NMP (N-Methyl Pyrrolidone) wastewater pretreatment process

Abstract

The invention discloses an NMP (N-Methyl Pyrrolidone) wastewater pretreatment process which is characterized in that before the NMP wastewater is subjected to biochemical treatment, persulfate is firstly used for oxidation treatment. According to the method, NMP in the wastewater can be completely treated only by reacting a small amount of oxidizing agent at 80-90 DEG C for about one hour, the NMP in the wastewater is oxidized into organic nitrogen and nitrate nitrogen which can be easily biochemically treated, and subsequent biochemical treatment is facilitated. And moreover, the oxidizing agent can achieve the effect by using a small amount, the residual quantity is extremely low, and secondary treatment is not needed. After the treatment of the process, the residual NMP in the NMP wastewater (equivalent to 30000 ppm) with the concentration of 3% is lower than 200 ppm, the removal rate of the NMP reaches up to 99%, and the NMP can be detected out when exceeding the detection limit to the minimum extent; and the content of residual persulfate can be controlled to be lower than 0.5%.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and in particular to a pretreatment process for NMP-containing wastewater, a treatment agent and an application thereof. Background Art

[0002] The full name of NMP is N-Methylpyrrolidone, and its English name is N-Methylpyrrolidone. Its chemical formula is C5H9NO. It is a colorless to light yellow transparent liquid. It is miscible with water in any proportion and can also be dissolved in most organic and inorganic compounds, polar gases, and natural and synthetic polymer compounds.

[0003] NMP is an excellent, high-grade solvent, a polar solvent with strong selectivity and excellent stability. It is widely used in the petrochemical industry, plastics industry, pharmaceuticals, pesticides, fuels, and lithium-ion battery manufacturing. It is an excellent cleaning agent for high-precision electronics, circuit boards, lithium batteries, etc. In the petrochemical industry, NMP is also used as a solvent in the partial oxidation of natural gas to acetylene concentration process.

[0004] During the synthesis process of NMP and in applications where NMP is used as a solvent or cleaning agent, a large amount of wastewater containing NMP is generated. This wastewater is generally recovered by extraction or distillation. After recovery, wastewater with a high NMP content still remains and requires treatment, such as usually by biochemical processes.

[0005] However, NMP-containing wastewater contains high concentrations of organic matter and ammonia nitrogen. As a relatively stable nitrogen heterocyclic organic compound, NMP is difficult to ring-open and has poor biodegradability. Therefore, the biodegradability of this wastewater is very poor. Once entering the biochemical treatment system, its degradation rate is slow, which can easily lead to incomplete treatment. Biochemical effluent still contains high levels of ammonia nitrogen and total nitrogen, failing to meet emission requirements. Therefore, pretreatment is required before NMP wastewater enters the biochemical treatment process to oxidize NMP into easily biodegradable substances and reduce the difficulty of NMP wastewater treatment. Common pretreatment methods include ozone oxidation, hydrogen peroxide oxidation (such as Fenton's reagent), photocatalytic oxidation, and electrolysis.

