Pervaporation and Vapor Permeation Characteristics of a Porous SiO 2 -ZrO 2 Membrane for Separation of Organic Solvents/
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AA11.5.1
Pervaporation and Vapor Permeation Characteristics of a Porous SiO2-ZrO2 Membrane for Separation of Organic Solvents/Water Mixtures Masashi Asaeda and Yasuhumi Tasaka Department of Chemical Engineering, Graduate School of Engineering Hiroshima University, Higashi-Hiroshima, 739-8527, Japan ABSTRACT The sol-gel techniques were applied to fabricate some improved porous SiO2-ZrO2(50%) membranes for separation of organic solvents/water mixtures by pervaporation and vapor permeation methods at the normal boiling points of mixtures such as iso-propanol(IPA)/water and 1-propanol /water mixtures. The porous SiO2-ZrO2 membranes were found quite stable even at a high water content in the feed mixtures. They showed quite large pervaporation fluxes more than 450moles/(m2 h) at 73mol% of IPA in the feed, for example, while the water flux for vapor phase separation at the same conditions was around 250mol/(m2 h). The separation characteristics of organic chemicals/water mixtures by pervaporation and the vapor permeation methods are largely different in many points. Especially in this work separation by vapor permeation has been studied to compare with that of pervaporation taking into account the vapor-liquid equilibrium characteristics of the mixtures.
INTRODUCTION Many aqueous solutions of organic chemicals show azeotropic characteristics in their vapor-liquid equilibrium, because of which the conventional separation process requires some extra equipment and a large amount of separation energy. Membrane separation of such azeotropic aqueous organic solutions has been considered quite effective and energy conservative. Some inorganic porous membranes (silica, zeolites, porous silica-zirconia) have been found quite effective for separation of aqueous organic mixtures. They show high stability against most organic chemicals at high temperature. Separation by pervaporation at higher temperature preferably gives a higher flux, requiring a smaller membrane area. The separation characteristics and the mechanism of pervaporation of molecular mixtures with porous silica-zirconia membranes have been studied in the previous woks [1,2]. Inorganic membranes can also be applied to separation of vapor mixtures, the separation characteristics and the mechanisms of which, however, have not been studied well enough for their application to industries. In this work have been compared the observed separation performances of pervaporation and vapor permeation of aqueous organic solvents such as IPA/water and 1-propanol/water mixtures at their normal boiling points to study the separation mechanisms.
EXPERIMENTAL Some silica zirconia membranes are fabricated by the sol-gel procedures proposed in the previous work [2]. And their separation performances are tested with a conventional
AA11.5.2
pervaporation apparatus and a vapor permeation apparatus for separation of some aqueous organic chemicals (IPA/water, 1-propanol/water mixtures) at their normal boiling points. Membrane fabrication The sol-gel methods for membrane fabrication are w
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