Treatment process for wastewater containing trimellitic acid, cobalt and manganese

Abstract

The invention relates to the technical field of wastewater treatment, and provides a process for treating wastewater containing trimellitic acid, cobalt and manganese. Comprising the following steps: adding an extracting agent into wastewater containing trimellitic acid, cobalt and manganese for counter-current extraction, rectifying a water phase, adjusting the pH value, precipitating cobalt and manganese, carrying out electrolytic treatment, adding an extracting agent for counter-current extraction, combining extraction phases in the wastewater treatment process, and carrying out primary rectification, secondary rectification, crystallization and filtration treatment. And various substances generated in the process can be synchronously recovered, separated and reutilized. According to the technical scheme, the wastewater generated during preparation of 2, 6-NDA through oxidation of 2, 6-DIPN is treated, cobalt and manganese ions, trimellitic acid and other components in the wastewater are effectively recovered, meanwhile, an extracting agent and a treatment product used in the wastewater treatment process are recovered and recycled, and the content of 2, 6-NDA is greatly reduced. The raw material consumption and the wastewater treatment cost of 6, 6-NDA production are reduced, and excellent economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a wastewater treatment process containing trimellitic acid and cobalt manganese. Background Technology

[0002] Polyethylene naphthalate (PEN) is a novel industrial polyester material made from 2,6-naphthalenedicarboxylic acid (2,6-NDA) and ethylene glycol (EG). It exhibits excellent physical properties, mechanical properties, heat resistance, chemical stability, and gas barrier properties, and has become a key basic material in the food packaging industry, automotive industry, electronics and information industry, biomedicine, and aerospace industry. Specifically, it can be used in food packaging films, automotive airbags, tire frames, electronic component insulation, cell carriers, liquid crystal display substrates, and engineering plastic components, making it a polyester material with great application prospects. Currently, the main industrial-scale production route for 2,6-NDA from PEN feedstock involves the catalytic oxidation of 2,6-dimethylnaphthalene (2,6-DMN). However, the high cost of separating 2,6-DMN from its isomer, 2,7-DMN, due to their similar properties, limits the large-scale production of 2,6-NDA. In contrast, 2,6-diisopropylnaphthalene (2,6-DIPN) is easily separated and purified from the isomer mixture, and its operating cost is lower. Therefore, from an industrial production and economic cost perspective, the oxidation of 2,6-DIPN to 2,6-NDA is more promising. However, the catalytic oxidation system for 2,6-DIPN to 2,6-NDA contains ions such as cobalt, manganese, and potassium, and the catalyst concentration is high, almost exceeding that of the 2,6-DIPN feedstock. Furthermore, the proportion of trimellitic acid generated as a byproduct is high. Therefore, researching catalyst recovery and byproduct recovery technologies is highly significant.

[0003] For example, patent application CN119350156A discloses a 2,6 Diisopropylnaphthalene oxidation to produce high-purity 2,6 The method for preparing naphthalene dicarboxylic acid includes: 2,6 Diisopropylnaphthalene, catalyst, solvent, and additives are added to a titanium reactor for reaction. The catalyst is a homogeneous metal catalyst, and the solvent is acetic acid. The catalyst concentration is high, and if it is not recovered, it will increase costs.

[0004] In an acetic acid solution system containing cobalt and manganese catalysts, 2,6-DIPN is reacted with oxygen to prepare 2,6-NDA. The crude product is then purified by acid washing and water washing. Wastewater is typically generated from water washing, and the proportion of cobalt and manganese catalysts in the wastewater is approximately 20% of the input. Trimericic acid, a byproduct, accounts for 90% of the generated amount. Therefore, recovering cobalt and manganese ions and trimellitic acid from the wastewater is crucial for reducing production costs. Summary of the Invention

[0005] This invention proposes a wastewater treatment process containing trimellitic acid and cobalt manganese, which solves the problems in related technologies that do not treat the wastewater from the oxidation of 2,6-DIPN to prepare 2,6-NDA, resulting in high production costs and difficulty in recovering cobalt manganese ions and trimellitic acid from the wastewater.

