EMLG-JMLG Annual Meeting 2010

Complex liquids: Modern trends in
exploration, understanding and application

European Molecular Liquids Group (EMLG)    Japanese Molecular Liquids Group (JMLG)
Institute for Condensed Matter Physics of National Academy of Sciences of Ukraine

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Organisation for the Prohibition of Chemical Weapons

Understanding the Solubility of Gases in Ionic Liquids from Molecular Simulations

Daniela Kerlé

Ionic liquids (ILs) are organic salts with a low melting point (< 100 °C) and represent a relatively new class of non-molecular materials with unique properties and various potential applications. The solvation process of gases in ILs is of fundamental interest for gas separation processes and flue gas decontamination. In particular the phase behaviour of carbon dioxide with ILs might be important for the development of potential carbon sequestration applications.

The imidazolium-based IL 1-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnMIM][NTf2]) with varying chain length n = 2, 4, 6, 8 is investigated by molecular dynamics simulations. Previous we have shown that our force field describes structural and thermodynamic properties of the neat IL very well. Now we demonstrate that also the solubility of light gases like carbon dioxide, oxygen, nitrogen, hydrogen and the noble gases is very well reproduced. The solubility is calculated from free energies of solvation, determined by Widom-Particle-Insertion technique.

While experiments are difficult and time consuming, this method is rather quick and provides hints on the solvation mechanism. A large temperature range from 300 K to 500 K is examined. Carbon dioxide shows an “anomalous” temperature dependence of the solvation in ILs at infinite dilution that is characterized by counter-compensating negative entropies and enthalpies of solvation.

Literature:

1. Köddermann, T., Paschek, D., and Ludwig, R., “Molecular Dynamics Simulation of Ionic Liquids: A Reliable Description of Structure, Thermodynamics and Dynamics.” ChemPhysChem. 8, 2464-2470 (2007)
2. Kerlé, D., Ludwig, R., Geiger, A., and Paschek, D., “On the Temperature Dependence of the Solubility of Carbon Dioxide in Imidazolium-based Ionic Liquids.” Journal of Physical Chemistry B. 113, 12727-12735 (2009)
3. Kerlé, D., Ludwig, R., and Paschek, D., “On the Temperature and Chain Length Dependence of the Solubility of Llight Gases in Imidazolium-based Ionic Liquids.” Angewandte Chemie, in preparation