Abstract: In the process of producing ethyl formate with formic acid and ethanol as raw materials, the unreacted ethanol and ethyl formate will form an azeotrope, which is difficult to separate. In this work, the method of extractive distillation is used to separate the ethyl formate-ethanol azeotrope system with the ionic liquid as an extractant. The ionic liquid is screened by the COSMO-RS model, and the ionic liquid is determined to be 1-ethyl-3-methylimidazole diethyl phosphate ([EMIM][DEP]) and 1-butyl-3-methylimidazole diethyl phosphate ([BMIM][DEP]). The vapor-liquid equilibrium (VLE) data of the ethyl formate+ethanol binary system and the ethyl formate+ethanol+ ionic liquid ternary system are determined, and the experimental data are correlated with the NRTL model. Finally, the separation mechanism is explored by excess enthalpy analysis and σ-profile analysis (probability distribution of surface charge density). The results show that the relative volatility of ethyl formate increases with the increase in the molar fraction of two ionic liquids (ILs). When the ionic liquid concentration is 0.030, the relative volatility of ethyl formate to ethanol is greater than 1, and it can be seen that the separation effect of [EMIM][DEP] is better than that of [BMIM][DEP] ionic liquid. Through excessive enthalpy analysis, it is found that hydrogen bonds and van der Waals forces are more easily formed between ionic liquid and ethanol molecules, and the interaction between molecules is stronger than that between ionic liquid and ethyl formate, which promotes the separation of ethyl formate and ethanol. With the increase in ionic liquid concentration, the interaction between molecules is enhanced. Finally, the σ-profile analysis shows that ionic liquid is more inclined to interact with ethanol to separate ethyl formate, and it can be concluded that the shorter the cationic carbon chain of ionic liquid, the better the separation effect.

Key words: Alcohol ester separation, Extractive distillation, Ionic liquid, COSMO-RS, NRTL model

摘要： 以甲酸和乙醇为原料生产甲酸乙酯的过程中，未反应的乙醇与甲酸乙酯会形成共沸物，难以分离，本工作通过萃取精馏的方法，以离子液体作为萃取剂分离甲酸乙酯-乙醇共沸体系。通过COSMO-RS模型筛选离子液体，确定离子液体为1-乙基-3-甲基咪唑磷酸二乙酯([EMIM][DEP])和1-丁基-3-甲基咪唑磷酸二乙酯([BMIM][DEP])，测定了甲酸乙酯+乙醇二元体系以及甲酸乙酯+乙醇+离子液体三元体系的气液相平衡(VLE)数据，并将实验数据与非随机双液体(NRTL)模型方程关联。最后，通过过量焓分析和σ-profile分析(表面电荷密度为σ的概率分布)探究了分离机理。结果表明，两种离子液体(ILs)摩尔分数越大，甲酸乙酯相对挥发度逐渐增强；在离子液体浓度为0.030时，甲酸乙酯对乙醇的相对挥发度大于1，同时可以看出[EMIM][DEP]的分离效果优于[BMIM][DEP]离子液体。通过过量焓分析得出离子液体与乙醇分子之间更易形成氢键与范德华力，其分子间相互作用强于离子液体与甲酸乙酯，从而促进甲酸乙酯与乙醇的分离；随着离子液体浓度的增加，分子间相互作用随之增强。最后，通过σ-profile分析得出离子液体更倾向于和乙醇相互作用，从而将甲酸乙酯分离出来，同时可以得出离子液体的阳离子碳链越短，分离效果越好。

关键词: 醇酯分离, 萃取精馏, 离子液体, COSMO-RS, NRTL模型