Low-temperature micro-negative pressure flash evaporation preparation method of high-quality spherical superfine ammonium perchlorate

Abstract

The invention discloses a low-temperature micro-negative pressure flash evaporation preparation method of high-quality spherical superfine ammonium perchlorate, and belongs to the technical field of solid propellants. The invention aims to solve the problems of irregular morphology, low sphericity, hollow and porous particles, high sensitivity, high risk of a preparation process, low production efficiency and complex process of superfine AP prepared in the prior art. The method comprises the following steps: 1, adding ammonium perchlorate into an organic solvent; 2, adding sodium hyaluronate into water; 3, dropwise adding the sodium hyaluronate solution into the ammonium perchlorate solution; and 4, flash evaporation. The method is used for low-temperature micro-negative-pressure flash evaporation preparation of high-quality spherical superfine ammonium perchlorate.

Description

Technical Field

[0001] The invention belongs to the technical field of solid propellants. Background Art

[0002] As a commonly used oxidant in solid propellants, ammonium perchlorate has the advantages of high oxygen content and high density, and can change the particle size distribution to achieve changes in the burning rate of solid propellants, which is of great significance for the design and regulation of the burning rate of various solid propellants. The burning rate of the propellant increases with the increase in the proportion of small-particle AP. Therefore, the proportion of small-particle AP in high and ultra-high burning rate solid propellants is extremely high. However, due to factors such as the small particle size, irregular morphology, large specific surface area, and wide particle size distribution of AP, the viscosity of the solid propellant is high during drug formulation, and the process performance deteriorates, making it difficult to apply. In addition, ultrafine AP is a special energetic material. As the particle size decreases, it becomes more sensitive to stimuli such as heat, shear, friction, impact, and sparks, and is more prone to combustion and explosion, especially when ultrafine AP and catalysts are present at the same time.

[0003] The processing and preparation of ultrafine AP must ensure the safety of the process. The methods reported so far mainly include airflow pulverization, mechanical ball milling, spray drying, supercritical fluid method, etc. The basic principle of airflow pulverization is to accelerate the particles by jetting airflow and achieve crushing through mutual collision between particles; Liu Hongying, Deng Guodong and others from Nanjing University of Science and Technology prepared ultrafine AP by gas pulverization, but their scanning electron microscopy results showed that its overall morphology was irregular. Since ultrafine AP is sensitive to impact, the preparation of ultrafine AP by airflow pulverization is relatively dangerous (Deng Guodong, Liu Hongying. Research on the preparation of ultrafine ammonium perchlorate powder [J]. Explosive Materials, 2009, 38(01): 5-7). Mechanical ball milling is a method of preparing ultrafine powders by crushing large-sized materials in a grinding chamber under the action of a ball mill, which is subjected to the impact, shearing, grinding and pressure of the grinding balls. Song Jian used mechanical grinding to prepare submicron ultrafine AP, but the impact sensitivity and friction sensitivity of ultrafine AP increased by 18.7% and 20.0% respectively. The preparation of ultrafine AP by mechanical ball milling is also very dangerous, and its production cycle is long, and the production efficiency of preparing ultrafine powders is not high (Song Jian, Liu Jie, Yang Qing, et al. Preparation and performance study of submicron ammonium perchlorate [J]. Explosive Materials, 2015, 44(01): 7-11). The basic principle of the spray drying method is to dissolve AP in an organic solvent, and to achieve rapid drying of the droplets by controlling the drying temperature to achieve sphericalization and micronization of the particles. Although it has a high preparation efficiency, the ultrafine AP prepared by spray drying is a hollow, porous AP with a low density. Makoto Kohga of Japan has studied in detail the preparation of porous AP by spray drying and the application of porous AP in solid propellants. The results of the study show that the solid propellant prepared by this method has a low density (Kohga M, Hagihara Y. Burning Behavior of Composite Propellant Containing Fine Porous Ammonium Perchlorate [J]. Propellants, Explosives, Pyrotechnics, 1998, 23 (4): 182-187; Kohga M. Effect of Voids inside AP Particles on Burning Rate of AP / HTPB Composite Propellant [J]. Propellants, Explosives, Pyrotechnics, 2008, 33 (4): 249-254). Therefore, spray drying is not suitable.The fluid has a strong solubility for certain energetic materials, and the solubility increases significantly with increasing density. By utilizing this property, the supercritical fluid solution can be expanded rapidly, and the energetic materials in the solution can be rapidly precipitated as extremely fine particles to obtain ultrafine powders. This method has a high cost for producing ultrafine AP and also requires high quality of operators, and is mainly prepared in small batches in the laboratory. Summary of the invention

