00048 1.01065 0.014 0.014
1.99911 2.02460 0.032 0.031
3.99824 4.04747 0.060 0.059
7.00080 7.08150 0.099 0.098
8.99966 9.09472 0.123 0.122
9.99776 10.09713 0.135 0.133
10.99879 11.10143 0.146 0.144
12.99765 13.10089 0.168 0.167
14.99878 15.09343 0.190 0.189
16.99003 17.06199 0.209 0.208
18.99704 19.03147 0.228 0.227
Table 6-22: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09901 0.10206 0.002 0.002
0.50003 0.50608 0.011 0.011
1.00128 1.00664 0.021 0.021
1.99924 2.01784 0.043 0.042
3.99851 4.00901 0.083 0.083
7.00013 6.92609 0.137 0.138
8.99900 8.84470 0.171 0.174
9.99976 9.79322 0.188 0.192
10.99879 10.73520 0.204 0.209
12.99792 12.60515 0.235 0.243
14.99865 14.44223 0.263 0.275
16.99818 16.24426 0.290 0.305
18.99690 18.02759 0.317 0.335
160
Table 6-23: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09634 0.10317 0.002 0.002
0.49950 0.50879 0.009 0.009
0.99821 1.01847 0.019 0.018
1.99938 2.04498 0.038 0.037
3.99851 4.05196 0.072 0.071
7.00093 6.98725 0.118 0.118
9.00033 8.90924 0.147 0.148
9.99642 9.85639 0.161 0.163
10.99906 10.81563 0.175 0.178
13.00245 12.71613 0.202 0.207
14.99771 14.57324 0.228 0.236
17.00738 16.41388 0.253 0.263
19.00811 18.22785 0.277 0.289
Table 6-24: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09967 0.10940 0.002 0.002
0.49990 0.50484 0.007 0.007
0.99901 1.01692 0.015 0.015
1.99978 2.05342 0.032 0.031
3.99904 4.05638 0.061 0.059
6.99693 7.00682 0.100 0.100
9.00153 8.95586 0.126 0.126
9.99963 9.91029 0.138 0.139
10.99906 10.85807 0.149 0.151
12.99725 12.76183 0.172 0.176
15.00025 14.61691 0.194 0.199
16.99537 16.44949 0.214 0.222
18.99650 18.23384 0.232 0.243
161
Table 6-25: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09754 0.10643 0.003 0.003
0.49896 0.52412 0.013 0.012
0.99888 1.03619 0.025 0.024
2.00031 2.08044 0.050 0.048
4.00158 4.12090 0.097 0.094
6.99907 7.05287 0.159 0.157
8.99926 8.96272 0.197 0.198
9.99856 9.90149 0.215 0.218
11.00079 10.84211 0.233 0.238
12.99912 12.68633 0.267 0.276
15.00052 14.50634 0.300 0.314
16.99751 16.30026 0.332 0.351
18.99677 18.03165 0.360 0.385
Table 6-26: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10141 0.10936 0.003 0.002
0.50083 0.50859 0.011 0.010
0.99888 1.01267 0.021 0.020
2.00045 2.06102 0.044 0.042
3.99837 4.06515 0.084 0.081
6.99867 6.96919 0.137 0.138
8.99846 8.85891 0.170 0.173
9.99869 9.79880 0.187 0.191
10.99932 10.71688 0.202 0.208
12.99925 12.54493 0.232 0.242
14.99771 14.36318 0.261 0.276
17.00538 16.12872 0.288 0.307
18.99664 17.82853 0.313 0.337
162
Table 6-27: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]
(1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10127 0.10976 0.002 0.002
0.50003 0.49986 0.009 0.009
0.99741 1.01381 0.019 0.018
1.99951 2.05956 0.039 0.037
3.99824 4.04531 0.074 0.072
6.99907 6.93965 0.122 0.123
8.99819 8.83254 0.152 0.155
9.99709 9.77781 0.167 0.171
10.99973 10.70768 0.181 0.187
12.99872 12.53017 0.208 0.217
14.99878 14.33234 0.234 0.247
16.99951 16.08285 0.258 0.275
18.99784 17.83185 0.282 0.303
163
Table 6-28: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN
(1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10101 0.10524 0.002 0.002
0.50017 0.51260 0.009 0.008
1.00102 1.01519 0.017 0.016
2.00205 2.05070 0.034 0.033
4.00011 4.09396 0.067 0.065
7.00013 7.05023 0.112 0.111
8.99873 8.99090 0.141 0.141
9.99815 9.94783 0.155 0.156
10.99879 10.90524 0.169 0.171
12.99765 12.80587 0.196 0.201
14.99251 14.64214 0.221 0.229
17.00138 16.53758 0.248 0.259
19.00665 18.34682 0.272 0.287
Table 6-29: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN]
(1) + CO2 (2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed XCO2
0.10234 0.11261 0.002 0.002
0.50017 0.51016 0.008 0.007
0.99741 1.00642 0.015 0.014
1.99831 2.03831 0.030 0.029
4.00158 4.05666 0.059 0.057
6.99613 6.97560 0.098 0.098
9.00140 8.91191 0.123 0.124
9.99749 9.87323 0.136 0.138
11.00293 10.82688 0.148 0.151
12.99672 12.73672 0.173 0.178
14.99718 14.59825 0.196 0.203
16.99804 16.44996 0.219 0.229
19.00611 18.26883 0.240 0.254
164
Table 6-30: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN]
(1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed XCO2
0.09981 0.11068 0.002 0.001
0.49963 0.49071 0.006 0.006
0.99915 0.99040 0.013 0.012
2.00005 1.99762 0.026 0.025
3.99811 3.96963 0.050 0.050
6.99787 6.83641 0.084 0.085
8.99913 8.72683 0.105 0.108
10.00016 9.68440 0.116 0.120
11.00052 10.61143 0.127 0.132
12.99925 12.47901 0.148 0.155
14.99731 14.32065 0.168 0.177
17.00712 16.10056 0.186 0.199
Table 6-31: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.99888 1.00400 0.087 0.087
2.00151 2.00536 0.116 0.116
3.99864 3.99817 0.152 0.152
6.99947 6.99723 0.189 0.189
8.99793 8.99817 0.209 0.209
9.99829 10.00055 0.218 0.218
10.99973 11.00407 0.227 0.227
12.99712 13.00496 0.242 0.242
14.99891 15.00777 0.256 0.256
17.00058 17.00506 0.271 0.271
18.99810 18.99065 0.283 0.283
165
Table 6-32: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.99901 0.99436 0.071 0.071
3.99784 3.96857 0.130 0.130
