Special precision ultrafiltration membrane for separating papermaking black liquor and preparation method thereof

Abstract

The present application relates to a kind of papermaking black liquor separation special precision ultrafiltration membrane and its preparation method, comprising the following steps, S1.polyether sulfone, fluororesin C9F 17 OC4H9O3, butyl acetate, organic solvent, into the reaction kettle is configured into mixed liquor, to the mixed liquor stirring heating;S2.the mixed liquor prepared in S1 Stirring is uniform, vacuum degassing treatment and cooling after cooling down to prepare ultrafiltration membrane casting solution;S3.the casting solution in S2 By metering pump, from the ring spinneret extrusion, into gel tank phase solidification and shaping into nascent hollow fiber membrane;S4.the nascent hollow fiber membrane in S3 Further modified into membrane by high-temperature oven, by traction, winding obtains composite polyether sulfone hollow fiber ultrafiltration membrane, finally by pure water cleaning.The finished product of the application has higher filtration precision, higher filtration flux, better anti-pollution, better alkali resistance.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and in particular to a special precision ultrafiltration membrane for separating black liquor in papermaking and its preparation method. Background Technology

[0002] Papermaking black liquor contains a large amount of suspended solids, organic pollutants, and toxic substances, which can cause serious pollution if directly discharged into water bodies. Its main hazards include: papermaking wastewater containing large amounts of fiber, pigments, and inorganic salts will turn water bodies black and have a distinctive foul odor; the biochemical oxygen demand (BOD) of papermaking black liquor containing high concentrations of organic pollutants can reach 5000~40000 g / L, consuming large amounts of dissolved oxygen in the water and affecting water quality; and the large amount of alkaline substances present in black liquor will cause a sharp increase in the pH value of the water body, disrupting the balance of the aquatic environment.

[0003] Currently, commonly used black liquor treatment technologies for papermaking include alkali recovery, flocculation and sedimentation, membrane separation, acid precipitation, aerobic activated sludge, and biotechnology.

[0004] After concentrating and separating the black liquor from papermaking using ultrafiltration technology, the wastewater enters the downstream deep treatment process to recover water resources and alkali. The concentrated water is then treated to recover lignin and hemicellulose, which not only protects the environment but also realizes the recycling of resources.

[0005] Ultrafiltration technology is a type of membrane filtration. The unique pore size of ultrafiltration membranes (0.01~0.1µm) can effectively trap bacteria, viruses, colloids, etc., to achieve separation, classification, purification, and concentration.

[0006] Ultrafiltration, due to its lack of phase change and simple operation, is widely used in water treatment, food industry, and biochemical engineering. With advancements in ultrafiltration technology, its contribution to human society will continue to grow.

[0007] However, ultrafiltration membranes suffer from problems such as rapid fouling, low separation efficiency, poor separation effect, poor alkali resistance, and difficulty in cleaning and maintenance during the concentration and separation of black liquor in papermaking. Therefore, it is necessary to develop hollow fiber ultrafiltration membranes with higher filtration precision, higher filtration flux, better fouling resistance, and better alkali resistance.

[0008] Hollow fiber ultrafiltration membranes have advantages over spiral-wound and flat-sheet ultrafiltration membranes, including higher packing density, easier production process control, and lower production costs, making them the main form of ultrafiltration membranes and the current mainstream in the market.

[0009] The main materials used in ultrafiltration membranes include PVDF, PES, PS, PVC, PAN, and PP.

[0010] Among many materials, polyethersulfone has excellent properties such as mechanical properties, chemical stability, heat resistance, corrosion resistance, oxidation resistance, and heat resistance.

[0011] The main problems with polyethersulfone hollow fiber filtration membranes currently on the market are: (1) Due to the low surface energy and strong hydrophobicity of polyethersulfone material, the water wettability of the membrane surface is poor, resulting in low water flux. During concentration and separation, it is easy to adsorb organic matter in the material, which will block the membrane pores and cause a decrease in water flux. (2) Polyethersulfone hollow fiber ultrafiltration membranes have wide pore size distribution, large pore size, and low retention accuracy, resulting in poor separation effect, low product purity, and large material waste during material concentration. (3) During use, the acid and alkali corrosiveness of the material will damage the membrane material and accelerate the aging rate of the membrane material.

