Improved AlPO-18 membranes for light gas separation

High-quality AlPO-18 membranes were synthesized using low-cost symmetric alumina supports by a single hydrothermal step, and showed to be useful for light gas separation. Single-gas permeances of CO2, N-2, CH4 and C3H8 decreased with increasing kinetic diameter. Single CO2 and CH4 permeance dependence of pressure drop was predicted by the Maxwell-Stefan diffusion model and was in agreement with experimental data. The best AlPO-18 membrane showed smaller-component permeances of 6.5, 6.3 and 1.0 x 10(-7) mol (m(2) s Pa)(-1) (equal to 1940, 1880 and 300 GPU) and mixture selectivities of 220, 45 and 22 for equimolar CO2/CH4, CO2/N-2 and H-2/CH4 binary mixtures at room temperature and 0.2 MPa pressure drop, respectively. The effects of temperature and pressure on the membrane's separation performance in the three binary mixtures were discussed.