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, ca talyzed by p-toluene sulfonic acid. After polymerization and crosslink ing the polymer was carbonized by slow heating to 600 degrees C and CV D of silica was carried out at 600 degrees C by alternating flows of S iCl4 and H2O. During CVD the carbon residue inside the pores limits th e penetration of SiCl4 resulting in a thinner deposit layer. After CVD the carbon was removed by oxidation. The hydrogen permeance of the de posit layer obtained using the carbon barriers was 2-4 times higher th an the permeance achieved without the use of carbon barriers. Thermogr avimetric experiments were carried out to obtain information about the amount and spatial distribution of the carbon within the porous suppo rt.