Study On Thermal Safety During The Reaction Process Of Nitrifying Methenamine

Hexogen is one of the most important elementary explosives at present with a large amount of application.As high explosive,it has the advantages of high power,high strength and good chemical stability,and it has been widely used in the manufacture of detonators,explosives and rocket propellants.There are many methods for preparation of hexogen,and direct method with nitric acid is the major production technology in our country.The reaction process is complex with high reaction heat generation,therefore the direct method with nitric acid for the preparation of hexogen is easily thermal runaway with high risks.In this paper,the method of cooling failure is used to classify the severity of thermal runaway and evaluate the degree of risk,which is of great significance to the safety production and inherent safety.Reaction calorimeter was employed to study the whole process on-line.The results showed that the exothermic of the methenamine nitrifying process under the production process was 335.4 k J·mol–1 which indicated a large exothermic in nitrification process,a low heat release in mature process and the reaction hault in nitrification process.Decreasing the nitrification temperature and mature temperature can increase the yield.The lowest moore heat release,325.5 k J·mol–1 was found with a 0 ? nitrification process.Decreasing the feeding time could increase the heat release rate.The higher the temperature of the mature temperature,the higher the adiabatic temperature rise.Considering the economy and safety,the best selection is that the nitrification temperature is 0 ?,feeding time is 20 min,mature temperature is 30 ?.Differential scanning calorimeter-thermogravimetric analysis(DSC-TG)was employed to study the thermal decomposition and thermal classification kinetics of the raw materials-urotropine,the products-hexogen and nitrate solution liquid in the reaction process.The results show that the raw materials and products are stable for a higher decomposition temperature.Due to the complexity of fluid system in nitrate solution,there were three obvious endothermic peak and two obvious exothermic peak.Corresponding to the Kissinger method and Flynn-Wall-Ozawa method and the TG data of different heating rates,the kinetics parameter values E and A were obtained.Their activation energy calculated by Flynn-Wall-Ozawa equation are 54.08 k J·mol–1 and 205.38 k J·mol–1,meanwhile the apparent activation the pre-exponential factor acquired by Flynn-Wall-Ozawa equation 50.83 k J·mol–1,193.19 k J·mol–1 and 5.01×106 s–1?2.87×1019 s–1.Adiabatic acceleration calorimeter was employed to study the thermal behavior of the nitrate solution of the reaction process.The results showed that there was a gentle decomposition processes in the solution which was the decomposition of nitric acid and a small amount of by-products and a distinct exothermic decomposition processes which was the decomposition of hexogen and 3,5-dinitro-1-oxygen-3,5-diazacyclohexane,the onset temperature of urotropin were 70.40 ? and 195.08 ?,and the offset temperature of urotropin were 85.02 ? and 215.42 ?,with a violent exothermic and large gas production reaction.Indicated that once the decomposition happens,it would be very difficult to control.Cooling failure method was used to assess the process,if the nitrification temperature was 16 ?,the mature temperature was 22 ?,the severity of thermal runaway was intermediate,the possibility of secondary classification was very small and the risk was ‘2'.