Impurity treatment method for PVDF rubber powder and CNT conductive paste in NMP-containing cleaning waste liquid

Abstract

The invention discloses a method for treating impurities of PVDF (polyvinylidene fluoride) rubber powder and CNT (carbon nanotube) conductive paste in NMP (N-Methyl Pyrrolidone)-containing cleaning waste liquid, which comprises the following steps: adding industrial water into the waste liquid for modification, separating out part of impurities, and fishing out to obtain modified liquid; adding a flocculating agent into the modified liquid for coagulation, adjusting the pH value, and filtering to obtain filtrate and filter residues; the filtrate is distilled to recover NMP, and the obtained product is high in purity and low in moisture and meets the comprehensive utilization standard; and sending the separated and fished-out substances into a cement kiln for harmless treatment, and incinerating the filter residues in an incinerator to enrich cobalt and nickel in the filter residues for recycling. Industrial water is added into the NMP cleaning waste liquid for water modification treatment, the working procedures of flocculating agent coagulation and filtration are matched, efficient removal of impurities in the waste liquid is achieved, NMP is recycled in the follow-up process in combination with a distillation process, the obtained recycled NMP is high in purity and low in moisture content and can meet the comprehensive utilization standard, and meanwhile after fished-out matter generated by the waste liquid is subjected to harmless treatment through a cement kiln, the waste liquid can be recycled. And the filter residues enter an incinerator to be incinerated, cobalt and nickel elements are enriched, and convenience is provided for follow-up recycling.

Description

Technical Field

[0001] This invention relates to the field of NMP cleaning waste liquid recovery and NMP resource utilization technology, and in particular to a method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP cleaning waste liquid. Background Technology

[0002] The NMP-containing cleaning wastewater (N-methylpyrrolidone produced from residual positive electrode slurry in cleaning equipment and pipelines) is a waste organic solvent and is classified as hazardous waste, posing a harmful toxicity to the production environment and human health. While attempting to recover and utilize the NMP, the presence of impurities such as PVDF powder and CNT conductive paste presents challenges. During distillation, these impurities easily cover the heating surfaces of the equipment, severely impacting heat transfer efficiency and disrupting continuous production. Furthermore, direct filtration pretreatment can lead to PVDF powder and CNT conductive paste clogging the filter cloth, preventing filtration altogether.

[0003] Existing treatment methods generally employ direct distillation of wastewater containing impurities, flocculant pretreatment, and membrane separation, but these methods have the following drawbacks: When treating waste liquid using direct distillation, impurities easily adhere to the inner wall of the distillation equipment, causing scaling and blockage, resulting in a significant decrease in heat transfer efficiency. Furthermore, the recovered NMP has low purity and high impurity content. When using membrane separation for waste liquid filtration, PVDF powder and CNTs in the NMP-containing waste liquid are colloidal impurities that easily aggregate and clog membrane pores, leading to a rapid decrease in membrane flux. This necessitates frequent replacement of membrane modules, resulting in high costs. Additionally, the membrane material (such as PTFE) is easily adsorbed and contaminated by impurities, leading to low treatment efficiency. While flocculant pretreatment is used, its flocculation effect on colloidal impurities such as PVDF powder and CNTs in the waste liquid is limited, resulting in a low impurity removal rate. Residual impurities may still cause scaling in subsequent distillation equipment, and the recovered NMP purity is only around 90%, with high water content, making it difficult to meet comprehensive utilization requirements. Summary of the Invention

[0004] This invention provides a method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning waste liquid, in order to overcome the above-mentioned problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning waste liquid includes the following steps: S1: Add industrial water to the NMP-containing cleaning waste liquid to modify and precipitate some PVDF adhesive powder and CNT conductive paste impurities, and remove the impurities from the surface of the reaction liquid to obtain the precipitate and the modified liquid. S2: Add flocculant to the modified liquid for coagulation, adjust the pH of the modified liquid to weakly alkaline, and then pre-treat by filtration to obtain filtrate and filter residue; S3: Distill the filtrate to recover the NMP product; S4: The dredged material described in S1 is sent to a cement kiln for harmless treatment; the filter residue described in S2 is sent to an incinerator for incineration to enrich the cobalt and nickel therein for recycling and reuse.

