A DMF waste liquid recovery and treatment process

Abstract

This application relates to the field of waste liquid recycling and treatment technology, specifically disclosing a DMF waste liquid recycling and treatment process. The DMF waste liquid recycling and treatment process includes the following steps: S1, adding a modified polyethyleneimine adsorbent to DMF waste liquid from the electronics industry, stirring and reacting, and then filtering to obtain a residue-free waste liquid; S2, adding a heavy metal chelating agent to the residue-free waste liquid, stirring and reacting to obtain a mixture containing precipitate; S3, centrifuging the mixture, then adding anhydrous calcium chloride, allowing it to stand, and then filtering to obtain a purified solution; the purified solution is sent to a vacuum distillation column for distillation, and the bottom fraction is collected to obtain regenerated DMF. The recycling and treatment process of this application can effectively remove heavy metal ions and organic resins from DMF waste liquid, thus facilitating the recycling and reuse of DMF.

Description

Technical Field

[0001] This application relates to the field of waste liquid recycling and treatment technology, and more specifically, it relates to a DMF waste liquid recycling and treatment process. Background Technology

[0002] N,N-Dimethylformamide (DMF), as a polar aprotic solvent, is widely used in many fields such as chemical engineering, pharmaceuticals, electronics, pesticides, and dyes due to its excellent solubility, chemical stability, and good compatibility with water and most organic solvents. In the electronics industry, DMF is often used in key processes such as photoresist stripping of semiconductor chips and cleaning of flexible circuit boards, effectively dissolving photoresist or removing flux residues to ensure the production precision and performance of electronic components. However, the use of DMF inevitably generates a large amount of waste liquid. This waste liquid not only contains incompletely consumed DMF but also various impurities introduced during production. Direct discharge would result in a serious waste of this high-value solvent, increasing production costs for enterprises. Furthermore, DMF has a certain degree of toxicity, which can pollute water bodies, soil, and other ecological environments, and also harm human health. Therefore, the recycling and treatment of DMF waste liquid has significant economic and environmental value.

[0003] In related technologies, such as the application document with publication number CN115417786A, a method for purifying and recovering DMF waste solvent is disclosed. The steps include: adding liquid acid to DMF waste solvent from synthetic leather production to adjust the pH value to 7-8, forming a neutralized solution of DMF waste solvent; sending the neutralized solution of DMF waste solvent into a first-stage vacuum distillation, with the side stream discharged to recover crude DMF components; subjecting the recovered DMF components to a second-stage vacuum distillation to purify refined DMF components; and subjecting the obtained refined DMF components to two-stage flash evaporation and cooling crystallization to obtain the DMF product. This method overcomes the difficulties in treating DMF waste solvent and addresses the problems of existing distillation methods where DMF undergoes hydrolysis upon heating with water and thermal decomposition at 90°C. It offers advantages such as simple operation, low energy consumption, low production cost, and high production efficiency.

[0004] While the aforementioned methods for purifying and recovering DMF waste solvents have shown good purification effects for DMF wastewater generated in synthetic leather production, they still have limitations when dealing with complex wastewater from specific industries. Particularly in the electronics industry, DMF wastewater, due to the specific nature of its production processes, commonly contains not only DMF and water but also heavy metal ions such as copper and nickel ions, as well as difficult-to-treat impurities like photoresist resin residue. The core two-stage vacuum distillation and flash crystallization processes in related technologies can only separate DMF from water, and their effectiveness in removing these impurities is insufficient. Therefore, the treatment processes in these technologies suffer from the drawback of being unable to remove heavy metal ions and organic resins from DMF wastewater. Summary of the Invention

[0005] In order to effectively remove heavy metal ions and organic resins from DMF waste liquid and thus recycle and reuse DMF, this application provides a DMF waste liquid recycling and treatment process.

[0006] The DMF waste liquid recycling and treatment process provided in this application adopts the following technical solution:

[0007] A DMF waste liquid recycling and treatment process includes the following steps:

[0008] S1. Add modified polyethyleneimine adsorbent to DMF waste liquid from the electronics industry, stir and react at a speed of 300-400 r / min for 30-40 min, and filter through a ceramic membrane to obtain a residue-free waste liquid.

[0009] S2. Add a heavy metal chelating agent to the residue-free waste liquid, while maintaining the pH of the system at 6.5-7.5, and stir the reaction at 30-40℃ for 80-100 min to obtain a mixture containing precipitate; the raw materials of the heavy metal chelating agent include N-hydroxyethyl ethylenediamine triacetic acid, sodium dithiocarbamate encapsulated by β-cyclodextrin, hydroxyphosphoric lime nanoparticles, sodium acetate and ferric chloride;

[0010] S3. Centrifuge the mixture to obtain a preliminary purified solution. Add anhydrous calcium chloride to the preliminary purified solution, let it stand for 20-30 minutes, and then filter to obtain a purified solution. Send the purified solution into a vacuum distillation column, control the vacuum degree to 0.09-0.10 MPa, and the column bottom temperature to 80-90℃. Collect the column bottom fraction to obtain regenerated DMF.

