Development of a H2-selective SiO2-membrane for the catalytic dehydrogenation of propane

Commercial alumina ceramic tubes of asymmetric cross section were used as supports for the deposition Of SiO2 layers by the sol-gel technique. The SiO2 gel layer has been built up on the gamma -alumina ultrafiltration (UF)-layer of the support by dip-coating with a SiO2-polymer sol. The sol was prepared by a two-step acidic-base hydrolysis of tetraethylorthosilicate (TEOS) in alcoholic solution with a relative low content of water (H2O:TEOS = 4.3:1). The following step of hydrolysis and condensation was varied by different amounts of NH4OH. These sols of lowly branched SiO2 polymers with 60-70% Q(3) units were used for dip-coating. After drying (2 h at ambient temperature) the membranes have been calcined at 600 degreesC. The resulting membranes show hydrogen fluxes greater than or equal to 20 m(3)(STP)/m(2) h bar and permselectivities hydrogen:propane between 30 and 75 in a temperature region of 450-550 degreesC. The membranes were tested in membrane supported propane dehydrogenation. The propene yield in the membrane reactor can be higher than in a conventional fixed-bed reactor if the hydrogen is removed by a H-2-selective membrane. After several regeneration cycles, stable and acceptable membrane properties are found. (C) 2001 Elsevier Science B.V. All rights reserved.