[0006] For example, Chinese patent document CN 204550267U discloses a system for treating wastewater from lithium batteries containing methylpyrrolidone (NMP), wherein wastewater is sequentially passed through an acidification tank, a Fenton oxidation tank, a pH adjustment tank, a flocculation tank, a mixed liquor settling tank, and a plate-and-frame filter press for filtration treatment. The filtrate enters an intermediate water tank, and the effluent from the intermediate water tank is sequentially filtered through a bag filter and a precision filter. The effluent after filtration is discharged, and the dry sludge after the plate-and-frame filtration is bagged for treatment. The document specifically discloses a system for treating wastewater from lithium batteries containing methylpyrrolidone (NMP), which mainly includes a wastewater collection tank (1), an acidification tank (2), a Fenton oxidation tank (3), a pH adjustment tank (4), a flocculation reaction tank (5), a mixed liquor settling tank (6), a plate-and-frame filter press (7), an intermediate water tank (8), a bag filter (9), and a precision filter (10), which are sequentially connected.The wastewater collection tank (1) is provided with a set of simple mechanical grilles for intercepting and removing large particles of garbage and foreign matter in the wastewater to prevent it from entering the subsequent process and clogging the pump or pipeline; a set of float liquid level gauges (29) is provided in the wastewater collection tank (1), and the wastewater in the wastewater collection tank can be automatically lifted to the acidification tank (2) by the wastewater lifting pump (12) according to the liquid level; the acidification reaction tank (2), Fenton oxidation tank (3), pH adjustment tank (4), and flocculation reaction tank (5), these four reaction tanks are connected in series in sequence, and a stirrer (13-16) is provided in the middle of each reaction tank. Each tank is connected in a way of upper inlet and lower outlet, lower inlet and upper outlet. The flocculation reaction tank (5) is connected to the mixed liquid static tank through a pipeline. The residence time of each of the four reaction tanks is 20 minutes. The acidification reaction tank (2) is provided with one set of online pH meter (32), one set of sulfuric acid dosing device (19, 24), and one set of reaction mixer (13). Automatic sulfuric acid dosing is achieved through feedback chain control between the online pH meter and the sulfuric acid dosing device to ensure that the pH in the acidification tank (2) is within the range of 2-4. The Fenton oxidation tank (3) is provided with a reaction mixer (14). 1 set, ferrous sulfate dosing device (20, 25) 1 set, hydrogen peroxide dosing device (21, 26) 1 set, the ferrous sulfate dosing device and the hydrogen peroxide dosing device are all linked with the wastewater lifting pump (12); the pH adjustment tank (4) is provided with an online pH meter (33) 1 set, a liquid alkali dosing device (22, 27) 1 set, and a reaction mixer (15) 1 set, and the online pH meter and the liquid alkali dosing device are feedback-linked controlled to realize automatic liquid alkali dosing, thereby ensuring that the pH in the pH adjustment tank (4) is within the range of 8-9; the flocculation reaction tank (5) is provided with a PAM dosing device. A set of drug-making devices (23, 28) and a set of reaction mixer (16) are provided. By controlling the amount of PAM flocculant added, the flocculation tank can achieve the best reflection effect. A set of float level gauge (30) is provided in the mixed liquid static tank (6). The mixed liquid in the mixed liquid static tank can be automatically lifted to the plate and frame filter press (7) for treatment by the pneumatic diaphragm pump (17) according to the liquid level. The filtrate after filtration by the plate and frame filter press (7) flows into the intermediate water tank (8) by gravity through the pipeline. The dry sludge after filtration is bagged and handed over to a professional solid waste disposal company for disposal. A float level gauge (30) is provided in the intermediate water tank (8). One set of ball level gauges (31), two intermediate water tank lifting pumps (18), the intermediate water tank lifting pumps (18) and the float level gauge (31) are interlockedly controlled to realize high opening and low stopping; the bag filter (9) is equipped with a filter bag with a filtration aperture of 1um, which can intercept and remove suspended matter with a particle size greater than 1um, and the filtered water enters the precision filter for filtration; the precision filter (10) is equipped with a PP fiber filter element with a filtration aperture of 0.5um, which can intercept and remove suspended matter with a particle size greater than 0.5um, and the filtered water is discharged.The article claims that its technology is suitable for the treatment of wastewater discharged from the lithium battery production industry containing organic matter such as NMP and pollutants such as SS. It has the characteristics of compact structure, small footprint, simple installation and operation, and stable operation effect.

