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 O-2/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 O-2/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 cm(3)/min, and an electrode gap distance of 10 mm. In comparisons between the separate feed and the mixed feed of C2H4 and O-2 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. (C) 2013 Elsevier B.V. All rights reserved.