A Group Contribution Method for the Thermal Properties of Ionic Liquids

Abstract

Missing substance properties can become a limiting factor in research and process design. Especially for ionic liquids (ILs), experimental data are often not available and measurement is expensive and time-consuming. To cope with this issue, an estimation scheme for the heat capacity and the thermal conductivity of ILs has been developed. To achieve a wide range of application, first-order group contributions have been chosen to describe the molecular structure of the ions. 2419 experimental heat capacity data points for 106 ILs have been used in two separate subsets for parameter fitting and testing to allow for a reliable external validation. In the case of thermal conductivity, 372 data points for 39 ILs have been processed analogously. The data for ILs from the subset not used for the fitting could be reproduced with a mean absolute error of 5.4% in the case of heat capacity and of 8.1% in the case of thermal conductivity. Using these estimation schemes, it is possible to screen a huge number of potential combinations of cations and anions to find candidates suited best for a specific task before performing the experimental measurement.

A simple group contribution correlation for the prediction of ionic liquid heat capacities at different temperatures

“…Such approaches include the empirical-based models such as correlations, group contributions, artificial intelligence methods, etc., while others can be more theoretically-based, such as computational methods or derivations from equations of states [10][11][12][13][14][15][16][17].…”

Thermophysical properties of imidazolium tricyanomethanide ionic liquids: experiments and molecular simulation

“…11,[21][22][23][24] Currently it is well accepted that ILs are highly structured fluids in which the ion pairs arrange themselves into polar and non-polar domains. [25][26][27][28][29][30] The structural segregation in these systems depends on the relative size of the high-charge and low-charge regions in each ion and the size of the alkyl chain length.…”

Novel 2-alkyl-1-ethylpyridinium ionic liquids: synthesis, dissociation energies and volatility

“…[17][18][19][20][21][22][23][24][25] Due to the large number of possible ionic liquids, predictive models have been proposed to overcome this limitation. [26][27][28][29][30] Until recently, ionic liquids were regarded as non-volatile, and thus did not exhibit measurable vapor pressures, even at higher temperatures. However, Earle et al 29 have shown that some ionic liquids can be distilled at low pressures without decomposition.…”