离子液体水溶液pH值测定及酸碱特性研究

doi:10.6023/A13091014

摘要/Abstract

在离子液体水溶液作为新一代优良吸收工质的工业应用研究和开发中，对该体系的物理化学性质（诸如离子液体在水中存在性状及其酸碱性问题等）的深入认识和掌握尤为重要. 本文采用pH酸度计和精密pH试纸两种方法，对水质量分数分别为0.04～0.95的1-乙基-3-甲基咪唑醋酸盐（[EMIM]Ac）和0.01～0.96的1-己基-3-甲基咪唑氯盐（[HMIM]Cl）离子液体水溶液的pH值进行测试和定量分析. 测试结果表明pH酸度计和精密pH试纸两种方法的测试结果有较大的差异，这种差异是由于离子液体-水混合体系中局部形态与整体特性不同造成的. 本文成功拟合了pH精密试纸测定值，计算获得的这两种离子液体水溶液的酸浓度与测定值基本符合，精密试纸测定的pH值可用于表征离子液体水溶液整体酸碱特性. 基于离子液体在水溶液中形成惰化聚合膜的假设，提出了分别表征聚合膜水溶解度和离子液体水溶液水活度系数的溶液理论模型，根据溶液相平衡理论建立了聚合膜中氢离子浓度与水溶液中氢离子浓度差别的计算方法，成功拟合了pH酸度计测定值. 研究结果为离子液体水溶液体系的pH值和酸碱度分析提供了实验依据和预测理论模型.

关键词: 离子液体, 水溶液, pH值, 酸碱性

The ionic liquids (ILs) and their aqueous solutions have been considered as a new generation of absorption working substances for applications in gas separation and absorption refrigeration processes. It is important to understand the physicochemical properties of ionic liquids in aqueous solutions, such as chemical potential and acid-base properties before any industry application. In this study, we focused on the acid-base properties of the IL aqueous solutions by testing the pH values of the aqueous solutions of two ionic liquids, 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl). All the tests were carried out at 25 ℃ and in a well controlled dry air surrounding. There were 16 water mass fractions for each of [EMIM]Ac and [HMIM]Cl aqueous solutions tested in range of 0.04 to 0.95 and 0.01 to 0.96, respectively. There, two methods, the sophisticated pH paper and the pH meter, were applied for the tests and the differences between the two test methods were detected. The test data from the two test methods and their differences were then evaluated with an aggregation film model and the activity theory for the film and aqueous solution phases. The results show that the difference of the pH values tested by the two methods is significant. The pH data from the sophisticated pH paper test present the bulk acid-base property of the IL aqueous solutions, while the pH meter can only reflect the hydrogen ion concentration in the IL aggregation film which was formed on the surface of the electrode of the pH meter. With analysis of acid-base reaction in the IL aqueous solution, a calculation model for the pH value of the bulk solution region was developed, and the data of the sophisticated pH paper test were correlated and the solution acid-base values were obtained. Based on analysis of the water species equilibrium in the IL aggregation film and the bulk aqueous solution phases and its effect on the concentration of hydrogen ions in the aggregation film, a method for calculation of the difference of pH values between the aggregation film and the bulk solution was proposed and the data from the pH meter were then fitted with the proposed calculation method. The results provide experimental data and a quantitative method for analysis of the acid-base property of IL aqueous solution systems.

Key words: ionic liquid, aqueous solution, pH value, acid-base property

引用此文

杨翠莲, 皇甫立霞, 粟航, 郭开华. 离子液体水溶液pH值测定及酸碱特性研究[J]. 化学学报, 2014, 72(4): 495-501.

Yang Cuilian, Huangfu Lixia, Su Hang, Guo Kaihua. Determination of pH Value and Acid-base Property of Ionic Liquid Aqueous Solutions[J]. Acta Chimica Sinica, 2014, 72(4): 495-501.

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