[0006] The technical solution of the present invention is as follows: This invention proposes a wastewater treatment process containing trimellitic acid and cobalt-manganese, comprising the following steps: S1. Add an extractant to wastewater containing trimellitic acid and cobalt-manganese and perform countercurrent extraction to obtain extract phase B and aqueous phase C; distill the aqueous phase C to obtain wastewater D; S2. Adjust the pH of the wastewater D to 9.5~10.5, perform solid-liquid separation to obtain wastewater E and cobalt-manganese precipitate; wash and dry the cobalt-manganese precipitate to obtain cobalt salt and manganese salt; S3. Electrolyze the wastewater E to obtain an acidic aqueous solution F and an alkaline aqueous solution G; S4. Add an extractant to the acidic aqueous solution F and perform countercurrent extraction to obtain the extract phase H and the raffinate phase I. S5. The extractant phase B and extractant phase H are mixed and subjected to a first batch distillation to obtain a mixture J of acetic acid and trimellitic acid and an extractant; the mixture J is further subjected to a second batch distillation to obtain a mixture K of acetic acid and trimellitic acid and acetic acid; the mixture K is crystallized and filtered to obtain a filtrate and a filter cake; the filter cake is dried to obtain trimellitic acid.

[0007] As a further technical solution, in step S1, the distillation is atmospheric distillation with 10 to 30 theoretical plates and a reflux ratio of 1 to 10.

[0008] As a further technical solution, the solid-liquid separation method includes one or both of filtration and centrifugation.

[0009] As a further technical solution, in step S1, the mass of the extractant is 0.8 to 2.4 times the mass of the wastewater containing trimellitic acid and cobalt manganese; In step S4, the mass of the extractant is 0.5 to 1.5 times the mass of the acid aqueous solution F; As a further technical solution, the theoretical number of plates for both the primary batch distillation and the secondary batch distillation is 20 to 40. The reflux ratio of the single-pass batch distillation is 1~5, and the bottom temperature is 117~127℃; The reflux ratio of the secondary batch distillation is 0.1~1, and the bottom temperature is 140~180℃; In step S2, the regulator is an alkaline compound, which includes potassium-based or sodium-based compounds. The potassium-based compounds include potassium hydroxide and potassium carbonate; The sodium-based compounds include sodium hydroxide and sodium carbonate.

[0010] As a further technical solution, in steps S1 and S4, the number of countercurrent extraction stages is independently 6 to 12 stages.

[0011] As a further technical solution, the alkaline aqueous solution G is evaporated to obtain water and an alkaline compound. The alkaline compound obtained can be reused in step S2 to adjust the pH of the wastewater D. The raffinate phase I is distilled to obtain an extractant and water. The extractant can be reused in countercurrent extraction, and the water can be used as a washing solvent. When the raffinate phase I is distilled, atmospheric distillation is used with a theoretical plate number of 10 to 30 and a reflux ratio of 1 to 10. The cobalt and manganese salts are neutralized with acetic acid to yield cobalt acetate and manganese acetate, which can be used to catalyze 2,6-dimethylaminopropionate (2,6-dimethylaminopropionate) oxidation. In the oxidation reaction for the preparation of 2,6-naphthalenedicarboxylic acid from diisopropylnaphthalene; The extractant obtained in step S5 can be reused in countercurrent extraction.

[0012] As a further technical solution, in steps S1 and S4, the extractants added in the countercurrent extraction each independently include alcohol solvents and / or ester solvents.

[0013] As a further technical solution, the alcohol solvent includes one or both of n-butanol and isobutanol; The ester solvents include one or more of n-butyl acetate, isobutyl acetate, n-propyl acetate, and isopropyl acetate.

[0014] As a further technical solution, in steps S1 and S4, the extractant added in the countercurrent extraction each independently includes one or both of n-butanol and isobutanol.

