A comparison between four cubic equations of state in predicting the inversion curve and spinodal curve loci of methane

Four equations of state, the Redlich-Kwong (RK), Peng-Robinson (PR) modified by Melhem et al., Trebble-Bishnoi (TB), and Jan-Tsai, were compared in predicting the inversion and spinodal curve loci of methane. The inversion locus of methane was also generated from a PVT framework based on the experimental data of gaseous methane. This enables us to judge the accuracy of the results obtained from the different equations of state. The calculated inversion curves were also compared to that fitted by the Gunn-Chueh-Prausnitz correlation. Results predicted by the PR equation modified by Melhem et al. showed good agreement with the experimental behavior up to a reduced pressure of 10, The RK equation shows a clear underestimate of the high pressures (above a reduced pressure of 9.5). The TB equation shows a comparable behavior to that of RK but with better predictions in high-pressure regions. The TB equation shows a good performance up to a reduced temperature of 2.3 after which it shows a deviation from the experimental data. The Jan-Tsai equation was found to be the poorest among the four equations considered in this work.