A process and device for continuously preparing ultrafine nitroguanidine

Abstract

The present invention discloses a process and device for continuously preparing ultrafine nitroguanidine. By adopting the supergravity technology, ultrafine nitroguanidine is prepared in one step during the acid solution precipitation crystallization process of nitroguanidine. An impact flow - rotating packing bed is used as the crystallization device. Using nitroguanidine acid solution and water as raw materials, through primary mixing and explosive nucleation, the crystal nuclei of nitroguanidine are formed and grow rapidly, shear - controlled forming is carried out for crystal form transformation and growth control, crystal form optimization and regrowth are carried out for crystal form improvement and further growth to increase the yield, and through a post - treatment process, ultrafine nitroguanidine is obtained. Ultrafine nitroguanidine with a Fisher average particle size of 2 - 6 μm and uniform particle size is continuously prepared with a small volume, short residence time, and wide operation range. The present invention solves the problems of long process flow, high energy consumption, and unstable quality in the industrial production of nitroguanidine. At the same time, it improves the disadvantages of poor flowability and poor mechanical properties of nitroguanidine, and is a low - risk and high - efficiency production method, expanding the application of supergravity technology in the control of energetic material crystals.

Description

Technical Field

[0001] The invention belongs to the field of preparation of energetic materials, and particularly relates to a process and device for continuously preparing ultrafine nitroguanidine. Background Art

[0002] As an important industrial raw material, nitroguanidine is widely used in the military, civilian, and pharmaceutical industries. However, when nitroguanidine is prepared by the sulfuric acid method, the nitroguanidine obtained during the liquid-phase precipitation of the nitroguanidine acid solution and ice water is hollow long needle-shaped crystals with a large aspect ratio. Inevitably, stress concentration will occur at the tip, which has an adverse effect on the mechanical properties and combustion properties of the propellant, causing cracks in the grains. Moreover, since the raw material of nitroguanidine is flocculent and not easily dispersed, it is very difficult to be evenly distributed during the kneading process, thus affecting the process performance and mechanical properties of the propellant. When crude nitroguanidine is applied to explosives and automotive airbags, there are defects such as poor flowability and poor mechanical properties. Ultrafining the energetic material to prepare short, thin, and better-flowable ultrafine nitroguanidine is the key to solving this problem.

[0003] The preparation of nitroguanidine using guanidine nitrate and concentrated sulfuric acid as raw materials mainly includes three steps: nitration, ice water precipitation, and recrystallization. A series of studies on the ultrafining of nitroguanidine have been conducted at home and abroad. Chinese Patent CN 102702034 B discloses a continuous preparation process for ultrafine nitroguanidine, and ultrafine nitroguanidine is obtained by recrystallization. Gao Sijing (Preparation of spherical nitroguanidine by solvent / non-solvent method. Journal of Explosives & Propellants, 2014, 37(06): 44-47.) prepared spherical nitroguanidine using N-methylpyrrolidone as the solvent, acetone as the non-solvent, and nickel nitrate as the additive. The above studies control the crystal form of nitroguanidine by recrystallization, all of which conduct recrystallization research on the basis of crude nitroguanidine, increasing the process, reducing the yield, introducing new organic impurities, having a high cost, and being difficult to achieve large-scale production.

[0004] Therefore, the key of this invention is how to simplify the process, reduce the cost, improve the quality of the primary crystallization product, and prepare ultrafine nitroguanidine that meets the particle size requirements of the national standard "GJB1441A-2005 Specification for Nitroguanidine" (Type I: Fisher average particle size 3.4 - 6.0 μm; Type II: ≤ 3.3 μm). The primary crystallization process of nitroguanidine, which is also the antisolvent crystallization process of ice-water precipitation, is to add nitroguanidine acid solution into ice water to obtain nitroguanidine crystals. Chinese Patent CN 105152984 A discloses a continuous synthesis method of nitroguanidine, in which the nitroguanidine acid solution is continuously fed into an ice-dissolving kettle for precipitation to obtain nitroguanidine crystals. It has low operation intensity and high production efficiency, but it takes a long time. The nitroguanidine acid solution stays in the ice-dissolving kettle for 2 - 2.5 h, and only crude nitroguanidine can be obtained, and ultrafine nitroguanidine cannot be prepared in one step. It is a semi-continuous process. Chinese Patent CN 111217723 A discloses a preparation process of ultrafine particle nitroguanidine, which uses an immersion impinging stream reactor for precipitation reaction. The process is relatively stable, but the accumulation amount of raw materials is large, there are potential safety hazards, and the particle size distribution of ultrafine nitroguanidine is relatively wide. The reactors used above are generally batch or semi-continuous operations. As the reaction progresses, backmixing of materials will occur, the dilution ratio gradually deviates from the optimal conditions, and the crystallization temperature changes. Therefore, it is necessary to optimize the reactor to maintain uniform reaction conditions, keep the material ratio and reaction temperature stable, and at the same time achieve efficient mixing of materials.

