Accuracy of vapour – liquid critical points computed from cubic equations of state
Juha-Pekka Pokki, Juhani Aittamaa, Kari Keskinen
The calculation methods for the critical point of vapour – liquid mixtures can be classified into empirical and rigorous methods. Both methods are briefly presented and calculated critical points are compared to measured ones. The rigorous methods are found to be more accurate. The rigorous methods are divided into indirect and direct methods and they utilise some equation of state. In the indirect method the whole phase envelope is calculated and the critical point is interpolated. In this work the direct method of Heidemann and Khalil is studied with three equations of state: Soave – Redlich – Kwong (SRK), Peng – Robinson (PR), and Adachi – Lu – Sugie (ALS), together with volume translation added to SRK and PR. These equations of state are accurate in critical temperature and pressure but PR and ALS are more accurate in critical molar volume than SRK.