Preparation and gas permeation properties on pure silica CHA-type zeolite membranes

Pure silica CHA-type zeolite (Si-CHA) membranes were synthesized by a hydrothermal secondary growth method on porous alpha-alumina supports. Using Si-CHA seed crystals as a crystalline nuclei allowed the formation of a dense Si-CHA layer. The Si-CHA membranes prepared in this study showed excellent gas permeance derived from their large pore volume and effective molecular sieve performance for gas separation. The Si-CHA membranes exhibited excellent H-2 and CO2 permeance of 1.1x10(-6) and 1.7x10(-6) mol/m(2) s Pa, respectively. The ideal selectivity of H-2/CH4 and CO2/CH4 were 34 and 54, respectively. The stability test in the presence of water vapor on the Si-CHA membranes was performed and the Si-CHA membranes demonstrated good water vapor resistance, more so than the topologically analogous aluminosilicate zeolite membrane (SSZ-13). The SiCHA membranes were unlikely to present pore blockages by water adsorption because of their hydrophobic pore systems.