[0007] However, this technology uses the Fenton oxidation process, which requires the use of large amounts of hydrogen peroxide as an oxidizing agent. It also requires the introduction of ferrous ion compounds to generate hydroxyl radicals to oxidize NMP. This method is not easy to oxidize NMP, consumes a large amount of oxidant, and cannot be used as a resource. Furthermore, a large amount of the added oxidant (hydrogen peroxide and ferrous ion compounds) will remain in the wastewater, hindering subsequent treatment and potentially significantly impacting downstream biochemical systems. Furthermore, the treatment system disclosed in this document is relatively complex and expensive, hindering its widespread application.

[0008] Chinese patent document CN 111170531A discloses a wastewater treatment process for NMP synthesis. The process combines Fenton oxidation with electrolysis, allowing the wastewater to generate large amounts of hydroxyl radicals and high-energy oxygen under the action of hydrogen peroxide, light, and electrolysis. Both hydroxyl radicals and high-energy oxygen have strong oxidizing properties, thereby decomposing organic matter in the wastewater and making it biodegradable. The document specifically discloses a wastewater treatment process for NMP synthesis. The process involves pumping wastewater into an inlet distributor, adding hydrogen peroxide to the distributor, and mixing the wastewater. The mixed wastewater is then pumped into an electrolytic reactor, where it undergoes a decomposition reaction under UV light and electrode materials. The COD content of the wastewater discharged from the electrolytic reactor is less than 500 mg / L. Its technical principle and effect are as follows: NMP is a colorless, transparent, oily liquid that is miscible with water, alcohols, ethers, esters, aromatic hydrocarbons, etc., and is sensitive to light. In addition, NMP undergoes hydrolysis in an acidic environment with water; and NMP can be oxidized by hydroxyl groups in the aqueous phase. Therefore, taking into account the characteristics of NMP, high-concentration wastewater is thoroughly mixed with hydrogen peroxide through a water distributor, and then enters the electrolysis reactor for UV light decomposition reaction. At the same time, the large amount of hydroxyl radicals generated by electrolysis are used to oxidize and decompose NMP and tetrahydrofuran and other difficult-to-biodegrade compounds in the wastewater, thereby achieving the purpose of improving biodegradability. The process is stable, easy to operate and manage, and has low operating costs. The article claims: The technical solution in this patent achieves biodegradable treatment of high-concentration NMP wastewater, while the process is stable, easy to operate and manage, and has low operating costs.

[0009] However, this technology also uses the Fenton oxidation process, which requires the use of large amounts of hydrogen peroxide as an oxidation agent and the introduction of ferrous ion compounds to generate hydroxyl radicals to oxidize NMP. This method of treating NMP is not easy to oxidize, consumes a large amount of oxidant, and cannot achieve resource utilization. Furthermore, a large amount of the added oxidant (hydrogen peroxide and ferrous ion compounds) will remain in the wastewater, which is not conducive to subsequent treatment and may have a significant impact on downstream biochemical systems. Furthermore, the technology disclosed in this document also requires an electrolytic reactor and UV light, which requires additional equipment and costs, making it unfavorable for its widespread application.

