CNT-containing NMP cleaning solution recovery method

Abstract

The invention relates to the technical field of NMP (N-Methyl Pyrrolidone) recovery, and particularly discloses a CNT (Carbon Nanotube)-containing NMP cleaning solution recovery method. A CNT-containing NMP cleaning liquid recovery method comprises the following specific steps: adding water into a CNT-containing NMP cleaning waste liquid, uniformly stirring to form a primary treatment liquid, and adding a flocculating agent into the primary treatment liquid according to a mass ratio of the cleaning waste liquid to the water to the flocculating agent of 1: (0.05-0.1): (0.0005-0.0015) until particles appear in the primary treatment liquid; the primary treatment liquid is subjected to filter pressing separation, filtrate and a filter cake are obtained, filter pressing filter cloth is polypropylene fiber filter cloth, the mesh number of the polypropylene fiber filter cloth is 600-900, the filtrate is taken and subjected to membrane filtration and rectification in sequence, an NMP finished product is obtained, and NMP recovery is completed; the recovered NMP has good purity, the carbon nanotubes in the generated filter cake can be recycled in time, and the recovery efficiency and the energy utilization efficiency are improved.

Description

Technical Field

[0001] The present application relates to the technical field of NMP recovery, and in particular to a method for recovering a CNT-containing NMP cleaning liquid. Background Art

[0002] NMP (N-methylpyrrolidone) is a colorless transparent liquid with good chemical and thermal stability, high polarity, low volatility, and infinite miscibility with water and many organic solvents. It has been widely used in the fields of electronics and chemical industry. Especially in the manufacturing process of lithium-ion batteries, NMP is one of the indispensable key solvents used in the preparation and coating process of positive electrode slurry. In addition, NMP is a good polar solvent and is often used as a cleaning agent, especially in the production process of lithium-ion batteries as a cleaning agent and a cleaning agent for printed circuit boards and electronic devices.

[0003] In the lithium battery manufacturing process, NMP is also used for cleaning when the dispersion devices such as the stirring kettle need to be cleaned. In this process, cleaning waste liquid containing solids such as lithium iron phosphate, carbon nanotubes (CNT), binders, and dispersants will be generated. In particular, lithium iron phosphate has extremely high economic value. The traditional process of separating the above mixtures mostly uses industrial processes such as concentration, distillation, and refining to recover NMP from the NMP waste liquid. However, NMP has a high boiling point, so the process requires a large reflux ratio, resulting in high energy consumption for the process. Once the first tower fluctuates, the purity of the NMP product in the second tower cannot be guaranteed. At the same time, the wastewater, tail gas, and kettle residue generated by the device cannot be effectively utilized, and the CNT in the cleaning waste liquid cannot be recovered in time. Summary of the invention

[0004] In order to improve the separation effect of the mixture in the NMP cleaning solution, the present application provides a method for recovering the NMP cleaning solution containing CNTs.

[0005] The present application provides a method for recovering a CNT-containing NMP cleaning liquid, which adopts the following technical solution: A method for recovering a CNT-containing NMP cleaning liquid comprises the following specific steps: adding water to a CNT-containing NMP cleaning waste liquid, wherein the mass ratio of the cleaning waste liquid to the water is 1:(0.05-0.1), stirring evenly to form a primary treatment liquid, adding a flocculant to the primary treatment liquid according to a mass ratio of the cleaning waste liquid to the flocculant of 1:(0.0005-0.0015), until particles appear in the primary treatment liquid; performing filter pressing separation on the primary treatment liquid to obtain a filtrate and a filter cake, wherein the filter cloth for the filter pressing is a polypropylene filter cloth, wherein the mesh number of the polypropylene filter cloth is 600-900 meshes, and taking the filtrate and sequentially performing membrane filtration and rectification to obtain an NMP finished product, thereby completing the recovery of the NMP.

