Phase behaviour of water+nonionic surfactant systems: experiments and modelling applying the Peng–Robinson equation of state with the Wong–Sandler mixing rules and the UNIQUAC gE-model

In this work, experimental liquid–liquid phase equilibrium data of the systems water+C6E4 and water+C7E4 at pressures up to 100 MPa and in a temperature range between 315 and 355 K are presented. Further, modelling results of several water+nonionic surfactant systems at various pressure are shown. The investigated binary water+surfactant systems contained besides C6E4 and C7E4 the following other surfactants: C4E1, C6E3, C7E3, and C7E5. As a model, the Peng–Robinson equation of state with the Wong–Sandler mixing rules and the UNIQUAC gE-model was used. The model parameters were adjusted to experimental phase equilibrium data at 0.1 MPa. The resulting parameter sets were used for the prediction of the phase behaviour at higher pressures. The fitted model expresses the experimentally found type of phase behaviour quite correctly. However, the pressure influence on the phase behaviour of these systems could only be described qualitatively.