[0010] Chinese patent document CN 114426346A discloses a method for treating NMP-containing wastewater previously employed by the applicant. This method is suitable for treating wastewater with a wide NMP concentration range (NMP mass concentration of 100 mg / L to 20,000 mg / L), boasts high NMP removal rates, does not affect subsequent treatment, does not cause high-temperature polymerization of NMP, and is energy-efficient and environmentally friendly. The specific technical solution is as follows: The method for treating NMP-containing wastewater includes pretreatment, resin adsorption, purging, resin desorption, and separation and purification of the desorption liquid at the resin outlet during the resin desorption process. During the resin adsorption process, the aspect ratio of the adsorption resin layer is controlled to be 3:1 to 10:1, and the wastewater flow rate is 0.5 to 4 BV / h. The separation and purification can be performed by flash evaporation or distillation, but is not limited to these two methods. The pretreatment includes prefiltration, secondary filtration, and pH adjustment. The filter medium used in the prefiltration can be, but is not limited to, quartz sand, coal powder particles, or activated carbon particles. The filter medium used in the secondary filtration has a pore size of 0.5 to 5 μm. The filter medium used in the secondary filtration can be, but is not limited to, a filter bag or a fiber filter layer. The pH adjustment refers to adjusting the pH to 5 to 8. The amount of the analytical solution used in the resin analysis process is 2 to 5 BV, and the flow rate is 0.5 to 4 BV / h. The analytical solution can be, but is not limited to, methanol. After the resin adsorption, a biochemical treatment process is also included. After the resin analysis, a secondary purge process and a tertiary purge process are also included. The purge process and the secondary purge process use compressed gas for purge. The tertiary purge process uses 0.1 to 0.15 MPa steam for purge. The applicant has found that this method is suitable for treating wastewater with a wide range of NMP concentrations (NMP mass concentration is 100 mg / L to 20,000 mg / L), has a high NMP removal rate of more than 99.5%, does not affect subsequent treatment, will not cause high-temperature polymerization of NMP, and is energy-saving and environmentally friendly. However, this process requires complex and expensive resins, which is not conducive to cost savings; and it is a physical method and cannot solve the problem that it is difficult to treat biochemically.

[0011] In summary, NMP-containing wastewater has very poor biodegradability, necessitating pretreatment before biochemical treatment to oxidize NMP into biodegradable substances and reduce the difficulty of NMP wastewater treatment. However, current NMP oxidation processes require large amounts of oxidants, which remain in the wastewater, hindering subsequent biochemical treatment. Furthermore, the equipment is complex and expensive. Summary of the Invention

[0012] In order to solve the above technical problems, the present invention provides a NMP wastewater pretreatment process, which includes performing oxidation treatment with persulfate before biochemical treatment of the NMP wastewater.

[0013] Preferably, the persulfate of the present invention is selected from one or more of sodium persulfate, potassium persulfate or ammonium persulfate.

[0014] Preferably, the persulfate is used in an amount with a mass ratio of 3:1 to 10:1 to NMP. More preferably, the persulfate is used in an amount with a mass ratio of 4:1 to 7:1 to NMP.

[0015] Furthermore, the process of the present invention has a treatment temperature of 60-100° C. and a reaction time of 20-80 min. Preferably, the process has a treatment temperature of 80-90° C. and a reaction time of 60-65 min.

[0016] Furthermore, the NMP wastewater described in the present invention is wastewater containing NMP generated in a process for synthesizing NMP, or wastewater containing NMP generated in a process using NMP as a solvent or cleaning agent.

[0017] Most preferably, the process of the present invention is specifically as follows: sodium persulfate is added to NMP wastewater in an amount of 4:1 by mass ratio of sodium persulfate:NMP, the mixture is thoroughly mixed and stirred, and the mixture is reacted at 90°C for 60 minutes, and the resulting wastewater is further subjected to conventional biochemical treatment and then discharged in compliance with the standards.

[0018] The present invention also provides a wastewater oxidation treatment agent used in the NMP wastewater pretreatment process of the present invention, wherein the wastewater oxidation treatment agent is persulfate.

[0019] The invention also provides the use of persulfate in the pretreatment of NMP wastewater.

[0020] The present invention has the following beneficial effects: The inventors' team discovered that when using existing oxidation technologies such as ozone and Fenton oxidation to pre-treat NMP wastewater, NMP contains pyrrole rings, making it difficult to biodegrade. Therefore, the amount of oxidant required is relatively large, and these oxidants will remain in the wastewater. If no secondary treatment is performed, it will affect the subsequent biochemical treatment. In the process of the present invention, persulfate, such as sodium persulfate, is used as a catalyst. Only a small amount of oxidant is required to react at 80-90°C for about one hour to completely treat the NMP in the wastewater, oxidizing the NMP in the wastewater into easily biodegradable organic nitrogen and nitrate nitrogen, which is beneficial for subsequent biochemical treatment. Moreover, the oxidant of the present invention can be used in small amounts to achieve the desired effect, and its residual amount is extremely low, and no secondary treatment is required.

