Volatility of Aprotic Ionic Liquids - A Review

Published

August 7, 2009

Author(s)

Jose M.S.S. Esperanca, Jose N. Canongia Lopes, Mohd Tariq, Luis M.N.B.F. Santos, Joe W. Magee, Luis P. Rebelo

Abstract

A review of research on the volatility of aprotic ionic liquids is presented. This topic is limited to aprotic liquids, since measurements have led to a generalization that this class of substances possesses an extremely low vapor pressure. For research related to this topic, the time period covered is 2003 to 2008. The review begins with a discussion of the earliest successful study of thermal vaporization of aprotic ionic liquids, the earliest indirect measurements of vapor pressure, the first proof of conventional distillation of ionic liquids, and competition of vaporization with thermal decomposition seen at moderately high temperatures of (200 to 300) °C. The review then moves to research on the nature of the vapor phase. This is followed by a review of various approaches to calculate predicted ionic liquid vapor-liquid equilibrium properties, including normal boiling point, vapor pressure and enthalpy of vaporization. Such predicted properties are then discussed in light of recent experimental approaches for the vapor pressure and enthalpy of vaporization. Excluded from this discussion is the normal boiling point temperature, whose best estimates are more than 200 °C higher than the observed onset of thermal decomposition for common ionic liquids. It is proposed that the most reliable thermodynamic data exists solely for the enthalpy of vaporization, and thus this property would be the best target for predictive approaches. Predictive approaches to calculate the enthalpy of vaporization are discussed in light of their ability to predict the experimentally observed trends with molar mass. The review concludes with a forward look at the following: expected effect of gas-phase ion clusters; anticipated trade-off between the energetic gain and the entropic penalty for cluster formation; and, possibility of a Trouton rule for ionic liquids vaporization.

Citation

Journal of Chemical and Engineering Data

Volume

55

Issue

1

Pub Type

Journals

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DOI Link

Keywords

boiling point, distillation, enthalpy of vaporization, ionic liquids, ion pairs, vapor pressure, volatility

Citation

Esperanca, J. , Canongia Lopes, J. , Tariq, M. , Santos, L. , Magee, J. and Rebelo, L. (2009), Volatility of Aprotic Ionic Liquids - A Review, Journal of Chemical and Engineering Data, [online], https://doi.org/10.1021/je900458w (Accessed April 25, 2024)