Selective protein transport through adsorptive membranes.

Abstract

This thesis details the investigation of a novel method for selective protein separations using an adsorptive membrane. The techniques used to obtain this selective protein transport through an adsorptive membrane are surface diffusion and recuperative parametric pumping. Our studies on surface diffusion of proteins conducted using a steady-state diffusion cell showed that selective protein flux due to enhanced diffusion is low (\approx10\sp{-3} mg/hr/cm\sp2); additionally, it could not be ascertained whether the enhanced diffusion was due to surface diffusion or to Donnan effects. On the other hand, studies on recuperative parametirc pumping, a cyclic adsorptive separation process, showed that selective protein flux due to the cyclic process is high $(\approx1$ mg/hr/cm\sp2). We have found that recuperative parametirc pumping in adsorptive membranes leads to two distinct mechanisms of separation, which we refer to as rejection and preferential transport. Rejection is simply a cyclic version of the two-step adsorption process; our results suggest that rejection can lead to a continuous concentrated stream of the adsorbing solute. Preferential transport, which is mechanistically more complicated than rejection, results from the adsorbing solute crossing over from the adsorbing to the desorbing region in the interior of the membrane. Using a protein mixture consisting of lysozyme and myoglobin we have found the conditions under which lysozyme is preferentially transported through an ion-exchange membrane cartridge while myoglobin is rejected by the membrane. Process variables were varied to optimize separation; experimental results agree with theoretical predictions. Additionally, we found that preferential transport can be used to selectively transport a solute up a concentration gradient. Preferential transport can lead to an integrated separation process because during preferential transport, an adsorbing protein is selectively transported across the membrane while non-adsorbing solutes and cells (larger than the membrane pore size) are retained by the membrane. We found that the oscillatory flows used in preferential transport alleviate the formation of cakes due to cell deposition on the membrane surface. This phenomenon was used to separate lysozyme directly from a feed containing lysozyme, myoglobin, and yeast. Theoretical results suggest that preferential transport can lead to continuous protein removal from a feed containing suspended solids.Ph.D.Applied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129665/2/9610064.pd