Method for increasing propylene oxide output of an integrated process for making propylene oxide and propylene glycol

A method for increasing propylene oxide output of an existing integrated process for making propylene oxide and propylene glycol, said integrated process comprising

• a) reacting propene with an oxidant to provide the propylene oxide,
• b) reacting a fraction of the propylene oxide provided in a) with water to provide an aqueous glycol solution comprising monopropylene glycol and dipropylene glycol, and
• c) separating the monopropylene glycol and the dipropylene glycol from said aqueous glycol solution by a multi-step distillation,
• said method comprising:
• d) reacting propene and hydrogen peroxide in the presence of a catalyst mixture, comprising a phase transfer catalyst and a heteropolytungstate, in a liquid reaction mixture comprising an aqueous phase with a maximum apparent pH of 6 and an organic phase, wherein apparent pH refers to a value determined by measurement with a glass electrode employing a commercial pH meter calibrated with aqueous buffer solution of known pH for measuring dilute aqueous solutions, and
• e) separating the liquid reaction mixture provided by d) into a further organic phase, which is recycled to d), and a further aqueous phase comprising monopropylene glycol and dipropylene glycol, which is passed to c),
• wherein said further aqueous phase provided by e) replaces the aqueous glycol solution provided by b), and at the same time reduces a fraction of the propylene oxide passed from a) to b) to lower an output of the aqueous glycol solution from b).