Utilization of ethylene in the product streams of oxidative coupling of methane for the production of ethylene oxide over supported silver catalysts

The epoxidation of ethylene over supported silver catalysts promoted with Ba, Cs and Cl in the presence of added hydrogen, carbon monoxide, carbon dioxide and methane was studied as a possible method for directly using ethylene in the product streams from the oxidative coupling of methane(OCM). Under conditions of moderate ethylene conversion(ca. 40%, at280°C), ethylene epoxidation was not affected when carbon monoxide in the streams was completely oxidized. However, either ethylene conversion, selectivity to ethylene oxide(EO) or carbon monoxide conversion was affected significantly when carbon monoxide was incompletely oxidized owing to carbon deposited on the catalyst surface. Selectivity to ethylene oxide decreased while ethylene conversion increased gradually when hydrogen was added to the stream. The effect was due to rapidly stripping of chlorine impregnated in the catalysts by hydrogen. The effect of hydrogen could be avoided by adding 5.6ppm 1,2-dichloroethane to the streams. Both hydrogen and carbon monoxide were oxidized much faster than ethylene over the supported silver catalysts. The inhibiting effect of carbon dioxide on epoxidation of ethylene was serious when the amount of carbon dioxide was beyond 2.6% in the streams. The combined effect of adding together hydrogen, carbon monoxide and methane and dichloroethane at ppm level to the streams was the same as that caused by separate addition of these substances.