Gas permeation through DDR‐type zeolite membranes at high temperatures

Abstract

DDR‐type zeolite membranes were prepared by the secondary growth method on porous α‐alumina disk, followed by on‐stream counter diffusion chemical vapor deposition modification to eliminate the intercrystalline micropores. Single gas permeation of He, H 2, CO 2, and CO through this zeolite membrane before and after CVD modification was measured in 25–500°C. Intracrystalline diffusivities for these four gases in DDR‐type zeolite were obtained from the permeation data above 300°C to examine the effects of the size and molecular weight of permeating gases on diffusion and permeation rate for this zeolite membrane. For the unmodified DDR‐type zeolite membrane with presence of a small amount intercrystalline micropores the diffusivity (or permeance) with a low activation energy depends on both the size and molecular weight of permeating gases. For the CVD‐modified DDR‐type zeolite membrane with intercrystalline micropores eliminated, the activation energy for diffusion and diffusivity increases with increasing molecular size of the permeating gases. © 2008 American Institute of Chemical Engineers AIChE J, 2008.