SIMULTANEOUS PREDICTION OF PHASE-EQUILIBRIA, INTERFACIAL-TENSION AND CONCENTRATION PROFILES

The gradient theory of inhomogeneous fluids, as originally introduced by Van der Waals and Cahn and Hilliard, was used in the reformulated f orm according to Carey et al. to reveal simultaneously the behaviour o f fluid interfaces and the bulk phases. The parameter present in the g radient approximation, the so-called influence parameter c, was evalua ted for pure components using interfacial tension data. The Peng-Robin son equation of state was selected to model the phase behaviour of the homogeneous fluid. In this study it was established that the interfac ial tensions of decane and benzene were predicted accurately, while th e interfacial tensions of carbon dioxide and water were less accuratel y predicted, due to incapabilities of the Peng-Robinson equation as we ll as the gradient approximation. In addition two different binary mix tures were studied: carbon dioxide-decane and water-benzene. For the f irst system, comparison with some experimental interfacial tensions sh owed that the theory can give accurate predictions for binary mixtures . For the second system no experimental data were available in literat ure. It appeared also that gradient theory was capable of revealing th e structure of the interface. This was shown near the upper critical e ndpoint of the three-phase equilibrium curve in the system carbon diox ide-decane.