Molecular Dynamics Analysis on Hydrogenation Process of Asphaltene Aggregate for Medium and Low Temperature Coal Tar

Abstract

In this paper, the average molecular structure models of middle-low temperature coal tar (MLCT) asphaltene before and after hydrogenation were obtained by 1H-NMR characterization. Then the aggregation structure models of MLCT asphaltenes before and after hydrogenation was constructed in Materials Studio 8.0 software. The comparative analysis of structural characteristics between original and hydrogenated asphaltenes were carried out. The final configuration, molecular rotation radius and interaction energy of asphaltene aggerates before and after hydrogenation were analyzed by molecular dynamic simulation in different solvents.The conclusions are as follows: (1) The MLCT asphaltenes exist in the form of asphaltene aggregates before and after hydrogenation. After structural optimization, the original asphaltene molecules become 2-3 asphaltene molecules with approximately parallel, orderly arrangement and polycyclic aromatic hydrocarbons (PAH) stacking aggregate structure. The molecular accumulation number of its aggregate is less than that of petroleum asphaltene, and more complex nano-aggregates are formed by self-assembly among multiple aggregates. The accumulation number of asphaltene molecules after MLCT hydrogenation are less than that of original asphaltene. (2) The total interaction between MLCT primary asphaltene and hydrogenated asphaltene mainly comes from the intermolecular Van der Waals force. Compared with original asphaltene, the van der Waals energy and electrostatic energy of hydrogenated asphaltene are smaller and more affected by temperature. This shows that the intermolecular interaction of hydrogenated asphaltene is weak and the structure of the aggregate is unstable. (3) Aromatic compounds, strong basic compounds and strong polar compounds have good dissociation effect on MLCT asphaltenes and can effectively inhibit the aggregation and asphaltenes.

Separation and Analysis of Oxygen-Containing Compounds in a Shaanxi Middle/Low-Temperature Coal Tar

“…3−5 With the large-scale exploitation and utilization of low-rank coal, the M/LTCT as an alternative fuel has great prospects in the future. 6 The M/LTCT is mainly composed of alkanes, aromatic hydrocarbons (AHCs), oxygen-containing arenes (OCAs), nitrogen-containing arenes (NCAs), and coal tar pitch. 7−9 Since 2015, the annual total production capacity of the M/LTCT in China has reached 4 Mt, 10 and most have been burned directly, causing serious environmental pollution and waste of resources.…”