A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid

Abstract

The present invention relates to the technical field of chemical waste treatment and resource recovery, and in particular to a method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid. The method comprises the following steps: step 1: performing detailed component analysis on the pyridine hydrochloride acetonitrile waste liquid by gas chromatography, determining the contents of pyridine hydrochloride and acetonitrile in the filtrate, calculating the amount of NaOH used, adding 2-5 wt% of solid NaOH and 1-5 wt% of polyethylene glycol to the filtrate under the condition of 10-20 degrees Celsius, and simultaneously treating the mixture with an ultrasonic device for 15-60 minutes to fully react with the filtrate to obtain a mixed solution; step 2: filtering the mixed solution obtained in step 1 through a sand core funnel organic filter membrane to remove sodium chloride and excess sodium hydroxide. The separation operation of the scheme is simple and convenient to operate. In the traditional treatment method, pyridine and water are azeotroped, and water is introduced in the alkali neutralization stage, resulting in separation difficulties. 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 in particular to a method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid. Background Art

[0002] In chemical production processes, pyridine hydrochloride is produced as a byproduct or waste, and it contains a large amount of valuable pyridine. However, due to the stability and processing difficulty of pyridine hydrochloride, traditional treatment methods are often inefficient and prone to environmental pollution. Therefore, how to efficiently recycle pyridine from pyridine hydrochloride has become an important issue in the current field of chemical waste treatment.

[0003] Patent CN103012252A discloses a method for recovering pyridine from an aqueous solution of pyridine hydrochloride. Using dichloroethane as the extractant, this method undergoes two extractive distillations followed by rectification, resulting in a higher pyridine recovery rate of 90-95%. This method reduces resource waste, does not pollute the environment, and can lower production costs and improve economic efficiency.

[0004] Patent CN102584684A discloses a method for recovering and recycling pyridine from pyridine hydrochloride, a waste product from the production of chloromethyl isopropyl carbonate. The method comprises the following steps: pyridine hydrochloride and water in a 1:2 ratio are placed in a container and stirred to produce a pyridine hydrochloride aqueous solution. The pyridine hydrochloride aqueous solution and a 2-fold concentration of pyridine hydrochloride in a liquid caustic soda are placed in an enameled reactor, stirred thoroughly, and reacted to produce pyridine and a sodium chloride aqueous solution. The pyridine and sodium chloride aqueous solutions automatically separate into separate layers in a static state, with the upper layer containing water-containing pyridine and the lower layer containing sodium chloride. The upper layer containing water-containing pyridine is removed and impurities are removed by precipitation. The remaining water is then removed by distillation to produce the finished product.

[0005] Currently, methods for recovering pyridine from pyridine hydrochloride primarily include distillation, alkalization, and extraction. However, these methods have limitations in practical application. For example, while distillation is simple and easy to implement, it suffers from high energy consumption and low recovery rates. While alkalization can improve recovery rates, it requires the use of large amounts of alkaline solution, increasing costs and environmental burdens. Extraction, on the other hand, suffers from high organic solvent consumption and complex operations. Therefore, a more efficient and environmentally friendly recovery method is needed.

[0006] It should be noted that the above content falls within the technical knowledge of the inventor and does not necessarily constitute prior art. Summary of the Invention

[0007] Technical problems to be solved: Although the distillation recovery method is simple and easy, 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, which increases costs and environmental burden; the extraction recovery method has problems such as high organic solvent consumption and complex operation.

[0008] In view of the shortcomings 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 technology.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0010] A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, the method comprising the following steps:

[0011] Step 1: Performing detailed component analysis of the reaction filtrate from the production of p-phenylene trimellitic dianhydride by gas chromatography to determine the contents of pyridine hydrochloride and acetonitrile in the filtrate, calculating the amount of NaOH to be used, adding 2-5 wt% of solid NaOH and 1-5 wt% of polyethylene glycol to the filtrate at 10-20 degrees Celsius, and simultaneously treating with an ultrasonic device for 15-60 minutes to allow the NaOH and polyethylene glycol to fully react with the filtrate to obtain a mixed solution;

[0012] Step 2: Filter the mixed solution obtained in step 1 through a sand core funnel organic filter membrane to remove sodium chloride and excess sodium hydroxide, and collect the organic phase Φ;

[0013] Step 3: introducing the organic phase Φ collected in step 2 into the reactor of a distillation tower, performing distillation at normal pressure, heating the distillation tower at normal pressure, and collecting the first fraction, acetonitrile, when the top temperature is 79-81 degrees Celsius;

[0014] Step 4: Continue heating and reflux the remaining organic phase Φ from step 3, with the top of the tower at 115-115.5 degrees Celsius, and collect the second fraction, pyridine.