4.99874 4.96472 0.143 0.143
6.99893 6.96169 0.164 0.164
9.99776 9.97154 0.191 0.190
18.99837 19.06563 0.250 0.250
Table 6-33: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[EMIM][LACTATE ](1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.499631 0.49406736 0.043 0.043
0.998479 0.98472573 0.060 0.060
1.999645 1.96934955 0.083 0.083
3.996237 3.93937429 0.112 0.112
6.9996 6.9271834 0.143 0.143
9.000729 8.9351463 0.159 0.159
9.998292 9.94119949 0.167 0.167
Table 6-34: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
bar
Experimental
XCO2
Regressed
XCO2
0.09930 0.09700 0.001 0.001
0.49800 0.48300 0.002 0.002
0.99900 0.96800 0.003 0.003
6.99933 6.83845 0.025 0.026
10.99973 10.80109 0.048 0.049
12.99712 12.76284 0.055 0.056
166
Table 6-35: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10101 0.09973 0.001 0.001
0.49977 0.48946 0.001 0.001
9.00060 8.99469 0.032 0.032
9.99789 10.00962 0.036 0.036
10.99879 11.02875 0.041 0.041
12.99765 13.05889 0.047 0.047
14.99998 15.09916 0.055 0.055
16.99951 17.13126 0.061 0.061
Table 6-36: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09770 0.09570 0.001 0.001
0.50000 0.48200 0.001 0.001
0.99900 0.97500 0.007 0.007
8.99833 8.99693 0.135 0.135
9.99802 10.00525 0.146 0.146
10.99959 11.01490 0.160 0.160
12.99765 13.02341 0.183 0.183
14.99931 15.02135 0.208 0.208
16.99924 16.99923 0.230 0.230
19.00011 18.94820 0.254 0.254
167
Table 6-37: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for
[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09820 0.09541 0.002 0.002
0.50030 0.48558 0.006 0.006
0.99968 0.97209 0.012 0.012
3.99837 3.93657 0.056 0.056
7.00053 6.95401 0.091 0.091
8.99913 8.98610 0.116 0.116
10.00109 10.00859 0.126 0.126
15.00238 15.13018 0.183 0.183
Table 6-38: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09901 0.09860 0.002 0.002
0.50003 0.49011 0.011 0.011
1.00128 0.97783 0.021 0.022
1.99924 1.97222 0.043 0.043
3.99851 3.96254 0.083 0.084
7.00013 6.94770 0.137 0.138
8.99900 8.95256 0.171 0.172
9.99976 9.95477 0.188 0.188
10.99879 10.95728 0.204 0.204
12.99792 12.96687 0.235 0.235
14.99865 14.96477 0.263 0.265
16.99818 16.94607 0.290 0.292
18.99690 18.92629 0.317 0.319
168
Table 6-39: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09634 0.09956 0.002 0.002
0.49950 0.49191 0.009 0.009
0.99821 0.98738 0.019 0.019
1.99938 1.99332 0.038 0.038
3.99851 3.98852 0.072 0.072
7.00093 6.96853 0.118 0.118
9.00033 8.95683 0.147 0.147
9.99642 9.94676 0.161 0.161
10.99906 10.95642 0.175 0.175
13.00245 12.97565 0.202 0.203
14.99771 14.97248 0.228 0.229
17.00738 16.97209 0.253 0.254
19.00811 18.96375 0.277 0.278
Table 6-40: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[PMPY][TF2N] (1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09967 0.10546 0.002 0.002
0.49990 0.48729 0.007 0.008
0.99901 0.98393 0.015 0.015
1.99978 1.99627 0.032 0.032
3.99904 3.97704 0.061 0.061
6.99693 6.95070 0.100 0.101
9.00153 8.94917 0.126 0.126
9.99963 9.93720 0.138 0.138
10.99906 10.92439 0.149 0.150
12.99725 12.92460 0.172 0.174
15.00025 14.89492 0.194 0.195
16.99537 16.86243 0.214 0.217
18.99650 18.79394 0.232 0.236
169
Table 6-41: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09754 0.10087 0.003 0.003
0.49896 0.49958 0.013 0.013
0.99888 0.99212 0.025 0.025
2.00031 2.00585 0.050 0.049
4.00158 4.02804 0.097 0.095
6.99907 7.02282 0.159 0.157
8.99926 9.02306 0.197 0.196
9.99856 10.01970 0.215 0.215
11.00079 11.02599 0.233 0.234
12.99912 13.02242 0.267 0.270
15.00052 15.01990 0.300 0.305
16.99751 17.01238 0.332 0.339
18.99677 18.95906 0.360 0.371
Table 6-42: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 323.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10141 0.10423 0.003 0.002
0.50083 0.48805 0.011 0.011
0.99888 0.97499 0.021 0.021
2.00045 1.99490 0.044 0.043
3.99837 3.98440 0.084 0.083
6.99867 6.94760 0.137 0.138
8.99846 8.92171 0.170 0.172
9.99869 9.91557 0.187 0.189
10.99932 10.89527 0.202 0.205
12.99925 12.86645 0.232 0.237
14.99771 14.85229 0.261 0.268
17.00538 16.80721 0.288 0.298
18.99664 18.71254 0.313 0.326
170
Table 6-43: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][TF2N] (1) + CO2 (2) system at 333.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10127 0.10507 0.002 0.002
0.50003 0.48229 0.009 0.009
0.99741 0.97991 0.019 0.019
1.99951 2.00041 0.039 0.038
3.99824 3.97544 0.074 0.073
6.99907 6.92713 0.122 0.122
8.99819 8.89983 0.152 0.153
9.99709 9.89600 0.167 0.169
10.99973 10.88431 0.181 0.184
12.99872 12.84290 0.208 0.212
14.99878 14.80484 0.234 0.240
16.99951 16.73604 0.258 0.267
18.99784 18.68382 0.282 0.293
Table 6-44: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 313.15 K
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.101007 0.10228235 0.002 0.002
0.500165 0.49928649 0.009 0.008
1.001015 0.99089577 0.017 0.016
2.002047 2.00638799 0.034 0.033
4.000107 4.02863206 0.067 0.066
7.000133 6.99998381 0.112 0.112
8.998728 8.97632411 0.141 0.141
9.99815 9.95848094 0.155 0.156
10.99879 10.945548 0.169 0.170
12.99765 12.9184655 0.196 0.199
