Permeation of methanol/methyl-t-butyl ether mixtures through poly(ethylene-co-vinyl acetate) films

The permeation of methanol and methyl-t-butyl ether (MTBE) liquid mixtures through poly(ethylene-co-vinyl acetate) (EVAc) films of different compositions have been investigated. Experiments were performed by contacting the polymer film with a liquid mixture and removing the vapour on the other side with an inert gas flux, a set-up for a membrane process of pervaporation with sweeping gas. In the presence of the liquid mixture, the membranes swell to an extent that increases as the vinyl acetate content in the membrane or the MTBE in the liquid increase. This behaviour can be explained by two main factors: the crystalline content of the polymer and the distance between the polar solubility parameters of the liquid mixture and the centre point of the copolymer solubility sphere. The pervaporation results evidence a methanol higher permeability with low separation factors for all the membrane compositions and high fluxes, which increase with the membrane swelling. Very high flux values have been observed for the copolymer with the greatest vinyl acetate content at liquid composition close to the azeotropic one. In steady state conditions, the permeants showed a Fickian behaviour which allowed to evaluate the activation energy of the diffusion process through the membranes.