Permeation properties of a graded structure composite ceramic membrane prepared by CVD method

Permeation properties of a hydrogen permselective ceramic membrane for single gases (H2, CH4, N2 and CO2) have been studied. The membrane was prepared by depositing a thin layer of SiO2 on the inner side of a tubular modified alumina layer by chemical vapor deposition (CVD) method. The modification process was carried out by coating the macroporous α-alumina substrate with different layers of γ-alumina to obtain a graded structure support. XRD, SEM and EDAX analysis were used to characterize the membrane. Cross-sectional and surface images obtained from SEM showed that the intermediate layer had a thickness of 2 μm with a median pore size of about 50 nm and the top selective silica layer was uniform and dense with a thickness of about 100 nm. Permeation tests showed that H2 permeation flux reduced from 5*10-5 molm-2s-1pa-1 to 6*10-7 molm-2s-1pa-1 as the CVD deposition time proceeded from 0 to 6 h and H2 selectivities over CH4, N2 and CO2 increased from 2.2, 5.6 and 7.9 to 105, 178 and 446, respectively