Model construction and optimization of molecule structure of high-rank coal in Feng County,Shaanxi Province

Molecular simulations are able to probe into the microcrystalline structural evolution of high-rank coal during the graphitization at molecular scale,which is of significance to the study of mineralization mechanism and utilization of coal-based graphite. The construction of molecular structure of high-rank coal is the foundation for the molecular simu- lations. The macromolecule structure of high-rank anthracite occurred in the coal-bearing strata of Carboniferous Ca- oliangyi formation in Feng County, Shanxi Province, was studied using the methods of proximate analysis, ultimate analysis,carbon nuclear magnetic resonance (13 C-NMR),Fourier transform infrared spectroscopy (FTIR),and X-ray photoelectric spectrometry ( XPS). The results showed that the aromatic structure of anthracite in Feng County was mainly composed of naphthalene,anthracene and phenanthrene. The aliphatic carbon occurred mainly in the form of methylene,methine,short aliphatic chains,and naphthenic hydrocarbons. The oxygen-containing functional groups ex- isted in the form of phenolic hydroxyl group,ether oxygen group,and a small number of carbonyl group. The nitrogen atom and sulfur atom were mainly in the form of pyrrole,and mercaptan and thiophenol,respectively. Based on the study of macromolecule structure,its averaged structure model was established. The constructed model was optimized, and then annealing molecular dynamics simulations were performed. The results showed that the total energy of model was decreased obviously after annealing molecular dynamics simulations. The aromatic carbon layers tended to be regu- larly parallelly arranged. The non-bonding potential energy was higher than the bonding potential energy in the total energy of final model,which is the main factor to stabilize coal structure. The van der Waals energy played a key role in non-bonding potential energy due to the π-π interactions between aromatic rings in high-rank coal,which is the main energy source to maintain the stability of high-rank coal structure. The molecular model construction of high-rank coal in Feng County provides a model foundation for further research on the microcrystalline structural evolution of high-rank coal during the graphitization at molecular scale.