SILICALITE-1 ZEOLITE COMPOSITE MEMBRANES

This review paper discusses the preparation of silicalite-l zeolite me mbranes, the experimental procedures used for gas separation measureme nts and the results of single gas and gas mixture experiments. Silical ite-alumina composite membranes were prepared by an in-situ zeolite sy nthesis method using an alumina membrane tube with a 5-nm-pore-diamete r, gamma-alumina layer as a substrate. Single gas permeances of H-2, A r, n-C4H10, i-C4H10 and SF6 were measured and mixtures of H-2/i-C4H10 and H-2/SF6 were separated to characterize the silicalite membrane. Th ese measurements were made from 300 to 737 K. Transport through the si licalite membrane appeared to be controlled by molecular size and adso rption properties. Permeances of all components studied were activated , and activation energies ranged from 8.5 to 16.2 kJ/mol. The ratio of single gas permeances was as high as 136 for H-2/SF6 and 1100 for H-2 /i-C4H10 at 298 K. Separation selectivities at elevated temperatures w ere significantly above Knudsen diffusion selectivity and were larger than ratios of pure gas permeances at the same temperature. The larges t permeance ratio for the separation of mixtures was 12.8 for H-2/SF6 at 583 K. Separation selectivities were higher when a pressure drop wa s maintained across the membrane than when an inert sweep gas was used because of counter diffusion of the sweep gas.