Abstract: The invention relates to a process for preparing an alkylene oxide, which process comprises: (a) oxidizing of an organic compound to obtain reaction product containing organic hydroperoxide; (b) washing at least part of the organic hydroperoxide containing reaction product with a basic aqueous solution; (c) separating the mixture obtained in step (b) into a hydrocarbonaceous phase and an aqueous phase; (d) washing at least part of the hydrocarbonaceous phase obtained in step (c) with water; (e) separating the mixture obtained in step (d) into a hydrocarbonaceous phase and an aqueous phase; and, (f) contacting at least part of the hydrocarbonaceous phase obtained in step (e) with an alkene and catalyst to obtain an alkylene oxide, in which process the separation of hydrocarbonaceous phase and aqueous phase of step (c) and/or (e) is carried out with the help of a coalescer containing polypropylene fibers.