Patent ID: 8197645

Claim:
A process for separating at least one propylene glycol from a mixture (M) comprising water and said propylene glycol, said process comprising (I) evaporating the mixture in at least two evaporation and/or distillation stages at decreasing operating pressures of the evaporators and/or distillation columns obtaining mixture (M′) comprising 80 to 99.9 wt.-% of water and 2.5 to 15 wt.-% of propylene glycol and mixture (M″) comprising 90 to 99.99 wt.-% of water and 0.01 to 0.5 wt.-% of propylene glycol, wherein mixture (M″) is further separated into mixture (M-Ia) comprising at least 90 wt.-% of water and mixture (M-Ib) comprising less than 95 wt.-% of water by subjecting mixture (M″) to reverse osmosis; and (II) separating the mixture (M′) obtained in (I) in at least one further distillation step, obtaining a mixture (M-I) comprising at least 70 wt.-% of water and a mixture (M-II) comprising less than 30 wt.-% of water.