CL-20 continuous recrystallization system and method based on microfluidic technology

Abstract

The application belongs to the field of energetic materials, and particularly relates to a CL-20 continuous crystal transformation system and method based on microfluidic technology. The system comprises fluid driving units, a recrystallization unit, a crystal transformation unit and a sample collection unit connected in sequence; the fluid driving units are used for driving and conveying solutions and non-solvents to the recrystallization unit respectively; the recrystallization unit generates explosive suspensions through coaxial focusing micro-mixers; the crystal transformation unit comprises a crystal transformation fluid driving device, an online monitoring device, an ultrasonic device and a crystal transformation generating device; and the precipitate in the sample collection unit is ε-CL-20 crystals. The application first generates CL-20 suspensions through the recrystallization unit, and then changes the crystallization environment of CL-20 by using the crystal transformation unit and completes the crystal transformation of CL-20, so that the continuous and efficient transformation from α-CL-20 to high-purity ε-CL-20 is realized.

Description

Technical Field

[0001] This invention belongs to the field of energetic materials, specifically relating to a CL-20 continuous crystallization system and method based on microfluidic technology. Background Technology

[0002] Explosives are compounds or mixtures primarily composed of oxidizers and combustibles, capable of independently undergoing chemical reactions and releasing energy. They have wide applications in engineering blasting, warhead destruction, solid rocket propellants, and pyrotechnic agents. Crystal form, the intrinsic manifestation of an explosive's structural morphology, is determined by its molecular packing pattern and has a significant impact on its performance. CL-20 is a typical polycrystalline explosive, possessing four crystal forms at room temperature and pressure: α-, β-, ε-, and γ-. Different crystal forms of CL-20 exhibit different physicochemical properties and detonation performance. Among them, ε-CL-20 has the highest density and energy and is the least sensitive, making it the ideal crystal form for explosive formulations. However, the product obtained from conventional CL-20 synthesis processes is α-CL-20, which cannot be used directly. It needs to be transformed into ε-CL-20 through crystal transformation to have practical application value. However, current research on CL-20 crystal transformation is limited both domestically and internationally, lacking stable transformation systems and methods.

[0003] Existing CL-20 crystal transformation experiments mostly employ the solvent-antisolvent method and are conducted in a batch reactor. On a macroscopic scale, mixing of the solvent and antisolvent is often achieved through stirring, inevitably resulting in mixing dead zones that affect the degree of CL-20 crystal transformation. Furthermore, the mixing effect produced by stirring is poor; at low stirring rates, CL-20 crystals are prone to twinning and agglomeration, while excessive stirring speeds easily lead to CL-20 crystal fragmentation. On a macroscopic scale, CL-20 crystal transformation often requires the addition of seed crystals, resulting in poor continuity of the crystallization process and hindering the micro- and nano-scale scaling of explosive crystals. Moreover, the low heat and mass transfer rates also lead to long crystal transformation times for CL-20, severely limiting the transformation efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a CL-20 continuous crystal transfer system and method based on microfluidic technology.

[0005] The technical solution to achieve the purpose of this invention is: a CL-20 continuous crystal transfer system based on microfluidic technology, including a fluid driving unit, a recrystallization unit, a crystal transfer unit and a sample collection unit;

[0006] The fluid drive unit delivers the α-CL-20 explosive solution and the non-solvent-driven material to the recrystallization unit respectively.

[0007] The recrystallization unit achieves the mixing of α-CL-20 explosive solution and non-solvent through a coaxial focusing micro-mixer to generate β-CL-20 explosive suspension;

[0008] The crystal conversion unit includes a crystal conversion fluid driving device, an online monitoring device, an ultrasonic device, and a crystal conversion generating device. The crystal conversion fluid driving device drives the crystal conversion fluid into the β-CL-20 explosive suspension. The online monitoring device monitors the crystal morphology of the explosive suspension before and after the introduction of the crystal conversion fluid. Under the ultrasonic action of the ultrasonic device, the crystals of the explosive suspension in the microchannel of the crystal conversion generating device are transformed from β-CL-20 crystals into ε-CL-20 crystals.

[0009] The sample collection unit is located at the outlet of the crystallization generator and is used to collect the ε-CL-20 explosive suspension.

[0010] Furthermore, the fluid drive unit includes two steady-flow drive subunits, which are used to drive the α-CL-20 explosive solution and non-solvent to the recrystallization unit, respectively.

