Preparation method of composite PVDF membrane

Abstract

The application discloses a preparation method of a composite PVDF membrane, and particularly relates to the following steps: drying material, and obtaining spinning dope A and spinning dope B by stirring and heating corresponding materials; respectively performing defoaming treatment on the spinning dope A and the spinning dope B; coating the defoaming-treated spinning dope A on a braided tube to form nascent membrane filaments; winding the nascent membrane filaments into a bundle after coagulation treatment to form a PVDF primary membrane; uniformly spraying the defoaming-treated spinning dope B on the PVDF primary membrane after atomization, winding the PVDF primary membrane into a bundle after coagulation treatment, and forming a PVDF composite membrane. The preparation method of the composite PVDF membrane uses a dry-wet phase inversion method; the method adopts a double-layer membrane forming method, has large membrane flux, high mechanical strength, good wear resistance, long service life, and is suitable for treatment of sewage containing high suspended solids such as mine water.

Description

Technical Field

[0001] This invention relates to the field of fiber membrane materials technology, and in particular to a method for preparing a composite PVDF membrane. Background Technology

[0002] Ultrafiltration (UF) membrane technology is a membrane-based filtration, separation, and concentration technique. Under pressure, small molecular weight solutes and solvents in the solution can pass through the micropores of the UF membrane, while large molecular weight solutes, impurities, algae, and viruses are retained on the other side of the membrane. Currently, UF membrane filtration technology is widely used in water treatment due to its excellent separation performance. With technological advancements, UF technology is gradually being applied in mine water treatment. However, because mine water contains many suspended particles, the pretreatment process requires the addition of large amounts of coagulants, leading to easy fouling of the downstream UF membrane. Furthermore, the hard texture of coal dust particles easily abrades the membrane surface, causing membrane fibers to break easily and reducing membrane lifespan. Traditional UF membranes are not performing well in mine water treatment. Therefore, developing a method for preparing PVDF membranes without adding coagulants is of great significance. Furthermore, the PVDF membranes produced by this method can be adapted to mine water with high suspended solids, exhibiting wear resistance and high flux characteristics. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a method for preparing a composite PVDF membrane.

[0004] The present invention provides a method for preparing a composite PVDF membrane, comprising the following steps:

[0005] 1) Drying materials: Dry ultra-high molecular weight polyethylene, polyvinylidene fluoride, sodium montmorillonite powder, TiO2 or SiO2 separately for later use;

[0006] 2) Ultra-high molecular weight polyethylene, polyvinylidene fluoride, sodium montmorillonite powder, and co-solvent are heated and stirred according to the specified ratio to obtain spinning solution A; ultra-high molecular weight polyethylene, polyvinylidene fluoride, TiO2 or SiO2, and co-solvent are heated and stirred according to the specified ratio to obtain spinning solution B.

[0007] 3) Defoaming treatment is performed on the spinning solution A and spinning solution B respectively;

[0008] 4) The defoamed spinning solution A is coated onto the braided tube to form nascent film fibers;

[0009] 5) The primary membrane fibers are solidified and then wound into bundles to form a PVDF primary membrane;

[0010] 6) The defoamed spinning solution B is atomized and evenly sprayed onto the PVDF primary film. After solidification, it is wound into a bundle to form a PVDF composite film.

[0011] Preferably, the heating and stirring conditions for preparing the spinning solution A are as follows: under stirring, the temperature is slowly raised to 60-70°C and held for 20-25 minutes, then raised to 120-140°C and held for 20-30 minutes, until the blended solution becomes transparent, thus obtaining the spinning solution A.

[0012] Preferably, the heating and stirring conditions for preparing the spinning solution B are as follows: under stirring, the temperature is slowly raised to 60-70°C and held for 20-25 minutes, then raised to 80-95°C and held for 20-30 minutes, until the blended solution becomes transparent, thus obtaining the spinning solution B.

[0013] Preferably, the formulation consists of 10-15 parts of ultra-high molecular weight polyethylene, 50-60 parts of polyvinylidene fluoride, 5-15 parts of TiO2 or SiO2, 5-15 parts of sodium montmorillonite powder, and 10-35 parts of co-solvent; wherein the co-solvent is N-dimethylacetamide.

[0014] Preferably, the ultra-high molecular weight polyethylene has a molecular weight higher than 1 million, and the polyvinylidene fluoride has a molecular weight of 500,000 to 520,000; the sodium montmorillonite powder is a refined powder with a particle size between 0.1 and 0.5 μm; and the TiO2 or SiO2 has a particle size between 0.5 and 1.0 μm.

