Faujasite-type zeolite membranes, having a thickness of approximately 20 mum, were synthesized on porous a-alumina supports using the secondary growth method. For the first time, a detailed investigation of the faujasite membrane's ability to separate propylene/propane mixtures has been performed. Single-component and binary mixture permeation experiments indicated that the membranes are propylene permselective. The maximum separation factor (13.7 +/- 1 at 100 degreesC) and the maximum ideal selectivity (28 at 35 degreesC) indicate that the membranes have improved performance, compared to previously reported results. Membrane permselective behavior was maintained over the entire range of feed compositions examined (P-total = 101 kPa and P-propylene = 12-93 kPa). The temperature dependence differences between the single-component and binary mixture permeation fluxes indicate that the presence of propylene enhances propane transport through the membrane.