A method for recovering a cleaning waste liquid of a casting solution filter

Abstract

The application provides a cast film solution filter cleaning waste liquid recovery method, which comprises the following steps: S1, disassembling the filter, and soaking the disassembled accessories in an alkali solution with a mass concentration of 10%-30% and a temperature of 30-50 DEG C, and ultrasonic cleaning for 0.5-1h; S2, immersing the filter cleaned in step S1 in a cleaning liquid with a temperature of 60-80 DEG C, and ultrasonic cleaning for 1-2h, then drying the cleaned filter accessories, and assembling; when the solid content in the cleaning liquid exceeds 30%, the cleaning liquid needs to be replaced; S3, adding a precipitant to the replaced cleaning liquid, uniformly stirring, precipitating for 5-10min, and filtering, and diluting the filtrate and using it for spinning coagulation bath. The application hydrolyzes the impurities on the filter by using alkali first, and then dissolves the filter by using an organic solvent, so that the cleaning efficiency is improved by matching the alkali hydrolysis and the organic solvent decomposition, and meanwhile, the filter is not damaged.

Description

Technical Field

[0001] This invention relates to the field of filter cleaning technology, and in particular to a method for recovering waste liquid from casting fluid filter cleaning. Background Technology

[0002] Ultrafiltration membranes are a type of membrane that separates media using pressure and pore size differences. They are primarily used in water treatment, biopharmaceuticals, and the food industry. The casting solution, the raw material for ultrafiltration membranes, is a polymer solution formed by dissolving high-molecular-weight compounds in a solvent and adding a pore-forming agent. Impurities in the casting solution can cause defects such as pores in the finished ultrafiltration membrane, affecting its performance. Therefore, the casting solution needs to be filtered before manufacturing the ultrafiltration membrane to remove impurities. The casting solution also needs to be filtered during the transfer from the preparation vessel to the spinning tank and before entering the spinning nozzle; otherwise, impurities in the casting solution will cause defects in the membrane fibers, affecting their performance. The core component of the filter is a 200-1000 mesh stainless steel screen. With continuous use, the screen becomes clogged with impurities, affecting filtration efficiency.

[0003] Patent CN103451748A discloses a cleaning method for a spinneret used in polyacrylonitrile (PA) filament spinning. The method involves sequentially employing ultrasonic cleaning with an organic solvent, ultrasonic cleaning with nitric acid containing inorganic particles, ultrasonic cleaning with water containing detergent, and ultrasonic cleaning with water. However, the addition of inorganic nitric acid particles, while cleaning the spinneret, can also corrode or scratch its surface. Therefore, a cleaning method for the casting solution filter that does not damage it and allows for the recycling of the cleaning solution is needed. Summary of the Invention

[0004] In view of this, the present invention proposes a method for recycling waste liquid from casting fluid filters that does not damage the casting fluid filter and allows the cleaning fluid to be recycled.

[0005] The technical solution of this invention is implemented as follows: This invention provides a method for recovering waste liquid from casting solution filter cleaning, characterized by comprising the following steps:

[0006] S1. Disassemble the filter and immerse the disassembled parts in an alkaline solution with a mass concentration of 10%-30% and a temperature of 30-50℃, and ultrasonically clean for 0.5-1 hour.

[0007] S2, Immerse the filter after alkaline washing in step S1 in a cleaning solution at 60-80℃ for ultrasonic cleaning for 1-2 hours, then dry the cleaned filter parts and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced.

[0008] S3, add precipitant to the replaced cleaning solution, stir well and let it settle for 5-10 minutes, then filter it. The filtrate is diluted and used in the spinning coagulation bath.

[0009] In step S2, the cleaning solution includes an organic solvent, which is one or a mixture of tetrahydrofuran, dimethylacetamide, dimethylformamide, methylpyrrolidone, and dimethyl sulfoxide.

[0010] In step S3, the precipitant is deionized water and chitosan quaternary ammonium salt.

[0011] Based on the above technical solutions, preferably, the cleaning agent further includes additives, namely polyvinylpyrrolidone and polyvinyl alcohol.

