A cyclic reactor study of ethylene epoxidation

Abstract

A modified cyclic reactor has been used to investigate the mechanism of ethylene epoxidation on a high activity silver catalyst and on a commercial silver catalyst. This periodic pulse reactor allows on line G.C. analysis of the reactor effluent at any chosen time interval from the beginning of the cycle. Three kinds of oxygen species on the silver surface can be postulated. Without inhibition with chlorine an atomic species is formed even at low temperatures and short oxygen pulses; during the C 2H 4 pulse this atomic oxygen is transformed essentially into combustion products or adsorbed byproducts. With the high activity catalyst in the absence of chlorine, but after a high temperature (180°C) long oxygen pulse the atomic oxygen and a molecular oxygen species coexist on the silver surface. This molecular oxygen cannot be desorbed by a N 2 pulse and has a fairly good selectivity for epoxidation. Another molecular oxygen species is also formed, either with the high activity catalyst or the commercial catalyst, in the presence of chlorine; this molecular oxygen is desorbable by nitrogen. Its selectivity for ethylene epoxidation is very high and no adsorbed byproduct is left on the silver surface at the end of the C 2H 4 pulse. In these conditions, with the commercial catalyst a 94% selectivity in ethylene oxide is obtained.