A treatment method for the wastewater from phenylacetic acid production

Abstract

The present invention relates to the technical field of industrial wastewater treatment, and specifically discloses a treatment method for wastewater produced in phenylacetic acid production. In the present invention, liquid alkali is used to convert sulfuric acid in the wastewater into sodium sulfate, and an alcohol solution is added at a specific temperature to extract various organic substances containing functional groups such as amino groups and isocyanide groups in the wastewater, so that the organic substances are fully separated from the sodium sulfate brine, obtaining a first aqueous phase and a first oil phase; the first aqueous phase obtained by separation is reacted with liquid alkali at a specific temperature to fully convert the sulfate of organic amine in the wastewater into organic amine and sodium sulfate, and then, the organic amine is fully extracted by adding an alcohol solution to achieve the full separation of the organic amine from the sodium sulfate alkaline brine, obtaining a second aqueous phase and a second oil phase; finally, the obtained second aqueous phase is adsorbed and purified by macroporous styrene adsorption resin to obtain a purified liquid; the purified liquid is successively subjected to oxidation, reduction, neutralization, and drying to obtain a sodium sulfate product with a purity of more than 99.5%.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial wastewater treatment, and particularly relates to a method for treating wastewater produced in the production of phenylacetic acid. Background Art

[0002] Phenylacetic acid can undergo typical reactions of carboxyl group, methylene hydrogen and benzene ring to generate many useful intermediates, and is an important chemical raw material. At present, the most widely used method for producing phenylacetic acid is the hydrolysis method of phenylacetonitrile. In this method, benzyl chloride reacts with sodium cyanide under the action of a catalyst to generate phenylacetonitrile, and then phenylacetonitrile is subjected to alkaline hydrolysis to obtain phenylacetic acid. Before the alkaline hydrolysis of phenylacetonitrile, it is necessary to use a sulfuric acid solution with a mass concentration of about 50% to carry out pickling pretreatment on phenylacetonitrile to remove the macromolecular organic compounds rich in functional groups such as amino group and isocyano group entrained in phenylacetonitrile, so as to avoid the influence of the existence of such organic impurities on the quality of phenylacetic acid products.

[0003] According to statistics, the high-concentration and difficult-to-degrade macromolecular organic compounds containing functional groups such as amino group and isocyano group in the by-product sulfuric acid wastewater generated by pickling phenylacetonitrile account for about 35% of the mass concentration of the by-product sulfuric acid wastewater, making the quality of the by-product sulfuric acid wastewater poor, with a strong odor emission. Moreover, the organic compounds containing functional groups such as amino group and isocyano group in the by-product sulfuric acid wastewater generated by pickling phenylacetonitrile are very difficult to be degraded by oxidation methods; at the same time, due to the strong corrosiveness of dilute sulfuric acid itself, it is difficult to achieve harmless treatment and resource utilization of such by-product sulfuric acid wastewater, thus easily causing serious environmental pollution problems. At the same time, it will also cause waste of sulfuric acid, resulting in high environmental protection treatment costs and raw material costs. Therefore, there is an urgent need to develop a treatment method for the by-product sulfuric acid wastewater generated by pickling phenylacetonitrile that can realize the resource utilization of the by-product sulfuric acid wastewater and will not cause secondary pollution. Summary of the Invention

[0004] Aiming at the problem that the by-product sulfuric acid wastewater generated by pickling phenylacetonitrile contains high-concentration and difficult-to-degrade macromolecular organic compounds containing functional groups such as amino group and isocyano group, and is difficult to carry out harmless treatment and resource utilization, the present invention provides a method for treating wastewater produced in the production of phenylacetic acid, which converts sulfuric acid in the wastewater into high-quality sodium sulfate by-products, and at the same time realizes the recovery of phenylacetonitrile and organic amine products, achieving harmless treatment and resource utilization of the production wastewater, and having high economic and environmental benefits.

[0005] To solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for treating wastewater produced in the production of phenylacetic acid, comprising the following steps:

[0007] Step a: Adjust the pH of the wastewater from phenylacetic acid production to neutral with liquid caustic soda. Add an alcohol solution at 30°C - 50°C, mix evenly, let stand, and separate the layers to obtain a first oil phase and a first aqueous phase.

