GAS-TRANSPORT AND SEPARATION WITH CERAMIC MEMBRANES .2. SYNTHESIS AND SEPARATION PROPERTIES OF MICROPOROUS MEMBRANES

Non-supported microporous silica (amorphous) and titania thin films were made by the polymeric gel route. The titania system consisted of particles smaller than 5 nm. Reproducible modification of supported gamma-alumina films with silica demands a strict control of every modification step. Silica films of 30-60 nm thickness on top of and presumably partly inside the gamma-alumina film were realised. The permeabilities of helium and hydrogen through this film are activated, while the propylene permeability was below the detection limit. Separation factors of a H-2-C3H6 mixture are larger than 200 at 200-degrees-C with a flux for the preferentially permeating hydrogen of 1.6 X 10(-6) mol/m2-sec-Pa. The pores must be of molecular dimensions to realise this (< 1 nm diameter). Preliminary research shows that changes in the synthesis parameters result in higher activation energies and improved separation properties. The relation between synthesis, resulting microstructure and gas separation properties, however, is not yet fully understood.