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

Abstract

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 noctylphenol (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.

Control of Asphaltene Deposition by Chemical Inhibitors in Calcite Pore: Molecular Dynamics Approach

“…In this research, two asphaltene structures with the continental structure, which is a dominant type of asphaltene structure, 40 are adopted from our previous studies to investigate the formation of hydrogen bonds. 41 Asphaltene 2 (A2) is a continental asphaltene with the potency to form hydrogen bonds due to having hydroxyl and pyridine groups, while asphaltene 3 (A3) is a similar continental asphaltene with no potential for forming hydrogen bonds (Figure 2). Also, the impact of two inhibitors, including a surfactant, namely n-octylphenol (OP), and an IL, namely 1butyl-3-methylimidazolium chloride, on asphaltene deposition in the asphaltene/n-heptane solution is studied.…”

“…The distance between the closest atoms with a cutoff threshold of 0.35 nm is considered the aggregation criterion for asphaltene. 41 The z-averaged aggregation number (g z ) quantifies the aggregate size along the simulation time (see eq 2). 27,41 This analysis is implemented with an in-house python script using the MDAnalysis package and the output coordinates of asphaltene molecules after the GROMACS simulation.…”

Inhibition of Asphaltene Precipitation by Ionic Liquid Polymers Containing Imidazole Pendants and Alkyl Branches

“…Common dispersants include small molecules, polymers, and ionic liquids. − As for small molecules, the intermolecular force between sodium dodecyl benzene sulfonate, sodium dodecyl sulfate (SDS), and asphaltenes was studied. − It is found that the van der Waals force between benzene ring surfactants and asphaltenes is greater than SDS without benzene rings. In addition, octylphenol can form a strong hydrogen bond with asphaltene and inhibit asphaltene aggregation …”

Effect of Aromatic Pendants in a Maleic Anhydride-co-Octadecene Polymer on the Precipitation of Asphaltenes Extracted from Heavy Crude Oil

“…Zheng et al 12 found that hydrophobic ionic liquids can dissolve and disperse asphaltenes well. Ghamartale et al 13 presented that surfactants, such as n-octylphenol (OP), are more effective in reducing the aggregation of continental asphaltenes with hydroxyl and pyridine groups, while metal ions introduced through nanoparticles are undesirable in the process of crude oil refining. Ionic liquids are expensive; surfactants will dissolve in water; and their efficacy is reduced.…”