FT-ICR MS and Molecular Dynamics Simulations Reveal Emulsifying Behavior of Polar Sulfur- and Oxygen-Containing Asphaltenes Subfractions

Understanding the molecular basis of emulsion stability in heavy crude oils remains a key challenge due to the complex nature of interfacially active asphaltenic (IAA) fractions. In this study, we combined experimental and computational methods to investigate the chemical composition and interfacial behavior of IAA subfractions obtained via wet-silica extraction from a Colombian heavy crude oil. FT-ICR MS (APPI+) and FTIR analyses revealed that these fractions are enriched with low-aromatic oxygen- and sulfur species, particularly those of the O2S2 and OS classes. Interfacial tension (IFT) measurements showed a concentration-dependent reduction of up to 50%, indicating high amphiphilicity. Molecular dynamics simulations of a representative O2S2-type molecule demonstrated spontaneous adsorption at the oil–water interface, with sulfoxide groups oriented toward water and aliphatic regions anchoring in the organic phase. These findings suggest that specific sulfur–oxygen functionalities contribute significantly to crude oil interfacial activity. Although this study focuses on a single molecular model, the results highlight the functional moities that may be relevant in stabilizing emulsions. This integrative approach advances the understanding of how the chemical structure influences interfacial behavior in complex petroleum systems.