Hydrogen Recovery from a H₂−H₂O−HBr Mixture Utilizing Silica-Based Membranes at Elevated Temperatures. 1. Preparation of H₂O- and H₂-Selective Membranes

Abstract

Amorphous silica-based membranes were prepared for use in recovering hydrogen at elevated temperatures from a H2−H2O−HBr mixture produced by a thermochemical water decomposition process (the UT-3 process). The silica-based membranes, which were formed on porous tubes by chemical vapor deposition of tetraethoxysilane at 650 °C with a forced cross-flow through the porous wall, exhibited a H2 or H2O selectivity, which was related to the preparation and posttreatment conditions. The microporous silica membrane formed on a macroporous α-alumina tube and heat-treated at 900 °C in an inert atmosphere showed a H2 permeance of (3−4) × 10-7 mol m-2 s-1 Pa-1 and a H2/H2O selectivity of 7−15 at permeation temperatures of 200−400 °C. The microporous silica membrane which was formed on a mesoporous γ-alumina layer coated on the α-alumina tube and then calcined in air showed a H2O permeance of the order of 10-6 mol m-2 s-1 Pa-1 and a H2O/H2 selectivity of 12−25 at 200−400 °C. This membrane rejected HBr at a H2O/HBr selectivity of 300−1000.