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Black plate (264,1) examined by pervaporation with binary water-ethanol mixtures and with pure water and pure ethanol. By comparing single and mixture permeance, it was deduced that different separation mechanisms operate for MFI and NaA membranes, which were influenced strongly by the structure of the membrane support138. An H-ZSM-5 membrane has been employed for xylene isomer- ization and for the separation of p-xylene from its other isomers. In this work, MFI membranes (silicalite-1 and H-ZSM-5) were prepared by seeded growth on porous stainless steel supports. The membranes were tested for separation of the xylene isomers in the temperature range 100–400C. The H-ZSM-5 membrane showed higher p-xylene permselectivity [ðparayorthoÞ 1⁄4 4:3 at 300C] and lower permeance to p-xylene (3.55610 8 mol m 2 s 1 Pa 1 at 300C) compared to the silicalite-1 membrane ðparayorthoÞ 1⁄4 2:1, permeance to p-xylene (7.4610 7 mol m 2 s 1 Pa 1 at 300C). However, neither were entirely defect-free139. A method for preparing Nafionyacid functionalized zeolite Beta (NAFB) nanocomposite membranes by in situ hydrothermal crystal- lization has been reported intended for use in a direct methanol fuel cell (DMFC). When tested with a 1 M methanol feed, the DMFCs with the NAFB composite membranes demonstrated a slightly higher open circuit voltage (OCV; 3%) and much higher maximum power density (21%) than those with the pure Nafion 115 membranes. When a higher methanol concentration (5 M) was used, the DMFCs with the NAFB composite membranes showed a 14% higher OCV and a 93% higher maximum power density than those with the pure Nafion 115 membranes140. The pervaporative dehydration of ethylene glycol (EG)ywater mixtures using commer- cial nanoporous NaA zeolite membranes has been investigated. The concentration range (C-EG470wt%) was selected according to existing industrial requirements, and at 70C with an initial EG concentration of 70 wt%, larger fluxes and separation factors could be obtained, i.e., 0.94 kg m 2 h 1 and 1177, respectively. The Pervaporation Separation Index (PSI) of the membrane was found to be high compared to that of polymeric membranes141. Other applications of pervaporation through zeolite membranes include the separation of water from ethanol-water mixtures using NaA and NaY membranes142, the separation of xylene isomers using polyurethane membranes containing ZSM-5143 and the separation of various dichlorinated compounds (dichloromethane, 1,2-dichloroethane and trans-1,2-dichloroethylene) from water in their aqueous solutions using a silicalite-1 membrane144. In the latter example, fluxes of dichlorinated compounds in the range 264 Christopher J. RhodesPDF Image | Properties and applications of zeolites
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