[0011] Furthermore, the constant flow drive subunit includes a pump assembly and a syringe.

[0012] Furthermore, the coaxial focusing micromixer includes an internal microtube, an external microtube, a cross-shaped four-way connector, and a Y-shaped three-way connector;

[0013] The outlet of the non-solvent-based flow-stabilizing drive subunit is connected to the inlet of the "Y"-type tee connector. The two outlets of the "Y"-type tee connector are respectively connected to the inlets on both sides of the "cross"-type four-way connector. The internal microtube and the external microtube are set inside the "cross"-type four-way connector, and the outlet end of the internal microtube extends into the inlet end of the external microtube. The flow-stabilizing drive subunit that drives the explosive solution is connected to the inlet of the internal microtube, and the outlet end of the external microtube is connected to the inlet of the online monitoring device.

[0014] Furthermore, the internal and external microtubes are made of stainless steel, PTFE, or glass.

[0015] The inner diameter of the internal microtubes is 250–1000 μm, and the outer diameter is 500–1800 μm; the inner diameter of the external microtubes is 1.2–1.5 times that of the outer diameter of the internal microtubes, and the outer diameter is 1600–3000 μm.

[0016] A method for systematically transforming the CL-20 crystal form as described above includes the following steps:

[0017] Step (1): Prepare α-CL-20 explosive solution, non-solvent and crystallization fluid;

[0018] Step (2): Through two constant flow drive sub-units, the α-CL-20 explosive solution and non-solvent are pushed into the coaxial focusing micro mixer, where the α-CL-20 explosive solution and non-solvent come into contact and mix to generate a β-CL-20 explosive suspension;

[0019] Step (3): Inject the crystal transfer fluid into the β-CL-20 explosive suspension using a crystal transfer fluid driving device;

[0020] Step (4): The β-CL-20 explosive suspension mixed with the crystal-transforming fluid enters the crystal-transforming device under ultrasonic action, and the CL-20 crystals achieve a complete transformation from β-crystal form to ε-crystal form in the crystal-transforming device;

[0021] Step (5): Collect the ε-CL-20 explosive suspension after crystallization through the sample collection unit.

[0022] Furthermore, in step (1), CL-20 explosive is dissolved in a solvent without adding a binder or with 20-30 g / L of binder to obtain an α-CL-20 explosive solution with a concentration range of 90-400 g / L.

[0023] The crystal transfer fluid in step (1) is a mixture of solvent and non-solvent, wherein the mixing ratio of solvent and non-solvent is 3 to 12 by mass percentage; the crystal transfer fluid may also be any one of air, nitrogen or helium.

[0024] Furthermore, the non-solvent is water, chloroform, or cyclohexane, the solvent is DMSO, DMF, acetone, or ethyl acetate, and the binder is Estane 5702, F2602, AR-14, or EVA-40W.

[0025] Furthermore, in step (2), the flow rate of the α-CL-20 explosive solution is 0.3 to 0.8 mL / min, the flow rate of the non-solvent is 1 to 5 mL / min, and the ratio of the non-solvent to the solution flow rate is 1 to 10.

[0026] The flow rate of the crystallization fluid ranges from 1 to 5 mL / min;

[0027] In the crystal transformation generator, the length of the pipeline subjected to ultrasonic treatment shall account for no less than 70% of the total pipeline length.

[0028] The above-described system is used to prepare ε-CL-20 single-element explosive or to prepare ε-CL-20-PBX explosive.

[0029] Based on the microscale continuous flow, the CL-20 solution and antisolvent can rapidly mix and diffuse at a state closer to the molecular scale, forming a stable supersaturation, temperature, and high mixing efficiency, thus creating a stable crystal transformation environment that facilitates the rapid and continuous transformation of the CL-20 crystal form. Furthermore, the microfluidic method offers lower reagent consumption and more precise control of reaction parameters, allowing for flexible regulation of the CL-20 crystal transformation environment and in-depth research into the CL-20 crystal transformation mechanism.

[0030] Compared with the prior art, the significant advantages of this invention are:

[0031] 1. The CL-20 continuous crystal transfer system of the present invention utilizes the advantages of microfluidic technology to achieve rapid and continuous crystal transfer of CL-20 in one process flow and complete the preparation of ε-CL-20-based PBX, thereby improving the performance and stability of CL-20 explosive and having practical and efficient characteristics.

