【作者】 赵瑾；

【导师】 李春喜；

【作者基本信息】 北京化工大学 ， 化学工程， 2007， 博士

【摘要】 离子液体是近年来兴起的一种新型溶剂，其挥发性极低，与各类溶剂之间的相溶性可调变，并具有良好的热稳定性、化学稳定性和电解质特性，由于这些优点使其在化学反应和化工分离过程中具有重要的应用前景。要开发其在分离方面的应用，首先要解决相平衡数据缺失的问题。目前，离子液体的价格比传统分子溶剂贵得多，这在很大程度上限制了其工业化的进程。为了制备出低成本的离子液体，要求其制备产品的产率高，制备和分离过程简单。为此，以N-甲基咪唑和磷酸三烷基酯或卤代烷烃为原料，通过一步反应制备出阴离子为磷酸酯和卤素离子的离子液体：1，3二甲基咪唑磷酸二甲酯盐（[MMIM][DMP]）、1-乙基-3-甲基咪唑磷酸二乙酯盐（[EMIM][DEP]）、1-丁基-3-甲基咪唑磷酸二丁酯盐（[BMIM][DBP]）、溴化1-丁基-3-甲基咪唑（[BMIM][Br]）、氯化1-丁基-3-甲基咪唑（[BMIM][Cl]）。另外，为了与常规离子液体进行比较，还制备了1-丁基-3-甲基咪唑六氟磷酸盐（[BMIM][PF₆]）。磷酸酯类离子液体的制备和提纯方法简单，收率在90％以上，其价格只有常见离子液体的30～40％，生态环境毒性低，是一类具有重要应用前景的离子液体品种。因此，本文着重研究了这类离子液体对醇、水体系汽液相平衡的影响。采用CP-I型双循环汽液平衡釜测定了含离子液体：[MMIM][DMP]，[EMIM][DEP]，[BMIM][Cl]，[BMIM][Br]或[BMIM][PF₆]的乙醇-水体系的等压（101.32kPa）汽液相平衡数据，离子液体质量含量大约为10％到30％。汽相和液相中挥发性组分的组成采用色谱法直接测定，液相中离子液体的含量采用差重法确定。根据所测定的等压汽液平衡数据可得到如下结论：本研究所考察的所有离子液体均能提高乙醇的相对挥发度，随着离子液体含量的增加，乙醇-水体系的共沸现象逐渐消失。含[BMIM]⁺阳离子的离子液体对乙醇的盐析效应顺序为：[BMIM][Cl]＞[BMIM][Br]＞[BMIM][PF₆]。磷酸酯类离子液体对乙醇的盐析效应顺序为：[MMIM][DMP]＞[EMIM][DEP]。利用拟静态法测定了由离子液体[MMIM][DMP]，[EMIM][DEP]或[BMIM][DBP]以及水、乙醇和甲醇组成的9个二元体系和4个三元体系的蒸汽压数据。实验结果表明：含磷离子液体[MMIM][DMP]，[EMIM][DEP]和[BMIM][DBP]均能降低水、甲醇和乙醇的蒸汽压，但降低的程度取决于离子液体的种类及含量，这是由不同离子液体与溶剂之间亲和力的差异造成的。采用插值方法，计算了离子液体摩尔分数为0.05时，9个二元体系的蒸汽压数据，考察了在离子液体摩尔浓度相同的情况下，不同离子液体对溶剂蒸汽压的影响规律，结果表明：离子液体对水的蒸汽压的影响次序为，[MMIM][DMP]＞[EMIM][DEP]＞[BMIM][DBP]，而对甲醇和乙醇则正好相反。这说明在水中，离子液体的“离子”特性占主导，而在乙醇、甲醇等有机溶剂中，离子液体的“分子”特性占主导。采用传统的适用于非电解质溶液的NRTL模型关联了所测定的含离子液体二元体系的蒸汽压数据。结果表明，该模型对所有考察的二元体系蒸汽压关联的平均绝对相对偏差均小于2％，对9个二元体系的整体平均绝对相对偏差为0.89％。利用回归得到的二元NRTL参数预测了乙醇-水-[MMIM][DMP]体系的蒸汽压数据，预测结果的平均绝对相对偏差为2.8％。为了检验二元NRTL参数的可靠性及模型的适用性，计算了353.15K时水、甲醇和乙醇在离子液体[MMIM][DMP]中的无限稀释活度系数，预测结果与文献测定值具有较好的一致性。这说明NRTL模型可以用于含离子液体体系汽液平衡数据的关联和预测。根据三元体系蒸汽压数据，对离子液体-溶剂之间的NRTL参数进行了调整，在此基础上预测了320K下，离子液体质量含量为50％时，乙醇-甲醇-[MMIM][DMP]、乙醇-甲醇-[EMIM][DEP]、乙醇-甲醇-[BMIM][DBP]及乙醇-水-[MMIM][DMP]的等温汽液平衡数据。结果表明：①对于乙醇-甲醇体系，离子液体对乙醇的盐析效应遵循如下顺序：[EMIM][DEP]＞[MMIM][DMP]＞[BMIM][DBP]；②离子液体的加入使得甲醇由轻组分转变为重组分；③离子液体[MMIM][DMP]可以消除乙醇—水体系的共沸现象。综上所述，离子液体的加入有助于将乙醇中混杂的甲醇和水同时脱除。利用平均球近似（MSA）积分方程理论、微扰理论以及基团贡献的基本思想，本文建立了一个适用于含离子液体体系中溶剂活度系数计算的新的分子热力学模型。该模型分别采用平均球近似理论（MSA）考虑了体系中离子-离子之间的长程静电作用、采用微扰理论考虑了离子-偶极溶剂分子之间的中程静电作用，采用UNIFAC基团贡献模型考虑了所有溶液基团（包含离子液体和溶剂组分的基团）之间的短程（主要为色散和诱导等）相互作用对体系的影响，并得到了溶剂组分化学位和活度系数的表达式。检验计算表明，新构建的模型对于含离子液体二元体系的蒸汽压数据具有较高的关联精度。另外，利用关联结果，分析了上述三种作用对溶剂活度系数的贡献随温度和溶液组成的变化规律，这为进一步完善模型奠定了基础。更多还原

【Abstract】 Ionic liquids （ILs） as a new kind of solvent have many unique attributes, e.g. negligible vapor pressure, tunable solubility for both polar and non-polar substances, good thermal and chemical stability and electrolytic property, which make them attractive and potential being used as a benign medium and/or solvent in chemical reaction and separation processes. In order to promote their industrial applications in separation processes, phase equilibrium data for IL-containing systems is of vital importance, however, which is extremely scarce heretofore. Toward this end, vapor-liquid equilibrium （VLE） data were measured and their modeling work was carried out in this paper.At present, the price of ILs is extremely high in comparison with traditional molecular solvents, which to a large extent limits its commercialization. In order to reduce the price of ILs, it is required that the production and separation process is as simple as possible along with a high yield for the