| 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.
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