The influence of biomass on the hydrodynamic behavior and stability of expanded beds

Expanded bed adsorption is an innovative chromatographic technology that allows the introduction of particle-containing feedstock without the risk of blocking the bed. Provided a perfectly classified fluidized bed (termed expanded bed) is formed in the crude feedstock and the biomass is not influencing protein transport towards the adsorbent surface, a sorption performance comparable to packed beds is found. The influence of biomass on the hydrodynamic stability of expanded beds is essential and was investigated systematically in this article. Residence-time distribution analyses were performed using model systems and a yeast suspension under various fluid-phase conditions. It is demonstrated that three factors (biomass/adsorbent interactions, biomass concentration, and flow rate) play an interdependent role disturbing the classified fluidization of an expanded bed. A clear correlation between the degree of aggregative fluidization--obtained by PDE modeling of RTD data--and the expansion behavior of the fluidized bed has been found. Thus, combining three analytical methods, namely cell transmission index analysis, expansion analysis, and RTD analysis provides a solid base for understanding and control of the fluidization behavior and thus further process design during the initial phase of process development.