A process is provided for the start-up of an ethylene epoxidation process comprising: (a) contacting a catalyst bed comprising a high selectivity epoxidation catalyst with a feed comprising ethylene, oxygen and an organic chloride for a period of time until an increase of at least 1×105 mole-% of vinyl chloride (calculated as the moles of vinyl chloride relative to the total gas mixture), preferably 2×105 mole-% of vinyl chloride is detected in a reactor outlet gas or a recycle gas loop; and (b) subsequently adjusting the quantity of organic chloride in the feed to a value sufficient to produce ethylene oxide at a substantially optimum selectivity.
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