Method for treating the large amount of wastewater produced in the oxidation step of the production of azobisdimethyl isobutyronitrile

Abstract

The present application belongs to wastewater treatment process technical field, and particularly relates to a method for treating a large amount of wastewater generated in an oxidation process in azobisdimethyl isobutyronitrile production. The method for treating the large amount of wastewater generated in the oxidation process in azobisdimethyl isobutyronitrile production adds a stable solvent before, during or after reaction in the oxidation process in azobisdimethyl isobutyronitrile production, and the organic phase is separated after standing and layering after the reaction is completed. The organic phase is neutralized to a pH of 7-10, filtered, and the organic phase is post-treated to produce azobisdimethyl isobutyronitrile products. The method for treating the large amount of wastewater generated in the oxidation process in azobisdimethyl isobutyronitrile production significantly reduces the discharge of wastewater in the azobisdimethyl isobutyronitrile production process from the source.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for treating a large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile. Background Technology

[0002] Azobisisobutyronitrile (AIBN) is an important free radical initiator and foaming agent, widely used in polymer polymerization, rubber, and plastics industries. Currently, the mainstream processes for producing AIBN in China mainly involve two oxidation steps: one using sodium bromide and hydrogen peroxide as oxidants, and the other directly using chlorine gas as the oxidant. Both of these traditional processes generate large amounts of wastewater during production, and the product washing process also consumes a significant amount of fresh water. Statistics show that, on average, producing one ton of AIBN requires 10-30 tons of fresh water for washing. This not only results in a huge waste of water resources but also generates large amounts of wastewater containing acidic substances, inorganic salts, and organic matter, leading to high treatment costs and significant environmental pressure.

[0003] In response to the aforementioned wastewater problem, some studies have attempted to optimize the process or wastewater treatment.

[0004] Regarding process improvements, patent CN1785963A discloses a method for preparing azobisisobutyronitrile (AIBN), which reduces residual chlorine emissions to some extent by controlling the pH of the condensation wastewater to 4-5 and recycling the released residual chlorine through negative pressure absorption. Patent CN108484444A discloses a method for producing AIBN using bromine and hydrogen peroxide, employing a three-phase reaction system to improve reaction efficiency. However, these methods still cannot fundamentally solve the problem of large wastewater generation: the hydrogen peroxide method must be carried out in an acidic system, resulting in a large volume of acidic wastewater; the chlorination method has an unstable reaction process, the reaction endpoint is difficult to control, and it easily generates many byproducts that are difficult to separate. Overall, these technologies mostly involve end-of-pipe treatment or local optimization of wastewater, failing to reduce wastewater discharge at the production source.

[0005] In addition, there are some technologies focusing on the post-treatment of azobisisobutyronitrile (AIB) production wastewater. For example, patent CN109160977A discloses a rapid settling organic flocculant adsorbent for removing suspended solids and organic matter from wastewater; patent CN103611514A discloses a multifunctional adsorption particle that can adsorb various pollutants in wastewater. However, these technologies all fall under the category of end-of-pipe wastewater treatment, which not only increases treatment steps and costs but also cannot replace source reduction measures. Other technologies use chemical precipitation to remove cyanide from wastewater, but this requires adding far more precipitant than theoretically recommended, and the resulting cyanide-containing sludge still needs to be disposed of as hazardous waste, increasing the pressure on solid waste treatment. The traditional method of neutralizing with alkali followed by multi-effect evaporation for desalination is economically unsound, and the distilled salt, when disposed of as hazardous waste, poses a risk of secondary pollution. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the problems of large amount of wastewater generated by the oxidation process, high water consumption and high wastewater treatment cost in the existing azobisisobutyronitrile (AIB) production process. The invention provides a method for treating the large amount of wastewater generated by the oxidation process in the AIB production process, thereby significantly reducing the discharge of wastewater in the AIB production process from the source.

[0007] The present invention relates to a method for treating a large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile (AIBN). In the oxidation process of producing AIBN, a stable solvent is added before, during, or after the reaction. After the reaction is completed, the mixture is allowed to stand and separate into layers to separate the organic phase. The organic phase is neutralized to a pH of 7-10, filtered, and then post-treated to obtain the AIBN product.

[0008] Furthermore, the method for producing azobisisobutyronitrile is the sodium bromide-hydrogen peroxide method, the chlorine method, or the bromine-hydrogen peroxide method.

