Alternation of asphaltene binding arrangement in the presence of chemical inhibitors: Molecular dynamics simulation strategy

Abstract

Asphaltene deposition is one of the challenging issues in petroleum production and transportation. Chemical inhibitors are commonly employed to mitigate the asphaltene aggregation, which is the primary stage in controlling asphaltene deposition. Design and selection of an effective chemical inhibitor have always been a challenge for the industry, considering substantial variations in characteristics and structures of asphaltene and petroleum. The chemical inhibitors interact with the asphaltene aggregation by alternating their binding arrangement, which is a key factor in the aggregate stability. Molecular studies that can reveal the main mechanisms are still scarce, and the available investigation techniques in this area need significant improvements. Therefore, in this work, molecular dynamics (MD) simulation is employed as a cost-effective and reliable method to study the impact of chemical inhibitors on the binding arrangement of two asphaltene structures. One asphaltene structure contains a hydroxyl group and pyridinic nitrogen in its polyaromatic core, while another lacks both groups. The chemical inhibitors are octylphenol (OP), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), and 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). The simulation results show OP cannot stop the quadrupole–quadrupole interactions between the asphaltenes since the force between OP’s benzene ring and asphaltene polyaromatic core is weaker than the force between the two polyaromatic cores. Nevertheless, OP forms a hydrogen bond with the asphaltene and prevents asphaltene molecules from approaching each other by providing steric hindrance around the molecules. As a result, OP does not show a promising potential to reduce the parallel stacking, especially for the asphaltene with no hydrogen bond potential, while it relatively reduces the T-shape arrangement for both asphaltenes. Ionic liquids (ILs) beat the quadrupole–quadrupole interactions between the asphaltene cores with cation-quadrupole force and notably reduce the parallel stacking. They also lower the number of T-shape binding arrangements between the asphaltene molecules. This research reveals the mechanism for the studied inhibitors to interfere with the asphaltene aggregation based on their functional groups. We introduce new criteria to distinguish different arrangements. The binding arrangement of polyaromatic compounds (such as asphaltene) are not only important in the petroleum industry but also play a crucial role in designing optical and electronic nanodevices. The introduced approach is a new pathway to improve the design of chemical materials to either inhibit or promote aggregation by changing binding arrangement of polyaromatic compounds.