| For the further expansion of the industrial applications of the membrane ultrafiltration (UF) technology for protein separation, the in-depth understanding of binary protein UF performance is of significant importance. This dissertation systematically studies the electrostatic contributions during binary protein UF.;The analysis of binary protein UF performance, however, was not possible without a thorough understanding of the single protein UF behavior. Particularly, the non-linear flux-pressure dependence for single protein UF - even without any electrostatic effect - was not previously well understood. Therefore, a fundamentally different model, the FSB model, was first developed based on the free-solvent model for osmotic pressure. The success of the FSB model shows that it is the osmotic pressure, instead of the widely conceived membrane fouling contribution, that dominates the non-linear flux-pressure dependence in protein UF. Subsequently, a new definition was developed for the critical flux phenomenon.;The pH dependence and ionic strength dependence of single protein UF flux behavior with electrostatic effects was then analyzed using the modified FSB flux model. This model successfully characterized the electrostatic effects to the flux behavior throughout the whole operating pressure range, which, to our knowledge, was not achieved previously.;For binary protein UF, the effects of both repulsive and attractive interaction were studied. For systems with only repulsive interaction, the permeate flux behavior was dominated by the presence of the rejected protein. The dependence of sieving behavior on repulsive interaction was successfully simulated by the hindered transport theory for both single and, for the first time to our knowledge, binary protein UF. For systems with attractive interaction, the presence of the permeable proteins appeared to contribute to the UF flux-pressure behavior in a similar manner as increased ionic strength. Sieving simulation using the hindered transport theory model for UF system with attractive interaction also achieved preliminary success, which was also not reported previously to our knowledge.;The deviation in UF performance observed for binary systems with similar size and charge properties were correlated to the specific electrostatic complex formation association between proteins. Anomalous sieving behaviors of 14 kDa proteins at pH 4.7 during binary protein UF were also observed. |
