A method of reducing impurities in a composition containing N-methylpyrrolidone

Abstract

The application discloses a method for reducing impurities in a composition containing N-methyl pyrrolidone, which comprises the following steps: performing a refining treatment on a mixture; the mixture comprises the composition and a maleic anhydride copolymer; wherein the composition comprises N-methyl pyrrolidone and impurities, and the impurities comprise amine compounds. The method can not only efficiently remove the impurity amine compounds, but also obtain a product with a suitable pH value.

Description

Technical Field

[0001] This invention relates to a method for reducing impurities in compositions containing N-methylpyrrolidone. Background Technology

[0002] N-Methylpyrrolidone (NMP) is an important chemical solvent, characterized by low toxicity, high boiling point, strong dissolving power, good selectivity, and good stability. It is the most commonly used solvent in the production of metal-ion batteries. On one hand, NMP can be used as a solvent in the preparation of electrode sheets; on the other hand, NMP can be used as a solvent in the preparation of battery electrolytes. Due to its production process, NMP contains a small amount of free amines from the raw material. However, free amines can polymerize during charge and discharge, reducing the conductivity of the electrolyte. Simultaneously, these substances react with LiPF6 to generate HF, affecting the battery's lifespan. Therefore, free amines are considered impurities in the finished product, and the battery industry typically requires the free amine content to be below 10 ppm. Currently, the free amine content in NMP is generally between 10-15 ppm, and sometimes even higher. It is difficult to reduce the free amine content to below 10 ppm using only a distillation system.

[0003] Chinese patent application CN116239514A discloses a method for reducing free amines in NMP (nitric acid). This method involves adding acid to the material to be treated to adjust the pH to between 6.5 and 7.5, followed by purification. This ensures that the heavy components formed after neutralization remain at the bottom of the column, reducing the free amines collected at the top. However, this method has certain problems. The solubility of the inorganic salts generated when using acid in NMP is significantly reduced, potentially leading to problems such as clogging of the packed column. Furthermore, the generated inorganic salts are unstable at high temperatures and may partially decompose, releasing free amines again.

[0004] Chinese patent application CN121248465A discloses a method and apparatus for removing alkanolamines from NMP. The method involves adding acid anhydride to the material to be treated and then refining it, thereby increasing the boiling point of the generated amides and reducing the free amines drawn from the top of the tower.

[0005] Therefore, a method is needed that can efficiently reduce impurity amine compounds. Summary of the Invention

[0006] In order to overcome the above-mentioned problems in the prior art, the present invention provides a method for reducing impurities in a composition containing N-methylpyrrolidone. This method can not only efficiently remove impurity amine compounds, but also obtain a product with a suitable pH value.

[0007] During their research, the inventors discovered that when the product obtained after removing free amines from NMP was directly used in the preparation of metal-ion batteries, the rate performance, cycle life, and safety of the resulting batteries all decreased significantly. Through repeated research, the inventors found that this was due to the excessively low pH value of the product obtained after removing free amines from NMP, leading to the aforementioned problems. However, further processing of the product after removing free amines from NMP (e.g., adding alkaline substances to increase the pH value) introduces other impurities, which in turn negatively impact battery performance. Further research by the inventors revealed that using maleic anhydride copolymers can effectively bind with free amine compounds in the composition. On one hand, maleic anhydride copolymers can bind more firmly to free amine compounds, reducing their volatilization into the final product. On the other hand, using maleic anhydride copolymers does not significantly affect the pH value of the final product. This not only efficiently removes impurity amine compounds but also yields a product with a suitable pH value.

[0008] The specific technical solution of the present invention is described below.

[0009] This invention provides a method for reducing impurities in a composition containing N-methylpyrrolidone, comprising the following steps:

[0010] The mixture is refined; the mixture comprises the composition and the maleic anhydride copolymer;

[0011] The composition includes N-methylpyrrolidone (NMP) and impurities, including amine compounds.

[0012] In this invention, the maleic anhydride copolymer refers to a polymer obtained by copolymerizing maleic anhydride (MAH, maleic anhydride) as one of the monomers and one or more other olefin monomers through a copolymerization reaction.

