Process for the preparation of nanosized copper nitrate amidine urea salt complexes and use of oxidizer n2o4 waste from liquid rocket propellants

Abstract

This invention relates to a method for treating waste oxidizer from liquid rocket propellants and a method for synthesizing energetic materials, specifically a method for preparing nano-sized amidine-urea copper salt complexes and the use of N2O4 waste oxidizer from liquid rocket propellants. To address the problems of low treatment efficiency and high risk of secondary pollution in existing methods for treating nitrogen tetroxide waste from rocket propellant oxidizers during ground testing of liquid rocket engines, and the problems of large particle size, low burning rate, and low yield in the synthesis methods of amidine-urea copper salt complexes, which cannot meet the technical requirements of high-speed response gas production performance in existing automotive airbags, this invention provides a method for preparing nano-sized amidine-urea copper salt complexes. This method uses nitrogen tetroxide as a raw material to generate copper nitrate, which is then reacted with dicyandiamide solution under the action of a complexing agent to ultimately obtain a high-performance nano-sized amidine-urea copper salt complex.

Description

Technical Field

[0001] This invention relates to a method for treating waste oxidizer from liquid rocket propellants and a method for synthesizing energetic materials, specifically a method for preparing nano-sized amidine urea copper salt complex and the use of waste N2O4 oxidizer from liquid rocket propellants. Background Technology

[0002] Nitrogen tetroxide (N2O4), used as an oxidizer in liquid rocket propellants, leaves residues in fuel tanks and pipelines after ground testing. This residual N2O4 is generally not recyclable and is disposed of as waste, a persistent challenge in the aerospace field. Existing N2O4 recovery processes, such as the absorption method disclosed in Chinese patent CN207950720U, typically suffer from low processing efficiency (generally only 60%–70%) and high risk of secondary pollution. Furthermore, it meets the definition of HW49 hazardous waste in the Hazardous Waste List, and direct discharge would cause air pollution and soil acidification. On the other hand, copper nitrate nitrate complexes, as energetic materials, are commonly used as fillers in automotive airbags. Existing synthesis methods (such as Chinese patent CN109836358A) mostly involve direct reactions of copper nitrate and dicyandiamide as raw materials, resulting in yields below 90% and product particle sizes mostly exceeding 10 μm. This limits the burning rate to only 15-20 mm / s (10 MPa), which is insufficient to meet the high-speed gas production requirements of current automotive airbags. Therefore, developing an integrated process that can efficiently recover nitrogen tetroxide and prepare high-performance copper nitrate nitrate complexes is of great significance. Summary of the Invention

[0003] The purpose of this invention is to address the technical problems of existing methods for treating nitrogen tetroxide waste from rocket propellant oxidizers in ground tests of liquid rocket engines, which suffer from low treatment efficiency and high risk of secondary pollution; and existing methods for synthesizing copper nitrate urea salt complexes, which suffer from low yield, large product particle size, and low burning rate, failing to meet the high-speed response gas production performance requirements of automotive airbags. This invention provides a method for preparing nanoscale copper nitrate urea salt complexes and the application of N2O4 waste from liquid rocket propellant oxidizers, applicable to the recycling of nitrogen tetroxide waste from rocket engine fuels, and the preparation of energetic materials—copper nitrate urea salt complexes.

[0004] The concept of this invention is to use nitrogen tetroxide, the oxidant waste of liquid rocket propellants, as a raw material for the synthesis of copper nitrate copper salt complex, thereby solving the problem of oxidant waste treatment of liquid rocket propellants. At the same time, the preparation method of copper nitrate copper salt complex is improved to achieve the preparation of nanoscale copper nitrate copper salt complex.

[0005] To achieve the above objectives and complete the above inventive concept, the technical solution provided by this invention is as follows:

[0006] A method for preparing nanoscale copper salt complexes of amidine nitrate is characterized by the following steps:

[0007] S1, N2O4 with a purity ≥98% is passed into water, mixed evenly and reacted. During the mixing process, the temperature is controlled at 0±1℃ to obtain a nitrous acid solution.

[0008] The mass ratio of N2O4 to water is 1:0.1~0.2;

[0009] The N2O4 with a purity of ≥98% is the N2O4 waste oxidizer of liquid rocket propellant used in ground tests of liquid rocket engines.

