Improvement of ethylene epoxidation in low-temperature corona discharge by separate ethylene/oxygen feed

•The ethylene epoxidation performance was improved by separate ethylene/oxygen feed.•The effects of C2H4 feed position and operational parameters were studied.•The C2H4 feed position of 2 mm provided high EO yield with low power consumption.•The separate feed exhibited higher activity, as compared to the mixed feed.

In this work, the ethylene epoxidation performance in a low-temperature corona discharge system was improved by initially producing oxygen free radicals prior to the reaction with unactivated ethylene molecules, in which the ethylene was separately fed into the system at various feed positions of the plasma zone. In addition, various operating parameters, including O2/C2H4 feed molar ratio, applied voltage, input frequency, total feed flow rate, and gap distance between pin and plate electrodes, were optimized for the separate feed system. The highest ethylene oxide (EO) yield was achieved under the operating conditions of a C2H4 feed position of 0.2 cm, an O2/C2H4 feed molar ratio of 1:2, an applied voltage of 18 kV, an input frequency of 500 Hz, a total feed flow rate of 100 cm3/min, and an electrode gap distance of 10 mm. In comparisons between the separate feed and the mixed feed of C2H4 and O2 under their own optimum conditions, the separate feed provided higher EO selectivity and yield with lower undesired product selectivities and lower power consumption, as compared to the mixed feed. The results confirm that the separate feed with a suitable C2H4 feed position has sufficient reaction time with minimum ethylene molecules to be activated which, in turn, can reduce all undesired reactions including cracking, dehydrogenation, hydrogenation, combustion, and coupling reactions of ethylene, resulting in superior ethylene epoxidation performance.