[0011] By adopting the above technical solution, the modified polyethyleneimine adsorbent can solve the problems of poor dispersibility and weak adsorption capacity for resin residues in the DMF system of traditional adsorbents. On the one hand, the modified polyethyleneimine adsorbent is designed based on the strong polar solvent characteristics of DMF. Through the core-shell structure (SiO2 core + PEI shell) and surface modified groups (isobornyl methacrylate, epoxy groups), it avoids swelling or dissolution in DMF and can be stably dispersed without the failure of adsorption sites due to agglomeration. On the other hand, the adsorbent targets the high molecular polymerization characteristics of photoresist resin residues. The hydrophobic groups introduced by isobornyl methacrylate can form hydrophobic interactions with the hydrophobic chains of resin molecules to achieve preliminary adsorption. Its epoxy groups can react chemically with the hydroxyl and carboxyl groups in the resin structure to form stable chemical covalent bonds, which strengthens the adsorption binding force. Furthermore, the porous characteristics of the core-shell structure of the adsorbent itself can further encapsulate the residue particles through physical pore adsorption, thereby effectively removing organic resins from DMF waste liquid.

[0012] From the perspective of the DMF environmental adaptability and treatment advantages of heavy metal chelating agents, they overcome the limitation of "incomplete heavy metal removal" in traditional neutralization precipitation methods. First, the agent formulation is designed for the DMF-water mixed system: sodium dithiocarbamate (DTC-Na) encapsulated by β-cyclodextrin is protected by the β-cyclodextrin cavity to prevent premature decomposition of DTC-Na in DMF, ensuring that DTC-Na is slowly released in step S2 to form stable sulfide precipitates with copper and nickel ions; N-hydroxyethylethylenediaminetriacetic acid (HEDTA), as a strong chelating agent, can capture trace amounts of free heavy metal ions in the system, forming a "broad-spectrum + deep" chelation synergistic effect with DTC-Na; hydroxyapatite nanoparticles, with their high specific surface area, not only assist in the adsorption of heavy metal precipitation but also can be stably dispersed in the DMF system, avoiding incomplete centrifugal separation caused by precipitation agglomeration. Secondly, the addition of sodium acetate can maintain the pH stability of the system, offset the influence of trace acidic impurities in DMF waste liquid on pH fluctuations, and ensure that the chelation reaction always takes place in the optimal pH range. Ferric chloride can promote precipitation and flocculation, improve the efficiency of subsequent centrifugation treatment, and ultimately effectively remove heavy metal ions from DMF waste liquid, thereby meeting the strict purity requirements for DMF reuse in the electronics industry.

[0013] Furthermore, the above-mentioned processing flow is highly adapted to the physicochemical properties of DMF: the vacuum distillation parameters in S3 precisely avoid the risk of DMF hydrolysis, while the addition of anhydrous calcium chloride can adsorb the trace chelating agent remaining in the preliminary purified liquid, preventing it from entering the distillation and contaminating the DMF, ultimately obtaining high-purity regenerated DMF. This not only achieves the recovery of high-value solvents but also avoids the discharge of toxic waste liquid, thus possessing significant economic value and environmental significance.

[0014] Optionally, the modified polyethyleneimine adsorbent is prepared using the following method:

[0015] (1) Dissolve polyethyleneimine in an ethanol solution, then add an isopropanol dispersion of nano-SiO2, stir at 200-300 r / min and keep warm at 50-60℃ for 2-3 h, centrifuge, wash and dry to obtain PEI / SiO2 core-shell intermediate;

[0016] (2) The PEI / SiO2 core-shell intermediate was dispersed in N,N-dimethylformamide to form a dispersion, and then a mixture of isobornyl methacrylate and maleic anhydride was added. Under nitrogen protection, azobisisobutyronitrile was added at 70-80℃ and reacted for 4-5 hours. Then, a mixture of epichlorohydrin and ethanol was added and reacted at 45-55℃ for 3-4 hours. After washing and vacuum drying, the modified polyethyleneimine adsorbent was obtained.

