Polyvinylidene fluoride dense membrane for the pervaporation of methyl acetate–methanol mixtures

Abstract

In the context of pervaporative separation of methyl acetate–methanol binary mixtures, polyvinylidene fluoride (PVDF) pervaporation membranes were prepared in order to selectively separate methyl acetate by pervaporation.The PVDF membranes were compared to chlorinated polypropylene and polyvinyl alcohol dense membranes (developed for the same application) by pervaporation of a quaternary equimolar methyl acetate–methanol–n-butyl acetate–n-butanol reference feed. PVDF membranes resulted in a permeate richer in methyl acetate than the corresponding quaternary feed, and in a selectivity methyl acetate/methanol higher than one for the same mixture. Chlorinated polypropylene and polyvinyl alcohol membranes gave a permeate richer of both methanol and methyl acetate than the corresponding feed and were thus not applicable during the extensive study on the binary methyl acetate–methanol mixture.These preliminary results performances were also assessed with the Hansen solubility parameters theory, which resulted inadequate for predicting the behavior of the two glassy-state and the rubbery-state (PVDF) polymeric membranes during pervaporation.Thus, pervaporation of methyl acetate–methanol binary mixtures by PVDF membranes was studied experimentally using feed concentrations in the range 11–78mol% methyl acetate, and temperatures in the range 30–44°C, resulting in separation factors methyl acetate/methanol above 1 (up to 2.1 at 11mol% methyl acetate in the feed), in the whole feed concentration range. High total fluxes up to 35kgm−2h−1 (at 78mol% methyl acetate and 44°C) were also observed.Interestingly, when removing the contribution of the driving force to the separation, for concentrations below 60mol% methyl acetate in the feed the membrane was selective for methanol, while for higher concentrations it was selective for methyl acetate (values up to 1.44).This work shows that methyl acetate selective membranes (starting from the improvement of PVDF membranes) are realistic and can be employed in order to concentrate low content methyl acetate–methanol industrial waste streams.