[0005] The high gravity technology is a chemical process intensification technology. High gravity equipment is known as the "transistor of the chemical industry" and is widely used in wastewater treatment, preparation of nanomaterials, chemical reaction intensification, etc. Applying the high gravity technology to liquid phase precipitation can achieve rapid and efficient good micro-mixing, ensure a stable supersaturation degree, reduce the residence time, and realize continuous production. Therefore, starting from the raw materials and process in the production process of nitroguanidine, this invention proposes a production process and device for continuously preparing ultrafine nitroguanidine without introducing new reaction processes and raw materials. Using nitroguanidine acid solution and water as raw materials and an impinging stream-rotating packed bed as the reactor, it can rapidly and efficiently achieve micro-mixing of materials and maintain the optimal ratio, and prepare ultrafine nitroguanidine in one step during the antisolvent crystallization process of ice-water precipitation, which can simplify the process, improve the yield, reduce the accumulation of raw materials, and improve the safety performance of the system. By using an impinging stream-rotating packed bed, the nucleation, growth, and crystal shape optimization of crystals are carried out in separate zones, reducing the consumption of water, ensuring a uniform crystal nucleation and growth environment, rapidly and continuously preparing ultrafine nitroguanidine, and having a very short residence time. At the same time, there is no need for recrystallization and no other substances need to be introduced, which is more environmentally friendly and efficient. Summary of the Invention

[0006] The present invention aims to provide a process and device for continuously preparing ultrafine nitroguanidine, which solves the problems of long process route, high energy consumption, and unstable quality of nitroguanidine in industrial production of nitroguanidine, shortens the process route, reduces production costs, reduces energy consumption, improves safety, and enhances product quality.

[0007] A process for continuously preparing ultrafine nitroguanidine provided by the present invention uses nitroguanidine acid solution and water as raw materials, adopts an impinging stream - rotating packed bed as the crystallization equipment, and through the processes of initial mixing and burst nucleation, shear - controlled shaping, crystal form optimization and regrowth, and post - treatment, prepares ultrafine nitroguanidine with a Feret average particle size of 2 - 6 μm and can achieve continuous production.

[0008] The present invention starts from the nitroguanidine production process and raw materials, and through initial mixing and burst nucleation, shear - controlled shaping, and crystal form optimization and regrowth, crystal nucleation, crystal growth, crystal form control, and crystal regrowth are carried out at different positions of the rotating packed bed respectively. At the same time, by controlling the movement path and mixing mode of the feed liquid, the crystal morphology and particle size of nitroguanidine are optimized. Generally speaking, the positions and control mechanisms of the crystal nucleation and growth processes are different. The high - gravity technology is applied to the preparation of ultrafine nitroguanidine by liquid - phase precipitation method. Crystal nucleation, crystal growth, crystal form control, and crystal regrowth are carried out at different positions of the rotating packed bed respectively. At the same time, by controlling the movement path and mixing mode of the feed liquid, the crystal morphology and particle size of nitroguanidine are optimized, and at the same time, two or more streams of materials contact in a plug - flow manner. The impinging stream - rotating packed bed separates the crystal nucleation and growth, reduces the water consumption, and can ensure a uniform crystal nucleation and growth environment. Ultrafine nitroguanidine can be continuously prepared while preparing the crude nitroguanidine, without the need for recrystallization, without introducing organic substances, with a very short residence time, and is more environmentally friendly and efficient. The present invention avoids the recrystallization process, shortens the process, and optimizes the process.

