THE SOL-GEL APPROACH TO PREPARE CANDIDATE MICROPOROUS INORGANIC MEMBRANES FOR MEMBRANE REACTORS

In catalytic membrane reactors, the membrane can play a multiple role such as promotion of an integrated catalytic reaction but also partitioning of the reactants and separation of the products. For these applications permselective membranes may be used that can work at high temperature (gas or liquid phase), in organic solvents or in contact with biomass. One type of possible membranes are the ceramic membranes which exhibit a connected microporosity. This kind of membrane can at present be made using the latest developments in sol-gel processing. We used this process to prepare various microporous ceramic membranes in aqueous media: ZrO2, Al2O3, LaOCl; and in organic media: SiO2, ZrO2. Attention has been paid to the microstructure of these membranes in order to identify the main parameters governing the evolution of these membrane materials during their preparation. The main feature of these membranes is the presence of non-aggregated nanosized particles after calcination. A peptization reaction and/or a chemical modification of the precursors has been shown to be of prime interest in the control of the precursor reactivity and in limiting the condensation rate so as to avoid inhomogeneous and rough products. Non-aggregated ceramic particles down to 4 nm in size can thus be obtained and result in microporous membrane formation.