Multi-scale analysis on the aggregation mechanism of oxygen-rich coal-derived asphaltene molecules

Significant differences exist in the structural features between coal-derived asphaltene and petroleum asphaltene (e.g., the degree of alkylation, aromatic nuclei size, heteroatom content, as well as morphology characteristics). The self-aggregation behavior exhibited by coal tar asphaltene for coal tar processing should be investigated in accordance with the structural characteristics of coal tar asphaltene. In this study, the focus was placed on the effect exerted by oxygen structure format, location and content on the aggregation behavior of asphaltene. The electrostatic potential (ESP) maps, theoretical reactivity parameters, molecular orbitals, dimerization interaction energies, and weak interactions of coal tar asphaltene were determined based on quantum chemistry. The self-aggregation behavior exhibited by coal-derived asphaltene was explored through molecular dynamics simulations. As indicated by the results of this study, the π-π interactions among asphaltenes were enhanced by the heteroatoms embedded in polycyclic aromatic hydrocarbons (PAHs). In the identical oxygen content, the π-π stacking of asphaltenes with five-membered heterocyclic structures turned out to be more intense. The carboxyl and hydroxyl were more likely to form hydrogen bonds, such that the stability of asphaltene aggregates was increased. Furthermore, as indicated by the molecular dynamics simulation results, the oxygen-containing structures far from PAHs exhibited small steric resistance and a higher probability of the formation of hydrogen bonds.