Treatment method of o-methylphenylacetic acid mother liquor

Abstract

The invention relates to the technical field of industrial wastewater treatment, and particularly discloses a treatment method of o-methylphenylacetic acid mother liquor. The invention provides a method for treating o-methylphenylacetic acid mother liquor, which comprises the following steps in sequence: primary constant-temperature crystallization, secondary multi-section temperature-control crystallization, bipolar membrane electrodialysis enrichment after secondary mother liquor alkalinity regulation, concentration and crystallization of enriched liquid under reduced pressure, solvent recovery through tertiary mother liquor under reduced pressure and the like. The method realizes graded recovery of o-methylphenylacetic acid and solvent cyclic utilization, greatly reduces resource waste and wastewater discharge, is high in industrial feasibility, meets the requirements of green chemical development, and has a wide industrial application prospect in the field of treatment of o-methylphenylacetic acid production mother liquor.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for treating o-tolueneacetic acid mother liquor. Background Technology

[0002] o-Tolueneacetic acid (OMA) is an important organic synthesis intermediate that plays an irreplaceable role in the pharmaceutical and pesticide industries. It is a core raw material for the synthesis of various high-value-added products such as ibuprofen and pyrethroids. Currently, the sodium cyanide process is widely used in industry to produce o-tolueneacetic acid. This process is mature and widely applied. Its core reaction process is as follows: o-methylbenzyl chloride reacts with sodium cyanide (NaCN) as a raw material to produce o-methylphenylacetonitrile, which is then subjected to alkaline hydrolysis and acidification to obtain the target product OMA.

[0003] However, the sodium cyanide process for producing OMA generates a large amount of mother liquor. Existing technologies for the recovery and treatment of OMA mother liquor face the following core problems: (1) Low yield and purity of target product: The yield of the direct cooling crystallization method is only 70%~80%, and a large amount of target product remains in the mother liquor, resulting in waste. Although OMA has low solubility in the mother liquor, it is easy to precipitate along with other impurities in the mother liquor during the crystallization process, resulting in low purity of the recovered product. The recovery of this type of mother liquor requires a lot of energy and reagents, resulting in poor economic feasibility of the recovery process. Most companies choose to give up the recovery, which not only wastes the target product, but also increases the pollutant load of subsequent wastewater treatment.

[0004] (2) High environmental pressure and high treatment cost: Acid precipitation method achieves product separation by adding sulfuric acid for acidification, but this process generates a large amount of high-salt wastewater containing sodium sulfate, which is difficult and costly to treat and is prone to secondary pollution; Solvent extraction method mostly uses ethyl acetate as extractant, which can improve product separation efficiency to a certain extent, but has the problems of large solvent consumption and high operating cost, and solvent residue will further affect product purity. At the same time, solvent recovery and treatment will also increase the environmental burden.

[0005] (3) Solvents in the mother liquor are not effectively reused: At present, most processes do not achieve effective recovery and recycling of solvents such as water and ethanol in the mother liquor, which not only wastes resources but also results in a large amount of wastewater discharge.

[0006] In summary, existing OMA mother liquor treatment technologies generally suffer from low OMA yield and purity, significant environmental impact, and resource waste, making them unsuitable for the current requirements of green chemical industry development. Therefore, developing a method for treating o-tolueneacetic acid mother liquor that can efficiently enrich and recover OMA, reduce environmental impact, and reuse solvents has significant practical implications and industrial application value. Summary of the Invention

[0007] To address the problems of low OMA yield and purity, significant environmental impact, and resource waste associated with existing OMA mother liquor treatment technologies, this invention provides a method for treating o-methylphenylacetic acid mother liquor. The method primarily involves steps such as gradient cooling crystallization, alkaline electrolysis to enrich o-methylphenylacetic acid, vacuum concentration, and staged washing to obtain high-purity o-methylphenylacetic acid. The remaining mother liquor after o-methylphenylacetic acid separation is then subjected to vacuum distillation to recover ethanol and water, achieving the recovery and utilization of effective components from the OMA mother liquor, thus demonstrating high economic and environmental benefits.

