Effect of the heteroatom presence in different positions of the model asphaltene structure on the self-aggregation: MD and DFT study

In this study, a series of heteroatoms including nitrogen, oxygen, and sulfur were added to different positions of the model asphaltene structure to study the effect of the heteroatom presence in the selfaggregation of the model asphaltenes. Molecular Dynamics was used to calculate Solubility Parameters, Radial Distribution Function, and Relative Solubility Parameters. Additionally, Reactivity Parameters, Electrostatic Potential, Reduced Density Gradient, and Independent Gradient Model were calculated using the Density Functional Theory to further investigate the Molecular Dynamics results. This study indicated that heteroatoms' diversity and their positions in the model asphaltene structure had an essential role in forming the model asphaltene aggregates. Four different sites in the model asphaltene structure were selected to study the impact of the heteroatom position in the self-aggregation. The presence of heteroatoms in the aliphatic side-chain proved to be more effective in increasing the selfaggregation process in comparison to the aromatic ring position. The heteroatoms' presence in the terminal position of the aliphatic side-chain increased the self-aggregation strength more than other sites in the aliphatic side-chain based on the terminal heteroatoms' ability to perform hydrogen bond formation. Additionally, heteroatoms in the middle of the aliphatic side-chain increased the CH...C dispersion interaction by the carbons' polarization. The heteroatoms in the aliphatic side-chain sites, especially in the terminal position, decreased the asphaltenes' solubility in the heptane and toluene more than the aromatic ring position. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the impact of adding nitrogen, oxygen, sulfur, and other heteroatoms to different positions of a model asphaltene structure on the self-aggregation process. The results showed that the diversity and positioning of heteroatoms played a crucial role in forming asphaltene aggregates.