Surface modification of α-alumina support in synthesis of silica membrane for hydrogen purification

In this work, an experimental study was carried out on the synthesis of silica membrane for hydrogen purification, in which synthesis of gamma-alumina intermediate layer using cheaper and safer source was investigated. For this purpose, aluminum hydroxide was selected and the bohmite sols were prepared by acid or base catalyzed hydrolysis of the different salts for comparing with alkoxide source. The SEM micrographs showed no distinct gamma-alumina layer on the substrate coated by base catalyzed sol of salt (sample 1), while a homogeneous gamma-alumina layer was formed by acid catalyzed sol of salt (sample 2). After gamma-alumina layer formation, the gas permeance mechanism was approximately changed. These results were similar to SEM results and N-2 permeance experiments of sample 3 in which substrate was coated with alkoxide sol. However, the gamma-alumina layer of sample 2 had no good adhesion to the substrate. Nevertheless, use of aluminum hydroxide can be promised to synthesis of gamma-alumina layer; the membrane was synthesized on the modified support with aluminum tri-sec-butylate sol. In particular, in the synthesized silica membrane as the temperature increases, permselectivity of H-2/CO2 and H-2/N-2 increases from 4.7 and 7.3 at room temperature to 9.4 and 11.6 at 100 degrees C and to 23.4 and 31.3 at 200 degrees C, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.