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°C for 90 min. Propyltrimethoxysilane (PrTMOS) was used as the silica source. PrTMOS and O₃ were provided from opposite sides of the porous alumina substrate. The CO₂/N₂ permeance ratio was the highest (20) using the membrane deposited at 270°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°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 N₂ was 5.6 kJ mol^-1. The negative activation energy indicates that the permeation is due to adsorption on the membrane.