[0013] In this invention, preferably, the maleic anhydride copolymer includes one or more of styrene-maleic anhydride alternating copolymers, ethylene-maleic anhydride alternating copolymers, methyl vinyl ether-maleic anhydride alternating copolymers, propylene-maleic anhydride alternating copolymers, and butadiene-maleic anhydride alternating copolymers. Specifically, the styrene-maleic anhydride alternating copolymer is a polymer obtained by copolymerizing styrene and maleic anhydride as monomers; the meanings of the other copolymers are analogous.

[0014] In some embodiments, the repeating unit of the styrene-maleic anhydride alternating copolymer has the chemical formula Cs. 12 H 10 O3, the molecular weight of the repeating unit is 202.2 g / mol.

[0015] In some embodiments, the repeating unit of the ethylene-maleic anhydride alternating copolymer has the chemical formula C6H6O3 and the molecular weight of the repeating unit is 126.1 g / mol.

[0016] In some embodiments, the repeating unit of the methyl vinyl ether-maleic anhydride alternating copolymer has the chemical formula C7H8O4 and the molecular weight of the repeating unit is 156.1 g / mol.

[0017] In some embodiments, the propylene-maleic anhydride alternating copolymer repeating unit has the chemical formula C7H8O3 and the molecular weight of the repeating unit is 140.1 g / mol.

[0018] In some embodiments, the repeating unit of the butadiene-maleic anhydride alternating copolymer has the chemical formula C8H8O3 and the molecular weight of the repeating unit is 152.1 g / mol.

[0019] In this invention, preferably, the molar content of maleic anhydride in the maleic anhydride copolymer is 10.5%-50%, for example, 25%. Here, molar content refers to the percentage of the molar amount of the structural units formed by maleic anhydride relative to the molar amount of the maleic anhydride copolymer.

[0020] In this invention, preferably, the weight-average molecular weight of the maleic anhydride copolymer is 5,500-130,000, for example, 9,500 or 60,000.

[0021] In this invention, preferably, the molar ratio of the repeating unit of the maleic anhydride copolymer to the amine compound is (0.3-2):1, more preferably (0.5-1.5):1, for example 1:1.

[0022] In this invention, the amine compound may be derived from a small amount of free amine raw material contained in the preparation of the electrode sheet.

[0023] In this invention, preferably, the amine compounds include alkylamines and / or alcoholamines.

[0024] Preferably, the alkylamines include one or more of monomethylamine, dimethylamine, and trimethylamine.

[0025] Preferably, the alkanolamines include one or more of monoethanolamine, diethanolamine, and propanolamine.

[0026] In this invention, preferably, the pH value of the mixture is 9-11.1, for example, 9.77, 10.3, 10.41, 10.54, 10.69, 10.73, 10.81 or 11.

[0027] In this invention, preferably, the composition further includes water.

[0028] In this invention, preferably, the mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%, for example, 0.02 wt%, 0.05 wt%, 0.1 wt% or 0.5 wt%.

[0029] In this invention, preferably, the mass concentration of N-methylpyrrolidone in the composition is 80 wt%-98 wt%, for example, 97.95 wt% or 89.98 wt%.

[0030] In some specific embodiments, the maleic anhydride copolymer is a styrene-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the styrene-maleic anhydride alternating copolymer is 50%, and the weight-average molecular weight of the maleic anhydride copolymer is 5500.

[0031] Specifically, the amine compound is ethanolamine and / or propanolamine.

[0032] Specifically, the mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%, for example, 0.02 wt%, 0.05 wt%, 0.1 wt% or 0.5 wt%.

[0033] In some specific embodiments, the maleic anhydride copolymer is an ethylene-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the ethylene-maleic anhydride alternating copolymer is 50%, and the weight average molecular weight of the maleic anhydride copolymer is 60,000.

[0034] Specifically, the amine compound is ethanolamine.

[0035] Specifically, the mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%, for example, 0.02 wt%, 0.05 wt%, 0.1 wt% or 0.5 wt%.

[0036] In some specific embodiments, the maleic anhydride copolymer is a methyl vinyl ether-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the methyl vinyl ether-maleic anhydride alternating copolymer is 50%, and the weight average molecular weight of the maleic anhydride copolymer is 130,000.

[0037] Specifically, the amine compound is propanolamine.