[0006] Furthermore, in S1, the mass ratio of the NMP-containing cleaning waste liquid to the industrial water is 1:1.

[0007] Further, in S2, the flocculant is polyferric sulfate; the ratio of the amount of polyferric sulfate added to the mass of the NMP-containing cleaning waste liquid is 3:1000.

[0008] Furthermore, in S2, after adding the flocculant, the pH of the modified liquid is adjusted to 6-7, making it weakly acidic. Then, industrial lime is added to adjust the pH of the modified liquid to 7-8, making it weakly alkaline.

[0009] Furthermore, after the aforementioned filtration pretreatment, the removal rate of PVDF adhesive powder and CNT conductive paste impurities in the cleaning waste liquid is greater than 97%.

[0010] Furthermore, in S2, the specific method of the filtration pretreatment is as follows: after the modified liquid has been adjusted to pH, it is first coarsely filtered through a plate and frame filter, and then finely filtered through a bag filter.

[0011] Furthermore, the various indicators of the industrial water are as follows: pH 6.5–8.5, turbidity ≤3 NTU, COD cr ≤50 mg / L, BOD5≤10 mg / L, iron≤0.3 mg / L, manganese≤0.1 mg / L, chloride ion≤250 mg / L, total hardness (calculated as calcium carbonate) is 450 mg / L, total alkalinity (calculated as calcium carbonate) is 350 mg / L, sulfate≤250 mg / L, ammonia nitrogen (calculated as N)≤10 mg / L, total phosphorus (calculated as P)≤1 mg / L, dissolved solids≤1000 mg / L.

[0012] The beneficial effects of this invention are: This invention discloses a method for treating impurities such as PVDF powder and CNT conductive paste in NMP-containing cleaning wastewater. The method involves adding industrial water to the NMP cleaning wastewater for water modification, followed by a single flocculant coagulation and filtration process to achieve efficient removal of impurities. Subsequent distillation is used to recover NMP, resulting in high-purity NMP with low moisture content, meeting comprehensive utilization standards. Simultaneously, the effluent from the wastewater undergoes harmless treatment in a cement kiln, and the filter residue is incinerated to enrich cobalt and nickel elements, facilitating subsequent recycling. This invention enables the production-scale recycling and treatment of NMP-containing cleaning wastewater, fully complying with the requirements of harmlessness, volume reduction, and resource recovery. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Example 1: A method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning waste liquid includes the following steps: 1000 kg of NMP-containing cleaning waste liquid was added to 1000 kg of industrial water. After stirring for ten minutes, the mixture was allowed to stand for half an hour. Some of the PVDF solids that had precipitated from the floating surface were removed (the precipitate). Then, with stirring, 3 kg of polyferric sulfate was added to the modified liquid after removing the precipitate, and the pH was adjusted to 6. Next, 3.5 kg of lime was added, and the pH was adjusted to 8. The mixture was stirred for half an hour. The reaction solution was then filtered sequentially through a plate and frame filter and a bag filter. After filtration, the impurity removal rate was 97.3%. The filtrate was subjected to negative pressure flash evaporation to recover NMP, yielding NMP with a purity of 99.75% and a water content of 0.69%, which was then utilized. The precipitate was sent to a cement kiln for harmless treatment. The filter residue was incinerated in an incinerator to enrich and recover cobalt and nickel.

[0015] A. Negative pressure flash evaporation conditions (normal conditions): The filtrate is first heated to 90~95℃ in a preheater, and then... 3 A stable flow rate of / h enters an effective volume of 1~1.5m³. 3The flash tank is equipped with a baffle plate gas-liquid separation structure. Inside the tank, a vacuum of -0.090 to -0.095 MPa (absolute pressure 5 to 10 kPa) is maintained through a combination of a water ring vacuum pump and a Roots vacuum pump unit, with pressure fluctuations ≤ ±0.002 MPa. The material residence time inside the tank is ≤10 seconds to achieve instantaneous vaporization, and the gas phase rising velocity is controlled at 1 to 1.5 m / s to ensure rapid gas-liquid separation. The flash vapor phase is introduced into a tube condenser (condensing medium is 25 to 30℃ circulating cooling water), where the aqueous phase is condensed and reused in the dilution and modification process. The liquid phase at the bottom of the flash tank (crude NMP with a purity ≥ 99.2% and a water content ≤ 0.2%) is introduced at a flow rate of 2 to 3 m / s, matching the feed flow rate. 3 The solution is continuously discharged at a rate of / h and can be sent to the subsequent distillation unit for further purification. The entire negative pressure flash evaporation process has no reflux stage. It achieves NMP coarse separation by relying on preheating → depressurization instantaneous vaporization → rapid gas-liquid separation, which is suitable for the continuous filtrate treatment requirements of this application.

