Development of silica membranes to improve dehydration reactions

Silica membranes for use in a membrane reactor were developed via counter diffusion chemical vapor deposition (CVD) method using tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS), n-butyltrimethoxysilane (BTMOS), and 3-aminopropyltrimethoxysilane (APrTMOS) as the silica precursors. The high temperature separation performances of the synthesized membranes were evaluated. The membranes prepared using TMOS and MTMOS at high temperature deposition showed H₂/N₂ selectivity of over 100. The membranes prepared using BTMOS and APrTMOS at 270°C showed H₂/N₂ selectivity of about 100 and N₂/SF₆ selectivity about 100. This indicate that thermal stability of the organic group of the silica precursor is vital for the membrane performances. Subsequently, decomposition of the organic group and deposition time were investigated. The membrane prepared by extending the deposition time of APrTMOS to 240 min showed high hydrogen permeance of 7.2 x 10^-7 mol/sq m-s-Pa and H₂/C₃H₈ selectivity of 21000. Additionally, high temperature gas permeation tests at 500°C were carried out using the membrane prepared using MTMOS. The mixed gas separation factor of about 100 for H₂/C₃H₈ separation test was the same as the single gas permeance ratio of 98 calculated from the result of the single gas permeance.