[0021] The process route of the present invention is simple. It only requires adding a persulfate oxidant to the wastewater for treatment before the wastewater can directly enter a subsequent biochemical treatment device. No other pretreatment such as electrolysis or illumination is required, no other treatment procedures and devices need to be introduced, and no secondary treatment is required before entering the biochemical treatment. Therefore, the modification cost of the equipment and process route is extremely low, and the invention is very suitable for industrial application, thereby improving the treatment effect of existing NMP wastewater and greatly reducing costs.

[0022] After treatment by the process of the present invention, the residual NMP in 3% concentration NMP wastewater (equivalent to 30,000 ppm) is less than 200 ppm, the NMP removal rate is as high as 99%, and the lowest NMP can exceed the detection limit without detection; the residual persulfate content can be controlled to be less than 0.5%. DETAILED DESCRIPTION

[0023] The following is further described in detail through specific embodiments. However, it should be noted that the following embodiments of the present invention are merely for the purpose of better illustrating the content of the present invention, and do not mean that the content of the present invention is limited to the examples. Therefore, those skilled in the art may make non-essential improvements and adjustments to the embodiments based on the above invention, which still fall within the scope of protection of the present invention and are subject to the scope of protection of the appended claims.

[0024] The NMP described herein stands for N-Methylpyrrolidone (NMP), with a chemical formula of C5H9NO, and contains a pyrrole nitrogen heterocycle. NMP is an excellent, high-grade solvent with strong selectivity and excellent stability. It is widely used in the petrochemical industry, plastics industry, pharmaceuticals, pesticides, fuels, and lithium-ion battery manufacturing. It is an excellent cleaning agent for high-precision electronics, circuit boards, lithium batteries, and other applications. NMP is the largest application in the lithium battery industry. Its applications in lithium battery manufacturing include: Slurry preparation: NMP acts as a solvent for the binder polyvinylidene fluoride (PVDF), mixing, dissolving, stirring, and dispersing various electrode materials, including the binder, conductive agent, and positive electrode active material, to form a uniform slurry. The quality of the slurry dispersion directly impacts the quality and performance of lithium-ion batteries. Coating: The next step after slurry preparation involves evenly coating the stable, viscous, and fluid slurry onto the positive electrode metal foil. As the liquid carrier for the slurry, NMP exhibits excellent wettability and fluidity, making it a mainstream coating solvent. This coating process is crucial for the capacity, service life, and safety of lithium-ion batteries. Drying: After coating, the positive electrode sheet is dried in a vacuum dryer at 120±5°C to remove the NMP from the electrode slurry and form a porous film with uniform pore size and distribution, consisting of the binder, conductive agent, and positive electrode material in the slurry. This film then covers the electrode sheet. As a solvent, NMP plays a core role in lithium battery production, and its quality directly impacts the quality of lithium battery coatings. The rapid expansion of power and energy storage batteries has led to a surge in demand for NMP in the lithium battery industry, creating space for NMP production expansion. According to relevant data, my country's consumption in 2021 was 1.06 million tons (including recycled content) and is expected to reach 4.43 million tons by 2025. In addition to being one of the key upstream materials in the new energy industry, NMP is also an essential chemical solvent involved in chemical reactions and dilution in the manufacturing of polymer materials such as aramid, polyphenylene sulfide, and polyimide, directly impacting the smooth completion of low-temperature polycondensation reactions and the transportation of materials and products. In the petrochemical industry, NMP is also used as a solvent in the partial oxidation of natural gas to acetylene concentration.

[0025] The process of the present invention is applicable to a large amount of wastewater containing NMP generated in the synthesis process of NMP and in the process of using NMP as a solvent or cleaning agent. The COD concentration of the wastewater exceeds 5000 mg / L, and some of the wastewater can reach a concentration of up to 100,000 mg / L. At the same time, the ammonia nitrogen concentration is very high, exceeding 500 mg / L, and some of the wastewater can reach a concentration of tens of thousands of mg / L.