[0010] S2, oxygen is introduced into the nitrous acid solution from step S1, and the reaction is stirred to obtain a nitric acid solution;

[0011] S3, add copper sheets to the nitric acid solution obtained in step S2 to react, filter to remove unreacted copper sheets, and obtain a filtrate containing copper nitrate;

[0012] S4, add the dicyandiamide solution dropwise to the filtrate containing copper nitrate obtained in step S3, wherein the mass ratio of dicyandiamide to N2O4 in the dicyandiamide solution is 0.65~0.8:1;

[0013] S5, after the addition is complete, adjust the pH to 7.0±0.2, add the complexing agent to carry out the reaction, the complexing agent is sodium citrate or sodium ascorbate;

[0014] S6. After the reaction is complete, the solid is cooled, filtered and collected, and finally dried to obtain nano-sized copper nitrate nitridine complex.

[0015] Furthermore, in step S1, N2O4 is introduced into the water at a rate of 5~10 mL / min;

[0016] In step S2, the amount of oxygen introduced is 0.2 to 0.3 times the mass of N2O4, and the reaction time is 12 to 13 hours.

[0017] Furthermore, in step S3, the mass ratio of copper sheet to N2O4 is 0.4~0.5:1, the reaction time is 23~25h, and the reaction temperature is 5℃~15℃;

[0018] In step S4, the mass concentration of the dicyandiamide solution is 35%~45%, and the dicyandiamide solution is added dropwise to the filtrate of step S3 at a rate of 1~2 mL / min, with a dropping temperature of 60℃~70℃.

[0019] Further, in step S5, the pH is adjusted with a sodium hydroxide solution with a concentration of 0.45~0.6mol / L, the amount of complexing agent is 2~3 times the mass of dicyandiamide in the dicyandiamide solution, the reaction temperature is 70℃~95℃, and the reaction time is 2~5h.

[0020] Furthermore, in step S6, the temperature is cooled to below 40°C. The drying is vacuum drying with a vacuum degree of 0.08~0.1MPa, a drying temperature of 78~85°C, and a drying time of 8~9h.

[0021] Further, in step S4, the dicyandiamide solution is prepared in the following manner:

[0022] Dicyandiamide was dissolved in deionized water at 60-70°C, and the mass concentration of the dicyandiamide solution was 40%-45%.

[0023] Furthermore, in step S1, the N2O4 introduction rate is 8 mL / min, and the stirring rate during mixing is 250 r / min;

[0024] In step S2, the amount of oxygen introduced is 0.2 times the mass of N2O4, and the reaction time is 12 hours.

[0025] In step S3, the mass ratio of copper sheet to N2O4 is 0.43:1, the reaction time is 24 h, and the reaction temperature is 15 °C.

[0026] In step S4, the mass concentration of the dicyandiamide solution is 43.6%, the dropping rate of the dicyandiamide solution is 1.5 mL / min, the dropping temperature is 68 °C, and the mass ratio of dicyandiamide to N2O4 is 0.71:1.

[0027] Furthermore, in step S5, the amount of the complexing agent is 2.5 times the mass of dicyandiamide, the reaction temperature is 80°C, and the reaction time is 5 hours.

[0028] In step S6, the vacuum degree is 0.09 MPa, the drying temperature is 80℃, and the drying time is 8 hours.

[0029] Meanwhile, the present invention also provides a use for N2O4 waste oxidizer of liquid rocket propellant, which is special in that it is used to prepare nano-sized copper salt complex of amidine nitrate.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] 1. This invention utilizes nitrogen tetroxide, an oxidant waste product of liquid rocket propellants, as a raw material to prepare nano-sized copper nitrate urea salt complexes. This solves the current problem of recycling nitrogen tetroxide in rocket propellants. Furthermore, the complexation process enables the product to be nano-sized during synthesis, significantly improving the application performance of the copper nitrate urea salt complex product.