[0004] The present invention aims to solve the problems that ultrafine AP prepared by the prior art has irregular morphology, low sphericity, hollow particles and pores, high sensitivity, high risk of preparation process, low production efficiency and complex process, and further provides a low-temperature micro-negative pressure flash evaporation method for preparing high-quality spherical ultrafine ammonium perchlorate.

[0005] A method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature micro-negative pressure flash evaporation is carried out according to the following steps:

[0006] 1. adding ammonium perchlorate to an organic solvent, and then stirring and ultrasonicating in sequence to obtain an ammonium perchlorate solution;

[0007] 2. Adding sodium hyaluronate into water, and then stirring and ultrasonicating in sequence to obtain a sodium hyaluronate solution;

[0008] 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution;

[0009] The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:(0.00-0.05);

[0010] 4. Under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate.

[0011] The beneficial effects of the present invention are:

[0012] The low-temperature micro-negative pressure flash evaporation preparation method provided by the present invention is to form a mixed solution by adding a sodium hyaluronate solution dropwise to an ammonium perchlorate solution, wherein sodium hyaluronate is in a saturated state due to being unable to be dissolved in an organic solvent (boiling point lower than water, miscible with water, and dissolving ammonium perchlorate), and ammonium perchlorate can be fully dissolved in water and organic solvents. Therefore, the preferential precipitation of sodium hyaluronate can be achieved during the drying process to ensure the spherical morphology of AP, and the strong water absorption and moisture retention of sodium hyaluronate can ensure the further contraction of AP droplets during the drying process, and the appropriate temperature gradient ensures that the particles are dried to form smaller, denser, free of voids and hollow particles. In addition, sodium hyaluronate is functionalized on the surface of spherical ultrafine AP, containing a large amount of hydroxyl groups and amide groups, which reduces its viscosity when the propellant slurry is mixed. Further, due to the molecular weight of sodium hyaluronate of about 200,000, it has the effect of long-chain softness and lubrication and buffering, and the impact sensitivity and friction sensitivity of the spherical ultrafine AP containing sodium hyaluronate are significantly reduced. The low-temperature micro-negative pressure flash evaporation method has the advantages of low cost, short time, scalable production and safety and reliability. The spherical ultrafine AP particles prepared by this method have a size between 500nm and 5μm, and have a spherical morphology, a smooth surface without voids, no hollow inside, and a high particle density. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 1;

[0014] Figure 2 This is the XRD pattern of the high-quality spherical ultrafine ammonium perchlorate prepared in Example 1;

[0015] Figure 3 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 2;

[0016] Figure 4 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 3;

[0017] Figure 5 This is a SEM image of the high-quality spherical ultrafine ammonium perchlorate prepared in Example 4;

[0018] Figure 6 This is a schematic diagram of the structure of the low-temperature slightly negative pressure flash evaporation equipment of the present invention, (a) blower, (b) heat exchanger, (c) drying tower, (d) atomizer, (e) temperature gradient control device, (f) collection barrel, (g) induced draft fan, (h) cyclone separator, and (i) collection barrel. DETAILED DESCRIPTION

[0019] Specific implementation method 1: This implementation method is a low-temperature micro-negative pressure flash evaporation method for preparing high-quality spherical ultrafine ammonium perchlorate, which is carried out according to the following steps:

[0020] 1. adding ammonium perchlorate to an organic solvent, and then stirring and ultrasonicating in sequence to obtain an ammonium perchlorate solution;

[0021] 2. Adding sodium hyaluronate into water, and then stirring and ultrasonicating in sequence to obtain a sodium hyaluronate solution;

[0022] 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution;

[0023] The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:(0.00-0.05);

[0024] 4. Under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate.

