Thermodynamic Properties of Ionic Liquids - Measurements and Predictions

Thermodynamic Properties of Ionic Liquids - Measurements and Predictions - 

Zhi-Cheng Tan, Urs Welz-Biermann, Pei-Fang Yan, Qing-Shan Liu and Da-Wei Fang China Ionic Liquid Laboratory and Thermochemistry Laboratory Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, 

For the general understanding of these materials it is of importance to develop characterization techniques to determine their thermodynamic and physicochemical properties as well as predict properties of unknown Ionic Liquids to optimize their performance and to increase their potential future application areas. 

Our laboratory in cooperation with several national and international academic and industrial partners is contributing to these efforts by the establishment of various dedicated characterization techniques (like activity coefficient measurements using GC technology) as well as determination of thermodynamic and physicochemical properties from a continuously growing portfolio of (functionalized) ionic liquids. Based on the received property data we published several papers related to the adjacent prediction of properties (like molar enthalpy of vaporization, parachor, interstice volume, interstice fractions, thermal expansion coefficient, standard entropy etc.). Additionally our laboratory created and launched a new most comprehensive Ionic Liquid property data base—delph-IL.(www.delphil.net). This fast growing collections of IL data will supvport researchers in the field to find and evaluate potential materials for their applications and hence decrease the time for new developments. 

In this chapter we introduce the following techniques, summarize recent published results completed by our own investigations  

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Chapter 11 provides an analysis of ionic liquids thermodynamic properties. Here, only a representative example is provided. A modified Redlich-Kwong cubic equation of state was used to correlate VLE and predict the VLLE of (fluorocarbon + ionic liquid).Because the ionic liquids have no measurable vapour pressure, the equation of state pure-component parameters were fit to the liquid density data and critical constants.To correlate the experimental VLE data at temperature over the range (283 to 348) K, Shiflett and Yokozeki" used three binary interaction parameters. These parameters were used, without further adjustment, to predict the VLLE of these mixtures. In Eigure 4.8, experimental data and correlation are shown for (1,1,1,2-tetrafluoroethane+ 1-butyl-3-methylimidazolium hexafluorophosphate [bmim ][PF6 ]). 

The phase behaviours of binary and ternary ionic liquid mixtures with carbon dioxide,organics " and water " have been determined using COSMO-RS. In the COSMO-RS framework, ionic liquids are considered to be completely dissociated into cations and anions. Ionic liquids are thus taken as an equimolar mixture of two distinct ions, which contribute as two different compounds. Because ionic liquids only dissociate in the presence of strongly polar substances, the COSMO-RS prediction of the phase behaviour of ionic liquid systems with polar compounds (water and alcohols) is more accurate than that of ionic liquid systems with nonpolar compounds (carbon dioxide and organics). Especially the COSMO-RS prediciton of the solubility of (relatively nonpolar) carbon dioxide in ionic liquids shows considerable deviations ( 15 %) from experimental values. lUPAC Technical Reports document the measurements of the thermodynamic and thermophysical properties of l-hexyl-3-methylimidazolium bis [(trifluoromethyl)sulfonyl]amide and the recommended values. ... 

The prediction of volatilities and melting points of pure ionic liquids was possible by associating first principles calculations and calorimetric measurements, as presented, for example, by Verevkin and co-workers. They showed that the knowledge of gas-phase thermodynamic properties is important for the modelling of vapour-liquid equilibrium on pure ionic fluids [97]. 

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