Correlating ionic liquids density over wide range of temperature and pressure by volume shift concept

The main purpose of this paper is the use of the conventional Peng-Robinson equation of state (PR EoS) and the concept of volume shift to correlate and predict pure ionic liquids (ILs) density in a wide range of temperature and pressure. A total number of 67 pure ILs (5020 data points) including different cations and anions were used in this study over temperature and pressure range of 273.15-473.15 K and 0.1-205 MPa. At first, the volume shift parameter (c) of 67 ILs in any temperature and pressure were optimized using genetic algorithm. An equation similar to Gardas and Coutinho (R. L. Gardas, J. A. P. Coutinho, Fluid Phase Equilibr. 263 (2008) 26-32) was used for c parameter and finally a generalized correlation was proposed for c as a function of temperature, pressure and critical molar volume. This equation was also used in predicting densities of eight new ILs not included in correlation section and it was able to improve the PR EoS prediction and reducing the error with respect to experimental data. Considering the importance of density in engineering, using this simple equation with the VTPR improves ILs density prediction and calculation, saves time and increases the accuracy engineering design. The average absolute percent deviation (AAPD) of the volume translated PR (VTPR) EoS and the conventional PR EoS were equal to 2.19% and 12.98%, respectively.