[0008] Step b: Heat the first aqueous phase to 95°C - 100°C, add liquid caustic soda to adjust the pH to 13 - 14, carry out a holding reaction, add an alcohol solution, cool down, let stand, and separate the layers to obtain a second oil phase and a second aqueous phase.

[0009] Step c: Filter the second aqueous phase, and add the obtained filtrate to a chromatography column filled with styrene macroporous adsorption resin for adsorption to obtain a purified solution.

[0010] Step d: Add an oxidant to the purified solution, carry out an oxidation reaction at 90°C - 100°C, and cool down to obtain an oxidized solution.

[0011] Step e: Add a reducing agent to the oxidized solution for a reduction reaction, add liquid caustic soda to adjust the pH to neutral, and dry to obtain sodium sulfate.

[0012] It should be noted that the wastewater from phenylacetic acid production in the present invention refers to the wastewater generated in the pickling of phenylacetonitrile. The mass concentration of sulfuric acid in the wastewater is 40% - 50%, and the mass concentration of high-concentration and difficult-to-degrade macromolecular organic substances containing functional groups such as amino groups and isocyano groups in the wastewater is 30% - 40%.

[0013] Compared with the prior art, the treatment method for the wastewater from phenylacetic acid production provided by the present invention uses liquid caustic soda to convert sulfuric acid in the wastewater into sodium sulfate, and at a specific temperature, by adding an alcohol solution, various organic substances containing functional groups such as amino groups and isocyano groups in the wastewater are fully extracted, so that the organic substances are fully separated from the sodium sulfate brine to obtain a first aqueous phase and a first oil phase; the separated first aqueous phase is reacted with liquid caustic soda at a specific temperature to fully convert the sulfate of organic amine in the wastewater into organic amine and sodium sulfate, thus laying a foundation for the subsequent separation of organic amine and inorganic salts. Then, by adding an alcohol solution, the organic amine is fully extracted to achieve the full separation of the organic amine and the sodium sulfate alkaline brine to obtain a second aqueous phase and a second oil phase; finally, the obtained second aqueous phase is adsorbed and purified by styrene macroporous adsorption resin to remove the residual organic substances in the second aqueous phase to obtain a purified solution; the purified solution is successively subjected to oxidation, reduction, neutralization, and drying to obtain a sodium sulfate product with a purity of more than 99.5%.

[0014] The treatment method for the wastewater from phenylacetic acid production provided by the present invention has a simple process route. No other anionic sodium salts other than sulfate substances are introduced during the whole treatment process. It not only realizes the harmless treatment of the wastewater, but also obtains a sodium sulfate product with a relatively high added value, realizing the resource utilization of the production wastewater, having relatively high economic and environmental benefits, and high practical value.

[0015] It should be noted that in step a, the main component in the first oil phase is phenylacetonitrile.

[0016] Preferably, in step a, the mass concentration of the liquid caustic soda is 25.3% - 25.5%.

[0017] It should be noted that in step a, "neutral" refers to a pH of 6.5 - 7.5.

[0018] The preferred concentration of the liquid caustic soda is convenient for controlling the heat of reaction generated by the acid-base reaction, and adding the alcohol solution under neutral pH conditions can ensure the effective separation of phenylacetonitrile in the phenylacetic acid production wastewater and improve the recovery rate of phenylacetonitrile.

[0019] Preferably, in step a, the alcohol solution is an aqueous methanol solution with a mass concentration of 30% - 40%, and its mass ratio to the phenylacetic acid production wastewater is 0.25 - 0.30:1.

[0020] Adding an aqueous methanol solution with a specific concentration at 30°C - 50°C and controlling its addition amount can, on the one hand, ensure the maximum solubility of sodium sulfate in the wastewater and avoid the precipitation of sodium sulfate from affecting the liquid separation effect; on the other hand, it can also reduce the entrainment of phenylacetonitrile in the sodium sulfate aqueous solution, minimizing the entrainment amount of phenylacetonitrile in the sodium sulfate aqueous solution and ensuring the full separation of phenylacetonitrile.

