Development of a model surface flow membrane by modification of porous vycor glass with a fluorosilane

An organic-inorganic hybrid membrane was developed by modification of a mesoporous Vycor glass with the organosilane heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (HDFS). The presence of silane on the surface of Vycor glass was confirmed by Fourier transform infrared spectroscopy. A decrease in the surface area of the membrane after modification, measured by N-2 adsorption, suggested that the silane molecules effectively filled or blocked the pores. The permeance was governed by the kinetic diameter of gases with contributions from the surface flow for condensable gases. The membrane showed selectivity for CO2 over other gases, whereas the untreated membrane was selective for n-C4H10. Mixed-gas selectivities were higher than pure-gas values for all gas pairs, which might be because of an enhanced permeance of CO2 at low pressure usually observed for glassy polymers. In comparison to the HDFS membrane, the sorption of gases controlled the permeance of the octadecyltrichlorosilane (ODS) modified membrane, resulting in a significant change in the order of selectivity. The order of the permeance was CO2 > Ar > CH4 > n-C4H10 > C2H6 > N-2 > SF6 > i-C4H10 for the HDFS membrane, which changed to n-C4H10 > i-C4H10 > CO2 > C2H6 > He > N-2 for the ODS membrane.