针对煤结构及其氧化反应机理不明等问题，以羟基(—OH)和煤自燃侧链活性基团—OCH,—CHOHCH₃和—OCH₃为研究对象，采用密度泛函理论(DFT)的B3LYP-311G(d,p)方法，构建出了羟基(—OH)处于侧链活性结构邻位的小分子结构模型。基于前线轨道理论和量子化学理论，采用Gaussian 16软件对小分子模型的静电势、前线轨道的能级和电荷分布及煤氧复合反应过程中的热力学参数进行了模拟计算，探究了侧链活性基团的低温氧化特性和羟基(—OH)对其的影响。计算结果显示，在侧链活性结构中，氢原子周边呈强正电势，为亲核反应活性位点，而氧原子附近呈强负电势，为亲电反应活性位点。当羟基(—OH)处于侧链活性基团邻位时，会削弱侧链活性基团的亲电反应能力，增加—CHO和—CHOHCH₃的亲核反应能力，而使—OCH₃的亲核反应能力消失;通过分析各活性基团最高占据轨道(HOMO:Highest Occupied Molecular Orbital)和最低未占轨道(LUMO:Lowest Unoccupied Molecular Orbital)可知，侧链活性基团的稳定性与其前线轨道的成键能力并不一致，而活性基团与氧气发生复合反应的难易程度主要取决于该基团前线轨道中LUMO的成键能力，成键能力越强，复合反应越容易发生;由于羟基(—OH)改变了侧链活性基团前线轨道上的电子特性，故当其与侧链基团共存时，会使 —CHO和 —CHOHCH₃与氧气的复合反应更容易发生，而使 —OCH₃与氧气的复合由自发的放热反应转变为非自发的吸热反应。该研究成果可为揭示煤自燃微观作用机理和研发煤自燃新型高效阻化材料提供参考。

Due to the extreme complexity of coal structure and the reaction between coal and oxygen,six molecule models were constructed based on hydroxyl (—OH) and side chain active groups including —OCH、—CHOHCH3 and—OCH3 by employing B3LYP-311G (d,p) method of Density Functional Theory (DFT). On the basis of frontier or- bital and quantum chemistry theories,the electrostatic potentials,frontier molecular orbital,and thermodynamic param- eters of these six constructed molecule models were simulated and calculated by using the software of Gaussian 16. Al- so,the oxidization characteristics of the side chain active groups and their responses to the hydroxyl (—OH) were in- vestigated. It was found that the electrostatic potentials near the hydrogen atoms were positive,and the negative electrostatic potentials concentrated around oxygen atoms. This phenomenon implied that active sites of the nucleophilic reac- tion lied on hydrogen atoms,whereas the oxygen atoms were active sites of the electrophilic reaction. Furthermore,it was found that the adjacent hydroxyl group (—OH) would reduce the electrophilic reactivity of the side chain active groups and increase the nucleophilic reactivity of —CHO and —CHOHCH3 . Nevertheless,the nucleophilic reactivity of —OCH3 would disappear when the hydroxyl group (—OH) located next to it. Analysis of the Highest Occupied Or- bital (HOMO) and the Lowest Unoccupied Orbital (LUMO) of each active group indicated that the stabilities of the active groups were not in agreement with the bonding abilities of their front orbitals. The propensity of active groups re- acted with oxygen mainly relied on the bonding ability of LUMO. The stronger the bonding ability was,the easier the active groups reacted with oxygen. Since hydroxyl (—OH) could change the characteristics of electrons in the front or- bital,it exhibited significant impact on the compound reactions between active groups. More specifically,the hydroxyl benefited the reactions between oxygen and —CHO as well as —CHOHCH3 . However,hydroxyl (—OH) converted the reaction between —OCH3 and oxygen from the spontaneous exothermic reaction to the nonspontaneous endothermic reaction. This study is of importance for revealing the microscopic mechanism of coal spontaneous combustion and de- veloping new efficient inhibitors of coal spontaneous combustion.

1 研究方法

2 结果与分析

   2.1 静电势与活性部位分析

   2.2 前线轨道与反应特性分析

   2.3 热力学参数分析

3 结论