[0009] The nitroguanidine acid solution is a mixed solution of nitroguanidine and concentrated sulfuric acid or nitric acid, which is the product of the nitration process, and the molar ratio of nitroguanidine to concentrated sulfuric acid (or nitric acid) is 1:1.5 - 1:3.

[0010] The process for continuously preparing ultrafine nitroguanidine is implemented as follows:

[0011] (1) Feed liquid preparation: Add the nitroguanidine acid solution and water into the storage devices respectively.

[0012] (2) Initial mixing and burst nucleation: The nitroguanidine acid solution and water are respectively input into the impinging stream - rotating packed bed in a continuous feeding manner. The two raw materials obtain a relatively high flow rate by pumps and are ejected through nozzles for impinging and mixing. The nitroguanidine acid solution and water quickly contact, the acid solution is rapidly diluted, the solubility of nitroguanidine rapidly decreases, burst nucleation occurs, a large number of nitroguanidine crystal nuclei are formed and grow rapidly.

[0013] (3)Shearing control forming: The reaction slurry after initial mixing is captured by the rotating packing at high speed. First, it enters the inner layer of dense packing, where the acid solution and water are more evenly mixed. While the nitroguanidine crystals are growing, they are violently sheared by the fine packing, and the longer needle-shaped crystals break. The slurry enters the looser outer packing, where the shearing becomes weaker, and the crystals grow evenly and gradually transition to rod-shaped.

[0014] (4)Crystal form optimization and regrowth: The slurry composed of nitroguanidine crystals and acid water is thrown out of the rotating packing and falls in a parabola in the form of micro-element liquid units. After directly contacting the atomized sprayed chilled water, it falls to the bottom of the equipment. Under the action of the stirring paddle, it is mixed and the crystals grow again, improving the defect of the hollow rod-shaped nitroguanidine crystals, growing densely inside, and increasing the system yield.

[0015] (5)Post-treatment: The dilute acid water containing nitroguanidine crystals enters the filtering equipment from the outlet at the bottom of the equipment to obtain ultrafine nitroguanidine crystals, and the filtrate enters the wastewater treatment system.

[0016] The volume ratio of the nitroguanidine acid solution to the water in step (1) can be 1:3 - 1:10; the volume ratio of the nitroguanidine acid solution to the atomized sprayed water can be 1:1 - 1:5.

[0017] The temperature range of the nitroguanidine acid solution is 0 - 40 °C, the temperature of the impact water is -5 - 20 °C, and the temperature of the atomized sprayed chilled water is -5 - 5 °C.

[0018] The present invention provides a device for continuously preparing ultrafine nitroguanidine, including an impact flow - rotating packing bed, a nitroguanidine acid solution storage tank, a pump, a freezer, a wastewater storage tank, a filter, a nitroguanidine storage tank, and a water storage tank; the nitroguanidine acid solution storage tank is connected to the nitroguanidine acid solution inlet of the impact flow - rotating packing bed through a pump; the water storage tank is connected to the water inlet of the impact flow - rotating packing bed through a pump; the water storage tank is also connected to the atomized spraying port of the impact flow - rotating packing bed through a pump and a freezer; the liquid outlet of the impact flow - rotating packing bed is connected to the filter; the filter is respectively connected to the nitroguanidine storage tank and the wastewater storage tank.

[0019] In the above device, the impact flow - rotating packing bed includes a packing rotor, a motor, a housing, a liquid distributor, an atomized spraying port, a stirring paddle, and a liquid outlet; the packing rotor is divided into two parts: inner packing and outer packing; two motors at the bottom respectively drive the stirring paddles connected to them, and the motor above the rotating shaft is the driving motor for the packing rotation; a liquid distributor is provided at the bottom of the impact flow - rotating packing bed, and the liquid distributor is composed of a nitroguanidine acid solution pipeline and 1 - 2 water pipelines. The nitroguanidine acid solution pipeline and the water pipelines are arranged in parallel, and the outlet nozzles of the two pipelines are arranged opposite to each other or at a 90° angle to control the 180° or 90° impact of the two liquids in the pipelines; the atomized spraying port includes two atomized spraying ports; the stirring paddle includes two symmetrically arranged stirring paddles.

