Process for Epoxidizing Propene

A process for the epoxidation of propene, comprising

• (a) reacting propene with hydrogen peroxide in the presence of methanol as solvent and a titanium zeolite catalyst and separating propylene oxide from the resulting reaction mixture to obtain a mixture (Ma) comprising methanol, water, at least one carboxylic acid having from 1 to 3 carbon atoms and at least one carbonyl compound having from 1 to 3 carbon atoms, wherein the carbonyl compound is an aldehyde or a ketone;
• (b) at least partially neutralizing the at least one carboxylic acid comprised in mixture (Ma) by adding a base to mixture (Ma) to obtain a mixture (Mb);
• (c) separating methanol from mixture (Mb) by distillation;
• (d) at least partially recycling the methanol obtained from (c) into (a).

A process for the epoxidation of propene, comprising

• (a) reacting propene with hydrogen peroxide in the presence of methanol as solvent and a titanium zeolite catalyst and separating propylene oxide from the resulting reaction mixture to obtain a mixture (Ma) comprising from 55 to 85 wt % methanol, from 10 to 40 wt % water, from 0.001 to 0.5 wt % of at least one carboxylic acid having from 1 to 3 carbon atoms and from wherein the at least one carboxylic acid is selected from the group consisting of formic acid, acetic acid, propionic acid, and a mixture of two or more thereof, and wherein the at least one carbonyl compound is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, and a mixture of two or more thereof;
• said mixture (Ma) further comprising from 0.1 to 1 wt % of 2-hydroperoxypropanol-1,1-hydroperoxypropanol-2 or a mixture of 2-hydroperoxy-propanol-1 and 1-hydroperoxypropanol-2;
• and
• subjecting mixture (Ma) to catalytic hydrogenation at a temperature of from 65 to 85° C. and at a hydrogen partial pressure of from 3 to 20 barz to give a mixture comprising from 0.1 to 1.3 wt % 1,2-dihydroxypropane, the hydrogenation catalyst comprising a catalytically active metal selected from the group consisting of Pd, Pt, Rh, Ir, Os and a mixture of two or more thereof;
• (b) at least partially neutralizing the at least one carboxylic acid comprised in the mixture obtained from catalytic hydrogenation by adding an aqueous solution comprising hydroxide ions to this mixture to obtain a mixture (Mb) which contains at least one compound having a boiling temperature lower than methanol and lower than water and which is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, methyl formate, formaldehyde dimethyl acetal, acetaldehyde dimethyl acetal, and a mixture of two or more thereof at a given pressure, wherein the molar ratio of hydroxide ions introduced relative to carboxylic acid comprised in the mixture obtained from catalytic hydrogenation is from 0.1 to 10;
• (c) separating methanol from mixture (Mb) by
• (c1) separating the at least one compound having a boiling temperature lower than methanol and lower than water from mixture (Mb) by distillation at a distillation pressure of from 0.5 to 2 bar to obtain a mixture (Mb1) and a mixture (Mb2), wherein mixture (Mb1) comprises from 40 to 85 wt % methanol and from 10 to 55 wt % water and at most 0.1 wt % of the at least one compound having a boiling point lower than methanol and water, and wherein mixture (Mb2) comprises from 5 to 50 wt % of the at least
• (c2) separating methanol from mixture (Mb1) in at least one distillation stage to obtain a mixture (Mc2i) comprising at least 85 wt % of methanol, up to 10 wt % of water and 200 ppm or less of carbonyl compounds, and a mixture (Mc2ii) comprising 1,2-dihydroxypropane and at least 90 wt % of water,
• (d) at least partially recycling the methanol obtained from (c2) into (a), the methanol comprising not more than 200 ppm of carbonyl compounds,
• (e) separating 1,2-dihydroxypropane from mixture (Mc2ii).