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

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 degrees C, because the organic linking ethane groups start to thermally decompose at temperatures higher than 300 degrees C. In the present study, however, thermal stability of BTESE membranes was further enhanced by firing at much higher temperatures (550-700 degrees C), which promises to enable future applications such as H-2 purification at high temperatures and gas separation under an oxidizing atmosphere. The selectivity of 700 degrees C-fired membranes for H-2/CH4 was as high as 100 with H-2 permeance of approximately 10(-6) mol m(-2) s(-1) Pa-1. Moreover, even after heat treatment at 550 degrees C under N-2 and then under air, BTESE-derived membranes prepared at 550 degrees C showed high selectivity values of approximately 100 and 2000 for H-2/CH4 and H-2/CF4, respectively. By comparison, the selectivities for H-2/CH4 and H-2/CF4 of membranes prepared at 300 degrees C were approximately 30 and 200, respectively. The BTESE powders were characterized by FT-IR, N-2 adsorption, Electro-Probe Microanalyzer (EPMA), and TGA. The large carbon/silicon ratio and residual weight for powders with multiple heat treatments under N-2 and then under air, suggested that high-temperature treatment under N-2 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.