Gas Permeation Properties of Ion-Exchanged Lta-Type Zeolite Membranes

NaA-type zeolite membranes were prepared on a 1.7-mm i.d. porous α-alumina tube by repeating a hydrothermal reaction. The membranes, which were prepared by four repetitions, were ion-exchanged with Ca2+ and K+, and the permeation for single-component and mixed gases were investigated at 35°C. The NaA-type membrane showed a hydrogen permeance of (0.8–2.6) × 10−8 mol · m−2 s−1 Pa−1 and a hydrogen/n-butane ideal separation factor of 12–15. The permeability properties of the membrane for binary mixtures were dependent on the size of the permeating molecules and their adsorptivity to the zeolite. The KA-type zeolite membrane showed a higher ideal separation factor for a hydrogen/nitrogen system than did the NaA- and CaA-type zeolite membranes. The pores of the CaA-type zeolite membrane were larger than those in the NaA- and KA-type zeolite membranes, and showed higher permeances to n-butane and i-butane. All the zeolite membranes contained non-zeolitic pores, which decreased the selectivity of permeation.