Abstract:Nowadays， the conventional batch preparation process is difficult to achieve accurate control of process parameters， product structure and properties due to the macro scale， resulting in poor product uniformity and significant safety risk in the preparation process. Therefore， how to achieve safe， controllable， and efficient preparation of energetic materials has become a popular research topic. Microreactors are well-suited for preparing energetic materials due to their advantages of miniaturization， integration， high safety， and excellent mass and heat transfer efficiencies. Consequently， microreactor technology has gradually attracted the wide attention of researchers and emerged in the preparation of energetic materials.. This paper provides a detailed overview of the domestic and international research progress on the application of microreactors in hazardous chemical synthesis processes and the preparation of energetic materials. Special attention is given to the potential application of microreactors in the preparation of monolithic and composite energetic materials. The future research direction was prospected， and the future development needs of microreactor technology were emphasized， including large-scale production， three wastes treatment and intelligent platform construction.

Abstract:Energetic materials are widely applied in the area of weaponry industry， aerospace and civil construction. The synthesis of energetic materials is very complex and of great danger in the conventional stirred tank， which can no longer fulfill the requirement of product quality and process safety. The microreaction technology， which has significant advantages of fast heat/mass transfer and excellent safety， has great potential in the synthesis of energetic materials. This review introduces the progress from four aspects， namely the principle of microreaction technology， energetic compound synthesis， production of energetic particles and ultrasonic microreactors. It aims to elaborate the application characteristics of microreaction technology in the area of energetic materials based on the viewpoint of chemical engineering. Finally， the challenges and future direction are summarized and outlooked， including reaction kinetics/thermal kinetics， mixing intensification of viscous and solid-involved fluids， reaction scale-up and intelligent system， waste treatment and how to embrace emerging technologies such as artificial intelligence.

Abstract:To better evaluate the thermal safety risk of continuous flow reactions， a study was conducted using a tubular reactor as an example. By constructing a reaction system model based on heat balance and material balance， the actual heat transfer and thermal safety risk of continuous flow reaction systems were investigated. To address the adiabatic temperature rise reaction phenomenon at the inlet end of a channel reactor， a method based on the critical reaction half-life was proposed as a criterion for thermal safety assessment. Two major reaction conditions with high thermal safety risk were identified： when the total heat release of the target reaction is greater than 800 J·g^-1， and the reaction half-life of the reaction at the reaction temperature is less than the critical reaction half-life； when the total heat release of the decomposition reaction is greater than 800 J·g^-1， and the reaction half-life of the target reaction at the reaction temperature is less than the critical reaction half-life， while the reaction half-life of the decomposition reaction at 100% MTSR（maximum temperature that the process reaction can reach） is also less than the critical reaction half-life.Furthermore，the accuracy and practicality were verified through the nitration reaction of chlorobenzene，and the results show that an explosively decomposition reaction could occur in the channel reactor under these conditions，thus confirming the high-risk thermal safety conditions of continuous flow reactions determined by this evaluation method.

Abstract:To enhance the thermal safety of microreactors utilized for preparing energetic materials， a computational fluid dynamics simulation based on the finite volume method was employed to investigate the impact of structural parameters on flow and heat transfer in a spiral microreactor. The findings reveal that centrifugal force induces continuous directional secondary flow disturbance within the spiral channel， thereby augmenting fluid heat transfer performance. Increasing the curvature of the spiral microreactor， reducing the dimensionless pitch value， and elevating fluid velocity effectively enhance Nusselt number while controlling drag coefficient along the reactor path. Notably， scaling up beyond a radius of 2.5 mm leads to a significant decline in heat transfer performance of a spiral microreactor exhibits a scale-up effect， with a significant decrease in heat transfer performance for spiral microreactors. By maintaining a controlled radius at 2.5 mm， high heat transfer performance can be sustained even with a 25 times increase in heat transfer fluid flux and an impressive 98.9% reduction in pressure drop.