[0015] The working principle and beneficial effects of this invention are as follows: 1. In this invention, for the first time, the wastewater from the oxidation of 2,6-DIPN to prepare 2,6-NDA is comprehensively treated. The treatment includes countercurrent extraction, pH adjustment to precipitate cobalt and manganese, electrolysis, distillation, crystallization and other operations. The wastewater is separated and recovered in a comprehensive and efficient manner, with high recovery efficiency. Countercurrent extraction is employed in steps S1 and S4. Countercurrent extraction allows the extractant to fully contact the wastewater and utilizes the concentration difference to transfer the target substance from the aqueous phase to the extraction phase, resulting in high mass transfer efficiency and more effective extraction of target substances such as trimellitic acid. In step S2, the pH of wastewater D is adjusted to 9.5-10.5, which precipitates cobalt and manganese ions. Through solid-liquid separation, the cobalt and manganese precipitate can be separated from the wastewater, achieving cobalt and manganese recovery. In step S3, wastewater E is electrolyzed, and electrode reactions cause the ions in the wastewater to undergo redox reactions, allowing the recovery and reuse of alkaline aqueous solutions, achieving simultaneous recovery and separation of multiple substances. Simultaneously, distillation is used in multiple steps to promote the separation of each component. Finally, the mixture K of acetic acid and trimellitic acid is crystallized to obtain high-purity trimellitic acid. Each step is interconnected to achieve the separation and recovery of multiple components such as trimellitic acid, cobalt and manganese, and acetic acid from wastewater containing trimellitic acid and cobalt and manganese.

[0016] 2. Currently, cobalt, manganese, and trimellitic acid raw materials are expensive. In this invention, the wastewater treatment process generated after the reaction of 2,6-DIPN with oxygen to prepare 2,6-NDA in an acetic acid solution system containing cobalt and manganese catalysts can recover a large amount of catalysts containing cobalt and manganese ions as well as the byproduct trimellitic acid, which can significantly reduce raw material costs and has excellent economic benefits. At the same time, by using processes such as extraction, neutralization, electrolysis, and distillation, the recovery rate of cobalt and manganese ion catalysts is >90%, and the recovery rate of trimellitic acid is >85%, which reduces the difficulty of wastewater treatment and can realize industrial application. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] The composition of the wastewater containing trimellitic acid and cobalt manganese in the following examples and comparative examples is shown in Table 1 below.

[0019] Table 1. Composition of wastewater containing trimellitic acid and cobalt-manganese