[0032] 2. The crystallization reaction of this system is carried out at the microscale, which has higher mixing efficiency and heat and mass transfer efficiency, which is conducive to the formation of a stable crystallization environment and improves the degree of crystallization of CL-20 and the quality of ε-CL-20.

[0033] 3. This system offers advantages such as low safety risk, high speed, short R&D cycle, low energy and material consumption, and minimal environmental pollution during CL-20 crystal conversion. It is highly suitable for optimizing and screening experimental parameters during the crystal conversion process.

[0034] 4. This system can easily connect recrystallization and crystallization units in parallel to achieve high-throughput screening and batch preparation. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the continuous preparation system of the present invention.

[0036] Figure 2 This is a morphological image of the ε-CL-20 sample obtained in Example 1 of this application.

[0037] Figure 3 This is a morphological image of the ε-CL-20 sample obtained in Example 2 of this application.

[0038] Figure 4 This is a morphology diagram of the ε-CL-20-PBX sample obtained in Example 3 of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1-Stable flow drive unit I, 2-Stable flow drive unit II, 3-Recrystallization unit, 4-Crystal transformation unit, 5-Crystal transformation fluid drive device, 6-Online monitoring device, 7-Crystal transformation generator, 8-Ultrasonic device, 9-Sample collection unit. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings.

[0042] Combination Figure 1This invention discloses a CL-20 continuous crystal transfer system based on a coaxial focusing micromixer, comprising a fluid drive unit, a recrystallization unit, a crystal transfer unit, a sample collection unit, and connecting components. The fluid drive unit provides flow driving force for the solution and non-solvent; the recrystallization unit achieves rapid mixing of the α-CL-20 explosive solution and non-solvent through the coaxial focusing micromixer, generating a β-CL-20 explosive suspension; after mixing the generated β-CL-20 explosive suspension with the crystal transfer fluid, rapid and continuous crystal transfer to ε-CL-20 is completed in the crystal transfer generator under the action of an ultrasonic device. The resulting suspension after crystal transfer flows into the sample collection unit, where the precipitate is ε-CL-20.

[0043] The non-solvent is water, chloroform, or cyclohexane; the solvent is DMSO, DMF, acetone, or ethyl acetate; the crystal transfer fluid is a mixture of solvent and non-solvent (the ratio of solvent to non-solvent is 3–12), air, nitrogen, or helium; the binder is Estane 5702, F2602, AR-14, or EVA-40W; the flow rate of the solution is 0.3–0.8 mL / min; the flow rate of the non-solvent is 1–5 mL / min; the ratio of non-solvent to solution flow rate is 1–10; the concentration of CL-20 explosive dissolved in the solvent is 90–400 g / L; the concentration of binder dissolved in the solvent is 0 g / L or 20–30 g / L; and the proportion of the crystal transfer device in the ultrasonic process is 70–100%.

[0044] The following embodiments are merely illustrative of the present invention and should not be construed as limiting the present invention.

[0045] Example 1

[0046] A rapid, continuous crystallization process from α-CL-20 to β-CL-20 and then to ε-CL-20 was achieved using a microfluidic-based crystallization system. Ethyl acetate was used as the solvent, and cyclohexane was used as the non-solvent for CL-20 recrystallization, without the addition of a binder. The microtubes were made of PTFE, with an inner tube diameter of Ф(1600, 800) μm and an outer tube diameter of Ф(3000, 2000) μm. α-CL-20 was dissolved in ethyl acetate at a concentration of 195 g / L, and the solution was pumped by a continuous flow-controlled syringe pump at a flow rate of 0.44 mL / min. The non-solvent was also pumped by a continuous flow-controlled syringe pump at a flow rate of 2.46 mL / min. The crystallization fluid was a mixture of cyclohexane and ethyl acetate (volume ratio 5:1), pumped by a continuous flow-controlled syringe pump at a flow rate of 2.9 mL / min. The fluid drive unit is switched on, and the α-CL-20 explosive solution and non-solvent flow into the coaxial focusing micro-mixer under the drive of the constant flow drive device. The solution and non-solvent come into contact and mix rapidly to form a β-CL-20 explosive suspension. Then, the crystal-transfer fluid drive device and the ultrasonic device are turned on, so that the crystal-transfer fluid and the β-CL-20 explosive suspension are mixed under ultrasonic conditions. The proportion of the crystal-transfer device in the ultrasonic process is 80%. After the mixed fluid flows into the crystal-transfer device, the crystallization environment of β-CL-20 changes, and it is transformed into ε-CL-20 crystals. After washing, filtering, and drying, a high-purity ε-CL-20 solid powder is obtained. Figure 2 ).

