Understanding the behaviors of toluene in asphaltene

Abstract During the aqueous-nonaqueous hybrid bitumen extraction (HBE) or the solvent extraction processes of unconventional oil ores, especially for the ores with high asphaltene content, solvent loss in tailings has been a major factor affecting environmental issues and operating costs. Herein, we proposed the experimental tests with molecular dynamic simulation methods to understand the cause and mechanism of solvent (e.g., toluene) loss together with asphaltenes. The experimental results by TG-MS clearly show that the asphaltenes can confine the toluene molecules (>0.19 wt %) in two different ways: i) a part of the toluene is adsorbed on the asphaltenes surface, and ii) a part of the toluene is trapped in asphaltenes ‘cage’, which could be released at much higher temperature (∼148-162 ℃, much higher than the boiling point of toluene). The relative amount of the confined toluene in the asphaltenes is also found to be asphaltene type-dependent. The asphaltenes with higher aromatic degree (i.e., Iran asphalt) showed stronger ability to entrain and confine toluene, leading to higher relative amount of solvent being occluded. To further understand how the asphaltenes confine the toluene molecules, the molecular dynamic simulation has been conducted. It is found that the van der Waals (vdW) forces between toluene and asphaltene are the major interactions which influence the escaping of toluene from asphaltene. The radial distribution function (RDF) analysis showed that the vdW force is mainly the π−π stacking between benzene ring in toluene and aromatic rings in asphaltenes. This finding would provide direct and fundamental understanding for the development of solvent recovery and viscosity reduction of heavy oils.