Updated versions of the generalized Soave α-function suitable for the Redlich-Kwong and Peng-Robinson equations of state

More than 40 years after their publication, updated versions of the generalized Soave α-function (α(Tr,ω)=[1+m(ω)(1−Tr0.5)]2) suitable for the Redlich-Kwong (RK) and Peng-Robinson (PR) equations of state (EoS) are proposed in this work. The new mathematical expressions of mRK(ω) and mPR(ω) have been determined by correlating the optimal m values, fitted on vapor pressures (Psat) and/or enthalpies of vaporization (ΔvapH) and/or saturated-liquid heat capacities (cP,liqsat) against the acentric factor ω. The correlations determined in this study can be considered as broad-based and sound since they were established for 1721 pure compounds belonging to many different chemical families (hydrocarbons, halogenated, oxygenated, sulfur, nitrogen compounds …) for which experimental data were available. Significant improvements on the reproduction of vapor pressures were obtained for the PR EoS with respect to the original version. The updated SRK EoS achieved similar average deviations for the three properties of interest (Psat,ΔvapH and cP,liqsat), in comparison with the original SRK equation. A substantial improvement is however noticeable for heavy molecules with an acentric factor larger than 0.9.