[0016] B. Cement kiln processing conditions (normal conditions): A new type of dry-process cement rotary kiln (size ≥ Φ4.0m × 60m, daily clinker production ≥ 2500t) is adopted. The slag is crushed to a particle size ≤ 50mm (moisture content > 30%, requiring dehydration to ≤ 15%) and fed into the kiln tail decomposition furnace. The decomposition furnace temperature is 850~950℃ (holding ≥ 2s), and the kiln shell firing zone temperature is 1450~1600℃ (holding ≥ 4s) to ensure complete decomposition of PVDF and CNT in the slag, and enrichment of cobalt / nickel in the clinker. The alkalinity within the kiln (KH value 0.88~0.96) is maintained by adjusting the limestone ratio, fixing acidic gases such as HF. The slag addition ratio is ≤ 5% of the clinker production (dry basis), and it can replace 5%~10% of pulverized coal if its calorific value meets the standards. The exhaust gas is treated by SNCR, bag filter dust collection, and dry desulfurization, and emissions of NOx, HF, and particulate matter meet environmental protection standards.

[0017] C. The specifications and parameters of the plate and frame filter equipment are as follows: (1) Specifications: Polypropylene plate and frame filter press, filter plate size 800×800mm, effective filtration area 20~30m² 2 ; (2) Parameters: Filter cloth parameters: Polyester long-fiber filter cloth, mesh size 200~300 mesh, air permeability 80~100L / m 2 s; Operating pressure: Feed pressure 0.3~0.5MPa (constant pressure filtration to avoid floc breakage); Filtration temperature: room temperature (25~30℃, to ensure NMP stability and floc structure integrity); Feed flow rate: 1~2m 3 / h (matching 1000kg (2m)3 (The liquid mixture is filtered in 3-3.5 hours). Filtrate solids content: ≤5% (to ensure the load of subsequent bag filtration).

[0018] D. The specifications and parameters of the bag filter equipment are as follows: (1) Specifications: 304 stainless steel single-bag filter, filtration area 0.5~1m² 2 ; (2) Parameters: Filter bag parameters: Nylon needle-punched felt filter bag, precision 50~100 mesh, temperature resistance ≥60℃, pressure resistance ≥0.6MPa; Operating pressure: 0.1~0.2MPa (to prevent filter bag damage and ensure retention efficiency); Feed flow rate: 0.8~1.5m 3 / h (matching the plate and frame filtrate discharge rate); Filtration method: series filtration at atmospheric pressure, single bag operation (with one bag available for backup to ensure continuous operation). The final filtrate has a solids content of ≤3%.

[0019] E. The specifications of the industrial water used are shown in Table 1 below: Table 1. Indicators of Industrial Water

[0020] Comparative Example 1: Compared with Example 1, the only difference in the operation steps of this comparative example is that 700 kg of industrial water was added in this comparative example. As a result, the filtration of the cleaning waste liquid was more difficult, and the filtration time was doubled to a total of 9.5 hours.

[0021] Comparative Example 2: Compared with Example 1, the only difference in the operation steps of this comparative example is that 400 kg of industrial water was added in this comparative example, and the result was that it could not be filtered.

[0022] Comparative Example 3: Compared with Example 1, the only difference in the operation steps of this comparative example is that: in this comparative example, only a plate and frame filter is used for filtration, and the impurity removal rate is 90.2%.

