Preparation of an H₂-permselective silica membrane for the separation of H₂ from the hydrogen iodide decomposition reaction in the iodine–sulfur process

A high-performance, H₂-permselective silica membrane derived from hexyltrimethoxysilane (HTMOS) was developed for application in the thermochemical water-splitting iodine–sulfur process. Silica membranes, referred to here as HTMOS membranes, were prepared via counter-diffusion chemical vapor deposition on γ-alumina-coated α-alumina support tubes with outer diameters of 10 mm. Special attention was devoted to obtain high H₂/HI selectivity, high H₂ permeance, and good stability in the presence of corrosive HI gas. The effects of the deposition conditions, temperature, and period were investigated. The HTMOS membrane prepared at 450 °C for 5 min exhibited high H₂/HI selectivity (>175) with H₂ permeance on the order of 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹. On the basis of stability experiments, it was found that the HTMOS membrane was stable upon HI exposure at a temperature of 400 °C for 11 h.