[0008] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A method for treating o-tolueneacetic acid mother liquor includes the following steps: Step a: Heat the o-tolueneacetic acid mother liquor to dissolve the o-tolueneacetic acid contained therein, then cool it to 40℃~50℃, keep it at the temperature to crystallize, filter it, and obtain primary o-tolueneacetic acid crystals and primary mother liquor; Step b: The primary mother liquor is heated to dissolve residual o-tolueneacetic acid, then cooled to 35°C~40°C at a first cooling rate and held for a first preset time; then cooled to 30°C~35°C at a second cooling rate and held for a second preset time; finally cooled to 25°C~30°C at a third cooling rate and held for a third preset time, then filtered to obtain secondary o-tolueneacetic acid crystals and secondary mother liquor; Step c: Adjust the pH of the secondary mother liquor to alkaline, then pass it into a bipolar membrane electrodialysis device, collect the acid chamber solution, and obtain o-tolueneacetic acid enriched solution; Step d: The o-tolueneacetic acid enrichment solution is concentrated under reduced pressure to obtain o-tolueneacetic acid concentrate and solvent removal solution; the o-tolueneacetic acid concentrate is cooled to 4℃~5℃, kept at the temperature to crystallize, centrifuged, and washed to obtain three-stage o-tolueneacetic acid crystals and three-stage mother liquor. Step e: Combine the three mother liquors and the solvent-removed liquors and perform vacuum distillation, collect the fractions, and obtain recovered water and ethanol; The ion-exchange membrane of the bipolar membrane electrodialysis device is an alkali-resistant homogeneous anion exchange membrane-AHT; the bipolar membrane is a bipolar membrane-BPS-1. Compared to existing technologies, the method for treating o-tolueneacetic acid mother liquor provided by this invention employs a combination of primary isothermal crystallization and secondary gradient cooling crystallization to achieve preliminary enrichment of the target product. First, primary isothermal crystallization enriches easily crystallizable o-tolueneacetic acid in the mother liquor at 40℃~50℃. Secondary gradient cooling gradually reduces the supersaturation of the system, promoting the orderly crystallization of low-concentration residual o-tolueneacetic acid, significantly increasing the overall yield while avoiding co-precipitation of impurities.

[0009] For low-concentration o-methylphenylacetic acid in the secondary mother liquor, a bipolar membrane electrodialysis process under alkaline conditions is employed, combined with a uniquely selective alkali-resistant homogeneous anion exchange membrane (AHT) and a bipolar membrane (BPS-1). This efficiently enriches the low-concentration o-methylphenylacetic acid in the secondary mother liquor into a high-concentration concentrate, solving the problem of difficult recovery of low-concentration products in traditional processes. The o-methylphenylacetic acid concentrate is concentrated under reduced pressure, achieving concentration at lower temperatures and reducing high-temperature decomposition losses of the target product. Subsequent low-temperature (4℃~5℃) crystallization further improves product purity and yield. Water and ethanol are recovered from the tertiary mother liquor through reduced pressure distillation, achieving high solvent recovery rates. The recovered solvent can be recycled for production, reducing resource waste and production costs.

[0010] The entire process of this invention is simple, safe and controllable. It can separate and recover o-tolueneacetic acid and solvent from the o-tolueneacetic acid mother liquor, avoiding the loss and waste of effective components. It realizes the harmless treatment and resource utilization of industrial wastewater. At the same time, the added value generated by the recovered by-products can also greatly reduce the treatment cost of o-tolueneacetic acid production wastewater. It has high economic and environmental benefits and high practical value.

[0011] It should be noted that the o-tolueneacetic acid mother liquor described in this invention is prepared by reacting o-toluenechlorobenzyl chloride with sodium cyanide (NaCN) to produce o-tolueneacetonitrile. Subsequently, the o-tolueneacetonitrile undergoes alkaline hydrolysis and acidification to obtain the target product, o-tolueneacetic acid. After separation (e.g., crystallization, filtration), the remaining liquid phase is the o-tolueneacetic acid mother liquor. The o-tolueneacetic acid mother liquor contains 5wt%~15wt% o-tolueneacetic acid, 1wt%~3wt% o-tolueneethanol, 3wt%~5wt% sodium chloride, and 70wt%~85wt% water / ethanol.