[0017] By adopting the above technical solution, the particle size and dispersibility of the core-shell intermediate can be precisely controlled, avoiding filter blockage due to excessively large adsorbent particles or loss with the filtrate due to excessively small particles. In step (2), the monomer copolymerization-epoxychloropropane post-modification under nitrogen protection not only prevents oxidation during the reaction of modified isobornyl methacrylate and maleic anhydride, but also precisely controls the grafting rate of surface modified groups, avoiding weak adsorption capacity of resin residue due to insufficient grafting, or decreased dispersibility of adsorbent in DMF due to excessive grafting. The preparation method has strong repeatability and can stably produce adsorbents with consistent performance, providing reliable material support for the industrial application of the processing technology of this application.

[0018] Optionally, in step (1), the concentration of the ethanol solution is 70%-80%, the mass concentration of the isopropanol dispersion of nano-SiO2 is 5%-7%, and the mass ratio of polyethyleneimine, ethanol solution and isopropanol dispersion of nano-SiO2 is 1:(8-10):(5-7).

[0019] By adopting the above technical solution, the above raw material ratio helps to form a PEI / SiO2 core-shell intermediate with stable structure and excellent performance, which lays the foundation for the subsequent preparation of a modified polyethyleneimine adsorbent that can efficiently adsorb resin residues and ensures that the adsorbent can fully exert its adsorption effect in the DMF system.

[0020] Optionally, in step (2), the mass concentration of the dispersion is 10%-15%; the mass ratio of the isobornyl methacrylate to maleic anhydride mixture is (2-3):1; the amount of the isobornyl methacrylate to maleic anhydride mixture added is 10%-20% of the mass of the dispersion; the volume ratio of epichlorohydrin to ethanol is 1:4; and the amount of the epichlorohydrin and ethanol mixed solvent added is 30%-40% of the mass of the dispersion.

[0021] By adopting the above technical solution, the above material parameter control is conducive to achieving uniform mixing and full reaction of each component during the preparation process, accurately controlling the grafting of surface modified groups of the adsorbent, ensuring that the adsorbent has suitable particle size, dispersibility and adsorption performance, and improving the adsorption effect on resin residue in DMF waste liquid.

[0022] Optionally, in S1, the amount of modified polyethyleneimine adsorbent added is 5-10 g / L.

[0023] By adopting the above technical solution, the appropriate amount of adsorbent can ensure that the resin residue in DMF waste liquid is fully adsorbed and the organic resin is effectively removed, while avoiding waste caused by excessive adsorbent addition, reducing treatment costs and improving the economic efficiency of the process.

[0024] Optionally, in S2, the raw materials for the heavy metal chelating agent include:

[0025] 10-15 parts of N-hydroxyethyl ethylenediamine triacetic acid;

[0026] 8-12 parts of sodium dithiocarbamate encapsulated by β-cyclodextrin;

[0027] 5-8 parts of hydroxyapatite nanoparticles;

[0028] 3-5 parts sodium acetate;

[0029] 2-4 parts of ferric chloride

[0030] 60-80 parts deionized water.

[0031] By adopting the above technical solution, the reasonable raw material ratio enables each component to fully exert its synergistic effect in the DMF-water mixture system, overcoming the limitation of "incomplete removal of heavy metals" in traditional neutralization precipitation methods. N-hydroxyethyl ethylenediamine triacetic acid and sodium dithiocarbamate encapsulated by β-cyclodextrin form a "broad-spectrum + deep" chelating synergistic effect. Hydroxyaphosphorus lime nanoparticles assist in the adsorption of heavy metal precipitates and prevent precipitate aggregation. Sodium acetate maintains the pH stability of the system, and ferric chloride promotes precipitate flocculation, thereby effectively removing heavy metal ions from DMF waste liquid and meeting the strict purity requirements for DMF reuse in the electronics industry.

[0032] Optionally, the heavy metal chelating agent is prepared by the following method:

[0033] A. Add β-cyclodextrin and sodium dithiocarbamate to an ethanol solution, stir and react at 50-60℃ for 30-40 min to form a suspension, and freeze-dry to obtain sodium dithiocarbamate encapsulated by β-cyclodextrin.

[0034] B. Dissolve N-hydroxyethyl ethylenediamine triacetic acid in deionized water, then add sodium dithiocarbamate and hydroxyapatite nanoparticles encapsulated with β-cyclodextrin, stir at 300-500 r / min for 20-30 min, then add sodium acetate and ferric chloride, continue stirring for 10-20 min, and obtain the heavy metal chelating agent after spray drying.

[0035] Optionally, in step A, the mass ratio of the β-cyclodextrin, sodium dithiocarbamate, and ethanol solution is (3-5):1:(8-10).

[0036] Optionally, in S2, the amount of heavy metal chelating agent added is 8-12 g / L.

