Pervaporation Separation of Benzene/Cyclohexane through Silica Hybrid Membranes Prepared by Using a Counter-Diffusion CVD Method

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A benzene-permselective silica hybrid membrane was successfully prepared by counter-diffusion CVD using PrTMOS (propyltrimethoxysilane) and O3 as reactants. Deposition temperatures and O3 flow rates were important parameters. The H2/N2 permeance ratio was 250 through a membrane deposited at 240°C. The pore size of the membrane was estimated at about 0.3 nm from the kinetic diameter of H2 (0.29 nm) and N2 (0.36 nm). On the other hand, the N2/SF6 permeance ratio was 529 through a membrane deposited at 270°C. From the kinetic diameter of SF6 (0.55 nm), the pore size of membranes was estimated as 0.4–0.5 nm. Thus, the pore size of the membranes increased with increasing the deposition temperature up to 270°C. SF6 permeances were proportional to total fluxes of pervaporation (PV) tests. This can be explained by the similar kinetic diameters of benzene (0.58 nm) and SF6. The maximum benzene selectivity over cyclohexane was 113 with the total flux of 2.2×10-4 kg m-2 h-1 through the membrane deposited at 320°C at an O3 flow rate of 0.4 L min-1.