EQUATION OF STATE WITH MULTIPLE ASSOCIATING SITES FOR WATER AND WATER HYDROCARBON MIXTURES

The associated-perturbed-anisotropic-chain theory (APACT) of Ikonomou and Donohue is extended to compounds with three associating sites per molecule. The number of associating species is calculated using an expression based on the first-order thermodynamic-perturbation theory (TPT-1) of Wertheim as simplified by Gubbins, Radosz, and co-workers. The new equation predicts accurately the thermodynamic properties of pure water from the triple point to the critical point. It is capable of describing quantitatively vapor-liquid equilibria (VLE), liquid-liquid equilibria (LLE) and vapor-liquid-liquid equilibria (VLLE) for mixtures of water with aliphatic and aromatic hydrocarbons over a wide range of temperature and pressure with one adjustable binary interaction parameter that is independent of temperature and density.