[0037] Optionally, in S3, the amount of anhydrous calcium chloride added is 3-5 g / L.

[0038] By adopting the above technical solution, an appropriate amount of anhydrous calcium chloride can adsorb the trace chelating agent remaining in the preliminary purification solution, preventing it from entering the distillation process and contaminating the DMF, ensuring that the final regenerated DMF has high purity. At the same time, it avoids waste caused by adding too much anhydrous calcium chloride and the possible introduction of new impurities, thereby improving the stability of the process and the quality of the product.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. This application uses a modified polyethyleneimine adsorbent to treat organic resins in DMF waste liquid from the electronics industry. The adsorbent is designed based on the strong polar solvent characteristics of DMF. Through its core-shell structure and surface modified groups, it avoids swelling or dissolution in DMF and can be stably dispersed. Targeting the high molecular polymerization characteristics of photoresist resin residues, it effectively removes organic resins through multiple mechanisms such as hydrophobic interactions, chemical covalent bonds, and physical pore adsorption. This solves the problems of poor dispersibility and weak adsorption capacity for resin residues in traditional adsorbents in DMF systems, and effectively removes organic resin impurities from DMF waste liquid.

[0041] 2. This application preferably uses a heavy metal chelating agent with a specific formulation designed for DMF-water mixed systems. β-cyclodextrin-encapsulated sodium dithiocarbamate prevents premature decomposition in DMF, while N-hydroxyethylethylenediaminetriacetic acid acts as a strong chelating agent to capture trace amounts of free heavy metal ions. The two form a "broad-spectrum + deep" chelating synergistic effect. Hydroxyaphosphorus lime nanoparticles assist in the adsorption of heavy metal precipitation and prevent precipitate aggregation. Sodium acetate maintains the pH stability of the system, and ferric chloride promotes precipitate flocculation. This achieves a breakthrough overcoming the limitation of "incomplete heavy metal removal" in traditional neutralization precipitation methods, effectively removing heavy metal ions from DMF waste liquid and meeting the stringent purity requirements for DMF reuse in the electronics industry. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments.

[0043] Example of preparation of modified polyethyleneimine adsorbent:

[0044] Preparation Example 1

[0045] The modified polyethyleneimine adsorbent was prepared by the following method:

[0046] (1) Dissolve 1 kg of polyethyleneimine in 8 kg of 70% ethanol solution, then add 5 kg of 5% isopropanol dispersion of nano-SiO2, stir at 200 r / min and keep warm at 50 °C for 2 h, centrifuge, wash and dry to obtain PEI / SiO2 core-shell intermediate.

[0047] (2) The PEI / SiO2 core-shell intermediate was dispersed in N,N-dimethylformamide to form a dispersion with a mass concentration of 10%. Then, a mixture of isobornyl methacrylate and maleic anhydride was added. The mass ratio of isobornyl methacrylate to maleic anhydride was 2:1, and the amount of the mixture of isobornyl methacrylate and maleic anhydride added was 10% of the mass of the dispersion. Then, under nitrogen protection, 2% of the total mass of azobisisobutyronitrile was added at 70°C and reacted for 4 hours. Then, a mixed solvent of epichlorohydrin and ethanol was added. The volume ratio of epichlorohydrin to ethanol was 1:4. The amount of the mixed solvent of epichlorohydrin and ethanol added was 30% of the mass of the dispersion. The reaction was carried out at 45°C for 3 hours. After washing and vacuum drying, the modified polyethyleneimine adsorbent was obtained.

[0048] Preparation Example 2

[0049] The modified polyethyleneimine adsorbent was prepared by the following method:

[0050] (1) Dissolve 1 kg of polyethyleneimine in 9 kg of 75% ethanol solution, then add 6 kg of 6% isopropanol dispersion of nano-SiO2, stir at 250 r / min and keep warm at 55 °C for 2.5 h, centrifuge, wash and dry to obtain PEI / SiO2 core-shell intermediate;

[0051] (2) The PEI / SiO2 core-shell intermediate was dispersed in N,N-dimethylformamide to form a dispersion with a mass concentration of 12%. Then, a mixture of isobornyl methacrylate and maleic anhydride was added. The mass ratio of isobornyl methacrylate to maleic anhydride was 2.5:1, and the amount of the mixture added was 15% of the mass of the dispersion. Then, under nitrogen protection, 2% of the total mass of azobisisobutyronitrile was added at 75°C and reacted for 4.5 h. Then, a mixture of epichlorohydrin and ethanol was added. The volume ratio of epichlorohydrin to ethanol was 1:4, and the amount of the mixture added was 35% of the mass of the dispersion. The reaction was carried out at 50°C for 3.5 h. After washing and vacuum drying, the modified polyethyleneimine adsorbent was obtained.