[0038] Specifically, the mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%, for example, 0.02 wt%, 0.05 wt%, 0.1 wt% or 0.5 wt%.

[0039] In some specific embodiments, the maleic anhydride copolymer is a styrene-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the styrene-maleic anhydride alternating copolymer is 25%, and the weight-average molecular weight of the maleic anhydride copolymer is 9500.

[0040] Specifically, the amine compound is ethanolamine and / or propanolamine.

[0041] Specifically, the mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%, for example, 0.02 wt%, 0.05 wt%, 0.1 wt%, or 0.5 wt%. The mass concentration of the amine compound in the composition refers to the percentage of the amine compound in the composition by mass before the introduction of the maleic anhydride copolymer.

[0042] In this invention, preferably, the refining process includes dehydration and distillation in sequence.

[0043] Preferably, the dehydration process is carried out in a dehydration tower.

[0044] Preferably, the temperature at the top of the dehydration treatment tower is 60-105°C, for example, 70°C.

[0045] Preferably, the pressure at the top of the dehydration treatment tower is 0.01-0.02 MPaA.

[0046] Preferably, the reflux ratio at the top of the dehydration treatment tower is 1:1.

[0047] Preferably, the distillation process is carried out in a distillation column.

[0048] Preferably, the top temperature of the distillation column is 100-120°C.

[0049] Preferably, the pressure at the top of the distillation column is 0.01-0.02 MPaA.

[0050] Preferably, the reflux ratio at the top of the distillation column is (1-4):1, for example, 2:1.

[0051] In this invention, the mixture may further include a solvent, such as water.

[0052] In this invention, preferably, the method for preparing the mixture includes mixing the maleic anhydride copolymer and the composition.

[0053] The mixing, for example, is stirring.

[0054] The stirring time is, for example, 2 hours.

[0055] In this invention, preferably, the method for preparing the mixture includes mixing a solution containing the maleic anhydride copolymer with the composition.

[0056] The mixing, for example, is stirring.

[0057] The stirring time is, for example, 2 hours.

[0058] Preferably, the solution containing the maleic anhydride copolymer further includes a solvent.

[0059] The solvent is, for example, NMP.

[0060] Preferably, the mass concentration of the maleic anhydride copolymer in the solution containing the maleic anhydride copolymer is 5%-15%, for example, 10%.

[0061] In this invention, preferably, the product obtained by the method for reducing impurities in a composition containing N-methylpyrrolidone has an amine compound content of less than 19 ppm and a pH value of 5.9 or higher.

[0062] The product in question is primarily composed of NMP.

[0063] The product obtained by the method of removing impurities from the composition can be used as a solvent for battery electrolyte, or as a solvent in the battery electrode preparation process.

[0064] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0065] The reagents and raw materials used in this invention are all commercially available.

[0066] The positive and progressive effects of this invention are as follows:

[0067] This invention uses maleic anhydride copolymers to reduce impurities in the composition. This method can not only efficiently remove impurity amine compounds, but also obtain products with suitable pH values. Detailed Implementation

[0068] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0069] Example 1:

[0070] Composition: N-methylpyrrolidone 89.98 wt%, monoethanolamine 0.02 wt%, water 10 wt%.

[0071] A solution containing maleic anhydride copolymer: This is a 10% (w / w) NMP solution containing styrene-maleic anhydride copolymer. The styrene-maleic anhydride alternating copolymer has a maleic anhydride molar content of 50%, a weight-average molecular weight of 5500, and the chemical formula of the repeating unit of the styrene-maleic anhydride alternating copolymer is C0. 12 H 10 O3, the molecular weight of the repeating unit is 202.2 g / mol.

[0072] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 3.31g of the above solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 0.331g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1:1, and the pH of the mixture was 10.3.

[0073] A method for reducing impurities in a composition containing N-methylpyrrolidone includes the following steps:

[0074] The mixture was fed into a dehydration column for dehydration treatment. The top temperature of the column was 70°C, the top pressure was 0.01 MPaA, and the reflux ratio was 1:1. An intermediate product was collected from the top of the dehydration column and then fed into a glass distillation column for distillation treatment. The top temperature of the glass distillation column was 120°C, the top pressure was 0.01 MPaA, and the reflux ratio was 2:1. The top product of the distillation treatment was collected in a collection bottle.