[0015] In one possible implementation, the reaction filtrate for producing p-phenylene-diphenyltrimethylol dianhydride in step 1 is specifically composed of acetonitrile, pyridine, and pyridine hydrochloride, wherein acetonitrile accounts for 83-89%, pyridine accounts for 2-5%, pyridine hydrochloride accounts for 2-6%, and impurities account for 1-2.5%.

[0016] In one possible implementation, the acetonitrile and pyridine recovery rates in step 3 and step 4 are calculated as follows:

[0017] 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;

[0018] 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.

[0019] In a possible implementation, the solid NaOH in step 1 can be in the form of flakes, powder, or granules.

[0020] In a possible implementation, in step three and step four, gas chromatography analysis is used to detect the purity of acetonitrile and pyridine.

[0021] In one possible implementation, the distillation tower described in step 3 and step 4 adopts a φ25 packed glass distillation tower, the packing is φ3 stainless steel triangular spiral packing, the tower column length is 400 mm, the equal plate height is 40 mm, and the theoretical plate number is 10. A high-separation filler can be added inside the distillation tower to improve the separation efficiency of acetonitrile and pyridine.

[0022] Beneficial effects compared with existing technologies:

[0023] 1. The separation operation of this scheme is simple and convenient. In the traditional treatment method, pyridine and water are azeotroped, and water is introduced in the alkali neutralization process, which makes separation difficult. This method does not introduce water, shortens the separation process, is easy to operate, and is suitable for large-scale production applications;

[0024] 2. This solution has low environmental pollution and high recovery rate. The recovery method adopted by the present invention does not require the use of additional extraction reagents, generates little waste, has little impact on the environment, and the recovery rate can reach more than 95%. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in detail. However, the present invention can be implemented in various forms, so the present invention is not limited to the embodiments described below.

[0026] The technical solution in the embodiments of the present application is to solve the problems of the above-mentioned background technology, and the overall idea is as follows:

[0027] Example 1:

[0028] A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, comprising the following steps:

[0029] (1) Take 100 g of the reaction filtrate of p-phenylene-diphenyltrimethylolpropane dianhydride and analyze its composition by gas chromatography, wherein 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 the reaction filtrate to the powdered NaOH and 1% of the reaction filtrate to the polyethylene glycol, and ultrasonically react at 10°C and 40 kHz for 15 minutes to obtain a mixed solution;

[0030] NaOH reacts with pyridine hydrochloride to form pyridine, sodium chloride, and water, reducing pyridine. Pyridine, water, and acetonitrile form a minimum azeotrope that is difficult to separate. Excess NaOH has a strong water absorption capacity, forming sodium hydroxide monohydrate, which destroys the azeotropic system and makes it easier 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 the organic and inorganic phases more easily separated.

[0031] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0032] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, heated and refluxed, and the fraction at 79°C is extracted as the first fraction, i.e., acetonitrile;

[0033] The distillation tower adopts a φ25 packed glass distillation tower, the packing is φ3 stainless steel triangular spiral packing, the tower column length is 400mm, the plate height is 40mm, and the theoretical plate number is 10. High-separation fillers can be added inside to improve the separation efficiency of acetonitrile and pyridine;

[0034] (4) The remaining organic phase Φ from step (3) is further heated and refluxed, and a fraction at 115°C is extracted as the second fraction, i.e., pyridine;

[0035] The obtained pyridine was weighed and recorded as m, and the recovery rate R was calculated, R = (m / m0) × 100%, m0 is the mass of pyridine in the pyridine hydrochloride acetonitrile waste liquid; the obtained acetonitrile was weighed and recorded as m2, and the recovery rate R was calculated, R = (m2 / m1) × 100%, m1 is the mass of acetonitrile in the pyridine hydrochloride acetonitrile waste liquid;

[0036] The recovery rate of acetonitrile was 84.43%, and the recovery rate of pyridine was 81.57%. The purity of acetonitrile and pyridine was detected by gas chromatography, and the purity of acetonitrile was 92.63%, and the purity of pyridine was 92.87%. The water content of acetonitrile and pyridine was determined to be below 50 ppm by a Karl-Heinz moisture analyzer.