[0015] Preferably, the degassing process involves transferring the stirred spinning solution A and spinning solution B to a degassing tank via a nitrogen pressure tank for degassing treatment.

[0016] Preferably, in step 4), the spinning solution A is brought into contact with the braided tube at the spinneret by a spinning pump, and the spinning solution A is coated onto the braided tube.

[0017] Preferably, the spinning solution B in step 6) is connected to a spraying pipe via a spraying pump. The spraying pipe has a diameter of 5-10 cm and a length of 50-100 cm. The spraying pipe has tiny micropores with a diameter of 0.5-2 mm distributed along its diameter.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) The method for preparing the composite PVDF membrane of the present invention uses the dry-wet phase conversion method; the method adopts a double-layer membrane formation method, which has high membrane flux, high mechanical strength, wear resistance, and long service life, and is suitable for the treatment of sewage containing high suspended solids such as mine water.

[0020] (2) This method adds sodium montmorillonite to the inner PVDF membrane. By utilizing the interlayer structure and water-swelling properties of sodium montmorillonite, the inner PVDF membrane has the characteristics of large pore size and high flux.

[0021] (3) This method adds TiO2 or SiO2 inorganic materials to the outer PVDF membrane. By combining the good rigidity of inorganic materials with the good chemical stability of polyvinylidene fluoride, the pressure resistance and chemical stability of the membrane material are improved. Furthermore, since the inorganic material particles change the hydrophilic angle of the polyvinylidene fluoride material, the hydrophilicity of the membrane material is improved, and the antifouling ability of the membrane material is enhanced, thus strengthening the rigidity, pressure resistance and antifouling ability of the obtained outer PVDF membrane.

[0022] (4) The method for preparing the composite PVDF membrane of the present invention involves adding a braided tube inside the PVDF membrane to enhance the strength of the PVDF membrane, and coating the outer surface of the braided tube with spinning solution A to achieve precise control of the structure of the pores on the surface of the PVDF membrane.

[0023] (5) The method for preparing the composite PVDF membrane of the present invention produces a PVDF membrane with a filament diameter of ≤2mm and a tensile strength of 100MPa or more, which is more than 10 times the tensile strength of polyvinylidene fluoride membrane prepared by general methods, and has the characteristics of high strength; the membrane has a porosity of about 85%, an average pore size of 0.01 to 0.2um, and a pure water flux of 400L / (m2.h), and has the characteristics of high flux.

[0024] (6) The method for preparing the composite PVDF membrane of the present invention combines the spinning solution formulation with the spinning process, which makes the production efficiency higher and the membrane quality more stable while ensuring high strength and high precision.

[0025] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0026] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0027] Figure 1 This is a schematic diagram of the spinning process;

[0028] Numbered in the diagram: 1. Nitrogen pressure tank #1; 2. Stirred reactor #1; 3. Deaerator #1; 4. Spinning pump #1; 5. Spinneret #1; 6. Braided tube; 7. Coagulation bath #1; 8. First winding machine; 9. Second winding machine; 10. Stirred reactor #2; 11. Nitrogen pressure tank #2; 12. Deaerator #2; 13. Spraying pump; 14. Spraying pipe; 15. PVDF primary film; 16. Third winding machine; 17. Coagulation bath #2; 18. Fourth winding machine; 19. PVDF composite film. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] Please refer to Figure 1 The present invention provides a method for preparing a composite PVDF membrane, comprising the following steps:

[0032] 1) Material drying: Dry ultra-high molecular weight polyethylene, polyvinylidene fluoride, sodium montmorillonite, TiO2 or SiO2 separately for later use;

[0033] 2) Place 10-15 parts of ultra-high molecular weight polyethylene, 50-60 parts of polyvinylidene fluoride, 5-15 parts of sodium montmorillonite powder, and 10-35 parts of co-solvent into stirred reactor 2 (No. 1) and slowly heat to 60-70℃ under stirring, hold for about 20-25 minutes, then heat to 120-140℃ and hold for about 20-30 minutes until the blended solution becomes transparent, thus obtaining spinning solution A.

[0034] 3) Transfer the stirred spinning solution A to the degassing tank 3 through nitrogen pressure tank 1 (1) for degassing; after degassing, release the vacuum of degassing tank 3 to atmospheric pressure, and then use nitrogen pressure tank 1 (1) to increase the pressure in degassing tank 3 to 0.2 MPa.