[0032] 2. In this invention, a complexing agent and Cu are used. 2+ Weak complexation, the generation of numerous micro-nuclei, and restriction of grain growth, combined with precise process control, enabled the preparation of nano-sized amidocyanate copper nitrate. The nano-sized amidocyanate copper nitrate complex prepared by this invention has a particle size D50 of 45-52 nm, D90 ≤ 105 nm, a burning rate ≥ 30 mm / s (10 MPa), an impact sensitivity ≥ 40 J, a friction sensitivity ≥ 360 N, and a thermal decomposition temperature ≥ 200 °C. The smaller particle size of the nano-sized product (D50 ≤ 60 nm) significantly increases the specific surface area, increasing the contact area of ​​the combustion reaction by 3-5 times, thereby improving the burning rate and gas production efficiency, and optimizing its compatibility with other additives in the gas production formulation. Furthermore, the surface effect of the nanoparticles enhances the stability of the product and reduces its sensitivity, thus improving the product quality of the amidocyanate copper nitrate complex.

[0033] 3. This invention can harmlessly recycle and utilize highly toxic and polluting dinitrogen tetroxide. Furthermore, by nano-sizing the copper salt complex of amidine nitrate, the combustion and explosion effects of the product are improved. The process conditions are mild, the entire process is green and environmentally friendly, and it is safe and easy to operate, thus showing good development prospects.

[0034] 4. This invention effectively improves the yield of copper nitrate amidourea salt complex, ultimately obtaining a yield of ≥88% and a purity of ≥99% for nano-sized copper nitrate amidourea salt complex. It can be widely used in the recovery of high-end rocket propellants and the preparation of energetic materials, and has significant economic value and environmental benefits. Attached Figure Description

[0035] Figure 1 The infrared absorption spectrum of the nano-sized copper nitrate nitrate complex obtained in Example 1 of this invention;

[0036] Figure 2 This is a schematic diagram of the DSC-TG (Differential Scanning Calorimetry-Thermogravimetric Analysis) curve of the nano-sized copper nitrate nitrate complex obtained in Example 1 of the present invention. Detailed Implementation

[0037] Example 1

[0038] The present invention provides a method for preparing a nano-sized copper nitrate amidourea salt complex, which specifically includes the following steps:

[0039] S1, Water absorption: 1 kg of 98.5% pure N2O4 is introduced into 0.173 L of water at a rate of 8 mL / min in a reaction vessel to obtain a nitrous acid solution. The system temperature is controlled at 0±1℃ to form an ice-water mixture. The stirring rate is 200~300 r / min, and in this example it is 300 r / min.

[0040] The mass ratio of N2O4 to water is 1:0.17. The N2O4 originates from the oxidizer waste of liquid rocket propellant during ground tests of the liquid rocket engine.

[0041] S2, Oxygen Oxidation: 0.2 kg of oxygen (0.2 times the mass of N2O4) is introduced into the reactor, and the mixture is stirred for 12 h to obtain a nitric acid solution.

[0042] S3, Copper Flake Reaction: 0.43 kg of copper flakes (mass ratio of copper flakes to N2O4 is 0.43:1) were added to the reactor, and the reaction was carried out at 10°C for 24 h. After the reaction was completed, the solid residue was filtered to obtain the filtrate, which was then transferred to the reactor.

[0043] S4, Preparation of dicyandiamide solution: Dissolve 0.7 kg of dicyandiamide in 0.9 L of deionized water (mass concentration of 43.8%) at 65 °C. After dissolution, add the solution dropwise to the filtrate of step S3 at a rate of 1.5 mL / min using a peristaltic pump. The dropwise temperature is 65 °C and the dropwise time is 1 h. The mass ratio of dicyandiamide to N2O4 is 0.7:1.

[0044] S5. After the addition is complete, increase the stirring speed to 400~600 r / min (500 r / min in this example), adjust the pH to 7.0 with a 0.5 mol / L sodium hydroxide solution, add 1.75 kg of sodium citrate (2.5 times the mass of dicyandiamide), and heat to 85°C for 3 h.

[0045] Sodium citrate, acting as a complexing agent, prepares nanoparticles through multiple effects: its citrate ions react with Cu... 2+ Weak complexation reduces the concentration of free copper ions, slows down the coordination crystallization rate, and generates a large number of tiny crystal nuclei. These nuclei selectively adsorb onto the active crystal faces of the crystals, blocking crystal growth sites, constraining particle size, and limiting crystal growth. Simultaneously, the adsorption onto the active crystal faces forms a coating layer, giving the particles a negative charge, preventing aggregation through electrostatic repulsion and steric hindrance of the organic carbon chains. Furthermore, it buffers the pH of the system, stabilizing the crystallization environment, ultimately yielding uniformly dispersed nano-sized amidourea copper nitrate.

