The use of theoretical methods for the study of asphaltene aggregation is of great importance because they can support the hypotheses proposed for both the aggregation models and the aggregation process. Classical molecular dynamics simulations allow to shed light on the link between the molecular structures and inter-molecular interactions which are the driving forces of the aggregations of asphaltens. Recent studies have proposed models for asphaltenes and two sub-fractions called A1 and A2. Molecular dynamics simulations of model molecules proposed for A1 and A2 subfractions showed that the presence of hydrogen bonds is a key factor in the aggregation of asphaltenes in addition to their H/C ratio. In this presentation we show the behavior of the proposed models, belonging to subfractions A1 and A2, using molecular dynamics simulations in various solvent; Toluene, heptane, tetrahydrofuran (THF), and chloroform. In a first simulation, the systems were built by randomly introducing the asphaltene molecules and the formation of aggregate in each solvent was followed. It was observed that in THF the formation of aggregates larger than dimers did not occur and their interaction was mainly π-stacking interactions. This result can be explained by the solubility of these subfractions in THF. In a second simulation, the aggregate is obtained in heptane and then introduced in THF. It was observed that the aggregate remained stable during the simulation. This gives support to two important points: firstly, the THF preserves the aggregates once formed which guarantees its analysis when using this solvent and corroborate previous experimental finding were aggregates of different size are observed including at very low concentration solutions; secondly it gives support to the idea that the aggregates could be filled with "trapped compounds", giving us an idea of the maturation of the crude oil.

Molecular cartography of asphaltens from classical molecular dynamics simulations

ACS Fall 2021

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