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Impact of retention on trans‐column velocity biases in packed columns
Authors:
Fabrice Gritti
Georges Guiochon
Affiliation:
Dept. of Chemistry, University of Tennessee, Knoxville, TN 37996
Abstract:
The heights equivalent to a theoretical plate of a weakly and strongly retained compounds were measured on two packed columns having different average mesopore sizes. The measurements were carried out in two different cases, with access to the mesopores by the sample molecules blocked (filled with n‐nonane) or not. The experimental results demonstrate that the eddy dispersion terms of both columns are significantly smaller for porous than for nonporous particles. Two simultaneous phenomena explain this observation. First, packed columns are radially heterogeneous which causes significant trans‐column velocity biases warping the bands. Second, radial dispersion contributes to mass transfer across the column, relaxing the radial concentration gradients that are caused by these velocity biases. The impact of these biases is minimized when the pores of the particles are not blocked; it decreases with increasing residence time and radial dispersion coefficient of the solutes. © 2009 American Institute of Chemical Engineers AIChE J, 2009
Keywords:
liquid chromatography
column efficiency
mass transfer kinetics
parking experiments
longitudinal diffusion coefficient
particle diffusivity
total pore blocking experiments
eddy dispersion
transcolumn eddies
soid‐liquid mass transfer resistance
film mass transfer
Sherwood number
transparticle mass transfer resistance
porous and nonporous particles
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