苯胺溶剂中偶氮二异丁腈热分解特性及动力学

偶氮二异丁腈(AIBN)是一种典型的相变吸热与分解放热重叠的物质, 该重叠现象的存在不利于其动力学规律的研究. 为了正确解析AIBN相变吸热对其分解放热的影响, 并研究AIBN在溶剂中的非等温热行为, 利用差示扫描量热仪(DSC)对苯胺、AIBN及AIBN-苯胺溶液(22.18%(w))进行动态扫描, 得到不同升温速率下AIBN在苯胺溶剂中起始分解温度T_onset的范围为79.90-94.47 ℃, 比放热量较固态AIBN高291 J·g^-1左右, 该数值可以视为其比相变热. 基于Kissinger法计算的AIBN与AIBN-苯胺溶液的活化能E和指前因子A的结果相差不大. 采用Friedman法对AIBN与AIBN-苯胺溶液的热分解过程进行计算, 发现固态AIBN相变吸热对其分解放热的影响主要发生在反应进度α小于0.20的范围内, 当α大于0.20后, 两者活化能E(α)和ln(A(α)·f(α))随α的变化趋势基本一致. 分析认为, 相对于AIBN的分解反应而言, 苯胺可以视为一种惰性溶剂, 即其不会干扰AIBN的分解机理. AIBN在苯胺溶剂中的分解机理可以视为固态AIBN的分解机理. 结合Friedman法的计算结果, 采用一般积分法, 即Coats-Redfern法得到AIBN在苯胺溶剂中分解反应的机理函数为G(α)=α^3/2, 符合Mampel power法则,平均表观活化能为139.93 kJ·mol^-1.

Thermal Decomposition Characteristic and Kinetics of AIBN in Aniline Solvent

2,2-Azobisisobutyronitrile (AIBN) is a typical material that shows overlap between endothermic phase change and exothermic decomposition. This phenomenon went against the kinetics of AIBN. To properly analyze the effect of endothermic phase change on the exothermic decomposition process and determine the non-isothermal behavior of AIBN in a solvent, a solution of AIBN (22.18% mass fraction) in aniline was tested under dynamic conditions by differential scanning calorimeter (DSC). Depending on heating rates, the onset temperature range of AIBN in aniline was from 79.90 to 94.47 ℃, and the decomposition enthalpy was 291 J·g^-1 greater than that in its pure state, which could be regarded as phase change enthalpy. Based on the Kissinger method, the differences of the activation energy E and the frequency factor A of AIBN and its solution were quite small. The thermal decomposition processes of AIBN and its solution were analyzed by the Friedman method, which showed that the reaction progress range was less than 0.20, in which the endothermic phase change of solid AIBN would disturb its exothermic decomposition. When α was greater than 0.20, the dependence of E(α) and ln(A(α)·f(α)) on α were roughly the same. These results show that aniline is an inertial solvent; that is, decomposition of AIBN is not disturbed by aniline. This means that the decomposition mechanism of AIBN in aniline could be regarded as the same as that in its solid state. The decomposition kinetics of AIBN could be described according to the Mampel power law, G(α)=α^3/2, which is based on the Friedman and Coats-Redfern integral methods, and the average apparent activation energy was 139.93 kJ·mol^-1.