Gas separation using Knudsen and surface diffusion II: Effects of surface modification of epoxy/porous SiO₂ composite

Epoxy/porous SiO2 composites were prepared with the pore surface modified using various silane coupling agents. The N2 adsorption and desorption isotherm shows that the porous SiO2 used for raw materials has sufficiently high pore volume. Their pore sizes, calculated using Barrett–Joyner–Halenda method as less than 20 nm was markedly smaller than the mean free path of the gases used for this study. The respective degrees of gas selectivity CO2/N2, CH4/N2, and O2/N2 were measured. Results show that the epoxy/porous SiO2 composite surface-modified by APTES only exhibits CO2/N2 gas selectivity at a lower pressure drop. It originates in the affinity between amino group of the APTES and CO2 gas. The epoxy/porous SiO2 composite treated by APTES also shows gas separation capability. The 80% N2/20% CO2 mix gas was converted into 68.2% N2/31.8% CO2 gas after gas separation tests at 25 °C. The gas separation capability was maintained at high temperatures. The 80% N2/20% CO2 mix gas was converted into 70.8% N2/29.2% CO2 gas at 100 °C.