A novel method to synthesize high performance silicalite-1 membrane

Silicalite-1 membranes supported on macroporous alumina tubes for hydrogen separation were successfully prepared by a specific synthesis protocol called counter-diffusion hydrothermal crystallization (CDHC). This method introduced silica source (tetraethyl orthosilicate, TEOS) and template agent (tetra-propyl ammonium bromide, TPABr) from opposite directions of the support wall, overwhelming the conventional in situ hydrothermal crystallization (ISHC). After an optimization process, the optimum molar composition of silicon precursor was 1SiO2:0.135Na2O:100H2O:2EtOH and that of template precursor was 1.5TPABr:100H2O. XRD and SEM analysis showed the as-prepared membranes were typical silicalite-1 membranes with high internal crystalline order as well as dense and continuous surface morphology. Single-gas permeation tests indicated the membrane prepared with optimized recipe combined high H2 permeance (1.24 × 10−6 mol m−2 s−1 Pa−1) and good H2 selectivity (αH2/SF6=155αH2/SF6=155) at room temperature, 0.1 MPa pressure drop. Moreover, the consumption of template in this novel method was about one third of that used in conventional hydrothermal synthesis. This concept can also be extended to other many types of zeolite membranes.