[0047] Example 2

[0048] A microfluidic-based crystal transfer system was used to achieve rapid and continuous crystal transfer from α-CL-20 to β-CL-20 and then to ε-CL-20. Ethyl acetate was used as the solvent, and cyclohexane was used as the non-solvent for CL-20 recrystallization, without the addition of a binder. The microtubes were made of PTFE, with an inner tube diameter of Ф(1600, 800) μm and an outer tube diameter of Ф(3000, 2000) μm. α-CL-20 was co-dissolved in ethyl acetate at a concentration of 97.5 g / L, and the solution was driven by a continuously variable injection pump at a flow rate of 0.44 mL / min. The non-solvent was also driven by a continuously variable injection pump at a flow rate of 2.46 mL / min. The crystal transfer fluid was air, driven by a continuously variable injection pump at a flow rate of 2.9 mL / min. The fluid drive unit is switched on, and the α-CL-20 explosive solution and non-solvent flow into the coaxial focusing micro-mixer under the drive of the steady-flow drive device. The solution and non-solvent come into contact and mix rapidly to form a β-CL-20 explosive suspension. Then, the crystal-transforming fluid drive device and the ultrasonic device are activated, with the crystal-transforming device accounting for 87% of the ultrasonic activity. The crystal-transforming fluid and the β-CL-20 explosive suspension mix in the microchannel and form a gas-liquid Taylor flow. The gas-liquid Taylor flow and ultrasonic action enhance the mixing intensity of the solid and liquid phases in the microchannel, which is beneficial to the crystal transformation of CL-20. After washing, filtering, and drying, a high-purity ε-CL-20 solid powder is obtained. Figure 3 ).

[0049] Example 3

[0050] A microfluidic-based crystallization system was used to achieve rapid and continuous crystallization from α-CL-20 to β-CL-20 and then to ε-CL-20, and ε-CL-20-PBX was continuously prepared. The microtubes were made of PTFE, with an inner tube diameter of Ф(1600, 800) μm and an outer tube diameter of Ф(3000, 2000) μm. Ethyl acetate was used as the solvent, and cyclohexane was used as the non-solvent for CL-20 recrystallization. Estane 5702 was selected as the binder. α-CL-20 and Estane 5702 were co-dissolved in ethyl acetate, with an α-CL-20 concentration of 97.5 g / L and an Estane 5702 concentration of 20.5 g / L. The solution was driven by a continuous flow-controlled syringe pump at a flow rate of 0.44 mL / min, and the non-solvent was driven by the same syringe pump at a flow rate of 2.46 mL / min. The crystallization fluid was air, driven by a continuous flow-controlled injection pump at a flow rate of 2.9 mL / min. When the fluid drive unit was switched on, the α-CL-20 explosive solution and non-solvent flowed into the coaxial focusing micro-mixer under the drive of the continuous flow-controlled device. The solution and non-solvent contacted and mixed rapidly, forming a β-CL-20 explosive suspension. Then, the crystallization fluid drive device and the ultrasonic device were activated, with the crystallization device comprising 87% of the ultrasonic component. The crystallization fluid and the β-CL-20 explosive suspension were mixed and crystallized in the crystallization device. To further obtain ε-CL-20-PBX, a cyclohexane solution was driven into the ultrasonic atomization device using a peristaltic pump. The cyclohexane was dispersed into droplets by ultrasonic atomization and fell into the ε-CL-20 explosive suspension. Under magnetic stirring, it rapidly mixed with the ε-CL-20 explosive crystals, and a binder precipitated on the surface, ultimately forming ε-CL-20-PBX. Figure 4 ).

