Separation of light gas mixtures using SAPO-34 membranes

Continuous SAPO-34 membranes were prepared on porous alumina tubular supports, and shown to be useful for light gas separations at low and high temperatures. Single-gas permeances of CO2, N-2 and CH4 decreased with increasing kinetic diameter. For the best membrane at 300 K, the He and H-2 permeances were less than that of CO2, because He, H-2, and CO2 were small compared to the SAPO-34 pore, and differences in the hear of adsorption determined the permeance order The smaller component permeated the fastest in CO2/CH4, CO2/N-2, N-2/CH4, H-2/CH4 and H-2/N-2 mixtures between 300 and 470 K. For H-2/CO2 mixtures, which were separated by competitive adsorption at room temperature, the larger component permeated faster below 400 K. The CO2/CH4 selectivity at room temperature was 36 and decreased with temperature. The H-2/CH4 mixture selectivity was 8 and constant with temperature up to 480 K. Calcination, slow temperature cycles, and exposure to water vapor had no permanent effect on membrane performance, but temperature changes of approximately 30 K/min decreased the membrane's effectiveness.