Synthesis of highly methanol selective membranes for separation of methyl tertiary butyl ether (MTBE)-methanol mixtures by pervaporation

Methyl tertiary butyl ether (MTBE) is now being extensively used as a lead-free octane enhancer for green fuel. Pervaporative separation process is used for separation of methanol-MTBE mixtures encountered during manufacturing of MTBE. Three different copolymers of acrylamide with increasing amount of 2-hydroxyethyl methacrylate (HEMA), i.e. PAMHEMA-1, -2 and -3 were synthesized and the cross-linked (gelled) copolymer membranes made from these sol copolymers were used for pervaporative separation of methanol from its mixtures with MTBE over the concentration range of 0-10 wt.% methanol in feed. These hydrophilic gel copolymer membranes were found to be highly methanol selective in both sorption and diffusion through the membranes. Methanol flux was found to decrease with increase in degree of cross-linking from PAMHEMA-1 to -3 copolymer membranes. Among the three membranes PAMHEMA-3 membrane showed highest selectivity and acceptable flux (511.7, 9.9 g/m² h for 0.53 wt.% of methanol in feed) while maximum flux with high selectivity was shown by PAMHEMA-l membrane (18.48 g/m² h, 243 for 0.53 wt.% of methanol in feed). MTBE was also found to have a negative coupling effect on methanol permeation. The membranes were found to show both sorption as well as diffusion selectivity for methanol.