(489d) Freezing Point Determination of Water-Ionic Liquid Mixtures

Yanrong Liu,^a,b,c Anne S. Meyer,^a Yi Nie,^c Suojiang Zhang,^c Yongsheng Zhao,^c Philip L. Fosbøl,^b Kaj Thomsen*^b

^aCenter for Bioprocess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads 227, 2800, Lyngby, Denmark

^bCenter for Energy Resources Engineering (CERE), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads 229, 2800, Lyngby, Denmark

^cBeijing Key Laboratory of Ionic Liquids Clean Process, Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, P. O. Box 353, Beijing, 100190, China

In many instances ionic liquids (ILs) end up being IL-water mixtures. No data are available on the freezing points of such mixtures, and assessment of the freezing point curves of IL–H₂O mixtures can also be used to understand the eutectic behavior of the solutions. In this work, freezing points of aqueous solutions of HOEtpyBr, HOEtmimBr, AmimCl, EtOMmimCl, EmimDep and EmimAc were measured using a modified Beckmann apparatus with automatic data logging. These ILs were chosen because they are potential ILs for dissolving cellulose. From the freezing point curves, it can be observed that the behavior of dilute solutions of ILs in water is very similar to that of dilute solutions of MgSO₄ and MgCl₂. Water activities in IL aqueous solutions were predicted by COSMO-RS and COSMO-SAC and compared to water activities derived from the experimentally determined freezing points. The COSMO-RS predictions were closer to the experimental water activities than the COSMO-SAC predictions. The experimental results indicate that the freezing points of IL–H₂O systems are affected by the nature of both cations and anions. However, according to the COSMO-RS excess enthalpy prediction results, the anions have a relatively higher influence than cations on the IL–H₂O interaction.

Figure 1. Freezing points of the studied IL solutions and of salt solutions compared at higher concentrations.

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