Permeation and separation studies on microporous sol-gel modified ceramic membranes

Permeation and separation experiments with H₂, CO₂, O₂, N₂, CH₄ and isobutane with microporous sol-gel modified supported ceramic membranes were performed to determine the gas transport characteristics and the hydrogen separation performance of these membranes. It is found that the permeation is activated, and for defectfree membranes the apparent activation energies are in the ranges 13–15 and 5–6 kJ mol⁻¹ for H₂ and CO₂, respectively. Correction for the pressure drop over the support results in apparent activation energies for the silica top-layer on the order of 17–22 and 10–15 kJ mol⁻¹ for H₂ and CO₂ respectively. Due to the very thin top-layer, the permeation is relatively high, with representative values of 6·10⁻⁷ and 20·10⁻⁷ mol m⁻²s−1 Pa⁻¹ for H₂ at 25 and 200°C, respectively. The H₂ permeation is almost pressure-independent up to pressures of at least 5 bar. Typical separation factors for H₂-CH₄ and H₂-isobutane are approximately ≈40 and ≈200, respectively, at 200°C for high-quality membranes. For moderate-quality membranes the H₂-CH₄ separation factor is around 10, while the H₂-isobutane separation factor remains at a high value of around 100 at 200°C and 120 at 300°C.