Molecular thermodynamics for fluids at low and high densities. Part II: Phase equilibria for mixtures containing components with large differences in molecular size or potential energy

Abstract

AbstractThe molecular‐thermodynamic correlation presented in Part I for pure fluids is extended to mixtures; this extension is particularly useful for mixtures of components with large differences in molecular size or potential energy. The novel feature of this correlation is a separation of the high‐density and low‐density contributions to the residual Helmholtz energy; this separation allows use of separate mixing rules for each density regime, guided by theoretically defined boundary conditions. Such flexibility is necessary to represent phase equilibria in highly asymmetric fluid mixtures such as water‐hydrocarbon systems. Phase equilibria are correlated for a variety of binary and multicomponent mixtures, including a petroleum reservoir fluid containing carbon dioxide and including a mixture of hydrogen and coal‐derived liquids.