Cohesion Factor Relations For Cubic Equations of State-Part I: Peng-Robinson Equation of State

Abstract

Major factor in the success of predictive capability of Cubic Equations of State is its temperature dependency through cohesion factor. Six cohesion function models for Peng Robinson (PR) Equations of State, available in literature have been compared. Comparison is based on estimation of pure component vapor pressures. 32 compounds have been selected for the study. Vapor pressures have been predicted using equi-fugacity criteria based algorithm implemented in MATLAB. The reduced temperatures were studied in three regions; (i) Tr < 0.7 (ii) Tr ≥0.7 and (iii) entire range from triple point to critical point. Both for the entire range of temperature and for the region of Tr <0.7, original Twu’s correlation [10] was found to be better compared to other models. For Tr 0.7, original PR relation modified by Gasem K A M et al [6] turns out to be better. For the region Tr <0.7, the accuracy level was much below that of the entire range as well as for the region Tr0.7. Behavior at supercritical conditions is also compared.