This paper presents the Wilson-NA model to evaluate phase equilibria for mixtures containing not only conventional solvents but also other chemicals, such as ionic liquids, fluorous solvents, deep eutectic solvents, bio-based solvents, and pharmaceuticals. The Wilson-NA model is obtained by simplifying the ratio \({v}_{j}^{\text{L}}/{v}_{i}^{\text{L}}\) in the original Wilson model. Then, the liquid molar volume, \({v}_{i}^{\text{L}}\) , is assumed to be proportional to the number of atoms (NA) other than hydrogen atoms, \({\nu }_{i}^{\text{NA}}\) , in the molecule. This originates from the Analytical Solution of Groups model, where the number of segments is evaluated for the combinatorial term. First, the relationship between \({\nu }_{i}^{\text{NA}}\) and \({v}_{i}^{\text{L}}\) , and the ratio for two compounds, \({\nu }_{j}^{\text{NA}}/{\nu }_{i}^{\text{NA}}\) and \({v}_{j}^{\text{L}}/{v}_{i}^{\text{L}}\) , are discussed. Next, we employed the Wilson-NA model to correlate the experimental binary data of vapor–liquid equilibria (VLE) and bubble point pressures, and the accuracy was compared with that from the original Wilson model. The VLE prediction was also extended to some ternary systems just by using the interaction parameters for the constituent binary systems. We also applied the method to a modified version of the Wilson model, proposed by Tsuboka and Katayama, to predict the liquid–liquid equilibria for binary and ternary systems containing compounds with high viscosity, fluorous solvents, and ionic liquids. Finally, the Wilson-NA model was evaluated to solid–liquid equilibria (SLE) for binary systems containing pharmaceutical, terpene, or eutectic solvent, for the purpose of considerations to complex systems.