14.99251 14.844459 0.221 0.227
17.00138 16.8443045 0.248 0.256
19.00665 18.7732977 0.272 0.283
171
Table 6-45: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10101 0.10228 0.002 0.002
0.50017 0.49929 0.009 0.008
1.00102 0.99090 0.017 0.016
2.00205 2.00639 0.034 0.033
4.00011 4.02863 0.067 0.066
7.00013 6.99998 0.112 0.112
8.99873 8.97632 0.141 0.141
9.99815 9.95848 0.155 0.156
10.99879 10.94555 0.169 0.170
12.99765 12.91847 0.196 0.199
14.99251 14.84446 0.221 0.227
17.00138 16.84430 0.248 0.256
19.00665 18.77330 0.272 0.283
Table 6-46: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[TDC][DCN] (1) + CO2 (2) system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09981 0.10792 0.002 0.002
0.49963 0.48287 0.006 0.006
0.99915 0.97521 0.013 0.013
2.00005 1.97100 0.026 0.025
3.99811 3.93739 0.050 0.050
6.99787 6.83509 0.084 0.085
8.99913 8.76798 0.105 0.108
10.00016 9.75223 0.116 0.119
11.00052 10.71114 0.127 0.130
12.99925 12.65281 0.148 0.153
14.99731 14.58368 0.168 0.175
17.00712 16.46891 0.186 0.195
172
Table 6-47: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMIM][LACTATE] (1) + CO2 (2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.99888 1.03701 0.087 0.081
2.00151 2.01555 0.116 0.113
3.99864 3.96379 0.152 0.152
6.99947 6.91639 0.189 0.191
8.99793 8.90596 0.209 0.211
9.99829 9.90958 0.218 0.221
10.99973 10.91508 0.227 0.229
12.99712 12.92572 0.242 0.245
14.99891 14.94907 0.256 0.259
17.00058 17.00301 0.271 0.274
18.99810 19.04888 0.283 0.286
Table 6-48: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMIM][LACTATE] (1) + CO2 (2) system at 323.15 K.
Experimental Pressure
(bar)
Estimated Pressure
(bar)
Experimental
XCO2
Estimated
XCO2
0.99901 1.02239 0.071 0.068
3.99784 3.93048 0.130 0.132
4.99874 4.91197 0.143 0.145
6.99893 6.88044 0.164 0.167
9.99776 9.87166 0.191 0.194
9.99776 9.87138 0.191 0.194
18.99837 19.00585 0.250 0.251
173
Table 6-49: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for
[EMMP][LACTATE] (1) + CO2 (2) system at 333.15 K.
Table 6-50: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09767 0.09963 0.016 0.016
0.49963 0.50377 0.023 0.023
0.99861 1.00189 0.034 0.034
1.99938 1.99877 0.055 0.055
3.99851 3.99085 0.094 0.095
6.99800 6.98393 0.146 0.148
8.99833 8.98402 0.178 0.180
9.99802 9.98486 0.193 0.195
10.99959 10.98983 0.209 0.210
12.99765 12.99796 0.238 0.240
14.99931 15.00800 0.266 0.267
16.99924 17.02047 0.292 0.293
19.00011 19.03159 0.317 0.317
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.49963 0.52689 0.043 0.039
0.99848 1.00516 0.060 0.058
1.99965 1.96479 0.083 0.084
3.99624 3.88872 0.112 0.117
6.99960 6.82345 0.143 0.148
9.00073 8.81065 0.159 0.164
9.99829 9.81011 0.167 0.172
174
Table 6-51: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09994 0.10036 0.002 0.002
0.49977 0.49704 0.009 0.009
0.99848 0.99378 0.017 0.018
2.00071 2.00153 0.036 0.036
4.00077 4.01204 0.070 0.070
6.99773 7.02759 0.114 0.114
8.99886 9.05777 0.143 0.143
10.00350 10.07897 0.157 0.156
11.00026 11.09870 0.171 0.170
12.99778 13.13481 0.197 0.195
15.00212 15.18056 0.221 0.218
16.99577 17.21968 0.245 0.241
18.99624 19.26835 0.267 0.263
Table 6-52: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2
(2) system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10087 0.10314 0.002 0.002
0.50017 0.49603 0.007 0.007
1.00048 1.00389 0.014 0.014
1.99911 2.03943 0.032 0.031
3.99824 4.07331 0.060 0.059
7.00080 7.08208 0.099 0.099
8.99966 9.03449 0.123 0.123
9.99776 10.00770 0.135 0.135
10.99879 10.98871 0.146 0.147
12.99765 12.97248 0.168 0.169
14.99878 14.96758 0.190 0.191
16.99003 16.91492 0.209 0.212
18.99704 18.86689 0.228 0.231
175
Table 6-53: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09901 0.10013 0.002 0.002
0.50003 0.49566 0.011 0.011
1.00128 0.98768 0.021 0.022
1.99924 1.99371 0.043 0.043
3.99851 4.00114 0.083 0.084
7.00013 7.00443 0.137 0.138
8.99900 9.02089 0.171 0.172
9.99976 10.02905 0.188 0.188
10.99879 11.03793 0.204 0.204
12.99792 13.06259 0.235 0.234
14.99865 15.08058 0.263 0.262
16.99818 17.08942 0.290 0.289
18.99690 19.10650 0.317 0.315
Table 6-54: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09634 0.10181 0.002 0.002
0.49950 0.49450 0.009 0.009
0.99821 0.99389 0.019 0.019
1.99938 2.01055 0.038 0.038
3.99851 4.02212 0.072 0.072
7.00093 7.02486 0.118 0.119
9.00033 9.03162 0.147 0.147
9.99642 10.03180 0.161 0.161
10.99906 11.05373 0.175 0.175
13.00245 13.10004 0.202 0.201
14.99771 15.12767 0.228 0.227
17.00738 17.16469 0.253 0.250
19.00811 19.20190 0.277 0.274
176
Table 6-55: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2
(2) system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09967 0.10804 0.002 0.002
0.49990 0.48181 0.007 0.008
0.99901 0.97748 0.015 0.016
1.99978 1.99544 0.032 0.032
3.99904 3.97910 0.061 0.061
6.99693 6.97221 0.100 0.101
9.00153 8.99289 0.126 0.127
9.99963 9.99292 0.138 0.138
10.99906 10.99343 0.149 0.150
12.99725 13.02780 0.172 0.173
15.00025 15.03468 0.194 0.194
16.99537 17.04691 0.214 0.215
