A Simple Method to Predict and Interpret the Formation of Azeotropes in Binary Systems Using Conventional Solvation Free Energy Calculations

Simple expressions are presented to determine if a binary system will exhibit a minimum or maximum boiling azeotrope using conventional free energy calculations using molecular simulation or electronic structure calculations in a continuum solvent. The expressions compare the solvation free energy of each component at infinite dilution relative to itself, requiring four total solvation free energy calculations per binary system. The solvation free energies can be related to intermolecular interactions and, therefore, shed insight into why an azeotrope occurs. The application of the expressions is demonstrated for 2366 binary systems using solvation free energies computed using electronic structure calculations in the SM12, SM8, and SMD universal solvent models. The overall success rate for predicting the correct phase behavior was 0.718, 0.711, and 0.685 for SM12, SM8, and SMD, respectively.