Chabazite-Type Zeolite Membranes for Effective CO2 Separation: The Role of Hydrophobicity and Defect Structure

Chabazite (CHA)-type zeolites are promising for the separation of CO 2 from larger molecules, such as N 2 (relevant to postcombustion carbon capture) and CH 4 (relevant to natural gas/biogas upgrading). In particular, the pore size of CHA zeolites (0.37 × 0.42 nm 2 ) can recognize slight molecular size differences between CO 2 (0.33 nm) and the larger N 2 (0.364 nm) or CH 4 (0.38 nm) molecules, thus allowing separation in favor of CO 2 through CHA membranes. Furthermore, the siliceous constituents in the CHA zeolite can reduce the adsorption capacity toward the smaller H 2 O molecule (0.265 nm) and, thus, the H 2 O permeation rate. This is highly desirable for securing good molecular sieving ability with CO 2 permselectivity in the presence of H 2 O vapor. Indeed, a siliceous CHA film obtained with a nominal Si/Al ratio of 100 (CHA_100) showed high CO 2 /N 2 and CO 2 /CH 4 separation per…