Mechanistic insights into the evolution of microscopic molecular structures of bituminous coal and lignite during carbonization: a ReaxFF molecular dynamics study

Abstract

Context

The development of the carbon network in coal during carbonization significantly affects the quality of the resulting coke. A detailed understanding of the atomic-scale mechanisms governing coal carbonization is crucial for optimizing the coking process. This research employed ReaxFF molecular dynamics simulations to examine the carbonization processes of two coal types: bituminous coal and lignite. During carbonization, large molecular clusters produced by pyrolysis undergo cross-linking through carbon–carbon bonds, forming a carbon network that expands outward. The carbonization effects of the two coal molecular models were compared, showing that the carbonization process of bituminous coal was more stable, yielding better results. Additionally, based on the observed expansion of the carbon network within coal molecules during the simulation, the growth mechanism of the carbon network was outlined. This research provides theoretical insights into the atomic-scale carbonization mechanisms of coal molecules and their application in the coking process, offering valuable references for advancing coking production technology.

Methods

Molecular dynamics simulations are conducted using the LAMMPS (Large-Scale Atomic/Molecular Massively Parallel Simulator), employing a reactive force field (ReaxFF). The modeling process incorporates a cyclic annealing method for structural relaxation of the molecules. The simulation is carried out in stages, with a temperature increment of 100 K per step. OVITO post-processing software is utilized to remove gas molecules from the system. During the post-processing phase, OVITO is used to visualize and analyze the carbonization process, investigating the evolution of coal molecular products and assessing the effectiveness of the carbonization.