Variation of the Axial Dispersion along the Bed Height for Adsorbents with a Density Difference and a Log-Normal Size Distribution in an Expanded Bed

Abstract

Unlike a normal packed bed, an expanded bed shows a distinct size distribution of adsorbents along the bed height, which certainly causes the nonuniform characteristics of bed voidage and variation of fluid hydrodynamics and liquid dispersion alone the axial direction. For analysis, modeling, and prediction of the biomolecule adsorption performance in expanded-bed chromatography, the understanding of liquid dispersion along the bed height is fundamental and necessary. On the basis of this background, axial dispersion in expanded beds for adsorbents with a density difference and a log-normal size distribution was investigated. The tracer pulse-response method combining in-bed sampling techniques was used to measure axial dispersion variations along the bed height in a 20-mm-i.d. expanded bed with UpFront FastLine SP adsorbents as test particles. The local effective axial dispersion coefficients along the bed height were calculated and analyzed. There is a decreasing trend of axial dispersion along the bed height at various liquid flowing velocities, which is more remarkable than that for those widely used Streamline particles with a normal size distribution and a relatively uniform density. An empirical correlation for the variations of effective axial dispersion coefficients is recommended based on the hydrodynamic performances within the bed also.