Grace: Development of Silica Membranes for Gas Separation at Higher Temperatures

This chapter discusses the development of silica membranes for gas separation at higher temperatures. Using a polymeric gel solution route, tubular micro-porous silica membranes showing high hydrogen permeance and high gas selectivities are prepared. Silica membranes are coated on top of steam-stable γ-Al₂O₃ intermediate membranes inside a high-quality tubular support. Tube ends are coated with glass giving a gastight changeover between support and membranes. Single dead-end gas permeance measurements performed at temperatures > 300 °C and 4 bar pressure difference showed hydrogen fluxes >1.10^-6 mol m^-2 s^-1 Pa^-1 while H₂/CO₂ permselectivity under these conditions is 80-100. H₂/CO₂ selectivity increases up to 200 with decreasing pressure down to 1 bar. Membranes are shown to be thermally stable for at least 2000 h at temperatures between 200 and 400 °C. Preliminary water-gas-shift experiments are performed at temperatures above 250 °C and showed higher than equilibrium CO conversion.