Hydrogen gas mixture separation by CVD silica membrane

In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H2 and CO2 at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and O2 were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H2 and He) whilst the larger kinetic diameter gases (CO2 and N2) showed negative activation energy. The single gas permeation of H2 increased from 5.1 × 10−7 to 7.0 × 10−7 mol m−2 s−1 Pa−1 in the temperature range 100–400 °C, and H2/CO2 and H2/N2 selectivities reached 36 and 57 at 400 °C, respectively. The H2 purity in the permeate stream also increased with temperature for H2:CO2 binary gas mixture, thus being beneficial for H2 diffusion. H2 competitively permeated through the membrane at a several range of gas mixtures, and a saturation level was achieved at H2:CO2 60:40 feed concentration, where the diffusion of CO2 molecules became negligible delivering ∼99% H2 purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 Å.