[0037] In summary, the recycling process mechanism is as follows:

[0038] 1. NaOH reacts with pyridine hydrochloride to generate pyridine, sodium chloride and water, and reduces pyridine hydrochloride;

[0039] 2. Polyethylene glycol has a certain solubility in NaOH, which can increase the mass transfer efficiency of the medium and make the reaction proceed faster;

[0040] 3. Pyridine-water-acetonitrile forms the lowest azeotrope which is difficult to separate. Excessive sodium hydroxide has a strong water absorption capacity, forming sodium hydroxide monohydrate, which destroys the azeotropic system and makes acetonitrile and pyridine easy to separate;

[0041] 4. Sodium hydroxide is insoluble in acetonitrile and pyridine. After absorbing water, the solubility of the generated sodium chloride is reduced, making the organic and inorganic phases better separated;

[0042] 5. Sodium hydroxide itself can be used as a dehydration solvent for pyridine dehydration, and plays a protective role on the generated pyridine;

[0043]

[0044] Example 2:

[0045] A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, comprising the following steps:

[0046] (1) Take 100 g of the reaction filtrate of p-phenylene-diphenyltrimethylolpropane dianhydride, add 5 g of the reaction filtrate of powdered NaOH and 5 g of polyethylene glycol, and ultrasonically react at 20°C and 40 kHz for 60 min to obtain a mixed solution;

[0047] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0048] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, heated and refluxed, and the fraction at 81°C is extracted as the first fraction, i.e., acetonitrile;

[0049] (4) The remaining organic phase Φ from step (3) is further heated and refluxed, and a fraction at 115.5°C is extracted as the second fraction, i.e., pyridine;

[0050] The recovery rate of acetonitrile was 95.61%, and the recovery rate of pyridine was 93.13%. The purity of acetonitrile and pyridine was tested by gas chromatography, and the purity of acetonitrile was 94.92%, and the purity of pyridine was 91.77%. The water content of acetonitrile and pyridine was less than 50 ppm as determined by a Karl-Heinz moisture analyzer.

[0051] Example 3:

[0052] A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, comprising the following steps:

[0053] (1) Take 100 g of the reaction filtrate of p-phenylene-diphenyltrimethylolpropane dianhydride, add 4.32 g of powdered NaOH and 5 g of polyethylene glycol, and ultrasonically react at 10°C and 40 kHz for 30 min to obtain a mixed solution;

[0054] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0055] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, heated and refluxed, and the fraction at 80.2°C is taken as the first fraction, i.e., acetonitrile;

[0056] (4) The remaining organic phase Φ from step (3) is further heated and refluxed, and a fraction at 115.2°C is extracted as the second fraction, i.e., pyridine;

[0057] The recovery rate of acetonitrile was 98%, and the recovery rate of pyridine was 97%. The purity of acetonitrile and pyridine was tested by gas chromatography, and the purity of acetonitrile was 99.82%, and the purity of pyridine was 99.57%. The water content of acetonitrile and pyridine was less than 50 ppm as determined by a Karl-Heinz moisture analyzer.

[0058] Comparative Example 1:

[0059] The difference between this comparative example and Example 1 is that flaky and granular NaOH is added;

[0060] (1) 100 g of pyridine hydrochloride acetonitrile waste liquid was placed in a 250 ml single-necked flask, 4.32 g of flaked NaOH and 5 g of polyethylene glycol were added, and ultrasonic treatment was performed at 10°C and 40 kHz for 30 min to obtain a mixed solution;

[0061] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0062] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, and the temperature is raised to 81.2°C and refluxed to recover the first fraction, i.e., acetonitrile;

[0063] (4) The remaining organic phase Φ from step (3) is further heated and refluxed to 115.5°C to recover the second fraction, i.e., pyridine.

[0064] The recovery rate and purity of acetonitrile and pyridine were determined as in Example 1. The recovery rate of acetonitrile and pyridine was 93% and 85% respectively. Compared with Example 1, the powder reacted faster and the flakes reacted even after a long time without affecting the purity. The organic phase was recovered by distillation, and the impurities remained at the bottom of the kettle.

[0065] The purity of acetonitrile was 99.32%, and the purity of pyridine was 99.27%. The water content was less than 50 ppm as determined by a Karl-Friedrich moisture analyzer. This indicates that the mass transfer between the flaky NaOH and the organic phase was poor, and that the pyridine hydrochloride could not be fully reduced, resulting in a reduced recovery of acetonitrile and pyridine.

[0066] Comparative Example 2:

[0067] The difference between this comparative example and Example 1 is that polyethylene glycol was not added;

[0068] (1) 100 g of pyridine hydrochloride acetonitrile waste liquid was placed in a 250 ml single-necked flask, 4.32 g of powdered NaOH was added, and ultrasonic treatment was performed at 20°C and 40 kHz for 30 min to obtain a mixed solution;

[0069] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0070] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, and the temperature is raised to 81.2°C and refluxed to recover the first fraction, i.e., acetonitrile;

[0071] (4) The remaining organic phase Φ from step (3) is further heated and refluxed to 115.5°C to recover the second fraction, i.e., pyridine.