[0020] The impinging flow-rotating packing bed is a trapezoidal structure, and the liquid thrown out of the rotating packing falls in a parabola in the form of micro-elements, directly contacts with the atomized frozen water, and then falls to the bottom and gathers, and is cooled and crystallized to optimize the crystal shape.

[0021] The packing of the impinging flow-rotating packed bed is designed in layers, the inner layer is a structured packing with dense packing and high shear frequency, and the outer layer is a structured packing with loose packing and low shear frequency or a random packing arranged according to certain rules.

[0022] In the impinging flow-rotating packed bed, by changing the number of liquid inlet pipes of the liquid distributor, an impingement distribution of a nitroguanidine acid liquid and one or two water streams is achieved, and the reaction heat is quickly removed (playing a cooling role) by increasing the amount of water, and the two liquids are impinged at 180° or 90° by controlling the direction of the liquid nozzle of the liquid inlet pipe.

[0023] The impinging flow-rotating packed bed liquid distributor nozzle is a circular hole with different diameters, and the inner diameter of the nozzle can be 0.5mm-2.0mm.

[0024] Beneficial effects of the present invention:

[0025] (1) The ultrafine nitroguanidine prepared by ultra-gravity technology shows a trend of decreasing length and increasing diameter; through the Fisher particle size test, the ultrafine nitroguanidine particle size is 2-6μm, which can meet the national standard requirements and achieve the goal of high-end products requiring shorter and thicker particles;

[0026] (2) The use of impinging stream-rotating packed bed to continuously prepare ultrafine nitroguanidine can quickly achieve microscopic mixing explosion nucleation, always maintain a uniform ratio and optimal conditions, and the product quality is stable;

[0027] (3) The device of the present invention has the advantages of small equipment size, short residence time, low risk and high efficiency, wide control range, green energy saving and environmental protection; at the same time, it can achieve one-step completion, and can prepare ultrafine nitroguanidine with a particle size that meets the national standard requirements when the nitroguanidine acid solution is precipitated in ice water, eliminating the recrystallization process, simplifying the process, improving quality, increasing yield, improving economy, and realizing continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic diagram of the overall structure of a device for continuously preparing ultrafine nitroguanidine;

[0029] Figure 2 This is a schematic diagram of the structure of the impinging flow-rotating packed bed used in the present invention;

[0030] Figure 3 The Fisher average particle size distribution diagram of the product purchased from the market and the ultrafine nitroguanidine prepared in Examples 1 to 3 of the present invention;

[0031] Figure 4 Optical microscope photos of ultrafine nitroguanidine; A is the optical microscope photo of the ultrafine nitroguanidine sold in the market, B is the optical microscope photo of the ultrafine nitroguanidine prepared in Example 1, C is the optical microscope photo of the ultrafine nitroguanidine prepared in Example 2, and D is the optical microscope photo of the ultrafine nitroguanidine prepared in Example 3;

[0032] Figure 5 It is the structure diagram of the liquid distributor.

[0033] In the figure: 1 - nitric acid guanidine acid liquid storage tank; 2 - pump; 3 - impinging stream - rotating packed bed; 4 - refrigerator; 5 - waste water storage tank; 6 - filter; 7 - nitroguanidine storage tank; 8 - water storage tank; 3.1 - packing rotor; 3.2 - motor; 3.3 - housing, 3.4 - liquid distributor; 3.5 - atomizing spray port; 3.6 - stirring paddle; 3.7 - liquid outlet; 3.8 - inner packing; 3.9 - outer packing; 3.10 - motor for driving the packing to rotate; 3.11 - nitroguanidine acid liquid inlet; 3.12 - water inlet. Specific embodiments

[0034] The present invention will be further described below by way of examples, but is not limited to the following examples.