[0075] The content of amine compounds in the product collected from the top of the distillation column was tested according to the national standard GB / T27563-2011. The amine compounds in the product were titrated with hydrochloric acid standard titration solution, and isopropanol was used as diluent. The potentiometer indicated the titration endpoint, and the content of amine compounds in the product was calculated. The test result was 0.000273wt%, or 2.73ppm.

[0076] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.05, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0077] Example 2:

[0078] The composition of the composition is the same as in Example 1.

[0079] A solution containing maleic anhydride copolymer: This is a 10% NMP solution containing the above-mentioned ethylene-maleic anhydride copolymer. The ethylene-maleic anhydride alternating copolymer contains 50% maleic anhydride in molar content, has a weight-average molecular weight of 60,000, and the repeating unit of the ethylene-maleic anhydride alternating copolymer has the chemical formula C6H6O3 and a molecular weight of 126.1 g / mol.

[0080] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 3.03g of the above solution containing maleic anhydride copolymer (the mass of ethylene-maleic anhydride copolymer was 0.303g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1.5:1, and the pH of the mixture was 10.41.

[0081] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0082] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.000437 wt%, or 4.37 ppm.

[0083] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.06, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0084] Example 3:

[0085] Composition: N-methylpyrrolidone 97.95 wt%, monoethanolamine 0.05 wt%, water 2 wt%.

[0086] A solution containing maleic anhydride copolymer: This is a 10% (w / w) NMP solution containing the above-mentioned methyl vinyl ether-maleic anhydride copolymer. The methyl vinyl ether-maleic anhydride alternating copolymer contains 50% maleic anhydride in molar content, has a weight-average molecular weight of 130,000, and the chemical formula of the repeating unit of the methyl vinyl ether-maleic anhydride alternating copolymer is C7H8O4, with a molecular weight of 156.1 g / mol.

[0087] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and then 9.6g of the above solution containing maleic anhydride copolymer (the mass of methyl vinyl ether-maleic anhydride copolymer was 0.960g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1.5:1, and the pH of the mixture was 10.73.

[0088] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0089] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.000885 wt%, or 8.85 ppm.

[0090] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.20, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0091] Example 4:

[0092] Composition: N-methylpyrrolidone 89.98 wt%, propanolamine 0.02 wt%, water 10 wt%.

[0093] Solution containing maleic anhydride copolymer: This is a 5% (w / w) NMP solution containing the above-mentioned styrene-maleic anhydride copolymer. The styrene-maleic anhydride alternating copolymer is the same as in Example 1.

[0094] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 5.38g of a solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 0.269g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1:1, and the pH of the mixture was 10.54.

[0095] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0096] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.000574 wt%, or 5.74 ppm.

[0097] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.09, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0098] Example 5:

[0099] Composition: N-methylpyrrolidone 97.95 wt%, propanolamine 0.05 wt%, water 2 wt%.

[0100] Solution containing maleic anhydride copolymer: This is a 15% NMP solution containing methyl vinyl ether-maleic anhydride copolymer. The methyl vinyl ether-maleic anhydride alternating copolymer contains 50% maleic anhydride in molar content, has a weight-average molecular weight of 130,000, and the repeating unit of the methyl vinyl ether-maleic anhydride alternating copolymer has the chemical formula C7H8O4 and a molecular weight of 156.1 g / mol.

[0101] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and then 5.153g of the above solution containing maleic anhydride copolymer (the mass of methyl vinyl ether-maleic anhydride copolymer was 0.773g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1.5:1, and the pH of the mixture was 10.81.

[0102] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0103] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.000736 wt%, or 7.36 ppm.

[0104] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.10, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0105] Example 6:

[0106] The composition of the composition is the same as in Example 1.

[0107] Solution containing maleic anhydride copolymer: This is a 15% NMP solution containing styrene-maleic anhydride copolymer. The styrene-maleic anhydride alternating copolymer is the same as in Example 1.

[0108] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 0.99g of the above solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 0.099g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 0.3:1, and the pH of the mixture was 11.10.

[0109] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0110] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.001837 wt%, or 18.37 ppm.

[0111] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.56, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0112] Example 7:

[0113] The composition of the composition is the same as in Example 1.

