Molecular Dynamics Study of Model Molecules Resembling Asphaltene-Like Structures in Aqueous Organic Solvent Systems

Abstract

Molecular dynamics (MD) simulations were used to study the aggregation of model molecules representing some structural features of asphaltenes in different solvents, namely, water, toluene, and heptane. Three different model molecules with similar molecular weights were developed as representatives of continental- and archipelago-type structures of asphaltenes. Two types of continental models were employed, one containing no charged entities and another containing one anionic terminal carboxylic group on an aliphatic chain. Analysis of the aggregate structures in single pure solvents indicate stacking of the polyaromatic rings as the dominant structural feature of the aggregates. Simulations were then conducted to study aggregation and partitioning of these model molecules in binary mixtures of water and toluene. A key observation from these simulations was that uncharged molecules did not congregate at the toluene−water interface, whereas charged terminal groups had a distinct affinity for the toluene−water interface. In the presence of charged entities, the resulting aggregate had a complex three-dimensional structure containing stacked polyaromatic rings tethered to the interface by the anionic terminal groups.

Model molecules mimicking asphaltenes

“…This means that key factor(s) ruling asphaltene self-association has (have) not been identified yet. MD study started by comparing the aggregation properties in water, toluene, and heptane of three different model molecules after 10 ns 25 . The molecules were found to selfassociate in single pure solvents by stacking of their polyaromatic rings.…”

“…The molecules studied were chosen to represent different models proposed to represent common structural and compositional aspects of petroleum asphaltenes: continental model, archipelago model and anionic continental model [25][26][27] .…”

Molecular Dynamics Simulation of Self-Aggregation of Asphaltenes at an Oil/Water Interface: Formation and Destruction of the Asphaltene Protective Film

“…Bhattacharjee et al studied the asphaltene-like structures in aqueous/organic solvent systems. 33 The simulations showed that the model molecules tend to form aggregates in pure solvent, and specific fractions with ionic terminal groups on the aliphatic chains could dramatically enhance the interfacial activity of the entire asphaltene population. Such findings indicated that the interfacial activity of the asphaltene molecules was probably related to their terminal group characteristics rather than the polyaromatic rings.…”

A DPD study of asphaltene aggregation: The role of inhibitor and asphaltene structure in diffusion-limited aggregation

“…Nano-aggregates in the correct size range (∼ 2 nm and above) formed without inhibitor, provided that the asphaltene side chains contained polar groups (with or without heteroatoms in the polyaromatic core). The nano-aggregates displayed internal π − π stacking of the polyaromatic rings [8,7,30]. Without the polar side chain groups, the aggregates were larger and above ∼ 4 nm (with heteroatoms) or non-existent (without heteroatoms).…”

“…It is generally accepted that the asphaltene polar groups are associated mainly to nitrogen, oxygen and sulphur that can be found in the polyaromatic ring structures (as heteroatoms) and in the side chains [7,8,9]. These groups enhance self-aggregation, precipitation and adsorption [10,11].…”