A pretreatment method of chemical wastewater

Abstract

The present application relates to the technical field of chemical wastewater, and discloses a pretreatment method of chemical wastewater, which solves the problems of high treatment cost, low organic matter removal rate and poor resource utilization rate of the existing production wastewater treatment of o-aminobenzoic acid, methyl o-aminobenzoate and sodium saccharin. The method first pretreats the salt components of the wastewater to eliminate the interference of inorganic salts on the subsequent reaction, then carries out hydrolysis / alkaline hydrolysis treatment, then carries out diazotization-coupling reaction to convert the o-aminobenzoic acid components into high-value-added 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazenyl)benzoic acid byproducts, and finally recovers crude o-phthalic acid by cooling and precipitation. The utilization rate of the o-aminobenzoic acid components in the wastewater reaches more than 99.9%, and the method has the advantages of low treatment cost, low equipment investment, short process flow, high resource utilization efficiency and complete wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of chemical wastewater technology, specifically to a pretreatment method for chemical wastewater. Background Technology

[0002] In the fine chemical production process, anthranilic acid, methyl anthranilate, and sodium saccharin are important pharmaceutical and food additive intermediates, generating large amounts of high-concentration organic wastewater. Specifically, the main organic pollutants in the wastewater from anthranilic acid production are phthalic acid and anthranilic acid, with a COD of 25,000–40,000 mg / L; the main organic pollutants in the wastewater from methyl anthranilate production are phthalic acid, anthranilic acid, methyl anthranilate, and methyl anthranilate, with a COD as high as 160,000–200,000 mg / L; and the main organic pollutants in the wastewater from sodium saccharin production are phthalic acid, anthranilic acid, and methyl anthranilate, with a COD of 15,000–20,000 mg / L.

[0003] The aforementioned wastewater not only has a large discharge volume, but also contains mostly benzene ring-based recalcitrant substances with few biodegradable groups, making wastewater treatment extremely difficult. Currently, publicly available wastewater treatment solutions in China mainly include MVR desalination, heavy metal complexation, flocculation sedimentation, biological treatment, Fenton oxidation, and resin adsorption and desorption processes. However, existing technologies have many insurmountable drawbacks:

[0004] The treatment costs are high, the equipment investment is large, the energy consumption is high, the process is complex, and a large amount of hazardous waste, solid waste and secondary waste gas are generated during the treatment process, which puts a heavy environmental burden on enterprises.

[0005] The recovery rate of characteristic organic pollutants in wastewater is low, the removal rate of organic matter in wastewater after pretreatment is insufficient, and the COD of wastewater cannot be significantly reduced, resulting in an extremely high load on subsequent biological treatment.

[0006] The method only performs simple separation of anthranilic acid in wastewater, resulting in high residual levels. It lacks effective treatment methods for components such as methyl anthranilate and methyl anthranilate in wastewater, and it does not achieve the separation and recovery of phthalic acid, the main impurity in wastewater.

[0007] The degree of resource utilization is extremely low, and it can only achieve the recovery of low-value-added raw materials, or even fail to achieve resource utilization and cannot transform pollutants in wastewater into products with economic value.

[0008] The lack of pretreatment of inorganic salts in the wastewater system can lead to changes in wastewater composition due to external conditions such as high heat during subsequent treatment, further reducing the recovery rate and treatment effect of organic pollutants.

[0009] To address the aforementioned issues, methods for recovering anthranilic acid from mother liquor wastewater, such as the one disclosed in CN102190590A, employ a copper salt complexation process. This requires multiple steps of repeated complexation and desorption, introducing a large amount of metal complexes into the system and generating new pollutants. Another method for recovering anthranilic acid from mother liquor or wastewater, disclosed in CN1923799, uses an ion exchange resin process, which suffers from low recovery rates, limited processing capacity, and high resin regeneration costs. A preparation method for recovering anthranilic acid from saccharin wastewater, disclosed in CN103193665, also employs a copper salt complexation process but adds a crude product decolorization and purification step, resulting in a longer process and higher costs. A method for treating saccharin production wastewater, disclosed in CN104478028, uses extraction to extract anthranilic acid, which suffers from large extractant usage, low extraction yield, difficulty in reusing the extractant, and the ability to extract only a small amount of anthranilic acid without separating other organic components in the wastewater.

