Pervaporation separation of benzene/cyclohexane through silica hybrid membranes prepared by using a counter-diffusion CVD method

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.