Contribution of the Individual Ions to the Heat Capacity of Ionic Liquids

Abstract

Heat capacity is a crucial parameter for process design. Ionic liquids (ILs) offer the opportunity to tailor the relevant properties for many processes, but heat capacity data often are not available. In this work, temperature-dependent contributions to the heat capacity for 39 cations and 32 anions are proposed. A database containing 104 ILs with 2443 data points was used for the development of this model. The experimental data in the test set could be reproduced with a mean relative error of 4.4%. This allows for a systematic screening of a huge IL database to determine the solvent best-suited for a task without the necessity to measure all the missing data. Furthermore, an optimization taking different substance properties into account by using respective mathematical tools is possible by combination with prediction models for other properties.

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].…”

“…The other two models compared in Table 6, i.e. the Sattari et al [11] and the Farahani et al [10] models, are both of the atomic-contribution type (combination of correlation and atomic- Also, a graphical presentation of the accuracy of the Muller and Albert [17], Sattari et al [11] and Farahani et al [10] methods, based on the validation data set, are presented in the Supplementary section as Figure S.1-3. These figures can be compared with that of the proposed model in this work, as given in Figure 1, since they all represent the same dataset.…”

“…The testing group heat capacities were calculated by their model with the mean absolute error of 5.4 %. In another study, Muller and Albert [17] proposed temperature-dependent contributions to the heat capacity of ILs. They developed their model using 39 cations and 32 anions, from a database containing 2443 data points from 104 ILs.…”

“…presents the resulting AARD% values.As can be seen in this table, the Muller and Albert model[17] give the best results, with a total AARD% of 2.38%, but only for the ILs which could be calculated by this model (as some ILs could not be calculated since their ionic values were not listed in the model). This high accuracy was to be expected because the Muller and Albert model is one of ion contributions, in which a separate group is specifically dedicated to each anion and cation.…”

“…For an investigation of the accuracy of the proposed model in this study, results have been compared with some other literature methods[10,11,17]. In order to have a fair evaluation of the proposed model and those from literature, we have chosen the validation dataset of ionic liquids only for the comparisons below.…”