Effect of adsorbent porosity on performance of expanded bed chromatographyof proteins

Expanded bed or fluidized bed adsorption has emerged as an important unit o peration in downstream processing of proteins. A number of specifically des igned commercial adsorbents are available today for expanded bed purificati on of proteins. Protein purification essentially requires adsorbent matrice s that have large pol e size. Very large pore size or macroporous adsorbent s can provide high efficiency in packed beds even at high flow rates on acc ount of reduced pore diffusion resistance resulting from finite intrapartic le flow in the macropores. This is reflected in leveling off of HETP (heigh t equivalent to theoretical plate) versus flow curve after a threshold velo city. Expanded bed operation, on the other hand, can also show plateauing o f the HETP curve, but not necessarily on account of macroporosity of adsorb ent. It is shown in this article how any adsorbent intended for protein ads orption in expanded bed mode can give plateauing HETP curve, regardless of pore size. As a result, RTD measurements on an expanded bed can give equal, and at times better, performance than a corresponding packed bed. Large po re size, on the other hand, can result in lesser retention of biomass and e asy flushing of the adsorbent to obtain an entirely particulate-free adsorb ent prior to the product elution step. Adsorbent with larger pores is also shown to provide faster and more efficient elution both in packed and expan ded bed modes.