DIRECT EPOXIDATION OF ETHYLENE IN A DILUTE REACTION STREAM IN OXIDATIVE COUPLING OF METHANE

The direct epoxidation of ethylene as a product of oxidative coupling of methane (OCM) was studied over supported silver catalysts promoted with Ba, K, Cs and Cl. The effects of by-products of OCM on the epoxidation of ethylene were separately investigated at typical operating conditions (reaction temperature 280-degrees-C; C2H4/O2 ratio 1.67; GHSV 2500 h-1). When carbon monoxide added to feed was completely oxidized, ethylene epoxidation was not affected. However, when carbon monoxide was not completely oxidized, the conversion of ethylene decreased significantly owing to deposited carbonaceous material. The selectivity to ethylene oxide decreased and ethylene conversion increased gradually as a function of time in the presence of 2.1 vol.-% H2. This effect is due to a rapid stripping of the chlorine with which the catalysts were impregnated. The effect of hydrogen can be eliminated by adding ppm levels of 1,2-dichloroethane (DCE) to the feed stream. Both hydrogen and carbon monoxide were oxidized much faster than ethylene over the silver catalyst. The inhibiting effect of carbon dioxide on ethylene epoxidation was observed when carbon dioxide concentration in the feed was higher than 7 vol.-%. When hydrogen, carbon monoxide, methane and ppm levels of 1,2-dichloroethane were included in the feed, their combined effects on ethylene epoxidation matched the individual effects. All these results show that it is possible to epoxidize ethylene to ethylene oxide in the effluent gas of OCM without separation.