Study On The Thermal Risk Assessment Of 2,6-diaminopyrazine-1-oxide Synthesis Process

2,6-diaminopyrazine-1-oxide（DAPO）is an important intermediate for the synthesis of2,6-diamino-3,5-dinitropyrazine-1-oxide（LLM-105）.At present,domestic and foreign research mainly focuses on the stability of LLM-105 itself and its synthesis method,but there is little research on the thermal risk of DAPO synthesis process.In order to improve the thermal safety of the synthesis process of LLM-105,this article explores the reaction mechanism of the DAPO synthesis process,and on this basis,conducts an in-depth study of the thermal hazard of the process.First,using Fourier transform infrared spectroscopy（FTIR）,500 MHz solid nuclear magnetic（NMR）,On-line infrared analyzer（React IR 15）,High performance liquid chromatography（HPLC）and other characterization methods to analyze the results of small-scale experiments and reaction calorimetry experiments were carried out,confirm the synthesis of DAPO mechanism:Triethylamine preferentially reacts with hydroxylamine hydrochloride to form free hydroxylamine.Free hydroxylamine undergoes a condensation reaction with the cyano group on the side of N-nitrosobis（cyanomethyl）amine.Excessive triethylamine catalyzes the elimination of NO.When—NO is removed,the N provided by hydroxylamine hydrochloride participates in the formation of the ring,and the final product DAPO is formed after proton transfer and aromatization.Secondly,according to the research results of the synthesis mechanism of DAPO,the reaction process is divided into two stages:the first half of triethylamine dosed,and the second half of triethylamine dosed until end of the reaction.Differential scanning calorimeter（DSC）and reaction calorimeter（RC1e）were used to study the thermal stability and exothermic characteristics of the two stages of materials.The specific results are as follows:The total exothermic heat of the DAPO synthesis process is 34 k J,of which the first-stage exothermic heat is 14.05 k J;for the first stage,the thermal stability of the reaction mixture at the end of the triethylamine dosed is the worst,and the onset decomposition temperature is 108.1^oC;For the second stage,the product liquid showed two exothermic peaks,corresponding to the decomposition of the side product N-nitrosoiminodiethylamine oxime and the target product DAPO respectively.Compared with the target product DAPO,N-nitrosoiminodiethylamine oxime has a lower onset decomposition temperature,a larger heat release,and a higher thermal risk.Finally,the risk analysis of thermal runaway was carried out on the synthesis process of DAPO.For the first stage,the maximum temperature of the synthesis reaction（MTSR）is12.5^oC,and the temperature corresponding to 24 hours to reach the maximum reaction rate under adiabatic conditions(T_D24)is 31.1^oC,according to the risk matrix method,the risk of thermal runaway is level I,and the risk of reaction thermal runaway based on the characteristic temperature classification method is level 2.For the second stage,the MTSR is 49.5^oC,and the T_D24 of the product liquid is 69.4^oC;According to the risk matrix method,the risk of thermal runaway is level I,the thermal runaway risk of the reaction based on the characteristic temperature classification method is level 1;Considering the dosing deviation,when the triethylamine is fed intermittently,the MTSR is 87.6^oC,and the risk of reaction thermal runaway obtained based on the characteristic temperature classification method is 4,and reliable technical measures for evaporation or pressure relief are needed to avoid the initiation of secondary decomposition reactions.