Process For Producing Propylene Oxide

The process for producing propylene oxide, comprising

• (I) reacting propene with hydrogen peroxide in the presence of a catalyst to give a mixture (GI) comprising of from 8 to 13 wt.-% of propylene oxide, of from 2 to 7 wt.-% of unreacted propene, of from 0.01 to 1 wt.-% of propane, and of from 0.02 to 0.5 wt.-% of oxygen;
• (II) separating propylene oxide from mixture (GI) to give a mixture (GII), optionally after an intermediate stage, comprising of from 85 to 90 wt.-% of propene, of from 5 to 10 wt.-% of propane, and of from 3 to 5 wt.-% of oxygen, in each case based on the total weight of the mixture (GII);
• (III) reducing the oxygen comprised in mixture (GII) at least partially by reaction with hydrogen in the presence of a catalyst comprising from 0.01 to 0.25 wt.-% of Sn and from 0.01 to 0.25 wt.-% of Pt supported on alpha-alumina, the catalyst further having an alkali metal content of not more than 0.001 wt.-% and an alkaline earth metal content of not more than 0.001 wt.-%, in each case based on the total weight of the alpha-alumina present in the catalyst, the alpha-alumina having a BET surface determined according to DIN 66131 in the range of from 7 to 11 m2/g and the weight ratio of Pt to Sn being in the range of from 1:2 to 1:0.5, mixture (GIII) having a preferred oxygen content of 150 ppm at most;
• (IV) separating propene from mixture (GIII) resulting from (III) and re-introducing the separated propene, having a preferred oxygen content of 10 ppm at most, into (I), wherein in (III), the reduction reaction is performed at a temperature in the range of from 260 to 350° C. and at a pressure in the range of from 10 to 20 bar, and wherein in (III), the hydrogen is added in an amount so that the molar ratio of hydrogen to oxygen is in the range of from 0.3:1 to 3.5:1.