[0006] By adopting the above technical solution, NMP is first mixed with water, the purpose is to utilize the better solubility of NMP in water to destroy the original combination of NMP and CNT and other binder dispersants, so that the subsequent flocculant can better flocculate and precipitate. Flocculants can cause carbon nanotubes and other suspended particles in the cleaning waste liquid to aggregate and form larger particles, which is convenient for subsequent filter press separation and improves the recovery effect. Using polypropylene filter cloth for filter press can effectively separate the filtrate and filter cake in the primary treatment liquid, effectively intercept the flocculated particles, recover the carbon nanotubes in the cleaning waste liquid, and improve the purity of the NMP solution. The resulting filter cake contains lithium iron phosphate and carbon nanotubes, which can realize the value reproduction of NMP and carbon nanotubes. At the same time, no new substances are introduced in the recycling process, which reduces the emission of pollutants and improves the recovery efficiency and energy utilization efficiency.

[0007] Preferably, the flocculant is one of polyacrylamide, alum and polyaluminium chloride.

[0008] By adopting the above technical solution, polyacrylamide, alum, and polyaluminium chloride as flocculants can promote the aggregation of CNTs and other suspended particles in the waste liquid through charge neutralization, bridging and adsorption, forming larger flocs, facilitating subsequent solid-liquid separation, and improving the purity and efficiency of NMP recovery. Among them, polyacrylamide and alum have good biodegradability, realizing an efficient and environmentally friendly NMP recovery process.

[0009] Preferably, the polyacrylamide is grafted with a natural polymer.

[0010] By adopting the above technical solution, the grafted polyacrylamide can enhance the adsorption capacity of carbon nanotubes and other suspended particles in the cleaned waste liquid through the long chain structure and multi-functional groups of natural polymers, improve the structure of flocs, form more stable and easier to filter flocs, improve the flocculation effect, and make particles easier to aggregate and settle. It helps to improve the efficiency of filter press separation, reduce the moisture content of filter cakes, and improve the purity of NMP recovery.

[0011] Preferably, the polyacrylamide grafting method comprises the following specific steps: The natural polymer and acrylamide are dissolved in an acetic acid solution, and under the protection of nitrogen, an initiator is added to seal the reaction and heated to 50-60° C. in a water bath, and the product is purified and washed with acetone, and dried to obtain the natural polymer grafted polyacrylamide.

[0012] Preferably, the natural polymer is chitosan.

[0013] By adopting the above technical solution, the surface of chitosan has a large number of amino and hydroxyl active groups, which can form a cationic polyelectrolyte with high charge density and good complexing and flocculation properties. After the polymerization of chitosan and acrylamide, amide groups are introduced into the molecular chain. At the same time, the increase of the polymer molecular chain enhances the adsorption and bridging ability of the flocculant, which can improve the thermal stability and flocculation effect of the flocculant.

[0014] Preferably, the mass ratio of acrylamide, natural polymer and initiator is 4:(1-1.5):(0.1-0.2).

[0015] Preferably, the membrane filtration uses a membrane filter with a mesh size of 300-400.

[0016] By adopting the above technical solution, membrane filtration can further remove tiny particles and impurities in the filtrate, including incompletely flocculated carbon nanotube residues, flocculant residues and other possible tiny suspended matter, and improve the recovery purity of NMP solution. Membrane filtration can reduce the entry of tiny particles into subsequent distillation equipment, avoid clogging or damage to equipment such as distillation towers, improve distillation efficiency, and improve NMP recovery effect.

[0017] Preferably, the distillation temperature is 90-150° C., the pressure is 1-2 kPa, and the distillation time is 7-16 h.

[0018] In summary, this application has the following beneficial effects: 1. Since the present application adopts the method of dissolving NMP first, the original combination of NMP and CNT and other binders and dispersants will be destroyed, and then a flocculant is used to flocculate and precipitate the carbon nanotubes and other suspended particles in the cleaning waste liquid, and then the flocculated particles are effectively retained by filter press separation to improve the purity of the NMP solution.

[0019] 2. In this application, polyacrylamide, alum and polyaluminium chloride are used as flocculants to promote the aggregation of carbon nanotubes and other suspended particles in the cleaning wastewater to form larger flocs, which are convenient for subsequent solid-liquid separation. Chitosan is grafted with polyacrylamide to form a polymer with a long chain structure, which improves the thermal stability and flocculation effect of the flocculant. DETAILED DESCRIPTION

[0020] The present application is further described in detail below with reference to the embodiments.

[0021] All raw materials in the examples are commercially available. Example

[0022] Example 1 This embodiment provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.08 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.001, a flocculant is added to the primary treatment liquid. The flocculant is alum, until particles appear in the primary treatment liquid.

