Preparation of patterned microfiltration membranes and their performance in crossflow yeast filtration

Abstract

Patterned microfiltration membranes were fabricated via Phase Separation MicroFabrication (PSMF) using vapor-induced phase separation to avoid skin formation on the nonpatterned surface. A starting solution of 10% PES, 60% PEG400, 5% water and 25% NMP yielded symmetric membranes with similar pore size all throughout the cross section when 10 or 15min of vapor exposure was used before further coagulation in water. On the other hand, 5min of vapor exposure resulted in what may be called inverse asymmetric membranes, which had smaller pores on the patterned (mold) side and macrovoids throughout the cross-section. The fidelity in replicating the pattern was higher when the vapor exposure was shorter and surface area enhancements of 103% and 52% were obtained when vapor exposure times were 5 and 10min, respectively. The phase inversion rates of the polymer solutions in liquid water, humid air and humid air followed by liquid water were examined by measuring the light transmission through the solutions in time. It was observed that water in the starting solution increased the overall phase inversion rate and decreased the delay time before phase separation, in consistence with the membrane morphologies obtained with the solutions with and without water under different coagulation conditions. The patterned and nonpatterned membranes were tested in constant flux crossflow filtration of yeast suspensions at different fluxes and it was seen that the fouling rate of nonpatterned membranes was higher than patterned membranes. However, the major contribution to the improved fouling behavior appears to be the increased surface area since when the fluxes were normalized by the patterned (actual) surface area for foulant deposition, the difference between the fouling rate of patterned and nonpatterned membranes was not significant.