This method (PRP) is a modification of the Peng-Robinson method in which an asymmetric mixing rule containing two parameters is used in determination of the a(T) term in the PR equation. Two adjustable interaction parameters are used, kij and kji. This significantly improves the accuracy of predictions for mixtures of polar and non-polar components. The mixture rule is flawed, however, in that it is not invariant to dividing a component into a number of identical pseudocomponents.
The PRP method in PRO/II uses an improved alpha correlation developed by SimSci. The improved correlation provides more accurate vapor pressure predictions than the original PR formulation for a wide range of components.
In addition to K-values, the PRP equation may be used to predict the enthalpies, entropies and densities for the liquid and vapor phases. The predicted liquid phase densities are not very accurate and the API method is selected by default when the PRP system is chosen.
See "Soave-Redlich-Kwong Panagiotopoulos-Reid (SRKP) and Peng-Robinson Panagiotopoulos-Reid (PRP)" under "Equations of State" in Chapter 2, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
Panagiotopoulos-Reid parameters for specific systems of polar compounds are available, or may be determined by regressing experimental data.