[0114] Solution containing maleic anhydride copolymer: This is a 10% NMP solution containing styrene-maleic anhydride copolymer. The styrene-maleic anhydride alternating copolymer is the same as in Example 1.

[0115] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 6.62g of the above solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 0.662g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 2:1, and the pH of the mixture was 9.77.

[0116] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0117] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.000216 wt%, or 2.16 ppm.

[0118] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 5.99, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0119] Example 8:

[0120] The composition of the composition is the same as in Example 1.

[0121] Solution containing maleic anhydride copolymer: This is a 10% NMP solution containing styrene-maleic anhydride copolymer. The styrene-maleic anhydride alternating copolymer has a maleic anhydride molar content of 25% and a weight-average molecular weight of 9500.

[0122] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 3.970g of the above solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 0.397g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1.2:1, and the pH of the mixture was 10.69.

[0123] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0124] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.00082 wt%, or 8.82 ppm.

[0125] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.22, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0126] Example 9:

[0127] Composition: N-methylpyrrolidone 89.98 wt%, monoethanolamine 0.5 wt%, water 9.52 wt%.

[0128] Solution containing maleic anhydride copolymer: This is a 10% NMP solution containing styrene-maleic anhydride copolymer. The styrene-maleic anhydride copolymer is the same as in Example 1.

[0129] Mixture: 500g of the above composition was placed in a 1000ml round-bottom flask, and 82.75g of the above solution containing maleic anhydride copolymer (the mass of styrene-maleic anhydride copolymer was 8.275g) was added. The mixture was stirred at room temperature for 2 hours to form a mixture. The molar ratio of repeating units of maleic anhydride copolymer to amine compounds in the mixture was 1:1, and the pH of the mixture was 10.81.

[0130] The method for reducing impurities in the composition containing N-methylpyrrolidone is the same as in Example 1.

[0131] The content of amine compounds in the product collected from the top of the distillation column was tested using the method in Example 1. The test result was 0.00076%, or 7.60 ppm.

[0132] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 6.22, indicating that the product collected from the top of the distillation column meets the NMP recovery requirements of the battery industry.

[0133] The embodiments 1-9 of the present invention can achieve an amine compound content of less than 18.37 ppm and a pH value of more than 5.99 in the product collected from the top of the distillation column, which meets the NMP recovery requirements of the battery industry. Furthermore, selecting a molar ratio of maleic anhydride copolymer repeating units to amine compounds of (0.5-1.5):1 can achieve an amine compound content of less than 8.85 ppm and a pH value of more than 6.05 in the product collected from the top of the distillation column, resulting in even better performance.

[0134] Comparative Example 1:

[0135] The composition of the composition is the same as in Example 1.

[0136] A method for reducing impurities in a composition containing N-methylpyrrolidone includes the following steps:

[0137] Place 500g of the above composition in a 1000ml round-bottom flask, and add 1.601g of 10%wt sulfuric acid, wherein the molar ratio of sulfuric acid to monoethanolamine is 1:1. Stir at room temperature for 2 hours.

[0138] The mixture can be subjected to dehydration and distillation treatments in sequence, with the parameters for dehydration and distillation treatments being the same as in Example 1.

[0139] The content of amine compounds in the product collected from the top of the distillation column was tested, and the result was 0.002379 wt%, or 23.79 ppm.

[0140] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 4.82, which is too low and does not meet the NMP recovery requirements of the battery industry.

[0141] Comparative Example 2:

[0142] The composition of the composition is the same as in Example 1.

[0143] A method for reducing impurities in a composition containing N-methylpyrrolidone includes the following steps:

[0144] Place 500g of the above composition in a 1000ml round-bottom flask, and add 0.239g of adipic acid, wherein the molar ratio of adipic acid to monoethanolamine is 1:1. Stir at room temperature for 2 hours.

[0145] The mixture can be subjected to dehydration and distillation treatments in sequence, with the parameters for dehydration and distillation treatments being the same as in Example 1.

[0146] The content of amine compounds in the product collected from the top of the distillation column was tested, and the result was 0.002524 wt%, or 25.24 ppm.

[0147] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 5.47, which is too low and does not meet the NMP recovery requirements of the battery industry.

[0148] Comparative Example 3:

[0149] The composition of the composition is the same as in Example 1.

