Construction and optimization of lignite molecular structure model
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摘要: 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/cm3，总能量为1 140.624 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。Abstract: 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, 13C-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/cm3 and the total energy was 1 140.624 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.
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Key words:
- lignite /
- macromolecular modeling /
- molecular dynamics /
- structure optimization
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图 2 褐煤X射线光电子能谱图检测谱图和C、O、N元素分峰拟合谱图
Figure 2. XPS detection spectrum and C, O, N element peak fitting spectrum of lignite
图 6 优化后褐煤大分子结构模型
Figure 6. Macromolecular structure model diagram of lignite after optimization
图 7 标准情况下密度-能量图和晶胞结构褐煤大分子结构图
Figure 7. Density-energy diagram under the standard conditions and molecular structure of lignite
表 1 13C-NMR谱图化学位移的结构归属
Table 1. Structural attribution of chemical shifts in 13C-NMR spectra
碳结构名称 主要归属 典型化学位移/10-6 碳结构名称 主要归属 典型化学位移/10-6 脂甲基碳 
14~16 质子化芳碳 
100~129 芳环甲基碳 
16~22 桥头芳香碳 
129~137 亚甲基碳、次甲基碳 
22~36 侧枝芳香碳 
137~148 次甲基碳、季碳 
36~50 氧取代芳香碳 
148~165 氧接甲基及氧接亚甲基碳 
50~56 羧基碳 
165~188 氧接次甲基碳 
60~70 醛、醌、苯基酮的羰基碳 
188~205 氧接季碳 
75~90 链烷酮、环烷酮的羰基碳 205~220 
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表 2 煤样元素构成
Table 2. Element composition of coal sample
质量/mg C/% H/% O/% N/% S/% 1.653 58.88 4.36 25.38 0.65 0.21
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表 3 结构归属及相对面积
Table 3. Structure and relative area
结构归属 结构比例/% 质子化芳碳 22.161 桥头芳香碳 19.698 亚甲基碳、次甲基碳 19.255 次甲基碳、季碳 11.987 侧枝芳香碳 10.166 氧取代芳香碳 7.151 氧接甲基及氧接亚甲基碳 4.697 芳环甲基碳 1.455 链烷酮、环烷酮的羰基碳 1.446 氧接次甲基碳 1.130 脂甲基碳 0.771 醛、醌、苯基酮的羰基碳 0.082
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表 4 褐煤13C-NMR结构参数
Table 4. 13C-NMR structural parameters in lignite
fa faC f′a faN faH faP 60.74 1.53 59.18 37.02 22.16 7.15 faS faB fal fal* falH falO 10.17 19.7 39.29 14.21 19.26 5.83
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表 5 优化后褐煤大分子结构能量
Table 5. Energy of macromolecular structure of lignite after optimization
kJ/mol 总能量 非成键能 价电子能 氢键能 范德华能 库仑能 键伸缩能 键角能 扭转能 反转能 优化前 45 036.044 0.000 31 114.270 -53.144 12 462.340 364.826 1 126.894 20.862 优化后 3 680.514 0.000 1 939.305 -141.607 487.150 522.143 852.746 20.779
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表 6 密度为1.2 g/cm3褐煤大分子结构能量
Table 6. Energy of macromolecular structure for lignite after optimization under 1.2 g/cm3
密度/(g·cm-3) 总能量/(kJ·mol-1) 非成键能/(kJ·mol-1) 价电子能/(kJ·mol-1) 氢键能 范德华能 氢键能 范德华能 氢键能 范德华能 氢键能 1.2 1 140.624 0 2 090.887 -3 353.010 443.876 833.981 1 058.200 66.693
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