[0021] Preferably, in step a, the standing time is 0.5h - 1.0h.

[0022] It should be noted that in step b, the main component in the second oil phase is dimethylbenzylamine.

[0023] Preferably, in step b, the mass concentration of the liquid caustic soda is 25.3% - 25.5%.

[0024] The preferred concentration of the liquid caustic soda can dissolve all the sodium sulfate generated by the reaction in the aqueous phase, so as to avoid incomplete dissolution of the generated sodium sulfate, resulting in the entrainment of the oil phase (mainly dimethylbenzylamine) in the sodium sulfate or causing blockage problems in the treatment system.

[0025] Preferably, in step b, the holding time for the reaction is 1.0h - 2.0h.

[0026] In the process of adding liquid caustic soda in step a to convert sulfuric acid in the wastewater into sodium sulfate, some organic amine substances will also be converted into sulfates of organic amines and be entrained into the sodium sulfate, affecting the purity of the subsequent sodium sulfate product.

[0027] Add liquid caustic at 95°C to 100°C, and control the addition amount of liquid caustic and the reaction time, so that the sulfate of organic amine in the first aqueous phase can be fully converted into organic amine and sodium sulfate, laying a foundation for the subsequent separation of the organic amine oil phase and the sodium sulfate brine inorganic phase; in addition, controlling the addition amount of liquid caustic to make the pH of the system 13 to 14 can improve the separation rate of the organic phase and the inorganic phase, reduce the standing time, and thus improve the treatment efficiency of the whole process.

[0028] Preferably, in step b, the alcohol solution is an aqueous methanol solution with a mass concentration of 30% to 40%, and its mass ratio to the phenylacetic acid production wastewater is 0.30 to 0.35:1.

[0029] The preferred alcohol solution and addition amount can fully separate the organic amine obtained by alkali hydrolysis from sodium sulfate, reduce the amount of organic amine entrained in the sodium sulfate inorganic phase to the lowest level, and thus ensure the maximum recovery rate of organic amine.

[0030] Preferably, in step b, cool down to 28°C to 30°C.

[0031] Preferably, in step b, the standing time is 0.5 h to 1.0 h.

[0032] Preferably, in step c, the filtration uses a filter element with a pore size of 0.1 μm to 0.3 μm.

[0033] Filtering the second aqueous phase with a filter element of the above pore size can effectively remove the suspended solids and impurities contained therein, laying a foundation for subsequent resin adsorption purification and improving the efficiency of subsequent adsorption purification.

[0034] Preferably, in step c, the type of the macroporous styrene adsorption resin is D3520.

[0035] Using the above-mentioned type of macroporous adsorption resin can adsorb and remove various organic substances such as a small amount of residual phenylacetonitrile or cyclic organic amine in the sodium sulfate brine, and improve the purity of the sodium sulfate product.

[0036] Preferably, in step d, the oxidant is sodium persulfate, and its addition amount is 0.2% to 0.25% of the mass of the purified liquid.

[0037] Preferably, in step d, the oxidation reaction time is 0.5 h to 1.0 h.

[0038] Using sodium persulfate to oxidize the sodium sulfate brine can fully oxidize and degrade the residual trace refractory organic substances in the sodium sulfate brine, such as cyclic organic substances, without introducing other anionic sodium salts, and control the COD of the sodium sulfate brine within 20 ppm.

[0039] Preferably, in step e, the reducing agent is sodium sulfite, and its dosage is 0.12% - 0.14% of the mass of the oxidation solution.

[0040] The preferred reducing agent and its dosage can reduce the residual sodium persulfate in the sodium sulfate aqueous solution without introducing other anionic sodium salts, so that the residual sodium persulfate is completely converted into sodium sulfate, reducing the introduction of impurities.

[0041] Preferably, in step e, the temperature of the reduction reaction is 20°C - 30°C, and the reaction time is 0.5h - 1.0h.

