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

A process for the fabrication of supported films and membranes of the microporous crystalline titanosilicate molecular sieve ETS-4 is reported for the first time. It involves the formation of a seed layer on a support by direct hydrothermal synthesis followed by secondary growth of the seed layer under appropriate hydrothermal synthetic conditions. The synthesized films and membranes can exhibit desirable b-out-of-plane preferred orientation that corresponds to the eight-member ring channels of ETS-4 oriented perpendicular 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/m2 s in room temperature pervaporation experiments using 1:1 water/ethanol mixtures. This performance, along with electron microscopy examination, suggests that the synthetic procedure can lead to well intergrown films with no large inter-crystalline defects. With increasing water content in the feed solution (in the range of 10–90%) the water flux is increasing linearly, whereas the selectivity does not change significantly. A temperature increase from room temperature (r.t.) to 50°C leads to an increase in the water flux by factor of three with no significant effect on selectivity. The selectivity of the ETS-4 membranes is similar to the highest reported for Na-X and Na-Y membranes, about 10 times lower than the selectivities of zeolite Na-A prepared in our laboratory and up to100 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 separation of permanent gases.