贮存期间硝化甘油的分解机理

为分析硝化甘油(NG)贮存期间的分解反应机理,采用热分解实验监测了55℃和60℃下硝化甘油分解放出的CO、NO、NO_2三种气体浓度变化。通过密度泛函理论和正则变分过渡态理论计算了O—NO_2基团消去反应、HONO消除反应、α位夺氢反应和β位夺氢反应四种反应通道在20~60℃内起始反应的速率常数。结果表明:在55℃和60℃下分别以90天和70天为时间节点,硝化甘油分解放出的NO和CO两种气体浓度随着热分解时间的增长逐渐增大,而NO_2气体浓度则呈现先增大后减小的规律。在20~60℃,β位夺氢自催化反应速率最快,为其他三类反应速率的102~1011倍,HONO消除分解反应速率最慢,为其他三种反应速率的1/1011~1/105,而α位夺氢反应速率较NO_2基团消去反应快约两个数量级。鉴于NO_2分子作为分解反应生成物和自催化反应反应物的双重属性,可将硝化甘油贮存期间的分解过程以NO_2气体浓度达到最大的时间点为基准划分为两个阶段,第一阶段O—NO_2基团消去反应为主反应通道,α位和β位夺氢自催化反应速率随NO_2气体浓度的升高逐渐加快,第二阶段β位夺氢自催化反应为主反应通道,α位夺氢自催化反应通道为次反应通道。在整个过程中,HONO消除反应对硝化甘油的分解作用最小。

Decomposition Mechanism of Nitroglycerin During Storage

To analye the decomposition mechanism of nitroglycerin ( NG ) during storage in detail, the change in the concentrations of three kinds of gases, including CO, NO, NO2 released by NG decomposition at 55℃and 60℃was monitored by thermal decomposition experiment.The rate constants of four k inds of initial reactions including the hemolytic cleavage reaction of O—NO2 group, HONO elimination reaction, hydrogen abstraction reaction atα-position and hydrogen abstraction reaction atβ-position at 20-60 ℃ were calculated by the density functional theory and canonical variational transition state theory.Results show that 90 days and 70 days respectively are two important time points at 55 ℃ and 60 ℃.With increasing the decomposition time gradually, the concentrations of CO and NO increase, but the concentration of NO2 increases first and then decreases.At 20-60 ℃, the rate constant of autocatalytic reaction of hydrogen abstraction at β-position is the fastest,which is 102-1011 times greater than those of the other three kinds of reactions and the rate of HONO elimination reaction is smallest which is 1/1011-1/105 times of the rate constants of the other three kinds of reactions.The rate of hydrogen abstraction reaction at α-position is about two orders of magnitude more than the rate of the hemolytic cleavage reaction of O—NO2 group.On basis of the double attribute of NO2 molecules as the decomposition reaction product and the reactants of catalytic reaction, taking NO2 gas concentration reaching the highest point in time as benchmark, the process of NG decomposition during storage can be divided into two stages.The hemolytic cleavage of O—NO2 is the main reaction channels of the first stage, and the rates of autocatalytic reaction of hydrogen abstraction at α=position and β-position increase with the NO2 concentration increasing.The autocatalytic reaction of hydrogen abstraction atβ-position is main reaction channel of the second stage.The autocatalytic reaction of hydrogen abstraction at α-position is secondary reaction channel of the second stage.HONO elimination reaction has minimum effects to NG decomposition throughout the entire process.