18.99650 19.02799 0.232 0.233
Table 6-56: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09754 0.09958 0.003 0.003
0.49896 0.49659 0.013 0.013
0.99888 0.98776 0.025 0.025
2.00031 1.99402 0.050 0.051
4.00158 4.00494 0.097 0.098
6.99907 6.99891 0.159 0.160
8.99926 9.00684 0.197 0.198
9.99856 10.01075 0.215 0.216
11.00079 11.02549 0.233 0.233
12.99912 13.04770 0.267 0.267
15.00052 15.08227 0.300 0.299
16.99751 17.12367 0.332 0.330
18.99677 19.14213 0.360 0.357
177
Table 6-57: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10141 0.10441 0.003 0.002
0.50083 0.49232 0.011 0.011
0.99888 0.98319 0.021 0.021
2.00045 2.00639 0.044 0.044
3.99837 4.00790 0.084 0.084
6.99867 6.99706 0.137 0.138
8.99846 8.99477 0.170 0.171
9.99869 10.00245 0.187 0.187
10.99932 10.99905 0.202 0.203
12.99925 13.00986 0.232 0.233
14.99771 15.04337 0.261 0.262
17.00538 17.06351 0.288 0.288
18.99664 19.04998 0.313 0.313
178
Table 6-58: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)
system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.101274 0.106270 0.002 0.002
0.50003 0.48993 0.009 0.009
0.99741 0.99455 0.019 0.019
1.99951 2.02760 0.039 0.039
3.99824 4.02947 0.074 0.074
6.99907 7.02489 0.122 0.122
8.99819 9.03144 0.152 0.152
9.99709 10.04628 0.167 0.167
10.99973 11.05552 0.181 0.181
12.99872 13.06241 0.208 0.208
14.99878 15.08227 0.234 0.233
16.99951 17.08431 0.258 0.257
18.99784 19.11571 0.282 0.281
Table 6-59: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.10101 0.10070 0.002 0.002
0.50017 0.49280 0.009 0.009
1.00102 0.98004 0.017 0.017
2.00205 1.98559 0.034 0.034
4.00011 3.99859 0.067 0.068
7.00013 6.98563 0.112 0.113
8.99873 8.98467 0.141 0.142
9.99815 9.98222 0.155 0.155
10.99879 10.98629 0.169 0.169
12.99765 12.99886 0.196 0.196
14.99251 14.97994 0.221 0.221
17.00138 17.03355 0.248 0.248
19.00665 19.03755 0.272 0.272
179
Table 6-60: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.10234 0.10817 0.002 0.002
0.50017 0.49706 0.008 0.008
0.99741 0.98454 0.015 0.015
1.99831 1.99938 0.030 0.030
4.00158 4.01648 0.059 0.059
6.99613 7.00454 0.098 0.098
9.00140 9.02261 0.123 0.123
9.99749 10.03367 0.136 0.135
11.00293 11.04614 0.148 0.147
12.99672 13.08526 0.173 0.172
14.99718 15.10811 0.196 0.194
16.99804 17.14448 0.219 0.217
19.00611 19.17591 0.240 0.238
Table 6-61: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)
system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.09981 0.10761 0.002 0.002
0.49963 0.48776 0.006 0.006
0.99915 0.98508 0.013 0.013
2.00005 1.99290 0.026 0.026
3.99811 3.99591 0.050 0.050
6.99787 6.97681 0.084 0.084
8.99913 8.97813 0.105 0.106
10.00016 9.99819 0.116 0.117
11.00052 10.99820 0.127 0.127
12.99925 13.02500 0.148 0.148
14.99731 15.05079 0.168 0.167
17.00712 17.04946 0.186 0.186
180
Table 6-62: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.99888 1.00606 0.087 0.088
2.00151 2.00787 0.116 0.118
3.99864 3.98541 0.152 0.156
6.99947 6.92117 0.189 0.196
8.99793 8.86029 0.209 0.218
9.99829 9.82755 0.218 0.229
10.99973 10.79099 0.227 0.238
12.99712 12.69983 0.242 0.256
14.99891 14.59751 0.256 0.272
17.00058 16.50170 0.271 0.289
18.99810 18.37668 0.283 0.303
Table 6-63: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.99901 1.01588 0.071 0.070
3.99784 4.02771 0.130 0.130
4.99874 5.02405 0.143 0.143
6.99893 7.00084 0.164 0.166
9.99776 9.94214 0.191 0.194
9.99776 9.94173 0.191 0.195
18.99837 18.59349 0.250 0.261
181
Table 6-64: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +
CO2 (2) system at 333.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.49963 0.51470 0.043 0.041
0.99848 1.02660 0.060 0.058
1.99965 2.05054 0.083 0.080
3.99624 4.07760 0.112 0.110
6.99960 7.09427 0.143 0.141
9.00073 9.08932 0.159 0.158
9.99829 10.07943 0.167 0.166
Table 6-65: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][HSO4]
(1) + CO2 (2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.09927 0.09916 0.001 0.001
0.49843 0.49355 0.002 0.002
0.99888 0.98206 0.003 0.003
6.99933 6.89043 0.025 0.026
10.99973 10.86691 0.048 0.049
12.99712 12.78427 0.055 0.056
182
Table 6-66: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][HSO4]
(1) + CO2 (2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental
XCO2
Regressed
XCO2
0.10101 0.10168 0.001 0.001
0.49977 0.49744 0.001 0.001
9.00060 9.12862 0.032 0.031
9.99789 10.14726 0.036 0.036
10.99879 11.17349 0.041 0.040
12.99765 13.20047 0.047 0.047
14.99998 14.85900 0.055 0.055
16.99951 16.61619 0.061 0.062
Table 6-67: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][TF2N]]
(1) + CO2 (2) system at 313.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.09767 0.09654 0.001 0.001
0.49963 0.48601 0.001 0.001
0.99861 0.98337 0.007 0.007
8.99833 9.03503 0.135 0.134
9.99802 10.04034 0.146 0.145
10.99959 11.04883 0.160 0.160
12.99765 13.04819 0.183 0.184
14.99931 15.03621 0.208 0.210
16.99924 16.99647 0.230 0.232
19.00011 18.93043 0.254 0.257
183
Table 6-68: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][TF2N]]
(1) + CO2 (2) system at 323.15 K.