[0035] As Figures 1-2 shown, a device for continuously preparing ultrafine nitroguanidine mainly includes an impinging stream - rotating packed bed 3, a nitric acid guanidine acid liquid storage tank 1, a pump 2, a refrigerator 4, a waste water storage tank 5, a filter 6, a nitroguanidine storage tank 7, and a water storage tank 8; the nitric acid guanidine acid liquid storage tank 1 is connected to the nitroguanidine acid liquid inlet 3.11 of the impinging stream - rotating packed bed 3 through the pump 2; the water storage tank 8 is connected to the water inlet 3.12 of the impinging stream - rotating packed bed 3 through the pump 2; the water storage tank 8 is also connected to the atomizing spray port 3.5 of the impinging stream - rotating packed bed 3 through the pump 2 and the refrigerator 4; the liquid outlet 3.7 of the impinging stream - rotating packed bed 3 is connected to the filter 6; the filter 6 is respectively connected to the nitroguanidine storage tank 7 and the waste water storage tank 5.

[0036] In the above device, the impinging stream-rotating packed bed 3 includes a packing rotor 3.1, a motor 3.2, a shell 3.3, a liquid distributor 3.4, an atomizing spray port 3.5, a stirring paddle 3.6, and a liquid outlet 3.7; the packing rotor 3.1 is divided into two parts, an inner packing 3.8 and an outer packing 3.9; the liquid distributor 3.4 includes a nitroguanidine acid liquid inlet 3.11 and a water inlet 3.12; the atomizing spray port 3.5 includes two atomizing spray ports; the stirring paddle 3.6 includes two symmetrically arranged stirring paddles. The impinging stream-rotating packed bed takes the axis as the symmetry center, and atomizing spray ports 3.5 are respectively arranged on both sides. The two motors 3.2 at the bottom respectively drive the stirring paddles 3.6 connected thereto, and the motor above the rotating shaft is a packing rotation driving motor 3.10.

[0037] The impinging flow-rotating packing bed is a trapezoidal structure. The liquid thrown out of the rotating packing falls in a parabola in the form of micro-elements, directly contacts with the atomized and sprayed chilled water, and then falls to the bottom and gathers to cool and crystallize to optimize the crystal shape.

[0038] The packing of the impinging stream-rotating packed bed is designed in layers, with the inner layer being tightly packed and the outer layer being loosely packed; the inner layer can be a tightly packed structured packing, and the outer layer can be a loosely packed structured packing or a random packing arranged according to a certain rule.

[0039] A liquid distributor is provided at the bottom of the impinging flow-rotating packed bed. Figure 5 As shown, the liquid distributor is composed of a nitroguanidine liquid pipeline and 1-2 water pipelines. The nitroguanidine liquid pipeline and the water pipeline are arranged in parallel, and the outlet nozzles of the two pipelines are arranged opposite to each other or at an angle of 90°, so as to control the two liquids in the pipeline to collide at 180° or 90°. Figure 5 Schematic diagram of the two-stream feed liquid distributor in the figure. The liquid distributor consists of a nitroguanidine liquid pipeline and a water pipeline. The nitroguanidine liquid pipeline and the water pipeline are arranged in parallel. The outlet nozzles of the two pipelines are arranged oppositely to control the nitroguanidine liquid and water in the pipeline to achieve a 180° collision. Figure 5 Schematic diagram of a three-stream feed liquid distributor, wherein the liquid distributor consists of a nitroguanidine liquid pipeline and two water pipelines. The nitroguanidine liquid pipeline and the water pipeline are arranged in parallel, and the outlet nozzles of the two liquid pipelines are arranged relative to each other or collide at 90°, so as to control the nitroguanidine liquid and water in the pipeline to achieve a 180° or 90° collision. Figure 5 For different liquid distributor structures; the number of liquid inlet pipes of the liquid distributor is changed according to demand to achieve two-stream or three-stream feeding.

[0040] The present invention realizes the impinging distribution of a nitroguanidine acid solution and one or two water streams by changing the number of liquid inlet pipes of the liquid distributor, rapidly removes the reaction heat by increasing the amount of water, and realizes the 180° or 90° impingement of the two liquids by controlling the direction of the liquid nozzles of the inlet pipes.

[0041] The nozzles of the impinging stream - rotating packing bed liquid distributor are round holes with different diameters, and the inner diameter of the nozzles can be 0.5 mm - 2.0 mm.

