Synthesis of ETS-4/TiO2 composite membranes and their pervaporation performance

A process for the fabrication of supported films and membranes of the micro porous crystalline titanosilicate molecular sieve ETS-4 is reported for the first time. It involves the formation of a seed layer on a support by dire ct hydrothermal synthesis followed by secondary growth of the seed layer un der appropriate hydrothermal synthetic conditions. The synthesized films an d membranes can exhibit desirable b-out-of-plane preferred orientation that corresponds to the eight-member ring channels of ETS-4 oriented perpendicu lar to the substrate. Membranes consisting of thin intergrown films of Na-ETS-4 on porous titania supports are highly water permselective with selectivities as high as 400 and a corresponding water flux of 0.01 mol/m(2) s in room temperature perva poration experiments using 1:1 water/ethanol mixtures. This performance, al ong with electron microscopy examination, suggests that the synthetic proce dure can lend to well intergrown films with no large inter-crystalline defe cts. With increasing water content in the feed solution tin the range of 10-90%) the water flux is increasing linearly, whereas the selectivity does not ch ange significantly. A temperature increase from room temperature (r.t.) to 50 degrees C leads to an increase in the water Aux by factor of three with no significant effect on selectivity. The selectivity of the ETS-4 membrane s is similar to the highest reported fur Na-X and Na-Y membranes, about 10 times lower than the selectivities of zeolite Na-A prepared in our laborato ry and up to 100 times lower than the highest selectivities reported in the literature (for zeolite Na-A membranes). The flux of water through Na-ETS- 4 membranes is comparable or higher than that through all zeolite A, X and Y membranes. Na-ETS-4 membranes may find applications in pervaporation as well as separa tion of permanent gases. (C) 2000 Elsevier Science B.V. All rights reserved .