Synthesis Of MFI Zeolite Membranes And Their Application In Separation Of Aqueous Ethanol Solution

MFI membranes could find potential applications as selective membranes,catalytic membranes, low-k materials and chemical sensors due to their well-definedunique pore structures as well as high stability. Silicalite-1and TS-1membranes withhigh hydrophobicity possess potential applications in separation of ethanol from itsaqueous solution by using pervaporation. The microstructure of MFI zeolitemembranes plays an important role in their performances. The control ofmicrostructure of MFI zeolite membranes is crucial for fabricating high-quality MFImembranes.In this dissertation, the b-oriented silicalite-1and TS-1films were synthesized bysecondary growth of b-oriented silicalite-1monolayer. Surface characteristics ofsubstrates have important influence on the growth of MFI films. Secondary growth ofb-oriented MFI seed layers on different kinds of substrates including nonporous glass,porous α-Al2O3, chitosan and PVA modified substrates was investigated. It was foundthat the chitosan layer promoted the growth of seed layer under microwave irradiation,thus continuous submicrometer-thick and solely b-oriented MFI zeolite film could begained on the chitosan supported substrates in1h of microwave-assisted secondarygrowth. For conventional heating, chitosan decreased the growth rate of zeolite, it wasdifficult to get continuous and uniformly b-oriented MFI films. The growth of b-orientedMFI seed layers in silicalite-1synthesis solution and TS-1synthesis solution wasdifferent under the conventional heating. In-situ aging in TS-1synthesis solution wasnecessary for highly b-oriented TS-1films fabirication. When aging time was12h,highly b-oriented TS-1films can be obtained.Three synthetic strategies were adopted to synthesize h0h-oriented silicalite-1membranes on α-Al2O3substrates by secondary growth of randomly oriented seedlayers. Those included second-time seeded growth procedure, preparation ofmembranes under near neutral pH using F-as the mineralizing agent and usingmicrowave-assisted secondary growth method. EDAX analysis comfirmed that themembrane synthesized after second-time seeded growth was thicker and had thehighest Si/Al ratio. Thin and oriented TS-1membranes were synthesized on α-Al2O3substrates by microwave-assisted secondary growth of randomly oriented silicalite-1 seed layers. TS-1membranes with different Si/Ti molar ratios were obtained bychanging Ti contents in mother sols. The Si/Al ratio in TS-1membranes could beincreased after second-time seeded growth. Ti atoms in the membrane were bound intothe tetrahedral framework and extra-framework Ti species were avoided.Removal of templates from silicalite-1and TS-1particulate by low-temperaturecalcination technique and calcination at high temperatures was investigated. Templatescould be removed by low-temperature calcination technique, the removal efficiencyfor TS-1zeolite was better than silicalite-1zeolite. Low-temperature calcinationtechnique for TS-1membranes could restrain the formation of cracks during thetemplates removal process and enhance the hydrophobicity of TS-1membranes, thusimprove the pervaporation performance. The hydrophobicity of TS-1membranesincreased as the Si/Al ratio went up which was helpful to improve of the separationselectivity of ethanol/water mixtures.