A method for synthesizing azobisisobutyronitrile based on ozone gas oxidation

Abstract

This invention belongs to the field of organic synthesis technology, specifically relating to a method for synthesizing azobisisobutyronitrile (AIB) based on ozone gas oxidation. The method includes the following steps: dissolving diisobutyronitrile hydrazine in dilute sulfuric acid to form a homogeneous phase, adding a solvent and mixing, introducing ozone gas, controlling the reaction temperature at 25-35°C, reacting for 1-4 hours, separating the layers, neutralizing the organic phase after separation, filtering to obtain the filtrate, crystallizing, separating the solid, and drying to obtain pure AIB. The method for synthesizing AIB based on ozone gas oxidation provided by this invention uses a single oxidant, achieving efficient and clean synthesis of AIB in a system with high purity and high yield.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for synthesizing azobisisobutyronitrile based on ozone gas oxidation. Background Technology

[0002] Azobisisobutyronitrile (AIBN) is the most widely used azo radical initiator in the polymer industry, and it can also be used as a foaming agent for resins such as polyvinyl chloride and polyolefins. With the rapid development of the polymer materials industry, the market demand for AIBN continues to grow, placing higher demands on product quality and the environmental friendliness of the production process. Currently, the mainstream industrial route for producing AIBN involves first condensing acetone cyanohydrin with hydrazine hydrate to obtain diisobutyronitrile hydrazine, and then oxidizing and dehydrogenating the diisobutyronitrile hydrazine to obtain the target product. The oxidation step is a key step that determines product quality and economic benefits.

[0003] In existing technologies, the hydrogen peroxide / sodium bromide oxidation method is a commonly used process. Chinese patent CN101134735A discloses a method for producing azobisisobutyronitrile (AIB) using hydrogen peroxide oxidation. In this method, diisobutyronitrile hydrazine and sodium bromide are added to a sulfuric acid solution, followed by the dropwise addition of hydrogen peroxide for oxidation. The product is then obtained through solid-liquid separation and water washing. While this method offers relatively mild reaction conditions, it still has significant drawbacks. For example, the introduction of sodium bromide as a catalyst inevitably results in sodium ions remaining in the product or entering the mother liquor, leading to a decrease in product purity. Furthermore, the treatment of saline wastewater increases the burden, and the reaction process generates solid salts such as sodium sulfate, which are difficult to recover and have high treatment costs. Additionally, hydrogen peroxide itself contains a large amount of water (common 27.5% hydrogen peroxide has a water content as high as 72.5%), and since the reaction medium is a dilute sulfuric acid solution, the entire reaction system has an extremely high water content, which not only reduces the yield efficiency per unit reaction volume.

[0004] To address the problems caused by sodium bromide, CN108484444A discloses a method for producing azobisisobutyronitrile using bromine and hydrogen peroxide. Although this process, which utilizes a three-phase catalytic oxidation method, represents an improvement in the substitution of sodium bromide, it has been found in practical applications that further improvements are needed to address issues such as bromide residues, safety and environmental hazards of organic solvents, long reaction times, high water content in the system, and complex operation.

[0005] Another mainstream process is the chlorine oxidation method, which directly introduces chlorine to oxidize diisobutyronitrile hydrazine, as disclosed in CN103333086A. Although this method avoids the introduction of sodium salt, it generates a large amount of waste hydrochloric acid, has a low reaction conversion rate (usually <70%), requires a large amount of alkali to neutralize, and causes heavy environmental pollution and high operational risks. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the existing technology, such as the introduction of sodium salt, high water content, and generation of chlorine-containing wastewater, and to provide a method for synthesizing azobisisobutyronitrile based on ozone gas oxidation. The method uses a single oxidant to synthesize azobisisobutyronitrile efficiently and cleanly in the system. The synthesized azobisisobutyronitrile has high purity and high yield.

[0007] To solve the above technical problems, the present invention proposes the following technical solution: A method for synthesizing azobisisobutyronitrile based on ozone gas oxidation includes the following steps: dissolving hydrazine diisobutyronitrile in dilute sulfuric acid solution to form a homogeneous phase, adding solvent to mix, introducing ozone gas, controlling the reaction temperature at 25~35℃, and the reaction time at 1~4h, separating the liquid and liquid phases, neutralizing the organic phase after separation, filtering to obtain the filtrate for crystallization, separating the solid and drying to obtain pure azobisisobutyronitrile.

