(338j) A Priori Phase Equilibria Predictions From First-Principles Solvation Calculations

Cubic equations of state have been widely used in process simulators for the description of fluid properties and phase behaviors. While these thermodynamic models are very accurate for pure fluids, experimental data on critical properties and accentric factor are often necessary, and additional approximiations (e.g., the mixing rules) must be introduced for mixtures. In this presentation we propose a promsing solutions for these issues based on solvation theory and recent advances in first-principles solvation calculations. Taking the Peng-Robinson equation of state as an example, we show that its energy a(T,x) and volume b(x) parameters can be determined from the result of quantum mecahnical solvation calculations. In this method, neither species dependent nor binary interaction parameter is used. As a consequence, the thermodynamic properties and phase behaviors of both pure and mixture fluids can be determined without using any experimental data. Furthermore, the accuracy of the such an EOS for liquids is comparable to that of a liquid activity coefficient model. We will illustrate the utilization of this method in the predctions of the critical properties, vapor pressure (as a function of temperature), the liquid phase density for pure substances, and the vapor-liquid liquid-liquid, and vapor-liquid-liquid equilibrium for mixtures.