Permeation of weakly adsorbing components through a silicalite-1 membrane

The permeation of helium and neon through a stainless-steel supported silicalite-1 membrane was studied in the temperature range from 200 to 600 K in order to get more insight in the permeation mechanism of these weakly adsorbing components and to characterize the membrane. There are three contributions to overall permeation of these gases, viz., diffusion through non-zeolitic pores, surface diffusion (E-a(s) = 4-5 kJ mol(-1)) and activated gaseous diffusion. The latter is relatively highly activated (E-a(g) = 17-18 kJ mol(-1)) and can be described by an Arrhenius-type relation. Surface diffusion is important up to 300 K for helium and neon. The effective membrane thickness is similar to 10 mu m, as derived from the activated gaseous diffusion of helium. The presence of non-zeolitic pores was concluded from the evolution of krypton permeation through the membrane during calcination. These data were used to estimate the maximum contribution of permeation through imperfections in the membrane for helium and neon. From experiments with 1,3,5-tri-isopropylbenzene and counter-diffusion of helium during experiments with adsorbing feed components, it was concluded that the size of the non-zeolitic pores was similar to 1 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.