[0008] Furthermore, the mass concentration of the dilute sulfuric acid solution is 25-50%, which serves to provide an acidic environment for the dissolution of diisobutyronitrile hydrazine, promote the dissociation of diisobutyronitrile hydrazine, and at the same time provide suitable acidity conditions for the ozone oxidation reaction, preventing ozone from decomposing in a neutral or alkaline environment and ensuring the oxidizing activity of ozone.

[0009] The solvent is carbon tetrachloride, tetrachloroethylene, or dichloroethane. These solvents are all non-polar and immiscible with water, enabling efficient extraction of the azobisisobutyronitrile (AIBN) produced in the reaction (AIBN is a non-polar compound with high solubility in non-polar solvents but very low solubility in water). Furthermore, these solvents are chemically stable, do not react with ozone, dilute sulfuric acid, or neutralizing agents, do not introduce new impurities, and have moderate boiling points, making them easy to recycle and reuse, thus reducing production costs. Dichloroethane is preferred due to its relatively low toxicity, better environmental friendliness, and higher extraction efficiency.

[0010] The ozone gas is a mixture of ozone and oxygen, with an ozone content of 9% to 12%, and the mass ratio of the mixture to diisobutyronitrile hydrazine is 6:1 to 12:1.

[0011] The flow rate of ozone gas introduced is 0.3 L / min to 1.2 L / min.

[0012] The organic phase neutralization involves adding one or more of the following: 5%–10% sodium carbonate solution, 8%–12% sodium bicarbonate solution, 5%–8% potassium carbonate solution, or 10%–15% sodium hydroxide solution. The purpose of using this type of neutralizing agent is to neutralize the small amount of dilute sulfuric acid entrained in the organic phase, making the organic phase neutral or weakly alkaline. This prevents the acidic environment from corroding subsequent crystallization equipment and also prevents acidic substances from affecting the crystallization effect of AIBN. Controlling the mass concentration of the neutralizing agent within the above range ensures both the neutralization effect and the intensity of the neutralization reaction, preventing excessively vigorous reactions that could raise the system temperature and damage the target product.

[0013] After neutralization to pH 7-9, the product is then precision filtered to a depth of 0.02μm-1μm. This precision filtration removes tiny solid impurities entrained in the organic phase (such as small amounts of carbonate precipitates generated during the neutralization reaction, incompletely dissolved diisobutyronitrile hydrazine impurities, etc.) to prevent these impurities from entering subsequent crystallization processes and affecting product purity. The filtration precision is controlled at 0.02μm-1μm, which effectively removes tiny impurities while ensuring filtration efficiency, meeting the needs of large-scale industrial production.

[0014] The filtrate was filtered and then cooled to -10℃ to -5℃ for crystallization. The solubility of AIBN in organic solvents decreases significantly with decreasing temperature. When cooled to -10℃ to -5℃, AIBN can crystallize out rapidly and completely, improving product yield.

[0015] After crystallization, the solid is filtered and dried at 30℃~40℃. Drying is carried out under vacuum. This rapidly removes residual solvent from the solid while ensuring that AIBN does not decompose. Vacuum drying lowers the boiling point of the solvent, accelerates the drying process, and prevents oxygen in the air from oxidizing AIBN, further ensuring product purity and quality.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention uses ozone as a single oxidant, replacing hydrogen peroxide / sodium bromide, bromine / hydrogen peroxide or chlorine in the existing process, which completely solves the problem of sodium salt and bromide residues introduced in the existing process, and avoids the defect of generating a large amount of chlorine-containing wastewater by chlorine oxidation method. After the ozone oxidation reaction is completed, it decomposes into oxygen, leaving no impurities in the system and no toxic or harmful byproducts. The production process is clean and environmentally friendly, with no salt or chlorine-containing wastewater discharge, which greatly reduces the wastewater treatment cost and environmental burden, and is in line with the development trend of green chemical production.

