Synthesis and Permeation Properties of Silicon−Carbon-Based Inorganic Membrane for Gas Separation

Recent Progress in Silicon Carbide-Based Membranes for Gas Separation

The scale of research for developing and applying silicon carbide (SiC) membranes for gas separation has rapidly expanded over the last few decades. Given its importance, this review summarizes the progress on SiC membranes for gas separation by focusing on SiC membrane preparation approaches and their application. The precursor-derived ceramic approaches for preparing SiC membranes include chemical vapor deposition (CVD)/chemical vapor infiltration (CVI) deposition and pyrolysis of polymeric precursor. Generally, SiC membranes formed using the CVD/CVI deposition route have dense structures, making such membranes suitable for small-molecule gas separation. On the contrary, pyrolysis of a polymeric precursor is the most common and promising route for preparing SiC membranes, which includes the steps of precursor selection, coating/shaping, curing for cross-linking, and pyrolysis. Among these steps, the precursor, curing method, and pyrolysis temperature significantly impact the final microstructures and separation performance of membranes. Based on our discussion of these influencing factors, there is now a good understanding of the evolution of membrane microstructures and how to control membrane microstructures according to the application purpose. In addition, the thermal stability, oxidation resistance, hydrothermal stability, and chemical resistance of the SiC membranes are described. Due to their robust advantages and high separation performance, SiC membranes are the most promising candidates for high-temperature gas separation. Overall, this review will provide meaningful insight and guidance for developing SiC membranes and achieving excellent gas separation performance.

Tailoring a Thermally Stable Amorphous SiOC Structure for the Separation of Large Molecules: The Effect of Calcination Temperature on SiOC Structures and Gas Permeation Properties

A SiOC membrane with high oxidative stability for gas separation was tailored by utilizing vinyltrimethoxysilane, triethoxysilane, and 1,1,3,3-tetramethyldisiloxane as Si precursors. Amorphous SiOC networks were formed via the condensation of Si-OH groups, the hydrosilylation of Si-H and Si-CH=CH₂ groups, and a crosslinking reaction of Si-CH₃ groups, respectively. The crosslinking of Si-CH₃ groups at temperatures ranging from 600 to 700 °C under a N₂ atmosphere was quite effective in constructing a Si-CH₂-Si unit without the formation of mesopores, which was confirmed by the results of N₂ adsorption and by the gas permeation properties. The network pore size of the SiOC membrane calcined at 700 °C under N₂ showed high oxidative stability at 500 °C and was appropriate for the separation of large molecules (H₂/CF₄ selectivity: 640, H₂/SF₆: 2900, N₂/CF₄: 98). A SiOC membrane calcined at 800 °C showed H₂/N₂ selectivity of 62, which was approximately 10 times higher than that calcined at 700 °C because the SiOC networks were densified by the cleavage and redistribution reactions of Si-C and Si-O groups.