Process for the recovery of distillation still residues from the preparation of acyl chlorides from solid organic acids

Abstract

The present application relates to a kind of distillation residue recovery method of solid organic acid preparation acyl chloride, the recovery method includes that distillation residue is mixed with first inorganic acid liquid and carries out hydrolysis reaction, so that acyl chloride and acid anhydride in distillation residue are dissociated to form organic acid, then mixed with organic extractant, obtain organic acid crude product solution, then mixed with lye to form organic salt, liquid separation, acidification, extraction, obtain organic acid solution;The organic acid solution obtained in the above recovery method can be used in the preparation process of acyl chloride, can realize the resource utilization of distillation residue, reduces the generation of solid waste in the preparation process of acyl chloride, reduces process cost.

Description

Technical Field

[0001] This invention belongs to the field of photoinitiator raw material preparation, and relates to a method for recovering distillation residues from the preparation of acyl chlorides from solid organic acids. Background Technology

[0002] Acyl chlorides are typically prepared by reacting carboxylic acids with various chlorinating agents in the presence of a catalyst. Commonly used chlorinating agents include thionyl chloride and phosgene. When solid organic acids are used as raw materials to react with chlorinating agents to prepare acyl chlorides, the proportion of distillation residue in the distillation vessel is relatively high after the acyl chloride is collected by subsequent distillation. Treating this residue as solid waste results in resource waste and increases process costs.

[0003] 2,4,6-Trimethylbenzoyl chloride is used as a photoinitiator in photopolymer materials, unsaturated resin models and recording materials, and as a stabilizer in plastics and paints to improve their light and heat resistance. It is also an important raw material for the preparation of acylphosphine oxide photoinitiators (exemplary examples include photoinitiators TPO, TPO-L or 819, etc.).

[0004] The preparation process of 2,4,6-trimethylbenzoyl chloride usually involves reacting 2,4,6-trimethylbenzoic acid with a chlorinating agent to obtain 2,4,6-trimethylbenzoyl chloride. The raw material, 2,4,6-trimethylbenzoic acid, is a solid organic acid. After the reaction, the product is recovered by distillation. However, a significant amount of residue remains in the distillation vessel after the distillation process, accounting for a high percentage of the total mass. Current technologies typically treat this residue as solid waste, resulting in high treatment costs, low process output, and a significant increase in production costs.

[0005] Therefore, developing a method for the resource recovery of distillation residues from the preparation of acyl chlorides from solid organic acids remains of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recovering distillation vessel residue from the preparation of acyl chlorides from solid organic acids. The recovery method includes mixing the distillation vessel residue with a first inorganic acid solution for hydrolysis, causing the acyl chloride and acid anhydride in the residue to dissociate and form an organic acid. This organic acid is then mixed with an organic extractant to obtain a crude organic acid solution, followed by mixing with an alkaline solution to form an organic salt. The solution is then separated, acidified, and extracted to obtain an organic acid solution. The organic acid solution obtained by this recovery method can be applied to the preparation process of acyl chlorides, enabling the resource utilization of the distillation vessel residue, reducing the generation of solid waste during acyl chloride preparation, and lowering process costs.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] This invention provides a method for recovering distillation residue from the preparation of acyl chlorides from solid organic acids, the recovery method comprising the following steps:

[0009] (1) The residue from the distillation vessel is mixed with the first inorganic acid solution to carry out a hydrolysis reaction to obtain the first mixture;

[0010] (2) Mix the first mixture obtained in step (1) with an organic extractant, extract, separate the liquid, and obtain a crude organic acid solution;

[0011] (3) Mix the crude organic acid solution from step (2) with the alkaline solution, separate the liquids, and obtain an aqueous solution of organic salt and an organic phase containing impurities;

[0012] (4) Acidify the organic salt aqueous solution in step (3) to obtain the second mixture;

[0013] (5) Mix the product obtained in step (4) with an organic extractant, extract, separate the liquid, and obtain an organic acid solution.

