Effect of CVD parameters on hydrogen permeation properties in a nano-composite SiO2-Al2O3 membrane

Tubular ceramic membranes were synthesized by depositing a dense layer of silica-alumina on top of a multilayer substrate using co-current chemical vapor deposition (CVD) method. The multilayer substrate was prepared by coating with a series of bohemite sols with certain particle sizes. Cross-sectional and surface images obtained from high resolution FESEM showed that the intermediate layer had a thickness of about 1 mu m and the top selective layer was uniform and dense with a thickness of less than 100 nm. Permeance tests, which were carried out with H-2, CO2, N-2 and CH4 at a high temperature range of 923-1073 K, indicated that gas permeation took place via different mechanisms through different layers of the membranes. During the deposition time, permeance values were reduced and after 6 h, H-2 permeation decreased from 5 x 10(-5) mol m(-2) s(-1) Pa-1 to 6.3 x 10(-7) mol m(-2) s(-1) Pa-1, but high selectivities of 105, 203 and 573 were obtained at 1073 K for H-2 over CO2, N-2 and CH4, respectively. Hydrothermal stability tests at 1073 K and in the presence of 30 mol% steam showed that using 10 mol% alumina precursor (ATSB) in the CVD method improved membrane stability, as after 96 h of exposure to humidity, H-2 permeance flux of silica-alumina membrane with ATSB/TEOS molar ratio of 0.1 was 1.9 times more than that of a pure silica membrane. (c) 2012 Elsevier B.V. All rights reserved.