INFLUENCE OF REACTION-PRODUCTS ON THE SELECTIVE OXIDATION OF ETHENE

The kinetics of the selective oxidation of ethene in air over an indus trial silver on a-alumina catalyst were studied. Special attention was paid to the influence of the reaction products on the reaction rates of epoxidation and complete combustion. Kinetic data were obtained in two different types of internal recycle reactor and in a cooled tubula r reactor, and were fitted separately to several reaction rate express ions based on different kinetic models. A Langmuir-Hinshelwood mechani sm, in which adsorbed ethene reacts with adsorbed molecular oxygen, wa s chosen as the best kinetic model. The reaction products compete for adsorption on the active sites and reduce the rates of both reactions. Carbon dioxide enhances the selectivity towards ethene oxide, whereas water has almost no influence on the selectivity. The fitting of the three individual data sets obtained in the three reactors results in a ccurate, but different, reaction rate expressions, whereas the fitting of the three data sets simultaneously results in less accurate reacti on rate expressions. The systematic deviations found may be explained, to some extent, by differences in the operating regimes in each react or. The main reason for the deviations is probably the different catal yst activities in the three reactors caused by poisoning. The effect o f the addition of products to the feed on the behaviour of the cooled tubular reactor can be described reasonably well by a mathematical mod el in which the kinetic equations obtained in the laboratory reactors are incorporated. The results of these simulations are sensitive to th e kinetics used.