“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.