Experimental pressure
(bar)
Regressed pressure
(bar)
Experimental XCO2 Regressed
XCO2
0.09820 0.10444 0.002 0.001
0.50030 0.48503 0.006 0.006
0.99968 0.96419 0.012 0.012
3.99837 4.05167 0.056 0.054
7.00053 6.92634 0.091 0.091
8.99913 8.88707 0.116 0.117
10.00109 9.79430 0.126 0.129
15.00238 14.53338 0.183 0.190
184
6.3 Henry’s Law Constants and Enthalpies and Entropies of Absorption
Table 6-69: Experimental fugacity of CO2 in [bmim][PF6] (Shiflett, 2005) at 283.15 K
Table 6-70: Experimental fugacity of CO2 in [bmim][PF6] (Shiflett, 2005) at 323.15 K
T=50° C Experimental
pressure (bar)
Experimental
XCO2
Experimental
KVL
Experimental
fCO2
0.1020 0.0020 499.5911 0.1019
0.5026 0.0060 166.6216 0.5025
1.0020 0.0120 83.3221 1.0019
3.9961 0.0470 21.2759 3.9960
7.0004 0.0790 12.6580 7.0003
9.9979 0.1090 9.1742 9.9978
13.0023 0.1360 7.3529 13.0022
15.0027 0.1550 6.4516 15.0026
19.9978 0.1970 5.0761 19.9977
T =10° C Experimental
pressure (bar)
Experimental
XCO2
Experimental
KVL
Experimental
fCO2
0.0969 0.0040 249.9879 0.0969
0.5009 0.0160 62.4993 0.5009
1.0018 0.0290 34.4825 1.0018
3.9956 0.1020 9.8039 3.9956
6.9959 0.1670 5.9880 6.9959
9.9996 0.2240 4.4643 9.9996
13.0027 0.2840 3.5211 13.0027
14.9980 0.3090 3.2362 14.9980
19.9975 0.3790 2.6385 19.9975
185
Figure 6.1: Determining the Henry’s law constant for CO2 in [bmim][PF6]
Figure 6.2: Determining the enthalpy of absorption for CO2 in [bmim][PF6]
y = 52.409x2 + 32.415xR² = 0.9993
y = 108.13x2 + 80.248xR² = 1
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4
fCO
2
XCO2
Experiment AT 283.15 K
Experiment AT 323.15 K
Poly. (Experiment AT 283.15 K)
Poly. (Experiment AT 323.15 K)
y = -2000.2x + 10.568R² = 0.9981
0
1
2
3
4
5
6
0 0.001 0.002 0.003 0.004
lnH
1/T
Series1
Linear (Series1)
186
Figure 6.3: Determining the entropy of absorption for CO2 in [bmim][PF6]
y = 6.3705x - 32.448R² = 0.9953
0
1
2
3
4
5
6
5.6 5.65 5.7 5.75 5.8 5.85 5.9
lnH
1/T
Series1
Linear (Series1)
187
Table 6-71: Experimental fugacity of CO2 in [Emmp][TF2N] at 313.15 And 323.15 K
SRK
T-40°C Experimental pressure
(bar)
Experimental X
CO2
Experimental
KVL
Experimental
f CO2
1 0.0977 0.0160 62.3318 0.0977
2 0.4996 0.0229 43.7410 0.4996
3 0.9986 0.0335 29.8209 0.9986
4 1.9994 0.0548 18.2618 1.9994
5 3.9985 0.0941 10.6249 3.9985
6 6.9980 0.1462 6.8418 6.9980
7 8.9983 0.1779 5.6198 8.9983
8 9.9980 0.1932 5.1747 9.9980
9 10.9996 0.2086 4.7944 10.9996
10 12.9977 0.2382 4.1976 12.9976
11 14.9993 0.2657 3.7641 14.9993
12 16.9992 0.2921 3.4231 16.9992
13 19.0001 0.3165 3.1591 19.0001
T-50°C Experimental pressure
(bar)
Experimental X
CO2
Experimental
KVL
Experimental
f CO2
1 0.0999 0.0021 476.3272 0.0999
2 0.4998 0.0088 114.1091 0.4998
3 0.9985 0.0175 57.2834 0.9985
4 2.0007 0.0363 27.5720 2.0007
5 4.0008 0.0701 14.2661 4.0008
6 6.9977 0.1144 8.7382 6.9977
7 8.9989 0.1432 6.9844 8.9989
8 10.0035 0.1570 6.3709 10.0035
9 11.0003 0.1711 5.8430 11.0003
10 12.9978 0.1969 5.0777 12.9978
11 15.0021 0.2212 4.5206 15.0021
12 16.9958 0.2448 4.0851 16.9958
13 18.9962 0.2673 3.7411 18.9962
188
Table 6-72: Experimental fugacity of CO2 in [Emmp][TF2N] at 333.15 K
T-°60C Experimental pressure
(bar)
Experimental X
CO2
Experimental
KVL
Experimental
f CO2
1 0.1009 0.0018 550.8477 0.1009
2 0.5002 0.0068 146.6770 0.5002
3 1.0005 0.0144 69.2369 1.0005
4 1.9991 0.0317 31.5770 1.9991
5 3.9982 0.0600 16.6584 3.9982
6 7.0008 0.0994 10.0586 7.0008
7 8.9997 0.1232 8.1174 8.9997
8 9.9978 0.1346 7.4287 9.9978
9 10.9988 0.1459 6.8536 10.9988
10 12.9977 0.1683 5.9427 12.9976
11 14.9988 0.1898 5.2676 14.9988
12 16.9900 0.2094 4.7758 16.9900
13 18.9970 0.2280 4.3860 18.9970
Figure 6.4: Determining the Henry’s law constant for CO2 in [Emmp][TF2N]
y = 76.484x2 + 36.149x
R² = 0.9988
y = 67.055x2 + 53.034x
R² = 1
y = 96.599x2 + 61.048x
R² = 0.9999
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4
fCO
2
XCO2
at 313.15 K
at 323.15 K
at 333.15 K
189