[0010] In summary, existing technologies cannot fundamentally solve the problem of treating wastewater from the production of anthranilic acid, nor can they simultaneously achieve the wastewater treatment goals of low cost, high removal rate, and high resource utilization. Summary of the Invention

[0011] (a) Technical problems to be solved

[0012] To address the shortcomings of existing technologies, this invention provides a pretreatment method for chemical wastewater. This method thoroughly separates organic pollutants in wastewater, achieves a high organic matter removal rate, and features a simple process flow, low equipment investment, and low treatment costs. Furthermore, it can convert pollutants in wastewater into by-products with high economic added value, realizing the resource utilization of wastewater and fundamentally solving the treatment problems of wastewater from the production of anthranilic acid, methyl anthranilate, and sodium saccharin.

[0013] (II) Technical Solution

[0014] To achieve the above objectives, the present invention provides the following technical solution: a pretreatment method for chemical wastewater, comprising the following steps:

[0015] (1) Salt component pretreatment: Based on the content and type of salt components in the chemical wastewater to be treated, the parameters of the wastewater system are adjusted to eliminate the interference of multi-component salts on subsequent chemical reactions, and pretreated wastewater is obtained;

[0016] The chemical wastewater to be treated is any one of the following: wastewater from the production of anthranilic acid, wastewater from the production of methyl anthranilate, and wastewater from the production of sodium saccharin.

[0017] (2) Hydrolysis and alkaline treatment: The pretreated wastewater obtained in step (1) is subjected to hydrolysis / alkaline treatment to remove ester groups and amide groups in the wastewater, and the organic components are converted into active components containing amino groups to obtain alkaline-hydrolyzed wastewater;

[0018] (3) Amino content determination: The amino group content A in the alkaline hydrolyzed wastewater obtained in step (2) was determined by titration.

[0019] (4) Acid adjustment and pre-cooling: Add acid to the alkaline wastewater to adjust the pH of the system to 3.0~3.5. After adding concentrated hydrochloric acid, cool the system to -5~0℃, keep it warm and stir to obtain the system to be diazotized;

[0020] (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and detect the reaction endpoint with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns slightly blue. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0021] (6) Preparation of coupling solution: Prepare a coupling solution containing 1,3,5-pyrazolone according to the amount M of sodium nitrite solution used in step (5);

[0022] (7) Coupling reaction: The coupling solution is added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred to obtain the coupling reaction solution.

[0023] (8) By-product recovery: Add hydrochloric acid to the coupling reaction solution to adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir, then cool down and separate the solid and liquid to obtain the first solid by-product 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the separated filtrate to 0~10℃, precipitate the solid and filter to obtain the second by-product crude phthalic acid, thus completing the wastewater pretreatment.

[0024] Furthermore, in step (1), the specific method for pretreatment of the salt components is as follows:

[0025] If the wastewater to be treated is wastewater from the production of anthranilic acid, its salt component is pure sodium chloride, and no salt treatment is required. It can be directly used as pre-treated wastewater in step (2).

[0026] If the wastewater to be treated is wastewater from the production of methyl anthranilate, its salt components are sodium carbonate and sodium bicarbonate. Concentrated hydrochloric acid is added to the wastewater to adjust the pH value of the system to 6.0~6.5. After stirring evenly, pretreated wastewater is obtained.

[0027] If the wastewater to be treated is wastewater from the production of sodium saccharin, add hydrochloric acid to the wastewater to adjust the pH value to 1.0~3.0, heat to 60~80℃, keep warm and stir for 1 hour to obtain pretreated wastewater.

[0028] Furthermore, in step (2), the specific method for the hydrolysis-alkali hydrolysis treatment is as follows:

[0029] If the wastewater to be treated is o-aminobenzoic acid production wastewater, which has no ester group or amide group, there is no need to perform hydrolysis and alkaline hydrolysis treatment. The pretreated wastewater can be directly used as alkaline hydrolysis wastewater and enter step (3).