[0023] S2: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is purified by a 350-mesh membrane filter. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0024] Example 2 Example 2 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.1 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.0015, a flocculant is added to the primary treatment liquid. The flocculant is alum, until particles appear in the primary treatment liquid.

[0025] S2: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is purified by a 350-mesh membrane filter. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0026] Example 3 Example 3 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.05 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant being 1:0.0005, a flocculant is added to the primary treatment liquid. The flocculant is alum until particles appear in the primary treatment liquid.

[0027] S2: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is purified by a 350-mesh membrane filter. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0028] Example 4 The difference between Example 4 and Example 1 is that the flocculant in the method for recovering the CNT-containing NMP cleaning liquid is polyaluminum chloride, and the Al2O3 content in the polyaluminum chloride is 27wt%.

[0029] Example 5 The difference between Example 5 and Example 1 is that the flocculant in the method for recovering the CNT-containing NMP cleaning liquid is polyacrylamide, and the molecular weight of the polyacrylamide is 18 million.

[0030] Example 6 Example 6 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Dissolve the natural polymer and acrylamide in a 1wt% acetic acid aqueous solution, wherein the natural polymer is chitosan. Under the protection of nitrogen, add the initiator ammonium persulfate, and the mass ratio of acrylamide, natural polymer and initiator is 4:1.3:0.15. Heat to 55°C in a water bath and seal the reaction for 30 minutes. Purify the product with acetone and then wash it with anhydrous ethanol. After drying, obtain the natural polymer grafted polyacrylamide.

[0031] S2: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.08 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.001, a flocculant is added to the primary treatment liquid. The flocculant is a natural polymer grafted polyacrylamide, until particles appear in the primary treatment liquid.

[0032] S3: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is filtered and purified using a 350-mesh membrane. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0033] Example 7 Example 7 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Dissolve the natural polymer and acrylamide in a 1wt% acetic acid aqueous solution, wherein the natural polymer is chitosan. Under the protection of nitrogen, add the initiator ammonium persulfate, and the mass ratio of acrylamide, natural polymer and initiator is 4:1:0.1. Heat to 55°C in a water bath and seal the reaction for 30 minutes. Purify the product with acetone and then wash it with anhydrous ethanol. After drying, obtain the natural polymer grafted polyacrylamide.

[0034] S2: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.08 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.001, a flocculant is added to the primary treatment liquid. The flocculant is a natural polymer grafted polyacrylamide, until particles appear in the primary treatment liquid.

[0035] S3: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is filtered and purified using a 350-mesh membrane. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0036] Example 8 Example 8 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Dissolve the natural polymer and acrylamide in a 1wt% acetic acid aqueous solution, wherein the natural polymer is chitosan. Under the protection of nitrogen, add the initiator ammonium persulfate, and the mass ratio of acrylamide, natural polymer and initiator is 4:1.5:0.2. Heat to 55°C in a water bath and seal the reaction for 30 minutes. Purify the product with acetone and then wash it with anhydrous ethanol. After drying, obtain the natural polymer grafted polyacrylamide.

[0037] S2: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.08 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.001, a flocculant is added to the primary treatment liquid. The flocculant is a natural polymer grafted polyacrylamide, until particles appear in the primary treatment liquid.

[0038] S3: The primary treatment liquid is sucked into a plate and frame filter press while stirring to obtain a filtrate and a filter cake. The filter press uses a polypropylene filter cloth with a mesh number of 800. The filtrate is filtered and purified using a 350-mesh membrane. Finally, it is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a finished NMP product, thereby completing the recovery of NMP.

[0039] Example 9 The difference between Example 9 and Example 6 is that the natural polymer in the method for recovering the CNT-containing NMP cleaning liquid is starch.

[0040] Comparative Example Comparative Example 1 Comparative Example 1 provides a method for recovering a CNT-containing NMP cleaning solution, comprising the following specific steps: S1: Add water to the NMP cleaning waste liquid containing CNTs and stir evenly. The mass ratio of the cleaning waste liquid to water is 1:0.08 to form a primary treatment liquid. According to the mass ratio of the cleaning waste liquid to the flocculant of 1:0.001, a flocculant is added to the primary treatment liquid. The flocculant is alum, until particles appear in the primary treatment liquid.