[0012] Furthermore, in step a, the temperature for heating is 60℃~70℃.

[0013] Furthermore, in step a, the time for heat preservation and crystallization is 1h to 2h.

[0014] By controlling the heat preservation time to 1-2 hours, the easily crystallizable o-methylphenylacetic acid can be separated in solid form to the maximum extent.

[0015] Furthermore, in step a, the pore size of the filter medium used for filtration is 10μm~20μm.

[0016] Furthermore, in step a, the temperature is lowered to 40℃~50℃ using a programmed cooling method, with a cooling rate of 5℃ / h~10℃ / h.

[0017] The optimized cooling rate can control the supersaturation of the system, promote more ordered and slow crystal growth, and generate coarse crystals with uniform particle size, complete structure and less impurity adsorption, laying the foundation for obtaining high-purity products.

[0018] Furthermore, in step b, the temperature for heating is 60℃~70℃.

[0019] Further, in step b, the first cooling rate is 4℃ / h~6℃ / h, and the first preset time is 3h~5h; the second cooling rate is 2℃ / h~3℃ / h, and the second preset time is 1.5h~2.5h; the third cooling rate is 1℃ / h~2℃ / h, and the third preset time is 2.5h~5h.

[0020] The purpose of step b is to minimize the concentration of o-tolueneacetic acid in the primary mother liquor, thereby increasing the yield of the crystallized product and reducing the processing load and energy consumption of subsequent electrodialysis. Simultaneously, staged crystallization can also reduce the co-precipitation of impurities and improve the purity of the recovered o-tolueneacetic acid.

[0021] Furthermore, in step b, the pore size of the filter medium used for filtration is 10μm~20μm.

[0022] Furthermore, in step c, alkalinity refers to a pH value of 9 to 12.

[0023] Further, in step c, the voltage of the bipolar membrane electrodialysis device is set to 10V~20V, and the current density is 10mA / cm². 2 ~15mA / cm 2 The temperature is 25℃~30℃.

[0024] By controlling the process parameters of the bipolar membrane electrodialysis device within the above-mentioned range, not only was efficient electrodriven migration and in-situ acidification enrichment of o-methylphenylacetic acid ions achieved, but also, through the synergistic regulation of electric field and appropriate temperature, co-migration of impurities was effectively suppressed, thereby improving the selective enrichment of the target product.

[0025] Specifically, in step c, electrolysis is performed until the residual amount of o-methylphenylacetic acid in the alkaline chamber is ≤1%, at which point electrodialysis is completed. The residual amount of o-methylphenylacetic acid in the alkaline chamber is monitored using HPLC.

[0026] Further, in step d, the pressure of the vacuum concentration is -0.085MPa to -0.095MPa, and the temperature is 20℃ to 40℃.

[0027] The mild reduced pressure conditions effectively prevent side reactions such as decarboxylation and polymerization that may occur with o-tolueneacetic acid at higher temperatures.

[0028] Specifically, in step d, vacuum distillation is carried out using an enamel-lined vacuum concentration kettle equipped with a scraper stirrer.

[0029] Further, in step d, the o-tolueneacetic acid concentrate is 40% to 45% of the mass of the o-tolueneacetic acid enrichment solution.

[0030] Furthermore, in step d, the time for heat preservation and crystallization is 2h~4h.

[0031] Specifically, in step d, a horizontal scraper centrifuge is used for solid-liquid separation. The centrifugation speed is 800 rpm to 1000 rpm.

[0032] Further, in step d, the washing specifically includes the following steps: The obtained solid was washed and filtered with ice water at 8℃~10℃ and cold ethanol at 8℃~10℃ in sequence.

[0033] Washing with ice water and cold ethanol can effectively dissolve and remove impurities remaining on the crystal surface, while minimizing product loss due to dissolution during washing, while ensuring efficient removal of impurities.

[0034] Further, in step e, the pressure of the vacuum distillation is -0.085MPa to -0.095MPa, and the temperature is 20℃ to 40℃.

