陕西凤县高煤级煤分子结构模型的构建与结构优化

分子模拟可从分子尺度探究高煤级煤石墨化过程中微晶结构的演化,对煤系石墨的成矿机理和开发利用具有重要意义。构建高煤级煤的分子结构模型是对其进行分子模拟的基础。通过工业分析、元素分析、核磁共振碳谱(13C-NMR)、傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)等手段,对陕西凤县地区赋存于石炭系草凉驿组含煤地层中的高煤级无烟煤的分子结构进行了研究,发现凤县无烟煤的芳香结构以萘、蒽和菲为主;脂肪碳以亚甲基、次甲基、脂肪侧链和环烷烃的形式存在,其中脂肪侧链以短链为主;含氧官能团以酚羟基和醚氧基为主,还含有少量的羰基;吡咯型氮是氮元素的主要赋存形态;硫元素的主要赋存形式是硫醇硫酚。依此构建了其大分子平均结构模型,并对构建的模型进行了结构优化和退火动力学模拟。经退火动力学模拟后,模型的总能量明显降低,模型中的芳香片层趋于规整的平行排列。在最终模型的能量构成中,非键结势能大于键结势能,是保持煤结构稳定的主要因素。范德华能在非键结势能中占主导地位,归因于高煤级煤中芳环之间的π-π相互作用,该作用是保持高煤级煤结构稳定的主要能量来源。本研究对凤县高煤级煤分子结构模型的构建为从分子尺度研究高煤级煤石墨化的微晶结构演化提供了模型基础。

Model construction and optimization of molecule structure of high-rank coal in Feng County,Shanxi 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 simulations.The macromolecule structure of high-rank anthracite occurred in the coal-bearing strata of Carboniferous Caoliangyi formation in Feng County,Shanxi Province,was studied using the methods of proximate analysis,ultimate analysis,carbon nuclear magnetic resonance (13C-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 existed 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 regularly 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.