[0025] This embodiment proposes a high-quality spherical ultrafine AP and a low-temperature micro-negative pressure flash preparation method thereof. The spherical ultrafine AP has lower sensitivity, higher sphericity, no hollows and pores, and can reduce the viscosity of the propellant slurry under the same formula. The spherical ultrafine AP has the above advantages due to the innovative introduction of high molecular weight polymer sodium hyaluronate in the preparation process. Its high water absorption makes the AP droplets fully shrink and the particle size decrease, and gives the AP a spherical structure during the drying process. In addition, the molecular weight of sodium hyaluronate is about 200,000, which has the effects of long-chain softness and lubrication and buffering. The impact sensitivity and friction sensitivity of the spherical ultrafine AP containing sodium hyaluronate are significantly reduced. Compared with the irregular ultrafine AP prepared by traditional gas pulverization, the spherical structure of the high-quality ultrafine AP changes its movement mode in the propellant slurry from sliding to rolling, so the viscosity of the slurry is lower at high shear rates. The active hydroxyl and amide groups in the sodium hyaluronate molecule can functionalize the surface of the spherical ultrafine AP, so the ultrafine AP has better wettability in the slurry. The low-temperature and safe micro-negative pressure flash evaporation technology of the present invention can safely and massively prepare high-quality ultrafine AP by designing a gradient drying temperature (not exceeding 80°C) and a micro-negative pressure system, which can meet the application demand of existing high and ultra-high burning rate solid propellants and is of great significance to the development of solid propellants.

[0026] The beneficial effects of this embodiment are:

[0027] The low-temperature micro-negative pressure flash evaporation preparation method provided in this embodiment is formed by adding sodium hyaluronate solution dropwise to ammonium perchlorate solution to form a mixed solution, at which sodium hyaluronate is in a saturated state due to being insoluble in an organic solvent (boiling point lower than water, miscible with water, and dissolving ammonium perchlorate), and ammonium perchlorate can be fully dissolved in water and organic solvents. Therefore, the preferential precipitation of sodium hyaluronate can be achieved during the drying process to ensure the spherical morphology of AP, and the strong water absorption and moisture retention of sodium hyaluronate can ensure the further contraction of AP droplets during the drying process, and the appropriate temperature gradient ensures that the particles are dried to form smaller, denser, void-free and hollow particles. In addition, sodium hyaluronate is functionalized on the surface of spherical ultrafine AP, containing a large number of hydroxyl groups and amide groups, which reduces its viscosity when the propellant slurry is mixed. Further, due to the molecular weight of sodium hyaluronate of about 200,000, it has the effect of long-chain softness and lubrication and buffering, and the impact sensitivity and friction sensitivity of the spherical ultrafine AP containing sodium hyaluronate are significantly reduced. The low-temperature micro-negative pressure flash evaporation method has the advantages of low cost, short time, scalable production and safety and reliability. The spherical ultrafine AP particles prepared by this method have a size between 500nm and 5μm, and have a spherical morphology, a smooth surface without voids, no hollow inside, and a high particle density.

[0028] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the organic solvent described in step 1 has a lower boiling point than water, is miscible with water, and dissolves ammonium perchlorate. Other aspects are the same as those of specific embodiment 1.

[0029] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the organic solvent in step 1 is one or a mixture of methanol, ethanol and tetrahydrofuran. Other aspects are the same as specific implementation method 1 or 2.