[0030] If the wastewater to be treated is wastewater from the production of methyl anthranilate, the content of methyl anthranilate in the wastewater is detected by liquid chromatography or gas chromatography using the external standard method. 1.1 to 1.2 molar amounts of liquid alkali are added to the wastewater, and the mixture is heated to 70 to 80°C and stirred for 1 hour. Alternatively, the wastewater can be directly sent to a methanol recovery tower. The methanol is recovered using the heat energy of the methanol recovery tower, and the ester groups are removed by alkaline hydrolysis at the same time, resulting in alkaline hydrolyzed wastewater.

[0031] If the wastewater to be treated is saccharin sodium production wastewater, first add liquid alkali to the pretreated wastewater to adjust the pH of the system to 6.5~7.0. Detect the content of methyl anthranilate in the wastewater by liquid chromatography or gas chromatography using the external standard method. Add 1.1~1.2 times the molar amount of liquid alkali to the wastewater, heat to 70~80℃ and stir for 1 hour to obtain alkaline hydrolysis wastewater.

[0032] Further, in step (3), the specific method for determining the amino group content A by titration is as follows: accurately weigh the sewage sample mg, accurate to 0.0002g, place it in a 150ml beaker, add 5ml of concentrated hydrochloric acid, stir evenly at room temperature, add 50ml of distilled water, cool the solution to below 15℃, titrate with a sodium nitrite standard solution with a known molar concentration Cmol / L, continuously stir during the titration process, and detect in real time with starch potassium iodide test paper. When the starch potassium iodide test paper shows a stable light blue color, the titration is terminated, and the volume of sodium nitrite standard solution consumed Vml is recorded.

[0033] Calculate the mass percentage A of amino groups in wastewater using the following formula:

[0034] A = 100 × C × V × 0.137 / m

[0035] In the formula, 0.137 is the millimolecular mass of anthranilic acid, in g / mmol.

[0036] Further, in step (4), the amount of concentrated hydrochloric acid added is measured as 1.8 times the product of the wastewater mass and the amino content A, and the mass fraction of concentrated hydrochloric acid is 30%; after cooling to -5~0℃, the heat preservation and stirring time is 10min.

[0037] Further, in step (6), the method for preparing the coupling solution is as follows: according to the mass ratio, add 1.6M parts of water, M / 12 parts of sodium carbonate, 0.5M parts of 32% liquid alkali, and 2M / 3 parts of 1,3,5-pyrazolone to the coupling vessel, stir until the materials are completely dissolved, and cool to 0°C to obtain the coupling solution.

[0038] Furthermore, in step (7), after the coupling solution is added dropwise, the reaction time is 2 hours of keeping warm and stirring.

[0039] Furthermore, in step (8), after heating to 70°C, the time for holding and stirring is 0.5h.

[0040] Compared with the prior art, the present invention has the following significant advantages:

[0041] This invention boasts extremely low processing costs. Aside from the basic chemical raw materials required for byproduct preparation, it consumes only a small amount of acid and alkali reagents, eliminating the need for expensive water treatment agents, resins, extractants, and other consumables. Furthermore, it fully utilizes existing process flow equipment in the production workshop, requiring no additional specialized equipment, resulting in minimal equipment investment and significantly reducing wastewater treatment costs for enterprises. This invention offers high processing capacity and efficiency. The process flow is short, without complex multi-step complexation analysis, regeneration, or distillation procedures. It features fast processing speed, continuous operation, and minimal reliance on new equipment resources, making it suitable for the wastewater treatment needs of large-scale industrial production.

[0042] This invention has a high degree of resource utilization and significant economic benefits. It breaks through the traditional approach of "pollutant separation and removal" in existing technologies. From the perspective of comprehensive resource utilization, it transforms anthranilic acid pollutants in wastewater into high-value-added azobenzoic acid organic products, while recovering crude phthalic acid. This not only solves the problem of wastewater treatment, but also brings additional economic benefits to enterprises, achieving the circular economy goal of "turning waste into treasure".

