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 H-2 and CO2 at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and (O-2 were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H-2 and He) whilst the larger kinetic diameter gases (CO2 and N-2) showed negative activation energy. The single gas permeation of H-2 increased from 5.1 x 10(-7) to 7.0 x 10(-7) Mol m(-2) s(-1) Pa-1 in the temperature range 100-400 degrees C. and H-2/CO2 and H-2/N-2 selectivities reached 36 and 57 at 400 degrees C, respectively. The H-2 purity in the permeate stream also increased with temperature for H-2:CO2 binary gas mixture, thus being beneficial for H-2 diffusion. H-2 competitively permeated through the membrane at a several range of gas mixtures. and a saturation level was achieved at H-2:CO2 60:40 feed concentration, where the diffusion of CO2 molecules became negligible delivering similar to 99% H-2 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 angstrom. (C) 2008 Elsevier B.V. All rights reserved.