Abstract:

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.

Key words: extractive distillation, compound solvents, azeotrope, phase equilibria, separation

摘要：

提出按溶剂之间复配形成氢键的情况和修正的UNIFAC模型相结合的方法选择分离共沸体系的萃取精馏复合溶剂。准确测量了共沸体系与萃取精馏单溶剂和复合溶剂的汽液平衡数据，结果表明采用的萃取精馏单溶剂和复合溶剂的选择方法具有较好的准确度，模拟值与实验值比较，相对偏差均小于9%。通过综合比较得到分离乙酸乙酯-乙醇、乙醇-水和环己烷-苯3个共沸体系的最佳复合溶剂及配比。在最佳复合溶剂组成下，原共沸体系的相对挥发度达到最大值，该值优于组成复合溶剂的单溶剂所达到的分离效果。在最佳复合溶剂组成下，改变原料体系组成，复合溶剂组成对原料体系相对挥发度的影响趋势基本相同，这表明复合溶剂在萃取精馏塔内不同原料组成下均能较好地增加体系的相对挥发度，为工业上在萃取精馏过程中使用复合溶剂提供了理论依据。

关键词: 萃取精馏, 复合溶剂, 共沸(混合)物, 相平衡, 分离