[0072] The recovery and purity of acetonitrile and pyridine were determined as in Example 1. The recovery of acetonitrile was 91%, and the recovery of pyridine was 84%. Compared to Example 1, the addition of polyethylene glycol increased the mass transfer efficiency of the medium, allowing the reaction to proceed more quickly without affecting the purity, because the organic phase was recovered by distillation, and impurities remained at the bottom of the reactor.

[0073] The purity of acetonitrile was 99.17%, and the purity of pyridine was 99.06%. The water content was less than 50 ppm as determined by a Karl-Friedman moisture analyzer. This indicates that without the addition of polyethylene glycol, the mass transfer between NaOH and the organic phase is poor, pyridine hydrochloride cannot be fully reduced, and the recovery rates of acetonitrile and pyridine are reduced.

[0074] Comparative Example 3:

[0075] The difference between this comparative example and Example 1 is that NaOH aqueous solution is added;

[0076] (1) 100 g of pyridine hydrochloride acetonitrile waste liquid was placed in a 250 ml single-necked flask, 43.2 g of 10% NaOH aqueous solution was added, and ultrasonic treatment was performed at 12 °C and 40 kHz for 30 min to obtain a mixed solution;

[0077] (2) filtering the mixed solution obtained in step (1) through a sand core funnel organic filter membrane to remove sodium chloride and excess sodium hydroxide, and collecting the organic phase Φ;

[0078] (3) The organic phase Φ obtained in step (2) is subjected to atmospheric distillation in a distillation tower, and the temperature is raised to 81.2° C. to reflux and recover the first fraction, i.e., acetonitrile;

[0079] (4) The remaining organic phase Φ from step (3) is further heated and refluxed to 115.5°C to recover the second fraction, i.e., pyridine;

[0080] The recovery and purity detection methods of acetonitrile and pyridine are as in Example 1. 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 the introduction of water into the reaction, acetonitrile and water form a binary azeotrope, and pyridine and water also form a binary azeotrope, which is not conducive to the recovery of pyridine.

[0081] Comparative Example 4:

[0082] The difference between this comparative example and Example 1 is that the ultrasonic treatment is performed at room temperature;

[0083] (1) 100 g of pyridine hydrochloride acetonitrile waste liquid was placed in a 250 ml single-necked flask, 4.32 g of powdered NaOH and 5 g of polyethylene glycol were added, and ultrasonic treatment was performed at room temperature and 40 kHz for 30 min to obtain a mixed solution;

[0084] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0085] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, and the temperature is raised to 81.2°C and refluxed to recover the first fraction, i.e., acetonitrile;

[0086] (4) The remaining organic phase Φ from step (3) is further heated and refluxed to 115.5°C to recover the second fraction, i.e., pyridine;

[0087] The recovery and purity detection methods of acetonitrile and pyridine are as in Example 1. The recovery of acetonitrile and the recovery of pyridine are 95% and 87% respectively. The purity of acetonitrile and pyridine are 99.25% and 99.16% respectively. The water content is less than 50 ppm as measured by a Karl-Heinz moisture meter. It can be seen that the temperature of the ultrasonic reaction has a greater influence on the reduction reaction effect. As an acid-base neutralization reaction, the reaction is set to 10°C. Cooling promotes the reaction. The effect at room temperature is slightly worse, which reduces the recovery rate.

[0088] Comparative Example 5:

[0089] The difference between this comparative example and Example 1 is that the amount of NaOH is reduced;

[0090] (1) 100 g of pyridine hydrochloride acetonitrile waste liquid was placed in a 250 ml single-necked flask, 2.2 g of powdered granular NaOH and 5 g of polyethylene glycol were added, and ultrasonic treatment was performed at 10°C and 40 kHz for 30 min to obtain a mixed solution;

[0091] (2) The mixed solution obtained in step (1) was passed through a sand core funnel organic filter membrane with a pore size of 0.22 μm to separate the solid and liquid, and the sodium chloride and excess sodium hydroxide were filtered out, and the organic phase Φ was collected;

[0092] (3) The organic phase Φ collected in step (2) is distilled in a distillation tower at atmospheric pressure, and the temperature is raised to 81.2°C and refluxed to recover the first fraction, i.e., acetonitrile;

[0093] (4) The remaining organic phase Φ from step (3) is further heated and refluxed to 115.5°C to recover the second fraction, i.e., pyridine.

