Phase equilibria modeling of cross-associating systems guided by a quantum chemical multi-conformational framework

Cross-association between molecules may result in several conformations of weakly bound molecular complexes with different association energies. However, the conventional combining rules used in equations of state account only for one conformation. Therefore, in the present work we introduce a framework that allows one to distinguish the cross-interactions between sites of different nature and to expand the number of captured conformations coexisting in the mixture. We incorporated the proposed approach into the Cubic-Plus-Association (CPA) equation of state and applied it to model the binary Vapor-Liquid Equilibrium (VLE) of aqueous mixtures with alcohols (methanol, ethanol, propan-2-ol, tert-butanol, and phenol), acetic acid, and CO2. For the mixtures with alcohols, we report the quantum chemical association energies calculated with the benchmark Domain-Based Local Pair Natural Orbital Coupled-Cluster Single, Double, and Perturbative Triple DLPNO-CCSD (T) approach and compare these values with association energies obtained by fitting to experimental data using a distinguishable interactions approach. Based on the updated results for the binary systems, we investigated how the new cross-association parameters will affect the predictions of the ternary Liquid-Liquid Equilibrium (LLE) of water-alcohol-hydrocarbon mixtures and VLE of water-acetic acid-CO2 mixtures.

Automated summary

The article introduces a new approach to describe the cross-association between molecules, allowing for the simulation of weakly bound molecular complexes with different conformations in mixtures. By incorporating this approach into the equation of state, accurate predictions of vapor-liquid equilibrium and liquid-liquid equilibrium can be made. The new method is validated through experiments on alcohol and acid mixtures, with the results compared to experimental data, demonstrating its accuracy and reliability.