Hydrodynamics and adsorption behaviour within an expanded bed adsorption column studied using in-bed sampling

Abstract

To study axial variations in particle size, bed voidage, liquid dispersion and dynamic capacity, a 5 cm diameter STREAMLINE expanded bed adsorption column was modified to allow liquid or particle sampling from various radial and axial positions within the fluidized bed. Particle size distributions of adsorbent samples withdrawn from within the expanded bed showed that there was no significant radial variation in particle size and confirmed that mean particle size was larger near the bottom of the column and smallest near the top. Residence time distribution (RTD) analysis was used to acquire hydrodynamic information from changes to the shape of a tracer pulse as it passed from the highly mixed region above the distributor to the calmer regions further up the expanded bed. Liquid jets issuing from the distributor bypassed a portion of the bottom 10 cm of the column. The velocity of liquid flow near the walls of the column was slower than at the centre, and the tracer pulse was more dispersed, resulting in a radial variation in the flow profile. The adsorption of pure lysozyme and bovine serum albumin (BSA) on STREAMLINE SP and STREAMLINE DEAE, respectively, were used to examine how adsorption behaviour was affected by the hydrodynamics of the flow through the different regions of the column. Dynamic capacity of the adsorbent was calculated for two different regions of the column: the bottom zone between the distributor and the height of 25 cm and the top zone between 25 and 40 cm . For both proteins, the dynamic capacity was more than 20% greater in the upper region than in the lower region. Although dynamic capacities were smaller in the lower region of the column, a higher total amount of adsorbate binding occurred here because of the greater adsorbent volume in this part of the bed that is due to the lower degree of bed expansion. Roughly twice the mass of adsorbate was bound (expressed as mg/ml column volume) to the adsorbent in the bottom zone compared to the top zone.