[0035] 4) Turn on spinning pump 4 to pump spinning solution A to spinneret 5. Braided tube 6 is pulled to spinneret 5 by first winding machine 8. Spinning solution A is coated on braided tube 6 at spinneret 5 to form nascent film filaments.

[0036] 5) The coated nascent membrane fibers are pulled through the No. 1 coagulation bath 7 by the first winding machine 8, and finally wound by the second winding machine 9; after passing through the No. 1 coagulation bath 7 and being processed by the second winding machine 9, the membrane fibers are wound into bundles, and the PVDF nascent membrane 15 is formed.

[0037] In this process, a PVDF primary membrane 15 is formed. Sodium montmorillonite powder is added to the PVDF primary membrane 15. By utilizing its expansibility and its own interlayer structure, the pore size of the PVDF primary membrane is increased, and the flux is increased.

[0038] 6) Place 10-15 parts of ultra-high molecular weight polyethylene, 50-60 parts of polyvinylidene fluoride, 5-15 parts of TiO2 or SiO2, and 10-35 parts of co-solvent into stirred reactor 10 (No. 2) and slowly heat to 60-70℃ under stirring, hold for 20-25 minutes, then heat to 80-95℃ and hold for 20-30 minutes until the blended solution becomes transparent, thus obtaining spinning solution B.

[0039] 7) Transfer the stirred spinning solution B to the degassing tank 12 through the nitrogen pressure tank 11 (2) for degassing; after degassing, release the vacuum in the degassing tank 12 to atmospheric pressure, and then use the nitrogen pressure tank 11 (2) to increase the pressure in the degassing tank 12 to 0.2 MPa.

[0040] 8) Turn on the spraying pump 13 to pump the spinning solution B to the spraying pipe 14. The PVDF primary film 15 is pulled to the spraying pipe by the third winding machine 16. The spinning solution B is atomized under high pressure and sprayed onto the PVDF primary film 15.

[0041] The spray pump 13 is connected to the spray pipe 14. The spray pipe 14 has a diameter of 5-10cm and a length of 50-100cm. The spray pipe 14 has tiny micropores along its diameter, with a pore diameter of about 0.5-2mm.

[0042] Specifically, the PVDF primary film 15 is pulled by the traction device through the spray pipe 14. When the PVDF primary film 15 passes through the spray pipe 14, under high pressure, the spinning solution B passes through the tiny micropores of the spray pipe 14 at high speed. The spinning solution B is atomized and uniformly sprayed onto the PVDF primary film 15, forming a thin film on the surface of the film, thus forming the PVDF secondary film.

[0043] 9) The PVDF reinforcing film fibers after the second spraying are pulled by the third winding machine 16 through the No. 2 coagulation bath 17 and wound into a bundle by the fourth winding machine 18 to form the PVDF composite film 19.

[0044] Preferably, the co-solvent is N-dimethylacetamide.

[0045] Preferably, the ultra-high molecular weight polyethylene has a molecular weight higher than 1 million, and the polyvinylidene fluoride has a molecular weight of 500,000 to 520,000; the sodium montmorillonite powder is a refined powder with a particle size between 0.1 and 0.5 μm.

[0046] Preferably, the particles are TiO2 or SiO2 with a particle size between 0.5 and 1.0 μm.

[0047] Preferably, the stirring speed in both the No. 1 and No. 2 stirred reactors is controlled at 60±10 r / min.

[0048] Preferably, the degassing vacuum degree of degassing tank #1 and degassing tank #2 is -0.10MPa, the degassing temperature is 60±10℃, and the degassing time is 5±1 hours.

[0049] Preferably, the thickness of the spinning solution A coated on the braided tube 6 is controlled by the No. 1 spinning pump 4, and the discharge speed is controlled at 10-80 r / min; the braided tube 6 serves as the inner lining structure of the PVDF membrane to enhance the strength of the PVDF membrane.

[0050] Preferably, the spinning solution A is wound by a winding wheel through a No. 1 spinneret 5, and the traction speed is the spinning speed, which is controlled at 15m / min. The wound PVDF initial film filaments are formed, and the film filaments pass through a No. 1 coagulation bath 7, which is a water bath with the temperature controlled at 40℃. The formed film filaments are then wound into bundles.

