Using hydrothermal synthesis, a highly hydrophobic DDR-type membrane was prepared on the outer surface of a porous α-alumina tube. The results showed that it was useful for CO2/CH4 separation. Single-gas permeation of CO2, CH4, H2, He, N2 and O2, and of CO2/CH4 binary gas permeation, were measured at pressures of up to 5 and 2MPa, respectively. The respective single-gas permeances of CO2 and CH4 at 298K, at a feed pressure of 0.2MPa and a pressure of 0.1MPa, were 4.2 x 10-7 and 1.2 x 10-9mol/m2sPa. The ideal selectivity for CO2/CH4 was 340. The permeances were in the order:  CO2 > H2 > He > O2 > N2 > CH4. The single-gas permeance depended upon the relative molecular size of the DDR pore diameter. However, CO2 permeance dominated adsorption affinity to the pore wall of DDR zeolite. In mixed-gas experiments using the sweep method, the DDR-type membrane exhibited high selectivity for CO2/CH4 mixtures of 200, and a high CO2 permeance of 3.0 x 10-7mol/m2sPa at 298K with a feed pressure of 0.2MPa.

Synthesis and Permeation Properties of a DDR-Type Zeolite Membrane for Separation of CO2/CH4 Gaseous Mixtures. S.Himeno, T.Tomita, K.Suzuki, K.Nakayama, K.Yajima, S.Yoshida: Industrial and Engineering Chemistry Research, 2007, 46[21], 6989-97

Table 18

Diffusion of Paraffins in Offretite-Erionite Zeolites