Molecular insights into asphaltene desorption from silica surface by ionic and non-ionic nitrogen-based additives

The strong adsorption of asphaltenes on reservoir minerals is a major constraint on heavy oil recovery. Although some nitrogen-based chemicals have shown promise in desorbing asphaltenes, their working mechanisms remain poorly understood. Herein, molecular dynamics (MD) and density functional theory (DFT) have been used to reveal the molecular-interaction mechanisms by which ionic liquids (ILc) and switchable-hydrophilicity solvents (in neutral (SHSn) and dicationic (SHSc) forms) facilitate asphaltenes desorption from silica surface. We identify two key functions of these nitrogen-based additives in enhancing the asphaltene desorption: (ⅰ) the nitrogen groups attack the asphaltene aggregates, reconstructing the hydrogen bonding between asphaltene molecules and dispersing the asphaltene aggregates through an encapsulation effect, and (ⅱ) replacing the asphaltenes by competitive adsorption on solid surface. In particular, ILc significantly reduces asphaltene–silica interactions via charge complementarity, while SHSn displaces asphaltenes through hydrogen bonding yet displays limited efficacy, and SHSc exhibits strong electrostatic binding while favoring encapsulation, thereby constraining overall dispersion. Overall, nitrogen functionalities amplify electrostatic attraction and help overcome exchange-repulsion, suggesting that optimizing both dispersion and interfacial displacement will improve oil–solid separation. These mechanistic insights provide a foundation for the rational design of advanced nitrogen-based additives for enhanced heavy oil recovery and sustainable separation processes.