Salinity-regulated interfacial interactions of asphaltene subfractions: Mechanistic insights into petroleum emulsion stability and destabilization.

Asphaltenes are problematic petroleum components that contribute to persistent oil-water emulsions and complicate produced water treatment. However, how asphaltene subfractions with distinct interfacial activities respond to brine salinity and regulate emulsion stability remains insufficiently understood. Here, the salinity-dependent adsorption, interfacial film formation, and intermolecular interactions of interfacially active asphaltenes (IAA) and interfacially non-active asphaltenes (INAA) were investigated at different NaCl concentrations using dynamic interfacial tension measurements, interfacial film characterization, surface force measurements, and emulsion stability tests. With increasing NaCl concentration, the extrapolated equilibrium interfacial tension of INAA-containing systems increased monotonically, whereas that of IAA-containing systems initially decreased and then increased. Apparent diffusion coefficients and crumpling ratios increased with NaCl concentration up to 1 M and decreased at 3 M, whereas compression energies remained elevated or increased further at 3 M. Droplet adhesion increased at 1-100 mM NaCl but declined sharply at 1-3 M. Bottle tests using a steam-assisted gravity drainage emulsion showed greater stability at low salinity and pronounced oil-water separation at high salinity. These results reveal a salinity-dependent transition from interfacial film strengthening to emulsion destabilization, providing mechanistic insights into the salinity-regulated interfacial interactions of asphaltene subfractions in stabilizing petroleum emulsions.