Abstract:Currently， microchannel reactors are extensively employed in the synthesis of energetic materials， significantly enhancing the safety of the synthesis process. However， it is still crucial to consider the thermal stability of these materials. Two important parameters that characterize the risk of thermal decomposition for hazardous chemicals and energetic materials are the time to maximum rate under adiabatic conditions（TMR_ad） and the initiation temperature（T_D24）， which corresponds to the time to maximum rate within 24 hours. The traditional calculation methods for these two parameters are the single-step N-order method and numerical calculations， which have drawbacks such as being time-consuming and labor-intensive during analysis. To address this issue， this study proposes a method for calculating characteristic parameters of thermal runaway decomposition based on the first peak observed after splitting a multi-peak curve in dynamic test curves obtained from Differential Scanning Calorimeter（DSC）. Furthermore， a comparison between this paper’s method and a modeling method using an exhaustive approach was conducted by evaluating T_D24 deviation. Numerical simulation was employed for verification purposes， enabling calculation of thermal runaway characteristic parameters of four substances， namely 1，8-dinitroanthraquinone， M-NQ， 1，5-dinitroanthraquinone， and DNTF based on literature experiments. The results indicate that numerical simulations demonstrate a maximum percentage T_D24 deviation of 2.88% and 6.9% for two-step and three-step consecutive reactions respectively. The maximum deviation observed was 6.41 ℃； for three-step continuous reactions， the T_D24 exhibited a maximum deviation of 5.39 ℃. Furthermore， experimental results employing the methodology proposed in this study demonstrated that the T_D24 values for four energetic materials were calculated with the deviations of -4.55 ℃， 0.71 ℃， 3.16 ℃， and -0.84 ℃ respectively； all absolute percentage deviations were less than 2% when compared to T_D24 obtained through model calculations. These findings validate the effectiveness of the proposed T_D24 calculation method presented in this paper as it exhibits minimal deviation during calculation while offering a straightforward computational process capable of accurately determining thermal decomposition runaway characteristic parameters.

Abstract:To meet the demand for rapid mixing of the reaction solution in the synthesis of silver azide （AgN₃， SA） primary explosives， a continuous reverse-rotating T-shaped micro-mixing chip was designed and fabricated. The influence of chip structure and reactant flow rates on mixing efficiency was investigated using Ansys Fluent simulation software， leading to optimization of an efficient micro-hybrid chip structure. This optimized chip was employed for the continuous synthesis of SA primary explosives. The morphology， compositional structure， and thermal properties of the resulting SA primary explosives were characterized using scanning electron microscopy （SEM）， X-ray diffraction （XRD）， Fourier transform infrared spectroscopy （FTIR）， and differential scanning calorimetry （DSC）. It was observed that a near 100% mixing efficiency could be achieved when employing a micro-mixing chip with a channel size of 1 mm， collision angle of 180°， and reactant flow rate above 4 mL·min^-1. By adjusting the flow rate， concentration， and surfactant content of the reactants， uniform morphology with narrow particle size distribution could be obtained for the SA primary explosives； their main component consisted of AgN₃ crystals exhibiting an orthorhombic crystal system. Compared to the conventional methods， the exothermic peak temperature decreased from 365.2 ℃ to 358.2 ℃ （a reduction by 7 ℃） while the exothermic amount increased from 851.6 kJ·kg^-1 to 976.7 kJ·kg^-1 （an increase by 14.7%） when utilizing microfluidic preparation techniques for SA primary explosives， indicating enhanced reactivity and energy.

Abstract:To achieve the crystallization regulation and batch production of explosives at the safety-critical scale， the ZS-1 microfluidic crystallization system was established based on the microfluidic technology. The experiments were carried out with DMSO as the solvent and deionized water as the anti-solvent. By changing the crystallization process parameters such as the two-phase flow rate ratio， explosive concentration and total flow rate， the particle size control of RDX and the polymorphic transformation of HMX at the microscale was studied， and high-throughput screening of crystallization parameters was explored. Batch preparation experiment of micron RDX was carried out on the ZS-1 microfluidic system. The results show that the average paritcle size of RDX is deduced by 22.2 times after recrystallization. Specifically， the D₅₀ of RDX samples is 3.35 μm， the SPAN number is 0.956 and the purity is 99.80%， and the hourly output of single system reaches 207.7 g. The ZS-1 microfluidic crystallization system verifies the feasibility of batch preparation of narrow size-distributed micron explosives at the microscale.

