A method for improving the stability of recycled NMP and its products

Abstract

The present invention relates to a method for improving the stability of recycled NMP (IPC classification number: C07D207 / 267), and particularly to a method for improving the stability of recycled NMP and its products. In the present invention, by adjusting the pH of NMP and the synergistic effect of the first distillation column, the second distillation column and the NMP distillation column, NMP is purified step by step, which can effectively ensure the yield and purity of the product. At the same time, the prepared NMP product has excellent stability and can be directly used in the production of lithium batteries.

Description

Technical Field

[0001] The present invention relates to a method for improving the stability of recycled NMP (IPC classification number: C07D207 / 267), and particularly to a method for improving the stability of recycled NMP and its products. Background Art

[0002] N-methylpyrrolidone (NMP) is a polar solvent and chemical raw material with strong selectivity and good stability, having advantages such as high boiling point, non-flammable, low toxicity, safe to use, strong dissolving ability, recyclable, and biodegradable. It is mainly used as an extractant for butadiene, aromatic hydrocarbons, etc., for the purification of acetylene, olefins, diolefins, as a solvent for many engineering plastics (such as polyvinylidene fluoride), as an electrode auxiliary material for lithium-ion batteries, a photoresist stripping solution, for the production of LCD liquid crystal materials, and for the cleaning of circuit boards in the semiconductor industry. During the production process of lithium batteries, a large amount of NMP waste liquid is generated. To reduce costs, the NMP waste liquid can be recovered, purified, and reused. However, NMP is unstable during long-term storage and easily discolors, causing certain difficulties to the analysis and detection methods. Currently, most patent applications focus on the purification methods of NMP, and there are few reports on how to prepare highly stable NMP.

[0003] In the method disclosed in patent application CN102001986A, NMP with stable quality was prepared, but when using ion exchange resin, it must be soaked in organic alcohol solvents, resulting in high solvent costs and reduced economic benefits. Currently, most patent applications focus on the purification methods of NMP, and there are few reports on how to prepare highly stable NMP.

[0004] Therefore, the method for improving the stability of recycled NMP provided by the present invention can effectively ensure the yield and purity of the product, and at the same time, the prepared NMP product has excellent stability and can be directly used in the production of lithium batteries. Summary of the Invention

[0005] To solve the above technical problems, the first aspect of the present invention provides a method for improving the stability of recycled NMP, and its steps include:

[0006] (1) Slowly drop a pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid.

[0007] (2) Transport the NMP waste liquid obtained in step (1) to a first rectification column for rectification to remove light components and extract heavy components.

[0008] (3) Transport the heavy components obtained from the bottom of the first rectification column to a second rectification column for rectification to remove light components and extract heavy components.

[0009] (4) Transfer the components obtained from the second rectification column to the NMP rectification column for separation, remove the heavy components, and extract the light components. The light components are the NMP products.

[0010] As a preferred solution, the pH regulator is one or more of aqueous solutions of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

[0011] As a preferred solution, the pH regulator is an aqueous solution of potassium hydroxide.

[0012] As a preferred solution, the mass concentration of the aqueous solution of potassium hydroxide is 20 - 40 wt%.

[0013] As a preferred solution, the pH of the NMP waste liquid in step (1) is 10.3 - 10.7.

[0014] As a preferred solution, the pH of the NMP waste liquid in step (1) is 10.4 - 10.6.

[0015] As a preferred solution, the temperature at the top of the first rectification column is 100 - 110 °C, and the temperature at the bottom of the column is 120 - 160 °C.

[0016] As a preferred solution, the pressure at the top of the first rectification column is -90 - -95 kPa, and the pressure at the bottom of the column is -85 - -90 kPa.

[0017] As a preferred solution, the reflux ratio of the first rectification column is 0.4 - 0.6.

[0018] As a preferred solution, the temperature at the top of the second rectification column is 120 - 130 °C, and the temperature at the bottom of the second rectification column is 110 - 120 °C.