[0046] In other embodiments of the present invention, sodium ascorbate may also be added as a complexing agent, in an amount 2 to 3 times the mass of dicyandiamide in the dicyandiamide solution. Sodium ascorbate can react with Cu... 2+It exhibits weak complexation, slowly releasing copper ions to achieve uniform and abundant nucleation. Its functional groups selectively adsorb onto active crystal faces, inhibiting directional grain growth. Simultaneously, ionization imparts a negative charge to the particles, and the organic carbon chains create steric hindrance, preventing nanoparticle aggregation. Furthermore, it possesses weak reducing properties, effectively removing dissolved oxygen and stabilizing the reaction pH, preventing the formation of coarse crystals from copper salt hydrolysis, ultimately yielding a uniformly sized nanoscale product.

[0047] S6. After the reaction is complete, the temperature is lowered to below 40°C, the solid is filtered and collected, and dried at 80°C under a vacuum of 0.09 MPa for 8 hours to obtain 1.51 kg of nano-sized amidine-urea copper salt complex. In this example, the yield of the nano-sized amidine-urea copper salt complex is 92.6%, and the purity is 99.2%; the particle size is D50=50 nm, D90=90 nm, and its infrared absorption spectrum is shown below. Figure 1 As shown.

[0048] The preparation principle of this invention is as follows: First, in step S1, N2O4 dissolves in an ice-water mixture to generate a mixture of nitric acid and nitrous acid. Low temperature conditions can inhibit the decomposition of N2O4 and improve the utilization rate of raw materials. Then, in step S2, oxygen is introduced to oxidize nitrous acid to nitric acid, with the reaction formula: 2HNO2 + O2 = 2HNO3, promoting the dissolution and conversion of N2O4 and providing sufficient nitrate ions for the subsequent formation of copper nitrate. In step S3, copper sheet reacts with nitric acid to generate copper nitrate, with the reaction formula: Cu + 4HNO3 (conc.) = Cu(NO3)2 + 2NO2↑ + 2H2O. Controlling the reaction temperature to 5℃~15℃ can avoid excessive decomposition of nitric acid and improve the yield of copper nitrate. In step S5, the complexing agent forms a temporary complex with copper ions, reducing the aggregation energy barrier between particles and controlling the crystal growth rate during the reaction, ultimately forming nanoscale particles. At the same time, adjusting the pH to a neutral environment can avoid the decomposition of dicyandiamide under acidic conditions and ensure the full progress of the complexation reaction. The overall reaction equation of this invention is shown below.

[0049]

[0050] Example 2

[0051] 1.2 kg of 98.5% pure N₂O₄ was introduced into 0.13 L of water (N₂O₄ to water mass ratio of 1:0.11) at a rate of 8 mL / min in a reactor. The temperature was controlled at 0℃, and the stirring rate was 250 r / min. Then, 0.24 kg of oxygen (0.2 times the mass of N₂O₄) was introduced into the reactor. After stirring and reacting for 12 h, 0.52 kg of copper sheets (copper sheets to N₂O₄ mass ratio of 0.43:1) were added to the reactor, and the reaction was carried out at 15℃ for 24 h. After the reaction was completed, the solid residue was filtered to obtain the filtrate, which was then transferred to the reactor. 0.85 kg of dicyandiamide was dissolved in 1.1 L of deionized water (43.6% by mass) at 70 °C. The dissolved solution was then added dropwise to the filtrate at a rate of 1.6 mL / min using a peristaltic pump. The addition temperature was 68 °C, and the addition time was 55 min (the mass ratio of dicyandiamide to N₂O₄ was 0.71:1). After the addition was complete, the stirring speed was increased to 500 r / min, the pH was adjusted to 7.0 with 0.5 mol / L sodium hydroxide solution, and 2 kg of sodium citrate (2.5 times the mass of dicyandiamide) was added. The mixture was heated to 80 °C and reacted for 5 h. After the reaction, the temperature was lowered to below 40 °C, the mixture was filtered, and the solid was collected. The solid was dried under vacuum of 0.09 MPa at 80 °C for 8 h to obtain 1.85 kg of nano-sized amidine-urea copper salt complex with a yield of 94.38% and a purity of 99.5%; particle size D50 = 45 nm, D90 = 83 nm.

