Separation of a Close-Boiling 1,2-Propanediol and Ethylene Glycol Mixture Using Pressure-Related Distillation
Cong Duan, Chunli Li, Hao Li
Abstract
Separation of 1,2-propanediol and ethylene glycol consumes much energy due to their close-boiling points and low relative volatility. By analyzing the influence of pressure on the vapor–liquid equilibrium of the system, it is found that high pressures facilitate the separation. Therefore, a high-pressure distillation process is proposed. For further energy saving, a pressure swing thermally coupled distillation method is used, which divides a distillation column into two columns with different pressures. Therefore, the condenser of the high-pressure column could serve as a reboiler of the low-pressure column. Further energy-saving methods via heat integration are proposed. A pressure swing thermally coupled distillation process with heat integration is finally obtained, which ultimately saves all the steam and only adds a little electricity. As a result, a 80.9% reduction of the energy consumption and a 35.5% reduction of the total annual cost are achieved compared with the single-column distillation at 101.3 kPa.