Synthesis Of Fe-MFI Membranes And Their Applications In Recovering Ethanol From Its Dilute Aqueous Solutions

MFI-type zeolite membranes have been extensively applied in field of separation,catalysis,sensors,and corrosion protection because of their good stabilities,well-defined unique pore structures and typical two-dimensional channel structures,which are suitable for separating materials at a molecular level.The preparation of defect-free,continuous and thin MFI membrane will become the development trend in the future,and full of great challenging.In this dissertation,we first used Langmuir-Blodgett technique to prepare silicalite-1 seed layer on?-Al₂O₃ supports,and based on the the formation of Fe-silicalite-1 membranes as the starting point,the influence of both water amount and Fe/Si ratio of synthesis solution on membrane synthesis were studied in detail.It was found that under the H₂O/Si ratio of 800 and Fe/Si ratio of 0.01,a well-intergrown and dense Fe-silicalite-1 membrane with the thickness of 1?m was formed as well as the excellent reproducibility of membrane synthesis.Then F-Fe-silicalite-1 zeolite crystals and membranes were prepared under the fluoride neutral system,which stucture and morphology could be affected by the kinds of silica source and the concentrations of template TPAOH?Tetrapropylammonium hydroxide?.It was proved that the smaller zeolite crystals could be obtained by using fumed silica as silica source and TPAOH/Si ratio of 0.5.Meanwhile,a continuous F-Fe-silicalite-1 membrane was synthesized under the same silica source and template concentration with the silicalite-1 seed layer.Furthermore,the more compact and continuous F-Fe-silicalite-1 membrane was fabricated by the“two-step method”,the combination of traditional alkaline synthesis solution and fluoride system.Generally speaking,the preferential b-oriented MFI films on porous supports can drastically decrease the transport resistance through the membrane.Herein,b-oriented F-Fe-silicalite-1 seed layers were prepared by manual assembly both on glass and?-Al₂O₃ supports.It was turned out that b-oriented membranes were favourable to formed when the supports were put upwards in the synthesis solution and chitosan was employed as modifier.The twin crystals could be avoided by microwave-assisted heating method,leading to the formation of the continuous and highly b-oriented Fe-MFI membranes both on glass plate?270 nm-thick?and porous?-Al₂O₃?1?m-thick?supported chitosan layers.Finally,the traditional high temperature and low temperature catalytic hydro-cracking calcination method were investigated to remove templates from Fe-silicalite-1 crystals and membranes.After a series of characterizations and pervaporation tests,it was proved that under the optimized molar composition combined with the catalytic hydro–cracking template removal method at 300?,the Fe-silicalite-1 membrane exhibited the best separation performance,the flux and separation factor were achieved as high as 2.35 kg m^-2 h^-1 and 91.69 for a 5 wt%ethanol/water mixture at 50?,respectively.The F-Fe-silicalite-1 membrane synthesized by“two-step method”also showed high pervaporation performance with the catalytic hydro–cracking template removal method.The flux was improved to3.58 kg m^-2 h^-1 by using the defect-free b-oriented Fe-MFI membrane that fabricated on?-Al₂O₃ supported chitosan films under microwave irradiation,while the separation factor was of 41.