[0042] Preferably, the first oil phase is rectified to obtain phenylacetonitrile.

[0043] Exemplarily, the rectification conditions are: the vacuum degree ≤ 1000 Pa, the distillation temperature is 140°C - 160°C, and the overhead fraction is collected.

[0044] Preferably, the second oil phase is rectified to obtain dimethylbenzylamine.

[0045] Exemplarily, the rectification conditions are: the vacuum degree ≤ 500 Pa, the distillation temperature is 120°C - 140°C, and the overhead fraction is collected.

[0046] Rectifying the first oil phase and the second oil phase respectively to obtain phenylacetonitrile and dimethylbenzylamine realizes the recovery of raw materials. Recycling them to different production processes of phenylacetonitrile can greatly reduce the production cost of phenylacetonitrile.

[0047] Optionally, in step e, spray drying is used for drying.

[0048] The treatment method of phenylacetic acid production wastewater provided by the present invention has simple process operation and low energy consumption. It realizes the harmless treatment of the pickling wastewater of phenylacetonitrile in the phenylacetic acid production process, and obtains a sodium sulfate by-product with a purity of more than 99.5%. It solves the technical problem that the by-product sulfuric acid wastewater of phenylacetic acid is difficult to treat due to its high concentration of macromolecular organic substances, realizes the comprehensive treatment and resource utilization of wastewater, has high economic and environmental benefits, and has extremely high promotion value. Specific Embodiments

[0049] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0050] To better illustrate the present invention, further examples are given below through embodiments.

[0051] The wastewater from phenylacetic acid production used in the following examples and comparative examples is the wastewater generated during the sulfuric acid pickling of phenylacetonitrile. The mass content of sulfuric acid is 40% - 50%, and the mass concentration of high-concentration and difficult-to-degrade macromolecular organic compounds containing functional groups such as amino groups and isocyano groups in the wastewater is 30% - 40%.

[0052] Example 1

[0053] This example provides a method for treating wastewater from phenylacetic acid production, which includes the following steps:

[0054] Step 1: Take 1200 g of wastewater from phenylacetic acid production, add 1490.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.5, heat up to 40 °C, add 300 g of methanol aqueous solution with a mass concentration of 30%, stir for 30 min, let stand for 1.0 h, separate the phases, and obtain 90 g of the first oil phase and 2899.4 g of the first water phase;

[0055] Step 2: Heat the 2899.4 g of the first water phase to 95 °C, add 229.2 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 13.0, keep the temperature for reaction for 1.0 h, add 360 g of methanol aqueous solution with a mass concentration of 30%, cool to room temperature, let stand for 1.0 h, separate the liquid, and obtain 360 g of the second oil phase and 3128 g of the second water phase;

[0056] Step 3: Filter the above-mentioned second water phase through a filter element with a pore size of 0.3 μm, and add it to a chromatography column filled with D3520 resin for adsorption to obtain 3120 g of purified liquid. The detected COD concentration is 285 mg / L;

[0057] Step 4: Heat the above-mentioned purified liquid to 95 °C, add 6.24 g of sodium persulfate, mix evenly, keep the temperature for reaction for 0.5 h, cool to room temperature, and obtain 3119.5 g of oxidized liquid. The detected TOC concentration is 3.2 mg / L;

[0058] Step 5: Add 3.75 g of sodium sulfite to the above-mentioned oxidized liquid, add 6.27 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.5, and perform spray drying to obtain 774.5 g of solid sodium sulfate with a pure white appearance, a content of 99.82%, and a yield of 99.46%.