[0014] The preparation of acyl chlorides by reacting organic acids with chlorinating reagents and then collecting them by distillation is a common process in acyl chloride preparation. When solid organic acids are used as raw materials, the distillation process of acyl chlorides produces a large amount of residue, which is usually treated as solid waste. However, the large amount of residue leads to high process costs. Taking the preparation of 2,4,6-trimethylbenzoic acid to 2,4,6-trimethylbenzoic acid as an example, the residue in the subsequent distillation process can reach 10%, resulting in resource waste and high solid waste treatment costs. Taking the distillation residue from the preparation of 2,4,6-trimethylbenzoic acid to 2,4,6-trimethylbenzoic acid as an example, the present invention, through component analysis, found that the main components of the residue are acid anhydrides and 2,4,6-trimethylbenzoic acid, which together account for more than 70% of the mass and have high recycling value. The present invention designs a recycling method for the above-mentioned distillation residue that can recover raw materials and intermediates from the distillation residue, reduce solid waste generation, and save production costs.

[0015] The recycling method described in this invention combines hydrolysis, extraction, separation, salt formation, separation, acidification, extraction, and separation to obtain an organic acid solution; it realizes the recovery of raw materials and intermediates from the distillation vessel residue, and the obtained organic acid solution can be recycled for the preparation of acyl chloride, thereby realizing the resource utilization of distillation vessel residue in the preparation of acyl chloride, reducing the amount of solid waste, reducing the cost of solid waste treatment, and making the acyl chloride production process more cost-effective.

[0016] Targeting the specific composition and properties of distillation vessel residue, the recovery method of this invention employs the following steps: First, the distillation vessel residue is mixed with a first inorganic acid solution for hydrolysis and dissociation reaction, converting the acyl chlorides and acid anhydrides in the residue into organic acids. Then, an organic extractant is added to extract and dissolve the organic acids, followed by separation to obtain a crude organic acid solution. At this point, some organic impurities are dissolved in the crude organic acid solution, requiring further purification. Next, the crude organic acid solution is mixed with an alkaline solution and reacted, followed by separation to obtain an organic salt aqueous solution and an impurity organic phase. At this point, most of the organic impurities dissolve in the impurity organic phase, thus achieving the effect of purifying the organic acid. Then, the organic salt aqueous solution is acidified, converting the organic salt into organic acid. An organic extractant is added, followed by separation, where the organic acid dissolves in the organic extractant, and then separation again to obtain a purified organic acid solution. This process enables the recovery of organic acids, acyl chlorides, and acid anhydrides from the distillation vessel residue, and the purification to obtain an organic acid solution. This reduces the generation of solid waste in the acyl chloride preparation process and lowers the process cost. Furthermore, the obtained organic acid solution can be recycled for acyl chloride preparation, increasing the yield of the acyl chloride preparation process.

[0017] Taking the preparation of 2,4,6-trimethylbenzoic acid into 2,4,6-trimethylbenzoyl chloride as an example, 2,4,6-trimethylbenzoic acid is a solid organic acid. The distillation residue obtained from it is used as raw material for the above-mentioned recovery operation. The purity of the recovered 2,4,6-trimethylbenzoic acid can reach more than 95%, and the mass can reach more than 83% of the mass of the distillation residue, which greatly reduces the output of solid waste.

[0018] Preferably, the distillation vessel residue contains organic acids and acid anhydrides.

[0019] Preferably, the mass percentage of organic acids and anhydrides in the distillation vessel residue is ≥65%, such as 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, or 90%; more preferably ≥70%.

[0020] Preferably, the distillation vessel residue also contains acyl chloride, wherein the mass percentage of the acyl chloride is ≤5%, for example, 0.5%, 1%, 2%, 3% or 4%.

[0021] In this invention, the mass percentage of organic acids and acid anhydrides in the distillation vessel residue is within the aforementioned range, making it suitable for the recovery method described in this invention and possessing significant recovery value. Analysis of the composition of the distillation vessel residue obtained from the preparation of 2,4,6-trimethylbenzoic acid with 2,4,6-trimethylbenzoyl chloride and subsequent distillation revealed that the mass percentage of 2,4,6-trimethylbenzoic acid and acid anhydrides in the residue can reach over 70% of the total mass, indicating significant recovery value.

