A New Group Contribution Method For Prediction of Density of Pure Ionic Liquids over a Wide Range of Temperature and Pressure

A detailed knowledge of reliable data on physical properties of ionic liquids (ILs) is of great importance, because ILs are still considered as potential replacements for volatile organic solvents in modern and sustainable ("greener") processes of chemical industry. In particular, liquid density is a very important property that is required in many design problems of chemical engineering and material science. Therefore, development of new methods for estimation of density of ILs is essential. In this work we propose a new method based on generalized empirical correlation and group contributions. It was developed based on a comprehensive database of experimental data containing over 18500 data points for a great variety of 1028 ILs. The collected data covers temperature and pressure ranges of 253–473 K and 0.1–300 MPa, respectively. Molar volume at reference temperature (298.15 K) and pressure (0.1 MPa) was assumed to be additive with respect to defined set of both cationic and anionic functional groups, whereas a Tait-type equation with four adjustable parameters was adopted to describe temperature–pressure dependence of density (P–ρ–T). The model parameters, including contributions to molar volume for 177 functional groups, as well as universal coefficients describing the P–ρ–T surface, were fitted to experimental data for 828 ILs with an average absolute relative deviation (%AARD) of 0.53%. Then, the model was evaluated by a calculation of density for 200 ILs not included in the correlation set. We showed that the proposed GCM allows the accurate prediction of high pressure densities for a variety of ILs. The resulting %AARD of prediction was 0.45% which is the one of the lowest values compared with similar correlations reported in literature. Moreover, we showed that the presented method is able to accurately capture other volumetric properties of pure ILs such as molar volume and derivative properties (thermal expansion coefficient and isothermal compressibility) as well as their temperature and pressure dependencies.