Figure 6.5: Determining the entropy of absorption for CO2 in [Emmp][TF2N]
y = -2746x + 12.393
R² = 0.942
3.5
3.6
3.7
3.8
3.9
4
4.1
4.2
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
lnH
1/T
190
Figure 6.6: Determining the entropy of absorption for CO2 in [Emmp][TF2N]
y = 8.4849x - 45.134
R² = 0.9377
3.5
3.6
3.7
3.8
3.9
4
4.1
4.2
5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82
lnH
lnT
191
Table 6-73: Experimental fugacity of CO2 in [PMPY][TF2N] at 313.15 And 323.15 K
SRK
T-40°C Experimental pressure (bar) Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.0990 0.0024 420.9515 0.0990
2 0.5000 0.0109 91.4021 0.5000
3 1.0013 0.0212 47.1882 1.0013
4 1.9992 0.0431 23.1912 1.9992
5 3.9985 0.0835 11.9777 3.9985
6 7.0001 0.1373 7.2821 7.0001
7 8.9990 0.1715 5.8318 8.9990
8 9.9998 0.1877 5.3286 9.9998
9 10.9988 0.2036 4.9113 10.9988
10 12.9979 0.2346 4.2632 12.9979
11 14.9987 0.2634 3.7971 14.9987
12 16.9982 0.2903 3.4447 16.9982
13 18.9969 0.3167 3.1576 18.9969
T-50°C Experimental pressure (bar) Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.0963 0.0023 437.3694 0.0963
2 0.4995 0.0093 107.7576 0.4995
3 0.9982 0.0187 53.5169 0.9982
4 1.9994 0.0379 26.4058 1.9994
5 3.9985 0.0725 13.7947 3.9985
6 7.0009 0.1185 8.4421 7.0009
7 9.0003 0.1470 6.8039 9.0003
8 9.9964 0.1606 6.2279 9.9964
9 10.9991 0.1748 5.7201 10.9991
10 13.0025 0.2024 4.9400 13.0025
11 14.9977 0.2282 4.3815 14.9977
12 17.0074 0.2526 3.9595 17.0074
13 19.0081 0.2766 3.6158 19.0081
192
Table 6-74: Experimental fugacity of CO2 in [PMPY][TF2N] at 333.15 K.
T-
60°C
Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.0997 0.0022 456.9450 0.0997
2 0.4999 0.0074 134.4821 0.4999
3 0.9990 0.0154 64.9621 0.9990
4 1.9998 0.0320 31.2161 1.9998
5 3.9990 0.0606 16.4955 3.9990
6 6.9969 0.1004 9.9582 6.9969
7 9.0015 0.1257 7.9544 9.0015
8 9.9996 0.1375 7.2718 9.9996
9 10.9991 0.1490 6.7109 10.9991
10 12.9973 0.1725 5.7978 12.9973
11 15.0003 0.1935 5.1670 15.0002
12 16.9954 0.2143 4.6655 16.9954
13 18.9965 0.2323 4.3041 18.9965
Figure 6.7: Determining the Henry’s law constant for CO2 in [PMPY][TF2N]
y = 51.089x2 + 43.67x
R² = 1
y = 60.176x2 + 52.132x
R² = 1
y = 91.247x2 + 60.077x
R² = 0.9999
0
2
4
6
8
10
12
14
16
18
20
0 0.1 0.2 0.3 0.4
fCO
2
XCO2
at 313.15
Kat 323.15
K
193
Figure 6.8: Determining the enthalpy of absorption for CO2 in [PMPY][TF2N]
y = -1665.2x + 9.0983
R² = 0.9979
3.75
3.8
3.85
3.9
3.95
4
4.05
4.1
4.15
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
lnH
1/T
194
Figure 6.9: Determining the entropy of absorption for CO2 in [PMPY][TF2N]
y = 5.1546x - 25.84
R² = 0.997
3.75
3.8
3.85
3.9
3.95
4
4.05
4.1
4.15
5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82
lnH
lnT
195
Table 6-75: Experimental fugacity of CO2 in [TDC][TF2N] at 313.15 And 323.15 K
SRK
T-
40°C
Experimental pressure
(bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.0975 0.0028 352.1008 0.0975
2 0.4990 0.0130 77.1127 0.4990
3 0.9989 0.0250 40.0136 0.9989
4 2.0003 0.0503 19.8701 2.0003
5 4.0016 0.0974 10.2671 4.0016
6 6.9991 0.1590 6.2884 6.9991
7 8.9993 0.1970 5.0756 8.9993
8 9.9986 0.2150 4.6502 9.9986
9 11.0008 0.2331 4.2900 11.0008
10 12.9991 0.2673 3.7416 12.9991
11 15.0005 0.3000 3.3329 15.0005
12 16.9975 0.3318 3.0135 16.9975
13 18.9968 0.3601 2.7774 18.9968
T-
50°C
Experimental pressure
(bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.1014 0.0025 393.9556 0.1014
2 0.5008 0.0105 95.0550 0.5008
3 0.9989 0.0209 47.9359 0.9989
4 2.0004 0.0437 22.8993 2.0004
5 3.9984 0.0837 11.9498 3.9984
6 6.9987 0.1373 7.2834 6.9987
7 8.9985 0.1704 5.8682 8.9985
8 9.9987 0.1866 5.3579 9.9987
9 10.9993 0.2018 4.9552 10.9993
10 12.9993 0.2317 4.3157 12.9993
11 14.9977 0.2614 3.8251 14.9977
12 17.0054 0.2881 3.4709 17.0054
13 18.9966 0.3127 3.1977 18.9966
196
Table 6-76: Experimental fugacity of CO2 in [TDC][TF2N] at 333.15 K
T-
60°C
Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.1013 0.0023 434.6161 0.1013