[0035] It should be noted that in step e, after the vacuum distillation is completed, the residual liquid at the bottom of the column (mainly containing sodium chloride and trace amounts of o-tolueneacetic acid) is sent to the biochemical wastewater treatment system and discharged after treatment to meet the standards.

[0036] In summary, this invention provides a method for treating o-tolueneacetic acid mother liquor. This method sequentially involves a first isothermal crystallization, a second multi-stage temperature-controlled crystallization, a second alkaline adjustment of the mother liquor followed by bipolar membrane electrodialysis enrichment, vacuum concentration and crystallization of the enriched solution, and a third vacuum distillation of the mother liquor to recover the solvent. This method achieves graded recovery of o-tolueneacetic acid and solvent recycling, significantly reducing resource waste and wastewater discharge. It has strong industrial feasibility, meets the requirements of green chemical development, and has broad industrial application prospects in the field of o-tolueneacetic acid production mother liquor treatment. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] To better illustrate the present invention, further examples are provided below.

[0039] The o-tolueneacetic acid mother liquor used in the following examples and comparative examples was prepared by reacting o-toluenechlorobenzyl chloride with sodium cyanide (NaCN) to produce o-tolueneacetonitrile. Subsequently, the o-tolueneacetonitrile underwent alkaline hydrolysis and acidification to obtain the target product, o-tolueneacetic acid. After separation (e.g., crystallization, filtration), the remaining liquid phase was the o-tolueneacetic acid mother liquor. The o-tolueneacetic acid mother liquor contained approximately 10 wt% o-tolueneacetic acid, approximately 2 wt% o-tolueneethanol, approximately 4 wt% sodium chloride, and approximately 42 wt% water and 42 wt% ethanol each.

[0040] The bipolar membrane electrodialysis device used in the following embodiments has an acid-base two-compartment configuration. The ion exchange membrane used is an alkali-resistant homogeneous anion exchange membrane (model AHT), and the bipolar membrane is a bipolar membrane (model BPS-1). All membrane materials are purchased from Hangzhou Lanran Technology Co., Ltd.

[0041] Example 1 This embodiment provides a method for treating o-tolueneacetic acid mother liquor (OMA mother liquor), the method comprising the following steps: Step 1: Heat 1000g of OMA mother liquor to 65℃ and stir at 50rpm for 30min to completely dissolve o-methylphenylacetic acid. Cool down to 45℃ at a rate of 8℃ / h and keep at this temperature for 1.5h. Filter through a 10μm filter cloth to obtain 40g of primary OMA crystals (yield 39.80%, purity 99.5%) and 960g of primary mother liquor (containing 6.27wt% OMA). Step 2: Heat the primary mother liquor to 65℃ and stir at 30 rpm for 20 min to dissolve residual OMA. Then, cool it down to 40℃ at 5℃ / h and keep it at that temperature for 5 h. Next, cool it down to 35℃ at 2℃ / h and keep it at that temperature for 2 h. Finally, cool it down to 30℃ at 1℃ / h and keep it at that temperature for 4 h to grow crystals. Filter the solution through a 10 μm filter cloth to obtain 31.60 g of secondary OMA crystals (yield 31.47%, purity 99.6%) and 928.4 g of secondary mother liquor (containing 3.09 wt% OMA). Step 3: Adjust the pH of the secondary mother liquor to 11 using a 10% sodium hydroxide solution, then pass it into a bipolar membrane electrodialysis device (AHT ion-exchange membrane, BPS-1 bipolar membrane), applying a voltage of 18V and a current density of 12mA / cm². 2 Electrolysis was performed at 28℃ until the residual OMA in the alkaline chamber was ≤1% (HPLC monitoring). The acid chamber solution was collected to obtain 320.2g of OMA-enriched solution (containing 8.73wt% OMA) and 608.2g of alkaline chamber solution (containing 0.13wt% OMA). Step 4: The OMA enrichment solution was fed into an enamel-lined vacuum concentrator equipped with a scraper stirrer and concentrated to 42% of its original mass at -0.09 MPa and 20°C. The solution was then cooled to 5°C and allowed to crystallize for 3 hours. The solid was centrifuged at 900 rpm using a horizontal scraper centrifuge. The solid was washed with ice water (8-10°C) and then with cold ethanol (8-10°C, 95% concentration) to obtain 27.85 g of triple OMA crystals (yield 27.71%, purity 99.5%) and 106.63 g of triple mother liquor (containing 0.23 wt% OMA). Step 5: Combine the mother liquor from the three stages, the solvent removed by vacuum concentration in Step 4, and the alkali chamber solution, and send them into a vacuum distillation tower. Distill at -0.088 MPa and 20℃, collect the fraction, and obtain 380g of recovered solvent. The residue at the bottom of the tower is directly sent to the biochemical wastewater treatment system for treatment and then discharged in compliance with standards.

