NaY-type zeolite membranes were synthesized on a porous support tube by a hydrothermal process. The membranes were ion-exchanged with Li~+ and K~+ ions, and permeances through the membranes were determined for an equimolar mixture of CO_2 and N_2, as well as for single-components thereof, at a temperature range of 0-400 deg C. The permeance to CO_2 showed a maximum at 100 deg C, but CO_2/N_2 selectivity decreased with increasing temperature. The zeolite membranes that were exchanged with K~+ and Li~+ ions gave higher and lower CO_2/N_2 selectivities, respectively, than were found for the NaY-type membrane. The permeation properties of the ion-exchanged zeolite membranes were analyzed using a sorption-diffusion model. The high CO_2/N_2 selectivity of the K-exchanged membranes can be explained by the decrease in N_2 sorptivity for the mixed feed.
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