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 α-alumina tube. The results of this study show that it is useful for CO 2 /CH 4 separation. Single-gas permeation for CO 2, CH 4, H 2, He, N 2, and O 2, and CO 2 /CH 4 binary gas permeation, were measured, respectively, at pressures up to 5 and 2 MPa. The respective single-gas permeances of CO 2 and CH 4 at 298 K at a feed pressure of 0.2 MPa and a permeate pressure of 0.1 MPa were 4.2 × 10 -7 and 1.2 × 10 -9 mol m -2 s -1 Pa -1; the ideal selectivity for CO 2 /CH 4 was 340. The permeances were in the following order: CO 2 > H 2 > He > O 2 > N 2 > CH 4 . Single-gas permeance was dependent on the relative molecular size of the DDR pore diameter. However, CO 2 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 CO 2 /CH 4 mixtures of 200 and high CO 2 permeance of 3.0 × 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 CO 2 /CH 4 selectivity and CO 2 permeance; the DDR-type zeolite membranes show better CO 2 /CH 4 separation and CO 2 permeance.