Extractive distillation is an effective separation process to deal with the separation of close-boiling compounds and azeotropic systems. The selection of appropriate solvent is the key factor for feasibility and economy in extractive distillation. A new method of screening mixed solvent of extractive distillation was proposed

which was according to the situation of forming the hydrogen bond and modified UNFAC model. To take the polar systems (ethyl acetate-ethanol

ethanol-water) and non-polar system (cyclohexane-benzene) as examples

the appropriate mixed-solvents and the optimal proportion were sought out. The vapor-liquid equilibrium data of solvents (single-solvents and mixed-solvents) and azeotropic system were determined by modified Othmer kettle. The results showed that the calculated values were in good agreement with the experimental data and the relative error was less than 9%. By taking into the synthetical evaluation to the solvents

the optimal mixed solvents to separate ethyl acetate-ethanol

ethanol-water

and cyclohexane-benzene were obtained respectively. Under the action of optimal mixed-solvent

the relative volatility of feed components reached maximum which was higher than the value by using any single solvent. At different feed components the trend of volatility of feed components changed by a mixed solvent was almost the same

which indicated that the mixed solvent could improve the volatility of feed components in any tray of extractive distillation column efficiently.