High-Selectivity, High-Flux Silica Membranes for Gas Separation

Abstract

Process improvements in silica membrane fabrication, especially the use of clean-room techniques, resulted in silica membranes without detectable mesoscopic defects, resulting in significantly improved transport properties. Supported membranes calcined at 400°C were 30 nanometers in thickness, showed a H₂ permeance at 200°C of 2 × 10⁻⁶ moles per square meter per second per Pascal (mol m⁻² s⁻¹ Pa⁻¹), and had a CH₄ permeance more than 500 times smaller. Molecules larger than CH₄ were completely blocked. Silica membranes calcined at 600°C showed no detectable CH₄ flux, with a H₂ permeance of 5 × 10⁻⁷ (mol m⁻² s⁻¹ Pa⁻¹) at 200°C. These results signify an important step toward the industrial application of these membranes such as purification of H₂ and natural gas as well as the selective removal of CO₂.