Phase behaviour of water plus nonionic surfactant systems: experiments andmodelling applying the Peng-Robinson equation of state with the Wong-Sandler mixing rules and the UNIQUAC g(E)-model

In this work, experimental liquid-liquid phase equilibrium data of the syst ems water+C6E4 and water+C7E4 at pressures up to 100 MPa and in a temperatu re range between 315 and 355 K are presented. Further, modelling results of several water+nonionic surfactant systems at various pressure are shown. T he investigated binary water+surfactant systems contained besides C6E4 and C7E4 the following other surfactants: C4E1, C6E3 , C7E3, and C7E5. As a mod el, the Peng-Robinson equation of state with the Wong-Sandler mixing rules and the UNIQUAC g(E)-model was used. The model parameters were adjusted to experimental phase equilibrium data at 0.1 MPa. The resulting parameter set s 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. (C) 2000 Elsevier Sci ence B.V. All rights reserved.