[0043] This invention utilizes the amino groups inherent in recalcitrant benzene ring compounds in wastewater. Through a diazotization-coupling reaction, the stability of the original recalcitrant macromolecules is broken, and they are directionally converted into easily separable azo crystals, thus completely removing high-concentration organic pollutants from the liquid phase. This method directionally converts organic pollutants into solid byproducts through chemical reactions, generating no hazardous waste or solid waste, and producing no exhaust gas emissions. It avoids the secondary pollution problems caused by metal complexes and extractants in existing technologies, resulting in significant environmental benefits.

[0044] This invention sets up targeted pretreatment and alkaline hydrolysis steps based on the characteristics of salt and organic components in different wastewaters, eliminating the interference of inorganic salts and different organic groups on the core reaction, ensuring the stable progress of the diazotization-coupling reaction, and showing excellent treatment effect on o-aminobenzoic acid production wastewater of different concentrations and components. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] In this embodiment of the invention, the method for determining the amino group content A is as follows: Accurately weigh the wastewater sample (mg, accurate to 0.0002g), place it in a 150ml beaker, add 5ml of concentrated hydrochloric acid, stir evenly at room temperature, then add 50ml of distilled water. Cool the solution to below 15℃, and titrate with a sodium nitrite standard solution of known molar concentration (Cmol / L). Stir continuously during the titration process, and monitor in real time with starch-potassium iodide test paper. The titration is terminated when the starch-potassium iodide test paper shows a stable faint blue color. Record the volume of sodium nitrite standard solution consumed (Vml). Calculate the mass percentage content A of amino groups in the wastewater using the following formula: A = 100 × C × V × 0.137 / m, where 0.137 is the millimolecular mass of anthranilic acid, in g / mmol.

[0047] Example 1

[0048] The wastewater to be treated in this embodiment is wastewater from the production of anthranilic acid. 500g of wastewater was taken, and the amino group content A was found to be 1.37%, the COD of the raw water was 36000mg / L, and the appearance was dark red.

[0049] The specific pretreatment steps are as follows: (1) Salt component pretreatment: The salt component of this wastewater is pure sodium chloride, which does not require salt treatment and can directly enter the subsequent steps;

[0050] (2) Hydrolysis and alkaline treatment: The wastewater has no ester groups and amide groups, so no alkaline treatment is required, and the amino content can be directly determined;

[0051] (3) Acid adjustment and pre-cooling: Add 30% concentrated hydrochloric acid to the wastewater. The amount added is 500×A×1.8=12.3g. After stirring evenly, cool down to -5℃ and keep warm and stir for 10min to obtain the diazotization system.

[0052] (4) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 13.7g of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0053] (5) Preparation of coupling solution: According to the amount of sodium nitrite solution used, M=13.7g, add water 1.6M=21.9g, sodium carbonate M / 12=1.15g, 32% liquid alkali 0.5M=6.85g, and 1,3,5-pyrazolone 2M / 3=9.13g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0054] (6) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0055] (7) By-product recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid, dry to obtain 15.5g of solid, which is the first by-product 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 1.2g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0056] The treated wastewater was tested and found to have a COD of 1300 mg / L, a pale yellow appearance, and an organic matter removal rate of 96.39%.

[0057] Example 2

[0058] The wastewater to be treated in this embodiment is wastewater from the production of anthranilic acid. 500g of wastewater was taken, and the amino group content A was found to be 0.91%, the COD of the raw water was 28000mg / L, and the appearance was dark red.

[0059] The specific preprocessing steps are as follows:

[0060] (1) Salt component pretreatment: The salt component of this wastewater is pure sodium chloride, which does not require salt treatment and can be directly introduced into the subsequent steps;

[0061] (2) Hydrolysis and alkaline treatment: The wastewater has no ester groups and amide groups, so no alkaline treatment is required, and the amino content can be directly determined;

[0062] (3) Acid adjustment and pre-cooling: Add 30% concentrated hydrochloric acid to the wastewater. The amount added is 500×A×1.8=8.2g. After stirring evenly, cool down to -5℃ and keep warm and stir for 10min to obtain the diazotization system.