[0042] The implementation of the present invention is described below through specific examples: Example 1

[0043] The nitroguanidine acid solution and water are respectively placed in two storage tanks. The molar ratio of nitroguanidine to concentrated sulfuric acid in the nitroguanidine acid solution is 1:2, the temperature of the nitroguanidine acid solution is 20 °C, and the water temperature is 5 °C. Start the motor of the pump of the impinging stream - rotating packing bed, and control the feed flow rate with a valve. The feed flow rate of the nitroguanidine acid solution is 15 L / h, and the water flow rate is 90 L / h. The inner packing of the impinging stream - rotating packing bed is a dense wire mesh, and the outer packing is a relatively loose wire mesh. The liquid distributor is for the impinging distribution of two raw materials facing each other. The nozzle diameter of the nitroguanidine acid solution is 0.5 mm, and the nozzle diameter of water is 1 mm. Set the rotation speed of the rotating packing bed to 2500 rpm. The two raw materials are impinged and mixed through the nozzles. The solubility of nitroguanidine in dilute acid decreases, and rapid nucleation occurs. The reaction slurry quickly reaches the packing and flows from the inner edge of the rotor to the outer edge of the rotor along the pores of the packing under the action of centrifugal force. The crystals are continuously sheared and controlled to form, and finally are thrown out of the rotor. The liquid flowing in a parabola is mixed with atomized sprayed water with a flow rate of 30 L / h and a temperature of 0 °C and then falls to the bottom, and remains in a moving state under the action of the stirring paddle for the optimization of crystal form. Finally, the liquid enters the filtration system and nitroguanidine crystals are obtained after post - treatment. Analyze that the Feret average diameter of the nitroguanidine crystals is 2.5 μm, the particle size distribution is relatively uniform, and the optical microscope photo is as shown in Figure 4 shown in B in Example 2

[0044] The nitroguanidine acid solution and water are respectively placed in two storage tanks. The molar ratio of nitroguanidine to concentrated nitric acid in the nitroguanidine acid solution is 1:2.5, the temperature of the nitroguanidine acid solution is 30 °C, and the water temperature is 20 °C. Start the liquid pump of the impinging stream - rotating packed bed, and control the feed flow rate with a valve. The feed flow rate of the nitroguanidine acid solution is 15 L / h, and the flow rate of water is 60 L / h, with a volume ratio of 1:4. The inner packing of the impinging stream - rotating packed bed is a dense wire mesh, the outer packing is Pall rings, and the liquid distributor is for the two raw materials to impinge obliquely for distribution, with an impinging angle of 30°. The nozzle diameter of the nitroguanidine acid solution is 1 mm, and the nozzle diameter of water is 1 mm. Set the rotation speed of the rotating packed bed to 2000 rpm. The two raw materials impinge and mix through the nozzles. The solubility of nitroguanidine in dilute acid decreases, and rapid nucleation occurs. The reaction slurry quickly reaches the packing and flows from the inner edge of the rotor to the outer edge of the rotor along the pores of the packing under the action of centrifugal force. The crystals are continuously sheared and controlled to form, and finally are thrown out of the rotor. The liquid flowing in a parabola is mixed with atomized sprayed water with a flow rate of 40 L / h and a temperature of 5 °C and then falls to the bottom, and keeps moving under the action of the stirring paddle for the optimization of crystal form. Finally, the liquid enters the filtration system and nitroguanidine crystals are obtained after post - treatment. The measured Feret average particle size of the nitroguanidine crystals is 3.2 μm, and the particle size distribution is relatively uniform. The optical microscope photograph is as shown in Figure 4 shown in C in Example 3

[0045] The inner packing of the impinging stream - rotating packed bed is wire mesh packing, the outer packing is plastic Pall rings, and the rotation speed of the rotating packed bed is set to 500 rpm. The liquid distributor has three inlets. The first is the nitroguanidine acid solution with a nozzle diameter of 2 mm; the second is water with a nozzle diameter of 1.5 mm; the third is water with a nozzle diameter of 1.5 mm. The molar ratio of nitroguanidine to concentrated sulfuric acid in the nitroguanidine acid solution is 1:3, the temperature of the nitroguanidine acid solution is 20 °C, and the water temperatures of the two water inlets are both 0 °C. The feeding flow rate of the nitroguanidine acid solution is 15 L / h, the flow rate of the first water inlet is 50 L / h, and the flow rate of the second water inlet is 50 L / h. The flow rate of the atomized sprayed water is 60 L / h and the temperature is 5 °C. The measured Feret average particle size of the obtained nitroguanidine crystals is 4.5 μm. The optical microscope photograph is as shown in Figure 4 shown in D in

