CALCULATION OF INTERACTION PARAMETERS FOR BINARY SOLID SCF EQUILIBRIA USING SEVERAL EOS AND MIXING RULES

Binary interaction parameters (BIPs) have been computed for the description of solid-supercritical-fluid equilibrium using solubility data. Several combinations of cubic equations-of-state and mixing rules have been studied, computing parameters and average errors for over 30 systems for which experimental data were available in the literature. The computation was done by defining an objective function, and minimizing it by a suited algorithm - Fibonacci (golden section) algorithm to find one binary interaction parameter and the Nelder and Mead (Simplex) method to find two interaction parameters. Equations-of-state (EOS's) chosen for this study were Redlich-Kwong (RK), Soave (SRK), and Peng-Robinson (PR), whereas the mixing rules used were quadratic (van der Waals) and cubic. Good agreement was found between computed values and the few values found in the literature. Results using one interaction parameter for the three EOS indicate that, globally, there is no significant difference in the prediction ability of these EOS. Differences among the EOS were found when the errors for individual systems were compared. These differences were explained in terms of the ability of the EOS to predict specific molecular interactions that occur in these systems. For the PR-EOS, two mixing rules were compared. The corresponding results show no substantial difference for these mixing rules. Finally, the results for the PR-EOS using one BIP were compared to those for which two BIPs were used. A marked reduction in the errors was observed when the second BIP was included in the analysis.