[0019] As a preferred solution, the pressure at the top of the second rectification column is -90 - -95 kPa, and the pressure at the bottom of the column is -85 - -90 kPa.

[0020] As a preferred solution, the reflux ratio of the second rectification column is 2 - 3.

[0021] As a preferred solution, the temperature at the top of the NMP rectification column is 100 - 140 °C, and the temperature at the bottom of the NMP rectification column is 120 - 140 °C.

[0022] As a preferred solution, the pressure at the top of the NMP rectification column is -90 - -95 kPa, and the pressure at the bottom of the column is -85 - -90 kPa.

[0023] As a preferred solution, the reflux ratio of the NMP rectification column is 1 - 3.

[0024] As a preferred solution, both the second distillation column and the NMP distillation column are vacuum columns.

[0025] The vacuum column in this application refers to a distillation column with a pressure inside the column lower than the atmospheric pressure; the bottom pressure and the top pressure of the column in this application are both relative pressures, that is, the pressures expressed based on the atmospheric pressure of 1 atm, where 1 atm = 101.325 kPa.

[0026] During the experiment, the applicant found that NMP is prone to discoloration during the recycling and storage process, and it is impossible to know what substance causes the discoloration through analysis and detection. At the same time, the applicant found that when the pH of NMP is alkaline, the color of NMP will change. First, it turns pink or purple, but as time goes by, the color turns yellow. Through continuous exploration and a large number of experiments in this application, it is found that there is a great relationship between the pH value of NMP and whether the NMP raw material turns yellow. By strictly controlling its pH value, the problem of NMP turning yellow can be improved. However, the applicant accidentally found that when the temperature of NMP after adding alkali is too high, it is prone to hydrolysis. Since there are too many hydrolysis products, the reaction pathway is difficult to determine. However, through a large number of experiments, the applicant found that when the temperature and pressure of the distillation column are within a certain range, the problem of NMP being prone to discoloration can be greatly solved. In addition, the three-stage distillation method distributes the purification of NMP, which also has a positive effect on improving the yield and purity.

[0027] Beneficial effects:

[0028] 1. By strictly controlling the NMP waste liquid within 10.4 - 10.6 in the present invention, the polymerization of hydrolysis products in the NMP waste liquid can be promoted, which is convenient for separation from the purified NMP, thereby improving the problem of the yellowing of the NMP product.

[0029] 2. By controlling the temperatures of the top and bottom of the distillation column in the present invention, the problem that alkaline NMP is prone to hydrolysis at high temperatures is avoided, thereby effectively ensuring the yield and purity of the product.

[0030] 3. In the present invention, when the pressure of the distillation column is negative, while increasing the mass concentration of the heavy components, the occurrence of the polymerization reaction is inhibited, thereby reducing the hydrolysis reaction rate of NMP.

[0031] 4. Through the synergistic effect of three distillation columns in the present invention, NMP is purified step by step, improving the purity of the final product. At the same time, the negative pressure increases the relative volatility between components, which to a certain extent makes up for the problem of reduced processing capacity caused by the negative pressure.

[0032] 5. By effectively recycling and separating the NMP waste liquid in the present invention, the prepared NMP product has excellent stability and can be directly used in the production of lithium batteries. Specific Embodiments

[0033] Examples

[0034] Example 1

[0035] The first aspect of this example provides a method for improving the stability of recycled NMP, and its steps include:

[0036] (1) Slowly drop the pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid.

[0037] (2) Transport the NMP waste liquid obtained in step (1) to the first distillation column for distillation to remove light components and extract heavy components.

[0038] (3) Transport the heavy components obtained from the bottom of the first distillation column to the second distillation column for distillation to remove light components and extract heavy components.

[0039] (4) Transport the components obtained from the second distillation column to the NMP distillation column for separation, remove heavy components, and extract light components. The light components are NMP products.

[0040] The pH regulator in this example is an aqueous potassium hydroxide solution.

