We present the latest developments in thermodynamic modeling using the SAFT-γ Mie group-contribution equation of state. The group database is updated, featuring now 58 groups; this expanded database incorporates new parameters for interactions between both like and unlike groups. This provides the capability to treat mixtures including alcohols, ethers, ketones, carboxylic acids, and acetates, amines, aromatic and cyclic compounds, electrolytes, inorganic acids, and some common solvents, such as water and acetone. A discussion is provided relating to the assignment of the groups, including some secondary groups that are introduced for multifunctional molecules to capture the influence of molecular polarization effects on the thermodynamic properties. Performance of the SAFT-γ Mie approach is illustrated for a wide variety of systems, highlighting its use in describing solid−liquid as well as vapor−liquid and liquid−liquid equilibria.

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The first-order thermodynamic perturbation theory of Wertheim (TPT1) is extended to treat ring aggregates, formed by inter-and intramolecular association. The expression for the residual association contribution to the Helmholtz free energy for ring aggregates, incorporating the appropriate terms in Wertheim's fundamental graph sum of the TPT1 density expansion, is derived to calculate the distribution of the molecular bonding states. This requires the introduction of two new parameters to characterise each possible ring type: the ring size τ , which is equal to one in the case of intramolecular association, and a parameter W that captures the likelihood of two ring-forming sites bonding. The resulting framework can be incorporated in equations of state that account for the residual association contribution to the free energy, such as the statistical associating fluid theory (SAFT) family, or the cubic plus association (CPA) equation of state. This extends the applicability of these equations of state to mixtures with an arbitrary number of association sites capable of hydrogen bonding to form intramolecular and intermolecular rings. The formalism is implemented within SAFT-VR Mie to calculate the fluid-phase equilibria of model chain-like molecules containing two associating sites A and B, allowing for the formation of open-chain aggregates and intramolecular bonds. The effect of adding a second component that competes for the association sites that mediate intramolecular association in the chain is also examined. Accounting for intramolecular bonding is shown to have a significant impact on the phase equilibria of such systems.

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