SYNTHESIS OF H2-PERMSELECTIVE MEMBRANES BY MODIFIED CHEMICAL VAPOR-DEPOSITION - MICROSTRUCTURE AND PERMSELECTIVITY OF SIO2/C/VYCOR MEMBRANES

A modified chemical vapor deposition technique was employed for the synthesis of inorganic membranes that are selective for hydrogen separation and can withstand temperatures up to 800-degrees-C. In an opposing reactants geometry and at 750-degrees-C triisopropylsilane (C3H7)3SiH vapors reacted with oxygen within the mouth of the pores of Vycor glass substrates to deposit SiO2/C nanostructures. Subsequent reaction resulted in the growth of a porous top layer on the Vycor substrate. The permselective properties of the membrane are dictated by the SiO2/C nanoscale deposits constricting the mouth of the substrate pores. Permeation of hydrogen occurs through a temperature-activated diffusion mechanism. At 750-degrees-C, the H-2:N2 flux varied between 30 and 250. The effect of the ratio of the partial pressures of the reactants on the permselective properties of the membrane was established. These inorganic membranes may be used in membrane reactors to improve the efficiency of industrial dehydrogenation reactions currently restricted by thermodynamic equilibrium.