This method (PRM) is a modification of the mixing rule for the PR-Panagiotopoulos-Reid by SimSci in which two more adjustable parameters, cij and cji are introduced. This improves the prediction for polar-nonpolar systems , where the nonideality is large or strongly asymmetric. SimSci has fit many binary systems of chemicals to this equation and the parameters are supplied in PRO/II.
The PRM 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 PRM 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 PRM system is chosen.
See "Soave-Redlich-Kwong Modified (SRKM) and Peng-Robinson Modified (PRM)" under "Equations of State" in Chapter 2, Volume 1 of the PRO/II Reference Manual for more information.
Application Guidelines
Three phase separators for water-hydrocarbon systems, such as those found in FCC gas plants and hydrocrackers. Lube oil and solvent de-waxing units. Natural gas systems containing polar compounds such as methanol. Any chemicals operation for which the parameters are supplied by PRO/II or may be determined by regression.