[0052] Example 3

[0053] In a reaction vessel, 0.5 kg of 98.5% pure N₂O₄ was introduced into 0.07 L of water (N₂O₄ to water mass ratio 1:0.14) at a rate of 8 mL / min. The temperature was controlled at 0℃, and the stirring rate was 200 r / min. Then, 0.1 kg of oxygen (0.2 times the mass of N₂O₄) was introduced into the vessel. After stirring and reacting for 12 h, 0.2 kg of copper sheets (copper sheet:N₂O₄ = 0.4:1) were added to the vessel, and the reaction was carried out at 15℃ for 24 h. After the reaction was completed, the solid residue was filtered to obtain the filtrate, which was transferred to the reaction vessel. 0.35 kg of dicyandiamide was dissolved in 0.5 L of deionized water (mass concentration 41.2%) at 60℃. After dissolution, the solution was added dropwise to the filtrate at a rate of 1.5 mL / min using a peristaltic pump at a dropping temperature of 62℃ for 45 min (dicyandiamide:N₂O₄ = 0.7:1). After the dropwise addition was completed, the stirring rate was increased to 500 r / min, the pH was adjusted to 7.0 with 0.5 mol / L sodium hydroxide solution, 1 kg of sodium citrate (2.5 times the mass of dicyandiamide) was added, and the mixture was heated to 90 °C for 2 h. After the reaction was completed, the temperature was lowered to below 40 °C, the mixture was filtered and the solid was collected. The solid was dried at 80 °C under a vacuum of 0.09 MPa for 8 h to obtain 0.72 kg of nano-sized copper nitrate complex with a yield of 88.7% and a purity of 99.1%; the particle size was D50 = 52 nm and D90 = 97 nm.

[0054] The particle size tests of the nano-sized copper nitrate nitrate complexes (referred to as samples 1-3) obtained in Examples 1 to 3 are shown in Table 1.

[0055] Table 1. Particle size test results

[0056]

[0057] The following methods were used to test the performance of samples 1-3:

[0058] 1. Particle size test: Malvern laser particle size analyzer (model: Mastersizer 3000) was used. The test conditions were water as the dispersion medium and ultrasonic dispersion of the sample for 5 min.

[0059] 2. Burning rate test: Refer to GJB 772A-97 "Test Methods for Explosives", test pressure 10MPa, temperature 25℃;

[0060] 3. Sensitivity test: Impact sensitivity refers to GJB 772A-97 method 601.1, and friction sensitivity refers to GJB 772A-97 method 602.1;

[0061] 4. Thermal stability test: A DSC-TG (Differential Scanning Calorimetry-Thermogravimetric Analysis) simultaneous thermal analyzer (model: NETZSCH STA 449F3) was used. The test range was room temperature to 400℃, the heating rate was 10℃ / min, and the atmosphere was nitrogen.

[0062] The thermal stability test results of the nanoscale copper nitrate complex of sample 1 are as follows: Figure 2 As shown in the DSC curve, the product exhibits a significant exothermic peak at 215℃, corresponding to a thermal decomposition reaction. The TG curve shows that the mass loss rate below 200℃ is ≤2%, indicating that the product has good thermal stability. At 300℃, the mass loss rate is ≥95%, indicating that the product is completely combusted and has high gas production efficiency.

[0063] The test results and comparisons for samples 1-3 are shown in Tables 2 and 3.

[0064] Table 2. Performance Comparison of Sample 1 with Existing Technology Products

[0065]

[0066] Table 3 Performance data of samples 1-3

[0067]

[0068] As can be seen from Tables 2 and 3, the yield of the nano-sized copper nitrate complex prepared by the present invention is ≥88%, the particle size D50 is 45~52nm, and all other performance indicators are significantly better than those of the products of the prior art.

