Effects of aging on the synthesis and performance of silicalite membranes on silica tubes without seeding

High-performance silicalite membranes were successfully prepared on porous tubular silica supports by in situ hydrothermal synthesis without seeding. The separation performance of the as-synthesized silicalite membranes was evaluated by separating ethanol/water mixtures. It was found that both the aging temperature and aging time had a significant influence on the performance of silicalite membranes when the silica tubes and synthesis solution were aged together. The tubular silica supports were filled with glycerol/water mixtures to reduce the penetration of synthesis solution, and it was found that this solution-filling method could effectively improve the membrane flux by about 27% with a higher separation factor. By using two-step hydrothermal synthesis, the silicalite membrane with a total flux of 0.58 kg/m2 h and ethanol/water separation factor of 95 at 333 K was obtained. The method in this work has been demonstrated a simple and effective way to skip the deposition of pre-formed nanosized seeds on tubular supports before the secondary growth of silicalite membrane.