UC Riverside

Ultrafiltration is used extensively in downstream processing of biopharmaceuticals. Although recent studies have demonstrated the importance of electrostatic interactions in both traditional ultrafiltration and electroultrafiltration, electrically conductive ultrafiltration membranes have yet to be investigated for enhancement of protein fractionation. For the effective industrial usage of membrane ultrafiltration for protein separation, a thorough understanding of the effect of electrostatic contributions on throughput and fractionation characteristics is necessary. This thesis investigates the performance of electrically conductive ultrafiltration membranes for single and binary protein electroultrafiltration and studies the effect of electrostatic contributions on the separation characteristics.

Electrically conductive ultrafiltration membranes were fabricated by deposition of a poly(vinyl alcohol)-carbon nanotube (PVA-CNT) composite layer onto a polysulfone (PS-35) ultrafiltration membrane support followed by cross-linking of the carbon nanotube network. The effects of an applied cathodic potential on the hydraulic permeability, permeate flux, sieving, and selectivity during single and binary protein crossflow electroultrafiltration were studied using the PVA-CNT/PS-35 ultrafiltration membranes. For the electroultrafiltration of BSA at an applied potential of -9 V, there was a marginal increase in permeate flux and no change in observed sieving behavior. The application of -9 V potential during electroultrafiltration of similarly sized but differently charged proteins of alpha-lactalbumin (αLA) and hen egg white lysozyme (HEL) at pH of 7.4 resulted in an enhancement in selectivity by a factor of 30 at the low transmembrane pressure of 1 psi and a factor of 4 at the moderate transmembrane pressure of 15 psi during the initial phase (< 16 minutes) of electroultrafiltration. For longer durations of electroultrafiltration (> 7.5 hours), the applied potential of -9 V had no effective improvement in selectivity. The decline in permeate flux during crossflow electroultrafiltration of single protein solutions of αLA and HEL at low and moderate transmembrane pressure indicate significant protein adsorption which contributes to the sieving behavior.