[0022] Preferably, the distillation residue is the residue remaining after a solid organic acid undergoes a chlorination reaction, followed by distillation to collect the acyl chloride. For example, 2,4,6-trimethylbenzoic acid is reacted with thionyl chloride to prepare 2,4,6-trimethylbenzoyl chloride, and the resulting distillation residue is obtained; the mass percentage of organic acid and acid anhydride in the above distillation residue can reach more than 70%.

[0023] Preferably, the solid organic acid includes 2,4,6-trimethylbenzoic acid.

[0024] The recovery method described in this invention is applicable to the distillation vessel residue obtained after preparing acyl chloride from solid organic acids and collecting the acyl chloride by distillation.

[0025] Preferably, the acyl chloride includes 2,4,6-trimethylbenzoyl chloride.

[0026] Preferably, in step (1), the first inorganic acid solution is selected from hydrochloric acid.

[0027] Preferably, the concentration of the first inorganic acid solution in step (1) is 2wt% to 20wt%, for example, 4%, 6%, 8%, 10%, 12%, 15% or 18%, and more preferably 5wt% to 10wt%.

[0028] In this invention, the first inorganic acid solution in the hydrolysis reaction of the distillation vessel residue is of the above concentration, which can realize the dissociation of acyl chloride and acid anhydride to obtain organic acid, resulting in a high organic acid yield.

[0029] Preferably, the temperature of the hydrolysis reaction in step (1) is selected from 70℃ to 90℃, such as 75℃, 80℃ or 85℃, and preferably 75℃ to 85℃.

[0030] In this invention, the temperature of the hydrolysis reaction is controlled within the above-mentioned range, which facilitates the full progress of the hydrolysis reaction.

[0031] Preferably, the organic extractant is selected from mesitylene.

[0032] In this invention, the organic extractant is used to extract dissolved solid organic acids, which facilitates separation and purification. The use of the above-mentioned mesitylene organic extractant also helps to avoid affecting subsequent application processes.

[0033] Preferably, the extraction temperature in step (2) is selected from 75℃ to 95℃, such as 80℃, 85℃ or 90℃, and more preferably 85℃ to 95℃.

[0034] In this invention, the extraction temperature is within the above-mentioned range, which facilitates the complete dissolution of solid organic acids in the organic extractant and facilitates the purification and separation process.

[0035] Preferably, the alkali in the alkaline solution in step (3) is selected from alkali metal hydroxides; more preferably, sodium hydroxide.

[0036] Preferably, the alkaline solution in step (3) is selected from an aqueous solution of sodium hydroxide with a concentration of 2wt% to 20wt% (exemplary values ​​include 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, or 18wt%).

[0037] In this invention, the purpose of the salt-forming reaction process is to purify organic acids and remove organic impurities from the crude organic acid solution; preferably, the concentration of the alkali solution is within the above-mentioned range.

[0038] Preferably, the amount of alkali solution added in step (3) is such that the pH of the organic salt aqueous solution obtained by extraction and separation is alkaline.

[0039] In this invention, the amount of alkali added makes the pH of the organic salt aqueous solution alkaline, thereby ensuring that the organic acid is completely converted into the organic salt and improving the yield of organic acid.

[0040] Preferably, the method for acidifying the organic salt aqueous solution in step (4) includes adding a second inorganic acid solution to the organic salt aqueous solution.

[0041] Preferably, the second inorganic acid solution is selected from hydrochloric acid.

[0042] Preferably, the concentration of the second inorganic acid solution is 25wt% to 45wt%, for example, 30wt%, 35wt%, or 40wt%.

[0043] In the acidification reaction of this invention, the organic salt aqueous solution is alkaline, and the acidification reaction is carried out using the above-mentioned second inorganic acid solution of a specific concentration, which is conducive to achieving a better reaction effect. After the acidification reaction is completed, organic acid crystals precipitate in the reaction solution and inorganic salts are generated at the same time. The inorganic salts dissolve in water to form a high hydrochloric acid solution. By further extraction and separation, the organic acid and the high hydrochloric acid solution can be separated to ensure the high purity of the organic acid.

[0044] Preferably, the endpoint of acidification of the organic salt aqueous solution in step (4) is that the pH of the aqueous solution is acidic.

