A continuous process for preparing ethylene oxide

A continuous process for preparing ethylene oxide in the presence of an activated heterogeneous silver catalyst, the process comprising feeding ethylene, at least one chlorinated moderator and at least one saturated hydrocarbon into an epoxidation reactor containing said catalyst, wherein the process further comprises

• (a) defining a target range of the work rate of the catalyst;
• (b) adjusting at least one of the ethylene feed rate and the reactor temperature to realize a work rate of the catalyst in the range defined according to (a);
• (c) adjusting the reactor inlet concentration of the at least one chlorinated moderator to maintain a factor F in the range of from 0.7×Ft to 1.3×F;
• wherein the factor F is a function of
• (i) the reactor inlet concentration of the at least one chlorinated moderator;
• (ii) the reactor inlet concentration of ethylene;
• (iii) the reactor inlet concentration of the at least one saturated hydrocarbon;
• (iv) the reactor temperature;
• wherein Ft is a target value of the factor F and defines a set of process conditions at which optimum ethylene oxide selectivity is achieved, namely when the set of process conditions (i) to (iv) is such that optimum ethylene oxide selectivity is achieved.