Synthesis and permeation properties of a DDR-type zeolite membrane for separation of CO2/CH4 gaseous mixtures

Using hydrothermal synthesis, a highly hydrophobic DDR-type zeolite membrane was prepared on the outer surface of a porous alpha-alumina tube. The results of this study show that it is useful for CO2/CH4 separation. Single-gas permeation for CO2, CH4, H-2, He, N-2, and O-2, and CO2/CH4 binary gas permeation, were measured, respectively, at pressures up to 5 and 2 MPa. The respective single-gas permeances Of CO2 and CH4 at 298 K at a feed pressure of 0.2 MPa and a permeate pressure of 0.1 MPa were 4.2 x 10(-7) and 1.2 x 10(-9) mol m(-2) s(-1) Pa-1; the ideal selectivity for CO2/CH4 was 340. The permeances were in the following order: CO2 > H-2 > He > O-2 > N-2 > CH4. Single-gas permeance was dependent on the relative molecular size of the DDR pore diameter. However, CO2 permeance dominated the adsorption affinity to the pore wall of DDR zeolite. In mixed-gas permeation experiments using the sweep method, the DDR-type zeolite membrane showed high selectivity for CO2/CH4 mixtures of 200 and high CO2 permeance of 3.0 x 10(-7) mol m(-2) s(-1) Pa-1 at 298 K with a feed pressure of 0.2 MPa. Furthermore, the DDR zeolite membranes were compared to- other zeolite membranes for evaluation of their CO2/CH4 selectivity and CO2 permeance; the DDR-type zeolite membranes show better CO2/CH4 separation and CO2 permeance.