[0045] Preferably, the temperature for acidifying the organic salt aqueous solution in step (4) is selected from 90℃ to 95℃, such as 91℃, 92℃, 93℃ or 94℃.

[0046] The acidification process is carried out at the above temperature, which helps to ensure the effectiveness of the acidification reaction and ensures that the organic salt is completely converted into organic acid.

[0047] Preferably, in step (2), the organic acid crude solution and the inorganic acid solution are obtained by separation, and the inorganic acid solution is used for the hydrolysis reaction in step (1).

[0048] In this invention, the inorganic acid solution used for hydrolysis is subjected to hydrolysis and separation operations. The resulting inorganic acid solution can be recycled for hydrolysis of the residue in the distillation vessel, which helps to improve the utilization rate of the acid solution, reduce the generation of waste acid solution, and will not affect the subsequent processes.

[0049] Preferably, the impurity organic phase in step (3) is distilled to obtain an organic solvent and impurity residue; the obtained organic solvent is used as an organic extractant in step (2).

[0050] In this invention, the impurity organic phase obtained after the salt-forming reaction is separated is distilled to recover the organic extractant, and the distilled impurities are treated as solid waste; the mass of the obtained solid distilled impurities is only less than 15% of the residual mass of the acyl chloride distillation vessel (exemplary examples include 5%, 10%, or 15%, etc.).

[0051] As a preferred embodiment of the present invention, the method for recovering the residue from the distillation vessel used in the preparation of acyl chloride from solid organic acids includes the following steps:

[0052] (a) The residue from the distillation vessel is mixed with hydrochloric acid with a concentration of 2wt% to 20wt%, and the mixture is heated to 70°C to 90°C for a hydrolysis reaction to obtain the first mixture.

[0053] (b) The first mixture obtained in step (a) and the organic extractant are mixed and kept at 75°C to 95°C. During the heat preservation process, the mixture is stirred until completely dissolved. After standing, the liquid is separated to obtain a crude organic acid solution and an inorganic acid solution. The inorganic acid solution is used in the heat preservation hydrolysis reaction in step (a).

[0054] (c) The crude organic acid solution obtained in step (b) is mixed with a sodium hydroxide aqueous solution with a concentration of 2wt% to 20wt%, and the mixing process is accompanied by stirring. After standing, the mixture is separated to obtain an organic salt aqueous solution and an impurity organic phase. The amount of sodium hydroxide aqueous solution added is such that the pH of the obtained organic salt aqueous solution is alkaline. The obtained impurity organic phase is distilled to recover the organic extractant for reuse in step (b), and the distilled impurities are treated as solid waste.

[0055] (d) The organic salt aqueous solution obtained in step (c) is mixed with hydrochloric acid with a concentration of 25wt% to 45wt%, and the pH is adjusted to acidic to obtain a second mixture. Then, solid-liquid separation is performed to obtain organic acid crystal slurry.

[0056] (e) The organic acid slurry obtained in step (d) is mixed with an organic extractant and heated to 90°C to 95°C with stirring. After standing, the mixture is separated to obtain an organic acid solution and a high-hydrochloric acid liquid phase. The organic acid solution is used for the preparation of acyl chloride.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The recovery method of the present invention obtains an organic acid solution by hydrolyzing, extracting, separating, salting, separating, acidifying, extracting and separating the distillation vessel residue for preparing acyl chloride from solid organic acid through steps of hydrolysis, extraction, separation, separation, acidification and separation. This realizes the recovery of acyl chloride, organic acid and acid anhydride in the distillation vessel residue. The obtained organic acid solution can be used for the preparation of acyl chloride, realizing the resource utilization of the distillation vessel residue.

