Gas permeation and diffusion in small and intermediate pore zeolite membranes

Success in synthesis of defect free small or intermediate pore zeolite membranes allows study of permeation and diffusion of small gases such as hydrogen in these zeolites at high temperatures. This paper reports experimental data of permeation for small gases including hydrogen, helium, carbon dioxide and carbon monoxide through the small pore DDR zeolite membrane and the intermediate pore MFI type silicalite membrane in 25-500°C. Due to small ratio of molecule size to silicalite pore diameter, permeation and diffusion of the small gas molecules in silicalite membrane exhibit characteristics of Knudsen diffusion. The permeance decreases with increasing temperature and is determined by the molecular weight, not the kinetic diameter of the molecules. Gas permeance through the small pore DDR membrane shows activated diffusion characteristics, with permeance increases with temperature and decreases with increasing molecule size of the permeating gases. These permeance and diffusion data can be explained by the gas translation diffusion model.