[0009] The timing of adding the stabilizing solvent can be optimized based on the characteristics of different oxidation processes: For the sodium bromide-hydrogen peroxide method, it is preferable to add a stable solvent to the reaction system after the reaction is complete.

[0010] For the chlorine method, it is preferable to add a stable solvent to the reaction system before the reaction begins.

[0011] For the bromine-hydrogen peroxide method, it is preferable to add a stable solvent to the reaction system during the reaction.

[0012] Furthermore, the stabilizing solvent is one or more of dichloromethane, trichloromethane, and carbon tetrachloride, and the amount of stabilizing solvent added is 10% to 50% of the total volume of the reaction system. When the stabilizing solvent is dichloromethane, the amount added is 20% to 40% of the total volume of the reaction system.

[0013] Furthermore, the organic phase neutralization uses a sodium hydroxide solution with a mass concentration of 0.5% to 30%, ammonia water with a mass concentration of 1% to 18%, or potassium hydroxide solution with a mass concentration of 1% to 20%.

[0014] Furthermore, the neutralization of the organic phase is carried out at a temperature of 10~40℃, and the neutralization time is controlled at 10~60min.

[0015] Furthermore, the filtration accuracy is 0.01~10μm, preferably 0.1~5μm, and the filtration pressure at room temperature is 0.1~0.5MPa.

[0016] Furthermore, the filtered organic phase can be directly used in the crystallization process of azobisisobutyronitrile (AIBN), or crude AIBN can be obtained by distillation to recover the solvent.

[0017] Specifically, as a preferred embodiment, when producing azobisisobutyronitrile (AIB) using the sodium bromide-hydrogen peroxide method, after the oxidation reaction is complete, 10%–40% (by volume) of dichloromethane is added to the reaction system as a stabilizing solvent. The mixture is stirred for 20–40 minutes to ensure the generated AIB is fully dissolved in the organic phase. After settling and separation, the lower organic phase is separated and transferred to a neutralization vessel. A 3%–10% sodium hydroxide solution is added dropwise at 15–35°C to adjust the pH to 7.5–9.0, and the neutralization time is 20–40 minutes. The neutralized organic phase is then filtered through a precision filter with a filtration accuracy of 0.5–2 μm at a pressure of 0.2–0.4 MPa. The filtered organic phase is directly fed into a crystallization vessel for cooling and crystallization. After centrifugation and drying, the AIB product is obtained. This method can reduce washing wastewater by more than 90%, and the product yield can reach more than 98%.

[0018] As another preferred embodiment, when producing azobisisobutyronitrile (AIB) using the chlorine method, carbon tetrachloride or chloroform (15%–30% of the total volume of the reaction system) is added to the reaction system as a stabilizing solvent before the reaction begins. During the reaction, the generated AIB continuously dissolves in the organic phase, preventing the precipitation of solid products and maintaining a homogeneous or well-contact two-phase reaction state. This eliminates the problem of low gas-liquid-solid three-phase reaction efficiency caused by solid product precipitation in the traditional chlorine method. After the reaction, the mixture is allowed to stand and separate into layers. The organic phase is then transferred to a neutralization vessel, and a 5%–15% (w / w) ammonia or potassium hydroxide solution is added at 10–30°C to adjust the pH to 7.5–8.5. The neutralization time is 15–30 min. The neutralized organic phase is then filtered through a precision filter with a filtration accuracy of 0.1–1 μm. The filtered organic phase can be distilled to recover the solvent and obtain crude AIB, or it can be directly used for subsequent recrystallization. This method not only reduces wastewater discharge, but also significantly improves the reaction conversion rate by avoiding three-phase reactions, and the product yield can be increased by 2-5% compared with the traditional chlorine method.

[0019] In another preferred embodiment, when producing azobisisobutyronitrile (AIB) using the bromine-hydrogen peroxide method, when the oxidation reaction reaches 30%–70%, 15%–35% of the total volume of the reaction system is added to the reaction system as a stabilizing solvent, consisting of chloroform or a mixture of dichloroform and chloroform. After adding the stabilizing solvent, the reaction is stirred until complete. After the reaction is complete, the mixture is allowed to stand and separate into layers. The organic phase is then transferred to a neutralization vessel, and a 10%–20% (w / w) potassium hydroxide solution or sodium hydroxide solution is added at 20–40°C to adjust the pH to 8.0–9.0. The neutralization time is 30–50 min. The neutralized organic phase is then filtered through a precision filter with a filtration accuracy of 0.2–0.8 μm at a filtration pressure of 0.3–0.5 MPa. The filtered organic phase can be used directly for crystallization or for solvent recovery through distillation. This method can effectively reduce subsequent washing water usage, achieving a wastewater reduction rate of over 90%.