2 0.5000 0.0090 110.9151 0.5000
3 0.9974 0.0188 53.1021 0.9974
4 1.9995 0.0391 25.5595 1.9995
5 3.9982 0.0741 13.4999 3.9982
6 6.9991 0.1218 8.2068 6.9991
7 8.9982 0.1519 6.5845 8.9982
8 9.9971 0.1668 5.9945 9.9971
9 10.9997 0.1810 5.5261 10.9997
10 12.9987 0.2078 4.8121 12.9987
11 14.9988 0.2338 4.2773 14.9988
12 16.9995 0.2578 3.8792 16.9995
13 18.9978 0.2817 3.5500 18.9978
Figure 6.10: Determining the Henry’s law constant for CO2 in [TDC][TF2N]
y = 42.776x2 + 37.21x
R² = 1
y = 54.816x2 + 43.363x
R² = 1
y = 64.157x2 + 49.312x
R² = 1
0
2
4
6
8
10
12
14
16
18
20
0 0.1 0.2 0.3 0.4
fCO
2
XCO2
at 313.15 K
at 323.15 K
at 333.15 K
197
Figure 6.11: Determining the enthalpy of absorption for CO2 in [TDC][TF2N]
Figure 6.12: Determining the entropy of absorption for CO2 in [TDC][TF2N]
y = -1469.7x + 8.3124
R² = 0.999
3.6
3.65
3.7
3.75
3.8
3.85
3.9
3.95
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
lnH
1/T
y = 4.55x - 22.528
R² = 0.9983
3.6
3.65
3.7
3.75
3.8
3.85
3.9
3.95
5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82
lnH
lnT
198
Table 6-77: Experimental fugacity of CO2 in [TDC][DCN] at 313.15 And 323.15 K
SRK
T-
40°C
Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.1010 0.0018 555.5556 0.1010
2 0.5002 0.0085 117.6471 0.5002
3 1.0010 0.0165 60.6061 1.0010
4 2.0020 0.0339 29.4985 2.0020
5 4.0001 0.0674 14.8368 4.0001
6 7.0001 0.1124 8.8968 7.0001
7 8.9987 0.1411 7.0872 8.9987
8 9.9982 0.1549 6.4558 9.9981
9 10.9988 0.1687 5.9277 10.9988
10 12.9977 0.1959 5.1046 12.9977
11 14.9925 0.2207 4.5310 14.9925
12 17.0014 0.2479 4.0339 17.0014
13 19.0067 0.2720 3.6765 19.0067
T-
50°C
Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.1023 0.0019 526.3158 0.1023
2 0.5002 0.0075 133.3333 0.5002
3 0.9974 0.0145 68.9655 0.9974
4 1.9983 0.0299 33.4448 1.9983
5 4.0016 0.0587 17.0358 4.0016
6 6.9961 0.0977 10.2354 6.9961
7 9.0014 0.1231 8.1235 9.0014
8 9.9975 0.1357 7.3692 9.9975
9 11.0029 0.1478 6.7659 11.0029
10 12.9967 0.1727 5.7904 12.9967
11 14.9972 0.1957 5.1099 14.9972
12 16.9980 0.2185 4.5767 16.9980
13 19.0061 0.2403 4.1615 19.0061
199
Table 6-78: Experimental fugacity of CO2 in [TDC][DCN] at 333.15 K
T-
60°C
Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
1 0.0998 0.0017 588.2353 0.0998
2 0.4996 0.0061 163.9344 0.4996
3 0.9991 0.0125 80.0000 0.9991
4 2.0000 0.0255 39.2157 2.0000
5 3.9981 0.0500 19.9920 3.9981
6 6.9979 0.0835 11.9760 6.9979
7 8.9991 0.1051 9.5147 8.9991
8 10.0002 0.1163 8.5985 10.0002
9 11.0005 0.1265 7.9051 11.0005
10 12.9993 0.1475 6.7797 12.9993
11 14.9973 0.1678 5.9595 14.9973
12 17.0071 0.1859 5.3792 17.0071
Figure 6.13: Determining the Henry’s law constant for CO2 in [TDC][DCN]
y = 46.706x2 + 57.221x
R² = 1
y = 52.848x2 + 66.34x
R² = 1
y = 74.724x2 + 77.303x
R² = 1
0
2
4
6
8
10
12
14
16
18
20
0 0.1 0.2 0.3
fCO
2
XCO2
at 313.15 K
at 323.15 K
at 333.15 K
200
Figure 6.14: Determining the enthalpy of absorption for CO2 in [TDC][DCN]
y = -1568.4x + 9.0532
R² = 0.9992
4
4.05
4.1
4.15
4.2
4.25
4.3
4.35
4.4
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
lnH
1/T
201
Figure 6.15: Determining the entropy of absorption for CO2 in [TDC][DCN]
y = 4.8583x - 23.874
R² = 0.9997
4
4.05
4.1
4.15
4.2
4.25
4.3
4.35
4.4
5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82
lnH
lnT
202
Table 6-79: Experimental fugacity of CO2 in [EMIM][LACTATE] at 313.15 ,323.15 and
333.15 K
Peng- Robinson (PR-EoS)
T=40°C Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
0.9989 0.0870 11.4940 0.9989
2.0015 0.1163 8.5972 2.0015
3.9986 0.1525 6.5587 3.9986
6.9995 0.1890 5.2908 6.9995
8.9979 0.2090 4.7858 8.9979
9.9983 0.2184 4.5787 9.9983
10.9997 0.2270 4.4055 10.9997
12.9971 0.2423 4.1269 12.9971
14.9989 0.2559 3.9084 14.9989
17.0006 0.2708 3.6932 17.0006
18.9981 0.2831 3.5320 18.9981
T=50°C Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
0.9990 0.0714 14.0132 0.9990
3.9978 0.1300 7.6935 3.9978
4.9987 0.1429 6.9970 4.9987
6.9989 0.1639 6.1026 6.9989
