Modelling of phase equilibria of glycol ethers mixtures using an association model

Vapor–liquid and liquid–liquid equilibria of glycol ethers (surfactant) mixtures with hydrocarbons, polar compounds and water are calculated using an association model, the Cubic-Plus-Association Equation of State. Parameters are estimated for several non-ionic surfactants of the polyoxyethylene type but mixture calculations are mostly presented for three compounds for which many data are available (2-methoxyethanol, 2-ethoxyethanol and 2-butoxyethanol). The way pure compound vapor pressures and liquid densities are estimated, and the way parameter trends against the van der Waals volume, Kamlet–Taft parameters and, perhaps most importantly, mixture liquid–liquid equilibria data with alkanes are used for choosing optimum parameter sets is illustrated. Vapor–liquid, liquid–liquid equilibria and second virial coefficient data are used for model validation, including aqueous and other cross-associating mixtures. The influence on the results of the association schemes, type of data available, combining rules for cross-associating mixtures and interaction parameters are discussed also in connection to other cross-associating mixtures, previously studied with the model. Finally, the capabilities and limitations of the Cubic-Plus-Association Equation of State in representing this type of multi-functional chemicals, glycol ethers, are discussed.