Carbonylation of methanol and ethanol on a rhodium–zeolite catalyst

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Abstract
The carbonylation of methanol and ethanol on a rhodium-X zeolite has been studied. Particular emphasis has been placed on the effect of the concentration of the required alkyl iodide “promoter” on the selectivity of the reaction. A maximum in selectivity for carbonylation is observed for both alcohols as the alkyl iodide content of the reactant stream is increased. The side products are dimethyl ether and ethylene with methanol and ethanol respectively. Some comparative experiments with either rhodium-on-carbon or the unmodified NaX support show that at least for ethanol the zeolite support offers a sufficiently high activity to account for the rate of formation of side product under carbonylation conditions.For methanol carbonylation the necessity to employ near-stoichiometric quantities of methyl iodide and the effects which the absence of “promoter” has on catalyst behaviour are discussed.Comparison between the action of rhodium catalysts in homogeneous and heterogenised forms leads to the conclusion that close similarities in behaviour exist, probably due to the operation of a common mechanism.

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