PERVAPORATION SEPARATION OF AQUEOUS MIXTURES USING CROSS-LINKED POLY(VINYL ALCOHOL) (PVA) .2. PERMEATION OF ETHANOL WATER MIXTURES

The pervaporation separation of ethanol-water mixtures was carried out on a series of chemically crosslinked poly(vinyl alcohol) (PVA) membranes which had been developed in our laboratory. For the preparation of these membranes, PVA was crosslinked with amic acid; subsequently the crosslinking agent, amic acid was imidized for an additional hour at 150°C. Optimum pervaporation results were obtained with crosslinked PVA membranes containing 12 wt.% crosslinking agent, giving separation factors of 70-380 and permeation rates of 30-1600 g/(m2-hr) depending on the operating temperature and feed mixture composition. Deviation of permeation rates from ideal rates was discussed with respect to the permeation ratio. These phenomena were explained in terms of both the plasticizing effect of water and the interaction between permeants within the polymer membrane. We have also defined a pervaporation separation index (PSI) as the product of permeation rate and separation factor; this could become a new measure of the pervaporation separation ability of a membrane for a binary mixture. The temperature dependence of the permeation rate for binary mixtures was expressed by an Arrhenius-type relation and activation energies of 5.21-9.55 kcal/mol were calculated for ethanol-water mixtures using the crosslinked PVA membrane with 12 wt.% crosslinking agent. The pre-exponential factor as well as the activation energy were found to be functions of the permeant concentrations. © 1990.