[0042] Total yield = (40 × 99.5% + 31.6 × 99.6% + 27.85 × 99.5%) / 100 = 98.98% (relative to 100g OMA in the mother liquor).

[0043] Example 2 This embodiment provides a method for treating o-tolueneacetic acid mother liquor (OMA mother liquor), the method comprising the following steps: Step 1: Heat 1000g of OMA mother liquor to 60℃ and stir at 60rpm for 40min to completely dissolve o-methylphenylacetic acid. Cool down to 40℃ at a rate of 5℃ / h and keep warm for 1h. Filter through a 20μm filter cloth to obtain 41.6g of primary OMA crystals (yield 41.43%, purity 99.6%) and 958.4g of primary mother liquor (containing 6.11wt% OMA). Step 2: Heat the primary mother liquor to 60℃ and stir at 30 rpm for 30 min to dissolve residual OMA. Then, cool it down to 35℃ at 4℃ / h and keep it at that temperature for 3 h. Next, cool it down to 30℃ at 3℃ / h and keep it at that temperature for 1.5 h. Finally, cool it down to 25℃ at 2℃ / h and keep it at that temperature for 2.5 h to grow crystals. Filter the solution through a 20 μm filter cloth to obtain 32.8 g of secondary OMA crystals (yield 32.67%, purity 99.6%) and 925.6 g of secondary mother liquor (containing 2.80 wt% OMA). Step 3: Adjust the pH of the secondary mother liquor to 10 using a 5% sodium hydroxide solution, then pass it into a bipolar membrane electrodialysis device (AHT ion-exchange membrane, BPS-1 bipolar membrane), applying a voltage of 10V and a current density of 10mA / cm². 2 Electrolysis was performed at 30℃ until the residual OMA in the alkaline chamber was ≤1% (HPLC monitoring). The acid chamber solution was collected to obtain 311.2g of OMA-enriched solution (containing 8.07wt% OMA) and 614.4g of alkaline chamber solution (containing 0.13wt% OMA). Step 4: The OMA enrichment solution was transferred to an enamel-lined vacuum distillation vessel equipped with a scraper stirrer and concentrated to 43% of its original mass at -0.085 MPa and 30°C. The solution was then cooled to 5°C and allowed to crystallize for 2 hours. The solid was centrifuged at 800 rpm using a horizontal scraper centrifuge. The solid was washed with ice water (8-10°C) and then with cold ethanol (8-10°C, 95% concentration) to obtain 24.92 g of triple OMA crystals (yield 24.85%, purity 99.7%) and 108.9 g of triple mother liquor (containing 0.25 wt% OMA). Step 5: Combine the mother liquor from the three stages, the solvent removed by vacuum concentration in Step 4, and the alkali chamber solution, and send them into a vacuum distillation tower. Distill at -0.095 MPa and 30°C, collect the fraction, and obtain 387g of recovered solvent. The residue at the bottom of the tower is directly sent to the biochemical wastewater treatment system for treatment and then discharged in compliance with standards.

[0044] Total yield = (41.6 × 99.6% + 32.8 × 99.6% + 24.92 × 99.7%) / 100 = 98.95% (relative to 100g OMA in the mother liquor).

