Temporary carbon barriers in the preparation of H_2-permselective silica membranes

Temporary carbon barriers were used to prepare hydrogen-permselective membranes by chemical vapor deposition (CVD) of silica on porous Vycor support tubes. The carbon barriers were introduced into the pores of the support by vapor deposition polymerization of furfuryl alcohol, catalyzed by p-toluene sulfonic acid. After polymerization and crosslinking the polymer was carbonized by slow heating to 600°C and CVD of silica was carried out at 600°C by alternating flows of SiCl_4 and H_2O. During CVD the carbon residue inside the pores limits the penetration of SiCl_4 resulting in a thinner deposit layer. After CVD the carbon was removed by oxidation. The hydrogen permeance of the deposit layer obtained using the carbon barriers was 2–4 times higher than the permeance achieved without the use of carbon barriers. Thermogravimetric experiments were carried out to obtain information about the amount and spatial distribution of the carbon within the porous support