Stability of a silica membrane prepared by CVD using γ- and α-alumina tube as the support tube in the HI–H2O gaseous mixture

The stability of a silica membrane prepared by chemical vapor deposition (CVD) in the HI–H2O gaseous mixture was evaluated aiming at the application for hydrogen iodide decomposition in the thermochemical IS process. Porous α- and γ-alumina tubes having pore sizes of 100 and 10 nm, respectively, were modified by chemical vapor deposition using tetraethoxysilane as the Si source. H2/N2 selectivities of the modified membranes which were measured by single-component permeation experiment showed 50.4, 7.5, 63.7, 7.7 and 3.8 at 600 °C for the NS-1, NS-2, NS-3, NS-4 and S-1 membranes, respectively. Stability experiment in the HI–H2O gaseous mixture was carried out at 450 °C. The prepared membrane using γ-alumina as the support tube was more stable than that using α-alumina as the support tube. The S-1 membrane using α-alumina as the support tube showed the high stability in the HI–H2O gaseous mixture and had the high H2/HI selectivity (240–2600 at 300–600 °C) in the H2–H2O–HI (molar composition; 0.09:0.78:0.13) gaseous mixture after the stability test.