Method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid

Abstract

The invention relates to the technical field of chemical waste treatment and resource recovery, in particular to a method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, which comprises the following steps: 1, carrying out detailed component analysis on the pyridine hydrochloride acetonitrile waste liquid by gas chromatography, determining the content of pyridine hydrochloride and acetonitrile in the filtrate, calculating the dosage of NaOH, adding solid NaOH accounting for 2-5wt% of the filtrate and polyethylene glycol accounting for 1-5wt% of the filtrate under the condition of 10-20 DEG C, and treating for 15-60 minutes through ultrasonic equipment, so that the solid NaOH and the polyethylene glycol fully react with the filtrate to obtain a mixed solution; 2, filtering out sodium chloride and excessive sodium hydroxide from the mixed solution obtained in the step 1 through a sand core funnel organic filter membrane; according to the scheme, separation operation is simple and convenient, separation is difficult due to azeotropy of pyridine and water and introduction of water in an alkali-adding neutralization section in a traditional treatment method, and the method does not introduce water, shortens the separation process, is easy to operate and is suitable for large-scale production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical waste treatment and resource recovery, and particularly to a method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid. Background Art

[0002] In the process of chemical production, pyridine hydrochloride is produced as a by-product or waste, which contains a large amount of valuable pyridine. However, due to the stability and treatment difficulty of pyridine hydrochloride, traditional treatment methods are often inefficient and prone to environmental pollution. Therefore, how to efficiently recover and utilize pyridine from pyridine hydrochloride has become an important topic in the current field of chemical waste treatment.

[0003] Patent CN103012252A invented a method for recovering pyridine from an aqueous solution of pyridine hydrochloride. In this method, dichloroethane is used as an extractant for two-stage extraction distillation, and then rectification is carried out. The obtained pyridine recovery rate is higher, reaching 90-95%. It can not only reduce resource waste but also not pollute the environment, reduce production costs, and improve economic benefits.

[0004] Patent CN102584684A invented a method for recovering pyridine from the waste pyridine hydrochloride in the production of chloromethyl isopropyl carbonate and recycling it. It includes the following technological steps: putting pyridine hydrochloride and water into a container in a ratio of 1:2 and stirring to obtain an aqueous solution of pyridine hydrochloride. Putting the aqueous solution of pyridine hydrochloride and liquid alkali twice the amount of pyridine hydrochloride into an enamel reaction kettle, stirring fully and reacting to generate pyridine and an aqueous solution of sodium chloride. The above pyridine and aqueous solution of sodium chloride are automatically layered under static conditions. The upper layer is pyridine with water, and the lower layer is an aqueous solution of sodium chloride. Taking out the upper layer of pyridine with water, removing impurities by the precipitation method, and removing the remaining water by the rectification method to obtain the finished product.

[0005] Currently, the methods for recovering pyridine from pyridine hydrochloride mainly include distillation recovery, alkalization treatment, extraction recovery, etc. However, these methods have certain limitations in practical applications. For example, the distillation recovery method is simple and easy to operate, but it has high energy consumption and low recovery rate; the alkalization treatment method can improve the recovery rate, but it requires a large amount of alkaline solution, increasing the cost and environmental burden; the extraction recovery method has problems such as large consumption of organic solvents and complex operation. Therefore, it is necessary to develop a more efficient and environmentally friendly recovery method.

[0006] It should be noted that the above content belongs to the technical cognition scope of the inventor and does not necessarily constitute the prior art. Summary of the Invention

[0007] Technical problems to be solved: Although the distillation recovery method is simple and easy to implement, it has high energy consumption and low recovery rate; although the alkalization treatment method can improve the recovery rate, it requires the use of a large amount of alkaline solution, increasing the cost and environmental burden; the extraction recovery method has problems such as large consumption of organic solvents and complex operations.

