Solvent effects on diffusion channel construction of organosilica membrane with excellent CO2 separation properties

In this work, bis (triethoxysilyl) ethane (BTESE)-derived organosilica membranes were fabricated via the sol-gel method. To obtain organosilica membranes with high perm-selectivity, the network of the membrane was tailored by using different solvents in the preparation of the BTESE-derived sol with different pore sizes and network structures. A solvent with small polarity and a small dielectric constant (εr) can lead to outstanding single gas separation performance on the membrane structure, because the precursors are completely hydrolyzed and effectively stacked into a dense structure, which is beneficial for forming a suitable network for gas separation. The influence of the solvent and membrane thickness on the BTESE-derived membrane were evaluated to determine the mechanism responsible for the separation; this mechanism was found to be controlled not only by molecular sieving but also by selective surface diffusion. The results show that the BTESE-derived membrane prepared using tetrahydrofuran as the solvent exhibited a small network with an optimum thickness (three coating cycles) and led to a high ideal selectivity for CO2/CH4 and CO2/N2, with selectivity values of 33 and 38, respectively; additionally, the permeance of CO2 was 6.32 × 10−8 mol m−2 s−1 Pa−1 at 25 °C.