[0041] S2: The primary treatment liquid is distilled and purified at 130° C. and a pressure of 1.5 kPa for 12 hours to obtain a NMP product, thereby completing the recovery of NMP.

[0042] Performance testing The NMP product recovered by the method for recovering the CNT-containing NMP cleaning liquid provided in Examples 1-9 and Comparative Example 1 of the present application was subjected to component analysis, and the specific performance test result data are shown in Table 1.

[0043] Detection Methods The purity of the NMP product was tested using an Agilent 7890A GC / MS instrument; the recovery rate was calculated based on the mass of the original NMP in the NMP cleaning solution and the recovered NMP product.

[0044] Table 1: Performance test results data table Example purity(%) Recovery rate (%) Example 1 93 90 Example 2 92 90 Example 3 93 89 Example 4 94 90 Example 5 95 91 Example 6 98 95 Example 7 97 94 Example 8 97 95 Example 9 96 93 Comparative Example 1 71 75 It can be seen from the performance test results that the purity of the NMP product recovered by this application reaches more than 90%, and the recovery rate can reach 95%. At the same time, the lithium iron phosphate and carbon nanotubes contained in the filter cake produced also have increased value, which can realize the value reproduction of NMP and carbon nanotubes. No new substances are introduced in the recovery process, which reduces the emission of pollutants and improves the recovery efficiency and energy efficiency of NMP. It can be seen from Examples 6-8 that by grafting polyacrylamide with natural polymers, it is easier to form a more stable and easier to filter floc structure, making solid particles easier to aggregate and settle. It can be seen from the comparison of Example 9 and Example 6 that the grafting effect of the natural polymer and polyacrylamide used in Example 6 is better.

[0045] By comparing Comparative Example 1 with Example 1, it can be seen that in Comparative Example 1, the process step of solid-liquid separation by filtration is reduced, and the primary treatment liquid is directly distilled. From the performance test results, it can be seen that the purity and recovery effect of NMP are greatly reduced, and at the same time, it is impossible to effectively recover usable substances such as carbon nanotubes.

[0046] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for recovering a CNT-containing NMP cleaning liquid, characterized in that: The method comprises the following specific steps: adding water to the NMP washing waste liquid containing CNT, wherein the mass ratio of the washing waste liquid to the water is 1: (0.05-0.1), stirring evenly to form a primary treatment liquid, adding a flocculant to the primary treatment liquid according to the mass ratio of the washing waste liquid to the flocculant being 1: (0.0005-0.0015), until particles appear in the primary treatment liquid; performing filter pressing separation on the primary treatment liquid to obtain a filtrate and a filter cake, wherein the filter cloth for the filter pressing is a polypropylene filter cloth, wherein the mesh number of the polypropylene filter cloth is 600-900 meshes, and taking the filtrate and performing membrane filtration and rectification in sequence to obtain an NMP finished product, thereby completing the recovery of NMP.

2. The method for recovering a CNT-containing NMP cleaning liquid according to claim 1, characterized in that: The flocculant is one of polyacrylamide, alum and polyaluminium chloride.

3. The method for recovering a CNT-containing NMP cleaning liquid according to claim 2, characterized in that: The polyacrylamide is grafted with natural polymer.

4. The method for recovering a CNT-containing NMP cleaning liquid according to claim 3, characterized in that: The grafting method of polyacrylamide comprises the following specific steps: The natural polymer and acrylamide are dissolved in an acetic acid solution, and under the protection of nitrogen, an initiator is added to seal the reaction and heated to 50-60° C. in a water bath, and the product is purified and washed with acetone, and dried to obtain the natural polymer grafted polyacrylamide.

5. The method for recovering a CNT-containing NMP cleaning liquid according to claim 4, characterized in that: The natural polymer is chitosan.

6. The method for recovering a CNT-containing NMP cleaning liquid according to claim 4, characterized in that: The mass ratio of acrylamide, natural polymer and initiator is 4:(1-1.5):(0.1-0.2).

7. The method for recovering a CNT-containing NMP cleaning liquid according to claim 1, characterized in that: The membrane filter used was a 300-400 mesh membrane filter.

8. The method for recovering a CNT-containing NMP cleaning liquid according to claim 1, characterized in that: The distillation temperature is 90-150° C., the pressure is 1-2 kPa, and the distillation time is 7-16 hours.