Revealing the non-covalent interactions between oxygen-containing demulsifiers and interfacially active asphaltenes: A multi-level computational simulation

Non-covalent interactions have been proved to be dominated in the process of demulsification. Herein, a hierarchical-three-level method of combined density functional theory (DFT) simulation has been proposed to understand the non-covalent interactions between a home-made demulsifier (MJTJU-2, oxygen-enriched non-ionic demulsifiers) and asphaltenes (IAA) from three levels: electrostatic interactions sites, strength of inter-molecular interactions, and water phase affinity of large molecules. It is found that the demulsifier molecules play the roles in breaking emulsions from several aspects: (i) The sites of electrostatic dominated interactions (i.e., hydrogen bond) were derived from the heterogeneity of electrostatic potential (ESP) at molecular surface. The multi-branched structure of demulsifier facilitated the superimposed effect, forming large span of ESP (−50.125 to 60.074) and multiple extreme points. (ii) The carboxyl groups and flexible structure of demulsifier led to the reconstruction of hydrogen bonds and dispersion effect (i.e., Van der Waals force, π-π stacking) between IAAs and demulsifiers. (iii) Finally, a cage-core hybrid solvent model was proposed specifically applicable to the oil–water interface system at molecular scale. Results showed that the interfacial activity of demulsifier derived from the hydrogen bonds between MJTJU-2 with water molecules, which presented high strength (−6.740 kcal/mol) and high density. These findings could provide significant insights for the development of new functional demulsifiers which are inspired by the relationships between structural characteristics and non-covalent interactions.