[0012] Based on the above technical solutions, preferably, the mass ratio of the auxiliary agent to the organic solvent is (3-8):50.

[0013] Based on the above technical solutions, preferably, the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol in the additive is (2-9):(11-18).

[0014] Based on the above technical solutions, preferably, the mass ratio of the precipitant to the organic solvent is (2-3):2.

[0015] Based on the above technical solutions, preferably, the precipitant comprises 90%-95% deionized water and 5%-10% chitosan quaternary ammonium salt, calculated as 100% by mass.

[0016] Based on the above technical solutions, preferably, the cleaning agent also includes sodium diethyldithiocarbamate.

[0017] Based on the above technical solutions, preferably, the sodium diethyldithiocarbamate is 3%-5% of the weight of the organic solvent.

[0018] Based on the above technical solutions, preferably, the alkaline solution is selected from any one or a mixture of several of sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution.

[0019] Based on the above technical solutions, preferably, in step S2, during the soaking period, the filter is taken out, and compressed air is used to blow air through the pores of the filter screen for 1-3 minutes, and then it is immersed in the cleaning solution to continue cleaning.

[0020] Based on the above technical solutions, preferably, in step S2, after cleaning, the filter is first rinsed with alkaline solution for 1-3 minutes, then rinsed with clean water for 1-3 minutes, and after rinsing, it is dried and assembled.

[0021] The method for recovering waste liquid from casting solution filter cleaning according to the present invention has the following advantages over the prior art:

[0022] (1) The present invention first uses bases to hydrolyze the impurities on the filter, and then uses organic solvents to dissolve them. The combination of alkaline hydrolysis and organic solvent decomposition improves the cleaning efficiency and does not damage the filter.

[0023] (2) The additives polyvinylpyrrolidone and polyvinyl alcohol in the cleaning solution of the present invention play a role in promoting decomposition and shortening the cleaning time; chitosan quaternary ammonium salt plays a role in flocculation and precipitation; sodium diethyldithiocarbamate prevents the dissolved components from repolymerizing.

[0024] (3) The alkaline solution of the present invention can be reused after simple filtration, and the cleaning solution can be used in the spinning coagulation bath after precipitation and filtration, which saves a lot of costs. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Deionized water with a resistivity greater than 15 MΩ is required, and the ultrasonic cleaning frequency is 20 kHz. All reagents used in this invention are commercially available. The amount of alkali solution and cleaning agent used is calculated as 500g to ensure complete immersion of the filter components.

[0027] Example 1

[0028] The method for recovering waste liquid from casting solution filter cleaning in this embodiment includes the following steps:

[0029] S1. Disassemble the filter and immerse the disassembled parts in a sodium hydroxide solution with a mass concentration of 10% and a temperature of 30°C, and ultrasonically clean for 0.5 hours; the amount of sodium hydroxide solution is sufficient to ensure that the parts are completely immersed in it.

[0030] S2, Immerse the filter after alkaline washing in step S1 into a cleaning agent containing 200g tetrahydrofuran and 300g dimethylacetamide at 60℃, and ultrasonically clean for 2 hours. Then dry the cleaned filter parts and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced.

[0031] S3. Add a precipitant containing 450g of deionized water and 50g of chitosan quaternary ammonium salt to the replaced cleaning solution, stir evenly and precipitate for 10 minutes, then filter, and use the diluted filtrate as a spinning coagulation bath.

[0032] Example 2

[0033] The method for recovering waste liquid from casting solution filter cleaning in this embodiment includes the following steps:

[0034] S1. Disassemble the filter and immerse the disassembled parts in a sodium bicarbonate solution and a potassium bicarbonate solution with a mass concentration of 15% and a temperature of 40°C, and ultrasonically clean for 40 minutes.

