Sol-gel processed magnesium-doped silica membranes with improved H₂/CO₂ separation

Magnesium-doped silica membranes were synthesized and a large increase in H₂/CO₂ permselectivity is achieved as compared to undoped silica membranes. Three magnesium concentrations were studied, namely 10, 15 and 20 mol%, in order to find the optimal Mg-concentration for the highest H₂/CO₂ separation performance. The physical properties of these sol-gel derived Mg-doped silica gels and membranes were characterized by dynamic light scattering, X-ray diffraction and high-resolution scanning electron microscopy. After the incorporation of magnesium into amorphous silica network, the membrane structure remained amorphous. Membrane performance was tested by single gas permeance of He, H₂, CO₂, N₂ and CH₄. With 20 mol% Mg doping, H₂/CO₂ permselectivity values of more than 350 were achieved with a H₂ permeance of 70 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹. For pure silica membranes, a H₂/CO₂ permselectivity of 9 was observed with a H2 permeance of 526 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹.