ETHYLENE OXIDATION ON SILVER CATALYSTS: EFFECT OF ETHYLENE OXIDE AND OF EXTERNAL TRANSFER LIMITATIONS

Abstract

Ethylene oxidation to ethylene oxide and to carbon dioxide over silver catalysts was studied in a CSTR. The effects of two factors on the catalyst performance were examined. The first was the presence of excess ethylene oxide in the feed. A kinetic model was introduced which assumed that ethylene and ethylene oxide compete for the same sites on the catalyst surface. This model provided reasonable quantitative agreement with kinetic and potentiometric measurements. The second factor that was studied was the presence of external heat and mass transfer limitations. It was found that such limitations cause a significant decrease of the selectivity to ethylene oxide. This decrease is a result of the temperature difference between the catalyst surface and the bulk of the gas phase and of the fact that the activation energy of ethylene combustion is greater than that of ethylene epoxidation. The contribution of other factors such as inhibition by CO₂ or possible incomplete mixing in the reactor is shown to be insignificant.