Ethylene oxide oxidation over a supported silver catalyst: I. Kinetics of uninhibited oxidation

Abstract

The kinetics of the complete oxidation of ethylene oxide over a supported silver catalyst in the absence of dichloroethane was studied by the flow circulation method. The temperature range 100–300°C was investigated under steady-state conditions and at atmospheric pressure. The kinetic measurements showed that ethylene oxide oxidation starts at 190°C. Below this temperature, the ethene oxidation over a silver catalyst proceeds according to the parallel reaction scheme. At 300°C and an oxygen: ethylene oxide feed ratio of 1:2 catalytic decomposition of ethylene oxide to ethene and oxygen was observed. A sequential experimental design was applied for the determination of the parameters and the simultaneous discrimination of rival kinetic models. A kinetic model is proposed that describes the rate of uninhibited ethylene oxide oxidation in the temperature range 250–300°C. The model corresponds to a mechanism in which ethylene oxide and oxygen adsorption (dissociative and non-dissociative) are fast steps at equilibrium. The rate-limiting steps are ethylene oxide oxidation to formaldehyde and further to carbon dioxide and water with the participation of both atomic and molecular adsorbed oxygen. These steps are irreversible. The calculated kinetic constants offer the possibility of evaluating tentatively the rate constants of the irreversible steps and the equilibrium constants of the fast reversible steps.