[0020] In all the above embodiments, the stable solvents used can be recovered and reused by distillation, with a solvent recovery rate of over 94%, further reducing production costs and resource consumption.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention significantly reduces wastewater discharge and is environmentally friendly. Traditional processes require 10-30 tons of fresh water for washing to produce 1 ton of azobisisobutyronitrile, generating a large amount of difficult-to-treat acidic, saline organic wastewater. This invention uses in-situ extraction with a stable solvent, replacing the traditional large-volume water washing process with organic solvent washing, which can reduce washing wastewater discharge by more than 90%, reducing wastewater generation per ton of product to less than 1.2 tons. At the same time, the stable solvent can be recycled, with a solvent recovery rate of over 94%, reducing organic waste liquid discharge and achieving clean production from the source, meeting the requirements of green chemical industry.

[0022] (2) This invention improves resource utilization and reduces processing costs. The methane chloride-based stable solvent used in this invention is chemically stable and can be recovered by distillation and recycled, significantly reducing raw material consumption. The azobisisobutyronitrile in the organic phase can be directly used for subsequent crystallization without repeated dissolution. The product yield can reach 97%~98.5%. Due to the significant reduction in wastewater volume and the avoidance of the generation of large amounts of acidic wastewater, the construction and operation costs of wastewater treatment facilities are significantly reduced, and the environmental treatment cost per ton of product can be reduced by more than 60%, resulting in significant economic benefits.

[0023] (3) This invention is simple and safe to operate, and the product quality is stable. This invention does not change the main equipment and process conditions of the existing oxidation reaction. It only requires the addition of simple unit operations such as solvent addition, layering, neutralization, and filtration. The modification investment is small, the cycle is short, and it is easy to promote and apply to existing production equipment. The methane chloride solvent used is chemically stable and not easily oxidized and decomposed, so the operation is highly safe. By neutralizing and adjusting the pH value and through precision filtration, acidic substances and trace impurities in the organic phase are effectively removed, and the product purity can reach more than 99.3%, with stable and reliable quality. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments.

[0025] Example 1 In this embodiment, a stable solvent is added after the reaction, and the oxidation reaction of azobisisobutyronitrile is carried out according to the sodium bromide-hydrogen peroxide method. The specific steps are as follows: (1) Oxidation reaction: In a 1000L reactor, add 500L of 25% dilute sulfuric acid, start stirring, add 200kg of diisobutyronitrile hydrazine, and stir until completely dissolved. Then add 15kg of sodium bromide and dissolve evenly. Control the temperature of the reaction solution at 20℃, and slowly add 270kg of 27.5% hydrogen peroxide dropwise while stirring, controlling the dropping rate to maintain the reaction temperature between 20~25℃. After the addition is complete, continue stirring for 1.5h to complete the oxidation reaction.

[0026] (2) Solvent extraction: After the reaction is completed, add 100L of dichloromethane (about 10% of the total volume of the reaction system) to the reaction system, stir for 30min to fully dissolve the generated azobisisobutyronitrile, and let it stand to separate into layers.

[0027] (3) Separation and neutralization: Separate the lower layer of dichloromethane organic phase and transfer it to a neutralization vessel. Turn on the stirrer and control the temperature at 10°C. Slowly add a 0.5% sodium hydroxide solution to adjust the pH of the organic phase to 9.0. The neutralization time is 60 min.

[0028] (4) Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 0.01 μm at a filtration pressure of 0.1 MPa to obtain a clear organic solution.

[0029] (5) Post-processing: The filtered organic phase is sent to a crystallization kettle, cooled to 0°C for crystallization, centrifuged, and the solid is vacuum dried at 40°C to obtain azobisisobutyronitrile product.

