| Aniline is an important organic chemical raw material and is widely used in the production of polyurethane, dyes, rubber agents, pesticides, photographic chemicals, pharmaceutical and explosives etc. the product process of aniline is regarded as a high-risk unit not only because there are a large amount of inflammable and explosive, toxic and harmful chemicals are used on the aniline production and its supporting device, but also because of the complex processing technology and demanding strict security technology of the nitration and hydrogenation reaction process. In recent years safety accidents of production of aniline occurred frequently, which caused complete catastrophe and loss. So it is necessary to analyze the risk and hazard factor, thermal decomposition characteristics of hazard materials and its thermodynamics and kinetics characteristics of the production process of aniline in order to reveal the mechanism of possible aniline production accident.In this paper, several hazard chemicals from the aniline production unit were selected as the object of the risk analysis. And the three part of researches were executed as follow:(1) the calculate and comparison of the BDE of nitrobenzene, aniline, nitrosobenzene, nitrophenol, nitrophenol sodium and dinitrobenzene by the methods of Gaussian03simulate computation, and experimental value database query and estimation method. The results show Gaussian calculations are slightly lower than the experiment query value. The thermolysis trigger bond of nitrobenzene and nitrophenol is C-NO2bond. The trigger bond of nitrosobenzene and aniline are C-NO and N-H bond respectively.(2) The researches were proceeded, using C80calorimetry, PY-GC-MS, from these three aspects:①Thermal decomposition behavior of nitrobenzene and aniline;②Influence of nitric acid, sulfuric acid and there mixed acid on Thermal decomposition behavior of nitrobenzene and aniline;③Influence of intermediate products and by-products on Thermal decomposition behavior of nitrobenzene and aniline.In the first research topic, thermal decomposition behavior of nitrobenzene and aniline was observed under the constant heating rate experiment. A GCT gas chromatography-time of flight mass spectrography was used to analyze the thermal decomposition of pure nitrobenzene and aniline under high temperature. The thermal decomposition mechanism of nitrobenzene and its mixture with nitric acid was conjectured.In the second topic, A CALVET calorimeter C80was used to analyze the thermal behavior of pure nitrobenzene and its mixtures with sulfuric acid and nitric acid. The chemical reaction kinetic parameters such as activation energy, frequency factor, and heat of reaction were calculated based on C80experimental data. Based on theses parameters and the Semenov thermal explosion theory, the self-accelerating decomposition temperature (SADT) of the samples were calculated and compared. The results show that the impurity of sulfuric acid, nitric acid and their mixture acid decrease the Ton-set and SADT and also increase the risk of the nitrobenzene mixture. The mechanism of new insoluble impurity after the sulfuric acid’s mixture with nitrobenzene was conjectured.In the third topic, the thermal decomposition behavior of intermediate products and by-products and their influence on the decomposition behavior of nitrobenzene were researched by using C80calorimetry.(3) Based on results of above analysis and experiment, the cause and development mechanism of an accident was discussed. The immediate cause is the self-accelerating exothermic reaction process of raw nitrobenzene catalyzed by the impurity of acids. The follow-up mechanism is the high-risk by-products’oxidation by air and the exothermic reaction in the vacuum distillation tower, then the heat accumulation lead to an explosion accident at last. |
PDF Full Text Request