[0012] Chinese patent application number CN202110653069 discloses an internal pressure hollow fiber ultrafiltration membrane, its preparation method and application. The core liquid in the patent is a mixture of ethanol, polyethylene glycol 600, N-methylpyrrolidone and water, and the pure water flux of the prepared membrane reaches 800 LMH.

[0013] Chinese patent application CN202110653069.4 discloses an internal pressure hollow fiber ultrafiltration membrane, its preparation method, and its application. The membrane is prepared by spinning, washing, post-treatment, and drying a casting solution composed of polyethersulfone, sulfonated polyethersulfone, additives, and solvent. This invention uses a mixture of polyethersulfone and sulfonated polyethersulfone as the membrane-forming polymer. The introduction of sulfonic acid groups improves the hydrophilicity and antifouling ability of the hollow fiber ultrafiltration membrane. The use of hydroxyl-containing carboxylic esters as additives adjusts the hydrophilicity of the polyethersulfone hollow fiber ultrafiltration membrane, allowing for controllable pore structure.

[0014] MokS et al. used X-rays to irradiate and graft PEG onto the surface of PES hollow fiber membranes and found that the absorption of porcine protein on the inner surface of the hollow fiber membrane was reduced, resulting in reduced fouling of the modified membrane when treating porcine protein solutions.

[0015] Tianjin University of Technology has announced a method for preparing an antibacterial PVC ultrafiltration membrane. The method uses tertiary amines to quaternize the original PVC membrane, introducing a certain number of quaternary ammonium groups onto the PVC molecular chain to endow the PVC membrane with antibacterial properties.

[0016] If a membrane with good hydrophilicity, high pure water flux, uniform pore size distribution, and antibacterial properties could be developed, with dry membrane fibers free of protective liquid and bacteria, it would be more suitable for the food processing industry, and the production process would be simple and easy to industrialize. This would greatly improve the separation efficiency of whey papermaking black liquor, extend the service life of ultrafiltration membranes, and reduce system operating costs. Summary of the Invention

[0017] In view of the shortcomings of the prior art, the present invention provides a special precision ultrafiltration membrane for papermaking black liquor separation and its preparation method. It not only solves the problems of rapid fouling, low separation efficiency, poor separation effect, poor alkali resistance, and difficult cleaning and maintenance of hollow fiber ultrafiltration membranes in the process of papermaking black liquor concentration and separation, but also achieves more precise and efficient separation of papermaking black liquor.

[0018] To achieve the above and other related objectives, the present invention provides the following technical solution:

[0019] A special precision ultrafiltration membrane for separating black liquor from papermaking is mainly composed of the following parts by weight:

[0020] 15-25 parts of polyethersulfone

[0021] 1-7 parts of fluororesin

[0022] 5-18 parts of butyl acetate

[0023] Solvent 50-70 parts.

[0024] Furthermore, it is mainly composed of the following components by weight: 15 parts polyethersulfone, 3 parts fluororesin, 5 parts butyl acetate, and 50 parts solvent.

[0025] Furthermore, it is mainly composed of the following parts by weight: 20 parts polyethersulfone, 4 parts fluororesin, 11.5 parts butyl acetate, and 60 parts solvent.

[0026] Furthermore, the molecular weight of the polyethersulfone is between 50,000 and 70,000.

[0027] Furthermore, the fluoropolymer has the molecular formula C9F. 17 OC4H9O3.

[0028] Furthermore, the solvent is selected from one or more of dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

[0029] To achieve the above and other related objectives, the present invention also provides a method for preparing a special precision ultrafiltration membrane for papermaking black liquor separation, comprising the following steps:

[0030] S1. By weight, add 15-25 parts of polyethersulfone, 1-7 parts of fluororesin, 5-18 parts of butyl acetate and 50-70 parts of solvent to a reaction vessel to prepare a mixture, and heat and stir the mixture.

[0031] S2. Stir the mixture obtained in step S1 until it is homogeneous, degas it under vacuum and cool it down to obtain the ultrafiltration membrane casting solution.

[0032] S3. The ultrafiltration membrane casting solution is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0033] S4. The nascent hollow fiber membrane is further modified into a membrane by passing it through a high-temperature oven. After being drawn and wound, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidifying room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for separating black liquor in papermaking.

[0034] Furthermore, in step S1, the heating temperature is 50-60℃ and the stirring time is 8-10h.

[0035] Furthermore, in step S2, the liquid is cooled to 10-15°C after vacuum degassing.

[0036] Furthermore, in step S4, the temperature of the high-temperature oven is 160-165°C.