[0030] Specific embodiment 4: This embodiment differs from one of specific embodiments 1 to 3 in that the mass ratio of ammonium perchlorate to the volume ratio of the organic solvent in step 1 is 1 g: (10-1500) mL. The rest is the same as specific embodiment 3.

[0031] Specific embodiment 5: This embodiment differs from Specific embodiments 1 to 4 in that the mass ratio of sodium hyaluronate to water in step 2 is 1 g: (2000-50000) mL. The rest is the same as Specific embodiments 1 to 4.

[0032] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that the stirring and ultrasonication described in step 1 and step 2 are specifically carried out according to the following steps: stirring for 5 min to 15 min at a rotation speed of 10 rpm to 1000 rpm, and then ultrasonication for 5 min to 15 min at an ultrasonic power of 10 Hz to 100 Hz. The rest is the same as specific embodiments 1 to 5.

[0033] Specific implementation method seven, combined with Figure 5 Specific description: This embodiment is different from one of the specific embodiments 1 to 6 in that: the low-temperature micro-negative pressure flash evaporation equipment described in step 4 is obtained by modifying the spray drying equipment through an induced draft fan and a temperature gradient control device, specifically, an induced draft fan is set at the outlet end of the cyclone separation device of the spray drying equipment, and the temperature gradient control device is to weld n electric heating elements to the drying tower wall of the spray drying equipment, and use software to control the heating temperature at different points to achieve gradient temperature control, where n = 3 to 10. Others are the same as the specific embodiments 1 to 6.

[0034] The low-temperature micro-negative pressure flash evaporation equipment of this specific embodiment is mainly modified on the traditional spray drying equipment, and the main modification is to introduce the induced draft fan and the temperature gradient control device, and the vacuum degree of the drying system is controlled by changing the induced draft fan and the blower in the original traditional spray drying equipment. The initiator is installed after the cyclone separation device to suck out the hot carrier gas. The temperature gradient control device is welded on the wall of the drying tower through an electric heating element, and the heating temperature at different points is controlled by software to achieve gradient temperature control.

[0035] Specific embodiment 8: This embodiment differs from any one of specific embodiments 1 to 7 in that the induced air volume of the induced draft fan in step 4 is greater than the blowing volume of the blower in the spray drying equipment; the induced air volume of the induced draft fan is 20m 3 / min~201m 3 / min, the air volume of the blower is 1m 3 / min~200m 3 / min, the absolute pressure is controlled by the air volume, and a slight negative pressure of 101.325 kPa to 0.01 kPa is formed, and the slight negative pressure is the difference between the atmospheric pressure and the absolute pressure. The rest is the same as the specific embodiments 1 to 7.

[0036] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that the temperature gradient described in step 4 is specifically controlled by the following method:

[0037] ① Calculate the initial temperature T at the feed position of the drying tower in the spray drying equipment according to formula (1);

[0038]

[0039] Wherein: B is the total mass percentage of sodium hyaluronate and ammonium perchlorate in the mixed solution of step 3, in %; T is the initial temperature of the gradient, in K; P is the absolute pressure, in kPa;

[0040] ② Control the electric heating elements in the drying tower so that the feeding position of the drying tower and the n electric heating elements form a temperature gradient point that gradually decreases from the initial temperature T, wherein the interval length of adjacent temperature gradient points is 1 / n meter to 3 / n meter, and the temperature difference of the interval of adjacent temperature gradient points is (T-20°C) / n. The rest is the same as the specific embodiments 1 to 8.

[0041] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the delivery speed of the mixed solution in step 4 is 100 mL / min to 5000 mL / min. The rest is the same as specific embodiments 1 to 9.