[0052] Preparation Example 3

[0053] The modified polyethyleneimine adsorbent was prepared by the following method:

[0054] (1) Dissolve 1 kg of polyethyleneimine in 10 kg of 80% ethanol solution, then add 7 kg of 7% isopropanol dispersion of nano-SiO2, stir at 300 r / min and keep warm at 60 for 3 h, centrifuge, wash and dry to obtain PEI / SiO2 core-shell intermediate.

[0055] (2) The PEI / SiO2 core-shell intermediate was dispersed in N,N-dimethylformamide to form a dispersion with a mass concentration of 15%. Then, a mixture of isobornyl methacrylate and maleic anhydride was added. The mass ratio of isobornyl methacrylate to maleic anhydride was 3:1, and the amount of the mixture of isobornyl methacrylate and maleic anhydride added was 20% of the mass of the dispersion. Then, under nitrogen protection, 2% of the total mass of azobisisobutyronitrile was added at 80°C and reacted for 5h. Then, a mixed solvent of epichlorohydrin and ethanol was added. The volume ratio of epichlorohydrin to ethanol was 1:4, and the amount of the mixed solvent of epichlorohydrin and ethanol added was 40% of the mass of the dispersion. The reaction was carried out at 55°C for 4h. After washing and vacuum drying, the modified polyethyleneimine adsorbent was obtained.

[0056] Example of preparation of heavy metal chelating agents:

[0057] Preparation Example 4

[0058] The heavy metal chelating agent, whose raw material components and formulations are shown in Table 1, was prepared by the following method:

[0059] A. Add β-cyclodextrin and sodium dithiocarbamate to a 25% ethanol solution with a mass ratio of 3:1:8. Stir the mixture at 50°C for 30 min to form a suspension. Freeze-dry the suspension to obtain sodium dithiocarbamate encapsulated by β-cyclodextrin.

[0060] B. Dissolve N-hydroxyethyl ethylenediamine triacetic acid in deionized water, then add sodium dithiocarbamate and hydroxyapatite nanoparticles encapsulated with β-cyclodextrin, stir at 300 r / min for 20 min, then add sodium acetate and ferric chloride, continue stirring for 10 min, and obtain the heavy metal chelating agent after spray drying.

[0061] Preparation Example 5

[0062] The heavy metal chelating agent, whose raw material components and formulations are shown in Table 1, was prepared by the following method:

[0063] A. Add β-cyclodextrin and sodium dithiocarbamate to a 25% ethanol solution with a mass ratio of 4:1:9. Stir the mixture at 55°C for 35 minutes to form a suspension. Freeze-dry the suspension to obtain sodium dithiocarbamate encapsulated by β-cyclodextrin.

[0064] B. Dissolve N-hydroxyethyl ethylenediamine triacetic acid in deionized water, then add sodium dithiocarbamate and hydroxyapatite nanoparticles encapsulated with β-cyclodextrin, stir at 400 r / min for 25 min, then add sodium acetate and ferric chloride, continue stirring for 15 min, and obtain the heavy metal chelating agent after spray drying.

[0065] Preparation Example 6

[0066] The heavy metal chelating agent, whose raw material components and formulations are shown in Table 1, was prepared by the following method:

[0067] A. Add β-cyclodextrin and sodium dithiocarbamate to a 25% ethanol solution with a mass ratio of 5:1:10. Stir the mixture at 60°C for 40 min to form a suspension. Freeze-dry the suspension to obtain sodium dithiocarbamate encapsulated by β-cyclodextrin.

[0068] B. Dissolve N-hydroxyethyl ethylenediamine triacetic acid in deionized water, then add sodium dithiocarbamate and hydroxyapatite nanoparticles encapsulated with β-cyclodextrin, stir at 500 r / min for 30 min, then add sodium acetate and ferric chloride, continue stirring for 20 min, and obtain the heavy metal chelating agent after spray drying.

[0069] Table 1. Raw material components and proportions (kg) of the heavy metal chelating agents prepared in Examples 4-6.

[0070]

[0071] Preparation Example 7

[0072] The heavy metal chelating agent differs from that in Preparation Example 4 in that an equal amount of sodium dithiocarbamate is used instead of sodium dithiocarbamate encapsulated by β-cyclodextrin in this preparation example.

[0073] Example:

[0074] The DMF waste liquid used in this embodiment was collected from the waste liquid collection tank of the semiconductor chip photoresist stripping process production line: the 8-inch wafer back side photoresist removal process adopts the "DMF solvent immersion + ultrasonic-assisted stripping" process, and the stripping target is positive photoresist (model AZ4620). The specific indicators of the DMF waste liquid in the electronics industry are shown in Table 2.