[0026] The redox process is a common method for wastewater treatment. It converts toxic and harmful pollutants in wastewater into non-toxic or slightly toxic substances through redox reactions between chemicals and pollutants in the water. This method primarily treats inorganic pollutants, such as heavy metals and oxides. It utilizes strong oxidants such as sodium hypochlorite, liquid chlorine, ozone, potassium permanganate, potassium perchlorate, fluorine, pure oxygen, peracetic acid, hydrogen peroxide, and benzoyl peroxide to oxidize and decompose harmful substances in wastewater into harmless substances.

[0027] Oxidants are classified by chemical composition into inorganic and organic oxidants, with most commonly used oxidants being inorganic. They can also be further categorized by their chemical properties into acidic oxidants (such as hydrogen peroxide, peracetic acid, sodium dichromate, chromic acid, nitric acid, potassium permanganate, and ammonium persulfate), alkaline oxidants (such as sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate), and neutral oxidants (such as bromine and iodine). The electron-accepting property of an oxidant is called its oxidizing power, which is determined by the electron-accepting tendency of the high-valent elements in the substance. Substances can be classified as strong, moderate, and weak oxidants based on their electron-accepting ability. In solution, according to double-layer theory, the oxidizing power is reflected by the standard hydrogen electrode potential of the oxidant. Higher potential indicates stronger oxidizing power, while lower potential indicates weaker oxidizing power. Furthermore, the oxidizing power of an oxidant is influenced by the symmetry of its molecules; generally, more symmetrical molecules are more stable.

[0028] The persulfates described herein are a class of oxidants, including peroxymonosulfates (PMS) and peroxydisulfates (PDS). They are salt derivatives of hydrogen peroxide (also known as hydrogen peroxide) and can be considered salt derivatives formed by replacing one or two sulfonate groups with either of the two hydrogen atoms of hydrogen peroxide. Peroxydisulfates, such as sodium peroxydisulfate, potassium peroxydisulfate, and ammonium peroxydisulfate, are more commonly used as oxidants. The sodium peroxydisulfate, potassium peroxydisulfate, and ammonium peroxydisulfate described herein can be used in either the PMS or PDS form.

[0029] In the process described in the present invention, the residual NMP content is determined using the gas chromatography method disclosed in Chinese patent document CN114426346A. The specific method is as follows: 1) Preparation of standard solution: Prepare five 100mL volumetric flasks, add 100g of distilled water to three volumetric flasks, weigh the result to the nearest 0.0001g, add 0.5g, 1.0g, 2.0g, 2.5g, and 3.0g of NMP (chromatographically pure) reagent, weigh the NMP (chromatographically pure) to the nearest 0.0001g, and calculate the percentage of NMP in the prepared standard solution; 2) Calibrate the analytical method: Calibrate the prepared standard solution according to the chromatograph operating procedure. 1 μL of the sample was injected according to the chromatograph operating conditions, separated on a DB-624 column, and detected by an FID detector. 3) The correction factor for each standard solution was calculated based on its NMP concentration and peak area, and a standard curve was plotted with NMP concentration as the abscissa and peak area as the ordinate. 4) Sample testing: 1 μL of the sample to be tested was injected according to the chromatograph operating conditions, separated on a DB-624 column, and detected by an FID detector. The abscissa corresponding to the peak area on the standard curve was the NMP concentration of the sample to be tested. The relevant disclosure of this document is incorporated into this specification as part of the disclosure of this specification. Of course, those skilled in the art may also use other methods known in the art to determine NMP content.