[0150] Mixture: 500g of the above composition and 0.303g of maleic anhydride, with a molar ratio of maleic anhydride to amine compound of 1:1. The preparation method of this mixture is the same as in Example 1.

[0151] The method for removing impurities from the composition is the same as in Example 1.

[0152] The content of amine compounds in the product collected from the top of the distillation column was tested, and the result was 0.000268%, or 2.68 ppm.

[0153] The pH value of the product collected from the top of the distillation column was determined according to the national standard GB / T 27563-2011. The pH value was 5.49.

[0154] Although Comparative Example 3 can achieve a similar content of amine compounds as Example 1, the pH value of the product collected from the top of the distillation column is too low and does not meet the NMP recovery requirements of the battery industry.

Claims

1. A method for reducing impurities in a composition containing N-methylpyrrolidone, characterized in that, It includes the following steps: The mixture is refined; the mixture comprises the composition and the maleic anhydride copolymer; The composition includes N-methylpyrrolidone and impurities, the impurities including amine compounds; The maleic anhydride copolymer is selected from one or more of styrene-maleic anhydride alternating copolymer, ethylene-maleic anhydride alternating copolymer, methyl vinyl ether-maleic anhydride alternating copolymer, propylene-maleic anhydride alternating copolymer and butadiene-maleic anhydride alternating copolymer; The amine compounds are selected from alkylamines and / or alcoholamines; The molar ratio of the repeating unit of the maleic anhydride copolymer to the amine compound is (0.3-1.5):1; The pH of the mixture is 9-11.1; the composition also includes water; The refining process includes dehydration and distillation.

2. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, The weight-average molecular weight of the maleic anhydride copolymer is 5,500-130,000.

3. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, The weight-average molecular weight of the maleic anhydride copolymer is 9,500 or 60,000.

4. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, It satisfies any one of the following conditions: (a) The maleic anhydride copolymer is a styrene-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the styrene-maleic anhydride alternating copolymer is 50%, and the weight average molecular weight of the maleic anhydride copolymer is 5500. (a) The maleic anhydride copolymer is an ethylene-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the ethylene-maleic anhydride alternating copolymer is 50%, and the weight average molecular weight of the maleic anhydride copolymer is 60,000. (c) The maleic anhydride copolymer is a methyl vinyl ether-maleic anhydride alternating copolymer, wherein the molar content of maleic anhydride in the methyl vinyl ether-maleic anhydride alternating copolymer is 50%, and the weight average molecular weight of the maleic anhydride copolymer is 130,000.

5. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, It meets one or more of the following conditions: (a) The molar ratio of the repeating unit of the maleic anhydride copolymer to the amine compound is (0.5-1.5):1; (b) The alkylamines include one or more of monomethylamine, dimethylamine, and trimethylamine; (c) The alkanolamines include one or more of monoethanolamine, diethanolamine, and propanolamine; (d) The pH value of the mixture is 9.77, 10.3, 10.41, 10.54, 10.69, 10.73, 10.81 or 11.

6. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, It meets one or more of the following conditions: (a) The mass concentration of the amine compound in the composition is 0.01 wt%-1 wt%; (b) The N-methylpyrrolidone concentration in the composition is 80 wt%-98 wt%; (c) The method for preparing the mixture includes mixing the maleic anhydride copolymer and the composition; (d) The method for preparing the mixture includes mixing a solution containing the maleic anhydride copolymer with the composition.

7. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, It meets one or more of the following conditions: (a) The dehydration process is carried out in a dehydration tower; (b) The temperature at the top of the dehydration treatment tower is 60-105℃; (c) The pressure at the top of the dehydration treatment tower is 0.01-0.02 MPaA; (d) The reflux ratio at the top of the dehydration treatment tower is 1:1; (e) The distillation process is carried out in a distillation column; (f) The top temperature of the distillation column is 100-120℃; (g) The pressure at the top of the distillation column is 0.01-0.02 MPaA; (h) The reflux ratio at the top of the distillation column is (1-4):

1.

8. The method for reducing impurities in a composition containing N-methylpyrrolidone as described in claim 1, characterized in that, The obtained product contains less than 19 ppm of amine compounds and has a pH value of more than 5.9.