Synthesis Of Silicalite-1and Fe-silicalite-1Membranes And Their Applications In Pervaporation

In this paper, we systematically investigated the synthesis and characterization ofSilicalite-1and Fe-silicalite-1membranes and their applications in pervaporation.Silicalite-1crystals with a size of400nm were chosen as the seeds to prepare the seedlayer, and the as-prepared seed layer was randomly oriented, with a thickness of1.5μm. Then, a well-designed two-step seeded growth method was used to synthesizeSilicalite-1and Fe-silicalite-1membranes on porous α-Al2O3substrate. A5μm thick,(h0l) oriented silicalite-1membrane and a4.5μm thick,(h0l) and a-orientedFe-silicalite-1membrane were synthesized after the second-time seeded growth at150℃, and these membranes were continues and dense. For Fe-silicalite-1membrane,the results of the FT-IR, UV-vis spectra indicated the iron was introduced into thezeolite framework. And the existence of Fe3+in synthesis solution could accelerate theintergrowth of zeolite crystals, leading to the as-prepared Fe-silicalite-1membranewas much more continues and denser than the as-synthesized silicalite-1membrane.High temperature calcination could absolutely remove the templates in the silicalite-1and Fe-silicalite-1membranes, but cracks formed at the same time, which conducethese membranes almost lost separating effect, and PV results of these membraneswere that the flux was very high, but the separation factor was very low. Lowtemperature calcination couldn’t remove the template of silicalite-1membrane. While,owing to the introduction of Fe into the zeolite framework, the catalytic activity of theFe-silicalite-1membrane was increased. So low temperature calcination couldeffectively remove the template of Fe-silicalite-1membrane, and the membrane wascrack-free, because the size of the biggest pore was under1.1nm, and the size of mostpores was between0.45nm and0.85nm. After the template was removed by the lowtemperature calcination method, the Fe-silicalite-1membranes showed a flux of1.54,2.05and2.64kg/(m2·h) at313,323and333K, respectively, which were higher thanliterature data. However, due to the aluminum leaching from the α-Al2O3substrate,the Si/Al ratio of the membrane was very low, and the membrane was hydrophilic,with a average contact angle of69.7degree, so the separation factor was very low,only ranged from18to20. Both the flux and separation factor increased with theincreasing PV temperature for the5wt.%ethanol feed solution. However, the increase of separation factor was lower than that of flux. When low temperaturecalcination method was used to remove the template, the Fe-silicalite-1membranesshowed a very high PV separation repeatability at the same PV temperature.