Towards a predictive Cubic Plus Association equation of state

The Cubic Plus Association (CPA) equation of state combines the Soave-Redlich-Kwong equation of state with the association term from the Wertheim theory. To describe the phase behaviour of chemical com- pounds, three parameters are required for non-associating compounds and five are needed for associat- ing compounds.

However, these parameters are hard to find for some chemical compounds, for example, ionic liquids, pharmaceuticals, polymers and other heavy compounds. Being so, there is a need to pre- dict them. Using a database with 197 chemical compounds of different families, correlations for param- eters and properties were investigated between groups of similar species.

Then, four different methods, which used correlated and fitted parameters, were used in predicting vapour pressure and liquid density from 0.5 ·Tc to 0.95 ·Tc and the results were compared with data from the DIPPR database. Moreover, in a database with 219 binary interaction parameters ( kij ), the exponents n of the Mie potential function were calculated using the Hudson-McCoubrey theory and following two different methods.

Overall, by exploring the common behaviour of the properties and parameters of similar chemical compounds, the predictive ability of the CPA EoS model was successfully enlarged.