褐煤分子结构模型构建与优化

Construction and optimization of lignite molecular structure model

针对煤分子建模方法较多且不统一的现状,本文从微观角度出发,选取对分子结构影响较小的物理方法,探究了褐煤大分子结构并对其进行优化,提出了一种较为简便的煤大分子建模方法。基于元素分析、核磁共振碳谱测试及X射线光电子能谱测试的实验方式,利用分子动力学模拟软件对褐煤进行了分析研究并搭建分子结构模型。研究表明,褐煤大分子中芳香结构多为并五苯,脂肪碳结构多为亚甲基及次甲基结构,烷烃链多为环烷烃结构;氧原子以醚键氧形式为主,其次为羧基氧和羰基氧;氮原子以吡啶氮结构形式存在。优化后煤分子模型结构更加紧凑,能量明显变小,范德华势能作为非键势能的主要组成部分及保持煤分子结构稳定的主要因素,变化最明显。为了构建煤分子晶胞,加入周期性边界条件,根据能量变化得到晶胞密度为1.2 g/cm^(3),总能量为1140.624 kJ/mol,与实际情况基本相符,验证了该建模方法的实效性。该研究为直观认识煤大分子结构提供了方法,并对煤与瓦斯突出、煤自燃等灾害事故的机理研究及防治具有重要意义。

In view of the current situation that there are many but no uniform coal molecular modeling methods,this paper explores the structuve of lignite macromolecules and optimizes them from a microscopic perspective by selecting physical methods that have less impact on molecular structure.A relatively simple coal macromolecule modeling method was put forward.Based on the experimental methods of elemental analysis,^(13)C-NMR and XPS,molecular dynamics simulation software method was used to analyze and study lignite and build molecular structure models.The results show that the aromatic structure of lignite macromolecules is mostly pentaphenyl.The fat carbon structure is mostly methylene and methine,and the alkane chain is mostly cycloalkanes.Oxygen atoms are mostly ether bond oxygen,followed by carboxyl oxygen and carbonyl oxygen.Nitrogen atom exist in the form of Pyridinic nitrogen N-6.After the optimization,the structure of the coal molecular model is more compact and the energy is obviously reduced.As the main component of the non-bonding potential energy and the main factor to maintain the stability of the coal molecular structure,the van der Waals potential energy has the most obvious change.In order to construct coal molecular cell,periodic boundary conditions were added.According to the energy variation,the cell density was 1.2 g/cm^(3) and the total energy was 1140.624 kJ/mol,which was basically consistent with the actual situation and verified the effectiveness of the modeling method.This study provides a method for the direct understanding of the macromolecular structure of coal,and is of great significance for the mechanism research and prevention of coal and gas outburst,coal spontaneous combustion and other disasters.