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;
• b) separating the liquid reaction mixture into a separated aqueous phase (Pa) comprising 1,2-propanediol and a separated organic phase (Po);
• c) recycling at least a part of the separated organic phase (Po) to a);
• and
• d) recovering the 1,2-propanediol from the separated aqueous phase (Pa);
• wherein in d), the 1,2-propanediol is separated from the separated aqueous phase (Pa) by distillation and an apparent pH of the separated aqueous phase (Pa) is adjusted to a value of at least 9 prior to the distillation, and
• wherein apparent pH is 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.