9.9978 0.1907 5.2444 9.9978
18.9984 0.2499 4.0012 18.9984
T=60°C Experimental
pressure (bar)
Experimental
X CO2
Experimental
KVL
Experimental
f CO2
0.4996 0.0430 23.2743 0.4996
0.9985 0.0598 16.7345 0.9985
1.9996 0.0829 12.0611 1.9996
3.9962 0.1124 8.8995 3.9962
6.9996 0.1427 7.0084 6.9996
9.0007 0.1595 6.2709 9.0007
203
Figure 6.16: Determining the Henry’s law constant for CO2 in [EMIM][LACTATE]
Figure 6.17: Determining the enthalpy of absorption for CO2 in [EMIM][LACTATE]
y = 46.182x - 3.144
R² = 0.9835
y = 54.442x - 2.9155
R² = 0.9948
y = 64.838x - 2.816
R² = 0.9596
-5
0
5
10
15
20
0 0.05 0.1 0.15 0.2
fCO
2
XCO2
Series1
y = -644.06x + 6.3527
R² = 0.9722
4.28
4.3
4.32
4.34
4.36
4.38
4.4
4.42
4.44
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
lnH
1/T
204
Figure 6.18: Determining the entropy of absorption for CO2 in [EMIM][LACTATE]
y = 1.9915x - 7.148
R² = 0.9692
4.28
4.3
4.32
4.34
4.36
4.38
4.4
4.42
4.44
5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82
lnH
lnT
205
Table 6-80: Experimental fugacity of CO2 in [(CH2)4SO3HMIm] [HSO4] at 313.15 And
323.15 K
Peng-Robinson (PR-EoS)
T=40°C Experimental
pressure
(bar)
Experimental X
CO2
Experimental
KVL
Experimental
f CO2
0.0993 0.0008 1308.2550 0.0993
0.4984 0.0018 570.5489 0.4984
0.9989 0.0030 337.7090 0.9989
6.9993 0.0253 39.5220 6.9993
10.9997 0.0482 20.7501 10.9997
12.9971 0.0552 18.1189 12.9971
T=50°C Experimental
pressure
(bar)
Experimental X
CO2
Experimental
KVL
Experimental
f CO2
0.1010 0.0006 1784.1086 0.1010
0.4998 0.0012 864.9262 0.4998
9.0006 0.0319 31.3251 9.0006
9.9979 0.0365 27.4136 9.9979
10.9988 0.0408 24.5344 10.9988
12.9977 0.0473 21.1411 12.9976
15.0000 0.0548 18.2429 15.0000
16.9995 0.0614 16.2957 16.9995
206
Figure 6.19: Determining the Henry’s law constant for CO2 in [(CH2)4SO3HMIm]
[HSO4]
y = -1304.4x2 + 301.42xR² = 0.9973
y = 20.891x2 + 274xR² = 0.9994
-2
0
2
4
6
8
10
12
14
16
18
0 0.02 0.04 0.06 0.08
fCO
2
XCO2
313.15 K
323 K
Poly. (313.15 K)
Poly. (323 K)
207
Figure 6.20: Determining the enthalpy of absorption for CO2 in [(CH2)4SO3HMIm]
[HSO4]
y = -965.16x + 8.6952
R² = 1
5.6
5.62
5.64
5.66
5.68
5.7
5.72
0.00308 0.0031 0.00312 0.00314 0.00316 0.00318 0.0032
lnH
1/T
208
Figure 6.21: Determining the entropy of absorption for CO2 in [(CH2)4SO3HMIm]
[HSO4]
y = 3.0342x - 11.823
R² = 1
5.6
5.62
5.64
5.66
5.68
5.7
5.72
5.745 5.75 5.755 5.76 5.765 5.77 5.775 5.78
lnH
lnT
209
Table 6-81: Experimental fugacity of CO2 in [(CH2)4SO3HMIm][TF2N] at 313.15 And
323.15 K
T=40°C Experimental
pressure (bar)
Experimental
XCO2
Experimental
KVL
Experimental
fCO2
0.0977 0.0013 758.7253 0.0977
0.4996 0.0013 758.7253 0.4996
0.9986 0.0073 136.2212 0.9986
8.9983 0.1349 7.4138 8.9983
9.9980 0.1455 6.8725 9.9980
10.9996 0.1596 6.2675 10.9996
12.9977 0.1829 5.4662 12.9977
14.9993 0.2082 4.8028 14.9993
16.9992 0.2296 4.3552 16.9992
19.0001 0.2538 3.9405 19.0001
T=50°C Experimental
pressure (bar)
Experimental
XCO2
Experimental
KVL
Experimental
fCO2
0.0982 0.0016 634.5178 0.0982
0.5003 0.0062 161.0565 0.5003
0.9997 0.0122 81.8331 0.9997
3.9984 0.0557 17.9520 3.9984
7.0005 0.0909 11.0038 7.0005
8.9991 0.1159 8.6252 8.9991
10.0011 0.1258 7.9503 10.0011
15.0024 0.1826 5.4774 15.0024
210
Figure 6.22: Determining the Henry’s law constant for CO2 in
[(CH2)4SO3HMIm][TF2N]
y = 61.723x2 + 59.4xR² = 0.9988
y = 63.12x2 + 70.781xR² = 0.9997
0
5
10
15
20
25
0 0.05 0.1 0.15 0.2 0.25 0.3
fCO
2
XCO2
313.15
323.15
Poly.(313.15)
Poly.(323.15)
211
Figure 6.23: Determining the enthalpy of absorption for CO2 in
[(CH2)4SO3HMIm][TF2N]
y = -1773.9x + 9.749
R² = 1
4.06
4.08
4.1
4.12
4.14
4.16
4.18
4.2
4.22
4.24
4.26
4.28
0.00308 0.0031 0.00312 0.00314 0.00316 0.00318 0.0032
lnH
1/T
212
Figure 6.24: Determining the entropy of absorption for CO2 in
[(CH2)4SO3HMIm][TF2N]
y = 5.5766x - 27.963
R² = 1
4.06
4.08
4.1
4.12
4.14
4.16
4.18
4.2
4.22
4.24
4.26
4.28
5.745 5.75 5.755 5.76 5.765 5.77 5.775 5.78
lnH
lnT