【作者】 陈利平；

【导师】 彭金华； 陈网桦；

【作者基本信息】 南京理工大学 ， 工程力学， 2009， 博士

【摘要】 甲苯的多段硝化是重要的化学反应过程,其各段硝化产物在医药、染料、炸药、农药等方面应用广泛。由于这些硝化反应是复杂的液-液两相反应,受到动力学和传质的共同作用,且反应过程放热剧烈,所以通常认为此类反应热失控的危险性很大。本文采用风险矩阵法和失控情景分析方法评估此反应的热失控危险,对反应中的一些影响因素展开比较和分析,并结合实验结果,从理论角度进一步分析了各硝化产物分解的难易性和硝化反应亲电取代的硝化机理,这些工作对准确评估反应的热危险,减少反应失控事故具有重要的参考价值。首先采用差式扫描量热仪（DSC）、加速度绝热量热仪（ARC）和反应量热仪（RC1e）研究了甲苯一段硝化反应过程的热危险性,结果表明:选定条件下反应的热危险性均较低,但略高于同等反应条件下苯的硝化;温度的升高使甲苯硝化的反应速率加快,体系比热容增加,副反应加剧;加快搅拌速度能促进甲苯硝化;而减少硝酸与甲苯摩尔比会使甲苯反应不充分;甲苯一段硝化反应速率的数量级为10^-4 mol·L^-1·s^-1,反应的活化能平均值为30kJ·mol^-1。采用同样的方法对二段硝化反应进行研究,结果表明:二段硝化反应的热失控危险性也较低;延长加料时间,有利于反应完全;而随着硝酸与一硝基甲苯（MNT）摩尔比的减小,硝化难以进行完全;在选定温度范围内升高温度,产物得率无显著变化,反而易导致放热加剧,增加体系的热失控危险。在对三段硝化反应进行热危险性评估时发现,三段硝化反应的温度很高,氧化副反应随温度升高而加剧,风险矩阵法和失控情景分析方法难以准确评估该情况下的热失控危险,但实验结果表明降低反应温度,减缓加料速率能有效地防止热积累,减小反应过程中的热危险性。为了考察不同阶段氧化副反应对反应放热的贡献,用反应物和产物的标准生成焓推得氧化反应的理论反应热,计算结果表明,各段硝化的氧化副反应均为放热反应,其中三段硝化反应由于反应温度最高,氧化反应的温度系数比硝化反应高,故氧化副反应对三段硝化影响最大。此外,本文还考察了酸对反应的影响,研究结果表明酸在118℃以上会与不锈钢发生反应,放热迅速,同时酸还会催化产物的热分解,加大了反应过程中的危险性。最后,采用Hartree-Fock方法（HF）和密度泛函方法（DFT）计算了各硝化反应中主要有机物的Mulliken键级、最高占有轨道能和最低空轨道能,采用“最小键级原理”（PSBO）和“最易跃迁原理”（PET）判断出三硝基甲苯（TNT）最易分解,这与实验结果一致。在DFT-B3LYP/6-311G**水平下计算得到了各硝化反应的反应物、过渡态和Wheland中间体络合物的分子结构和能量,并且发现空间位阻是影响活化能的主要因素。更多还原

【Abstract】 Mononitration, dinitration and trinitration of toluene are very important reactions. Products of these reactions are widely used in medicine, dyestuff, explosive, pesticide, etc. These reactions are complex heterogeneous liquid-liquid reactions, which are affected by kinetics and mass transfers. Furthermore, these reactions are accompanied with high heat generation; therefore, they are commonly regarded to be of great thermal runaway hazards. Here, Risk Assessment Code （RAC） matrix method and runaway scenario analysis method were used to evaluate the thermal runaway criticality, and some reaction conditions were compared and analyzed as well. At last, based on the experimental results, the theoretical calculation was adopted to analyze the decomposition of nitration product and the electrophilic substitution mechanism of these nitration reactions. All these work are of important value for the correct evaluation of thermal risk and the decrease of chemical reaction runaway accidents.First of all, Differential Scanning Calorimeter （DSC）, Accelerating Rate Calorimeter （ARC） and Reaction Calorimeter （RC1e） were employed to study thermal hazards of the mononitration of toluene, and the results showed that thermal risks of these nitrations under given conditions were low, but a bit higher than benzene nitration under the same conditions; high temperature could accelerate reaction rate, increase the specific heat of reaction system and support side reactions; high stirring rate could accelerate reaction as well; decreasing the molar ratio of nitric acid to toluene made an insufficient conversion of toluene. And it was also found that the reaction rate was 10^-4 mol L^-1 s^-1 order of magnitude, the average activation energy of second order kinetic is about 30kJ·mol^-1.The same methods were used to study toluene dinitration, and the results indicated that the thermal runaway risks of these reactions were low too; prolonging dosing duration was helpful to the conversion of all nitrotoluene; decreasing the molar ratio of nitric acid to mononitrotoluene （MNT） would make an insufficient conversion; among the given temperatures, rising reaction temperature couldn’t markedly change the yield coefficient, but lead more heat generation and higher thermal runaway risk.Studies on the trinitration of toluene showed that, the trinitration temperatures were high enough to intensify oxidation, and the two thermal hazard evaluation methods mentioned above couldn’t evaluate the situation well. Results were found from the reaction calorimeter experiments that lower reaction temperature and decelerating dosing rate could prevent thermal accumulation and decrease thermal hazard efficiently.To assess the thermal contribution from oxidation reaction, the standard formation enthalpes of all reactants and products were used to calculate the oxidation enthalpies. It could be found that all oxidation reactions were exothermic. And oxidation played a more important role during the toluene trinitration at high temperature, because the reaction temperature of toluene trinitration is the higher than mononitration and dinitration, and the temperature coefficient of oxidation is higher than that of trinitration too. Besides, the effects of mixed acid on the reaction were analyzed, and the results indicated the mixed acid would react with stainless steel at the temperature higher than 118℃with a sharp exothermal, and could catalyze product decomposition, increase thermal hazards as well.At last, Hartree-Fock （HF） and Density Functional Theory （DFT） was used to calculate the Mulliken bond orders, HOMO and LUMO. The "principle of the smallest bond order" （PSBO） and the "principle of the easiest transition" （PET） were selected to judge the decomposition potential of the nitration products, and the results indicated trinitrotoluene （TNT） would decompose easier than other product, and it was consistent with the experimental results. After that, the reactants, transition states and Wheland intermediate complexes were fully optimized at the B3LYP/6-311G^** level to get the information of the molecular geometries and energies, and it was found that the steric effect was the main influence factor on activation energy.更多还原