Application Of Microchannel Reactor In Nitration Of Nitrogenous Compounds

Nitration of nitrogenous compounds is generally accompanied by a strong exotherm and suffered a poor process safety.The product is extremely sensitive to temperature,and the excessive waste acid can caused environmental pollution.By means of their micron to submillimeter dimensions,microreactors possess a huge specific surface area,providing rapid heat and efficient mass transfer,ensuring the heat evenly to entire process,achieving the accurate control to nitration of nitrogen compounds.In this paper,we established a microreaction system which the core was a special structure of micromixer.The application of this microreactior technology can precise control of the stoichiometric reactants,reduce the usage of strong acids radically,eliminate the possibility of side-product formation.(1)4,5-dinitroimidazole(4,5-DNI)has been recognized as a key intermediate for the synthesis of energetic materials,and is important for the preparation of drugs and pharmaceutical active ingredients.However,the reported synthesis of 4,5-DNI in conventional batch reactors have suffered from low yields,energy-intensive production,and high dangerous operating environment.Here,we presented the details on the development of a two-step preparation of 4,5-DNI from imidazole in interdigital multilamination microreactors under continuous flow microfluidic system.After optimizing conditions,the single step yield of 4-NI was obtained in 96.1%and total yield of 4,5-DNI reached 88.8%.The space time conversion(STC)was 5 orders of magnitude higher than that of the conventional reactors.We also investigated the mechanism of the synthesis of 4,5-dinitroimidazole in the microchannel reactor and summarized the advantages of the synthesis of 4,5-dinitroimidazole in the microreaction system.(2)1-methyl-4,5-dinitroimidazole(4,5-MDNI)was synthesized in the interdigital multilamination microreactor as a core of microreaction system.During the process of nitration,a large amount of heat will be released at the instant of mixing 1-methylimidazole and nitric-sulfuric acid.It's difficult to precisely control the temperature.In order to avoid overreaction,it must strictly control the feed speed and the reaction time is lengthy.Also it's likely to produce by-product,and the yield of 1-methyl-4,5-dinitroimidazole is low.In the constructed microreaction system,1-methylimidazole was used as the raw material and nitric-sulfuric mixed acid as the nitrating agent.Owing to study the flow rate and the internal structure size of the microreactor,the mass transfer and heat transfer process of the reaction was strengthened,and the safety of the experimental operation was improved.The optimum operation with tight temperature control of 100?and accurate total volume flow rate of 18mL/h in a single microreactor could be continuous and efficient synthesis of 1-methyl-4,5-dinitroimidazole,at a yield of 87%.(3)O-methyl-n-nitroisouea(NIO)has been synthesized in the microreactor system..The method of synthesis o-methyl-n-nitroisourea by nitrating of o-methylisourea sulfate was studied.Comparing with conventional reactor,continuous flow microreactor improved the safety of synthesis o-methyl-n-nitroisourea without reducing it's yield The representative benefits in microreactor system including accurate temperature control,reduced reaction time,and improved product purity It provided an important theoretical basis for the production saftey of o-methyl-n-nitroisourea.