[0008] In view of the deficiencies of the prior art, the present invention provides a method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, thereby solving the technical problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, the method comprising the following steps: Step 1: Conduct a detailed component analysis of the reaction filtrate for producing p-phenylene-bis(trimellitic anhydride) by gas chromatography, determine the contents of pyridine hydrochloride and acetonitrile in the filtrate, calculate the dosage of NaOH, add 2-5 wt% of solid NaOH and 1-5 wt% of polyethylene glycol to the filtrate at 10-20 °C, and simultaneously treat it with an ultrasonic device for 15-60 minutes to fully react with the filtrate to obtain a mixed solution; Step 2: Filter the mixed solution obtained in Step 1 through a sand core funnel organic filter membrane to remove sodium chloride and excessive sodium hydroxide, and collect the organic phase Φ; Step 3: Introduce the organic phase Φ collected in Step 2 into the bottom of the distillation column and distill it at atmospheric pressure. The distillation column is heated at atmospheric pressure. When the top temperature of the column is 79-81 °C, collect the first fraction of acetonitrile; Step 4: Continue to heat and reflux the remaining organic phase Φ in Step 3. When the top of the column is at 115-115.5 °C, collect the second fraction of pyridine.

[0010] In a possible implementation, the reaction filtrate for producing p-phenylene-bis(trimellitic anhydride) in Step 1 specifically consists of acetonitrile, pyridine, and pyridine hydrochloride, where acetonitrile accounts for 83-89%, pyridine accounts for 2-5%, pyridine hydrochloride accounts for 2-6%, and impurities account for 1-2.5%.

[0011] In a possible implementation, the calculation methods for the recovery rates of acetonitrile and pyridine in Step 3 and Step 4 are as follows: Weigh the acetonitrile obtained in Step 3, denoted as m2, and calculate the recovery rate R, R = (m2 / m1) × 100%, where m1 is the mass of acetonitrile in the pyridine hydrochloride acetonitrile waste liquid; Weigh the pyridine obtained in Step 4, denoted as m, and calculate the recovery rate R, R = (m / m0) × 100%, where m0 is the mass of pyridine in the pyridine hydrochloride acetonitrile waste liquid.

[0012] In a possible implementation, the solid NaOH in Step 1 can be selected from one of flaky, powdery, and granular forms.

[0013] In a possible implementation, gas chromatography analysis is used to detect the purity of acetonitrile and pyridine in Step 3 and Step 4.

[0014] In a possible implementation, the distillation column in Step 3 and Step 4 is a packed glass distillation column with a diameter of φ25. The packing is φ3 stainless steel triangular spiral packing. The column length is 400 mm, the height equivalent to a theoretical plate is 40 mm, and the number of theoretical plates is 10. High-resolution packing can be added inside to improve the separation efficiency of acetonitrile and pyridine.

[0015] Advantages compared with the prior art: 1. The separation operation of this solution is simple and convenient. In the traditional treatment method, pyridine forms an azeotrope with water, and the introduction of water in the alkali neutralization section causes separation difficulties. This method does not introduce water, simplifies the separation process, is easy to operate, and is suitable for large-scale production applications. 2. This solution has little environmental pollution and a high recovery rate. The recovery method adopted in the present invention does not require the use of additional extraction reagents, produces less waste, has little impact on the environment, and the recovery rate can reach over 95%. Specific implementation mode

[0016] The preferred embodiments of the present invention are described in detail. However, the present invention can be implemented in various different forms. Therefore, the present invention is not limited to the embodiments described below. The technical solutions in the embodiments of the present application are to solve the problems in the above background technology. The general idea is as follows: Example 1: A method for recovering anhydrous acetonitrile and anhydrous pyridine from a pyridine hydrochloride - acetonitrile waste liquid, the specific steps are as follows: (1) Take 100 g of the reaction filtrate of p-phenylene-bis(phthalic anhydride), analyze its components by gas chromatography. Among them, acetonitrile accounts for 88.3%, pyridine accounts for 4.4%, pyridine hydrochloride accounts for 5.2%, and impurities account for 2.1%. Add 2% of powdery NaOH and 1% of polyethylene glycol to the reaction filtrate, and perform ultrasonic reaction at 10 °C and 40 KHz for 15 min to obtain a mixed solution. NaOH reacts with pyridine hydrochloride to generate pyridine, sodium chloride and water, reducing pyridine. Pyridine - water - acetonitrile forms a minimum azeotrope and is difficult to separate. Excessive NaOH has a strong water absorption capacity, forming sodium hydroxide monohydrate, destroying the azeotropic system, and making it easy to separate acetonitrile and pyridine. NaOH is insoluble in acetonitrile and pyridine. After absorbing water, it reduces the solubility of the generated sodium chloride, making it easier to separate the organic phase and the inorganic phase. (2) Perform solid-liquid separation on the mixed solution obtained in step (1) through a sand core funnel organic filter membrane with a pore size of 0.22 μm to filter out sodium chloride and excessive sodium hydroxide, and collect the organic phase Φ; (3) The organic phase Φ collected in step (2) is rectified under normal pressure in a rectification column, heated to reflux, and the fraction collected at 79 °C is the first fraction, namely acetonitrile; The rectification column is a packed glass rectification column with a diameter of φ25, the packing is φ3 stainless steel triangular spiral packing, the column length is 400 mm, the height equivalent to a theoretical plate is 40 mm, and the number of theoretical plates is 10. High-resolution packing can be added inside it to improve the separation efficiency of acetonitrile and pyridine; (4) Continue to heat the remaining organic phase Φ in step (3) to reflux, and the fraction collected at 115 °C is the second fraction, namely pyridine; Weigh the obtained pyridine and record it as m, calculate the recovery rate R, R = (m / m0) × 100%, where m0 is the mass of pyridine in the pyridine hydrochloride acetonitrile waste liquid; weigh the obtained acetonitrile and record it as m2, calculate the recovery rate R, R = (m2 / m1) × 100%, where m1 is the mass of acetonitrile in the pyridine hydrochloride acetonitrile waste liquid; After detection, the recovery rate of acetonitrile is 84.43%, and the recovery rate of pyridine is 81.57%; use gas chromatography to analyze and detect the purity of acetonitrile and pyridine. After detection, the purity of acetonitrile is 92.63%, the purity of pyridine is 92.87%, and the Karl Fischer moisture analyzer measures that the water content of acetonitrile and pyridine is below 50 ppm.

