Determination of an optimum entrainer for extractive distillation based on an isovolatility curve at different pressures

The selection of a proper entrainer is a key factor affecting the feasibility of extractive distillation. Presently, we simply compare the relative volatility based on the same pressure to select the entrainer. In this work, we found that the separation effect on entrainers was impacted by pressure to a different extent. Two binary azeotropic systems, ethanol-benzene and ethanol-ethyl acetate, were used to demonstrate the entrainer selection based on an isovolatility curve at different pressures. The results indicated that ethanol-benzene with 1,2-propanediolas an entrainer can save 7.42% of the total annual cost compared to ethanol-benzene with p-xylene as an entrainer at atmospheric conditions, but after the pressure was considered, the ethanol-benzene-p-xylene system can save a 9.17% total annual cost compared to the ethanol-benzene-1,2-propanediol system. The relationship between pressure and total annual cost was nonlinear, and there was a minimum total annual cost at the corresponding pressure. Similar to the ethanol-benzene system, the above situation also existed in the ethanol-ethyl acetate system. The change in the isovolatility curve with the change in pressure shows different trends, and the change in pressure results in a change in the selection of the entrainer. The results provide more insight for the choice of an entrainer in extractive distillation.