[0023] The processing results of the methods in Example 1 and Comparative Examples 1-3 are shown in Table 2; Table 2. Processing results of the methods in Example 1 and Comparative Examples 1-3

[0024] As can be seen from the data in Table 1, the fastest filtration time in Example 1 was 3.5 hours, with a purification rate of 97.3%, a recovered NMP purity of up to 99.64%, a moisture content of 0.58%, and cobalt and nickel contents of 1.53% and 11.26%, respectively. Comparing Example 1 and Comparative Example 1, it can be seen that when the mass ratio of industrial water to NMP-containing cleaning waste liquid is less than 1:1, the filtration process slows down significantly, taking up to 9.5 hours, resulting in low efficiency and making it unsuitable for continuous industrial production. Comparing Example 1 and Comparative Example 2, it can be seen that when the industrial water volume is less than half the mass of the NMP-containing cleaning waste liquid, the NMP-containing cleaning waste liquid cannot be filtered, thus preventing the extraction of NMP products and the harmless recovery and reuse of cobalt and nickel in the waste liquid. This shows that the amount of industrial water added in this scheme has a significant impact on the purity of the recovered NMP. When only a plate and frame filter is used for filtration (Comparative Example 3), the impurity removal rate is reduced to only 90.2%, and the purity of the recovered NMP is 98.71%, which is lower than that of Example 1.

[0025] This invention discloses a method for treating NMP-containing cleaning solutions to remove impurities such as PVDF adhesive powder and CNT conductive paste from positive electrode slurries. The method involves water modification to precipitate some PVDF solids, stepwise coagulation with polyferric sulfate and lime to adjust pH, and filtration using a plate and frame filter and bag filter. The effluent is then subjected to harmless treatment in a cement kiln. The filter residue is incinerated in the cement kiln to enrich cobalt and nickel for recycling. The filtrate is then subjected to a negative pressure flash evaporation process to recover NMP. This method achieves the integrated goal of resource recovery of NMP-containing cleaning solutions, deep removal of impurities, and harmless disposal of solid waste.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater, characterized in that, Includes the following steps: S1: Add industrial water to the NMP-containing cleaning waste liquid to modify and precipitate some PVDF adhesive powder and CNT conductive paste impurities, and remove the impurities from the surface of the reaction liquid to obtain the precipitate and the modified liquid. S2: Add flocculant to the modified liquid for coagulation, adjust the pH of the modified liquid to weakly alkaline, and then pre-treat by filtration to obtain filtrate and filter residue; S3: Distill the filtrate to recover the NMP product; S4: The dredged material described in S1 is sent to a cement kiln for harmless treatment; the filter residue described in S2 is sent to an incinerator for incineration and enrichment, and the cobalt and nickel therein are recycled and reused.

2. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 1, characterized in that, In S1, the mass ratio of the NMP-containing cleaning waste liquid to the industrial water is 1:

1.

3. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 1, characterized in that, In S2, the flocculant is polyferric sulfate; the ratio of the amount of polyferric sulfate added to the mass of the NMP-containing cleaning waste liquid is 3:1000.

4. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 1, characterized in that, In S2, after adding the flocculant, the pH of the modified solution is adjusted to 6-7, which is weakly acidic. Then, industrial lime is added to adjust the pH of the modified solution to 7-8, which is weakly alkaline.

5. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 1, characterized in that, After the aforementioned filtration pretreatment, the removal rate of PVDF adhesive powder and CNT conductive paste impurities in the cleaning waste liquid is greater than 97%.

6. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 5, characterized in that, In S2, the specific method of filtration pretreatment is as follows: after the pH of the modified liquid is adjusted, it is first coarsely filtered through a plate and frame filter, and then finely filtered through a bag filter.

7. The method for treating impurities such as PVDF adhesive powder and CNT conductive paste in NMP-containing cleaning wastewater according to claim 1, characterized in that, The indicators of the industrial water are as follows: pH 6.5–8.5, turbidity ≤3 NTU, COD cr ≤50 mg / L, BOD5≤10 mg / L, iron≤0.3 mg / L, manganese≤0.1 mg / L, chloride ion≤250 mg / L, total hardness (calculated as calcium carbonate)≤450 mg / L, total alkalinity (calculated as calcium carbonate)≤350 mg / L, sulfate≤250 mg / L, ammonia nitrogen (calculated as N)≤10 mg / L, total phosphorus (calculated as P)≤1 mg / L, dissolved solids≤1000 mg / L.

Images