SIZE EXCLUSION CYCLIC SEPARATION (CHROMATOGRAPHY)

YOON-MO KOO, Purdue University

Abstract

Sephadex G and Bio-Gel P, well known gels in size exclusion chromatography, show a large change in their elution behaviors as temperature changes. To clarify the causes of this change, temperature effects on the interstitial porosity in a gel column, the adsorption and the intraparticular diffusion were measured experimentally for the binary model solutes, Blue Dextran 2000 and nickel nitrate. The interstitial porosities changed from 0.33 to 0.36 for Sephadex G-25, and from 0.39 to 0.32 for Bio-Gel P-2 as temperature changed from 5(DEGREES)C to 45(DEGREES)C. The adsorption isotherms of nickel nitrate onto Sephadex G-25 were expressed in a Langmuir form at both temperatures. The intrastitial diffusivities of nickel nitrate in an aqueous solution were found to be 0.150 x 10('-5) and 0.210 x 10('-5) cm('2)/sec at 5(DEGREES)C and 45(DEGREES)C in a Sephadex G-25 particle. The microstructure of the crosslinked Dextran gel was studied to obtain the intrastitial porosity of Sephadex G gel. To this end, the concept of the consistent force field and the Laurent-Ogston model were employed. A series of size exclusion parametric pumping experiments in the direct thermal mode were carried out to separate the binary mixtures in both batch and continuous processes. Separation factors for Blue Dextran and nickel nitrate with Sephadex G-25 were 4.7 and 6.2, respectively, after 30 cycles in the batch parametric pumping. Sephadex G gels were found to separate the excluded and the non-excluded solutes while Bio-Gel P gels do not. The combined separation factor was 1824 when two gel columns, one packed with Sephadex G-25 and the other with Bio-Gel P-2, were coupled and run continuously. Experimental separation performances in the batch size exclusion parametric pumping were compared with the predictions by both the local equilibrium model and the dispersion model. The dispersion model which includes the axial dispersion term gave a better fit of the experimental data. Experimentally obtained adsorption isotherms and intrastitial diffusivities were used in the distributed parameter dispersion model to predict the separation performance of nickel nitrate in the Sephadex gel column. The resulting simultaneous partial differential equations were solved by the quasilinearization method with the aid of the computer.

Degree

Ph.D.

Subject Area

Chemical engineering

COinS