The prediction of vapour pressures and enthalpies of vaporization of [cncnim][ntf2] ionic liquids with cosmo-rs


B. Schröder 1, L. Santos2, M. Rocha2 and J. Coutinho1

1CICECO, Universidade de Aveiro, Departamento de Química, Aveiro, Portugal
2Centro de Investigação em Química, Faculdade de Ciências da Universidade do Porto, Porto, Portugal

Keywords: COSMO-RS predictions
property: vapour pressure, enthalpy of vapourization
material: ionic liquids

COSMO-RS, the conductor-like screening model for real solvents [1], combines quantum chemistry, dielectric continuum models, electrostatics surface interactions and statistical thermodynamics and can predict thermodynamic properties in the liquid phase. The method is based on a very small number of adjustable parameters only, which are independent of any molecular or structural information, that is, no group interaction parameters [2]. The vapour-liquid equilibria predictive capabilities of COSMO-RS on vapour pressures and enthalpies of vaporization will be demonstrated on [CnCnim][NTf2] ionic liquids. To tackle the problem for 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids [Cnmim][NTf2], Diedenhofen et al. presented two approaches: the liquid phase considered as a 50 : 50 mixture of the two separate ions, with ion pair formation in the gas phase; both phases (vapour and liquid) consisting of ion pairs only, with the latter approach yielding more realistic vapour pressure predictions. In this work, we report on vapour pressures and enthalpies of vaporization based on this approach, being focussed on errors arising from the enthalpic corrections to the reference temperature and the importance of a correct definition of the conformer equilibria description, in order to explore how accurate COSMO-RS can describe the vapour liquid equilibria of the title ILs. This work was supported by FCT Portugal. M. A. A. Rocha and B. Schröder acknowledge the financial support from FCT for the award of a research grant with reference SFRH/BD/60513/2009 and SFRH/BPD/38637/2007, respectively.

References
  1. A. Klamt, COSMO-RS: From quantum chemistry to fluid phase thermodynamics and drug design, (Elsevier, Amsterdam, 2005)

  2. F. Eckert, A. Klamt, AIChE J. 48. 369 (2002)

  3. M. Diedenhofen, A. Klamt, K. Marsh, A. Schäfer, Phys. Chem. Chem. Phys. 9, 4653 (2007)

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