Critical-Point Temperature of Ionic Liquids from Surface Tension at Liquid−Vapor Equilibrium and the Correlation with the Interaction Energy

• Published in: Industrial & engineering chemistry research 2010-12, Vol.49 (24), p.12696-12701
• Main Authors: Ghatee, Mohammad Hadi, Moosavi, Fatemeh, Zolghadr, Amin Reza, Jahromi, Razyeh
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; General Research
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie1013772

The critical temperature of ionic liquids is predicted by scaling-law, Guggenheim, and Eötvös approaches, using surface tension data measured in the temperature range of 293−393 K. The available surface tension data for imidazolium-, phosphonium-, and ammonium-based ionic liquids, with different anions content, show that the predicted critical temperature is a function of cation type and its alkyl chain length as well as the anion type. According to this dependence on the nature of the ionic liquid, the anion−cation interaction energy (E inter) was calculated by quantum mechanical density functional theory and the correlation with the predicted critical temperature was studied. The predicted critical temperature has a direct correlation to the absolute value of E inter. The ionic liquids with the BF4 − anion, which consistently have the highest critical point temperature, also have the largest absolute value of E inter. As the alkyl chain length increases, the critical temperature decreases. When the surface tension is measured under a liquid−vapor equilibrium, the prediction has the meaningful feature of producing the critical-point temperature.