[0037] The present invention has the following positive effects:

[0038] 1. Compared with ordinary hollow fiber ultrafiltration membranes, the polyethersulfone hollow fiber special ultrafiltration membrane of the present invention has higher filtration accuracy, higher filtration flux, better antifouling properties, and better alkali resistance. Moreover, the production process is simple and easy to industrialize, solving the problems of rapid fouling, low separation efficiency, poor separation effect, poor alkali resistance, and difficult cleaning and maintenance in the process of using hollow fiber ultrafiltration membranes for black liquor concentration and separation in papermaking.

[0039] 2. The casting solution of this invention incorporates fluororesin, which, due to the presence of multiple hydroxyl groups on its molecular chain, exhibits self-crosslinking properties. During the membrane fiber forming process, when passing through a high-temperature oven at approximately 160 degrees Celsius, it undergoes self-crosslinking and solidification into a network structure, exhibiting excellent properties such as acid and alkali resistance, high-temperature resistance, and antifouling properties. Simultaneously, since the fluororesin is uniformly distributed within the membrane pores, the crosslinking and solidification process reduces the membrane pore size, thus enabling the preparation of a small-pore ultrafiltration membrane with a molecular weight cutoff of 6000 Da and a retention rate greater than 95%, achieving more precise and efficient separation of papermaking black liquor.

[0040] 3. In this invention, butyl acetate is added to the casting solution. This serves two purposes: firstly, as a solvent for dissolving the fluororesin, and secondly, as a pore-forming agent during the gelation and phase separation process. Because it is insoluble in water, most of it remains in the casting solution during gelation and phase separation in the first gelation tank. When the nascent hollow fiber membrane is passed through a high-temperature drying oven, the butyl acetate in the membrane fibers evaporates, forming membrane pores. This significantly increases the porosity of the membrane fibers and substantially increases the filtration flux, achieving a pure water flux of over 1000 LMH.

[0041] 4. In this invention, the addition of fluororesin to the casting solution leads to a cross-linking reaction, forming a network structure with fluorine atoms on the molecular chains. This improves the chemical properties of the membrane material, giving it strong alkali resistance and stain resistance. During the treatment of papermaking black liquor, the material structure will not age or deteriorate due to excessively high alkalinity of the treatment solution.

[0042] 5. This invention features a simple preparation process, combining various steps such as pore size adjustment, hydrophilic modification, alkali resistance modification, and flux improvement. Through a special formulation process, various materials can play multiple roles and have synergistic effects, thus preparing a polyethersulfone hollow fiber special ultrafiltration membrane for black liquor concentration in papermaking. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0044] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0045] Example 1: As Figure 1 As shown, a special precision ultrafiltration membrane for separating black liquor in papermaking is prepared by the following steps:

[0046] S1. By weight, add 20 parts of polyethersulfone, 2 parts of fluororesin, 10 parts of butyl acetate and 68 parts of solvent to a reaction vessel to prepare a mixture. Heat and stir the mixture at 50 degrees Celsius for 8 hours.

[0047] S2. Stir the mixture obtained in S1 until it is homogeneous, degas it under vacuum and cool it down to 10 degrees to obtain the ultrafiltration membrane casting solution.

[0048] S3. The casting solution in S2 is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0049] S4. The nascent hollow fiber membrane from S3 is further modified and dried in a high-temperature oven at 160 degrees Celsius. After traction and winding, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidified room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for papermaking black liquor separation.

[0050] Example 2: Figure 1 As shown, a special precision ultrafiltration membrane for separating black liquor in papermaking is prepared by the following steps:

[0051] S1. By weight, add 20 parts of polyethersulfone, 3 parts of fluororesin, 10 parts of butyl acetate and 67 parts of solvent to a reaction vessel to prepare a mixture. Heat and stir the mixture at 50 degrees Celsius for 8 hours.

[0052] S2. Stir the mixture obtained in S1 until it is homogeneous, degas it under vacuum and cool it down to 10 degrees to obtain the ultrafiltration membrane casting solution.

[0053] S3. The casting solution in S2 is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0054] S4. The nascent hollow fiber membrane from S3 is further modified and dried in a high-temperature oven at 160 degrees Celsius. After traction and winding, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidified room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for papermaking black liquor separation.

