New Molecular Insights into Aggregation of Pure and Mixed Asphaltenes in the Presence of n-Octylphenol Inhibitor

摘要

Asphaltene stability can be perturbed during the oil production and transportation, leading to asphaltene precipitation and deposition. Chemical inhibitors are usually added to the oil phase to postpone asphaltene deposition. The chemical bonding between asphaltene and inhibitor molecules, and the steric hindrance are the key mechanisms of aggregation inhibition. Nevertheless, the interaction mechanisms between asphaltenes and chemical inhibitors still need more research investigations. In this paper, we use an advanced computational chemistry tool, molecular dynamics (MD), to analyze the inhibitory effect of n-octylphenol (OP) on three different asphaltene structures at 1 bar and 300 K. To meet the objectives, the asphaltene aggregation and aggregate characterization in both cases of pure and mixed asphaltenes are studied. It is concluded that the archipelago asphaltene (A1) does not aggregate appreciably in the absence of OP; nevertheless, OP reduces the aggregation. The addition of OP is more effective in reducing the aggregation rate for the continental asphaltene, containing hydroxyl and pyridine groups (A2), which is due to the formation of strong hydrogen bonds between the asphaltene and OP, compared to the aromatic stacking between asphaltene and asphaltene. The presence of hydrogen bonds significantly changes the characteristics of aggregates in both scenarios: in the absence and presence of OP. Hence, OP exhibits less efficiency for the continental asphaltene case without hydrogen bond potential (A3). For the mixed asphaltene systems, OP considerably lowers the aggregation rate when A2 and A3 are simultaneously present; the higher relative portion of OP to A2 is the main reason for this behavior. This study reveals that the OP can be an effective inhibitor, depending on the distribution of different types of asphaltenes in the crude oil. The same strategy can be used to screen proper inhibitors or inhibitor mixtures for various types of asphaltenes.