Carbon membranes were prepared by coating thin layers of a phenolic resin on the outer surface of a porous alumina substrate and then carbonizing the polymer under nitrogen atmosphere at 500-800°C for 1 hour. With increasing carbonization temperature, the gas permeance and selectivity decreased, because the membranes became denser and their pore size decreased. The membrane carbonized at 500°C showed high benzene selectivity for pervaporation and vapor permeation of benzene/cyclohexane and benzene/n-hexane mixtures. The carbon membrane behaves like a molecular sieve in the benzene/cyclohexane system. On the other hand, preferential sorption of benzene in the micropores determines the overall permeation performance for the benzene/n-hexane system.
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