[0035] S2, after the alkaline washing in step S1, immerse the filter in a cleaning solution containing 250g dimethylformamide, 250g methylpyrrolidone, 13.5g polyvinylpyrrolidone, 16.5g polyvinyl alcohol, and 15g sodium diethyldithiocarbamate at 65℃ for ultrasonic cleaning for 1.5h. Then, dry the cleaned filter components and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced. During the immersion, remove the filter and blow compressed air through the pores of the filter screen for 1 minute, then immerse it in the cleaning solution again to continue cleaning. After cleaning, first rinse the filter with alkaline solution (15% sodium bicarbonate solution) for 1 minute, then rinse the filter with clean water for 1 minute. After rinsing, dry and assemble it.

[0036] S3, add 460g of deionized water and 40g of chitosan quaternary ammonium salt and precipitant to the replaced cleaning solution, stir evenly and precipitate for 5 minutes, then filter, and use the diluted filtrate as a spinning coagulation bath.

[0037] Example 3

[0038] The method for recovering waste liquid from casting solution filter cleaning in this embodiment includes the following steps:

[0039] S1. Disassemble the filter and immerse the disassembled parts in a sodium carbonate solution and a potassium carbonate solution with a mass concentration of 20% and a temperature of 40°C, and ultrasonically clean for 50 minutes.

[0040] S2, after the alkaline washing in step S1, immerse the filter in a cleaning solution containing 400g dimethylacetamide, 100g dimethyl sulfoxide, 12.5g polyvinylpyrrolidone, 37.5g polyvinyl alcohol, and 20g sodium diethyldithiocarbamate at 75°C for ultrasonic cleaning for 1 hour. Then, dry the cleaned filter components and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced. During the immersion, remove the filter and blow compressed air through the pores of the filter screen for 2 minutes, then immerse it in the cleaning solution again to continue cleaning. After cleaning, first rinse the filter with alkaline solution (15% sodium bicarbonate solution) for 2 minutes, then rinse the filter with clean water for 2 minutes. After rinsing, dry and assemble it.

[0041] S3. Add a precipitant containing 690g of deionized water and 60g of chitosan quaternary ammonium salt to the replaced cleaning solution, stir evenly and precipitate for 8 minutes, then filter, and use the diluted filtrate as a spinning coagulation bath.

[0042] Example 4

[0043] The method for recovering waste liquid from casting solution filter cleaning in this embodiment includes the following steps:

[0044] S1. Disassemble the filter and immerse the disassembled parts in a sodium bicarbonate solution with a mass concentration of 30% and a temperature of 50°C, and ultrasonically clean for 60 minutes.

[0045] S2, after the alkaline washing in step S1, immerse the filter in a cleaning solution containing 300g dimethylacetamide, 200g tetrahydrofuran, 8g polyvinylpyrrolidone, 72g polyvinyl alcohol, and 25g sodium diethyldithiocarbamate at 80℃ for ultrasonic cleaning for 1.5 hours. Then, dry the cleaned filter components and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced. During the immersion, remove the filter and blow compressed air through the pores of the filter screen for 3 minutes, then immerse it in the cleaning solution again to continue cleaning. After cleaning, first rinse the filter with alkaline solution (15% sodium bicarbonate solution) for 3 minutes, then rinse the filter with clean water for 3 minutes. After rinsing, dry and assemble it.

[0046] S3. Add a precipitant containing 475g of deionized water and 25g of chitosan quaternary ammonium salt to the replaced cleaning solution, stir evenly and precipitate for 7 minutes, then filter, and use the diluted filtrate as a spinning coagulation bath.

[0047] Example 5

[0048] The method for recovering waste liquid from casting solution filter cleaning in this embodiment includes the following steps:

[0049] S1. Disassemble the filter and immerse the disassembled parts in a sodium hydroxide solution with a mass concentration of 30% and a temperature of 45°C, and ultrasonically clean for 30 minutes.

[0050] S2, after the alkaline washing in step S1, immerse the filter in a cleaning solution containing 150g dimethyl sulfoxide, 350g tetrahydrofuran, 14g polyvinylpyrrolidone, 56g polyvinyl alcohol, and 20g sodium diethyldithiocarbamate at 60°C for ultrasonic cleaning for 1 hour. Then, dry the cleaned filter components and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced. During the immersion, remove the filter and blow compressed air through the pores of the filter screen for 2 minutes, then immerse it in the cleaning solution again to continue cleaning. After cleaning, rinse the filter with alkaline solution (15% sodium bicarbonate solution) for 1 minute, then rinse the filter with clean water for 1 minute. After rinsing, dry and assemble it.

