Engineering aspects of the aqueous noble metal catalysed alcohol oxidation

The aqueous noble metal catalysed alcohol oxidation is a reaction which can profitably be applied in fine-chemistry and for carbohydrate conversion. I n this paper engineering aspects of this reaction are treated, i.e. the rea ction kinetics, oxygen mass transfer restrictions, catalyst deactivation an d reactivation, and implications for reactor design and operation. First a reaction mechanism is proposed, which is very helpful for understan ding the observed phenomena. Also a short summary is given on catalyst deac tivation mechanisms. Two different reaction regimes can clearly be distinguished: the oxygen mas s transfer limited regime and the intrinsic kinetic regime, which are treat ed separately Oxidations using noble metal catalysts promoted with less nob le metals, like Pb, Pi, generally fall in the first regime, those using unp romoted noble metals in the second. Reaction rate data are evaluated for th e Pd/Bi catalysed oxidation of glucose and the Pt catalysed oxidation of me thyl-glucoside, respectively, illustrating the typical kinetic behaviour in both regimes. From oxidation kinetics in the mass transfer limited regime, it is conclude d that adherence of catalyst particles to the gas-liquid interface, is a ma jor factor determining reaction kinetics. Oxygen transfer, direct from the gas to the catalyst particle, is likely. For the Pt catalysed oxidation, a kinetic model is presented for catalyst deactivation by over-oxidation and for catalyst reactivation. Finally specific reactor options and suggestions for future engineering res earch are given: slurry catalyst versus fixed bed catalyst operation, avoid ance of explosion risks, redox cycle reactors, electrochemical reactors, an d multi-functional reactors. (C) 2000 Elsevier Science B.V. All rights rese rved.