Vapor permeation characteristics of TiO₂ composite membranes prepared on porous stainless steel support by sol-gel method

Composite membranes with a titania layer were prepared by soaking-rolling method with the titania sol of nanoparticles formed in the sol-gel process and investigated regarding the vapor permeation of various organic mixtures. The support modification was conducted by pressing SiO₂ xerogel of 500 nm in particle size under 10 MPa on the surface of a porous stainless steel (SUS) substrate and designed the multi-layered structure by coating the intermediate layer of γ-Al₂O₃. Microstructure of titania membrane was affected by heat-treatment and synthesis conditions of precursor sol, and titania formed at calcination temperature of 300 °C with sol of [H ⁺]/[TIP]=0.3 possessed surface area of 210 m²/g, average pore size of 1.25 nm. The titania composite membrane showed high H ₂/N₂ selectivity and water/ethanol selectivity as 25-30 and 50-100, respectively. As a result of vapor permeation for water-alcohol and alcohol-alcohol mixture, titania composite membrane showed water-permselective and molecular-sieve permeation behavior. However, water/methanol selectivity of the membrane was very low because of chemical affinity of permeants for the membrane by similar physicochemical properties of water and methanol.