Development of dynamic PVA/PAN membranes for pervaporation: Correlation between kinetics of gel layer formation, preparation conditions, and separation performance

Abstract

Thin film composite (TFC) membranes possessing polyvinyl alcohol (PVA) selective layer and polyacrylonitrile membrane-support were developed via dynamic mode technique based on concentration polarization phenomenon. The effect of the molecular weight cut-off (MWCO) of membrane-support, concentration of PVA solution and filtration mode on the gel layer formation was studied via the analysis of kinetic curves of flux and PVA rejection in ultrafiltration. The effects of concentrations of PVA, glutaraldehyde (GA) and hydrochloric acid (HA), filtration time, and transmembrane pressure (TMP) on the structure and pervaporation (PV) performance of TFC membranes for ethanol dehydration were investigated. It was found that an increase in PVA concentration, duration of filtration and TMP results in an increase in the TFC membrane selective layer thickness. It was shown that pervaporation permeate flux decreased when TFC membranes were prepared using higher PVA concentration and longer time of PVA filtration. The pervaporative permeate flux through TFC membranes passed through the maximum at TMP of 3 bar, then became practically stable for membranes prepared at TMP in the range of 4-8 bar. It was attributed to the formation of microdefects of the selective layer due to the compaction-relaxation behavior of membrane support during selective layer formation at elevated pressures. It was also shown that the dependence of PV separation factor on the duration of PVA solution filtration passes through the maximum which is consistent with the time of the stable gel-layer formation calculated from the kinetic curves. The found optimal conditions for preparation of TFC dynamic membranes were following: dead-end ultrafiltration mode, the component concentrations in the solution — 1.0 wt.% PVA, 0.06 wt.% GA, 0.5 wt.% HA, using the simultaneous application technique (SimAT) with the filtration time — 10 min and TMP — 3 bar.