低温等离子体中甲苯降解机理的量子化学研究

Quantum chemistry study on mechanism of toluene degradation in non-thermal plasma

为了实现生物质气化合成气中焦油的定向转化,提升合成气品质,采用密度泛函理论的B3LYP方法,研究了甲苯在低温等离子体中电离形成C7H3+8后的降解机理。在NBO的方法下,计算不同电离程度下原子电荷分布。模拟结果表明:找到了8条主要的降解路径,C1-C2键断裂反应是最容易发生的。产生H和CH3反应活化能的顺序为C7-H <C1-C7 <C4-H <C3-H <C2-H,开环反应活化能顺序为C1-C2 <C3-C4 <C2-C3。C7H3+8在降解过程中可以生成H2、烃类(CH4、C2H6、C2H4等)和聚合产物,与文献结果一致。低温等离子体的电离反应对C7H8物理结构产生很大影响,由于存在未成对电子,使得苯环C-C键有所降低,特别是与C1相连的化学键。

In order to achieve directional conversion of tar in biomass gasification and improve the quality of the synthesis gas,by using the B3LYP method based on density functional theory,calculations have been performed to investigate the dissociation pathways of toluene so as to understand the mechanism of dissociative ionization of toluene into C7H38+after being attacked by high energy electrons in non-thermal plasma.In this study,atomic charge distributions are derived for different ionization levels by means of Natural Bond Orbital method.The simulation results demonstrate that a total of eight major degradation pathways are found,among which the C1-C2 bond breaking reaction occurs most easily.The order of activation energy for reactions of H and CH3 generation is C7-H<C1-C7<C4-H<C3-H<C2-H,and that of the activation energy for ring opening reaction is C1-C2<C3-C4<C2-C3.C7H8^3+can dissociate into H2,hydrocarbons(CH4,C2H6,C2H4,etc.)and polymerization products during the degradation process,which is in accord with the results reported in literature.The ionization reaction of low-temperature plasma has a profound influence on the physical structure of C7H8.Resulting from the existence of unpaired electrons,the C-C bond in the benzene ring,especially the chemical bond connecting C1,is reduced to a certain extent.