[0042] The following examples are used to verify the beneficial effects of the present invention:

[0043] Embodiment 1:

[0044] A method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature micro-negative pressure flash evaporation is carried out according to the following steps:

[0045] 1. adding ammonium perchlorate to an organic solvent, stirring for 15 min at a rotation speed of 1000 rpm, and then ultrasonicating for 15 min at an ultrasonic power of 100 Hz to obtain an ammonium perchlorate solution;

[0046] The mass ratio of the ammonium perchlorate to the volume ratio of the organic solvent is 1 g:1202.5 mL; the organic solvent is methanol;

[0047] 2. Add sodium hyaluronate to water, then stir for 5 minutes at a rotation speed of 10 rpm, and then ultrasonicate for 5 minutes at an ultrasonic power of 10 Hz to obtain a sodium hyaluronate solution;

[0048] The mass ratio of the sodium hyaluronate to the volume of water is 1g:2000mL;

[0049] 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution;

[0050] The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:0.05;

[0051] Fourth, under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device through a peristaltic pump for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate;

[0052] The low-temperature micro-negative pressure flash evaporation equipment described in step 4 is obtained by modifying the spray drying equipment through an induced draft fan and a temperature gradient control device. Specifically, an induced draft fan is set at the outlet end of the cyclone separation device of the spray drying equipment. The temperature gradient control device is to weld n electric heating elements to the drying tower wall of the spray drying equipment, and use software to control the heating temperature at different points to achieve gradient temperature control, wherein n=3;

[0053] The induced air volume of the induced draft fan in step 4 is greater than the blowing volume of the blower in the spray drying equipment; the induced air volume of the induced draft fan is 20m 3 / min, the air volume of the blower is 1m 3 / min, the absolute pressure is controlled by air volume to be 87.3kPa, then the slight negative pressure is the difference between atmospheric pressure and absolute pressure = 101.325kPa-87.300kPa = 14.025kPa;

[0054] The temperature gradient described in step 4 is specifically controlled by the following method:

[0055] ① According to formula (1), the initial temperature T of the feed position of the drying tower in the spray drying equipment is calculated to be 80°C, at which time B is 0.100%;

[0056]

[0057] Wherein: B is the total mass percentage of sodium hyaluronate and ammonium perchlorate in the mixed solution of step 3, in %; T is the initial temperature of the gradient, in K; P is the absolute pressure, in kPa;

[0058] ② Control the electric heating elements in the drying tower so that the feeding position of the drying tower and the three electric heating elements form temperature gradient points that gradually decrease from the initial temperature T, wherein the interval length of adjacent temperature gradient points is 0.33m, and the interval temperature difference of adjacent temperature gradient points is (T-20°C) / n=20°C, specifically 80°C (feeding position), 60°C (first electric heating element), 40°C (second electric heating element), 20°C (third electric heating element);

[0059] The delivery rate of the mixed solution in step 4 is 100 mL / min.

[0060] Embodiment 2:

[0061] A method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature micro-negative pressure flash evaporation is carried out according to the following steps:

[0062] 1. adding ammonium perchlorate to an organic solvent, stirring for 5 min at a rotation speed of 10 rpm, and then ultrasonicating for 5 min at an ultrasonic power of 10 Hz to obtain an ammonium perchlorate solution;

[0063] The mass ratio of the ammonium perchlorate to the volume ratio of the organic solvent is 1 g:30.56 mL; the organic solvent is methanol;

[0064] 2. Add sodium hyaluronate to water, then stir at a rotation speed of 1000 rpm for 15 minutes, and then ultrasonicate at an ultrasonic power of 100 Hz for 15 minutes to obtain a sodium hyaluronate solution;

[0065] The mass ratio of the sodium hyaluronate to the volume of water is 1 g:14000 mL;

[0066] 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution;

[0067] The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:0.05;

[0068] Fourth, under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device through a peristaltic pump for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate;

