(193aa) Prediction of Conformation Distribution with the PR+COSMOSAC Equation of State

Most engineering thermodynamic models do not explicitly take into account the existence of multiple molecular conformations; therefore it is questionable to properly describe the phase behavior of a system containing conformationally flexible molecules over a wide range of conditions with such models. In this presentation, we show that the recently developed PR+COSMOSAC equation of state allows for the inclusion of conformation effects in phase equilibrium calculations in a rigorous manner. The conformation distribution of a molecule is obtained by treating the change between any two conformers as a chemical reaction, where the equilibrium constant is determined from the partial molar Gibbs free energy (chemical potential) of all conformers using the PR+COSMOSAC EOS. As a validation of our method, we first compare the calculated and experimental conformation distribution of butane, dichloroethane, cyclohexane, and Glycerol. By treating association as one conformation, it is also possible to examine the change of equilibrium vapor pressure of acetic acid with and without formation of dimers, and the degree of dissociation of electrolyte in water.