[0075] Table 2 Specific parameters of DMF waste liquid from the electronics industry

[0076]

[0077] Example 1

[0078] A DMF waste liquid recycling and treatment process includes the following steps:

[0079] S1. Add modified polyethyleneimine adsorbent to DMF waste liquid from the electronics industry. The modified polyethyleneimine adsorbent used is the one prepared in Preparation Example 1. The amount of modified polyethyleneimine adsorbent added is 5 g / L. Stir the reaction at 300 r / min for 30 min, and filter through a 0.2 μm ceramic membrane to obtain a residue-free waste liquid.

[0080] S2. Add a heavy metal chelating agent to the residue-free waste liquid. The heavy metal chelating agent used is the one prepared in Preparation Example 4. The amount of heavy metal chelating agent added is 8 g / L. At the same time, the pH of the waste liquid system is maintained at 6.5-7.5 by adding potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer solution. Stir the reaction at 30°C for 80 min to obtain a mixed liquid containing precipitate.

[0081] S3. The mixture is fed into a disc centrifuge and the heavy metal chelate precipitate is separated and removed at 15000 r / min to obtain a preliminary purified solution. Anhydrous calcium chloride is added to the preliminary purified solution at a concentration of 3 g / L. After standing for 20 min, the solution is filtered to obtain a purified solution. The purified solution is fed into a vacuum distillation column, and the vacuum degree is controlled at 0.09 MPa and the bottom temperature is 80℃. The bottom fraction is collected to obtain regenerated DMF.

[0082] Example 2

[0083] A DMF waste liquid recycling and treatment process includes the following steps:

[0084] S1. Add modified polyethyleneimine adsorbent to DMF waste liquid from the electronics industry. The modified polyethyleneimine adsorbent used is the one prepared in Preparation Example 2. The amount of modified polyethyleneimine adsorbent added is 8 g / L. Stir the reaction at 350 r / min for 35 min, and filter through a 0.2 μm ceramic membrane to obtain a residue-free waste liquid.

[0085] S2. Add a heavy metal chelating agent to the residue-free waste liquid. The heavy metal chelating agent used is the one prepared in Preparation Example 4. The amount of heavy metal chelating agent added is 10 g / L. At the same time, the pH of the waste liquid system is maintained at 6.5-7.5 by adding potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer solution. The mixture is stirred at 35°C for 90 min to obtain a mixed liquid containing precipitate.

[0086] S3. The mixture is fed into a disc centrifuge and the heavy metal chelate precipitate is separated and removed at 15000 r / min to obtain a preliminary purified solution. Anhydrous calcium chloride is added to the preliminary purified solution at a concentration of 4 g / L. After standing for 25 min, the solution is filtered to obtain a purified solution. The purified solution is fed into a vacuum distillation column, and the vacuum degree is controlled at 0.10 MPa and the bottom temperature is 85℃. The bottom fraction is collected to obtain regenerated DMF.

[0087] Example 3

[0088] A DMF waste liquid recycling and treatment process includes the following steps:

[0089] S1. Add modified polyethyleneimine adsorbent to DMF waste liquid from the electronics industry. The modified polyethyleneimine adsorbent used is the one prepared in Preparation Example 3. The amount of modified polyethyleneimine adsorbent added is 10 g / L. Stir the reaction at 400 r / min for 40 min, and filter through a 0.2 μm ceramic membrane to obtain a residue-free waste liquid.

[0090] S2. Add a heavy metal chelating agent to the residue-free waste liquid. The heavy metal chelating agent used is the one prepared in Preparation Example 4. The amount of heavy metal chelating agent added is 12 g / L. At the same time, the pH of the waste liquid system is maintained at 6.5-7.5 by adding potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer solution. Stir the reaction at 40°C for 100 min to obtain a mixed liquid containing precipitate.

[0091] S3. The mixture is fed into a disc centrifuge and the heavy metal chelate precipitate is separated and removed at 15000 r / min to obtain a preliminary purified solution. Anhydrous calcium chloride is added to the preliminary purified solution at a concentration of 5 g / L. After standing for 30 min, the solution is filtered to obtain a purified solution. The purified solution is fed into a vacuum distillation column, and the vacuum degree is controlled at 0.10 MPa and the column bottom temperature is 90℃. The column bottom fraction is collected to obtain regenerated DMF.

[0092] Example 4

[0093] A DMF waste liquid recycling process differs from Example 1 in that the heavy metal chelating agent used in Example S2 is the heavy metal chelating agent prepared in Preparation Example 5.