[0030] Comparative Example 1 The comparative example follows the traditional sodium bromide-hydrogen peroxide washing process as follows: In a 1000L reactor, step (1) of Example 1 is completely repeated for the oxidation reaction. After the reaction, dichloromethane is not added; instead, the reaction solution is directly transferred to the washing reactor. An equal volume of clean water is added to the washing reactor for the first wash, followed by stirring, settling, and removal of the lower acidic layer. The washing process is repeated twice with the same amount of clean water as the first wash. The wastewater from the three washes is combined, resulting in a large total volume. The washed crude product is then neutralized with alkali (5% sodium hydroxide solution), washed with water until neutral, filtered, and dried to obtain the azobisisobutyronitrile (AIB) product.

[0031] Example 2 In this embodiment, a stable solvent is added before the reaction, and the oxidation reaction of azobisisobutyronitrile is carried out according to the chlorine method. The specific steps are as follows: (1) Solvent pre-addition and oxidation reaction: In a 1000L reactor, add 400L of 30% dilute sulfuric acid, start stirring, add 200kg of diisobutyronitrile hydrazine, and stir until completely dissolved. Then, before the reaction begins, add 400L of carbon tetrachloride (accounting for 50% of the total volume of the reaction system) to the reaction system to form an aqueous-organic two-phase system. Control the temperature of the reaction solution at 25℃, and continuously introduce chlorine gas (flow rate of about 2.0kg / h) for oxidation reaction. By controlling the chlorine gas introduction rate, the reaction temperature is maintained between 25~30℃, and the reaction is carried out for 3 hours.

[0032] (2) Separation and neutralization: After the reaction is completed, let it stand to separate the layers, separate the lower organic phase of carbon tetrachloride, and transfer it to a neutralization vessel. Turn on the stirrer and control the temperature at 40°C. Add ammonia water with a mass concentration of 18% to adjust the pH of the organic phase to 7.5 and neutralize for 10 min.

[0033] (3) Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 10 μm at a filtration pressure of 0.5 MPa.

[0034] (4) Post-processing: The filtered organic phase was subjected to vacuum distillation to recover carbon tetrachloride. The remaining crude product was recrystallized with methanol and dried to obtain azobisisobutyronitrile product.

[0035] Comparative Example 2 The comparative example follows the traditional chlorine-based water washing process as follows: 400L of 30% dilute sulfuric acid and 200kg of diisobutylonitrile hydrazine were added to a 1000L reactor and dissolved. Chlorine gas was introduced at 25℃ and the reaction was carried out for 3 hours. After the reaction, solvent extraction was not performed. The reaction solution was transferred to a water washing reactor and repeatedly washed and separated with a large amount of clean water (three times the volume of the reaction solution) to remove the acidic mother liquor. Subsequent neutralization, washing, filtration, and drying steps were the same as in Comparative Example 1. Wastewater generation includes the total mass of water introduced from the raw materials in the production process and water generated during the reaction process (including post-treatment washing water, centrifugal washing water, and alkali neutralization water).

[0036] Even with the wastewater treatment approach based on CN1785963A, the amount of washing wastewater generated is still enormous.

[0037] Example 3 In this embodiment, a stable solvent is added to the reaction, and the oxidation reaction of azobisisobutyronitrile is carried out according to the bromine-hydrogen peroxide method. The specific steps are as follows: (1) Oxidation reaction and mid-process solvent addition: In a 1000L reactor, add 300L of 35% dilute sulfuric acid, start stirring, add 200kg of diisobutyronitrile hydrazine, and stir until completely dissolved. Add 10kg of bromine and stir evenly. Control the reaction solution temperature at 15℃, and slowly add 240kg of 27.5% hydrogen peroxide. When the hydrogen peroxide has been added to 60% of the total volume (i.e., the reaction has proceeded to 50%), add 180L of chloroform (accounting for 30% of the total volume of the reaction system at this time) to the reaction system, and continue to add the remaining hydrogen peroxide. After the addition is complete, continue the reaction at 20℃ for 2 hours.

[0038] (2) Separation and neutralization: After the reaction is completed, the mixture is allowed to stand and separate into layers. The lower layer of chloroform organic phase is separated and transferred to a neutralization vessel. The temperature is controlled at 25°C, and a 20% potassium hydroxide solution is added to adjust the pH of the organic phase to 8.0. The mixture is then neutralized for 30 minutes.