[0051] S3. Add a precipitant containing 465g of deionized water and 35g of chitosan quaternary ammonium salt to the replaced cleaning solution, stir evenly and precipitate for 6 minutes, then filter, and use the diluted filtrate as a spinning coagulation bath.

[0052] Comparative Example 1

[0053] Example 1, which lacks alkaline washing, serves as Comparative Example 1. The cleaning agent contains only organic solvents, and the remaining steps are the same as in Example 1.

[0054] Comparative Example 2

[0055] Comparative Example 2 uses the precipitant of Example 1, which lacks chitosan quaternary ammonium salt, and the remaining steps are the same as in Example 1.

[0056] After cleaning, the filter pores were inspected using an optical microscope, and the results are shown in Table 1.

[0057] Table 1 Cleaning effects of examples and comparative examples

[0058]

[0059]

[0060] In Examples 1 to 5, no filter pores were found to be clogged; the filters were thoroughly cleaned and free of residue. In Comparative Example 1, residue was present, and some filter pores remained clogged, indicating incomplete cleaning. Comparative Example 2 exhibited a longer sedimentation time and poorer recovery efficiency.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering waste liquid from casting fluid filter cleaning, characterized in that: Includes the following steps: S1. Disassemble the filter and immerse the disassembled parts in an alkaline solution with a mass concentration of 10%-30% and a temperature of 30-50℃, and ultrasonically clean for 0.5-1 hour. S2, Immerse the filter after alkaline washing in step S1 in a cleaning solution at 60-80℃ and ultrasonically clean it for 1-2 hours. Then dry the cleaned filter parts and assemble them. When the solid content in the cleaning solution exceeds 30%, the cleaning solution should be replaced. S3, add precipitant to the replaced cleaning solution, stir well and let it settle for 5-10 minutes, then filter it. The filtrate is diluted and used in the spinning coagulation bath. In step S2, the cleaning solution includes an organic solvent, an additive, and sodium diethyldithiocarbamate. The organic solvent is one or a mixture of tetrahydrofuran, dimethylacetamide, dimethylformamide, methylpyrrolidone, and dimethyl sulfoxide. The additive is polyvinylpyrrolidone and polyvinyl alcohol. In step S3, the precipitant is deionized water and chitosan quaternary ammonium salt.

2. The method for recovering waste liquid from casting fluid filter cleaning as described in claim 1, characterized in that: The mass ratio of the additive to the organic solvent is (3-8):50, and the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol in the additive is (2-9):(11-18).

3. The method for recovering waste liquid from casting fluid filter cleaning as described in claim 1, characterized in that: The mass ratio of the precipitant to the organic solvent is (2-3):

2.

4. The method for recovering waste liquid from casting solution filter cleaning as described in claim 3, characterized in that: The precipitant comprises 90%-95% deionized water and 5%-10% chitosan quaternary ammonium salt, calculated as 100% by mass.

5. The method for recovering waste liquid from casting solution filter cleaning as described in claim 1, characterized in that: The sodium diethyldithiocarbamate is 3%-5% of the weight of the organic solvent.

6. The method for recovering waste liquid from casting fluid filter cleaning as described in claim 1, characterized in that: The alkaline solution is selected from any one or a mixture of several of the following: sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution.

7. The method for recovering waste liquid from casting solution filter cleaning as described in claim 1, characterized in that: In step S2, during the soaking process, the filter is removed and the pores of the filter screen are blown with compressed air for 1-3 minutes before being immersed in the cleaning solution for further cleaning.

8. The method for recovering waste liquid from casting fluid filter cleaning as described in claim 1, characterized in that: In step S2, after cleaning, the filter is first rinsed with alkaline solution for 1-3 minutes, then rinsed with clean water for 1-3 minutes. After rinsing, it is dried and assembled.

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