[0046] Figure 3 are the Feret average particle size distribution diagrams of nitroguanidine (commercially available product) produced by Ningxia Dongwu Agro - Chemical Co., Ltd. purchased from the market and the ultrafine nitroguanidine prepared in Examples 1 - 3 of the present invention; it can be seen from the figure that the Feret average particle size of the nitroguanidine from Ningxia Dongwu Agro - Chemical Co., Ltd. is 5.5 μm, while the Feret average particle size of the ultrafine nitroguanidine prepared by the present invention is concentrated in the range of 2.5 - 4.5 μm, and the particle size of the ultrafine nitroguanidine prepared by the present invention is much lower than that of the products sold in the market.

[0047] Figure 4 Optical microscope photos of ultrafine nitroguanidine; A is the optical microscope photo of ultrafine nitroguanidine produced by Ningxia Dongwu Agrochemical Co., Ltd., B is the optical microscope photo of ultrafine nitroguanidine prepared in Example 1, C is the optical microscope photo of ultrafine nitroguanidine prepared in Example 2, and D is the optical microscope photo of ultrafine nitroguanidine prepared in Example 3; It can be seen from the figure that at the same magnification, the particle size of the ultrafine nitroguanidine produced by Ningxia Dongwu Agrochemical Co., Ltd. is very large, showing a needle shape as a whole, and the particle size distribution is uneven. Relatively speaking, the length of the ultrafine nitroguanidine prepared by the present invention is greatly reduced, showing a short rod shape, and the particle size distribution is relatively uniform, and the prepared ultrafine nitroguanidine is finer.

Claims

1. A process for continuously preparing ultrafine nitroguanidine, characterized in that: Using nitroguanidine acid solution and water as raw materials, an impinging stream-rotating packed bed is used as the crystallization equipment. Through the processes of initial mixing and burst nucleation, shear-controlled shaping, crystal form optimization and regrowth, and post-treatment, crystal nucleation, crystal growth, crystal form control, and crystal regrowth are carried out at different positions of the rotating packed bed. At the same time, by controlling the movement path and mixing method of the feed liquid, the crystal morphology and particle size of nitroguanidine are optimized, and ultrafine nitroguanidine with a Feret average particle size of 2-6 μm is prepared, and continuous production can be achieved; The process for continuously preparing ultrafine nitroguanidine is as follows: (1) Feed liquid preparation: Add nitroguanidine acid solution and water to the storage devices respectively; (2) Initial mixing and burst nucleation: The nitroguanidine acid solution and water are respectively input into the impinging stream-rotating packed bed in a continuous feeding manner. The two raw materials obtain a high flow rate by pumps and are ejected through nozzles for impinging and mixing. The nitroguanidine acid solution and water come into rapid contact, the acid solution is rapidly diluted, the solubility of nitroguanidine rapidly decreases, burst nucleation occurs, a large number of nitroguanidine crystal nuclei are formed and grow rapidly; (3) Shear-controlled shaping: The reaction slurry after initial mixing is captured by the rotating packing at high speed. First, it enters the inner layer of dense packing, where the acid solution and water are mixed more evenly. While the nitroguanidine crystals are growing, they are violently sheared by the fine packing, and the longer needle-shaped crystals break; The slurry enters the looser outer packing, the shear becomes weaker, and the crystals grow evenly and gradually transition to rod-shaped; (4) Crystal form optimization and regrowth: The slurry composed of nitroguanidine crystals and acid water is thrown out of the rotating packing and falls in a parabola in the form of microelement liquid units. After directly contacting the atomized sprayed chilled water, it falls to the bottom of the equipment. It is mixed under the action of the stirring paddle and undergoes secondary growth of the crystals, improving the defect of the hollow of the rod-shaped nitroguanidine crystals, growing densely inside, and increasing the system yield; (5) Post-treatment: The dilute acid water containing nitroguanidine crystals enters the filtration equipment from the outlet at the bottom of the equipment to obtain ultrafine nitroguanidine crystals, and the filtrate enters the wastewater treatment system.

