Developing models for correlating ionic liquids density: Part 2 – Density at high pressures

• Correlations are reported for density of ionic liquids at high pressure.
• First correlation is similar to Taylor's series of reduced pressure.
• Second correlation is in the form of Padé approximation.
• The paper correlations are also compared to AK and GC equations.

In this paper, two models for calculation of ionic liquids density above 0.1 MPa are presented. The range of pressure was from 0.1 MPa to 200 MPa. The volume at 0.1 MPa (v0) in both models was calculated by our recent proposed correlation which was a modification of Rackett equation. In order to consider effect of pressure on v0, two methods were applied. The first method was based on Taylor's series expansion of ionic liquid volume and the second model was in the form of Padé’s approximation of volume as a function of pressure. The models involved adjustable parameters in terms of ionic liquid's thermodynamic properties which were obtained by correlating experimental data. The models results were compared to experimental data and these correlations were accurate enough to calculate ionic liquid density above 0.1 MPa where average absolute percent deviation for 32 ionic liquids was 1.09 and 1.12 for two models, respectively. To evaluate the accuracy of the correlations, Aalto and Keskinen model which is a reliable correlation for compressed liquid density calculation and Gardas and Coutinho equation were applied and more agreement between presented correlations and experimental data was observed.