MODELING OF THE INHIBITING EFFECT OF CARBON-DIOXIDE ON THE SELECTIVE OXIDATION OF ETHENE OVER SILVER CATALYST

The inhibiting effect of high feed carbon dioxide concentrations (12-33%) on ethene epoxidation and combustion reactions over Ag/Al2O3 catalyst was studied by the flow-circulation method. Kinetic measurements have been carried out under steady-state conditions, at atmospheric pressure and in the temperature range 483-565 K. It has been established that the feed carbon dioxide inhibits considerably both the epoxidation and the combustion of ethene, the effect on the latter being stronger. Therefore, the presence of carbon dioxide in the feed affects the selectivity favourably. The inhibiting effect is described quantitatively by a kinetic model consisting of two rate equations, one for the epoxidation and the other for the combustion reactions. The model is to be used when the carbon dioxide concentration in the reaction mixture is higher than 10% and the temperature is in the range 513-565 K. The model is empirical and it is compared with a mechanistic model derived on the basis of the assumed reaction mechanism. The empirical model fits the experimental results better. © 1990.