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Experimental vapour pressure of binary systems for 2,2,2-trifluoroethanol + ionic liquids. PC-SAFT modelling


J. Garcia2, M. Curras1,2, M. Costa-Gomes3, A. Padua1, P. Husson1 and J. Vijande2

1Universite´ Blaise Pascal, Laboratoire Thermodynamique et Interactions Moléculaires, Aubière, France
2Departamento de Física Aplicada, Edificio de Ciencias Experimentais, Universidade de Vigo, Vigo, Spain
3CNRS, Laboratoire Thermodynamique et Interactions Moléculaires, Aubière, Clermont Universite´, France

Keywords: ionic liquids, refrigerant, absorbent, vapour pressure, absorption cycles
property: vapour pressures
material: 2,2,2-trifluoroethanol, 1-etyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate

In absorption technology a fluid with strong volatility can be used as refrigerant, whereas a second fluid with much smaller volatility but strong affinity to the former is employed as absorbent. Vapour pressures can be useful to evaluate the affinity between a refrigerant and an absorbent and are of outmost importance for modelling absorption heat pump cycles. Previously, Kim et al. [1] measured the vapour pressures of 2,2,2-trifluoroethanol (TFE) and two ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF4] and 1-butyl-3-methylimidazolium bromide, [bmim][Br]. They concluded that the permanent ion–dipole interaction between ILs and TFE causes a negative deviation from Raoult’s law. Wang et al. [2] determined the vapour pressure for TFE + 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] and showed that, these systems are promising alternatives for absorption cycles. If the vapor pressure changes significantly with small variations of temperature, the regeneration will be easier, but the coefficient of performance (COP) will be lower. We have analyzed in previous works several thermophysical properties of IL + TFE mixtures such as densities, viscosities or mixing enthalpies. In this work, we have measured the vapour pressures for TFE + [emim][BF4] and TFE + [bmim][BF4] in the overall range of mole fractions and at 303 K. A comparison between the two systems is made. PC-SAFT [3] equation was used to model the systems studied, including association term. The equation gives good results for vapor pressures using a unique interaction binary parameter for each system, which means that this model could be useful for refrigeration industry. ACKNOWLEDGMENTS This work was supported by Xunta de Galicia (PGIDIT07PPXIB314132PR) and by the Spanish-French joint action (HF2007-0053). M. R. Currás would like to acknowledge the grant for short mission of Vigo University.

References
  1. K.S. Kim, B.-K. Shin, H. Lee, F. Zielgler, Fluid Phase Equilib. 218, 215 (2004).

  2. J. Wang, D. Zheng, L. Fan, L. Dong , J. Chem. Eng. Data 55, 2128 (2010)

  3. J. Gross, G. Sadowski, Ind. Eng. Chem. Res.41,5510 (2002)

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