Pore plugging synthesis and characterization of silicalite-1 membranes using tubular TiO2 supports: Effect of support pore size on membrane performance

In this study, we present a detailed synthesis procedure and characterization of porous inorganic silicalite-1 membranes. The membranes were synthesized in-situ using a pore plugging method with the inclusion of a 12h thermal break promoting secondary growth within the active layer pores of the tubular TiO2 supports. The effect of the support pore size on membrane performance was examined with pore sizes ranging from 0.3m to 1.4m. Characterization using SEM and EDS analysis confirm the penetration and formation of silicalite-1 crystals within porous supports up to a depth of 10-12 mu m for all membranes. With the exception of the membranes synthesized on the support with 1.4m pore size, all membranes were more permeable to probe gas N-2 compared to He. The highest ideal N-2/He selectivity of 2.3 +/- 0.5 was observed for the membranes synthesized on supports with 0.8m pore size. Single gas permeance for the membranes was high, ranging between 3.7x10(-7) and 1.3x10(-5)mol/m(2)sPa, and was independent of gas kinematic diameter with the order of permeation being CH4>CO2>N-2>He. Binary equimolar CO2/N-2 separation experiments show better membrane CO2/N-2 permselectivity compared to the ideal selectivity calculated from the single gas experiments. Comparing the observed membrane gas diffusivity and the adsorbate gas uptake rate within the zeolite material alone shows that these favourable selective properties are the result of adsorption surface diffusion and that Knudsen diffusion is minimized.