[0069] The low-temperature micro-negative pressure flash evaporation equipment described in step 4 is obtained by modifying the spray drying equipment through an induced draft fan and a temperature gradient control device. Specifically, an induced draft fan is set at the outlet end of the cyclone separation device of the spray drying equipment. The temperature gradient control device is to weld n electric heating elements to the drying tower wall of the spray drying equipment, and use software to control the heating temperature at different points to achieve gradient temperature control, wherein n=10;

[0070] The induced air volume of the induced draft fan in step 4 is greater than the blowing volume of the blower in the spray drying equipment; the induced air volume of the induced draft fan is 200m 3 / min, the air volume of the blower is 110m 3 / min, the absolute pressure is controlled by air volume to be 44.300 kPa, then the slight negative pressure is the difference between atmospheric pressure and absolute pressure = 101.325 kPa-44.300 kPa = 57.025 kPa;

[0071] The temperature gradient described in step 4 is specifically controlled by the following method:

[0072] ① According to formula (1), the initial temperature T of the feed position of the drying tower in the spray drying equipment is calculated to be 60°C, at which time B is 0.145%;

[0073]

[0074] Wherein: B is the total mass percentage of sodium hyaluronate and ammonium perchlorate in the mixed solution of step 3, in %; T is the initial temperature of the gradient, in K; P is the absolute pressure, in kPa;

[0075] ② Control the electric heating elements in the drying tower so that the feeding position of the drying tower and the 10 electric heating elements form temperature gradient points that gradually decrease from the initial temperature T, wherein the interval length of adjacent temperature gradient points is 0.3m, and the interval temperature difference of adjacent temperature gradient points is (T-20°C) / n=4°C, specifically 60°C (feeding position), 56°C (first electric heating element), 52°C (second electric heating element), 48°C (third electric heating element), 44°C (fourth electric heating element), 40°C (fifth electric heating element), 36°C (sixth electric heating element), 32°C (seventh electric heating element), 28°C (eighth electric heating element), 24°C (ninth electric heating element), 20°C (tenth electric heating element);

[0076] The delivery rate of the mixed solution in step 4 is 5000 mL / min.

[0077] Embodiment three:

[0078] A method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature micro-negative pressure flash evaporation is carried out according to the following steps:

[0079] 1. adding ammonium perchlorate to an organic solvent, stirring for 7.5 min at a rotation speed of 500 rpm, and then ultrasonicating for 7.5 min at an ultrasonic power of 50 Hz to obtain an ammonium perchlorate solution;

[0080] The mass ratio of the ammonium perchlorate to the volume ratio of the organic solvent is 1 g:133.0 mL; the organic solvent is methanol;

[0081] 2. Add sodium hyaluronate to water, then stir at a rotation speed of 500 rpm for 7.5 minutes, and then ultrasonicate at an ultrasonic power of 50 Hz for 7.5 minutes to obtain a sodium hyaluronate solution;

[0082] The mass ratio of the sodium hyaluronate to the volume of water is 1g:2000mL;

[0083] 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution;

[0084] The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:0.05;

[0085] Fourth, under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device through a peristaltic pump for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate;

[0086] The low-temperature micro-negative pressure flash evaporation equipment described in step 4 is obtained by modifying the spray drying equipment through an induced draft fan and a temperature gradient control device. Specifically, an induced draft fan is set at the outlet end of the cyclone separation device of the spray drying equipment. The temperature gradient control device is to weld n electric heating elements to the drying tower wall of the spray drying equipment, and use software to control the heating temperature at different points to achieve gradient temperature control, where n=5;

[0087] The induced air volume of the induced draft fan in step 4 is greater than the blowing volume of the blower in the spray drying equipment; the induced air volume of the induced draft fan is 100m 3 / min, the air volume of the blower is 60m 3 / min, the absolute pressure is controlled by air volume to be 63.300 kPa, then the slight negative pressure is the difference between atmospheric pressure and absolute pressure = 101.325 kPa-63.300 kPa = 38.025 kPa;

[0088] The temperature gradient described in step 4 is specifically controlled by the following method:

[0089] ① According to formula (1), the initial temperature T of the feed position of the drying tower in the spray drying equipment is calculated to be 70°C, at which time B is 0.512%;

[0090]

[0091] Wherein: B is the total mass percentage of sodium hyaluronate and ammonium perchlorate in the mixed solution of step 3, in %; T is the initial temperature of the gradient, in K; P is the absolute pressure, in kPa;

[0092] ② Control the electric heating elements in the drying tower so that the feeding position of the drying tower and the five electric heating elements form temperature gradient points that gradually decrease from the initial temperature T, wherein the interval length of adjacent temperature gradient points is 0.25m, and the interval temperature difference of adjacent temperature gradient points is (T-20°C) / n=10°C, specifically 70°C (feeding position), 60°C (first electric heating element), 50°C (second electric heating element), 40°C (third electric heating element), 30°C (fourth electric heating element), 20°C (fifth electric heating element);

[0093] The delivery rate of the mixed solution in step 4 is 2000 mL / min.

[0094] Example 4: This example is different from Example 1 in that step 2 is eliminated and the addition of sodium hyaluronate solution is omitted in step 3. The rest is the same as Example 1.

[0095] Comparative Experiment 1: This comparative experiment differs from Example 1 in that in step 4, an unmodified conventional spray drying device is used, and the process is carried out at normal pressure and a temperature of 80° C. at the feed position of the drying tower to obtain ultrafine AP. The rest is the same as Example 1.

[0096] Comparative Experiment 2: This comparative experiment is different from Example 1 in that the temperature gradient control in step 4 is eliminated, and the temperature at the feed position of the drying tower is 80° C. The rest is the same as Example 1.

[0097] Comparative Experiment 3: This comparative experiment is different from Example 1 in that in step 4, the absolute pressure is controlled to be 101.325 kPa by air volume, and the slight negative pressure is the difference between the atmospheric pressure and the absolute pressure = 101.325 kPa - 101.325 kPa = 0 kPa. The rest is the same as Example 1.

[0098] The ammonium perchlorate prepared in Examples 1 to 4 and Comparative Experiments 1 to 3 was subjected to impact sensitivity, friction sensitivity, viscosity test during slurry mixing and density test. The impact and friction sensitivity test standard is GJB 772A-1997. The ammonium perchlorate prepared in Examples 1 to 4 and Comparative Experiments 1 to 3 was mixed with HTPB adhesive (Type IV) at a mass ratio of 68:11 to obtain a slurry. The viscosity of the slurry during mixing was measured by the shear rate scanning method in the rotation mode of the rotational rheometer. The steady-state rheological properties of the samples were tested at a temperature of 60°C. The test used a PP-25 rotor, a spacing of 1 mm, and a shear rate of 1 s -1 The results are shown in Table 1.

[0099] Table 1

[0100] Impact, J friction,% <![CDATA[1s -1 Viscosity, Pa·s]]> <![CDATA[Density, g·cm -3 > Embodiment 1 22.0J 42％ 65.25 1.92 Embodiment 2 20.9J 36％ 64.95 1.91 Embodiment 3 25.1J 40％ 63.53 1.92 Embodiment 4 15.6J 27％ 85.6 1.75 Comparative Experiment 1 16.2J 30％ 72.5 1.69 Comparative Experiment 2 19.5J 35％ 73.2 1.78 Comparative Experiment 3 18.3J 39％ 74.3 1.80

[0101] Figure 1 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 1; Figure 3 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 2; Figure 4 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 3; Figure 5 This is a SEM image of high-quality spherical ultrafine ammonium perchlorate prepared in Example 4; it can be seen from the image that the sample has a smooth surface, good sphericity, and good dispersibility. In addition, the high-quality spherical ultrafine ammonium perchlorate has no pores, hollows, or defects, and the particle size is in the range of 1 μm to 5 μm.