[0063] (4) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 9.1g of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0064] (5) Preparation of coupling solution: According to the amount of sodium nitrite solution used, M=9.1g, add water 1.6M=14.56g, sodium carbonate M / 12=0.76g, 32% liquid alkali 0.5M=4.55g, and 1,3,5-pyrazolone 2M / 3=6.1g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0065] (6) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0066] (7) Byproduct recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid, dry to obtain 10.3g of solid, which is the first byproduct 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 0.8g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0067] The treated wastewater was tested and found to have a COD of 1500 mg / L, a pale yellow appearance, and an organic matter removal rate of 94.64%.

[0068] Example 3

[0069] The wastewater to be treated in this embodiment is wastewater from the production of methyl anthranilate. 500g of wastewater was taken, and the COD of the raw water was measured to be 215,000 mg / L. The appearance of the wastewater was red.

[0070] The specific preprocessing steps are as follows:

[0071] (1) Salt component pretreatment: Add 40g of 30% concentrated hydrochloric acid to the wastewater, adjust the pH of the system to 6.3, stir for 10min to eliminate the interference of sodium carbonate and sodium bicarbonate, and obtain pretreated wastewater;

[0072] (2) Hydrolysis and alkaline treatment: 8g of 32% liquid alkali was added to the pretreated wastewater and sent to a methanol distillation column to recover methanol. The bottom temperature of the distillation column was controlled at 110℃ and the top temperature at 65~68℃. The alkaline hydrolysis of ester groups was completed while recovering methanol. After the methanol was recovered, 431g of alkaline hydrolyzed wastewater was obtained.

[0073] (3) Determination of amino group content: The amino group content A in alkaline hydrolysis wastewater was determined to be 3.05% by titration.

[0074] (4) Acid adjustment and pre-cooling: Add 30% concentrated hydrochloric acid to the alkaline wastewater to adjust the pH value of the system to 3.2. After the yellow solid precipitates, add 30% concentrated hydrochloric acid again. The amount added is 431×A×1.8=23.7g. After stirring evenly, cool down to -5℃ and keep warm and stir for 10min to obtain the system to be diazotized.

[0075] (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 26.3g of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0076] (6) Preparation of coupling solution: Based on the amount of sodium nitrite solution used, M=26.3g, add water 1.6M=42g, sodium carbonate M / 12=2.2g, 32% liquid alkali 0.5M=13.15g, and 1,3,5-pyrazolone 2M / 3=17.5g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0077] (7) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0078] (8) Byproduct recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid, dry to obtain 30.2g of solid, which is the first byproduct 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 0.8g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0079] The treated wastewater was tested and found to have a COD of 1400 mg / L, a pale yellow appearance, and an organic matter removal rate of 99.35%.

[0080] Example 4

[0081] The wastewater to be treated in this embodiment is wastewater from the production of methyl anthranilate. 500g of wastewater was taken, and the COD of the raw water was tested to be 186,000 mg / L. The appearance was red.

[0082] The specific pretreatment steps are as follows: (1) Salt component pretreatment: Add 40g of 30% concentrated hydrochloric acid to the sewage, adjust the pH value of the system to 6.3, stir for 10min to eliminate the interference of sodium carbonate and sodium bicarbonate, and obtain pretreated sewage;

[0083] (2) Hydrolysis and alkaline treatment: 8g of 32% liquid alkali was added to the pretreated wastewater and sent to a methanol distillation column to recover methanol. The bottom temperature of the distillation column was controlled at 110℃ and the top temperature at 65~68℃. The alkaline hydrolysis of ester groups was completed while recovering methanol. After the methanol was recovered, 435g of alkaline hydrolyzed wastewater was obtained.

[0084] (3) Determination of amino content: The amino group content A in alkaline hydrolyzed wastewater was determined to be 2.41% by titration.

[0085] (4) Acid adjustment and pre-cooling: Add 30% concentrated hydrochloric acid to the alkaline wastewater to adjust the pH of the system to 3.2. After the yellow solid precipitates, add another 30% concentrated hydrochloric acid. The amount added is 435×A×1.8=18.9g. After stirring evenly, cool down to -5℃ and keep warm and stir for 10min to obtain the system to be diazotized.