[0017] In summary, the mechanism of this recovery process is as follows: 1. NaOH reacts with pyridine hydrochloride to generate pyridine, sodium chloride and water, reducing pyridine hydrochloride; 2. Polyethylene glycol has a certain solubility for NaOH, which can increase the mass transfer efficiency of the medium and make the reaction proceed faster; 3. Pyridine - water - acetonitrile forms a minimum azeotrope and is difficult to separate. Excessive sodium hydroxide has a strong water absorption capacity to form sodium hydroxide monohydrate, destroying the azeotropic system and making it easy to separate acetonitrile and pyridine; 4. Sodium hydroxide is insoluble in acetonitrile and pyridine. After absorbing water, it reduces the solubility of the generated sodium chloride, making it easier to separate the organic phase and the inorganic phase; 5. Sodium hydroxide itself can be used as a dehydration solvent for pyridine dehydration, playing a protective role for the generated pyridine;

[0018] Example 2: A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, the specific steps are as follows: (1) Take 100 g of the reaction filtrate of p-phenylene-bis(trimellitic anhydride), add 5 g of powdered NaOH and 5 g of polyethylene glycol to the reaction filtrate, and carry out an ultrasonic reaction at 20 °C and 40 KHz for 60 min to obtain a mixed solution; (2) Carry out solid-liquid separation on the mixed solution obtained in step (1) through a sand core funnel organic filter membrane with a pore size of 0.22 μm, filter off sodium chloride and excessive sodium hydroxide, and collect the organic phase Φ; (3) The organic phase Φ collected in step (2) is rectified at atmospheric pressure through a rectification column, heated to reflux, and the fraction collected at 81 °C is the first fraction, namely acetonitrile; (4) Continue to heat the remaining organic phase Φ in step (3) to reflux, and the fraction collected at 115.5 °C is the second fraction, namely pyridine; The recovery rate of acetonitrile is detected to be 95.61%, and the recovery rate of pyridine is 93.13%; the purity of acetonitrile and pyridine is detected by gas chromatography analysis. After detection, the purity of acetonitrile is 94.92%, the purity of pyridine is 91.77%, and the Karl Fischer moisture analyzer measures that the water content of acetonitrile and pyridine is less than 50 ppm; Example 3: A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, the specific steps are as follows: (1) Take 100 g of the reaction filtrate of p-phenylene-bis(trimellitic anhydride), add 4.32 g of powdered NaOH and 5 g of polyethylene glycol, and carry out an ultrasonic reaction at 10 °C and 40 KHz for 30 min to obtain a mixed solution; (2) Carry out solid-liquid separation on the mixed solution obtained in step (1) through a sand core funnel organic filter membrane with a pore size of 0.22 μm, filter off sodium chloride and excessive sodium hydroxide, and collect the organic phase Φ; (3) The organic phase Φ collected in step (2) is rectified at atmospheric pressure through a rectification column, heated to reflux, and the fraction collected at 80.2 °C is the first fraction, namely acetonitrile; (4) Continue to heat the remaining organic phase Φ in step (3) to reflux, and the fraction collected at 115.2 °C is the second fraction, namely pyridine; The recovery rate of acetonitrile is detected to be 98%, and the recovery rate of pyridine is 97%; the purity of acetonitrile and pyridine is detected by gas chromatography analysis. After detection, the purity of acetonitrile is 99.82%, the purity of pyridine is 99.57%, and the Karl Fischer moisture analyzer measures that the water content of acetonitrile and pyridine is less than 50 ppm; Comparative Example 1: The difference between this comparative example and Example 1 is that flaky or granular NaOH is added; (1) Take 100 g of pyridine hydrochloride acetonitrile waste liquid and place it in a 250 ml single-necked flask, add 4.32 g of flaky NaOH and 5 g of polyethylene glycol, and carry out ultrasonic treatment at 10 °C and 40 KHz for 30 min to obtain a mixed solution; (2) The mixed solution obtained in step (1) is subjected to solid-liquid separation through a sand core funnel organic filter membrane with a pore size of 0.22 μm to filter off sodium chloride and excessive sodium hydroxide, and the organic phase Φ is collected; (3) The organic phase Φ collected in step (2) is rectified under atmospheric pressure in a rectification column, heated and refluxed to 81.2 °C to recover the first fraction, i.e., acetonitrile; (4) The remaining organic phase Φ in step (3) is continuously heated and refluxed to 115.5 °C to recover the second fraction, i.e., pyridine.