[0030] In the process described herein, the residual persulfate content is determined by sodium thiosulfate titration. According to national standard GB / T 23940-2009, sodium persulfate is primarily determined by reacting potassium iodide with sodium persulfate to generate free iodine. This is titrated with a standard sodium thiosulfate solution in a weakly acidic solution using starch as an indicator. The specific steps are as follows: 1. Weigh 0.3g of sample, accurate to 0.0002g, and place it in a 250ml iodine volumetric flask; 2. Add 30ml of water to dissolve it, add 4g of potassium iodide, cover the bottle with a stopper, shake well, and seal with water; 3. Place in a dark place for 30 minutes, add 2 ml of ice ethanol solution and 25 ml of water, and titrate with sodium thiosulfate standard titration solution. When the titration is close to the end point, add 3 ml of starch indicator solution and continue titrating until the blue color of the solution disappears. 4. Conduct a blank test at the same time.

[0031] Example 1 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a 90 °C constant temperature water bath to raise the temperature to 90 °C; Take 12g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 4:1). After the addition of the drug is completed, continue stirring at 90℃ for 60 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and the NMP content was determined by gas chromatography. The residual NMP content was 136 ppm. After 24 hours of stabilization, the residual NMP content was 179 ppm. The residual sodium persulfate content was determined to be 0.022 wt% by titration with sodium thiosulfate.

[0032] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.40%.

[0033] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0034] Example 2 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a 90 °C constant temperature water bath to raise the temperature to 90 °C; Take 15g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 5:1). After the addition of the drug is completed, continue stirring at 90℃ for 60 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and the NMP content was determined by gas chromatography. The residual NMP content was 85 ppm. After 24 hours of stabilization, the residual NMP content was 103 ppm. The residual sodium persulfate content was determined to be 0.11 wt% by titration with sodium thiosulfate.

[0035] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.66%.

[0036] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0037] Example 3 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a 90 °C constant temperature water bath to raise the temperature to 90 °C; Take 18g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 6:1). After the addition of the drug is completed, continue stirring at 90℃ for 60 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and the NMP content was determined by gas chromatography. The residual NMP content was 2.6 ppm. After 24 hours of stabilization, the residual NMP content was 9.7 ppm. The residual sodium persulfate content was determined to be 0.11 wt% by titration with sodium thiosulfate.

[0038] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.97%.

[0039] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0040] Example 4 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a 90 °C constant temperature water bath to raise the temperature to 90 °C; Take 21g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 7:1). After the addition of the drug is completed, continue stirring at 90℃ for 60 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and assayed for NMP by gas chromatography. No residual NMP was detected. After 24 hours of stabilization, 5.6 ppm of residual NMP was detected. Residual sodium persulfate was determined to be 0.219 wt% by titration with sodium thiosulfate.

[0041] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.98%.

[0042] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0043] It can be seen from Examples 1-4 that when the mass ratio of sodium persulfate to NMP is above 4:1, NMP in the wastewater can be effectively oxidized, the residual NMP can be reduced to below 200 ppm, and the residual NMP amount is further reduced as the proportion of oxidant increases.

[0044] Example 5 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a constant temperature water bath at 85 °C and heated to 85 °C; Take 18g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 6:1). After the addition of the drug is completed, continue stirring at 85℃ for 65 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and the NMP content was determined by gas chromatography. No residual NMP was detected. After 24 hours of stabilization, 6.3 ppm of residual NMP was detected. Residual sodium persulfate was determined to be 0.203 wt% by titration with sodium thiosulfate.

[0045] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.98%.

[0046] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0047] Example 6 The specific steps of NMP wastewater pretreatment process are as follows: 100 g of NMP-containing wastewater (tested, the mass content of NMP is 3 wt%) was placed in a 500 ml three-necked flask and placed in a constant temperature water bath at 80 °C and heated to 80 °C; Take 18g of sodium persulfate and add it into the above NMP wastewater under stirring (drug ratio 6:1). After the addition of the drug is completed, continue stirring at 80℃ for 60 minutes; After the reaction was completed, the mixture was allowed to cool to room temperature. The supernatant was then collected and the NMP content was determined by gas chromatography. The residual NMP content was 30 ppm. After 24 hours of stabilization, the residual NMP content was 38 ppm. The residual sodium persulfate content was determined to be 0.47 wt% by titration with sodium thiosulfate.