[0017] (2) The present invention uses dilute sulfuric acid solution as the reaction medium and controls the water content of the system to be at a low level. Compared with the existing hydrogen peroxide oxidation method (the water content of the system is extremely high), it significantly improves the output efficiency per unit reaction volume and reduces the equipment occupation cost. At the same time, the dilute sulfuric acid solution can completely dissolve diisobutyronitrile hydrazine and ozone gas can be uniformly dispersed in the system and fully contact the reactants. Combined with the optimized reaction parameters, the reaction conversion rate, product yield and product purity are much higher than those of the existing process.

[0018] (3) The present invention is simple to operate and highly safe. It does not require the use of toxic and corrosive substances such as bromine and chlorine. The storage and transportation of ozone are relatively safe. The reaction conditions are mild, the equipment investment cost is low, and the reaction time is short (1~4h). Compared with the existing process (reaction time 6~8h), the production efficiency is greatly improved. At the same time, the organic solvent (halogenated hydrocarbon solvent) used for extraction can be recycled and reused, which further reduces the production cost and makes it easy to achieve industrial-scale production. It has significant economic benefits and industrial application value. Attached Figure Description

[0019] Figure 1 The image shows the high-performance liquid chromatography (HPLC) chromatogram of the azobisisobutyronitrile prepared in Example 1. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Specifically, the method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: dissolving diisobutyronitrile hydrazine in a 25-50% (w / w) dilute sulfuric acid solution to form a homogeneous phase, adding an organic solvent, introducing ozone gas (oxygen source) at a flow rate of 0.3 L / min-1.2 L / min, controlling the reaction temperature at 25-35°C, the reaction time at 1-4 h, extracting and separating the layers, taking the organic phase and adding it to an alkaline solution to neutralize to pH 7-9, finely filtering at 0.02 μm-1 μm, cooling the obtained filtrate to -10°C--5°C to crystallize, and vacuum drying the filtered solid at 30°C-40°C to obtain pure azobisisobutyronitrile.

[0022] In the following examples, the purity of the diisobutyronitrile hydrazine (AIBN) used was 99.5%, and the ozone content was 9% (volume fraction). All ozone introduced was a mixture of 9% ozone and 91% oxygen. The flow rate was measured at standard atmospheric pressure and 25°C. The dilute sulfuric acid solution, neutralizing agent, and organic solvents were all industrial-grade reagents. Product purity was determined using high-performance liquid chromatography (HPLC), and the yield was calculated using the following formula: Yield = (Actual AIBN mass / Theoretical AIBN mass) × 100%. The theoretical AIBN mass was calculated based on the mass of the diisobutyronitrile hydrazine and the stoichiometric ratio of the reaction.

[0023] In the examples and comparative examples below, the actual controlled temperature range of ozone oxidation reaction was 25~35℃. Specific values ​​are not recorded, but it is sufficient to control it within this range. Similarly, the pH during neutralization was controlled at 7~9, the temperature during crystallization was controlled at -10~-5℃, and the drying temperature was 30~40℃. Specific values ​​are not recorded for these examples as well.

[0024] Example 1 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolving: In a 500mL four-necked flask, add 200mL of 30% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved, and then add 100mL of carbon tetrachloride organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.3L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 2.8h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 5% sodium carbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.2 μm to remove tiny carbonate precipitates and a small amount of impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 2 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 4 hours to obtain pure azobisisobutyronitrile.

[0025] Test results: The product weight was 8.8g, the purity was 99.96%, and the yield was 88% (based on diisobutyronitrile hydrazine); no toxic or harmful byproducts were generated during the reaction, no salt- or chlorine-containing wastewater was discharged, the organic solvent carbon tetrachloride was recyclable, and no sodium ion residue was detected in the product. The high-performance liquid chromatography (HPLC) chromatogram of the prepared azobisisobutyronitrile is shown below. Figure 1 As shown, the peak values ​​are listed in Table 1.

[0026] Table 1 Peak Value Table

[0027] Example 2 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolving: In a 500mL four-necked flask, add 200mL of 30% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved, and add 100mL of carbon tetrachloride as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.3L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 3.4h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 5% sodium carbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.2 μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 2 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 4 hours to obtain pure azobisisobutyronitrile.

