Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Richard G. Rice

Abstract

The separation of a methane/n-butane mixture was demonstrated using radial flow through compressed, pancake-shaped beds of fine alumina powder. The compacted stationary phase improved performance relative to an uncompressed sorbent by assuring flow uniformity through the bed, reducing band-broadening and tailing (by decreasing interstitial hold-up) and decreasing effective plate height (through an increase in the capacity ratio of the chromatograph). Dispersion was identified as the key dissipative effect in the prototype radial flow adsorber. An exact analytical solution derived for the transport equations describing such a device compared favorably with experimental data. The dispersion coefficients were found to be strong functions of the individual solute sorption constants. The dispersion coefficient for weakly adsorbed solutes such as methane was found to reduce to molecular diffusivity. This phenomenon is believed to result from a combination of classical Taylor dispersion and pore hold up effects such as that suggested by Dayan and Levenspiel (D2) for conventional, axial flow patterns. The elementary Peclet number defining the order of the Bessel functions appearing in the analytical solution was shown to control the shape of the response curve. The system time constant that determines retention is seen to vary with--among other parameters--the equilibrium sorption constant and the radius of the adsorber. The inverse dependence of both the Peclet number and the time constant on interstitial porosity indicates that increased compression will sharpen the response while increasing retention. A theoretical comparison of inward and outward flow configurations indicates that the order of the Bessel functions defining the response is higher for the inward flow option. This suggests that the inward flow configuration may ultimately offer performance advantages. Unfortunately, mechanical difficulties prevented experimental verification of this trend. Methods for improving separation--including the use of greater sorbent bed compression, temperature programming and stacking of individual sorbent discs--are discussed briefly.

Pages

202

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