[0086] (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 20.8g of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0087] (6) Preparation of coupling solution: Based on the amount of sodium nitrite solution used, M=20.8g, add water 1.6M=33.3g, sodium carbonate M / 12=1.73g, 32% liquid alkali 0.5M=10.4g, and 1,3,5-pyrazolone 2M / 3=13.87g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0088] (7) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0089] (8) By-product recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid. After drying, 24.1g of solid is obtained, which is the first by-product 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 0.75g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0090] The treated wastewater was tested and found to have a COD of 1300 mg / L, a pale yellow appearance, and an organic matter removal rate of 99.30%.

[0091] Example 5

[0092] The wastewater to be treated in this embodiment is wastewater from the production of sodium saccharin. 500g of wastewater was taken, and the COD of the raw water was tested to be 18000mg / L. The appearance was red.

[0093] The specific pretreatment steps are as follows: (1) Salt component pretreatment: Add 3g of 30% concentrated hydrochloric acid to the sewage, adjust the pH value of the system to 2.3, heat to 70℃, keep warm and stir for 1h to obtain pretreated sewage;

[0094] (2) Hydrolysis and alkaline treatment: Add 6g of 32% liquid alkali to the pretreated wastewater, adjust the pH of the system to 6.5~7.0, heat to 80℃, keep warm and stir for 1h to complete the alkaline hydrolysis of ester groups and amide groups, and obtain alkaline hydrolyzed wastewater;

[0095] (3) Determination of amino group content: The amino group content A in alkaline hydrolyzed wastewater was determined to be 1.6% by titration.

[0096] (4) Acid adjustment and pre-cooling: Add 30% concentrated hydrochloric acid to the alkaline wastewater to adjust the pH value of the system to 3.2. After the yellow solid precipitates, add 30% concentrated hydrochloric acid again. The amount added is 500×A×1.8=14.4g. After stirring evenly, cool down to -5℃ and keep warm and stir for 10min to obtain the system to be diazotized.

[0097] (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 16g ​​of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the system at -5~0℃ to react and obtain the diazonium salt reaction solution.

[0098] (6) Preparation of coupling solution: According to the amount of sodium nitrite solution M=16g, add water 1.6M=25.6g, sodium carbonate M / 12=1.33g, 32% liquid alkali 0.5M=8g, and 1,3,5-pyrazolone 2M / 3=10.7g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0099] (7) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0100] (8) Byproduct recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid, dry to obtain 18.5g of solid, which is the first byproduct 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 0.5g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0101] The treated wastewater was tested and found to have a COD of 1400 mg / L, a pale yellow appearance, and an organic matter removal rate of 92.22%.

[0102] Example 6

[0103] The wastewater to be treated in this embodiment is wastewater from the production of sodium saccharin. 500g of wastewater was taken, and the COD of the raw water was measured to be 15500mg / L. The appearance of the wastewater was red.

[0104] The specific preprocessing steps are as follows:

[0105] (1) Salt component pretreatment: Add 3g of 30% concentrated hydrochloric acid to the wastewater, adjust the pH of the system to 2.3, heat to 70℃, keep warm and stir for 1h to obtain pretreated wastewater;

[0106] (2) Hydrolysis and alkaline treatment: Add 6g of 32% liquid alkali to the pretreated wastewater, adjust the pH of the system to 6.5~7.0, heat to 80℃, keep warm and stir for 1h to complete the alkaline hydrolysis of ester groups and amide groups, and obtain alkaline hydrolyzed wastewater;

[0107] (3) Amino content determination: The amino group content A in the alkaline hydrolysis wastewater was determined to be 1.8% by titration; (4) Acid adjustment and pre-cooling: 30% concentrated hydrochloric acid was added to the alkaline hydrolysis wastewater to adjust the pH value of the system to 3.2. After the yellow solid precipitated, 30% concentrated hydrochloric acid was added again. The amount added was 500×A×1.8=16.2g. After stirring evenly, the temperature was lowered to -5℃ and kept warm and stirred for 10min to obtain the diazotization system;

[0108] (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and continuously detect with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns a stable light blue color. A total of 18g of sodium nitrite solution is consumed. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution.

