Structure optimization of water-permselective membrane surfaces by reconstruction

The pervaporation performance with operating time through poly(vinyl alcohol) (PVA) membrane for the separation of various alcohol/water (methanol–water, ethanol–water, isopropanol–water) mixtures was investigated. The water selectivity through the air-side surface of a PVA membrane increased and finally reached an equilibrium value, which was lower than that through the glass-side surface, implying the structure on the glass-side surface of PVA membrane is favorable towards the enhancement of the water permselectivity compared to that on the air-side surface. This phenomenon was attributed to the reconstruction occurred at the air-side surface of the membrane, hence a more hydrophilic membrane surface was formed when it was in contact with the feed mixtures. In order to optimize the water permselective structure on the air-side surface of PVA membrane, the membrane was pre-treated in 80% methanol/water mixtures. For dehydration ethanol and isopropanol, the separation factor through the air-side surface of the pre-treated PVA membrane was improved greatly, approaching that through the glass-side surface. Our results indicate that a desirable structure at the air-side surface can be optimized by surface reconstruction in various environments, which is very useful for the industrial applications of pervaporation membranes because their air-side surfaces are usually in contact with the feed.