Fabrication And Application Of Zeolite Membranes
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FABRICATION AND APPLICATION OF ZEOLITE MEMBRANES Hidetoshi Kita Department of Advanced Materials Science and Engineering, Faculty of Engineering, Yamaguchi University Tokiwadai 2-16-1, Ube, Yamaguchi 755-8611, Japan ABSTRACT Zeolite membranes were prepared on a porous ceramic support by hydrothermal synthesis using conventional heating system and microwave heating. NaA and T type zeolite membranes were highly selective for permeating water preferentially with the high permeation flux, while silicalite membranes exhibited preferential organic compound permeation from water such as ethanol/water. NaY and NaX zeolite membranes showed a high alcohol selectivity for several feed mixtures with methanol or ethanol and a high benzene selectivity for benzene/cyclohexane and benzene/n-hexane separation. The performance of the zeolite membranes was the most favorable one for pervaporation membranes which have been published so far and a tubular type module using A type zeolite membrane for dehydration of organic liquids has been put into industrial operation. The tubular type pervaporation and vapor permeation module can produce 99.8 wt% ethanol from 600 l/h, 90 wt% ethanol feed at 120 ºC. For the mass production of zeolite membrane a new synthetic method using a microwave heating is also proposed. INTRODUCTION Strong interest exists in the synthesis of high performance membranes that exhibit both higher permeabilities and higher selectivities than presently available polymers[1]. Zeolite is a promising candidate for the high performance membrane because of the unique characteristics of zeolite crystals. In the last decades the synthesis of zeolite membranes and their potential separation properties have extensively studied[2,3]. We have reported a variety of zeolite membranes prepared on porous support materials and their high pervaporation performance[4-8]. The membranes consist of intergrown zeolite crystals which tend to be very closely bound together with little space between them and form a continuous layer. The performance of the zeolite membranes is the most favorable one for pervaporation membranes which have been published so far and is very high enough to put these membranes into practical use. Zeolite membranes have been also synthesized using a microwave heating[9]. Microwave radiation allows a homogeneous heating throughout a reaction vessel and a reduction of processing time and energy cost, compared to conventional heating. In the present study, the fabrication of zeolite membranes applicable for large scale uses in pervaporation and vapor permeation will be addressed. EXPERIMENTAL Zeolite membranes were grown hydrothermally on the surface of a commercial porous cylindrical support (10 or 12 mm outer diameter and 1-2 µm average pore size). The hydrothermal synthesis of NaA zeolite membrane was performed as follows. An aluminate solution was prepared by dissolving sodium hydroxide and aluminium hydroxide in distilled water. A silicate solution was prepared by dissolving sodium silicate in distilled wat
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