[0059] (2) The recycling method described in this invention reduces the generation of solid waste during the preparation of acyl chloride and reduces the process cost of acyl chloride preparation. Attached Figure Description

[0060] Figure 1 This is a process flow diagram of the method for recovering distillation vessel residue in the preparation of acyl chloride from solid organic acids according to the present invention;

[0061] Figure 2 This is an optical image of the liquid state during the separation process after hydrolysis and extraction are completed in Embodiment 1 of the present invention;

[0062] Figure 3 This is an optical image of the liquid state during the separation process after the salt formation reaction in Example 1 of the present invention;

[0063] Figure 4 This is an optical image of the liquid state during the separation process after acidification extraction in Example 1 of the present invention;

[0064] Figure 5 This is an optical image of the remaining distilled impurities after the organic phase distillation of impurities is completed in Example 1 of the present invention. Detailed Implementation

[0065] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0066] The process flow diagram of the method for recovering distillation residue in the preparation of acyl chloride from solid organic acids according to the present invention is as follows: Figure 1 As shown, by Figure 1 As can be seen, the process flow includes the following steps;

[0067] (1) The residue from the distillation vessel is mixed with the first inorganic acid solution to carry out a hydrolysis reaction to obtain the first mixture;

[0068] (2) The first mixture obtained in step (1) is mixed with an organic extractant, extracted, and separated to obtain a crude organic acid solution and an inorganic acid liquid phase. The inorganic acid liquid phase is recycled for hydrolysis reaction.

[0069] (3) Mix the crude organic acid solution in step (2) with the alkaline solution, separate the liquids to obtain an organic salt aqueous solution and an impurity organic phase; the impurity organic phase is distilled to recover the organic extractant and recycled in step (2), and the distilled impurities are treated as solid waste.

[0070] (4) Mix the organic salt aqueous solution from step (3) with the second inorganic acid solution and acidify it to obtain the second mixture;

[0071] (5) The product obtained in step (4) is mixed with an organic extractant, extracted, and separated to obtain an organic acid solution and a high hydrochloric acid liquid phase. The high hydrochloric acid liquid phase is separated into an aluminum chloride solution for sale.

[0072] Example 1

[0073] This embodiment provides a method for recovering distillation residue from the preparation of acyl chlorides from solid acids, specifically including:

[0074] In this embodiment, the raw material distillation vessel residue is selected from the reaction of 2,4,6-trimethylbenzoic acid with thionyl chloride to prepare 2,4,6-trimethylbenzoyl chloride, and the product is distilled to obtain the distillation vessel residue. Testing showed that the above distillation vessel residue contained 30.05 wt% 2,4,6-trimethylbenzoic acid, 41.75 wt% acid anhydride, and 1.78% 2,4,6-trimethylbenzoyl chloride, with the remainder being impurities. The method for recovering the distillation vessel residue includes the following steps:

[0075] (a) Add 300 kg of distillation vessel residue to the reaction apparatus, turn on heating and stirring, add 500 kg of 6% dilute hydrochloric acid, maintain the temperature at 80°C, and hydrolyze and dissociate for 6 h.

[0076] (b) Add 600 L of mesitylene to the reaction apparatus of step (a), start stirring and heat to 90 °C and maintain the temperature until completely dissolved; transfer to a separatory apparatus for separation to obtain an upper layer of crude organic acid solution and a lower layer of inorganic acid liquid phase; take samples for the mixture separation experiment. The experimental results are as follows: Figure 2 As shown, the two phases are clearly separated;

[0077] (c) Transfer the upper layer of crude organic acid solution obtained in step (b) to a reaction vessel, add 1000 kg of a 10% sodium hydroxide solution to the reaction vessel, start stirring, and carry out the salt formation reaction to obtain a mixed solution; transfer the mixed solution to a separatory device and allow it to stand for separation to obtain an upper layer of impurity organic phase and a lower layer of organic salt aqueous solution phase. The pH of the organic salt aqueous solution is alkaline; the experimental results of the mixed solution layer separation experiment are as follows: Figure 3 As shown, the two phases are clearly separated;

[0078] (d) Transfer the lower organic salt aqueous solution phase from step (c) to a reaction vessel. Add 30% concentrated hydrochloric acid to the reaction vessel to adjust the pH to acidic. Acidification reaction yields an organic acid precipitate. Add 750 L of mesitylene to the organic acid precipitate, heat to 95°C, and stir for 30 min to obtain a mixture. Transfer the mixture to a separatory apparatus, allow it to stand, and separate the layers to obtain an upper 2,4,6-trimethylbenzoic acid solution phase and a lower high-hydrochloric acid liquid phase. The experimental results of the mixture separation experiment are as follows: Figure 4 As shown, the two phases are clearly separated;

[0079] An experiment was conducted to recover the organic extractant by distillation of the impurity organic phase from step (c). The experimental results are as follows: Figure 5 As shown, the amount of residue in the still is significantly reduced compared to the residue in the still of the raw material distillation.