production process of ILs. Among various ILs known heretofore, the ILs with such anions as halides or alkylphosphates seem more competitive since they can be produced via a one step reaction with very high yield using N-methylimidazole and trialkylphosphate or alkyl halides as feedstocks. Such kind of ILs prepared in this thesis include 1-methyl-3-methylimidazolium dimethylphosphate （[MMIM][DMP]）, -ethyl-3-methylimidazolium diethylphosphate （[EMIM][DEP]）, 1-butyl-3-methylimidazoliumdibutylphosphate （[BMIM][DBP]）, l-butyl-3-methylimidazolium chloride （[BMIM][Cl]） and l-butyl-3-methylimidazolium bromide （[BMIM][Br]）. Besides, 1-butyl-3-methylimidazolium hexafluorophosphate （[BMIM][PF₆]） was also prepared via a metathesis reaction for comparison with the above ILs. The ILs with alkylphosphate anion show some notable merits, namely ease of preparation and purification, high reaction yield（>90%）, low cost being about 30-40% of other conventional ILs, as well as their low toxicity to the environment, therefore, they are important and promising ILs with great potential to be used in some industrial applications. In this regard, the influence of theses ILs on the VLE of water, ethanol and methanol was studied in detail.Isobaric VLE data for ethanol-water systems containing an IL, viz, [MMIM][DMP], [EMIM][DEP], [BMIM][Cl], [BMIM][Br] or [BMIM][PF₆] at different IL contents（from about 10wt% to 30wt%） were measured at atmospheric pressure（101.32kPa） by a dual circulation vapor-liquid equilibrium still （CP-I type）, and the effect of ILs on the VLE behavior of ethanol-water system was discussed briefly. The equilibrium compositions of the volatile components in both vapor and liquid phase were analyzed by gas chromatography, while the IL content in the liquid phase was determined with gravimetric method. The results indicated that all ILs studied showed a salting out effect for ethanol, giving rise to an enhancement of relative volatility of ethanol and even to an elimination of the azeotropic phenomenon at specific IL content. For [BMIM]⁺ series ILs, their salting out effect on ethanol follows the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆], and for the phosphate-type ILs, the salting out effect on ethanol follows the order of [MMIM][DMP]>[EMIM][DEP].Vapor pressure data were measured for nine binary systems containing water, methanol or ethanol with an IL, viz. [MMIM][DMP], [EMIM][DEP] or [BMIM][DBP] and four ternary systems, namely ethanol+methanol+[MMIM] [DMP], ethanol+methanol+[EMIM][DEP], ethanol+methanol+[BMIM][DBP], and ethanol+water+[MMIM][DMP] at varying temperature and IL mass percent using a quasi-static method. The experimental results of binary systems indicated that the ILs studied can lower the vapor pressure of solvents due to the affinity between IL and the solvent, while the lowering degree depended on the type and content of IL involved. Based on the vapor pressure data of binary systems interpolated at mole fraction of 0.05 for IL component, the influence of different ILs on the vapor pressure of different solvent was elucidated. It was showed that the effect of ILs on the vapor pressure lowering followed the order [MMIM][DMP]>[EMIM][DEP]>[BMIM][DBP] for water, while a reverse order was