[0019] The detection methods for the recovery rates and purities of acetonitrile and pyridine are as in Example 1. After detection, the recovery rate of acetonitrile is 93%, and the recovery rate of pyridine is 85%. Compared with Example 1, the reaction of the powder is faster, and the reaction of the flakes also occurs over a longer time, which does not affect the purity because the organic phase is recovered by rectification and impurities will remain at the bottom of the kettle; After detection, the purity of acetonitrile is 99.32% and the purity of pyridine is 99.27%. The water content is determined to be less than 50 ppm by a Karl Fischer moisture meter. It can be seen that the mass transfer between the flaky NaOH and the organic phase is poor, and the pyridine hydrochloride cannot be fully reduced, resulting in a decrease in the recovery rates of acetonitrile and pyridine; Comparative Example 2: The difference between this comparative example and Example 1 is that polyethylene glycol is not added; (1) Take 100 g of the pyridine hydrochloride acetonitrile waste liquid and place it in a 250 ml single-necked flask. Add 4.32 g of powdered NaOH and ultrasonically treat it at 20 °C and 40 KHz for 30 min to obtain a mixed solution; (2) The mixed solution obtained in step (1) is subjected to solid-liquid separation through a sand core funnel organic filter membrane with a pore size of 0.22 μm to filter off sodium chloride and excessive sodium hydroxide, and the organic phase Φ is collected; (3) The organic phase Φ collected in step (2) is rectified under atmospheric pressure in a rectification column, heated and refluxed to 81.2 °C to recover the first fraction, i.e., acetonitrile; (4) The remaining organic phase Φ in step (3) is continuously heated and refluxed to 115.5 °C to recover the second fraction, i.e., pyridine.