Claims

1. A method for transforming the crystal form of CL-20 using a CL-20 continuous crystal transformation system based on microfluidic technology, characterized in that, The system includes a fluid drive unit, a recrystallization unit (3), a crystal transfer unit (4), and a sample collection unit (9). The fluid drive unit delivers the α-CL-20 explosive solution and the non-solvent to the recrystallization unit (3). The recrystallization unit (3) mixes the α-CL-20 explosive solution and the non-solvent through a coaxial focusing micro-mixer to generate a β-CL-20 explosive suspension. The crystal transfer unit (4) includes a crystal transfer fluid drive device (5), an online monitoring device (6), an ultrasonic device (8), and a crystal transfer generator (7). The crystal transfer fluid drive device (5) drives the crystal transfer fluid into the β-CL-20 explosive suspension. In the α-CL-20 explosive suspension, the online monitoring device (6) monitors the crystal morphology of the explosive suspension before and after the introduction of the crystal-transforming fluid. Under the ultrasonic action of the ultrasonic device, the crystals of the explosive suspension in the microchannel of the crystal-transforming device (7) are transformed from β-CL-20 crystals to ε-CL-20 crystals. The sample collection unit (9) is set at the outlet of the crystal-transforming device (7) to collect the ε-CL-20 explosive suspension. The fluid drive unit includes two steady flow drive subunits, which are used to drive the α-CL-20 explosive solution and non-solvent to the recrystallization unit (3), respectively. The method includes the following steps: Step (1): Prepare α-CL-20 explosive solution, non-solvent and transcrystallization fluid; Step (2): Through two constant flow drive sub-units, the α-CL-20 explosive solution and non-solvent are pushed into the coaxial focusing micro mixer, where the α-CL-20 explosive solution and non-solvent come into contact and mix to generate a β-CL-20 explosive suspension; Step (3): Inject the crystal-transforming fluid into the β-CL-20 explosive suspension using a crystal-transforming fluid driving device; Step (4): The β-CL-20 explosive suspension mixed with the crystal-transforming fluid enters the crystal-transforming device under ultrasonic action, and the CL-20 crystals achieve a complete transformation from β-crystal form to ε-crystal form in the crystal-transforming device; Step (5): Collect the ε-CL-20 explosive suspension after crystallization through the sample collection unit.

2. The method according to claim 1, characterized in that, In step (1), CL-20 explosive is dissolved in a solvent without adding binder or with 20~30 g / L binder to obtain an α-CL-20 explosive solution with a concentration range of 90~400 g / L. The crystal transfer fluid in step (1) is a mixture of solvent and non-solvent, wherein the mixing ratio of solvent and non-solvent is 3 to 12 by mass percentage; or the crystal transfer fluid is any one of air, nitrogen or helium.

3. The method according to claim 2, characterized in that, The non-solvent is water, chloroform or cyclohexane, the solvent is DMSO, DMF, acetone or ethyl acetate, and the binder is Estane 5702, F2602, AR-14 or EVA-40W.

4. The method according to claim 3, characterized in that, In step (2), the flow rate of the α-CL-20 explosive solution is 0.3~0.8 mL / min, the flow rate of the non-solvent is 1~5 mL / min, and the flow rate ratio of the non-solvent to the α-CL-20 explosive solution is 1.25~10. The flow rate of the crystallization fluid is in the range of 1~5 mL / min; In the crystal transformation device, the length of the pipeline subjected to ultrasonic treatment shall account for no less than 70% of the total length of the pipeline.

5. The method according to claim 4, characterized in that, The constant flow drive subunit includes a pump unit and a syringe.

6. The method according to claim 5, characterized in that, The coaxial focusing micromixer includes an internal microtube, an external microtube, a cross-shaped four-way connector, and a Y-shaped three-way connector; The outlet of the non-solvent-based flow-stabilizing drive subunit is connected to the inlet of the "Y" type tee connector. The two outlets of the "Y" type tee connector are respectively connected to the inlets on both sides of the "cross" type four-way connector. The internal microtube and the external microtube are set inside the "cross" type four-way connector, and the outlet end of the internal microtube extends into the inlet end of the external microtube. The flow-stabilizing drive subunit that drives the explosive solution is connected to the inlet of the internal microtube, and the outlet end of the external microtube is connected to the inlet of the online monitoring device (6).

7. The method according to claim 6, characterized in that, The internal and external microtubules are made of stainless steel, PTFE, or glass. The inner diameter of the internal microtubes is 250~1000 μm, and the outer diameter is 500~1800 μm; the inner diameter of the external microtubes is 1.2~1.5 times that of the outer diameter of the internal microtubes, and the outer diameter is 1600~3000 μm.

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