[0041] The mass concentration of the aqueous potassium hydroxide solution in this example is 30 wt%.

[0042] The pH of the NMP waste liquid in step (1) of this example is 10.5.

[0043] The temperature at the top of the first distillation column in this example is 105 °C, and the temperature at the bottom of the column is 150 °C.

[0044] The pressure at the top of the first distillation column in this example is -92 kPa, and the pressure at the bottom of the column is -87 kPa.

[0045] The reflux ratio of the first distillation column in this example is 0.5.

[0046] The temperature at the top of the second distillation column in this example is 125 °C, and the temperature at the bottom of the second distillation column is 115 °C.

[0047] The pressure at the top of the second distillation column in this example is -90 kPa, and the pressure at the bottom of the column is -85 kPa.

[0048] The reflux ratio of the second distillation column in this example is 2.5.

[0049] The temperature at the top of the NMP distillation column in this example is 130 °C, and the temperature at the bottom of the third distillation column is 120 °C.

[0050] The top pressure of the NMP distillation column in this embodiment is -90 kPa, and the bottom pressure of the third distillation column is -85 kPa.

[0051] Example 2

[0052] The first aspect of this embodiment provides a method for improving the stability of recycled NMP, and its steps include:

[0053] (1) Slowly drop the pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid. (1) Slowly drop the pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid.

[0054] (2) Transport the NMP waste liquid obtained in step (1) to the first distillation column for distillation to remove the light components and extract the heavy components.

[0055] (3) Transport the heavy components obtained from the bottom of the first distillation column to the second distillation column for distillation to remove the light components and extract the heavy components.

[0056] (4) Transport the components obtained from the second distillation column to the NMP distillation column for separation to remove the heavy components and extract the light components. The light components are the NMP products.

[0057] The pH regulator in this embodiment is an aqueous potassium hydroxide solution.

[0058] The mass concentration of the aqueous potassium hydroxide solution in this embodiment is 40 wt%.

[0059] The pH of the NMP waste liquid in step (1) of this embodiment is 10.5.

[0060] The top temperature of the first distillation column in this embodiment is 100 °C, and the bottom temperature is 130 °C.

[0061] The top pressure of the first distillation column in this embodiment is -90 kPa, and the bottom pressure is -90 kPa.

[0062] The reflux ratio of the first distillation column in this embodiment is 0.5.

[0063] The top temperature of the second distillation column in this embodiment is 120 °C, and the bottom temperature of the second distillation column is 120 °C.

[0064] The top pressure of the second distillation column in this embodiment is -90 kPa, and the bottom pressure is -85 kPa.

[0065] The reflux ratio of the second distillation column in this embodiment is 3.

[0066] The top temperature of the NMP distillation column in this embodiment is 130 °C, and the bottom temperature of the third distillation column is 120 °C.

[0067] In this embodiment, the top pressure of the NMP rectification column is -90 kPa, and the bottom pressure of the third rectification column is -85 kPa.

[0068] Example 3

[0069] The first aspect of this embodiment provides a method for improving the stability of recycled NMP, and its steps include:

[0070] (1) Slowly drip a pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid.

[0071] (2) Transport the NMP waste liquid obtained in step (1) to the first rectification column for rectification to remove light components and extract heavy components.

[0072] (3) Transport the heavy components obtained from the bottom of the first rectification column to the second rectification column for rectification to remove light components and extract heavy components.

[0073] (4) Transport the components obtained from the second rectification column to the NMP rectification column for separation to remove heavy components and extract light components, and the light components are NMP products.

[0074] The pH regulator in this embodiment is an aqueous potassium hydroxide solution.

[0075] The mass concentration of the aqueous potassium hydroxide solution in this embodiment is 20 wt%.

[0076] The pH of the NMP waste liquid in step (1) of this embodiment is 10.6.

[0077] In this embodiment, the top temperature of the first rectification column is 105 °C, and the bottom temperature is 150 °C.