[0055] Example 3: As Figure 1 As shown, a special precision ultrafiltration membrane for separating black liquor in papermaking is prepared by the following steps:

[0056] S1. By weight, add 20 parts of polyethersulfone, 2 parts of fluororesin, 10 parts of butyl acetate and 68 parts of solvent to a reaction vessel to prepare a mixture. Heat and stir the mixture at 60 degrees Celsius for 8 hours.

[0057] S2. Stir the mixture obtained in S1 until it is homogeneous, degas it under vacuum and cool it down to 10 degrees to obtain the ultrafiltration membrane casting solution.

[0058] S3. The casting solution in S2 is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0059] S4. The nascent hollow fiber membrane from S3 is further modified and dried in a high-temperature oven at 160 degrees Celsius. After traction and winding, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidified room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for papermaking black liquor separation.

[0060] Example 4: Figure 1 As shown, a special precision ultrafiltration membrane for separating black liquor in papermaking is prepared by the following steps:

[0061] S1. By weight, add 20 parts of polyethersulfone, 2 parts of fluororesin, 10 parts of butyl acetate and 68 parts of solvent to a reaction vessel to prepare a mixture. Heat and stir the mixture at 50 degrees Celsius for 8 hours.

[0062] S2. Stir the mixture obtained in S1 until it is homogeneous, degas it under vacuum and cool it down to 10 degrees to obtain the ultrafiltration membrane casting solution.

[0063] S3. The casting solution in S2 is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0064] S4. The nascent hollow fiber membrane from S3 is further modified and formed into a membrane by passing it through a high-temperature oven at 165 degrees Celsius. After traction and winding, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidified room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for papermaking black liquor separation.

[0065] Example 5: Figure 1 As shown, a special precision ultrafiltration membrane for separating black liquor in papermaking is prepared by the following steps:

[0066] S1. By weight, 20 parts of polyethersulfone, 2 parts of fluoropolymer, 15 parts of butyl acetate, and 63 parts of solvent are added to a reaction vessel to prepare a mixture. The mixture is heated and stirred at 50 degrees Celsius for 8 hours.

[0067] S2. Stir the mixture obtained in S1 until it is homogeneous, degas it under vacuum and cool it down to 10 degrees to obtain the ultrafiltration membrane casting solution.

[0068] S3. The casting solution in S2 is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane.

[0069] S4. The nascent hollow fiber membrane from S3 is further modified and dried in a high-temperature oven at 160 degrees Celsius. After traction and winding, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidified room with a certain temperature and humidity to prepare a special precision ultrafiltration membrane for papermaking black liquor separation.

[0070] Comparative Example 1: A special precision ultrafiltration membrane for separating black liquor in papermaking, the preparation process includes the following steps:

[0071] S1. By weight, 20 parts of polyethersulfone, 10 parts of PEG, 5 parts of PVP, and 65 parts of dimethylformamide are added to a reaction vessel to prepare a mixture. The mixture is stirred and heated at 60°C for 8 hours. The molecular weight of polyethersulfone is 59,000, the molecular weight of PEG is 400, and the PVP is K17.

[0072] S2. Stir the mixture obtained in S1 until it is homogeneous, and then degas it under vacuum to obtain the ultrafiltration membrane casting solution.

[0073] S3. The casting solution in S2 is squeezed out from the annular spinneret through a metering pump, and pure water at 30°C is introduced into the inner cavity of the annular spinneret. After passing through a 1cm air section, the membrane fiber enters the gel tank for phase separation and solidification. After traction and winding, the nascent membrane fiber is obtained.

[0074] S4. After soaking and cleaning the membrane fibers from S3, soak them in glycerol protective solution, and finally air dry them to obtain the finished membrane fibers.

[0075] Comparative Example 2: A special precision ultrafiltration membrane for separating black liquor in papermaking, the preparation process includes the following steps:

[0076] S1. By weight, 15 parts of polyethersulfone, 8 parts of PEG, 3 parts of PVP, and 70 parts of dimethylformamide are added to a reaction vessel to prepare a mixture. The mixture is stirred and heated at 60°C for 8 hours. The molecular weight of polyethersulfone is 59,000, the molecular weight of PEG is 400, and the PVP is K17.

[0077] S2. Stir the mixture obtained in S1 until it is homogeneous, and then degas it under vacuum to obtain the ultrafiltration membrane casting solution.