[0048] The removal rate of NMP was calculated according to the formula, and the removal rate of NMP was measured to be 99.87%.

[0049] The wastewater treated by this process can meet the discharge standards after subsequent conventional biochemical treatment.

[0050] It can be seen from Examples 3, 5 and 6 that, under the same reagent ratio, the effects achieved by lowering the reaction temperature or increasing the reaction time are comparable, but lowering both the temperature and time will result in a slightly worse treatment effect, with both residual NMP and residual sodium persulfate increasing.

[0051] In summary, the process described herein for treating NMP wastewater, using a persulfate such as sodium persulfate as a catalyst, requires only a small amount of oxidant and a reaction temperature of 80-90°C for approximately one hour to nearly completely remove NMP from the wastewater, oxidizing the NMP into readily biodegradable organic nitrogen and nitrate nitrogen, which facilitates subsequent biochemical treatment. Furthermore, the oxidant described herein can be used in small quantities to achieve the desired effect, and its residual content is extremely low, eliminating the need for secondary treatment. After treatment using the process described herein, residual NMP in 3% NMP wastewater (equivalent to 30,000 ppm) is less than 200 ppm, achieving an NMP removal rate exceeding 99%, with the lowest NMP removal exceeding the detection limit. The residual persulfate content can be controlled to less than 0.5%.

[0052] The above is only an embodiment of the present invention. The commonly known technical common sense in the scheme is not described in detail here. Those of ordinary skill in the art are aware of all the common technical knowledge in the technical field to which the invention belongs before the application date, can obtain all the existing technologies in the field, and have the ability to apply conventional experimental means before that date. Those of ordinary skill in the art can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical commonly known technologies should not become obstacles for those of ordinary skill in the art to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several adjustments and improvements can be made, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A NMP wastewater pretreatment process, characterized in that, Before the biochemical treatment of NMP wastewater, it is first oxidized with persulfate.

2. NMP wastewater pretreatment process according to claim 1, is characterized in that, The persulfate is selected from one or more of sodium persulfate, potassium persulfate or ammonium persulfate.

3. The NMP wastewater pretreatment process according to claim 1 or 2, wherein The mass ratio of the persulfate to NMP is 3:1-10:

1.

4. NMP wastewater pretreatment process according to claim 3, is characterized in that, The mass ratio of the persulfate to NMP is 4:1-7:

1.

5. according to the NMP wastewater pretreatment process described in any one of claims 1-4, it is characterized in that, The processing temperature of the process is 60-100° C., and the reaction time is 20-80 minutes.

6. NMP wastewater pretreatment process according to claim 5, is characterized in that, The processing temperature of the process is 80-90° C., and the reaction time is 60-65 minutes.

7. The NMP wastewater pretreatment process according to any one of claims 1 to 6, wherein The NMP wastewater is wastewater containing NMP generated in a process of synthesizing NMP, or wastewater containing NMP generated in a process of using NMP as a solvent or a cleaning agent.

8. The NMP wastewater pretreatment process according to any one of claims 1 to 6, wherein Sodium persulfate was added to NMP wastewater at a mass ratio of sodium persulfate to NMP of 4:1, the mixture was fully mixed and stirred, and the mixture was reacted at 90°C for 60 minutes. The resulting wastewater was further subjected to conventional biochemical treatment and then discharged in compliance with the standards.

9. A wastewater oxidation treatment agent, used in the NMP wastewater pretreatment process according to any one of claims 1 to 8, wherein the wastewater oxidation treatment agent is persulfate.

10. Application of persulfate in NMP wastewater pretreatment.