Carbon-based molecular sieve membranes for gas separation by inductively-coupled-plasma chemical vapor deposition

Carbon-based molecular sieve (CMS) films for gas separation have been deposited on porous Al2O3 disks using hexamethyldisiloxane (HMDSO) by a remote inductively-coupled-plasma (ICP) chemical vapor deposition (CVD) method. The H2/N2 selectivities of the as-deposited films falled into the range of 5-10, higher than the Knudsen diffusion selectivity, 3.7. After pyrolysis of the as-deposited film at 873 K, the permeance increased by one order of magnitude with no significant change of the selectivity. A surface treatment method was further employed by bombarding the as-deposited film with high energy ions of HMDSO. After pyrolysis at 823 K, the surface-treated film exhibits a very significant increase of H2/N2 selectivity without any reduction of the permeance. The H2/N2 selectivity could reach 30-45 with an extremely high permeance around 2 × 10−6 mol m−2 s−1 Pa−1 at 423 K. The O2/N2 selectivity reached 3.8 and the O2 permeance was about 2 × 10−7 mol m−2 s−1 Pa−1 at 298 K. Therefore, a new method for preparing carbon-based molecular sieve membranes has been introduced by combining the surface treatment with high energy ion bombardment and the subsequent high temperature pyrolysis.