[0059] Example 2

[0060] This example provides a method for treating wastewater from phenylacetic acid production, which includes the following steps:

[0061] Step 1: Take 1200 g of phenylacetic acid production wastewater, add 1478.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, heat up to 50 °C, add 360 g of methanol aqueous solution with a mass concentration of 30%, stir for 30 min, let stand for 1.0 h, separate the phases to obtain 120 g of the first oil phase and 2918 g of the first water phase;

[0062] Step 2: Heat the 2918 g of the first water phase to 100 °C, add 231.6 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 14.0, keep the temperature for reaction for 1.0 h, add 420 g of methanol aqueous solution with a mass concentration of 30%, cool to room temperature, let stand for 1.0 h, separate the liquid to obtain 400 g of the second oil phase and 3168 g of the second water phase;

[0063] Step 3: Filter the above-mentioned second water phase through a filter element with a pore size of 0.1 μm, and add it to a chromatography column filled with D3520 resin for adsorption to obtain 3166 g of purified liquid, and the detected COD concentration is 260 mg / L;

[0064] Step 4: Heat the above-mentioned purified liquid to 100 °C, add 7.91 g of sodium persulfate, mix evenly, keep the temperature for reaction for 0.5 h, cool to room temperature to obtain 3172.5 g of oxidized liquid, and the detected TOC concentration is 1.6 mg / L;

[0065] Step 5: Add 4.43 g of sodium sulfite to the above-mentioned oxidized liquid, add 7.95 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, and spray dry to obtain 773.5 g of solid sodium sulfate with a pure white appearance, a content of 99.88%, and a yield of 99.65%.

[0066] Example 3

[0067] This example provides a method for treating phenylacetic acid production wastewater, including the following steps:

[0068] Step 1: Take 1200 g of phenylacetic acid production wastewater, add 1484 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.0, heat up to 30 °C, add 330 g of methanol aqueous solution with a mass concentration of 40%, stir for 30 min, let stand for 0.5 h, separate the phases to obtain 140 g of the first oil phase and 2873.5 g of the first water phase;

[0069] Step 2: Heat the 2873.5 g of the first water phase to 98 °C, add 227 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 13.5, keep the temperature for reaction for 2.0 h, add 400 g of methanol aqueous solution with a mass concentration of 40%, cool to room temperature, let stand for 1.0 h, separate the liquid to obtain 425 g of the second oil phase and 3075 g of the second water phase;

[0070] Step 3: Filter the above second aqueous phase through a filter cartridge with a pore size of 0.3 μm, and add it to a chromatography column filled with D3520 resin for adsorption to obtain 3070 g of purified liquid. The detected COD concentration is 272 mg / L.

[0071] Step 4: Heat the above purified liquid to 90 °C, add 6.95 g of sodium persulfate, mix evenly, keep the temperature for reaction for 1.0 h, and cool to room temperature to obtain 3074 g of oxidized liquid. The detected TOC concentration is 2.7 mg / L.

[0072] Step 5: Add 3.90 g of sodium sulfite to the above oxidized liquid, add 6.99 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.5, and perform spray drying to obtain 772.08 g of solid sodium sulfate with a pure white appearance, a content of 99.85%, and a yield of 99.54%.

[0073] Example 4

[0074] This comparative example provides a method for treating waste water from phenylacetic acid production. The only difference from Example 2 is the macroporous adsorption resin. The specific steps are as follows:

[0075] Step 1: Take 1200 g of waste water from phenylacetic acid production, add 1478.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, heat to 50 °C, add 360 g of methanol aqueous solution with a mass concentration of 30%, stir for 30 min, stand for 1.0 h, separate the phases to obtain 120 g of the first oil phase and 2918 g of the first aqueous phase.

[0076] Step 2: Heat 2918 g of the first aqueous phase to 100 °C, add 231.6 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 14.0, keep the temperature for reaction for 1.0 h, add 420 g of methanol aqueous solution with a mass concentration of 30%, cool to room temperature, stand for 1.0 h, and separate the liquid to obtain 400 g of the second oil phase and 3168 g of the second aqueous phase.

[0077] Step 3: Filter the above second aqueous phase through a filter cartridge with a pore size of 0.1 μm, and add it to a chromatography column filled with HYA-108 resin for adsorption to obtain 3166 g of purified liquid. The detected COD concentration is 440 mg / L.

[0078] Step 4: Heat the above purified liquid to 100 °C, add 7.92 g of sodium persulfate, mix evenly, keep the temperature for reaction for 0.5 h, and cool to room temperature to obtain 3171.2 of oxidized liquid. The detected TOC concentration is 45 mg / L.

