Prediction of second order derivative thermodynamic properties of ionic liquids using SAFT-VR Morse equation of state

Abstract

The variable range statistical associating fluid theory (SAFT-VR) equation of state (EoS) based on the Morse potential was used to describe the second order derivative thermodynamic properties of ionic liquids. The isothermal compressibility coefficient, heat capacities, thermal expansion coefficient, isentropic compressibility coefficient, thermal pressure coefficient, and speed of sound of ionic liquids were predicted up to high pressure and temperature. In this regard, the ionic liquids were considered long chain molecules with two associating sites on cation and anion. The model parameters were obtained by fitting the experimental liquid density data. The average deviation of the calculated liquid density was about 0.09%. The predicted results were compared to the ePC-SAFT EoS to evaluate the capability of the SAFT-VR Morse model. The performance of SAFT-VR Morse EoS was comparable with ePC-SAFT, especially in the heat capacity coefficient and the speed of sound. The average deviation of predicted the isothermal compressibility coefficient, thermal expansion coefficient, isochoric heat capacities, isobaric heat capacities, thermal pressure coefficient, isentropic compressibility coefficient, and speed of sound are 6.46%, 8.32%, 8.18%, 9.55%, 8.10%, 2.67%, and 2.98%, respectively. Obtained results prove that SAFT-VR Morse can be used efficiently to predict second order derivative thermodynamic properties of ionic liquid over a wide range of pressure and temperature.