[0102] Figure 2 This is the XRD diagram of the high-quality spherical ultrafine ammonium perchlorate prepared in Example 1; it can be seen from the figure that the sample did not decompose during the preparation process and maintained the phase structure of the raw material ammonium perchlorate.

Claims

1. A method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation, characterized in that It is carried out in the following steps:

1. adding ammonium perchlorate to an organic solvent, and then stirring and ultrasonicating in sequence to obtain an ammonium perchlorate solution; 2. Adding sodium hyaluronate into water, and then stirring and ultrasonicating in sequence to obtain a sodium hyaluronate solution; 3. adding the sodium hyaluronate solution dropwise into the ammonium perchlorate solution to obtain a mixed solution; The mass ratio of sodium hyaluronate in the sodium hyaluronate solution to ammonium perchlorate in the ammonium perchlorate solution is 1:(0.00-0.05); 4. Under the conditions of slight negative pressure and temperature gradient, the mixed solution is transported to a low-temperature slight negative pressure flash evaporation device for preparation and collection to obtain high-quality spherical ultrafine ammonium perchlorate.

2. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The organic solvent described in step 1 has a boiling point lower than that of water, is miscible with water, and dissolves ammonium perchlorate.

3. The low-temperature, slightly negative pressure flash evaporation method for preparing high-quality spherical ultrafine ammonium perchlorate according to claim 2, characterized in that The organic solvent described in step 1 is one or a mixture of methanol, ethanol and tetrahydrofuran.

4. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The mass ratio of the ammonium perchlorate described in step 1 to the volume ratio of the organic solvent is 1 g: (10-1500) mL.

5. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The mass ratio of the sodium hyaluronate to the volume of water described in step 2 is 1 g: (2000-50000) mL.

6. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The stirring and ultrasonication in step 1 and step 2 are specifically carried out according to the following steps: stirring for 5 min to 15 min at a rotation speed of 10 rpm to 1000 rpm, and then ultrasonication for 5 min to 15 min at an ultrasonic power of 10 Hz to 100 Hz.

7. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The low-temperature micro-negative pressure flash evaporation equipment described in step 4 is obtained by modifying the spray drying equipment through an induced draft fan and a temperature gradient control device. Specifically, an induced draft fan is set at the outlet end of the cyclone separation device of the spray drying equipment. The temperature gradient control device is to weld n electric heating elements to the drying tower wall of the spray drying equipment, and use software to control the heating temperature at different points to achieve gradient temperature control, where n=3~10.

8. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 7, characterized in that The induced air volume of the induced draft fan in step 4 is greater than the blowing volume of the blower in the spray drying equipment; the induced air volume of the induced draft fan is 20m 3 / min~201m 3 / min, the air volume of the blower is 1m 3 / min~200m 3 / min, the absolute pressure is controlled by the air volume, and a slight negative pressure of 101.325kPa ~ 0.01kPa is formed. The slight negative pressure is the difference between atmospheric pressure and absolute pressure.

9. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 7, characterized in that The temperature gradient described in step 4 is specifically controlled by the following method: ① Calculate the initial temperature T at the feed position of the drying tower in the spray drying equipment according to formula (1); Wherein: B is the total mass percentage of sodium hyaluronate and ammonium perchlorate in the mixed solution of step 3, in %; T is the initial temperature of the gradient, in K; P is the absolute pressure, in kPa; ② Control the electric heating elements in the drying tower so that the feeding position of the drying tower and the n electric heating elements form a temperature gradient point that gradually decreases from the initial temperature T, wherein the interval length of adjacent temperature gradient points is 1 / n meter to 3 / n meter, and the interval temperature difference of adjacent temperature gradient points is (T-20℃) / n.

10. The method for preparing high-quality spherical ultrafine ammonium perchlorate by low-temperature and slightly negative pressure flash evaporation according to claim 1, characterized in that The delivery speed of the mixed solution in step 4 is 100 mL / min to 5000 mL / min.

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