Mechanism of Gas Separation through Amorphous Silicon Oxycarbide Membranes

Polymer-derived amorphous silicon oxycarbide (SiOC) ceramics are designed for hydrogen separation at high temperatures. To form amorphous SiOC top-coating with the thickness of about 300 nm, tubular porous gamma-Al2O3/a-Al2O3 substrates with gradient porosity are threefold coated by vinyl-functionalized polysiloxane and pyrolyzed at 700 degrees C under argon. N-2-physisorption measurement confirms formation of microporous material with a specific surface area of about 400 m(2) g(-1). Single gas permeance characterization of the SiOC membrane at 300 degrees C reveals H-2/CO2 and H-2/SF6 ideal permselectivities of about 10 and 320, respectively. The experimental gas permeance data are modeled using solid-state diffusion (for He and H-2) and gas translational diffusion (for CO2 and SF6) mechanisms.