Correlations of Equilibrium Interfacial Tension Based on Mutual Solubility/Density: Extension to n-Alkane–Water and n-Alkane–CO2 Binary/Ternary Systems and Comparisons With the Parachor Model

Abstract

In this study, new and pragmatic interfacial tension (IFT) correlations for n-alkane–water and n-alkane–CO2 systems are developed based on the mutual solubility of the corresponding binary systems and/or density in a pressure range of 0.1–140.0 MPa and temperature range of 283.2–473.2 K. In addition to being more accurate (i.e., the absolute average relative deviation (AARD) is 1.96% for alkane–water systems, while the AARDs for alkane–CO2 systems are 8.52% and 25.40% in the IFT range of >5.0 mN/m and 0.1–5.0 mN/m, respectively) than either the existing correlations or the parachor model (the AARDs for alkane–CO2 systems are 12.78% and 35.15% in the IFT range of >5.0 mN/m and 0.1–5.0 mN/m, respectively), such correlations can be applied to the corresponding ternary systems for an accurate IFT prediction without any mixing rule. Both a higher mutual solubility and a lower density difference between two phases involved can lead to a lower IFT, while pressure and temperature exert effects on IFT mainly through regulating the mutual solubility/density. Without taking effects of mutual solubility into account, the widely used parachor model in chemical and petroleum engineering fails to predict the IFT for CO2/methane–water pair and n-alkane–water pairs, though it yields a rough estimate for the CO2–water and methane–water pair below the CO2 and methane critical pressures of 7.38 and 4.59 MPa, respectively. However, the parachor model at least considers the effects of solubility in the alkane-rich phase to make it much accurate for n-alkane–CO2 systems. For n-alkane–CO2 pairs, the correlations developed in this work are found to be much less sensitive to the liquid density than the parachor model, being more convenient for practical use. In addition, all the IFTs for the CO2–water pair, methane–water pair, and alkane–CO2 pair can be regressed as a function of density difference of a gas–liquid system with a high accuracy at pressures lower than the critical pressures of either CO2 or methane.