Permeation properties and hydrothermal stability of allylhydridopolycarbosilane (AHPCS)-derived silicon carbide (SiC) membranes

Abstract

Among various membrane materials used for gas separation, silicon carbide (SiC) is promising because of its structural stability and mechanical strength. In this study, allylhydridopolycarbosilane (AHPCS) was used as a precursor for SiC membranes to improve gas permeance and hydrothermal stability. The membrane was prepared by coating AHPCS sols on a SiO₂–ZrO₂ intermediate layer as the top layer, followed by firing at 500–800 °C. The highest H₂ permeance of (2.3–3.0) × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ with H₂/N₂ of 10–30 and a H₂/SF₆ permeance ratio higher than 1000 was obtained on AHPCS-derived SiC membranes fired at 500–700 °C. The AHPCS-derived SiC membranes were then subjected to hydrothermal treatment. After being exposed to steam, the N₂ permeance decreased from 2.4 × 10⁻⁸ and reached stable permeances of ∼3 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹. In the separation of binary mixtures of H₂O/N₂ at 400 °C, the AHPCS membrane showed an excellent water selectivity, and permeance ratio for H₂O/N₂ of approximately 100, with an H₂O permeance of (5.5–8.0) × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹. The temperature dependence of gas permeance in binary mixtures was measured in the range of 200–400 °C. The AHPCS-derived SiC membranes are promising materials for future applications in high temperature dehydration processes.