A novel approach to phase equilibria predictions using ab initio methods

Molecular orbital ab initio calculations have been used to compute interact ion energies between pairs of molecules in a large molecular cluster. These energies are then used as the interaction energy parameters in the widely used Wilson and UNIQUAC activity coefficient models. Low-pressure vapor-liq uid equilibria predictions based on the calculated parameters have been com puted for binary systems of water with methanol, ethanol, 1-propanol, 2-pro panol, formic acid, acetic acid, acetone, acetonitrile, acetaldehyde, and m -methylformamide. Excellent predictions are obtained with the UNIQUAC model , whereas poor results are found with the Wilson model. In several cases, o ur predictions are also superior to those obtained from UNIFAC. In addition , using the same parameters and the UNIQUAC model, high-pressure vapor-liqu id equilibria predictions were made using the Peng-Robinson-Stryjek-Vera eq uation of state and the Wong-Sandler mixing rule for methanol, ethanol, 2-p ropanol, and acetone separately with water. The low- and high-pressure resu lts demonstrate that this unique approach can lead to accurate vapor-liquid equilibrium predictions for hydrogen-bonding mixtures based only on pure-c omponent properties and the structure of the molecules.