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

Abstract

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.

Hydrogen Selective SiCH Inorganic–Organic Hybrid/γ-Al2O3 Composite Membranes

“…Thus, the observed E a values for He and H 2 permeations could depend on the density of the AHPCS-derived SiCH organic–inorganic hybrid network. However, a unique point was that, regardless of the synthesis temperature, the E a for H 2 permeation was found to be smaller than that for He permeation, which was a clear contrast to those evaluated for the H 2 -selecitve microporous amorphous silica membranes [ 10 , 11 , 65 , 66 , 67 ]. Then, an attempt was made for study on the hydrogen affinity of the AHPCS-derived SiCH organic–inorganic hybrid: The amount of H 2 adsorption on the AHPCS-derived SiCH film was measured by using a quartz-crystal microbalance (QCM).…”

“…However, under the given operating conditions [ 5 , 6 , 8 ], it is difficult to apply conventional H 2 -selective membranes, which require higher operation temperatures, approximately above 90, 180 and 350 °C for polymer [ 9 ], silica [ 10 , 11 , 12 ] and metal membranes [ 13 , 14 , 15 ], respectively. There are also technical issues such as water-induced swelling for polymer membranes, lower H 2 permeance for supported liquid membranes [ 16 , 17 , 18 ] and gas permeability degradation for intrinsically hydrophilic silica-based membranes [ 8 , 19 , 20 ].…”

Development of Hydrogen Permselective Membranes for Propylene Production

“…is showed the possibly of pore size control when using this method. Investigations are also underway to change the number of organic substituents of the precursor structures for gas separation (Akamatsu et al, 2019;Kato et al, 2019). Additionally, H 2 /hydrocarbon selective membrane performance in the permeation method has been investigated.…”

Permeation Properties of Ions through Inorganic Silica-Based Membranes

“…Inorganic membranes, such as zeolites, have also been investigated for use in gas separations, vapor separations, and pervaporation [4][5][6][7][8][9]. However, only a few reports [9][10][11] on liquid permeation and separation through inorganic NF membranes have been published to date.…”