2. The process for continuously preparing ultrafine nitroguanidine according to claim 1, characterized in that: The nitroguanidine acid solution is a mixed solution of nitroguanidine and concentrated sulfuric acid or nitric acid, which is the product of the nitration process, and the molar ratio of nitroguanidine to concentrated sulfuric acid or nitric acid is 1:1.5 - 1:

3.

3. The process for continuously preparing ultrafine nitroguanidine according to claim 1, characterized in that: The volume ratio of the nitroguanidine acid solution to the water in step (1) is 1:3 - 1:10; the volume ratio of the nitroguanidine acid solution to the atomized sprayed water is 1:1 - 1:

5.

4. The process for continuously preparing ultrafine nitroguanidine according to claim 1, characterized in that: The temperature range of the nitroguanidine acid solution is 0 - 40 °C, the temperature of the impinging water is -5 - 20 °C, and the temperature of the atomized sprayed chilled water is -5 - 5 °C.

5. An apparatus for continuously preparing ultrafine nitroguanidine, characterized in that: It includes an impinging stream-rotating packed bed, a nitroguanidine acid solution storage tank, pumps, a freezer, a wastewater storage tank, a filter, a nitroguanidine storage tank, and a water storage tank; the nitroguanidine acid solution storage tank is connected to the nitroguanidine acid solution inlet of the impinging stream-rotating packed bed through a pump; the water storage tank is connected to the water inlet of the impinging stream-rotating packed bed through a pump; the water storage tank is connected to the atomized spraying port of the impinging stream-rotating packed bed through a pump and a freezer; the liquid outlet of the impinging stream-rotating packed bed is connected to the filter; the filter is respectively connected to the nitroguanidine storage tank and the wastewater storage tank; The packing of the impinging flow-rotating packed bed is designed in layers, the inner layer is a structured packing with dense packing and high shear frequency, and the outer layer is a structured packing with loose packing and low shear frequency or a random packing arranged according to certain rules.

6. The apparatus for continuously preparing ultrafine nitroguanidine according to claim 5, wherein: The impinging stream-rotating packed bed comprises a packing rotor, a motor, a shell, a liquid distributor, an atomizing spray port, a stirring paddle, and a liquid outlet; the packing rotor is divided into two parts, an inner packing and an outer packing; the two motors at the bottom respectively drive the stirring paddles connected thereto, and the motor above the rotating shaft is a motor for driving the packing to rotate; a liquid distributor is arranged at the bottom of the impinging stream-rotating packed bed, and the liquid distributor consists of a nitroguanidine liquid pipeline and 1 to 2 water pipelines, the nitroguanidine liquid pipeline and the water pipeline are arranged in parallel, and the outlet nozzles of the two pipelines are arranged relative to each other or at an angle of 90°, so as to control the two liquids in the pipeline to achieve 180° or 90° collision; the atomizing spray port comprises two atomizing spray ports; the stirring paddle comprises two symmetrically arranged stirring paddles; the impinging stream-rotating packed bed is a trapezoidal structure, and the liquid thrown out of the rotating packing falls in the form of micro-element in a parabolic curve, directly contacts with the atomized frozen water, and then falls to the bottom to converge, and is cooled and crystallized to optimize the crystal shape.

7. The device for continuously preparing ultrafine nitroguanidine according to claim 5, characterized in that: In the impinging flow-rotating packed bed, by changing the number of liquid inlet pipes of the liquid distributor, an impingement distribution of a nitroguanidine acid liquid and one or two water streams is achieved, the reaction heat is quickly removed by increasing the amount of water, and the 180° or 90° impingement of the two liquids is achieved by controlling the direction of the liquid nozzle of the liquid inlet pipe.

8. The device for continuously preparing ultrafine nitroguanidine according to claim 7, characterized in that: The impinging flow-rotating packed bed liquid distributor nozzle is a circular hole with different diameters, and the inner diameter of the nozzle can be 0.5mm-2.0mm.

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