NEW CERAMIC BASED MEMBRANES FOR CATALYTIC MEMBRANE REACTORS - MEMBRANES MODIFIED BY COBALT COMPLEXES WITH 1,3-DIAZOLES

Modification of the surfaces of inorganic membranes which have the com position 70% Al2O3 + 30% ZrO2 stabilized by Y2O3 has been carried out. This was done by first reacting them with silica and then with gamma- aminopropyltriethoxysilane, cyanuric chloride (or diiododecene) and 1, 3-diazole (imidazole or histamine). It was found that the modification of membrane materials by disperse silica occurred only in the subsurf ace layer and this resulted in the microfiltration membrane acquiring ultrafiltration properties. The retentions of the silica-modified memb ranes with respect to dextrans of different molecular weights differed from those of the unmodified membranes. Heterogenized metal complexes of transition metals with 1,3-diazoles, grafted onto the membrane sur faces, were obtained. It was established that the cobalt metal complex es with I,3-diazoles had a deformed tetrahedral structure and it was o nly the nitrogen atoms of the grafted heterocycles of imidazole which were involved in the formation of four-coordinate metal complexes. The catalytic properties of the obtained membrane materials in the model reaction of the liquid-phase oxidation of cumene have been studied and the occurrence of a radical-chain process with the participation of t he catalytically active membranes has been established. The formation of radicals takes place due to the oxygenation of heterogenized metal complexes, according to the following reaction: O-2. Co(II)-->O-2(-). Co(III). The catalytic reaction of cumene oxidation proceeds with the participation of Co(III) catalysts according to a mechanism involving electron transfer. The synthesized catalytic membrane materials can be used for the processes of oxidation of organic compounds under mild c onditions. (C) 1998 Elsevier Science B.V. All rights reserved.