Estimation of critical curves by empirical and rigorous modelling methods: Case studies on n-alkane + dimethyl carbonate and n-alkane + chloroalkane

Abstract

The determination of critical curves is important for the design of chemical processes. The accuracy of fast and rigorous methods for estimating the vapour-liquid critical curves of n-alkane + dimethyl carbonate, and n-alkane + chloroalkane binary systems is tested. The n-alkanes range from propane to n-decane, whereas the chloroalkanes are dichloromethane, 1,1-dichloroethane and 1,2-dichloroethane. The fast estimation methods evaluated are: the conformal solution theory (CM); the method of He et al. (2017); and the method of Tang et al. (2024). The rigorous methods studied are: the corresponding states principle (CSP) with the one-fluid van der Waals equation of state (vdW EoS); and the Heidemann-Khalil-Michelsen (HKM) method with the Peng-Robinson EoS. Despite the simplicity of the EoS, CSP provides the best correlations, resulting in overall average absolute relative errors ($\mathrm{AARE}$) for temperature and pressure of $\mathrm{AARE}{T}^c=0.36\%$ and $\mathrm{AARE}{p}^c=1.68\%$, respectively. CM is the only recommended fast method due to its scientific soundness and accuracy ($\mathrm{AARE}{T}^c=0.55\%$ $\mathrm{and}\mathrm{AARE}{p}^c=5.10\%$). The methods of He and Tang exhibit parameter degeneracy, questioning their reliability. This work underscores the importance to reconsider CSP as a reliable method for estimating critical curves and presents, for the first time, the explicit equations required to apply this method using the VdW EoS.