[0079] Step 5: Add 4.44 g of sodium sulfite to the above oxidation solution, add 8.03 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, and perform spray drying to obtain 771.4 g of solid sodium sulfate with a brown-yellow appearance, a content of 97.89%, and a yield of 99.45%.

[0080] Comparative Example 1

[0081] This comparative example provides a method for treating phenylacetic acid production wastewater. The only difference from Example 1 is that both Step a and Step b use water for extraction. The specific steps are as follows:

[0082] Step 1: Take 1200 g of phenylacetic acid production wastewater, add 1490.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.5, heat up to 40 °C, add 300 g of water, stir for 30 min, let stand for 1.0 h, separate the phases to obtain 60 g of the first oil phase and 2929 g of the first water phase;

[0083] Step 2: Heat the 2929 g of the first water phase to 95 °C, add 231.6 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 13.0, hold the reaction for 1.0 h, add 360 g of water, cool to room temperature, let stand for 1.0 h, and separate the liquid to obtain 300 g of the second oil phase and 3128 g of the second water phase;

[0084] Step 3: Filter the above second water phase through a filter element with a pore size of 0.3 μm, and add it to a chromatography column filled with D3520 resin for adsorption to obtain 3126 g of purified liquid. The detected COD concentration is 1658 mg / L;

[0085] Step 4: Heat the above purified liquid to 95 °C, add 6.43 g of sodium persulfate, mix evenly, hold the reaction for 0.5 h, and cool to room temperature to obtain 3221.9 g of oxidation solution. The detected TOC concentration is 676 mg / L;

[0086] Step 5: Add 3.90 g of sodium sulfite to the above oxidation solution, add 6.46 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 7.5, and perform spray drying to obtain 744.5 g of solid sodium sulfate with a yellow appearance, a content of 96.40%, and a yield of 99.30%.

[0087] Comparative Example 2

[0088] This comparative example provides a method for treating phenylacetic acid production wastewater. The only difference from Example 2 is that the adsorption and purification step of macroporous adsorption resin is omitted. The specific steps are as follows:

[0089] Step 1: Take 1200 g of phenylacetic acid production wastewater, add 1478.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, heat up to 50 °C, add 360 g of methanol aqueous solution with a mass concentration of 30%, stir for 30 min, let stand for 1.0 h, separate the phases to obtain 120 g of the first oil phase and 2918 g of the first water phase;

[0090] Step 2: Heat the 2918 g of the first water phase to 100 °C, add 231.6 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 14.0, hold the reaction at a constant temperature for 1.0 h, add 420 g of methanol aqueous solution with a mass concentration of 30%, cool to room temperature, let stand for 1.0 h, separate the liquid to obtain 400 g of the second oil phase and 3168 g of the second water phase;

[0091] Step 3: Heat the above-mentioned second water phase to 100 °C, add 7.91 g of sodium persulfate, mix evenly, hold the reaction at a constant temperature for 0.5 h, cool to room temperature to obtain 3174.3 g of oxidation liquid, and detect that the TOC concentration is 5348 mg / L;

[0092] Step 5: Add 4.43 g of sodium sulfite to the above-mentioned oxidation liquid, add 7.80 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, and spray dry to obtain 771.9 g of solid sodium sulfate with a brown appearance, a content of 94.30%, and a yield of 99.46%.

[0093] Comparative Example 3

[0094] This comparative example provides a method for treating phenylacetic acid production wastewater, which is only different from Example 2 in that the macroporous adsorption resin is different. The specific steps are as follows:

[0095] Step 1: Take 1200 g of phenylacetic acid production wastewater, add 1478.4 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, heat up to 50 °C, add 360 g of methanol aqueous solution with a mass concentration of 30%, stir for 30 min, let stand for 1.0 h, separate the phases to obtain 120 g of the first oil phase and 2918 g of the first water phase;

[0096] Step 2: Heat the 2918 g of the first water phase to 100 °C, add 231.6 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 14.0, hold the reaction at a constant temperature for 1.0 h, add 420 g of methanol aqueous solution with a mass concentration of 30%, cool to room temperature, let stand for 1.0 h, separate the liquid to obtain 400 g of the second oil phase and 3168 g of the second water phase;

