Using Molecular Orbital Calculations To Describe the Phase Behavior of Cross-associating Mixtures

In previous studies, we have used molecular orbital calculations to determine the thermodynamic changes of dimerization for a number of pure and cross-associated species. We have shown that by using these results in a physical equation of state, the statistical associating fluid theory (SAFT), we are able to accurately model the phase behavior of pure self-associating compounds and binary mixtures of a self-associating compound and a nonassociating compound with a reduction in the number of adjustable parameters. In this study, we consider the phase behavior of binary mixtures in which cross-associated species may occur. To determine the equation of state parameters describing cross association, we introduce a mixing rule based on the results of our molecular orbital calculations. We show that using information derived from our quantum-mechanical calculations results in correlations of mixture vapor−liquid equilibrium data with fewer adjustable parameters and no loss of accuracy, indeed frequently with improved accuracy, compared to the original SAFT model.