Evaluation of the polar contribution in the SAFT-VR Mie equation of state for simultaneous correlation of condensed-phase density, condensed-phase speed of sound, saturated density and saturated pressure of pure polar fluids

Abstract

Polar forces affect significantly the thermodynamic properties and phase equilibria of pure fluids. In this work, the original SAFT-VR Mie equation of state was modified by the introduction of an explicit term to account for multipolar effects. Two approaches were evaluated: the Polar SAFT-VR Mie (PSAFT-VR Mie) and the Truncated Polar SAFT-VR Mie (tPSAFT-VR Mie). For non-associating molecules the agreement between experimental data and model predictions are very good. The tPSAFT-VR Mie equation of state presented better results than the SAFT-VR Mie and PSAFT-VR Mie models correlating condensed-phase density, condensed-phase speed of sound, saturated density and saturated pressure with lower deviations. For associating molecules the results obtained with the tPSAFT-VR Mie model were equivalent to the ones obtained with the SAFT-VR Mie equation of state. In order to the tPSAFT-VR Mie model better predict second-derivative thermodynamic properties, such as the speed of sound and the isobaric heat capacity, some information about this type of property must be used in the pure components parameters regression. All evaluated models predicted similar values for the second virial coefficient.