(181p) Modeling of the Surface Tension of Pure Components and Mixtures Using the Density Gradient Theory and a Theoretically Derived Influence Parameter Correlation

Interfacial tension is a very important thermophysical property for many technological processes, including industrial separations, (enhanced) oil recovery, and specialty products such as paints and detergents. Since the determination of interfacial properties by experimental techniques is time-consuming and expensive, reliable methods to predict these properties are highly desired. This work focuses on the application of the density gradient theory for the prediction of surface tensions of pure components and mixtures with hydrocarbons. With the density gradient theory surface tensions can be predicted when the Helmholtz free energy of the homogeneous fluid is known as well as an influence parameter, which determines the importance of the contribution of density gradients in the interface to the total Helmholtz energy of the system. The PC-SAFT equation of state is used to calculate the Helmholtz energy and other thermodynamic properties of the system. Because of its good predictive capabilities PC-SAFT has been widely applied for phase equilibria calculations of pure components and mixtures, including complex systems such as solutions with polymers and petroleum mixtures. The influence parameter has a molecular definition, but is often calculated from experimental data or semi-empirical expressions. In this work a correlation for the influence parameter is developed using its theoretical definition as starting point. With the developed correlation influence parameters can be calculated for a component or pseudo-component, provided that its PC-SAFT pure component parameters are known and its phase behavior is well-predicted. It will be shown that the developed influence parameter correlation in combination with the density gradient theory and the PC-SAFT equation of state gives good predictions of surface tensions for pure components as well as binary and ternary mixtures with hydrocarbons.