[0039] (3) Precision filtration: The neutralized organic phase is filtered through a precision filter with a filtration accuracy of 1 μm at a filtration pressure of 0.3 MPa.

[0040] (4) Post-processing: The filtered organic phase is directly cooled and crystallized, centrifuged and dried to obtain azobisisobutyronitrile product.

[0041] Comparative Example 3 The comparative example follows the traditional bromine-hydrogen peroxide washing process as follows: In a 1000L reactor, step (1) of Example 3 is completely repeated for the oxidation reaction, but chloroform is not added during the process. After the reaction is completed, the product is obtained by the same multiple washing, neutralization, washing and drying process as in Comparative Example 1.

[0042] Table 1 shows the product testing and consumption during the preparation of azobisisobutyronitrile products in the above examples and comparative examples. The wastewater reduction rate of Example 1 was calculated based on Comparative Example 1; the wastewater reduction rate of Example 2 was calculated based on Comparative Example 2; and the wastewater reduction rate of Example 3 was calculated based on Comparative Example 3.

[0043] Table 1 Test Results

[0044] The embodiments 1, 2, and 3 of the present invention above achieved in-situ extraction of the product azobisisobutyronitrile by adding a specific volume (10%-50%) of stable solvent (dichloromethane, carbon tetrachloride, chloroform) at appropriate times before, during, and after the reaction. Subsequent neutralization (pH 7-10, temperature 10-40℃, time 10-60 min) and precision filtration (accuracy 0.01-10 μm, pressure 0.1-0.5 MPa) effectively removed acids and impurities from the organic phase. The results show that the method of the present invention, while maintaining or even slightly improving product yield (≥97.8%) and purity (≥99.3%), drastically reduced the fresh water consumption and process wastewater generated per ton of product from 15-30 tons in traditional processes to 1 ton, achieving a reduction rate of over 90%. Solvent recovery rates were all above 94%, achieving recycling and significantly reducing pollutant emissions and resource consumption at the source.

[0045] Comparative examples 1-3 demonstrate the results of using the traditional water washing-neutralization route for the three corresponding processes. To obtain a qualified product, a large amount of clean water (15-25 tons / ton of product) must be consumed for multiple washes to remove the acidic mother liquor, generating an equal or even greater amount of acidic saline wastewater. Although the product yield and purity are acceptable, the huge water consumption and wastewater treatment costs constitute a serious environmental and economic burden.

Claims

1. A method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile (AIBN), characterized in that, In the oxidation process of producing azobisisobutyronitrile, a stable solvent is added before, during, or after the reaction. After the reaction is completed, the mixture is allowed to stand and separate into layers. The organic phase is then neutralized to a pH of 7-10, filtered, and post-treated to obtain the azobisisobutyronitrile product.

2. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 1, characterized in that, The method for producing azobisisobutyronitrile is the sodium bromide-hydrogen peroxide method, the chlorine method, or the bromine-hydrogen peroxide method.

3. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 2, characterized in that, The sodium bromide-hydrogen peroxide method involves adding a stable solvent to the reaction system after the reaction is complete.

4. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 2, characterized in that, The chlorine method involves adding a stable solvent to the reaction system before the reaction begins.

5. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 2, characterized in that, The bromine-hydrogen peroxide method involves adding a stable solvent to the reaction system during the reaction process.

6. The method for treating a large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to any one of claims 1-5, characterized in that, The stabilizing solvent is one or more of dichloromethane, trichloromethane, and carbon tetrachloride, and the amount of stabilizing solvent added is 10% to 50% of the total volume of the reaction system.

7. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 6, characterized in that, The organic phase neutralization uses a sodium hydroxide solution with a mass concentration of 0.5% to 30%, ammonia water with a mass concentration of 1% to 18%, or potassium hydroxide solution with a mass concentration of 1% to 20%.

8. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 7, characterized in that, The neutralization of the organic phase was carried out at a temperature of 10-40℃, and the neutralization time was controlled at 10-60 min.

9. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 6, characterized in that, The filtration accuracy is 0.01~10μm, and the filtration pressure is 0.1~0.5MPa.

10. The method for treating the large amount of wastewater generated during the oxidation process in the production of azobisisobutyronitrile according to claim 6, characterized in that, The filtered organic phase can be used directly in the crystallization process of azobisisobutyronitrile, or crude azobisisobutyronitrile can be obtained by distillation to recover the solvent.

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