Interfacial tension in water/n-decane/naphthenic acid systems predicted by a combined COSMO-RS theory and pendant drop experimental study

Kristian B. Olesen, Anne-Sofie Dahl Pedersen, Lasse V. Nikolajsen, Martin P. Andersson, Theis I. Sølling, Stephan P. A. Sauer, Kurt V. Mikkelsen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


The interfacial tension of systems containing water, n-decane, and model naphthenic acids were investigated using a predictive model based on COSMO-RS theory and experimental pendant drop measurements. Five naphthenic acid homologues that are considered to be representative of surfactants inherent to crude oil were dissolved in n-decane at equal concentrations. The interfacial tensions of the five systems at an acid concentration of 1.66 mol% relative to n-decane were experimentally determined to be 27–30 mN/m. The interfacial tensions of the five different acid-decane phases against water were also predicted using density functional theory (DFT) calculations and COSMO-RS theory. The accuracy of the predictions was very good as confirmed through pendant drop measurements of the interfacial tension. The mean-absolute-deviation between experimental and predicted values was 2.6 mN/m thus demonstrating the high predictive power of COSMO-RS theory for calculating the interfacial tension at oil–water interfaces in the presence of surface-active compounds.
Original languageEnglish
JournalMolecular Physics
Publication statusAccepted/In press - 2020

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