SynopsisIn recent years polymers have been utilized as binding sites for transition metal catalysts (e.g. crosslinked polystyrene beads). However, general problems exist with the above system. The rate of reaction depends on the presence of solvents that adequately swell the polystyrene bead in order to allow access to the catalyst sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed where the catalyst is bound to polyethylene single crystal surfaces, this has solved the above problems. However, polyethylene single crystals are small and plate-like causing a new problem, when trying to filter the separate product the crystals cause clogging of the filtering system and limit the reactions to batch process. This paper describes the use of fine microporous polyethylene hollow fibers as the supporting polymer. This gives the advantages of the single crystal support, plus allows for the use of a fixed-bed flow reaction system.
INTRODUCTIONCommercial processes based on homogeneously catalyzed routes are becoming increasingly important. However, these processes can exhibit problems of product contamination and catalyst loss, where products are not readily separated from catalyst. In recent years several attempts have been made to combine the advantages of homogeneous and heterogeneous catalysis.' Anchoring homogeneous catalysts to polymers or other supports effectively " heterogenizes" them, allowing their use in " fixed-bed" type reactions and simplifying catalyst recovery. Thus the problems associated with anchoring homogeneous catalysts has recently been the object of much r e s e a r~h .~,~The most commonly used polymer for supporting catalysts has been crosslinked polystyrene (PS) beads.'-Although PS-supported catalysts show many advantages over homogeneous catalysts, various problems associated with the system have prevented it from being used on an industrial scale. For example, the rate of reaction depends on the presence of solvents that adequately swell the polystyrene beads in order to allow access to the catalytic sites (in the *Author to whom inquiries should be addressed. In the chemical industry large scale processes are typically carried out using a fixed-bed flow reaction process. In this case, reactants can continually flow over a supported catalyst where the reaction takes place. The main advantage of this system over that of the previously mentioned PS or PE-supported catalysts is that a continuous reaction process is maintained. It is not necessary to completely stop the reaction in order to remove the products, instead the product is removed with the flow of the reaction.A new polymer support has been developed that shows potential for use in a fixed-bed flow reaction system. Fine microporous polyethylene hollow fibers (EHF) manufactured by Mitsubishi Rayon Co. have a very high porosity (approx. 60%) and a very small outer diameter (approx. 400 pm).' Wilkinson's catalyst has been bound to these polyethylene hollow fibers. Onc...
