Study on the association driving force of low temperature coal tar asphaltenes

Abstract

The aggregation of petroleum asphaltenes has been studied for decades by numerous experimental techniques, however, few studies had been performed on the special supramolecular structure of coal tar asphaltenes. In this paper, the methylation, alkylation experiments and molecular dynamics simulation were used to study the π-π interaction and hydrogen bond between coal tar asphaltenes. The results showed that the inter aromatic layer distance (Me) of asphaltenes, methylated and alkylated asphaltenes were 3.74, 2.12 and 1.73 respectively, and the average number of aromatic sheets (dm) was increased compared with asphaltenes. Asphaltenes existed in the form of aggregates in the toluene, as the concentration increased, the particle size also increased significantly, moreover, the particle size and the Me of alkylated asphaltenes are significantly less than asphaltenes, indicating that the π-π interaction was the main driving force for asphaltene association. Meanwhile, molecular simulation results showed the π-π interaction energy of asphaltenes dimers was -165.269 kcal·mol−1, which was much larger than the hydrogen bond energy -5.807 kcal·mol−1. In addition, the asphaltenes dimer layer spacing in quinoline, toluene and ethanol were 3.836 Å, 2.57 Å, and 4.783 Å respectively, which were all larger than the interlayer spacing of asphaltenes dimer 1.99 Å, and the asphaltenes dimer had a better disaggregates effect in quinolone.