[0080] The 2,4,6-trimethylbenzoic acid obtained in this embodiment has a content of over 95%, which meets the requirements for recycling in the preparation process of acyl chloride. The mass ratio of the obtained 2,4,6-trimethylbenzoic acid to the mass of the residue in the raw material distillation vessel is 87.6%.

[0081] In this embodiment, after the organic extractant is recovered by distillation in step (c), the remaining impurities are treated as solid waste. The amount of solid waste produced is less than 15% of the residual mass of the raw material distillation vessel, which greatly reduces the generation of solid waste in the preparation of acyl chloride.

[0082] Example 2

[0083] This embodiment provides a method for recovering distillation vessel residues from the preparation of acyl chlorides from solid acids;

[0084] The only difference between this embodiment and Embodiment 1 is that the hydrolysis temperature in step (a) is replaced with 60°C, while the other parameters and conditions are exactly the same as in Embodiment 1.

[0085] The 2,4,6-trimethylbenzoic acid obtained in this embodiment has a content of over 95%, which meets the requirements for recycling in the preparation process of acyl chloride. The mass ratio of the obtained 2,4,6-trimethylbenzoic acid to the mass of the raw material distillation vessel residue is 72.6%.

[0086] In step (c) of this embodiment, after the organic extractant is recovered by distillation of the impurity organic phase, the remaining impurities are treated as solid waste, and the amount of solid waste produced is about 30% of the residual mass of the raw material distillation vessel.

[0087] Comparative Example 1

[0088] The only difference between this comparative example and Example 1 is that steps (c) and (d) are omitted, and only steps (a) and (b) are performed to obtain a crude organic acid solution.

[0089] The product obtained in this comparative example, 2,4,6-trimethylbenzoic acid, has a content of only 76%, and cannot be directly applied to the preparation of acyl chlorides.

[0090] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for recovering distillation still bottoms from the preparation of acyl chlorides from solid organic acids, characterized in that The recycling method includes the following steps: (1) The residue from the distillation vessel is mixed with the first inorganic acid solution to carry out a hydrolysis reaction to obtain the first mixture; (2) Mix the first mixture obtained in step (1) with an organic extractant, extract, separate the liquid, and obtain a crude organic acid solution; (3) Mix the crude organic acid solution from step (2) with the alkaline solution, separate the liquids, and obtain an aqueous solution of organic salt and an organic phase containing impurities; (4) Acidify the organic salt aqueous solution in step (3) to obtain the second mixture; (5) The product obtained in step (4) is mixed with an organic extractant, extracted, and separated to obtain an organic acid solution, which is used for the preparation of acyl chloride; Wherein, the solid organic acid is 2,4,6-trimethylbenzoic acid, the acyl chloride is 2,4,6-trimethylbenzoyl chloride, and the organic extractant is selected from mesitylene; The temperature of the hydrolysis reaction in step (1) is selected from 70℃ to 90℃.

2. The recycling method according to claim 1, characterized in that, The residue from the distillation vessel contains organic acids and acid anhydrides.

3. The recycling method according to claim 1, characterized in that, The mass percentage of organic acids and acid anhydrides in the distillation vessel residue is ≥65%.

4. The recycling method according to claim 3, characterized in that, The mass percentage of organic acids and acid anhydrides in the distillation vessel residue is ≥70%.

5. The recycling method according to claim 2, characterized in that, The residue from the distillation vessel also contains acyl chloride.

6. The recycling method according to claim 5, characterized in that, The mass percentage of the acyl chloride is ≤5%.

7. The recycling method according to claim 1, characterized in that, The distillation vessel residue is the residue remaining after the solid organic acid undergoes a chlorination reaction and is then distilled to collect the acyl chloride.

8. The recycling method according to claim 1, characterized in that, Step (1) The first inorganic acid solution is selected from hydrochloric acid.

9. The recycling method according to claim 1, characterized in that, Step (1) The concentration of the first inorganic acid solution is 2wt% to 20wt%.