Claims

1. A method for preparing a nanoscale copper complex of amidine urea nitrate salt, characterized in that, Includes the following steps: S1, N2O4 with a purity ≥98% is passed into water, mixed evenly and reacted. During the mixing process, the temperature is controlled at 0±1℃ to obtain a nitrous acid solution. The mass ratio of N2O4 to water is 1:0.1~0.2; The N2O4 with a purity of ≥98% is the N2O4 waste oxidizer of liquid rocket propellant used in ground tests of liquid rocket engines. S2, oxygen is introduced into the nitrous acid solution from step S1, and the reaction is stirred to obtain a nitric acid solution; S3, add copper sheets to the nitric acid solution obtained in step S2 to react, filter to remove unreacted copper sheets, and obtain a filtrate containing copper nitrate; S4, add the dicyandiamide solution dropwise to the filtrate containing copper nitrate obtained in step S3, wherein the mass ratio of dicyandiamide to N2O4 in the dicyandiamide solution is 0.65~0.8:1; S5, after the addition is complete, adjust the pH to 7.0±0.2, add the complexing agent to carry out the reaction, the complexing agent is sodium citrate or sodium ascorbate; S6. After the reaction is complete, the solid is cooled, filtered and collected, and finally dried to obtain nano-sized copper nitrate nitridine complex.

2. The method for preparing the nano-sized amidine urea copper salt complex according to claim 1, characterized in that: In step S1, N2O4 is introduced into the water at a rate of 5~10 mL / min; In step S2, the amount of oxygen introduced is 0.2 to 0.3 times the mass of N2O4, and the reaction time is 12 to 13 hours.

3. The method for preparing the nano-sized amidine urea copper salt complex according to claim 2, characterized in that: In step S3, the mass ratio of copper sheet to N2O4 is 0.4~0.5:1, the reaction time is 23~25h, and the reaction temperature is 5℃~15℃. In step S4, the mass concentration of the dicyandiamide solution is 35%~45%, and the dicyandiamide solution is added dropwise to the filtrate of step S3 at a rate of 1~2 mL / min, with a dropping temperature of 60℃~70℃.

4. The method for preparing the nano-sized amidine urea copper salt complex according to claim 3, characterized in that: In step S5, the pH is adjusted with a sodium hydroxide solution with a concentration of 0.45~0.6mol / L, the amount of complexing agent is 2~3 times the mass of dicyandiamide in the dicyandiamide solution, the reaction temperature is 70℃~95℃, and the reaction time is 2~5h.

5. The method for preparing the nanoscale copper nitrate amidine urea salt complex according to claim 4, characterized in that: In step S6, the temperature is cooled to below 40°C. The drying is vacuum drying with a vacuum degree of 0.08~0.1MPa, a drying temperature of 78~85°C, and a drying time of 8~9h.

6. The method for preparing the nanoscale copper nitrate amidine urea salt complex according to any one of claims 1 to 5, characterized in that, In step S4, the dicyandiamide solution is prepared in the following manner: Dicyandiamide was dissolved in deionized water at 60-70°C, and the mass concentration of the dicyandiamide solution was 40%-45%.

7. The method for preparing the nano-sized amidine urea copper salt complex according to claim 6, characterized in that: In step S1, the N2O4 introduction rate is 8 mL / min, and the stirring rate during mixing is 250 r / min; In step S2, the amount of oxygen introduced is 0.2 times the mass of N2O4, and the reaction time is 12 hours. In step S3, the mass ratio of copper sheet to N2O4 is 0.43:1, the reaction time is 24 h, and the reaction temperature is 15 °C. In step S4, the mass concentration of the dicyandiamide solution is 43.6%, the dropping rate of the dicyandiamide solution is 1.5 mL / min, the dropping temperature is 68 °C, and the mass ratio of dicyandiamide to N2O4 is 0.71:

1.

8. The method for preparing the nano-sized amidine urea copper salt complex according to claim 7, characterized in that: In step S5, the amount of the complexing agent is 2.5 times the mass of dicyandiamide, the reaction temperature is 80°C, and the reaction time is 5 hours. In step S6, the vacuum degree is 0.09 MPa, the drying temperature is 80℃, and the drying time is 8 hours.

9. Use of oxidizer N2O4 waste of liquid rocket propellants, characterized in that: Used to prepare nanoscale copper salt complexes of amidine nitrate.

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