[0109] (6) Preparation of coupling solution: According to the amount of sodium nitrite solution used, M=18g, add water 1.6M=28.8g, sodium carbonate M / 12=1.5g, 32% liquid alkali 0.5M=9g, and 1,3,5-pyrazolone 2M / 3=12g to the coupling reaction flask, stir until the materials are completely dissolved, and cool to 0℃ to obtain the coupling solution;

[0110] (7) Coupling reaction: The coupling solution is slowly added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred for 2 hours to obtain the coupling reaction solution.

[0111] (8) By-product recovery: Add 30% concentrated hydrochloric acid to the coupling reaction solution, adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir for 0.5h, cool down and filter to obtain an orange-yellow solid, dry to obtain 20.8g of solid, which is the first by-product 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the filtrate obtained by filtration to 0~10℃, precipitate the solid and filter again, dry to obtain 0.6g of light yellow crude phthalic acid, and complete the wastewater pretreatment.

[0112] The treated wastewater was tested and found to have a COD of 1600 mg / L, a pale yellow appearance, and an organic matter removal rate of 89.68%.

[0113] 1. Methods for determining chemical oxygen demand (COD)

[0114] The chemical oxygen demand (COD) before and after wastewater treatment was determined using the potassium dichromate method.

[0115] Specifically, take an appropriate amount of wastewater sample to be tested, and dilute it if necessary to ensure that its concentration is within the linear range of the test; then digest and titrate it according to the potassium dichromate standard method to determine the chemical oxygen demand of the sample, and express the result in mg / L.

[0116] To ensure data accuracy, each sample was measured at least twice in parallel, and the average value was taken as the final result. The treatment effect was evaluated by the change in COD before and after treatment.

[0117] 2. The organic matter removal rate is calculated using the following formula:

[0118] Organic matter removal rate (%) = (COD0 - COD1) / COD0 × 100%

[0119] Where: COD0 is the chemical oxygen demand of the wastewater before treatment; COD1 is the chemical oxygen demand of the wastewater after treatment.

[0120] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0121] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0122] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A method for pretreatment of chemical wastewater, characterized in that, Includes the following steps: (1) Salt component pretreatment: Based on the content and type of salt components in the chemical wastewater to be treated, the parameters of the wastewater system are adjusted to eliminate the interference of multi-component salts on subsequent chemical reactions, and pretreated wastewater is obtained; The chemical wastewater to be treated is any one of the following: wastewater from the production of anthranilic acid, wastewater from the production of methyl anthranilate, and wastewater from the production of sodium saccharin. (2) Hydrolysis and alkaline treatment: The pretreated wastewater obtained in step (1) is subjected to hydrolysis / alkaline treatment to remove ester groups and amide groups in the wastewater, and the organic components are converted into active components containing amino groups to obtain alkaline-hydrolyzed wastewater; (3) Amino content determination: The amino group content A in the alkaline hydrolyzed wastewater obtained in step (2) was determined by titration. (4) Acid adjustment and pre-cooling: Add acid to alkaline wastewater to adjust the pH of the system to 3.0~3.

5. After adding concentrated hydrochloric acid, cool the system to -5~0℃, keep it warm and stir to obtain the system to be diazotized; (5) Diazotization reaction: Prepare a 30% sodium nitrite solution and add it dropwise to the system to be diazotized. During the dropwise addition process, control the system temperature at -5~0℃ and detect the reaction endpoint with starch-potassium iodide test paper. Stop the dropwise addition when the test paper turns slightly blue. After the dropwise addition is completed, keep the reaction at -5~0℃ to obtain the diazonium salt reaction solution. (6) Preparation of coupling solution: Prepare a coupling solution containing 1,3,5-pyrazolone according to the amount M of sodium nitrite solution used in step (5); (7) Coupling reaction: The coupling solution is added dropwise to the diazonium salt reaction solution, and the reaction temperature is controlled at 0~15℃. After the addition is completed, the mixture is kept warm and stirred to obtain the coupling reaction solution. The coupling solution is prepared by adding 1.6M parts of water, M / 12 parts of sodium carbonate, 0.5M parts of 32% alkali solution, and 2M / 3 parts of 1,3,5-pyrazolone to the coupling vessel according to the mass ratio. The mixture is stirred until the materials are completely dissolved and cooled to 0℃ to obtain the coupling solution. (8) Byproduct recovery: Add hydrochloric acid to the coupling reaction solution to adjust the pH of the system to 2.5~3.0, heat to 70℃ and stir, then cool down and separate the solid and liquid to obtain the first solid byproduct 2-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazyl)benzoic acid; cool the separated filtrate to 0~10℃, precipitate the solid and filter to obtain the second byproduct crude phthalic acid, thus completing the wastewater pretreatment; In step (1), the specific method for pretreatment of the salt components is as follows: If the wastewater to be treated is wastewater from the production of anthranilic acid, its salt component is pure sodium chloride, and no salt treatment is required. It can be directly used as pre-treated wastewater in step (2). If the wastewater to be treated is wastewater from the production of methyl anthranilate, its salt components are sodium carbonate and sodium bicarbonate. Concentrated hydrochloric acid is added to the wastewater to adjust the pH value of the system to 6.0~6.