[0045] Example 3 This embodiment provides a method for treating o-tolueneacetic acid mother liquor (OMA mother liquor), the method comprising the following steps: Step 1: Heat 1000g of OMA mother liquor to 70℃ and stir at 30rpm for 20min to completely dissolve o-methylphenylacetic acid. Cool to 50℃ at a rate of 10℃ / h and keep warm for 2h. Filter through a 10μm filter cloth to obtain 40.7g of primary OMA crystals (yield 40.5%, purity 99.5%) and 959.3g of primary mother liquor (containing 6.20wt% OMA). Step 2: Heat the primary mother liquor to 70℃ and stir at 30 rpm for 15 min to dissolve residual OMA. Then, cool it down to 38℃ at 6℃ / h and keep it at that temperature for 4 h. Next, cool it down to 33℃ at 2℃ / h and keep it at that temperature for 2.5 h. Finally, cool it down to 28℃ at 2℃ / h and keep it at that temperature for 5 h to grow crystals. Filter the solution through a 10 μm filter cloth to obtain 30.64 g of secondary OMA crystals (yield 30.52%, purity 99.6%) and 928.66 g of secondary mother liquor (containing 3.12 wt% OMA). Step 3: Adjust the pH of the secondary mother liquor to 12 using an 8% sodium hydroxide solution, then pass it into a bipolar membrane electrodialysis device (AHT ion-exchange membrane, BPS-1 bipolar membrane), applying a voltage of 20V and a current density of 15mA / cm². 2Electrolysis was performed at 25°C until the residual OMA in the alkaline chamber was ≤1% (HPLC monitoring). The acid chamber solution was collected to obtain 316.6g of OMA-enriched solution (containing 8.57wt% OMA) and 612.06g of alkaline chamber solution (containing 0.30wt% OMA). Step 4: The OMA enrichment solution was fed into an enamel-lined vacuum concentrator equipped with a scraper stirrer and concentrated to 40% of its original mass at -0.095 MPa and 40°C. The solution was then cooled to 4°C and allowed to crystallize for 4 hours. The solid was centrifuged at 1000 rpm using a horizontal scraper centrifuge. The solid was washed with ice water (8-10°C) and then with cold ethanol (8-10°C, 95% concentration) to obtain 26.94 g of triple OMA crystals (yield 26.86%, purity 99.7%) and 99.7 g of triple mother liquor (containing 0.27 wt% OMA). Step 5: Combine the mother liquor from the three distillations, the solvent removed by vacuum concentration in Step 4, and the alkali chamber solution, and send them into a vacuum distillation tower. Distill at -0.085 MPa and 40°C, collect the fraction, and obtain 391g of recovered solvent. The residue at the bottom of the tower is directly sent to the biochemical wastewater treatment system for treatment and then discharged in compliance with standards.

[0046] Total yield = (40.7 × 99.5% + 30.64 × 99.6% + 26.94 × 99.7%) / 100 = 97.88% (relative to 100g OMA in the mother liquor).

[0047] Comparative Example 1 This comparative example provides a method for treating o-tolueneacetic acid mother liquor (OMA mother liquor). The only difference between this method and Example 1 is the gradient cooling rate in step two; the remaining steps are identical. The specific steps are as follows: Step 1, same as in Example 1. Step 2: Heat the primary mother liquor to 70℃ and stir at 30 rpm for 20 min to dissolve the residual OMA. Then, cool it down to 40℃ at 10℃ / h and keep it at that temperature for 5 h. Next, cool it down to 35℃ at 10℃ / h and keep it at that temperature for 2 h. Finally, cool it down to 30℃ at 5℃ / h and keep it at that temperature for 4 h to grow crystals. Filter the solution through a 10μm filter cloth to obtain secondary OMA crystals and secondary mother liquor. Steps three through five are the same as in Example 1.

[0048] The yield of secondary OMA crystals was 26.5%, with a purity of 90.3%, which is lower than 99%, making the product unqualified.

[0049] Comparative Example 2 This comparative example provides a method for treating o-tolueneacetic acid mother liquor (OMA mother liquor). The only difference from Example 1 is the ion exchange membrane and bipolar membrane used in step three. The ion exchange membrane is a standard homogeneous anion exchange membrane-ATG-10, and the bipolar membrane is a bipolar membrane-BP-2, both purchased from Hangzhou Lanran.

