(180s) Modelling the Liquid Phase Behaviour of Aqueous Non-Ionic Amphiphilic Mixtures in the Presence of Oil and Salt Modelled with SAFT-VRE

The liquid phase behaviour of aqueous alykylpolyoxyethylene (CiEj) nonionic amphiphilic mixtures is of great interest in many industrial processes. We propose a model for these mixtures with the SAFT-VR [1] framework and study the coexistence properties of these systems in the presence of oil and salt. The surfactant is modelled with short-range attractive interaction sites that allow the explicit treatment of hydrogen bonding between the water and surfactant molecules. A transferable model for CiEj amphiphiles of varying size is presented, which reproduces the region of liquid-liquid immiscibility of the solutions. We introduce an n-alkane model and study the complex three component (water + amphiphile + oil) phase behaviour; under certain conditions these mixtures exhibit three coexisting liquid phases. We describe the liquid phase behaviour of these systems at ambient pressure and different temperatures comparing with experimental data and provide predictions the high pressure phase behaviour.

The influence of strong electrolytes on the phase behaviour of these systems is studied using the extension of SAFT-VR for electrolytes [2], in which additional terms for the long-range Coulombic interaction and the solvation energies of the ions are incorporated. The Coulombic forces are modelled with the mean spherical approximation in the primitive model. We find the dielectric constant of these systems, which appears in the Coulombic term, has a crucial effect on the phase behaviour of the systems. We study the phase behaviour of water + amphiphile + salt mixtures and predict salting out in agreement with experimental data.

[1] A. Gil-Villegas, A. Galindo, P. J. Whitehead, S. J. Mills, G. Jackson, and A. N. Burgess, ?Statistical associating fluid theory for chain molecules with attractive potentials of variable range (SAFT-VR)?, Journal of Chemical Physics, 106, 4168-4186 (1997).

[2] A. Galindo, A. Gil-Villegas, G. Jackson, and A. N. Burgess, ?SAFT-VRE: Phase behaviour of electrolyte solutions using the statistical associating fluid theory for potentials of variable range?, Journal of Physical Chemistry B, 103, 10272-10281, (1999).