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

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 Taylorʹs 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 liquidʹs 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.