Synthesis of membranes for the dehydration of water/acetic acid mixtures by pervaporation, 2. Poly(vinyl alcohol) membranes containing covalently bonded carboxylic groups

Poly(vinyl alcohol) (PVA) membranes containing small amounts of fixed carboxylate groups were prepared by two methods: reaction with chloroacetic acid in alkaline medium, and polymerization of acrylic acid on radical sites issued from Ce4+ ‐oxidation of PVA membranes. In the first method, when the reaction was carried out on the dissolved PVA, the crystallinity was greatly reduced, leading to a large increase in permeation flux, a slight decrease in selectivity and a significant increase in the overall performance. The activation energy of permeation was slightly decreased after the reaction. Clear qualitative correlations between different properties were obtained. In the second method, grafting was carried out on the solid membrance and the crystallinity degree was not significantly altered, yet enough to yield membranes with slightly lower selectivity and higher permeability. The Arrhenius plots of permeation rates for some membranes in acetic acid/water mixtures of different compositions showed a transition temperature which is reminiscent of a glass transition temperature the value of which is decreased by the presence of solvent molecules.