Fluidization characteristics of and protein adsorption on fluoride-modified porous zirconium oxide particles

Abstract

Porous zirconia particles of specific gravity ∼3.2 g/ml, mean particle sizes of ∼50 μm, and terminal settling velocity of ∼2.8 mm/s in water, were synthesized using an oil emulsion method from 1000 Å colloids and were evaluated for their potential use in expanded bed protein adsorption. Expanded beds of particles were stable even for small volume, shallow beds (settled bed: 10 ml, height to diameter ratio <1.0) and even for fluidization velocities common to much larger particles (210 cm/h for a three-fold bed expansion). When the surface of these particles was modified by fluoride adsorption, the total bed capacity for bovine serum albumin (BSA) adsorption was 42±2 mg BSA/ml of settled bed volume at linear velocities of 109–210 cm/h. Residence time distribution studies of several solutes under non-binding conditions were performed to assess the degree of liquid mixing and channeling in the expanded bed as a function of fluidization velocity. Liquid mixing and channeling were also studied as a function of distributor design. With these very dense particles, the degree of channeling and mixing did not worsen with the degree of expansion. Elution of adsorbed BSA while the bed was expanded (by a step increase in ionic strength) was rapid resulting in a narrow peak at high fluidization velocities without resorting to settling of the bed. The dynamic binding capacity of BSA at 5% breakthrough (protein effluent concentration equal to 5% of the inlet concentration) was the same for a two-fold expanded bed as for a settled bed (22±2 mg BSA/ml of settled bed volume), though it decreased for higher bed expansions. BSA binding was reproducible following repeated cleaning of the adsorbent with 0.25 M sodium hydroxide.