Ionic Liquids: A New Chemical Platform for CO2 Separations · 2016-12-08 · 2 capture process to...
Transcript of Ionic Liquids: A New Chemical Platform for CO2 Separations · 2016-12-08 · 2 capture process to...
W. F. Schneider CCTR - 4 June 2009
Ionic Liquids: A New Chemical Platform for
CO2 Separations
Bill Schneider
Dept. of Chemical and Biomolecular Engineering
University of Notre Dame
Indiana CCTR Advisory Committee Meeting
Indiana University, Bloomington
June 4, 2009
Why CO2 capture and sequestration (CCS)?
• Energy consumption is projected to grow significantly in
the coming decades
• Coal will necessarily be a major component of the
energy equation
• CCS essential to mitigate deleterious increases in
atmospheric CO2 concentration
W. F. Schneider CCTR - 4 June 2009
Current technology and challenges
• Existing drop-in technologies based on aqueous amine chemistry
• Short-comings including energy overhead, cost, corrosivity, NOx/SOx cross reactivity, H2O content, decomposition, …
W. F. Schneider CCTR - 4 June 2009
HO
NH2
CO2HO
NH
O
O
HO
NH3+
H2O CO2 H+ HCO3-
2
Absorption isotherms
W. F. Schneider CCTR - 4 June 2009
Langmuir (single site) absorption
A + CO2 (g) ↔ A⋅CO2 Keq(T)
xCO
2
KP
CO2
1 KPCO
2
, K eG / RT
CO2
CO2
A-CO2
A-CO2A
PCO2
xCO2
T
O2
N2
H2O
liquid
gas
Carrying capacity
W. F. Schneider CCTR - 4 June 2009
Langmuir (single site) absorption
A + CO2 (g) ↔ A⋅CO2 Keq(T)
Absorption
Low T, low P
Desorption
High T, high P
Carrying capacity
Mol CO2/mol absorbent
Absorption optimization
W. F. Schneider CCTR - 4 June 2009
K(T ) eG (T )/RT , G(T ) H (T )TS(T )
S
t
r
o
n
g
b
i
n
d
i
n
g
W
e
a
k
b
i
n
d
i
n
g
A CO
O
Background – What Are Ionic Liquids?
• Salts that are liquid at
ambient temperatures
• Huge diversity of
potential compounds
– Mix and match cations
and anions
W. F. Schneider CCTR - 4 June 2009
Why investigate ionic liquids?
• IL properties favorable for CO2 capture
– Negligible volatility
– High intrinsic physical selectivity for CO2
• Can add chemical functionality
– Opportunity to “tune” properties
– Computational methods enable molecule “design”
– “Molecularomics”
• Potential for drop-in or unique process configurations
• Possible to achieve better performance than aqueous
amines
W. F. Schneider CCTR - 4 June 2009
Gravimetric gas adsorption
• Mass vs. temperature and pressure
W. F. Schneider CCTR - 4 June 2009
Gravimetric microbalance Magnetic Suspension
Balance
Physical solubility of CO2 in ILs
• ILs have high physical CO2 solubility
• Good selectivity over O2 and N2
W. F. Schneider CCTR - 4 June 2009
Gravimetric solubility
1-n-hexyl-3,5-
dimethylpyridinum
bis(trifluoromethane-
sulfonyl)amide
Henry’s Law
Pa = Hxa
Predicting properties with computation
W. F. Schneider CCTR - 4 June 2009
Findings from previous work
• Physical solubility: low enthalpy of absorption
– ~ 12 kJ/mol
– Very low regeneration energy and temperature, but…
– CO2 capacity too low ⇒ high circulation rates
– Desorption at too low pressure ⇒ high compression costs
• Increase capacity by adding chemical functionality
– Increases enthalpy of absorption / desorption and capacity
– Increases regeneration temperature and energy, but reduces
circulation rates
W. F. Schneider CCTR - 4 June 2009
Task-specific ionic liquids (TSILs)
• Build on aqueous amine chemistry:
• Tether amines to ionic liquid:
W. F. Schneider CCTR - 4 June 2009
NH22 +
O
C
ONH
CO-+ NH3
+1:2
O
1 atm CO2
Room temp.
In situ vibrational spectroscopy
N2
Vacuum
ThermocoupleP
I
R
Silicon
probe
CO2
P-controller
trap
vent
vent
W. F. Schneider CCTR - 4 June 2009
Volumetric gas absoprtion
W. F. Schneider CCTR - 4 June 2009
Purge
CO2
Syringe PumpReservoir
(<300 cm3)
Vacuum
Purge
Glass Tank
(150-200 cm3)
Purge
101.0121 g (T)
Balance
Pressure
SensorHeise
50 mbar
Pressure
Sensor Heise
1550 mbar
Four Channels
Temperatute Sensor
40.01 ºCCell
2
1 2 3 4
Oven
Extra Volumen
(150 cm3)
Magnetic
Stirrer
Glass
Vessel-Cell
Problems with conventional TSILs
• Liquid becomes quite viscous upon contact with CO2
• 2:1 mechanism is inefficient…1:1 mechanism possible?