[0028] Test results: The product weight is 9.0g, the purity is 99.95%, and the yield is 90% (calculated as diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent carbon tetrachloride can be recycled and reused, and no sodium ion residues are detected in the product.

[0029] Example 3 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolution: In a 500mL four-necked flask, add 200mL of 30% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved, and add 100mL of dichloroethane as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.5L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 2.5h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 5% sodium carbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.2 μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 2 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 4 hours to obtain pure azobisisobutyronitrile.

[0030] Test results: The product weight is 8.5g, the purity is 99.91%, and the yield is 85% (based on diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent dichloroethane can be recycled and reused, and no sodium ion residues are detected in the product.

[0031] Example 4 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolution: In a 500mL four-necked flask, add 200mL of 40% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved. Add 100mL of dichloroethane as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.6L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 1.6h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 8% sodium bicarbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 1μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 2.5 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 3 hours to obtain pure azobisisobutyronitrile.

[0032] Test results: The product weight is 8.8g, the purity is 99.92%, and the yield is 88% (calculated as diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent dichloroethane can be recycled and reused, and no sodium ion residues are detected in the product.

[0033] Example 5 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolving: In a 500mL four-necked flask, add 200mL of 25% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved, and add 100mL of carbon tetrachloride as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.9 L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 1.2h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 5% potassium carbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.8 μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 1.8h to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 3.5h to obtain pure azobisisobutyronitrile.

[0034] Test results: The product weight is 8.7g, the purity is 99.93%, and the yield is 87% (calculated as diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent carbon tetrachloride can be recycled and reused, and no sodium ion residues are detected in the product.

[0035] Example 6 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolution: In a 500mL four-necked flask, add 200mL of 35% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved. Add 100mL of tetrachloroethylene as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 1.2L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 1.0h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 10% sodium carbonate solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 1.0 μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 1.5 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 2 hours to obtain pure azobisisobutyronitrile.

[0036] Test results: The product weight is 8.5g, the purity is 99.90%, and the yield is 85% (calculated as diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent tetrachloroethylene can be recycled and reused, and no sodium ion residues are detected in the product.

[0037] Example 7 The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation of the present invention includes the following steps: 1. Dissolution: In a 500mL four-necked flask, add 200mL of 45% dilute sulfuric acid, turn on the stirrer, and slowly add 10.0g of diisobutyronitrile hydrazine while stirring. Continue stirring until the diisobutyronitrile hydrazine is completely dissolved. Add 100mL of tetrachloroethylene as an organic solvent. 2. Ozone oxidation: Start the ozone generator, adjust the ozone flow rate to 0.5L / min, and continuously introduce ozone into the above homogeneous reaction system through the gas distributor. Turn on the constant temperature water bath, control the reaction temperature to 25~35℃, and the reaction time to 2.1h. 3. Extraction: After the reaction is complete, transfer the reaction solution to a separatory funnel, shake and stir thoroughly for 30 min, let stand for 30 min to separate the layers, and then separate and collect the organic phase; 4. Neutralization: Slowly add 12% sodium hydroxide solution dropwise to the collected organic phase while stirring, until the pH of the organic phase reaches 7-9, then stop adding the solution to complete the neutralization reaction; 5. Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.4 μm to remove tiny impurities entrained in the organic phase, resulting in a clear filtrate; 6. Crystallization: Transfer the clarified filtrate to a crystallization tank, slowly cool it to -10℃~-5℃, and keep it at this temperature for 2.2 hours to crystallize. A large amount of white crystals were observed to precipitate. 7. Solid-liquid separation and drying: The crystallized mixture was separated into solid and liquid by vacuum filtration to obtain a white solid. The white solid was placed in a vacuum drying oven and dried at 30~40℃ under vacuum for 2.5h to obtain pure azobisisobutyronitrile.

[0038] Test results: The product weight is 8.65g, the purity is 99.91%, and the yield is 86.5% (calculated as diisobutyronitrile hydrazine); no toxic or harmful byproducts are generated during the reaction process, no salt or chlorine-containing wastewater is discharged, the organic solvent tetrachloroethylene can be recycled and reused, and no sodium ion residues are detected in the product.