[0078] S3. The casting solution in S2 is squeezed out from the annular spinneret through a metering pump, and pure water at 30°C is introduced into the inner cavity of the annular spinneret. After passing through a 1cm air section, the membrane fiber enters the gel tank for phase separation and solidification. After traction and winding, the nascent membrane fiber is obtained.

[0079] S4. After soaking and cleaning the membrane fibers from S3, soak them in glycerol protective solution, and finally air dry them to obtain the finished membrane fibers.

[0080] The products obtained in the above embodiments were subjected to performance testing, and the test results are shown in Table 1:

[0081]

[0082] The test items adopt industry-standard testing methods.

[0083] The test data shows that the pure water flux of the hollow fiber ultrafiltration membrane in the present invention embodiment is significantly greater than that of the ordinary ultrafiltration membrane in the comparative example, indicating that the ultrafiltration membrane prepared according to the preparation method of the present invention has higher porosity and better pore structure.

[0084] The hollow fiber ultrafiltration membrane in this embodiment of the invention achieves a rejection rate of over 95% for a molecular weight of 6000 Da, while the rejection rate in the comparative example is only 38%. This indicates that the hollow fiber ultrafiltration membrane in this embodiment of the invention has a smaller and more uniform pore size, enabling more precise separation and concentration of materials.

[0085] The contact angle alkali resistance of the hollow fiber ultrafiltration membrane in this embodiment is also significantly better than that of the ordinary hollow fiber ultrafiltration membrane in the comparative example.

[0086] Therefore, compared with ordinary hollow fiber ultrafiltration membranes, the polyethersulfone hollow fiber special ultrafiltration membrane of the present invention has higher filtration accuracy, higher filtration flux, better antifouling properties, and better alkali resistance, and the production process is simple and easy to industrialize.

[0087] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A special precision ultrafiltration membrane for separating black liquor in papermaking, characterized in that, It is mainly composed of the following components in parts by weight: 15-25 parts of polyethersulfone 1-7 parts of fluororesin 5-18 parts of butyl acetate Solvent 50-70 parts; The fluororesin has the molecular formula C9F. 17 OC4H9O3; The preparation method of the special precision ultrafiltration membrane for separating papermaking black liquor includes the following steps: S1. By weight, add 15-25 parts of polyethersulfone, 1-7 parts of fluororesin, 5-18 parts of butyl acetate and 50-70 parts of solvent to a reaction vessel to prepare a mixture, and heat and stir the mixture. S2. Stir the mixture obtained in step S1 until it is homogeneous, degas it under vacuum and cool it down to obtain the ultrafiltration membrane casting solution. S3. The ultrafiltration membrane casting solution is extruded from the annular spinneret through a metering pump and enters the gel tank for phase separation and solidification to form a nascent hollow fiber membrane. S4. The nascent hollow fiber membrane is further modified into a membrane by passing it through a high-temperature oven. After being drawn and wound, a composite polyethersulfone hollow fiber ultrafiltration membrane is obtained. Finally, it is washed with pure water and hung to dry in a dehumidifying room with a certain humidity to prepare a special precision ultrafiltration membrane for separating black liquor in papermaking.

2. The special precision ultrafiltration membrane for separating black liquor in papermaking according to claim 1, characterized in that, It is mainly composed of the following components in parts by weight: 15 parts polyethersulfone, 3 parts fluororesin, 5 parts butyl acetate, and 50 parts solvent.

3. The special precision ultrafiltration membrane for separating papermaking black liquor according to claim 1, characterized in that, It is mainly composed of the following parts by weight: 20 parts polyethersulfone, 4 parts fluororesin, 11.5 parts butyl acetate, and 60 parts solvent.

4. The special precision ultrafiltration membrane for separating papermaking black liquor according to claim 1, characterized in that: The molecular weight of the polyethersulfone is between 50,000 and 70,000.

5. The special precision ultrafiltration membrane for separating black liquor in papermaking according to claim 1, characterized in that: The solvent is selected from one or more of dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

6. The special precision ultrafiltration membrane for separating papermaking black liquor according to claim 1, characterized in that, In step S1, the heating temperature is 50-60℃ and the stirring time is 8-10h.

7. The special precision ultrafiltration membrane for separating black liquor in papermaking according to claim 1, characterized in that, In step S2, the liquid is cooled to 10-15°C after vacuum degassing.

8. The special precision ultrafiltration membrane for separating papermaking black liquor according to claim 1, characterized in that, In step S4, the temperature of the high-temperature oven is 160-165°C.

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