[0097] Step 3: Filter the above-mentioned second water phase with a filter element with a pore size of 0.1 μm, and adsorb it in a chromatography column filled with HP388 resin to obtain 3166 g of purified liquid, and detect that the COD concentration is 8260 mg / L;

[0098] Step 4: Heat the above purification liquid to 100 °C, add 7.91 g of sodium persulfate, mix evenly, keep the temperature for reaction for 0.5 h, cool to room temperature to obtain 3171.8 g of oxidation liquid, and the detected TOC concentration is 2753 mg / L;

[0099] Step 5: Add 4.43 g of sodium sulfite to the above oxidation liquid, add 8.0 g of liquid caustic soda with a mass concentration of 25.3% to adjust the pH to 6.5, and spray dry to obtain 772.4 g of solid sodium sulfate with a brownish-yellow appearance, a content of 95.60%, and a yield of 99.51%.

[0100] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A treatment method for the wastewater produced in the production of phenylacetic acid, wherein the wastewater produced in the production of phenylacetic acid is the wastewater generated in the process of pickling phenylacetonitrile, and the mass concentration of sulfuric acid in the wastewater produced in the production of phenylacetic acid is 40% - 50%. It is characterized in that, It includes the following steps: Step a: Adjust the pH of the wastewater from phenylacetic acid production to neutral with liquid caustic soda, add an alcohol solution at 30°C - 50°C, mix evenly, let it stand, and separate the liquid to obtain a first oil phase and a first aqueous phase. In step a, the alcohol solution is an aqueous methanol solution with a mass concentration of 30% - 40%, and the mass ratio of it to the wastewater from phenylacetic acid production is 0.25 - 0.30:1; Step b: Heat the first aqueous phase to 95°C - 100°C, add liquid caustic soda to adjust the pH to 13 - 14, carry out a heat-preserving reaction, add an alcohol solution, cool down, let it stand, and separate the liquid to obtain a second oil phase and a second aqueous phase. In step b, the alcohol solution is an aqueous methanol solution with a mass concentration of 30% - 40%, and the mass ratio of it to the wastewater from phenylacetic acid production is 0.30 - 0.35:1; Step c: Filter the second aqueous phase, and add the obtained filtrate into a chromatography column filled with styrene macroporous adsorption resin for adsorption to obtain a purified liquid; Step d: Add an oxidant to the purified liquid, carry out an oxidation reaction at 90°C - 100°C, and cool down to obtain an oxidation liquid; Step e: Add a reducing agent to the oxidation liquid for a reduction reaction, add liquid caustic soda to adjust the pH to neutral, and dry to obtain sodium sulfate.

2. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, In step a and step b, the mass concentration of the liquid caustic soda is both 25.3% - 25.5%.

3. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, In step a, the standing time is 0.5h - 1.0h.

4. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, In step b, the heat-preserving reaction time is 1.0h - 2.0h; and / or In step b, cool down to 28°C - 30°C; and / or In step b, the standing time is 0.5h - 1.0h.

5. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, In step c, the filtration uses a filter element with a pore size of 0.1μm - 0.3μm; and / or In step c, the model of the styrene macroporous adsorption resin is D3520.

6. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, In step d, the oxidant is sodium persulfate, and its addition amount is 0.2% - 0.25% of the mass of the purified liquid; and / or In step d, the oxidation reaction time is 0.5h - 1.0h.

7. The treatment method of phenylacetic acid production wastewater according to claim 1, wherein In step e, the reducing agent is sodium sulfite, and its addition amount is 0.12% - 0.14% of the mass of the oxidation liquid; and / or In step e, the reduction reaction temperature is 20°C - 30°C, and the reaction time is 0.5h - 1.0h.

8. The treatment method of phenylacetic acid production wastewater according to claim 1, characterized in that, Rectify the first oil phase to obtain phenylacetonitrile; and / or Rectify the second oil phase to obtain dimethylbenzylamine.