[0039] Comparative Example 1 The specific steps for preparing azobisisobutyronitrile (AIBN) are as follows: In a 500 mL four-necked flask, add 200 mL of 15% dilute sulfuric acid. While stirring, add 10.0 g of hydrazine diisobutyronitrile (DIBN) and 1.5 g of sodium bromide (catalyst). After complete dissolution, slowly add 27.5% hydrogen peroxide (molar ratio of DIBN to hydrazine diisobutyronitrile 1.2:1). Control the reaction temperature at 40 °C and react for 2 h. After the reaction is complete, follow the post-processing steps of Example 1 (extraction, neutralization, fine filtration, crystallization, and drying) to obtain the AIBN product.

[0040] Test results: Product weight 7.8g, purity 98.5%, yield 78%, sodium ion residue detected in the product, reaction mother liquor is saline wastewater with moderate acidity, requiring additional treatment before discharge.

[0041] Comparative Example 2 The specific steps for preparing azobisisobutyronitrile (AIBN) are as follows: In a 500 mL four-necked flask, add 200 mL of 20% dilute sulfuric acid, and while stirring, add 10.0 g of hydrazine diisobutyronitrile. After complete dissolution, continuously purge with chlorine gas (flow rate 0.3 L / min), control the reaction temperature at 40 °C, and react for 2 h. After the reaction is complete, follow the post-treatment steps in Example 1 to obtain the azobisisobutyronitrile product.

[0042] Test results: Product weight 6.5g, purity 97.8%, yield 65%, no sodium ion residue detected in the product, but the reaction solution pH < 1, extremely high acidity, requires a large amount of alkali solution for neutralization, generates a large amount of chlorine-containing wastewater, and has a heavy environmental burden.

[0043] Comparative Example 3 The specific steps for preparing azobisisobutyronitrile (AIBN) are as follows: In a 500 mL four-necked flask, add 200 mL of 30% dilute sulfuric acid, and while stirring, add 10.0 g of hydrazine diisobutyronitrile, 0.8 g of bromine, and 10 mL of dichloroethane. After complete dissolution, slowly add 27.5% hydrogen peroxide dropwise, controlling the reaction temperature at 35 °C, and react for 6 hours. After the reaction is complete, follow the post-treatment steps in Example 1 to obtain the azobisisobutyronitrile product.

[0044] Test results: Product weight 8.0g, purity 98.8%, yield 79%, trace bromide residue was detected in the product, reaction time was long (6h), large amount of organic solvent was used, recovery was difficult, and there are safety hazards of bromine corrosion, flammability and explosion.

Claims

1. A method for synthesizing azobisisobutyronitrile based on ozone gas oxidation, characterized in that, The process includes the following steps: dissolving hydrazine diisobutyronitrile in dilute sulfuric acid to form a homogeneous phase, adding solvent to mix, introducing ozone gas, controlling the reaction temperature at 25~35℃, and reacting for 1~4 hours, separating the liquid and liquid phases, neutralizing the organic phase after separation, filtering to obtain the filtrate for crystallization, separating the solid and drying to obtain pure azobisisobutyronitrile.

2. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 1, characterized in that, The mass concentration of the dilute sulfuric acid solution is 25-50%.

3. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 1, characterized in that, The solvent is carbon tetrachloride, tetrachloroethylene, or dichloroethane.

4. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 1, characterized in that, The ozone gas is a mixture of ozone and oxygen, and the mass ratio of the mixture to diisobutyronitrile hydrazine is 6:1 to 12:

1.

5. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 4, characterized in that, The ozone content is 9%~12%.

6. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 5, characterized in that, The flow rate of ozone gas introduced is 0.3 L / min to 1.2 L / min.

7. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 1, characterized in that, The organic phase neutralization is achieved by adjusting the pH to 7-9 using an alkaline solution.

8. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 7, characterized in that, After neutralization, the filtration precision is 0.02μm~1μm, and the filtrate is cooled to -10℃~-5℃ for crystallization.

9. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 8, characterized in that, After crystallization, the solid is filtered and dried at 30-40°C.

10. The method for synthesizing azobisisobutyronitrile based on ozone gas oxidation according to claim 9, characterized in that, Drying is carried out in a vacuum.

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