ANPyO高温下热分解过程的分子动力学模拟

Thermal Decomposition Behaviour of ANPyO at High Temperature by Molecular Dynamics Simulation

采用Reax FF力场研究了凝聚相ANPy O在不同温度(T=1500 K、2000 K、2500 K、3000 K、3500 K)的热分解,通过指数函数拟合势能演化曲线得到了平衡和诱导期以及整体反应时间和热解活化能Ea(88.65 k J·mol-1)。结果表明,晶胞中的ANPy O分子几乎完全分解时系统的势能开始显著衰减,但是在不同的温度表现出不同的反应机理。在低温(1500 K≤T≤2000 K)下ANPy O热解的初始反应为—NH_2上H转移至ortho—NO_2生成H_2O和NO分子;在高温(2500 K≤T≤3500 K)下热解的主要初始反应为C-NO_2键的断裂和C—NO_2→C—ONO重排布断裂产生NO_2和NO。有限时间步长的产物识别分析结果表明,ANPy O热解的主要产物为H_2O、N_2、NO_2、NO、CO_2、CO、OH以及HONO。氧化性中间产物NO_2、NO、OH以及HONO与NH_2、H再次反应,产生系统最稳定的产物H_2O和N2,从而使其分布显示出剧烈的波动特征。环上基团相互反应或直接脱落后主环间C-C和C-N才发生断裂,一部分分解成CO_2、CO和NO,另一部分聚集生成碳团簇。

The initial decomposition of the condensed phase ANPyO crystal at various temperature （T=1500 K、2000 K、2500 K、3000 K and 3500 K） were studied by using ReaxFF reactive molecular dynamics simulation. The time evolution curve of the potential energy can be described reasonably well by a single exponential function from which the initial equilibration and induction time as well as the overall characteristic time of pyrolysis were obtained. Afterward, the activation energy Ea （88.65 kJmol-1） also was obtained from these simulations. Result show when the ANPyO molecules in the unit cell almost decomposed, the potential energy of the system significantly attenuated. Meanwhile ANPyO showed different reaction mechanisms at different temperatures. At lower temperatures （1500 K≤T≤2500 K） the hydrogen from NH2 transferred to ortho—NO2 and promote C—NO2 bond fission, while the H2O and NO molecules formed. At very high temperatures 2500 K≤T≤3500 K）, the C-NO2 homolytic cleavage and C—NO2→C—ONO rearrangement hemolysis are thermo dynamically favorable pathways in the early thermal decomposition of ANPyO. According to calculations using limited time steps, the main products are H2O、N2、NO2、NO、CO2、CO、OH and HONO. Secondary products are mainly NO2、NO、OH and HONO, which has strong oxidizing property, so that the distribution has a dramatic fluctuation characteristics. It is found that H2O and N2 are the main stable products of thermal decomposition. Pyridine ring fission does not take place until most of the attached groups have interacted or disconnected, and increasing temperature accelerates fission of Pyridine ring and further decomposition to generate both CO2, CO, NO, and amount of carbon-containing clusters.