Modeling Pervaporation of Ethanol/Water Mixtures within 'Real' Zeolite NaA Membranes

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• 作者：Marc Pera-Titus ; Carles Fité ; Victor Sebasti&aacute ; n ; Esther Lorente ; Joan Llorens ; Fidel Cunill
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2008
• 出版时间：May 7, 2008
• 年：2008
• 卷：47
• 期：9
• 页码：3213 - 3224
• 全文大小：407K
• 年卷期：v.47,no.9(May 7, 2008)
• ISSN：1520-5045

文摘

A modified version of the adsorption-diffusion model derived form the Maxwell-Stefan theory developed ina previous study (Pera-Titus, et al. Catal. Today 2006, 118, 73) is presented in this paper to describe thedehydration behavior of zeolite NaA membranes for pervaporation of ethanol/water mixtures. Compared tothe former version, two additional contributions are included in the model: (1) the adsorbed solution theoryof Myers and Prausnitz is used instead of the extended Langmuir isotherm to account for binary adsorptionequilibria of water and ethanol on zeolite A, and (2) the explicit role of pressure-driven mechanisms in largeintercrystalline defects (macrodefects) to permeation is considered. These refinements in the Maxwell-Stefanequations provide a superior description of solvent dehydration using zeolite NaA membranes. The fittedsurface diffusivities at 323 K and at zero loading of water and ethanol for weak confinement show values inthe order of 10^-12 and 10^-13 m²·s^-1, respectively. The former values are 3-4 orders of magnitude higherthan those that have been measured from water adsorption kinetics experiments. This difference might beascribed to a certain role of nanosized grain boundaries between adjacent zeolite A crystals. Grain boundariesmight behave as fast diffusion paths or nanoscopic shortcuts due to anisotropy of zeolite layers, resulting inhigher apparent water surface diffusivities and lower apparent activation energies for surface diffusion.