[0094] The recovery and purity detection methods of acetonitrile and pyridine are as in Example 1. The recovery of acetonitrile and the recovery of pyridine are 95% and 88% respectively. The purity of acetonitrile and pyridine are 98.51% and 98.46% respectively respectively. The water content is greater than 100 ppm as determined by a Karl-Heinz moisture analyzer. Reducing the amount of NaOH may result in insufficient reaction and reduced acetonitrile and pyridine yields. A reasonable ratio promotes the full progress of the reaction and improves the recovery.

[0095] Comparative Example 6:

[0096] The difference between this comparative example and Example 1 is that the pyridine is recovered by extraction;

[0097] (1) Take 100g of pyridine hydrochloride acetonitrile waste liquid and distill it through a distillation tower at atmospheric pressure, raise the temperature and reflux it to 81.2℃ acetonitrile, and collect the remaining slurry;

[0098] (2) Add 50 g of dichloromethane and 22 g of 10% NaOH aqueous solution to the slurry obtained in step (1), ultrasonically treat at 10°C for 30 min, let it stand for phase separation, and collect the organic phase Φ;

[0099] (3) The organic phase Φ obtained in step (2) is heated and refluxed to extract a fraction at 39.8-40.2°C, i.e., dichloromethane;

[0100] (4) The organic phase Φ obtained in step (3) is further heated and refluxed to 115.5°C to recover pyridine;

[0101] The acetonitrile content was determined to be 93.12%, the water content was 6.88%, and the pyridine recovery rate was 81%. It can be seen that the extraction method for recovering pyridine is complex and has a limited recovery rate. The alkali treatment introduces water and azeotropes with pyridine, and the recovery of pyridine requires a complex dehydration process, which does not meet the treatment requirements of a simplified process.

[0102] In summary, the recovery rate of pyridine obtained by the recovery method of the present invention is 97%, and the purity is 99.57%; the recovery rate of acetonitrile is 98%, and the purity is 99.82%. The water content of acetonitrile and pyridine is less than 50 ppm as measured by a Karl Feixiu moisture meter. The recovery rate and purity are high, and the product can be directly used in the production of p-phenylene-diphenyltrimethylammonium dianhydride. The recovery process of the present invention is simple, the production efficiency is improved, the production cost is reduced, and the product can be applied to the large-scale and efficient recovery of pyridine from pyridine hydrochloride acetonitrile waste liquid.

[0103] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are described briefly because they are generally similar to the method embodiments. For relevant parts, refer to the description of the method embodiments.

[0104] Finally, it should be noted that the above embodiments are merely examples for the purpose of illustrating the present invention and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all embodiments. However, obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid, characterized in that: The method comprises the following steps: Step 1: Performing detailed component analysis of the reaction filtrate from the production of p-phenylene trimellitic dianhydride by gas chromatography to determine the contents of pyridine hydrochloride and acetonitrile in the filtrate, calculating the amount of NaOH to be used, adding 2-5 wt% of solid NaOH and 1-5 wt% of polyethylene glycol to the filtrate at 10-20 degrees Celsius, and simultaneously treating with an ultrasonic device for 15-60 minutes to allow the NaOH and polyethylene glycol 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 excess sodium hydroxide, and collect the organic phase Φ; Step 3: introducing the organic phase Φ collected in step 2 into the reactor of a distillation tower, performing distillation at normal pressure, heating the distillation tower at normal pressure, and collecting the first fraction, acetonitrile, when the top temperature is 79-81 degrees Celsius; Step 4: Continue heating and reflux the remaining organic phase Φ from step 3, with the top of the tower at 115-115.5 degrees Celsius, and collect the second fraction, 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-diphenyltrimethylol dianhydride in step 1 is specifically composed of acetonitrile, pyridine, and pyridine hydrochloride, wherein acetonitrile accounts for 83-89%, pyridine accounts for 2-5%, pyridine hydrochloride accounts for 2-6%, and impurities account for 1-3%, and the sum of the mass percentages of each component is 100%.

3. A method for recovering anhydrous acetonitrile and anhydrous pyridine from pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The calculation method of the acetonitrile and pyridine recovery rates in the steps 3 and 4 is 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 pyridine hydrochloride acetonitrile waste liquid according to claim 1, characterized in that: The solid NaOH in step 1 can be in the form of flakes, powders or granules.

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

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 tower described in step 3 and step 4 adopts a φ25 packed glass distillation tower, the packing is φ3 stainless steel triangular spiral packing, the tower column length is 400 mm, the equal plate height is 40 mm, and the theoretical plate number is 10. A high-separation filler is added inside the distillation tower to improve the separation efficiency of acetonitrile and pyridine.

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