[0094] Example 5

[0095] A DMF waste liquid recycling process differs from Example 1 in that the heavy metal chelating agent used in Example S2 is the heavy metal chelating agent prepared in Preparation Example 6.

[0096] Example 6

[0097] A DMF waste liquid recycling process differs from Example 1 in that the amount of heavy metal chelating agent added in Example S2 is 5 g / L.

[0098] Comparative example:

[0099] Comparative Example 1

[0100] A DMF waste liquid recycling and treatment process differs from Example 1 in that, in this comparative example S1, an unmodified polyethyleneimine adsorbent is used instead of a modified polyethyleneimine adsorbent.

[0101] Comparative Example 2

[0102] A DMF waste liquid recycling process differs from Example 1 in that the heavy metal chelating agent used in Comparative Example S2 is the heavy metal chelating agent prepared in Preparation Example 7.

[0103] Comparative Example 3

[0104] A DMF waste liquid recycling process differs from Example 1 in that a 1:1 mixture of sodium hydroxide and sodium sulfide is used instead of a heavy metal chelating agent in Comparative Example S2.

[0105] Comparative Example 4

[0106] A DMF waste liquid recycling and treatment process differs from Example 1 in that, in this comparative example S3, no wastewater calcium chloride was added, and the preliminary purified liquid was directly sent into a vacuum distillation column for distillation.

[0107] Performance testing

[0108] Test subjects: Regenerated DMF prepared in Examples 1-6 and Comparative Examples 1-4.

[0109] Test items:

[0110] 1. Organic resin residue: Take 100 mL of regenerated DMF, filter it under reduced pressure through a 0.22 μm polytetrafluoroethylene filter membrane, dry the filter membrane in an oven at 105 °C until constant weight, calculate the weight gain of the filter membrane (i.e., the mass of resin residue), and convert it to content (g / L).

[0111] 2. Heavy metal ion residue: Take the S2 preliminary purification solution / regenerated DMF sample and dilute it 10 times with 5% nitric acid solution; set the ICP-MS working parameters (RF power 1550W, sampling depth 8mm, carrier gas flow rate 1.0L / min), determine the characteristic ion peaks of Cu, Ni and Cr elements, and calculate the concentration by standard curve method.

[0112] 3. DMF purity: Gas chromatography (GC) was used for detection (Agilent 7890A, HP-5 capillary column, column temperature program: initial 50℃ for 2 min, 10℃ / min ramp to 200℃ for 5 min; detector: FID, injection volume 1 μL). The content was calculated using the external standard method with pure DMF as the standard.

[0113] Experimental results: see Table 3.

[0114] Table 3. Experimental Results

[0115]

[0116] As shown in Table 3, the residual organic resin in Examples 1-6 was below 10 mg / L, with Example 3 having the lowest residual amount at only 4.8 mg / L. In contrast, Comparative Example 1 (unmodified adsorbent) had a residual amount as high as 85.6 mg / L. This indicates that the core-shell structure and surface modified groups of the modified polyethyleneimine adsorbent enhanced the resin's adsorption capacity. Examples 1-3 also showed that appropriately increasing the amount of adsorbent could strengthen the adsorption effect, but excessive addition might lead to a decrease in efficiency due to competitive adsorption. Regarding the residual heavy metal ions, Examples 1-6 were all below 0.5 mg / L, with Example 3 having the lowest (0.06 mg / L), reflecting the synergistic effect of β-cyclodextrin-encapsulated DTC-Na, HEDTA, and hydroxyapatite nanoparticles. Comparative Example 2 (without DTC-Na encapsulation) and Comparative Example 3 (traditional sodium sulfide + sodium hydroxide) had higher residual amounts, indicating the limitations of β-cyclodextrin cavity protection and the traditional neutralization precipitation method. Furthermore, the examples show that the amount of reagent added and pH control affect the chelation efficiency.

[0117] In the DMF purity analysis, the DMF purity of Examples 1-6 was all higher than 99.5%, with Example 3 having the highest purity (99.864%). The reduced pressure distillation parameters avoided DMF hydrolysis and thermal decomposition, and anhydrous calcium chloride could adsorb residual chelating agents. The purity of Comparative Example 4 (without anhydrous calcium chloride) decreased, while the purity of Comparative Example 1 (without modified adsorbent) and Comparative Example 3 (traditional precipitation method) decreased due to resin and heavy metal residues. The examples, however, achieved high-purity DMF recovery by simultaneously removing resin and heavy metals.