• How to tune the chemistry?
W. F. Schneider CCTR - 4 June 2009
No CO2 17 mbar CO2
Fundamental chemical questions
• What functional groups should be used?– Mechanism
– Capacity
– Enthalpy
– Selectivity
– Rate
• Other questions– Viscosity
– Stability
– Cost
– Water solubility
– Corrosion
– Mass transport
W. F. Schneider CCTR - 4 June 2009
W. F. Schneider UW-Madison - 31 Mar 2009
Electronic Structure Method History
1920’s Schrödinger Equation (HΨ = EΨ)“The underlying physical laws necessary for the mathematical theory of a
large part of physics and the whole of chemistry are thus completely known,
and the difficulty is only that the exact application of these laws leads to
equations much too complicated to be soluble.”Dirac, P. A. M. Proc. R. Soc. London, 1929,123, 714
1960’s Kohn-Sham Equation (Ts[ρ]-υNe[ρ]+υee[ρ]-υXC[ρ])ψi=εiψi
Electron density replaces wavefunction as fundamental variable. Can be
described in terms of an exact (unknown) effective one-electron equation
1998 Noble Prize in Chemistry (J. Pople and W. Kohn)“…for pioneering contributions in developing methods that can be used for
theoretical studies of the properties of molecules and the chemical processes
in which they are involved.”
today astounding advances in theory + algorithms + inexpensive computer power
make application to a wide range of practical problems a reality
methods now be adopted in many progressive engineering departments
144 processor Opteron 265
dual-core computer being
purchased by Maginn,
Schneider, and Stadtherr groups
W. F. Schneider UW-Madison - 31 Mar 2009
First Principles Simulations for Catalysis
Electronic Structure Simulation
Define composition and structure
Define computational model
Select solution algorithms
Structures and thermodynamics Reaction pathways and kinetics Reaction dynamics
Primary Outputs
Distribution of electrons
Optimized structures
Absolute energy
Derived Outputs
Spectroscopy (vibrational, electronic, …)
Thermodynamics (heat capacities, entropies, …)
Kinetics (activation energies, prefactors, …)
Dynamics
Tools: TST, statistical mechanics
Example
alumina
supercell
~70 atoms
First-principles methodology
• Screen intrinsic functional group-CO2 reactivity
• Contrast tethering strategies
• Hybrid-DFT calculations implemented in Gaussian– B3LYP/6-311++G(d,p)
– Harmonic frequency analysis
– Standard ZPE and gas-phase free energy analysis
• Systematic exploration over conformation space
• Boltzmann averaged reaction energies
W. F. Schneider CCTR - 4 June 2009
++
N
O
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Reliability of first-principles models
�Grxn(T = 298 K)RR’NH + H+ RR’NH2+
Experimental
values as
tabulated in NIST
webbook
B3LYP/6-311++G(d,p)
Combined protonation and carbamate formation
• Intrinsic CO2capture energetics integrate both reactions
• Combine reactions on single energy correlation plot
• Reaction energies largely uncorrelated
• Potentially independent tunability
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0-5
-10-15
NH22 +
O
C
ONH
CO-+ NH3
+1:2
O
CO2 reaction stoichiometry in TSILs
• What effect does ion tethering have on energetics and
mechanism of amine-CO2 reaction?
• Might ion tethering favor more desirable reaction
pathways?
W. F. Schneider CCTR - 4 June 2009
NH
COH
O
1:1
MEA vs. Cation- vs. Anion-Tethered Amines
• Local cation tethering favors 2:1 binding
• Local anion tethering disfavors 2:1 binding
• Tethering ion and tethering point as important as functional groups in controlling CO2 reactions
+
-
MEA:
Pyridinium
amine
cation:
Amino
acetate
anion:
+
1:1
-
0
+2
-4
0 -
+ …NH3+
-17
2:1
+17
--
+
-
+ …NH3+
+ …NH3+
Reaction energies in kcal/mol relative to MEA
+CO2
+CO2
+CO2
-H+
-H+
-H+
W. F. Schneider CCTR - 4 June 2009
1:1 stoichiometry for anion-tethered IL?
