Evaluation and Mechanism of the Depolymerization Effect of Aromatic Hydrocarbons on Asphaltene: A Combined Experimental and Molecular Dynamics Simulation Study

Abstract

While earlier studies examined rejuvenator effects on asphaltenes, detailed mechanistic understanding and quantitative analysis remain limited. In particular, it remains unclear whether different rejuvenators exhibit distinct deagglomeration mechanisms and efficiencies, making it challenging to optimize rejuvenator selection. This study systematically investigates the various depolymerization mechanism and efficiency of different rejuvenators using three representative types of rejuvenators: light aromatic compounds (Benzene-Toluene-Xylene, BTX), polyaromatic hydrocarbons (PAHs), and straight-chain alkanes (BR1 and BR2). We used molecular dynamics simulations to evaluate several key properties. These included radial distribution functions (RDF), fraction of free volume (FFV), self-diffusion coefficients, average aggregation number ( g z ), and intermolecular interaction energies. The analysis was performed under both aging and rejuvenation conditions. The results show that BTX effectively restores the RDF profile of aged asphaltenes by eliminating the additional short-range peak associated with dimer formation. At elevated temperatures, all rejuvenators increase the FFV and self-diffusion coefficients of saturate, aromatics, resins, and asphaltenes (SARA) fractions and reduce the aggregation number. However, BTX consistently exhibits the strongest deagglomeration effect, while PAHs show limited impact and even reduce FFV and mobility at lower temperatures. BTX also significantly lowers the van der Waals and total interaction energies between aged asphaltenes, whereas PAHs exert only minor influence. Small-angle X-ray scattering (SAXS) experiments confirm the simulation findings, showing that both BTX and PAHs reduce the radius of gyration of asphaltene clusters. Notably, only BTX restores the aged asphaltene aggregates to a mass fractal structure, indicating effective structural recovery. A mechanistic model is proposed wherein aromatic rejuvenators intercalate into asphaltene PAH layers, increasing interlayer spacing and promoting exfoliation. BTX compounds, with their smaller molecular size, penetrate these layers more easily. In contrast, bulkier PAHs form stronger π – π interactions, limiting their intercalation and reducing their deagglomeration efficiency.