PERVAPORATION SEPARATION OF AQUEOUS MIXTURES USING CROSS-LINKED POLYVINYL-ALCOHOL MEMBRANES .3. PERMEATION OF ACETIC ACID-WATER MIXTURES

The pervaporation separation of acetic acid-water mixtures was carried out over the full range of compositions at temperatures varying from 30 to 70-degrees-C, using 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 and then the crosslinking agent, amic acid was imidized for an additional one hour at 150-degrees-C. The best condition for preparing the crosslinked PVA was found to be ca. 12 wt.% amic acid content. Pervaporation separation of acetic acid-water mixtures using the crosslinked PVA membrane containing 12 wt.% crosslinking agent gave separation factors of 13-42 and permeation rates of 79-2285 g/ (m2-hr) depending on the operating temperature and feed mixture composition. Deviation of permeation rates from ideal rates was discussed through the permeation ratio concept. These phenomena were explained in terms of both the plasticizing effect of permeants and the interaction between permeants in the polymer membrane. We have also defined a new term, the pervaporation separation index (PSI) as the product of permeation rate and separation factor, which could be a measure of the pervaporation separation ability of a membrane for a binary mixture under the specified experimental conditions. The temperature dependence of the permeation rate for binary mixtures was expressed by the Arrhenius-type relation and activation energies of 5.73-8.21 kcal/mol were calculated for acetic acid-water mixtures through the crosslinked PVA with 12 wt.% crosslinking agent. The pre-exponential factor as well as the activation energy were found to be functions of the permeant concentrations.