【作者】 陈晓亭；

【导师】 吴卫泽；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2010， 硕士

【摘要】 近年来,随着人们环保意识的增强,绿色化学受到越来越多的关注。离子液体作为一种极具应用前景的环境友好溶剂被应用于电化学反应介质。但是离子液体的黏度和表面张力都较大的特性限制了其电化学应用。超临界二氧化碳(CO2)是目前研究较多的另一类环境友好溶剂,由于具有粘度低、表面张力为零、经济易得、性质可调和较低的临界温度、临界压力等优点而被广泛应用于萃取分离、电化学反应等领域。本文探索将离子液体引入到超临界CO2体系中,试图赋予超临界CO2导电性,克服传统电解介质的高黏度和高表面张力的问题。另外对于该过程相关的相态和离子液体在超临界CO2中合成的相关相态也进行研究。工作总结如下：(1)高压相平衡是研究高压CO2混合体系的前提和理论基础。研究了CO2与1-溴丁烷、1-氯丁烷、1-甲基咪唑在不同溶质摩尔含量(0.0102-0.1495)、不同温度(308.2-337.4K)以及不同压力(6.21-19.04MPa)下混合体系的相平衡及密度。另外,还利用取样分析的方法测定了(293.15、309.75和323.2)K和(2.83-14.16)MPa下的超临界CO2与1-甲基咪唑气液平衡数据。研究表明：在实验研究的范围内,三种体系的相平衡有着类似的规律。混合体系的密度随着压力的升高而增大,随着温度的升高而减小,随着溶质摩尔分率的增大而增大；并且在分相点附近,密度对压力的变化非常敏感,用来表征压力对密度影响大小的KT变化也很大,而远离分相点时,密度受压力变化影响很小,KT很小,并且受压力影响也很小。超临界CO2与l-甲基咪唑混合体系在高温高压下存在三相(297.85K-313.95K,6.20MPa-8.67MPa),而且该体系的相图属于第四或第五类相图。CO2的溶解度随温度升高而减小,随压力升高而增大。(2)本文还利用合成法测定了乙腈作为共溶剂、不同的温度、压力情况下,离子液体[Bmim]BF4在超临界CO2中的溶解度,其中乙腈摩尔含量为0.1495和0.1990,温度范围为313.2K-332.2K。结果表明,离子液体在超临界CO2中的溶解度随着温度升高而减小,随着压力增大而增大,随着乙腈含量增多而增大。(3)本文研究了溶有离子液体的超临界CO2的导电性能,在高压变体积可视釜中测定了乙腈为共溶剂的情况下有离子液体([Bmim]BF4和[Bmim]PF6)时和没有离子液体时超临界CO2的导电性能,其中乙腈摩尔含量为0.1390-0.1971,温度范围为313.2K-332.2K。通过研究发现,只有共溶剂乙腈的情况下,超临界CO2的电导率非常小；而加入离子液体后,超临界CO2的电导率大大上升,并且电导率随着温度升高而降低,随着压力增大和乙腈含量增大而增强。更多还原

【Abstract】 Recently, much more attention has been focused on green chemistry along with people’s awareness of the importance of environment. Ionic liquid can be used in electrochemical reactions as environmentally benign solvent. However, the high viscosity and surface tension restrict its applications in electrochemistry. Because CO2 is readily available, inexpensive, nontoxic, nonflammable, has low viscosity and has a mild critical temperature (304.2 K) and critical pressure (7.38MPa), supercritical CO2 (scCO2) has been recognized as an environmentally benign solvent and has attracted much attention in many chemical processes, such as extraction and fractionation, chemical reactions, and so on. Ionic liquids were introduced to supercritical carbon dioxide to endow the latter with conductivity in order to decrease the high viscosity and high surface tension of traditional electrochemical medium. The related phase behaviors have also been studied in this work. The contents of our work are as following:The knowledge of high pressure phase behavior about carbon dioxide mixtures, especially the vapor-liquid equilibria (VLE) are essential in the design, development, and operation of supercritical fluid separation processes. This work has studied the phase behaviors of CO2+ 1-bromobutane, CO2+1-chlorobutane, CO2+1-methylimidazole, which are related to synthesis of imidazolium based ILs. The vapor-liquid equilibrium datas of the three mixtures were measured with concentrations of solute mole fractions (0.0102 to 0.1495), temperatres from (308.2 to 337.4) K and pressures from (6.21 to 19.04) MPa. The VLE data of CO2+ 1-methylimidazole were also determined using analytic method under (293.15,309.75,323.2) K and (2.83 to 14.16) MPa. The results indicate that the phase behaviors of three binary systems have similar tendency in the temperature range we studied. And the density of mixtures increases with increasing pressure and decreasing temperature, and with increasing solute mole fraction. It is also demonstrated that the density is sensitive to the pressure as the pressure approaches the phase transition points of binary mixtures; that is, KT is large and increases significantly. When the pressure is much higher than the phase transition pressure or the composition is far from the critical composition, KT is rather small, and the effect of pressure on KT is fairly limited. The phase boundary data of the binary mixtures can be correlated well by the Peng-Robinson equation of state (PR EoS) with two binary parameters. Th results also indicate that the liquid-liquid-vapor equilibria (LLV) of the CO2+1-methylimidazole binary system exists under temperatures from 297.85K to 313.95K and pressures from 6.20MPa to 8.67MPa. The experimental data were also correlated well by the Peng-Robinson equation of state with two van der Waals mixing rules. According to the experimental results, the phase behavior of the binary system might be classified to Type-IV or Type-V according to the classification of six principal types of binary phase diagrams. The solubility of carbon dioxide decreases along with increasing temperatre and increases as pressure increasing.The solubilities of ionic liquid ([Bmim]BF4) in supercritical CO2 with cosolvent (acetonitrile) have been investigated using static method at temperatures from 313.2K to 332.2K. The mole fraction of acetonitrile was from 0.1495 to 0.1990. And it is demonstrated that the solubility of ionic liquid in supercritical carbon dioxide increases with increasing pressure and mole fraction of acetonitrile, while it decreases with increasing temperature.The conductivity of ionic liquid in supercritical carbon dioxide has been studied In high-pressure variable-volume view cell, the conductivity of supercritical carbon dioxide with and without ionic liquids were measured. And the mole fraction of cosolvent (acetonitrile) was from 0.1390 to 0.1971, temperatures from 313.2K to 332.2K. At presence of identical concentration of acetonitrle, the conductivity of supercritical carbon dioxide without ionic liquid is very small, while it increases greatly with ionic liquid. And the coductivity decreases with increasing temperature, while it increases with increasing pressure and mole fraction of acetonitrile.更多还原