Preparation of zein-based membranes and their pervaporation for ethanol aqueous solution

Abstract

Zein-based microspheres and membranes were prepared by phase separation. Increasing the concentration of zein in the stock solution resulted in the formation of three different kinds of zein microstructures i.e. discrete microspheres, sponge-like microsphere membranes and continuous membranes. Zein single (ZS) membrane and zein composite (ZC) membrane were developed by spin coating zein solutions onto porous asymmetric alumina tablets. Both the ZS and ZC membranes effectively removed ethanol from dilute ethanol aqueous solutions via pervaporation. The pervaporation performances of the two membranes were evaluated using different process parameters, such as operating time, ethanol feed concentration and temperature. The separation factors for the ZS and ZC membranes were 3.2 and 3.4 respectively and the permeation fluxes were 0.62 and 0.73kg/m2hr respectively for a feed solution with 3wt % ethanol–97wt % water at 25°C. In a ternary feed solution with 1wt % acetic acid–3wt % ethanol–96wt % water, the pervaporation performances were slightly lower compared with those for the binary feed system. Single gas permeation of N2 confirmed that the membranes were free of defects before and after pervaporation. The ZS and ZC membranes showed good hydrophobic properties and ethanol permselectivity, which can be explained by the Switch Effect.