Abstract
The selective oxidation of ethylene over supported silver catalyst was studied in the presence of 0.2–16% feed water vapour. In addition to silver, alumina and silica, the catalyst also contains Li, Na, K, Mg, Ca, Ba, Mn and Fe additives in trace amounts. Steady-state kinetic measurements were carried out using a glass flow-circulation system at atmospheric pressure and in the temperature range 210–264°C, varying the oxygen-to-ethylene concentration ratio in the feed. The results show that the partial oxidation of ethylene is inhibited by the presence of feed water but the complete oxidation is promoted by it. This result contradicts the results of other workers. The reason for this contradiction is probably the presence of the additives in the studied catalyst. The effect of water is stronger at low feed concentrations (0.2–1.4%), at which the process is carried out in the industrial reactor. This fact could be of great importance for selecting the optimum conditions for the industrial process. The presence of feed water has an unfavourable effect on the selectivity for ethylene oxide, unlike the effect of carbon dioxide in the feed established in previous work over the same catalyst. An explanation of the effect of water vapour on the oxidation of ethylene is proposed on the basis of the assumed reaction mechanism.
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