High Hydrogen Permeance Silica Membranes Prepared by a Chemical Vapor Deposition Method
Pages 66-73
Ayumi Ikeda, Ryuhei Ono and Mikihiro Nomura

DOI: http://dx.doi.org/10.6000/1929-6037.2015.04.02.4

Published: 08 June 2015

Abstract: H₂ permselective silica hybrid membranes were successfully prepared by using a counter diffusion chemical vapor deposition (CVD) method. Hexyltrimethoxysilane (HTMOS), phenyltrimethoxysilane (PhTMOS) or diphenyldimethoxysilane (DPhDMOS) were used as silica precursors. The oxidants were O₃ or O₂. These reactants were provided at the opposite side of the γ-alumina substrates, and the deposition occurred in the pores of the substrates. The HTMOS/O₃ derived membrane deposited at 450°C showed the highest H₂ permselectivity. The H₂ permeace was 2.1×10^-6 mol m^-2 s^-1 Pa^-1 with the H₂/SF₆ permeance ratio of 5.9×10⁶. H₂ permeances through the HTMOS derived membranes increased with increasing the deposition temperatures. While the H₂ permeance through the PhTMOS and DPhDMOS derived membranes decreased with increasing the deposition temperatures. The PhTMOS derived membrane prepared at 150°C showed the H₂ permeance of 1.7×10^-6 mol m^-2 s^-1 Pa^-1 with the H₂/SF₆ permeance ratio of 13. The PhTMOS membrane prepared at 320°C showed the highest H₂/SF₆ permeance ratio of 1.8×10⁴among the PhTMOS derived membranes. However, the H₂/SF₆ permeance ratio through the DPhDMOS membranes showed the different trend. Higher H₂/SF₆ permeance ratio was found through the DPhDMOS derived membranes deposited at 180°C and 360°C. The maximum H₂/SF₆ permeance ratio was 4.2×10⁴ through the DPhDMOS membrane deposited at 180°C. The decomposition properties of organic groups on silica surface are investigated by using hydrolysis powders derived from the each silica precursor. The HTMOS powders showed O₃ stability after the high temperature treatment. Thus, high H₂ permselective membranes were prepared by the HTMOS at 450 °C.

Keywords: Silica hybrid membrane, counter diffusion CVD method, H₂permselective membrane, pore size control, silica precursors.