Synthesis of a silicalite zeolite membrane in ultradilute solution and its highly selective separation of organic/water mixtures

A continuous intergrown silicalite zeolite membrane with high pervaporation (PV) performance was successfully prepared on seeded tubular mullite supports in ultradilute solution with a H ₂O/SiO ₂ ratio of 800 and an inexpensive template of tetrapropylammonium bromide (TPABr) instead of tetrapropylammonium hydroxide (TPAOH). Several parameters were systematically investigated to evaluate their influence on crystallization and PV performance of the membranes, including the H ₂O/SiO ₂ ratio, template type, alkalinity, synthesis temperature, crystallization time, and silica source. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and PV tests were used to characterize the as-synthesized membranes. The crystal growth and separation quality of the silicalite membranes were very sensitive to the H ₂O/SiO ₂ ratio and alkalinity in the precursor solution and synthesis temperature. Under the optimized synthesis conditions, the outer surface of support was fully covered with well-intergrown silicalite zeolite layer to form the zeolite membrane. For silicalite membrane prepared with the typical molar composition of synthesis solutions of 1SiO ₂/0.1TPABr/0. 2TPAOH/800H ₂O at 180 °C for 16 h, the flux and separation factor are achieved to 1.91 kg·m ^-2·h ^-1 and 66 for a 5 wt % ethanol/water mixture at 60 °C, respectively. Moreover, the membrane prepared with pure TPABr template instead of TPAOH in ultradilute solution also showed the high PV performance with the flux of 1.77 kg·m ^-2·h ^-1 and separation factor of 63 under the same tests conditions. Due to the utilization of ultradilute precursor and cheap organic template to prepare the silicalite membrane on cheap mullite supports with high PV performance, the present developed technique could reduce the chemical consumption and decrease the costs of membrane toward an organic/water mixture separation.