[0020] Example 1 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor and isobutanol as the extractant, a 6-stage countercurrent extraction was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 1.6:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.02 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 20 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 0.02 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.0, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.015 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.0 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.015 wt%. The alkaline aqueous solution G is then evaporated using a triple-effect evaporator. The separated water can be reused upstream for the preparation of 2,6-NDA, and the separated alkaline compound, potassium hydroxide, can be reused in step S2 for a neutralization reaction. S4. Isobutanol was used as the extractant for a 6-stage countercurrent extraction of the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 0.8:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.03 wt% trimellitic acid, and 0.4 wt% acetic acid). The extraction rate of trimellitic acid reached 97.9%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25, a reflux ratio of 1, and a bottom temperature of [missing information]. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the bottom of the column is gradually increased, and the final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98wt% is obtained as the product at the top of the column, and the main impurity is water. The residue in the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, and trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.0wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0021] Example 2 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with n-butanol as the extractant, a 12-stage countercurrent extraction process was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 0.8:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.01 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 30 trays, with feed from the 10th tray and a reflux ratio of 1, yielding wastewater D containing 0.01 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.76 wt% potassium carbonate is added to adjust the pH to 10.5, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.010 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.3 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.012 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate the water, which can be reused upstream for the preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for the neutralization reaction. S4. Using n-butanol as the extractant, the acidic aqueous solution F was subjected to 12 stages of countercurrent extraction. The mass ratio of extractant to acidic aqueous solution F was 0.5:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.02 wt% trimellitic acid, and 0.5 wt% acetic acid). The extraction rate of trimellitic acid reached 98.6%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with 10 theoretical plates and a reflux ratio of 10. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the column bottom is gradually increased, and the final temperature of the column bottom is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 20 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 117°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.1 and the bottom temperature at 160°C. Acetic acid with a content of 98.1 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.5 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0022] Example 3 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with isobutanol as the extractant, wastewater containing trimellitic acid and cobalt manganese is subjected to 10 stages of countercurrent extraction. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese is 1.2:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C is reduced to 0.01 wt%. Aqueous phase C is then distilled to recover the residual extractant. The distillation process is atmospheric distillation with 10 trays, with feed from the 10th tray and a reflux ratio of 10, yielding wastewater D containing 0.01 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column is reused, while the water obtained from the azeotropic distillation with the solvent still contains extractant and is returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.55 wt% potassium carbonate is added to adjust the pH to 9.5, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.015 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.5 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate in wastewater E to trimellitic acid and acetic acid, respectively, so that the pH of the acid chamber reaches 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.014 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused in the upstream preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for neutralization reaction. S4. Isobutanol was used as the extractant for 10-stage countercurrent extraction of the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 1.0:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.01 wt% trimellitic acid, and 0.1 wt% acetic acid). The extraction rate of trimellitic acid reached 99.2%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with 30 theoretical plates and a reflux ratio of 5. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the column bottom is gradually increased, and the final temperature of the column bottom is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 40 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 5 and a bottom temperature of 127°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture of acetic acid and trimellitic acid J. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 1 and the bottom temperature at 160°C. Acetic acid with a purity of 99.5 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a purity of 99.3 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0023] Example 4 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with n-butanol as the extractant, a 6-stage countercurrent extraction was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 1.6:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.02 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 20 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 0.02 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.0, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.012 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.2 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate in wastewater E to trimellitic acid and acetic acid, respectively, so that the pH of the acid chamber reaches 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.010 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused in the upstream preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for neutralization reaction. S4. Using n-butanol as the extractant, a 6-stage countercurrent extraction was performed on the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 0.8:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.01 wt% trimellitic acid, and 0.5 wt% acetic acid). The extraction rate of trimellitic acid reached 99.2%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25, a reflux ratio of 1, and a bottom temperature of [missing information]. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the bottom of the column is gradually increased, and the final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1.0 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98.2 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.4 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0024] Example 5 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with n-propyl acetate as the extractant, a 12-stage countercurrent extraction process was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 1.6:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 1.0 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 20 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 1.0 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.0, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.014 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.1 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.011 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused upstream for the preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for the neutralization reaction. S4. Using n-propyl acetate as the extractant, a 12-stage countercurrent extraction was performed on the acid-water solution F. The mass ratio of extractant to acid-water solution F was 1:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.06 wt% trimellitic acid, and 1.0 wt% acetic acid). The extraction rate of trimellitic acid reached 95.9%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25 and a reflux ratio of 1. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the column bottom is gradually increased, and the final temperature of the column bottom is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98.0 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.2 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0025] Example 6 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with isopropyl acetate as the extractant, a 12-stage countercurrent extraction process was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 1.6:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.9 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 20 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 0.9 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.0, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.012 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.0 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.013 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate the water, which can be reused upstream for the preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for the neutralization reaction. S4. Isopropyl acetate was used as the extractant for a 12-stage countercurrent extraction of the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 1:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.07 wt% trimellitic acid, and 1.0 wt% acetic acid). The extraction rate of trimellitic acid reached 95.3%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with 25 theoretical plates and a reflux ratio of 1. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the column bottom is gradually increased, and the final temperature of the column bottom is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98.1 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.1 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0026] Example 7 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with n-butyl acetate as the extractant, a 12-stage countercurrent extraction was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 2.4:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.9 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 30 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 0.9 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.5, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.010 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.3 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.015 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused upstream for the preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for the neutralization reaction. S4. Using n-butyl acetate as the extractant, a 12-stage countercurrent extraction was performed on the acid-water solution F. The mass ratio of extractant to acid-water solution F was 1.5:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.09 wt% trimellitic acid, and 0.9 wt% acetic acid). The extraction rate of trimellitic acid reached 94.0%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25 and a reflux ratio of 5. The bottom temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the bottom of the column is gradually increased, and the final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 40 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 2.5 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture of acetic acid and trimellitic acid J. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 99.0 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 99.2 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0027] Example 8 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor with isobutyl acetate as the extractant, 12-stage countercurrent extraction was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 2.4:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 1.0 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 30 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 1.0 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 9.5, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.015 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.4 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Wastewater E is electrolyzed to reduce trimellitate and acetate in wastewater E to trimellitic acid and acetic acid, respectively, so that the pH of the acid chamber reaches 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.014 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused in the upstream preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for neutralization reaction. S4. Isobutyl acetate was used as the extractant for a 12-stage countercurrent extraction of the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 1.5:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.10 wt% trimellitic acid, and 1.0 wt% acetic acid). The extraction rate of trimellitic acid reached 93.3%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25 and a reflux ratio of 5. The bottom temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the bottom of the column is gradually increased, and the final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S5. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 40 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 3 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S6 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a purity of 99.2 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue at the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a purity of 99.3 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0028] Comparative Example 1 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Using a centrifugal extractor and isobutanol as the extractant, a 6-stage countercurrent extraction was performed on wastewater containing trimellitic acid and cobalt manganese. The mass ratio of extractant to wastewater containing trimellitic acid and cobalt manganese was 1.6:1, yielding extract phase B (organic phase, mainly extractant and acetic acid) and aqueous phase C (mainly water, trimellitic acid, cobalt manganese potassium ions, and extractant). The acetic acid content in aqueous phase C was reduced to 0.02 wt%. Aqueous phase C was then distilled to recover the residual extractant. The distillation process was atmospheric distillation with 20 trays, with feed from the 10th tray and a reflux ratio of 5, yielding wastewater D containing 0.02 wt% acetic acid and free of extractant. The extractant collected from the top of the distillation column was reused, while the water obtained from the azeotropic distillation with the solvent still contained extractant and was returned to aqueous phase C for further distillation. S2. 1.8 wt% KOH is added to wastewater D to bring the pH to 6.5, and then 3.66 wt% potassium carbonate is added to adjust the pH to 10.0, causing cobalt and manganese ions to precipitate. The precipitate is removed by filtration, reducing the cobalt and manganese ion content to 0.015 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt and manganese precipitate. The cobalt and manganese precipitate is washed twice with twice its weight of water and then dried to obtain cobalt and manganese carbonate with a content of 99.0 wt%. After neutralization with acetic acid, cobalt and manganese carbonate yield cobalt acetate and manganese acetate, which can be returned upstream as catalysts for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S3. Isobutanol was used as the extractant for a 6-stage countercurrent extraction of wastewater E. The mass ratio of extractant to wastewater E was 0.8:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 1.32 wt% trimellitic acid, and 0.1 wt% acetic acid). The extraction rate of trimellitic acid reached 13.4%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25, a reflux ratio of 1, and a controlled bottom temperature. At 105℃, an azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio remaining unchanged. Water is recovered from the top of the column, and the temperature of the bottom of the column is gradually increased. The final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S4. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S5 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98.1 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue in the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, and trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 59.0 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0029] Comparative Example 2 The wastewater treatment process containing trimellitic acid and cobalt-manganese includes the following steps: S1. Add 15.8 wt% KOH to wastewater containing trimellitic acid and cobalt manganese to bring the pH to 6.5. Then add 3.86 wt% potassium carbonate to adjust the pH to 10.0, causing cobalt manganese ions to precipitate. Filter to remove the precipitate, reducing the cobalt manganese ion content to 0.030 wt%, resulting in wastewater E. Wastewater E mainly contains potassium salts of trimellitic acid and acetic acid. The precipitate is cobalt manganese precipitate. Wash the cobalt manganese precipitate twice with twice its weight of water, then dry it to obtain cobalt manganese carbonate with a content of 95.1 wt%. After neutralization with acetic acid, cobalt manganese carbonate yields cobalt acetate and manganese acetate, which can be returned upstream as a catalyst for the preparation of 2,6-NDA, used in the oxidation reaction of 2,6-DIPN to prepare 2,6-NDA. S2. Wastewater E is electrolyzed to reduce trimellitate and acetate to trimellitic acid and acetic acid, respectively, bringing the pH of the acid chamber to 3.0, resulting in an acidic aqueous solution F. Meanwhile, potassium ions permeate through the cation exchange membrane, causing potassium hydroxide to accumulate in the alkaline chamber, resulting in an alkaline aqueous solution G with trimellitate ion and acetate ion contents of less than 0.015 wt%. The alkaline aqueous solution G is then subjected to triple-effect evaporation to separate water, which can be reused upstream for the preparation of 2,6-NDA. The separated alkaline compound, potassium hydroxide, can be reused in step S2 for the neutralization reaction. S3. Isobutanol was used as the extractant for a 6-stage countercurrent extraction of the acidic aqueous solution F. The mass ratio of extractant to acidic aqueous solution F was 1.6:1. Trimericic acid and acetic acid were recovered, yielding extract phase H (organic phase, mainly extractant, trimellitic acid, and acetic acid) and raffinate phase I (aqueous phase, mainly water, extractant, 0.15 wt% trimellitic acid, and 1.0 wt% acetic acid). The extraction rate of trimellitic acid reached 90.2%. Raffinate phase I was concentrated by atmospheric pressure batch distillation with a theoretical plate number of 25, a reflux ratio of 1, and a bottom temperature of [missing information]. The temperature is controlled at 105℃. An azeotrope of extractant and water is obtained at the top of the column. The azeotrope of extractant and water will separate into two layers. The upper layer is extractant containing a small amount of water, which can be reused as extractant for countercurrent extraction. The lower layer is water containing a small amount of extractant, which can be added as material to the next batch of raffinate phase I for distillation and extraction of extractant. After the extractant in the raffinate phase is removed by distillation, distillation continues with the reflux ratio unchanged. Water is recovered from the top of the column. The temperature of the bottom of the column is gradually increased, and the final temperature of the bottom of the column is controlled at 121℃. The water collected from the top of the column is reused as a washing solvent. S4. Extraction phase B and extraction phase H are mixed and fed into a batch distillation column with 30 trays. The distillation is carried out at atmospheric pressure with a reflux ratio of 1 and a bottom temperature of 120°C. The top of the column is collected as an organic phase (upper layer) and an aqueous phase (lower layer). The bottom material is a mixture J of acetic acid and trimellitic acid. The organic phase is an extractant containing a small amount of water, which can be reused as an extractant for countercurrent extraction. The aqueous phase is water containing a small amount of extractant, which can be added as a material to the raffinate phase I to recover the extractant. S5 and mixture J are further distilled in the above-mentioned batch distillation column, with the reflux ratio controlled at 0.5 and the bottom temperature at 160°C. Acetic acid with a content of 98.0 wt% is obtained as the product at the top of the column, and the main impurity is water. The residue in the bottom of the column is mainly a mixture of acetic acid and trimellitic acid, with trace impurities (mainly cobalt manganese potassium acetate). After cooling to 40°C, trimellitic acid crystallizes out. After filtration and washing twice with water, trimellitic acid crystals are obtained. After drying at 145°C, pure trimellitic acid with a content of 98.0 wt% is obtained. The mother liquor and washing water obtained from filtration are the treated wastewater, mainly composed of acetic acid, water and residual trimellitic acid. They are returned to the wastewater raw material for further treatment to recover cobalt manganese potassium salt.