[0078] In this embodiment, the top pressure of the first rectification column is -92 kPa, and the bottom pressure is -87 kPa.

[0079] In this embodiment, the reflux ratio of the first rectification column is 0.4.

[0080] In this embodiment, the top temperature of the second rectification column is 125 °C, and the bottom temperature of the second rectification column is 115 °C.

[0081] In this embodiment, the top pressure of the second rectification column is -90 kPa, and the bottom pressure is -85 kPa.

[0082] In this embodiment, the reflux ratio of the second rectification column is 2.5.

[0083] In this embodiment, the top temperature of the NMP rectification column is 100 °C, and the bottom temperature of the third rectification column is 120 °C.

[0084] In this embodiment, the top pressure of the NMP rectification column is -90 kPa, and the bottom pressure of the third rectification column is -85 kPa.

[0085] Comparative Example 1

[0086] The specific implementation manner of Comparative Example 1 is the same as that of Example 1; the difference is that the pH of the NMP waste liquid in step (1) of Comparative Example 1 is 12.

[0087] Comparative Example 2

[0088] The specific implementation manner of Comparative Example 2 is the same as that of Example 1; the difference is that in Comparative Example 2, the top temperature of the first rectification column is 130 °C, and the bottom temperature is 200 °C; the top pressure is -90 kPa, and the bottom pressure is -90 kPa; the reflux ratio of the first rectification column is 1.

[0089] Comparative Example 3

[0090] The specific implementation manner of Comparative Example 3 is the same as that of Example 1; the difference is that in Comparative Example 3, the top temperature of the second rectification column is 90 °C, and the bottom temperature is 110 °C; the top pressure is 50 kPa, and the bottom pressure is 45 kPa.

[0091] Performance test:

[0092] (1) Color stability at room temperature: Take 50 ml of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 3 and put them into a 50 ml glass test tube, seal it, and place it at room temperature for 3 months to observe the color of the samples.

[0093] (2) Purity: Detect with an Agilent 7890A gas chromatography-mass spectrometry instrument.

[0094] (3) Moisture: Detection method: Detect according to GB / T 6283-2008.

[0095] Performance test data:

[0096] Table 1 shows the performance test results of the highly stable recycled N-methylpyrrolidone prepared in Examples 1 to 3 and Comparative Examples 1 to 3.

[0097] Table 1

[0098]

[0099]

Claims

1. A method for improving the stability of recycled NMP, characterized in that, The steps include: (1) Slowly drop the pH regulator into the NMP waste liquid to adjust the pH of the NMP waste liquid; (2) Transport the NMP waste liquid obtained in step (1) to the first distillation column for distillation to remove light components and extract heavy components; (3) Transport the heavy components obtained from the bottom of the first distillation column to the second distillation column for distillation to remove light components and extract heavy components; (4) Transport the components obtained from the second distillation column to the NMP distillation column for separation to remove heavy components and extract light components, and the light components are NMP products; The pH regulator is an aqueous potassium hydroxide solution; The mass concentration of the aqueous potassium hydroxide solution is 30 wt%; The pH of the NMP waste liquid in step (1) is 10.5; The temperature at the top of the first distillation column is 105 °C, and the temperature at the bottom of the column is 150 °C; The pressure at the top of the first distillation column is -92 kPa, and the pressure at the bottom of the column is -87 kPa; The reflux ratio of the first distillation column is 0.5; The temperature at the top of the second distillation column is 125 °C, and the temperature at the bottom of the second distillation column is 115 °C; The pressure at the top of the second distillation column is -90 kPa, and the pressure at the bottom of the column is -85 kPa; The reflux ratio of the second distillation column is 2.5; The temperature at the top of the NMP distillation column is 130 °C, and the temperature at the bottom of the NMP distillation column is 120 °C; The pressure at the top of the NMP distillation column is -90 kPa, and the pressure at the bottom of the NMP distillation column is -85 kPa.

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