10. The recycling method according to claim 9, characterized in that, Step (1) The concentration of the first inorganic acid solution is 5wt% to 10wt%.

11. The recycling method according to claim 1, characterized in that, The hydrolysis reaction in step (1) is carried out at a temperature of 75℃~85℃.

12. The recycling method according to claim 1, characterized in that, The extraction temperature in step (2) is selected from 75℃ to 95℃.

13. The recycling method according to claim 12, characterized in that, The extraction temperature in step (2) is 85-95℃.

14. The recycling method according to claim 1, characterized in that, The alkali in the alkaline solution in step (3) is selected from alkali metal hydroxides.

15. The recycling method according to claim 14, characterized in that, The alkali metal hydroxide is sodium hydroxide.

16. The recycling method according to claim 15, characterized in that, The alkaline solution in step (3) is selected from an aqueous solution of sodium hydroxide with a concentration of 2wt% to 20wt%.

17. The recycling method according to claim 16, characterized in that, The amount of alkali added in step (3) makes the pH of the organic salt aqueous solution obtained by extraction and separation alkaline.

18. The recycling method according to claim 1, characterized in that, The method of acidifying the organic salt aqueous solution in step (4) includes adding a second inorganic acid solution to the organic salt aqueous solution.

19. The recycling method according to claim 18, characterized in that, The second inorganic acid solution is selected from hydrochloric acid.

20. The recycling method according to claim 19, characterized in that, The concentration of the second inorganic acid solution is 25wt% to 45wt%.

21. The recycling method according to claim 20, characterized in that, In step (4), the endpoint of acidification of the organic salt aqueous solution is reached when the pH of the aqueous solution is acidic.

22. The recycling method according to claim 1, characterized in that, The temperature for acidifying the organic salt aqueous solution in step (4) is selected from 90℃ to 95℃.

23. The recycling method according to claim 1, characterized in that, After acidification in step (4), the second mixture is further subjected to solid-liquid separation to obtain an organic acid crystal slurry. In step (5), the organic acid crystal slurry is mixed with an organic extractant, extracted, and separated to obtain an organic acid solution.

24. The recycling method according to any one of claims 1-23, characterized in that, In step (2), the organic acid crude solution and the inorganic acid solution are obtained by separation. The inorganic acid solution is used in the hydrolysis reaction in step (1).

25. The recycling method according to any one of claims 1-23, characterized in that, The impurity organic phase described in step (3) is distilled to obtain an organic solvent and impurity residue; the obtained organic solvent is used as an organic extractant in step (2).

26. The recycling method according to claim 1, characterized in that, The recycling method includes the following steps: (a) The residue from the distillation vessel is mixed with hydrochloric acid with a concentration of 2wt% to 20wt%, and the mixture is heated to 70°C to 90°C for a hydrolysis reaction to obtain the first mixture. (b) The first mixture obtained in step (a) and the organic extractant are mixed and kept at 75°C to 95°C. During the heat preservation process, the mixture is stirred until completely dissolved. After standing, the liquid is separated to obtain a crude organic acid solution and an inorganic acid solution. The inorganic acid solution is used in the heat preservation hydrolysis reaction in step (a). (c) The crude organic acid solution obtained in step (b) is mixed with a sodium hydroxide aqueous solution with a concentration of 2wt% to 20wt%, and the mixing process is accompanied by stirring. After standing, the mixture is separated to obtain an organic salt aqueous solution and an impurity organic phase. The amount of sodium hydroxide aqueous solution added is such that the pH of the obtained organic salt aqueous solution is alkaline. The obtained impurity organic phase is distilled to recover the organic extractant for reuse in step (b), and the distilled impurities are treated as solid waste. (d) The organic salt aqueous solution obtained in step (c) is mixed with hydrochloric acid with a concentration of 25wt% to 45wt%, and the pH is adjusted to acidic to obtain a second mixture. Then, solid-liquid separation is performed to obtain organic acid crystal slurry. (e) The organic acid slurry obtained in step (d) is mixed with an organic extractant and heated to 90°C to 95°C with stirring. After standing, the mixture is separated to obtain an organic acid solution and a high-hydrochloric acid liquid phase. The organic acid solution is used for the preparation of acyl chloride.

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