Method for the preparation of 1,2-propanediol

A method for the preparation of 1,2-propanediol, comprising:

• a) reacting propene with 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 comprising a solvent(S) having a solubility in water at 20° C. of less than 500 mg/kg, wherein apparent pH refers to a value determined by measurement with a glass electrode employing a commercial pH meter calibrated with aqueous buffer solutions of known pH for measuring dilute aqueous solutions;
• b) separating the liquid reaction mixture of a) into an aqueous phase (Pa) comprising 1,2-propanediol and an organic phase (Po);
• c) recycling at least a part of the organic phase (Po) to a);
• d extracting the aqueous phase (Pa) with an extractant solution comprising the same phase transfer catalyst and the same solvent(S) as used in a), to provide an extracted aqueous phase (Pac) and an extract phase (Pe) comprising a salt of the phase transfer catalyst and a heteropolytungstate or tungstate;
• e) recycling at least a part of the extract phase (Pe) to a);
• and
• f) recovering the 1,2-propanediol from the extracted aqueous phase (Pae).