• Synthesized anion-
tethered task-specific
ionic liquid
• Experimental isotherm
consistent with 1:1
reaction stoichiometry
W. F. Schneider CCTR - 4 June 2009
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.00 0.05 0.10 0.15P (MPa)
Mo
l C
O2 / M
ol IL
(m
ol/m
ol)
22 °C (RTA)
40 °C (ITA)
40 °C (High Temperature Apparatus)
Logarítmica (22 °C (RTA))
Logarítmica (40 °C (High TemperatureApparatus))
Literature precedence for 1:1 reaction
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> 0.5 CO2 mole fraction
consistent with 1:1 reaction
stoichiometry
P+H2N
CH
CH O-
O
Computational predictions of anion energies
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high low
Computational predictions of physical properties
• Quantitative prediction of properties like viscosity
– Often easier to compute at extreme conditions than measure
– Fill in gaps for process modeling
W. F. Schneider CCTR - 4 June 2009
Trimeric sensitivity analysis
• Process simulation was used to evaluate the sensitivity
of a representative 500 MW coal plant CO2 capture
process to ionic liquid properties
• Results of the sensitivity analysis will be used to guide
the development of next-generation ionic liquids
• Sensitivity variables
– Stoichiometry: ND proposed both 1:1 and 2:1 (IL:CO2)
stoichiometries; preliminary modeling to date assumed 1:1.
– Enthalpy of reaction: ND proposed a range of (low-high) based
on molecular modeling.
– Loading (Keq): Sensitivity includes a range of CO2 loadings that
result from the above enthalpies of reaction.
– Water miscibility: Both partially- and fully-miscible systems are
included. Activities coefficients modeled with NRTL using
experimental data
W. F. Schneider CCTR - 4 June 2009
Base case process modeling
• Conventional absorber / stripper configuration
– “Drop in” replacement for MEA
• Other configurations possible
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Preliminary parasitic energy predictions
• Courtesy Kevin Fisher, Duane Myers, Katherine Searcy, Trimeric Corp.
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58.749.3
62.3
45.3
9.0
4.9
46.5
29.5
23.6
0
20
40
60
80
100
120
140
160
40 50 60
Enthalpy of Reaction (kJ/gmole)
To
tal
Eq
uiv
ale
nt
Wo
rk (
MW
)
Compressor power
Pump power
Regeneration heat
Equivalent
Work for
Conventional
MEA System
(approx.)
Theoretical
Thermodynamic
Minimum
Energy (approx.)
low medium high
Ionic Liquids: Breakthrough Absorption
Technology for Post-Combustion CO2 CaptureNETL Project 43091
• Funding and cost share
– Total project: $3,550,718
– Federal portion: $2,447,138 (69%)
– Cost share: $1,103,580 (31%)
• Project performance dates: Mar 1, 2007-June 30, 2010
• Project participants
– Notre Dame (molecule design, thermodynamics, property measurement, synthesis, project management)
– Babcock and Wilcox (corrosion, design of lab scale unit)
– DTE (consultation, feasibility of process designs)
– Air Products (thermodynamics, process design, molecule design)
– EMD / Merck (synthesis, molecule design)
– Trimeric (process design and system analysis)
W. F. Schneider CCTR - 4 June 2009
Competing separation technologies
• Alternative CO2 capture chemistries
– Chilled NH3
– Enzyme-based (carbozyme)
– Nanoengineered materials
– Electrochemical
– …
• Physical separation
– Membranes
– Molecular sieves
• Pre-combustion
– Coal gasification
– Oxyfuel
W. F. Schneider CCTR - 4 June 2009
Carbon sequestration options
• Oil/gas wells
– Enhanced oil recovery
• Coal beds
– Methane recovery
• Saline aquifers
• Ocean floor
• Mineralization
• Industrial use
• Thermal/photolytic/electrolytic recovery
– CO2 CO, H2, CH3OH, …
W. F. Schneider CCTR - 4 June 2009
Notre Dame Team
Current members
• Prof. Edward Maginn
• Prof. Joan Brennecke
• Prof. Bill Schneider
• Prof. Jindal Shah
• Dr. Erica Price
• Dr. Zulema Lopes-Castillo
• Dr. Tom Rosch
• Devan Kestal
• Burcu Gurkan
• Alexandre Chapeaux
• Elaine Mindrup
• Marcos Perez-Blanco
• Hao Wu
• Brett Goodrich
• Mandy Danser
• Lindsey Ficke
Alumni
• Prof. Wei Shi
• Prof. Juan de la Fuenta
• Prof. Jessica Anderson
• Dr. JaNeille Dixon
• Dr. Keith Gutowski
• Dr. Manish Kelkar
W. F. Schneider CCTR - 4 June 2009
• CO2 capture from flue gas is viable but currently
expensive
• Alternative materials/chemistries/configurations hold the
promise of significant improvements over current
configurations
– Simulations can accelerate the discovery process
• Many fundamental and technical hurdles remain to be
overcome
+ CO2(g)NH2
TSIL
NH2
NHCO2−
NH3+
+
NH2
+ CO2(g)
NH-COOH NH-COO- NH3+
2 ΔGsolv
ΔGrxn ΔGrxn
ΔGsolv ΔGsolv
2
+
+
-
-
+
+
-
-
+ + +
K(T), k(T)
Conclusions
W. F. Schneider CCTR - 4 June 2009