Stability of a silica membrane prepared by CVD using γ- and a-alumina tube as the support tube in the HI-H_2O gaseous mixture

摘要

The stability of a silica membrane prepared by chemical vapor deposition (CVD) in the HI―H_2O 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 10nm, respectively, were modified by chemical vapor deposition using tetraethoxysilane as the Si source. H_2/N_2selectivities 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℃ for the NS-1, NS-2, NS-3, NS-4 and S-1 membranes, respectively. Stability experiment in the HI-H_2O gaseous mixture was carried out at 450℃. 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-H_2O gaseous mixture and had the high H_2/HI selectivity (240―2600 at 300―600℃) in the H_2―H_2O―HI (molar composition; 0.09:0.78:0.13) gaseous mixture after the stability test.