Impact of Asphaltene Surface Energy on Stability of Asphaltene-Toluene System: A Parametric Study

Asphaltene is a complex macromolecule whose abundance strongly affects the physical and interfacial properties of crude oil. Asphaltene molecules may precipitate during crude oil production/transportation, which may lead to plugging/clogging of wellbores, pipelines, and equipment. In this study, the solubility of asphaltene in toluene has been investigated by calculation of noncovalent interaction energies between asphaltenes in toluene medium. The results of this study revealed that the main interactions in the asphaltene-toluene system are Lifshitz-van der Waals and Lewis acid-base interactions, whereas the electrostatic double layer is of lower comparative order of significance specifically at lower separation distances and lower zeta potentials. However, the repulsive electrostatic double-layer interactions may assist in stabilizing the asphaltene-toluene system based on the comparative values of Lifshitz-van der Waals, Lewis acid-base, and electrostatic double-layer interactions. This is the case especially at higher separation distances and/or higher temperatures where asphaltene particles have greater values of zeta-potential. Furthermore, it is illustrated that when asphaltene has a lower electron-donor parameter, i.e., a lower basicity than toluene, then Lewis acid-base interactions between asphaltenes in toluene are repulsive. This repulsive Lewis acid-base interaction may compensate for the attractive van der Waals interactions between asphaltene particles at low asphaltene basicity. Finally, the electron donor/acceptor component of the surface energy strongly determines the fate of asphaltene in crude oil colloidal system.