“Molecular Chromatography” in Dense-Phase Carbon Dioxide Denis K. Okumu Tuesday, July 31, 2001...
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Transcript of “Molecular Chromatography” in Dense-Phase Carbon Dioxide Denis K. Okumu Tuesday, July 31, 2001...
“Molecular Chromatography” in Dense-PhaseCarbon Dioxide
Denis K. Okumu
Tuesday, July 31, 2001
The University of Mississippi
Presentation Overview
I. Introduction ““Classical Chromatography”definedClassical Chromatography”defined “ “Molecular Chromatography” in Molecular Chromatography” in dense-phase COdense-phase CO22
III. Results and Discussion
II. Materials and method InstrumentationInstrumentation
Experimental procedureExperimental procedure
Definition of Classical Chromatography
It describes a diverse and significant category of techniques used by scientists to obtain analytical separations in multi-component, complex chemical mixtures.
Such separations used to be carried out using batch procedures like distillation, precipitation, and extraction.
Why use Chromatography as a Separation Technique?
Chromatographic separations are fast, continuous, and produce much higher purity products than the batch processes.
NoStationary
Phase
Time
No SeparationPolymericStationary
Phase
Separation
Time
Detector
Mobile Phase ( CO2 )
Stationary Phase (Polymer)
MixtureInject
Classical Model of Chromatographic ColumnClassical Model of Chromatographic Column
Goal of this research
To explore the possibility of obtaining chromatographic-likeseparations in chromatographic columns containing no stationaryphases.
Current research results in our laboratory indicate that with liquid CO2 as the mobile phase under certain conditions of temperature,pressure, and density, this separation is actually possible.
Column
#1 #2
Vent
Sample Vent
Sample
He
MSD
260º C
Vent
150º C
GC InjectionPort
90º C
Valve Oven
GC Oven -50 to 120 ºC
Restrictor
Syringe Pumps
CO
2
Schematic Diagram of the Dense-Phase CO2 Instrument.
MSD
Pumps
GC
Injectionpump
InjectionValve
ActuatorsComputerized
Controller
CO2
Tank
DigitalFlowmeter
PressureSensor
MSD
Pumps
GC
InjectionValve
ActuatorsComputerized
Controller
CO2
Tank
DigitalFlowmeter
PressureSensor
Characteristics of Carbon Dioxide
o Inexpensive and available in high purity.
o Environmentally friendly
o Innocuous
o Critical Temperature (31oC)
o Critical Pressure (73 atm)
o Critical Density (0.47 g/mL)
HPLC
SFCGC
Pressure (atm)
0 10 20 30 40 50 60 70 80 90 100
Den
sity
(g/
mL
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
-50 -50 ooC C
-30 -30 ooC C
-10 -10 ooC C
10 10 ooC C 20 20 ooCC
31 31 ooCC35 35 ooCC
40 40 ooCCTwo PhaseRegion
CO2 ‘Phase Diagram’
CriticalPoint
ExperimentalExperimentalResultsResults
Time (min)
0 5 10 15 20 25 30 35 40
MS
Rep
onse
(co
un
ts)
Neon
Methane
Ethane
Propane
Butane
Pentane
Hexanes
20
15
30
39
58
72
86
Injection Peak
m/z
Column: 500 m x 25 m Stainless steelTemperature: 10oCPressure : 120 atmFlow Rate: 190 L/minDensity of CO2: 0.89 g/mL
Time (min)
0 1 2 3 4 5 6 7 8 9 10
Ab
un
da
nc
e
n-Propane
Neon
Ethane
n-Pentane
n-Hexane
n-Octane
m/z=20
30
39
72
86
114
X5
X2
X5
X50
X100
X2
Chromatogram Showing the Separation of a Series
of n-Alkanes.
Column: 250 m x 25 m Stainless Steel
Temperature: Ambient (~27oC)Pressure: 70 atmFlow Rate: 205 L/minCO2 Density: 0.73 g/mL (16.6M)
Time (min)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
MS
Res
pons
e (c
ount
s)
Neon
13CO2
Propane
Injection Peak
Chromatogram Showing the Chromatogram Showing the Resolution of Three GasesResolution of Three Gases
Column: 500m x 7.6 m Fused Silica-Lined Stainless Steel
Temperature: Ambient (~26ºC)
Pressure: 80 atm
Flow Rate: 250 L/min
Density of CO2: 0.78 g/mL
MS
Res
pons
e (c
ount
s)
Volume (mL)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
25 0 C
27 0 C
29 0
C
Neon
Propane
MS
Res
pons
e (c
ount
s)M
S R
espo
nse
(cou
nts)
CO2 Density: 0.78 g/mL
CO2 Density: 0.75 g/mL
CO2 Density: 0.72 g/mL
Some important observationsSome important observations
The following conditions seemed to be necessary, if not alwayssufficient, for the resolution of mixtures in empty columns:
The mobile phase must be CO2
The pressure in the column must be higher than the vapor pressure of liquid CO2 at the experimental temperature
The experimental temperature must be lower than the critical temperature of CO2
The density of the liquid CO2 mobile phase must be higher than 0.7 g/mL
The volumetric flow rate of CO2 through the column must be relatively low, i.e., < 400 L/min.
Summary PointsSummary Points Rigorous research is going on in this area
When the retention mechanism(s) finally become more apparent, this technique is expected to greatly revolutionize chromatography.
Eliminate toxic organic solvents currently employed in other chromatographic techniques.
No need for expensive stationary phases.
A highly efficient, fast, and simple technique.
Acknowledgements I wish to thank most sincerely my research director, Dr. Jon Parcher, and Dr. Phil Wells for their support and guidance throughout this period.
My sincere thanks also go to Numukunda Darboe (my mentor) and the graduate
students- Shuxia Zhou, Zheyuan Luo, and Yuan Xiong – for their support.
I would like to pay special tribute to Dr. Maurice Eftink and
Ms Juanyce Taylor for their dedication and support to this program. I would also like to thank my Chemistry professor and faculty advisor, Dr. Delphia Harris, for being such an able teacher.
I wish to acknowledge the support I have received from my girlfriend, Sonja Y. Grisle, throughout this program.
Last, but not least, I would like to thank my colleagues in the program for providing the social atmosphere necessary for this work.