Preparation of Silica Hybrid Membranes for High Temperature CO2 Separation

CO2 separation through membranes represents a solution for efficient CO2 recovery. A high temperature CO2 permselective membrane can be applied to a membrane reactor for reforming reactions. However, CO2 permselective membranes have been primarily developed as low temperature polymeric membranes. Only a few articles have reported high temperature CO2 permselective membranes. We prepared silica membranes using chemical vapor deposition (CVD) for high temperature hydrocarbon separation. In this study, the pore size control of the silica membranes was investigated. CVD was performed at 150-450 degrees C for 90 min. Propyltrimethoxysilane (PrTMOS) was used as the silica source. PrTMOS and O-3 were provided from opposite sides of the porous alumina substrate. The CO2/N-2 permeance ratio was the highest (20) using the membrane deposited at 270 degrees C. The deposition conditions were investigated using FT-IR measurements of the PrTMOS hydrolysis powder. Absorption at 2,960 cm(-1) indicated C-CH3 stretching. The ratio of the absorption at 2,960 cm(-1) of the as-made sample and the calcined sample was evaluated. This ratio was the maximum (0.41) with treatment at 270 degrees C. Thus, the CO2 permselectivity is likely due to the remaining alkyl groups on the membrane. The activation energy of CO2 permeation was negative, while that of N-2 was 5.6 kJ mol(-1). The negative activation energy indicates that the permeation is due to adsorption on the membrane.