5. After stirring evenly, pretreated wastewater is obtained. If the wastewater to be treated is saccharin sodium production wastewater, add hydrochloric acid to the wastewater to adjust the pH value to 1.0~3.0, heat to 60~80℃, keep warm and stir for 1 hour to obtain pretreated wastewater; In step (2), the specific method for hydrolysis and alkaline hydrolysis is as follows: If the wastewater to be treated is o-aminobenzoic acid production wastewater, which has no ester group or amide group, there is no need to perform hydrolysis and alkaline hydrolysis treatment. The pretreated wastewater can be directly used as alkaline hydrolysis wastewater and enter step (3). If the wastewater to be treated is wastewater from the production of methyl anthranilate, the content of methyl anthranilate in the wastewater is detected by liquid chromatography or gas chromatography using the external standard method. 1.1 to 1.2 molar amounts of liquid alkali are added to the wastewater, and the mixture is heated to 70 to 80°C and stirred for 1 hour. Alternatively, the wastewater can be directly sent to a methanol recovery tower. The methanol is recovered using the heat energy of the methanol recovery tower, and the ester groups are removed by alkaline hydrolysis at the same time, resulting in alkaline hydrolyzed wastewater. If the wastewater to be treated is saccharin sodium production wastewater, first add liquid alkali to the pretreated wastewater to adjust the pH of the system to 6.5~7.

0. Detect the content of methyl anthranilate in the wastewater by liquid chromatography or gas chromatography using the external standard method. Add 1.1~1.2 times the molar amount of liquid alkali to the wastewater, heat to 70~80℃ and stir for 1 hour to obtain alkaline hydrolysis wastewater.

2. The pretreatment method for chemical wastewater according to claim 1, characterized in that, In step (3), the specific method for determining the amino group content A by titration is as follows: accurately weigh the sewage sample, place it in a 150ml beaker, add 5ml of concentrated hydrochloric acid, stir evenly at room temperature, add 50ml of distilled water, cool the solution to below 15℃, and titrate with a sodium nitrite standard solution of known molar concentration Cmol / L. During the titration process, stir continuously and detect in real time with starch-potassium iodide test paper. When the starch-potassium iodide test paper shows a stable light blue color, the titration is terminated, and the volume of sodium nitrite standard solution consumed, Vml, is recorded. Calculate the mass percentage content A of amino groups in the sewage according to the following formula: A=100×C×V×0.137 / m where 0.137 is the millimolecular mass of anthranilic acid, in g / mmol, and m is the mass of the sewage sample.

3. The pretreatment method for chemical wastewater according to claim 1, characterized in that, In step (4), the amount of concentrated hydrochloric acid added is measured as 1.8 times the product of the wastewater mass and the amino content A, and the mass fraction of concentrated hydrochloric acid is 30%; after cooling to -5~0℃, the temperature is kept warm and stirred for 10 minutes.

4. The pretreatment method for chemical wastewater according to claim 1, characterized in that, In step (7), after the coupling solution is added dropwise, the reaction time is 2 hours of keeping warm and stirring.

5. The pretreatment method for chemical wastewater according to claim 1, characterized in that, In step (8), after heating to 70°C, the time for holding and stirring is 0.5h.