[0051] Preferably, the PVDF primary film is wound by a winding wheel at a speed that is also the spinning speed, controlled at 15 m / min. The spraying tube 14 has a diameter of 5-10 cm and a length of 50-100 cm, with tiny micropores arranged along its diameter, each with a diameter of approximately 0.5-2 mm. The spinning solution B is atomized and sprayed onto the PVDF primary film by the spraying pump 13 under high pressure, forming a second film. The thickness of the second film is approximately 50-100 μm. After the second spraying, the PVDF filaments are subjected to an air bath, and the formed filaments are wound into bundles.

[0052] Preferably, the membrane fibers are post-processed and hung to dry, thus completing the manufacturing of the composite PVDF membrane. The composite PVDF membrane has a double-layer structure, with the inner layer being a PVDF membrane primary layer containing sodium montmorillonite powder. The spatial structure and expansion properties of sodium montmorillonite are utilized to make the inner membrane have large pore size and high flux.

[0053] The inner membrane has a porosity of 85%, an average pore size of 0.01–0.2 μm, and a pure water flux of 400 L / (m²·h).

[0054] The outer PVDF membrane contains TiO2 or SiO2 inorganic materials, which have strong wear resistance, thus improving the wear resistance and fouling resistance of the PVDF membrane.

[0055] In the description of this specification, the terms "connection," "installation," and "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0056] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a composite PVDF membrane, characterized by, It comprises the following steps: 1) drying the material: UHMWPE, PVDF, Na-montmorillonite powder, TiO2 or SiO2 are dried respectively for standby; 2) UHMWPE, PVDF, Na-montmorillonite powder, cosolvent are mixed according to the ratio and treated by heating and stirring to obtain spinning dope A; UHMWPE, PVDF, TiO2 or SiO2, cosolvent are mixed according to the ratio and treated by heating and stirring to obtain spinning dope B; 3) the spinning dope A and the spinning dope B are respectively subjected to defoaming treatment; 4) the defoaming treated spinning dope A is coated on the braided tube to form a nascent membrane filament; 5) the nascent membrane filament is coagulated and wound into a bundle to form a PVDF primary membrane; 6) the defoaming treated spinning dope B is atomized and uniformly sprayed on the PVDF primary membrane, and then coagulated and wound into a bundle to form a PVDF composite membrane.

2. The method of claim 1, wherein the PVDF composite membrane is prepared by the steps of: The heating and stirring treatment conditions for preparing the spinning dope A are as follows: slowly heating to 60-70℃ under stirring, keeping for 20-25 min, then heating to 120-140℃ again, keeping for 20-30 min, until the blended solution becomes transparent, to obtain the spinning dope A.

3. The method of claim 1, wherein the PVDF membrane is prepared by a co-precipitation method. The heating and stirring treatment conditions for preparing the spinning dope B are as follows: slowly heating to 60-70℃ under stirring, keeping for 20-25 min, then heating to 80-95℃ again, keeping for 20-30 min, until the blended solution becomes transparent, to obtain the spinning dope B.

4. The method of claim 1, wherein the PVDF composite membrane is prepared by the steps of: The ratio is as follows: UHMWPE 10-15 parts, PVDF 50-60 parts, TiO2 or SiO2 5-15 parts, Na-montmorillonite powder 5-15 parts, cosolvent 10-35 parts; the cosolvent is N-dimethylacetamide.

5. The method of claim 1, wherein the PVDF composite membrane is prepared by the steps of: The molecular weight of the UHMWPE is higher than 1 million, the molecular weight of the PVDF is 500-520 thousand; the Na-montmorillonite powder is fine powder with a particle size of 0.1-0.5 μm; the TiO2 or SiO2 has a particle size of 0.5-1.0 μm.

6. The method of claim 1, wherein the PVDF composite membrane is prepared by the steps of: The defoaming treatment is carried out by transferring the stirred spinning dope A and the spinning dope B to a defoaming tank through a nitrogen pressure tank.

7. The method for preparing the composite PVDF membrane according to claim 1, characterized in that, The spinning dope A in step 4) is transferred to the braided tube through a spinning pump at the spinneret.

8. The method for preparing the composite PVDF membrane according to claim 1, characterized in that, The spinning dope B in step 6) is connected to a spraying tube through a spraying pump, the spraying tube has a diameter of 5-10 cm and a length of 50-100 cm, and is provided with fine micropores along the diameter direction, with a pore size of 0.5-2 mm.

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