Interfacial tension and phase equilibria for binary systems containing (CH₄-CO₂)+(n-dodecane; n-butanol; water)

This study aims to investigate and predict the interfacial tension at elevated pressure for binary systems, that are essential for the ongoing energy transition. A comprehensive review is carried out on saturated mixture densities as well as interfacial tension in binary, ternary and quaternary systems comprising nonpolar and polar compounds at elevated pressures. In view of the research gap especially with regard to quaternary model systems that contain H₂O, a hydrocarbon, a gas and a surface-active compound, new experimental and theoretical data on binary systems are presented that are required for systematically approaching the respective quaternary system. Mixture densities are determined for the nonpolar systems CO₂+n-dodecane and CH₄+n-dodecane, as well as systems comprising n-butanol with CO₂ or CH₄ at pressures up to 30 MPa in a range of temperatures between 313.15-353.15 K as well as its interfacial tension plus the systems CO₂+H₂O and CO₂+CH₄. In order to theoretically determine these properties, the Perturbed Chain Polar Statistical Associating Fluid Theory is applied for describing the bulk phase equilibrium, subsequently being combined with the Density Gradient Theory for calculating the concentrations across the interface from which the interfacial tension is derived. Experimental results are in very good agreement with the simulation as well as previously available data ranging from an absolute average deviation of 0.44 mN/m for CO₂+n-butanol to 2.58 mN/m for CO₂+water. Furthermore, the simulation is able to reflect the characteristic crossover with respect to pressure and temperature.