[0020] The detection methods for the recovery rates and purities of acetonitrile and pyridine are as in Example 1. After detection, the recovery rate of acetonitrile is 91%, and the recovery rate of pyridine is 84%. Compared with Example 1, adding polyethylene glycol can increase the mass transfer efficiency of the medium and make the reaction proceed faster, but it does not affect the purity because the organic phase is recovered by rectification and impurities will remain at the bottom of the kettle; After detection, the purity of acetonitrile is 99.17% and the purity of pyridine is 99.06%. The water content is determined to be less than 50 ppm by a Karl Fischer moisture meter. It can be seen that without adding polyethylene glycol, the mass transfer between NaOH and the organic phase is poor, and the pyridine hydrochloride cannot be fully reduced, resulting in a decrease in the recovery rates of acetonitrile and pyridine; Comparative Example 3: The difference between this comparative example and Example 1 is that an aqueous NaOH solution is added; (1) Take 100 g of the acetonitrile waste liquid of pyridine hydrochloride and place it in a 250 ml single-necked flask. Add 43.2 g of 10% aqueous NaOH solution and ultrasonically treat it at 12 °C and 40 KHz for 30 min to obtain a mixed solution; (2) Filter off sodium chloride and excess sodium hydroxide from the mixed solution obtained in step (1) through a sand core funnel organic filter membrane, and collect the organic phase Φ; (3) Subject the organic phase Φ obtained in step (2) to atmospheric distillation through a distillation column, heat up and reflux to 81.2 °C to recover the first fraction, that is, acetonitrile; (4) Continue to heat up and reflux the remaining organic phase Φ in step (3) to 115.5 °C to recover the second fraction, that is, pyridine; The detection methods for the recovery rates and purities of acetonitrile and pyridine are as in Example 1. After detection, the water content of acetonitrile is 28.4%, and the water content of pyridine is 18.6%. The final pyridine recovery rate is only 43%. After water is introduced into the reaction, acetonitrile forms a binary azeotrope with water, and pyridine also forms a binary azeotrope with water, which is not conducive to the recovery of pyridine; Comparative Example 4: The difference between this comparative example and Example 1 is that ultrasonic treatment is carried out at room temperature; (1) Take 100 g of the acetonitrile waste liquid of pyridine hydrochloride and place it in a 250 ml single-necked flask. Add 4.32 g of powdered NaOH and 5 g of polyethylene glycol, and ultrasonically treat it at room temperature and 40 KHz for 30 min to obtain a mixed solution; (2) Carry out solid-liquid separation on the mixed solution obtained in step (1) through a sand core funnel organic filter membrane with a pore size of 0.22 μm, filter off sodium chloride and excess sodium hydroxide, and collect the organic phase Φ; (3) Subject the organic phase Φ collected in step (2) to atmospheric distillation through a distillation column, heat up and reflux to 81.2 °C to recover the first fraction, that is, acetonitrile; (4) Continue to heat up and reflux the remaining organic phase Φ in step (3) to 115.5 °C to recover the second fraction, that is, pyridine; The detection methods for the recovery rates and purities of acetonitrile and pyridine are as in Example 1. After detection, the recovery rate of acetonitrile is 95%, and the recovery rate of pyridine is 87%; after detection, the purity of acetonitrile is 99.25%, and the purity of pyridine is 99.16%. The water content is measured to be less than 50 ppm by a Karl Fischer moisture meter. It can be seen that the temperature of the ultrasonic reaction has a greater impact on the reduction reaction effect. As an acid-base neutralization reaction, the reaction is set at 10 °C, and cooling promotes the reaction. The effect at room temperature is slightly worse, reducing the recovery rate.

[0021] Comparative Example 5: The difference between this comparative example and Example 1 is that the amount of NaOH used is reduced; (1) Take 100 g of pyridine hydrochloride acetonitrile waste liquid and place it in a 250 ml single-necked flask. Add 2.2 g of powdered granular NaOH and 5 g of polyethylene glycol, and ultrasonically treat for 30 min at 10 °C and 40 KHz to obtain a mixed solution; (2) Perform solid-liquid separation on the mixed solution obtained in step (1) through a sand core funnel organic filter membrane with a pore size of 0.22 μm to filter off sodium chloride and excessive sodium hydroxide, and collect the organic phase Φ; (3) The organic phase Φ collected in step (2) is rectified at atmospheric pressure through a rectification column. Heat up and reflux to 81.2 °C to recover the first fraction, that is, acetonitrile; (4) Continue to heat up and reflux the remaining organic phase Φ in step (3) to 115.5 °C to recover the second fraction, that is, pyridine.

[0022] The detection methods for the recovery rates and purities of acetonitrile and pyridine are as in Example 1. After detection, the recovery rate of acetonitrile is 95%, and the recovery rate of pyridine is 88%; after detection, the purity of acetonitrile is 98.51%, and the purity of pyridine is 98.46%. The water content measured by a Karl Fischer moisture meter is greater than 100 ppm. Reducing the amount of NaOH used can lead to incomplete reactions and reduced yields of acetonitrile and pyridine. A reasonable ratio promotes the full progress of the reaction and improves the recovery rate.

