Aggregation of modified hexabenzocoronenes as models for early stage asphaltene self-assembly

Abstract

Molecular dynamics simulations were performed on solvated systems containing three molecules of hexabenzocoronene (HBC) derivatives to model the initial self-association of asphaltenes. Specifically, the hexane-modified HBC (HBC6) and those with substitutions containing a side chain with sulphur at three positions (α-H6SA, β-H6SB, and γ-HBCS) and a nitrogen substitution (H6N1) are included. These molecules were solvated with 20 mol% heptane and 80% toluene. Intermediate aggregation states, partial (two molecule clusters), as well as full aggregation of trimer clusters were observed. The conformation of the associated clusters was characterised by π–π stacking, giving the cluster a pre-rod-like shape. The aggregates displayed stability and did not dissociate throughout the course of the simulation (100–530 ns). In particular, the H6SB system showed statistically significant difference in means for both the separation distance and overall interaction energy. H6N1 and H6SA systems differed from the others in terms of electrostatic contributions. To gain a thorough understanding of initial aggregation behaviour and conditions of asphaltenes, additional simulations need to be conducted, in particular those incorporating oxygen substitutions as oxygen is a common heteroatom in crude.