[0050] The yield of OMA crystals from the three trials was 25.31%, and the purity was 93.1%, which is less than 99%, making the product unqualified.

[0051] In summary, the method for treating o-tolueneacetic acid mother liquor provided by this invention can gradually and in stages recover o-tolueneacetic acid from the mother liquor, with a total recovery rate of over 95%. At the same time, it also achieves effective recovery and recycling of ethanol and water in the mother liquor, which is in line with the development trend of energy conservation, emission reduction, and green environmental protection. It is easy to implement in industry and has extremely high practical value.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating o-tolueneacetic acid mother liquor, characterized in that, Includes the following steps: Step a: Heat the o-tolueneacetic acid mother liquor to dissolve the o-tolueneacetic acid contained therein, then cool it to 40℃~50℃, keep it at the temperature to crystallize, filter it, and obtain primary o-tolueneacetic acid crystals and primary mother liquor; Step b: The primary mother liquor is heated to dissolve residual o-tolueneacetic acid, then cooled to 35°C~40°C at a first cooling rate and held for a first preset time; then cooled to 30°C~35°C at a second cooling rate and held for a second preset time; finally cooled to 25°C~30°C at a third cooling rate and held for a third preset time, then filtered to obtain secondary o-tolueneacetic acid crystals and secondary mother liquor; Step c: Adjust the pH of the secondary mother liquor to alkaline, then pass it into a bipolar membrane electrodialysis device, collect the acid chamber solution, and obtain o-tolueneacetic acid enriched solution; Step d: The o-tolueneacetic acid enrichment solution is concentrated under reduced pressure to obtain o-tolueneacetic acid concentrate and solvent removal solution; the o-tolueneacetic acid concentrate is cooled to 4℃~5℃, kept at the temperature to crystallize, centrifuged, and washed to obtain three-stage o-tolueneacetic acid crystals and three-stage mother liquor. Step e: Combine the three mother liquors and the solvent-removed liquors and perform vacuum distillation, collect the fractions, and obtain recovered water and ethanol; The ion exchange membrane of the bipolar membrane electrodialysis device is an alkali-resistant homogeneous anion exchange membrane-AHT; the bipolar membrane is a bipolar membrane-BPS-1.

2. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step a, the temperature for heating is 60℃~70℃; and / or In step a, the time for heat preservation and crystallization is 1h~2h; and / or In step a, the pore size of the filter medium used for filtration is 10μm~20μm; and / or In step a, the temperature is lowered to 40℃~50℃ using a programmed cooling method, with a cooling rate of 5℃ / h~10℃ / h.

3. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step b, the temperature for heating is 60℃~70℃.

4. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step b, the first cooling rate is 4℃ / h~6℃ / h, and the first preset time is 3h~5h; the second cooling rate is 2℃ / h~3℃ / h, and the second preset time is 1.5h~2.5h; the third cooling rate is 1℃ / h~2℃ / h, and the third preset time is 2.5h~5h.

5. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step c, alkalinity refers to a pH value of 9-12; and / or In step c, the voltage of the bipolar membrane electrodialysis device is set to 10V~20V, and the current density is 10mA / cm². 2 ~15mA / cm 2 The temperature is 25℃~30℃.

6. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step d, the pressure of the vacuum concentration is -0.085MPa to -0.095MPa, and the temperature is 20℃ to 40℃.

7. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step d, the o-tolueneacetic acid concentrate is 40% to 45% of the mass of the o-tolueneacetic acid enrichment solution.

8. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step d, the time for heat preservation and crystallization is 2h~4h.

9. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step d, the washing process specifically includes the following steps: The obtained solid was washed and filtered with ice water at 8℃~10℃ and cold ethanol at 8℃~10℃ in sequence.

10. The method for treating o-methylphenylacetic acid mother liquor as described in claim 1, characterized in that, In step e, the pressure of the vacuum distillation is -0.085MPa to -0.095MPa, and the temperature is 20℃ to 40℃.