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

•The silica membrane was synthesized for hydrogen purification.•ϒ-Alumina intermediate layer was synthesized using different precursors.•Aluminum hydroxide was promised as a cheap and safe precursor.•The activated molecular sieving was detected as the dominant mechanism.

In this work, an experimental study was carried out on the synthesis of silica membrane for hydrogen purification, in which synthesis of γ-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 γ-alumina layer on the substrate coated by base catalyzed sol of salt (sample 1), while a homogeneous γ-alumina layer was formed by acid catalyzed sol of salt (sample 2). After γ-alumina layer formation, the gas permeance mechanism was approximately changed. These results were similar to SEM results and N2 permeance experiments of sample 3 in which substrate was coated with alkoxide sol. However, the γ-alumina layer of sample 2 had no good adhesion to the substrate. Nevertheless, use of aluminum hydroxide can be promised to synthesis of γ-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 H2/CO2 and H2/N2 increases from 4.7 and 7.3 at room temperature to 9.4 and 11.6 at 100 °C and to 23.4 and 31.3 at 200 °C, respectively.