[0030] By comparing Examples 1-8 and Comparative Examples 1-2, it can be found that: compared with Example 1, Comparative Example 1, which does not involve an electrolysis step, produces a large number of inorganic ions (such as K+). +The presence of acetic acid in Example 2 makes it impossible to extract and recover trimellitic acid, resulting in a very low extraction rate and low recovered trimellitic acid content. In Comparative Example 2, the step of not extracting and recovering acetic acid requires the consumption of a large amount of potassium hydroxide, leading to a low recovery rate and content of cobalt and manganese. The acetic acid content after electrolysis is very high, requiring a significant increase in electrolysis power consumption and extractant consumption. The residual acetic acid and trimellitic acid content after extraction are also high. In addition, under the same conditions, the recovery of cobalt and manganese is incomplete, the trimellitic acid extraction rate is also low, there are many recovered impurities, and the recovered trimellitic acid content is also low. Compared to Example 1, in Examples 5-8, when ester solvents were used to extract wastewater containing trimellitic acid and cobalt-manganese, the extraction rate of trimellitic acid was less than 96%, and the residual acetic acid was relatively high. The treatment effect was worse than that of alcohol solvents in Example 1. In addition, the highest solvent ratio and the largest number of extraction stages were required during the treatment process. Furthermore, the wastewater treatment effect of butyl ester solvents was worse than that of propyl ester solvents. The extraction effect could not be achieved in the low solvent ratio range, and a better wastewater treatment effect could only be achieved in the high solvent ratio range, resulting in a large consumption of solvent.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wastewater treatment process containing trimellitic acid and cobalt-manganese, characterized in that, Includes the following steps: S1. Add an extractant to wastewater containing trimellitic acid and cobalt-manganese and perform countercurrent extraction to obtain extract phase B and aqueous phase C; distill the aqueous phase C to obtain wastewater D; S2. Adjust the pH of the wastewater D to 9.5~10.5, perform solid-liquid separation to obtain wastewater E and cobalt-manganese precipitate; wash and dry the cobalt-manganese precipitate to obtain cobalt salt and manganese salt; S3. Electrolyze the wastewater E to obtain an acidic aqueous solution F and an alkaline aqueous solution G; S4. Add an extractant to the acidic aqueous solution F and perform countercurrent extraction to obtain the extract phase H and the raffinate phase I. S5. The extractant phase B and extractant phase H are mixed and subjected to a first batch distillation to obtain a mixture J of acetic acid and trimellitic acid and an extractant; the mixture J is further subjected to a second batch distillation to obtain a mixture K of acetic acid and trimellitic acid and acetic acid; the mixture K is crystallized and filtered to obtain a filtrate and a filter cake; the filter cake is dried to obtain trimellitic acid.

2. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, In step S1, the distillation is atmospheric distillation with 10 to 30 theoretical plates and a reflux ratio of 1 to 10.

3. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, The solid-liquid separation method includes one or both of filtration and centrifugation.

4. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, In step S1, the mass of the extractant is 0.8 to 2.4 times the mass of the wastewater containing trimellitic acid and cobalt manganese; In step S4, the mass of the extractant is 0.5 to 1.5 times the mass of the acid aqueous solution F.

5. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, The theoretical plate number of both the primary batch distillation and the secondary batch distillation is 20 to 40. The reflux ratio of the single-pass batch distillation is 1~5, and the bottom temperature is 117~127℃; The reflux ratio of the secondary batch distillation is 0.1~1, and the bottom temperature is 140~180℃; In step S2, the regulator is an alkaline compound, which includes potassium-based or sodium-based compounds. The potassium-based compounds include potassium hydroxide and potassium carbonate; The sodium-based compounds include sodium hydroxide and sodium carbonate.

6. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, In steps S1 and S4, the number of countercurrent extraction stages is independently 6 to 12 stages.

7. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, The alkaline aqueous solution G is evaporated to obtain water and an alkaline compound. The alkaline compound obtained can be reused in step S2 to adjust the pH of the wastewater D. The raffinate phase I is distilled to obtain an extractant and water. The extractant can be reused in countercurrent extraction, and the water can be used as a washing solvent. When the raffinate phase I is distilled, atmospheric distillation is used, with a theoretical plate number of 10 to 30 and a reflux ratio of 1 to 10. The cobalt and manganese salts are neutralized with acetic acid to yield cobalt acetate and manganese acetate, which can be used to catalyze 2,6-dimethylaminopropionate (2,6-dimethylaminopropionate) oxidation. In the oxidation reaction for the preparation of 2,6-naphthalenedicarboxylic acid from diisopropylnaphthalene; The extractant obtained in step S5 can be reused in countercurrent extraction.

8. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, In steps S1 and S4, the extractants added during countercurrent extraction each independently include alcohol solvents and / or ester solvents.

9. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 8, characterized in that, The alcohol solvent includes one or both of n-butanol and isobutanol; The ester solvents include one or more of n-butyl acetate, isobutyl acetate, n-propyl acetate, and isopropyl acetate.

10. The wastewater treatment process containing trimellitic acid and cobalt-manganese according to claim 1, characterized in that, In steps S1 and S4, the extractant added in the countercurrent extraction each independently includes one or both of n-butanol and isobutanol.

Images