[0023] Comparative Example 6: The difference between this comparative example and Example 1 is that the extraction method is used to recover pyridine; (1) Take 100 g of pyridine hydrochloride acetonitrile waste liquid and rectify it at atmospheric pressure through a rectification column. Heat up and reflux to 81.2 °C to obtain acetonitrile, and collect the remaining slurry; (2) Add 50 g of dichloromethane to the slurry obtained in step (1), add 22 g of 10% NaOH aqueous solution, ultrasonically treat for 30 min at 10 °C, and after standing and phase separation, collect the organic phase Φ; (3) Heat up and reflux the organic phase Φ obtained in step (2), and collect the fraction at 39.8 - 40.2 °C, that is, dichloromethane; (4) Continue to heat up and reflux the organic phase Φ obtained in step (3) to 115.5 °C to recover pyridine; After determination, the content of acetonitrile is 93.12%, the water content is 6.88%, and the pyridine recovery rate is 81%. It can be seen that the process of recovering pyridine by the extraction method is complex and the recovery rate is limited. The alkali treatment introduces water and forms a binary azeotrope with pyridine, and a complex dehydration process is required to recover pyridine, which does not meet the requirements of simplified process treatment; In summary, the pyridine recovery rate obtained by the recovery method of the present invention is 97%, and the purity is 99.57%; the acetonitrile recovery rate is 98%, and the purity is 99.82%. The Karl Fischer moisture analyzer measures that the water content of acetonitrile and pyridine is less than 50 ppm. The recovery rate is high and the purity is high, and it can be directly used in the production of p-phenylene bis(trimellitic anhydride). The recovery process of the present invention is simple, improves production efficiency, reduces production costs, and can be applied to the large-scale and efficient recovery of pyridine from pyridine hydrochloride and acetonitrile waste liquid.

[0024] Each embodiment in this specification is described in a progressive manner. For the same and similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment.

[0025] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, rather than limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for recovering anhydrous acetonitrile and anhydrous pyridine from the waste liquid of pyridine hydrochloride and acetonitrile, characterized in that, The method includes the following steps: Step 1: Conduct a detailed component analysis of the reaction filtrate for producing p-phenylene bis(trimellitic anhydride dianhydride) by gas chromatography, determine the contents of pyridine hydrochloride and acetonitrile in the filtrate, calculate the dosage of NaOH, add 2-5 wt% of solid NaOH and 1-5 wt% of polyethylene glycol to the filtrate under the condition of 10-20 °C, and simultaneously process it with an ultrasonic device for 15-60 minutes to fully react with the filtrate to obtain a mixed solution; Step 2: Filter off sodium chloride and excessive sodium hydroxide from the mixed solution obtained in Step 1 through a sintered glass funnel organic filter membrane, and collect the organic phase Φ; Step 3: Introduce the organic phase Φ collected in Step 2 into the bottom of a distillation column, and distill it under atmospheric pressure. When the distillation column is heated under atmospheric pressure and the top temperature is 79-81 °C, collect the first fraction of acetonitrile; Step 4: Continue to heat the remaining organic phase Φ in Step 3 under reflux. When the top of the column is at 115-115.5 °C, collect the second fraction of pyridine.

2. A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The reaction filtrate for producing p-phenylene bis(trimellitic anhydride dianhydride) described in Step 1 is specifically composed of acetonitrile, pyridine, and pyridine hydrochloride, where acetonitrile accounts for 83-89%, pyridine accounts for 2-5%, pyridine hydrochloride accounts for 2-6%, and impurities account for 1-2.5%.

3. A method for recovering anhydrous acetonitrile and anhydrous pyridine from a pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The calculation methods for the recovery rates of acetonitrile and pyridine in Step 3 and Step 4 are as follows: Weigh the acetonitrile obtained in Step 3 and record it as m2. Calculate the recovery rate R, R = (m2 / m1) × 100%, where m1 is the mass of acetonitrile in the pyridine hydrochloride-acetonitrile waste liquid; Weigh the pyridine obtained in Step 4 and record it as m. Calculate the recovery rate R, R = (m / m0) × 100%, where m0 is the mass of pyridine in the pyridine hydrochloride-acetonitrile waste liquid.

4. A method for recovering anhydrous acetonitrile and anhydrous pyridine from a pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The solid NaOH described in Step 1 can be selected from one of flaky, powdery, and granular forms.

5. A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: Gas chromatography analysis is used to detect the purities of acetonitrile and pyridine in Step 3 and Step 4.

6. A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The distillation columns described in Step 3 and Step 4 are φ25 packed glass distillation columns with φ3 stainless steel triangular spiral packing, a column length of 400 mm, a height equivalent to one theoretical plate of 40 mm, and 10 theoretical plates. High-resolution packing can be added inside to improve the separation efficiency of acetonitrile and pyridine.

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