found for methanol and ethanol, suggesting that the "ionic" characteristic of ILs dominates in water, while the "molecule" characteristic prevails in organic solvent.The vapor pressure data of binary systems containing ILs studied were correlated by traditional NRTL model of non-electrolyte solution. The results showed that the NRTL model is applicable for the correlation of binary VLE data with overall average absolute relative deviation （ARD） being 0.89% and the maximum ARD within 2%. The fitted binary NRTL parameters can be used to predict the vapor pressure of the ternary system ethanol-water-[MMIM][DMP] with ARD of 2.8%. In order to check the reliability of the model parameters, the infinite dilution activity coefficients of water, ethanol and methanol at 353.15K in [MMIM][DMP] were predicted based on the binary NRTL parameters and the predicted values were found being qualitatively consistent with experimental ones, indicating that the NRTL model can be used to correlate and predict the VLE data of the systems containing ILs. In order to have a better representation for the ternary VLE behavior, the binary NRTL parameters for IL-solvent pair were finely readjusted in terms of the experimental vapor pressure data for ternary systems, on this basis, the isothermal VLE data for ethanol-methanol-[MMIM][DMP], ethanol-methanol-[EMIM][DEP], ethanol-methanol-[BMIM][DBP] and ethanol-water-[MMIM][DMP] systems at 320 K and IL mass fraction of 50% were predicted. The results indicated that①All ILs show a salting-out effect for ethanol and the salt effect follows the order [EMIM][DEP]> [MMIM][DMP]>[BMIM][DBP] for ethanol+methanol system.②The methanol component in the ethanol+methanol system is converted from a lighter component to a heavier one due to its stronger affinity to the IL involved.③The azeotropic phenomenon in the ethanol+water system can be completely removed under certain content of ILs. In conclusion, the addition of IL is helpful for the separation of methanol and water from their ethanol solutions.Based on the mean spherical approximation （MSA） integral equation theory, perturbation theory and group contribution concept, a new molecular thermodynamic model was established for the representation of activity coefficient of solvent in the IL-containing systems. In this model, the chemical potential arising from long range electrostatic interaction between ionic species, and the middle range interaction between ion and dipolar molecules were accounted for using mean spherical approximation （MSA） and perturbation theory, respectively, while the short range interaction contribution arising from dispersion and induction effects etc. among various groups of ILs and solvent molecules was represented using the UNIFAC group contribution model. The performance of the new model was preliminarily tested for the correlation of vapor pressure data for IL-containing binary systems, and good correlation accuracy was obtained. Moreover, the contribution of the above three kind of interaction on the activity coefficient of solvent as well as their dependence on the temperature and liquid composition was analyzed using the regressed model parameters, which laid a foundation for the further improvement of the model.更多还原