The Thermodynamic Properties of Non-Associating and Associating Fluids: A Systematic Evaluation of SAFT-Type Equations of State

Statistical Associating Fluid Theory (SAFT) equations of state (EoSs) have been extensively used for estimating thermodynamic properties of fluids. However, the predicted performance of SAFT-type EoSs for associating and non-associating fluids under the same thermodynamic conditions is poorly understood. In this work, four typical SAFT-type EoSs including the CPA, CK-SAFT, PC-SAFT, and SAFT-VR Mie EoSs are mainly employed and then a systematic evaluation is performed for the phase equilibria and derivative properties of the common non-associating (alkanes and carbon dioxide) and associating fluids (methanol and water). The results show that the misdescription of the residual Helmholtz free energy by SAFT-type EoSs is the major cause for the prediction accuracy of vapor–liquid equilibria (VLE). SAFT-VR Mie outperforms the others when predicting VLE of all the considered compounds, especially in conditions near the critical point, with an average absolute relative deviation (AARD) below 0.5%. PC-SAFT provides satisfactory enthalpy of vaporization (Δ H v ) predictions of alkanes, but its performance is inferior to PR due to the inaccurate description of the liquid-phase ∂ A /∂ T derivatives. Adopting a reasonable association scheme or including the Δ H v experimental data into the parameter regression routine can effectively improve the predictions accuracy of Δ H v for associating fluids. Overall, SAFT-VR Mie performs the best performance in correlating isobaric heat capacity ( C P ) due to the improved description of the ∂ 2 A /∂ V ∂ T and ∂ 2 A /∂ V 2 derivatives. Re-optimizing the universal constants of the dispersion term or employing higher-order perturbations can effectively improve the C P predictions.