Preparation and gas separation performance of zeolite T membrane

Abstract

Zeolite T membranes were prepared by hydrothermal synthesis on porous mullite tubes seeded with zeolite T crystals, using milk-like aluminosilicate gel with a molar composition of SiO2∶Al2O3∶Na2O∶K2O∶H2O = 1∶0.05∶0.26∶0.09∶14. A zeolite T crystal layer of about 20 µm in thickness was formed on the outer surface of the support after the synthesis at 373 K for 30 h. Single-gas and mixed-gas permeation experiments through zeolite T membranes were carried out by a vacuum method at 303∼473 K using He, H2, CO2, O2, N2, CH4, C2H6 and C3H8 single-component gases and CO2/N2, CO2/CH4 and other CO2/hydrocarbon mixtures, respectively. In single-gas permeation experiments, with increasing kinetic diameter from 0.33 nm for CO2 to 0.43 nm for C3H8, the gas permeance decreased by four orders in magnitude, indicating a kind of molecular sieving behavior for the zeolite T membranes prepared in this study, that is, they had little defects and their permeation behavior was controlled by zeolitic pores of erionite. Permeance of CO2 was much higher than those of N2 and CH4 and the ideal selectivities for CO2/N2 and CO2/CH4 were 31 and 266 at 343 K, respectively. In mixed-gas permeation experiments, zeolite T membranes showed the high selectivities for CO2/N2 and CO2/CH4 pairs of 107 and 400, respectively, at 308 K. The selectivity α decreased with an increase in temperature, but was still in a high level of 20 and 52 for CO2/N2 and CO2/CH4, respectively, even at 473 K. This is due to the synergetic effects of competitive adsorption of CO2 and molecular sieving of zeolitic pores. Because of the increasing effect of single file diffusion, the selectivities for CO2/C2H6 (α = 61) and CO2/C3H8 (α = 17) were rather low.