Deposition of sol–gel derived membranes on α-Al2O3 hollow fibers by a vacuum-assisted dip-coating process

A vacuum-assisted dip-coating process has been developed for the deposition of sol–gel derived membranes on thin-walled ceramic hollow fibers. A vacuum is applied on the opposite side of the membrane layer during dipping. Homogeneous γ-Al2O3 and Pd-γ-Al2O3 membranes have been obtained in this way. The membranes are proved to be suitable for H2 enrichment, because the gas transport is mainly controlled by Knudsen diffusion. The obtained asymmetric γ-Al2O3/α-Al2O3 and Pd-γ-Al2O3/α-Al2O3 fibers can further serve as substrates for very thin dense Pd membranes. These asymmetric membranes combine the high ratio of membrane area-to-volume of hollow fibers with the well known advantages of ceramic supports, namely good mechanical, thermal and chemical stability, which are attractive for gas separation and membrane catalysis at elevated temperatures.