[0118] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A DMF waste liquid recovery treatment process, characterized in that, The method comprises the following steps: S1, adding modified polyethyleneimine adsorbent to the electronic industry DMF waste liquid, stirring at a speed of 300-400 r / min for 30-40 min, filtering through a ceramic membrane to obtain a waste liquid without residue; the modified polyethyleneimine adsorbent is prepared by the following method: (1) dissolving polyethyleneimine in an ethanol solution, then adding an isopropyl alcohol dispersion solution of nano-SiO2, and reacting at 50-60°C for 2-3 h under stirring at 200-300 r / min, centrifuging, washing and drying to obtain a PEI / SiO2 core-shell intermediate; (2) dispersing the PEI / SiO2 core-shell intermediate in N,N-dimethylformamide to form a dispersion solution, then adding a mixed solution of isobornyl methacrylate and maleic anhydride, adding azobisisobutyronitrile under nitrogen protection at 70-80°C and reacting for 4-5 h, then adding a mixed solvent of epoxy chloropropane and ethanol, and reacting at 45-55°C for 3-4 h, and then washing, vacuum drying to obtain the modified polyethyleneimine adsorbent; S2, adding a heavy metal chelating agent to the waste liquid without residue while maintaining the pH of the system at 6.5-7.5, and stirring at 30-40°C for 80-100 min to obtain a mixed liquid containing precipitates; the raw materials of the heavy metal chelating agent include N-hydroxyethyl ethylenediamine triacetic acid, β-cyclodextrin-encapsulated sodium dithiocarbamate, hydroxyl apatite nanoparticles, sodium acetate and ferric chloride; S3, centrifuging the mixed liquid to obtain a preliminary purified liquid, adding anhydrous calcium chloride to the preliminary purified liquid, standing for 20-30 min, and filtering to obtain a purified liquid; the purified liquid is sent into a vacuum rectifying column, the vacuum degree is controlled at 0.09-0.10 MPa, the column bottom temperature is controlled at 80-90°C, and the column bottom fraction is collected to obtain regenerated DMF.

2. The DMF waste liquid recovery treatment process according to claim 1, characterized in that: In step (1), the concentration of the ethanol solution is 70%-80%, and the mass concentration of the isopropyl alcohol dispersion solution of nano-SiO2 is 5%-7%; the mass ratio of polyethyleneimine, ethanol solution and isopropyl alcohol dispersion solution of nano-SiO2 is 1:(8-10):(5-7).

3. The DMF waste liquid recovery treatment process according to claim 1, characterized in that: In step (2), the mass concentration of the dispersion solution is 10%-15%; the mass ratio of the mixed solution of isobornyl methacrylate and maleic anhydride is (2-3):1; the addition amount of the mixed solution of isobornyl methacrylate and maleic anhydride is 10%-20% of the mass of the dispersion solution; the volume ratio of epoxy chloropropane and ethanol is 1:4; and the addition amount of the mixed solvent of epoxy chloropropane and ethanol is 30%-40% of the mass of the dispersion solution.

4. The DMF waste liquid recovery treatment process according to claim 1, characterized in that: In S1, the addition amount of the modified polyethyleneimine adsorbent is 5-10 g / L.

5. The DMF waste liquid recovery treatment process according to claim 1, characterized in that: In S2, the raw materials of the heavy metal chelating agent include: N-hydroxyethyl ethylenediamine triacetic acid 10-15 parts; β-cyclodextrin-encapsulated sodium dithiocarbamate 8-12 parts; hydroxyl apatite nanoparticles 5-8 parts; sodium acetate 3-5 parts; ferric chloride 2-4 parts deionized water 60-80 parts.

6. The DMF waste solution recovery treatment process according to claim 5, characterized in that: The heavy metal chelating agent is prepared by the following method: A. β-cyclodextrin and sodium dithiocarbamate are added to an ethanol solution, stirred at 50-60℃ for 30-40min to form a suspension, and after freeze-drying, β-cyclodextrin inclusion sodium dithiocarbamate is obtained; B. N-hydroxyethyl ethylenediamine triacetic acid is dissolved in deionized water, then β-cyclodextrin inclusion sodium dithiocarbamate and hydroxyapatite nanoparticles are added, stirred at 300-500r / min for 20-30min, then sodium acetate and ferric chloride are added, continue to stir for 10-20min, and after spray drying, a heavy metal chelating agent is obtained.

7. The DMF waste liquor recovery process according to claim 6, wherein: In step A, the mass ratio of β-cyclodextrin, sodium dithiocarbamate and ethanol solution is (3-5):1:(8-10).

8. The DMF waste recovery process of claim 1, wherein: In S2, the addition amount of heavy metal chelating agent is 8-12g / L.

9. The DMF waste stream recovery process of claim 1, wherein: In S3, the addition amount of anhydrous calcium chloride is 3-5g / L.

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