Solubility, miscibility and their relation to interfacial tension in ternary liquid systems

Abstract

The terms, miscibility and solubility, are widely used in phase behavior studies of multicomponent hydrocarbon systems. The distinction between these two terms appears to be still hazy, leading to their synonymous use in some quarters. Also, the relation of these two thermodynamic properties with interfacial tension has largely remained unexplored. However, recently a new experimental technique of vanishing interfacial tension (VIT) has been reported relating miscibility with interfacial tension in gas–oil systems. Therefore, the objectives of this study are to correlate miscibility and solubility with interfacial tension and to investigate the applicability of the new VIT technique to determine miscibility conditions in ternary fluid systems. For this purpose, a standard ternary liquid system of benzene, ethanol and water was chosen since their phase behavior and solubility data were readily available. The interfacial tensions of benzene in aqueous ethanol at various ethanol enrichments were measured using the drop shape analysis (DSA) and capillary rise techniques. The experimental results indicate the applicability of VIT technique to determine miscibility conditions for ternary liquid systems as well. Comparison of IFT measurements with solubility data showed a strong mutual relationship between these two properties, in addition to demonstrating a clear distinction between solubility and miscibility. The interfacial tension appears to be independent of solvent–oil ratio in feed, provided that complete equilibration of fluid phases is allowed to incorporate all the mass transfer effects during experimentation. All these experimental observations have immense application in fluid–fluid phase equilibria studies and to determine the miscibility conditions of gas injection improved oil recovery projects.