Improved thermal and oxidation stability of bis(triethoxysilyl)ethane (BTESE)-derived membranes, and their gas-permeation properties

Abstract

The conventional method used to fabricate bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes begins with a coating of BTESE-derived sols that is then fired at temperatures that do not exceed 300 °C, because the organic linking ethane groups start to thermally decompose at temperatures higher than 300 °C. In the present study, however, thermal stability of BTESE membranes was further enhanced by firing at much higher temperatures (550–700 °C), which promises to enable future applications such as H₂ purification at high temperatures and gas separation under an oxidizing atmosphere. The selectivity of 700 °C-fired membranes for H₂/CH₄ was as high as 100 with H₂ permeance of approximately 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹. Moreover, even after heat treatment at 550 °C under N₂ and then under air, BTESE-derived membranes prepared at 550 °C showed high selectivity values of approximately 100 and 2000 for H₂/CH₄ and H₂/CF₄, respectively. By comparison, the selectivities for H₂/CH₄ and H₂/CF₄ of membranes prepared at 300 °C were approximately 30 and 200, respectively. The BTESE powders were characterized by FT-IR, N₂ adsorption, Electro-Probe Microanalyzer (EPMA), and TGA. The large carbon/silicon ratio and residual weight for powders with multiple heat treatments under N₂ and then under air, suggested that high-temperature treatment under N₂ increased the thermal stability and oxidizing resistance. These results showed that calcination temperatures, atmosphere, and heat treatment are the key factors influencing the thermal and oxidation stability of these BTESE membranes.