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Open AccessArticle

Gas Separation Silica Membranes Prepared by Chemical Vapor Deposition of Methyl-Substituted Silanes

1
Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8556, Japan
2
Department of Chemical Engineering, Virginia Tech, Blacksburg, VA 24061, USA
3
College of Chemical Engineering, Fuzhou University, Fuzhou 350116, China
*
Author to whom correspondence should be addressed.
Current address: Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Membranes 2019, 9(11), 144; https://doi.org/10.3390/membranes9110144
Received: 1 August 2019 / Revised: 27 October 2019 / Accepted: 30 October 2019 / Published: 3 November 2019
The effect on the gas permeance properties and structural morphology of the presence of methyl functional groups in a silica membrane was studied. Membranes were synthesized via chemical vapor deposition (CVD) at 650 °C and atmospheric pressure using three silicon compounds with differing numbers of methyl- and methoxy-functional groups: tetramethyl orthosilicate (TMOS), methyltrimethoxysilane (MTMOS), and dimethyldimethoxysilane (DMDMOS). The residence time of the silica precursors in the CVD process was adjusted for each precursor and optimized in terms of gas permeance and ideal gas selectivity criteria. Final H2 permeances at 600 °C for the TMOS-, MTMOS-, and DMDMOS-derived membranes were respectively 1.7 × 10−7, 2.4 × 10−7, and 4.4 × 10−8 mol∙m−2∙s−1∙Pa−1 and H2/N2 selectivities were 990, 740, and 410. The presence of methyl groups in the membranes fabricated with the MTMOS and DMDMOS precursors was confirmed via Fourier-transform infrared (FTIR) spectroscopy. From FTIR analysis, an increasing methyl signal in the silica structure was correlated with both an improvement in the hydrothermal stability and an increase in the apparent activation energy for hydrogen permeation. In addition, the permeation mechanism for several gas species (He, H2, Ne, CO2, N2, and CH4) was determined by fitting the gas permeance temperature dependence to one of three models: solid state, gas-translational, or surface diffusion. View Full-Text
Keywords: silica-based membrane; hydrogen separation; CVD; pore size control; tetramethyl orthosilicate; methyltrimethoxysilane; dimethyldimethoxysilane; separation mechanism silica-based membrane; hydrogen separation; CVD; pore size control; tetramethyl orthosilicate; methyltrimethoxysilane; dimethyldimethoxysilane; separation mechanism
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Kato, H.; Lundin, S.-T.B.; Ahn, S.-J.; Takagaki, A.; Kikuchi, R.; Oyama, S.T. Gas Separation Silica Membranes Prepared by Chemical Vapor Deposition of Methyl-Substituted Silanes. Membranes 2019, 9, 144.

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