recycled to the reaction stage i a build up of methylformate and dimethoxymethane is not observed although these compounds are not or only to a lesser extent converted in the hydrogenation reaction under the above specified conditions without wishing to be bound by theory it is believed that hydrogenation removes peroxides which otherwise would react in subsequent working up stages forming methylformate dimethoxymethane and precursors to these compounds at the same time hydrogenation also removes said and or other precursors to methylformate and dimethoxymethane like formaldehyde and prevents them from being recycled to the reaction stage with the solvent consequently the present invention leads to a more effective and cost efficient epoxidation process since the operation cycle between regeneration cycles of the epoxidation catalyst can be considerably prolonged and to an improved product quality these advantages can be achieved by a relatively simple measure of a hydrogenation step moreover the hydrogenation step can be easily integrated into the work up procedure of the epoxidation product according to one embodiment of the present invention the reaction mixture is separated in a pre evaporator into an overhead product containing propene possibly propane propene oxide and solvent and into a bottom product containing solvent water non converted hydrogen peroxide higher boiling point by products such as for example propylene glycol and if a suspension method is used for the epoxidation step suspended titanium silicalite catalyst the pre evaporator preferably has at most only 5 theoretical separation steps and is designed so that the stripping section corresponds to a simple evaporation and the remaining separation effect is achieved in the rectification section the pre evaporator is operated at a reflux ratio of at most 1 5 and.