Gas permeation through DDR-type zeolite membranes at high temperatures

DDR-type zeolite membranes were prepared by the secondary growth method on porous a-alumina disk, followed by on-stream counter diffusion chemical vapor deposition modification to eliminate the intercrystalline micropores. Single gas permeation of He, H-2, CO2, and CO through this zeolite membrane before and after CVD modification was measured in 25-500 degrees C. Intracrystalline diffusivities for these four gases in DDR-type zeolite were obtained from the permeation data above 300 degrees 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. (C) 2008 American Institute of Chemical Engineers.