Abstract:To improve the safety of the charging process of molecular perovskite energetic material （DAP-4）， spherical granulation of DAP-4-based energetic composite microspheres was realized by altering the composite ratio of the bonding agents， Glycidyl Azide Polymer （GAP） and nitrocellulose （NC） （constituting 2% of the mass of DAP-4） using the coaxial droplet microfluidic technology. The macro and micro morphology， crystal structure， thermal properties， combustion properties， and mechanical sensitivity of the samples were tested and analyzed by scanning electron microscope， X-ray diffractometer， differential thermal scanning calorimeter， thermogravimetric analyzer， high-speed photography， impact sensitivity tester and friction sensitivity tester. The results indicate that DAP-4 has the best sphericity when the ratio of GAP to NC is 4∶1. The crystal structure of DAP-4 is not changed after spheroidizing granulation， and the peak temperature of thermal decomposition is slightly advanced. The combustion time of DAP-4 microspheres is slightly longer than that of raw materials， overall with a very stable continuous combustion， retaining its excellent combustion performance. The GN41 microspheres can significantly improve fluidity while reducing mechanical sensitivity and improving the safety of the charging process.

Abstract:To improve the thermal safety and synthetic efficiency during the synthesis process of 3-Nitro-1，2，4-triazol-5-one （NTO） by conventional methods， a continuous flow reaction system was designed and prepared based on the solid contents and kinetics at different reaction stages of nitration. The continuous flow synthesis of NTO was realized by combining microfluidic reaction technology with tubular reaction technology， using 2，4-dihydro-1，2，4-triazol-5-one （TO） and 85% nitric acid as the main raw materials. The reaction conditions and continuous flow system were optimized. NTO with a purity of 99.53% and a yield of 81.4% was achieved at a reaction temperature of 45 ℃， a nitration residence time of 9 min， a molar ratio of n（TO）∶n（HNO₃） equals 1∶6. The chemical structure of NTO synthesized by the continuous flow method was characterized by ¹H and ¹³C NMR， element analysis （EA）， infrared spectroscopy （FT-IR）. In addition， the crystal form， particle morphology， thermal stability and mechanical sensitivity were characterized by the powder X-ray diffraction （XRD）， thermal analyzer （DSC-TG）， optical microscope and BAM technology. The results show that NTO grows into stable β-form. At the heating rate of 10 ℃·min^-1， the thermal decomposition peak temperature is 276.23 ℃ and the mass loss rate during thermal decomposition is 85.12%. The impact sensitivity is over 40 J， and the friction sensitivity is over 360 N. Compared with NTO synthesized by the flask method， the thermal decomposition peak temperature is increased by 2.95 ℃， and the mass loss rate is elevated by 4.44%. The mechanical sensitivities is similar， the crystal morphology is regular and the particle size distribution range is narrowed. The continuous flow synthesis time is 90% shorter than that of the flask process， with 3.4% higher of the yiel， and the preparation efficiency and safety are improved.

Abstract:The study investigated the nitration of 2-methyl-4，6-pyrimidinone （MPO） with nitrate sulfur mixed acid in a microchannel reactor， and further prepared 1，1-diamino-2，2-dinitroethylene （FOX-7） through hydrolysis reaction. N-octane was introduced as an inert solvent to generate slug flow for the reaction system. The reaction occurred inside disperse droplets， thus solving the problem of clogging of nitration intermediates in the microchannel reactor and achieving process intensification and continuous operation. The effects of reaction temperature， residence time， material ratio， and hydrolysis conditions on the product yield were investigated. The combination of microreactor and stirred reactor was proposed. At the molar ratio of nitric acid to MPO of 4.4， reaction temperature of 30 ℃， and residence time of 3 min in the microreactor followed by a 30 min insulation reaction in a stirred kettle， and the ring-opening realized by the hydrolysis with ice water for 2 h， the yield of FOX-7 could reach 90.1%， with a purity of over 99%.

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