H2/CO2 permeation through a silicalite-1 composite membrane

Single and binary H2/CO2 gas permeation was studied through a silicalite-1 composite membrane consisting of a thin zeolite film (<1 μm) supported on α-alumina. The temperature range for permeation measurements was 25–300 °C. To determine the quality of the membrane, i.e. the quantity and size of defects, n-hexane/helium permporometry measurements were performed. In general, single component fluxes decreased with increasing temperature whereas binary component fluxes showed a maximum value followed by a continuous decrease. A mass transport model that takes into account the surface diffusion and gas translational diffusion in the zeolite pores, Knudsen diffusion in defects, as well as viscous flow and Knudsen diffusion in the support material was developed to simulate the single and binary gas permeation measurements. Simulation results show that the surface diffusion was the dominant mass transport mechanism in the membrane. In addition, the transport resistance of the support material was not negligible and it was found to influence the permeation selectivity. The model adequately described the experimental results for both single and binary permeation. The model predictions indicated that a CO2/H2 separation factor exceeding 9.8 and a CO2 flux exceeding 4 mol/(m2 s) could be obtained at 0 °C and a feed pressure of 10 bar and atmospheric permeate pressure.