Anti-fouling PTFE hollow-fiber composite membrane and preparation method therefor

Abstract

The present invention relates to an anti-fouling PTFE hollow-fiber composite membrane and a preparation method therefor. The composite membrane comprises a PTFE hollow-fiber membrane main-body framework and a PVDF inlaying body embeded in a membrane pore of the main-body framework, wherein the main-body framework has a PTFE macroporous hollow-fiber membrane structure, and the pore diameter of the macropores is 50-100 μm; and the inlaying body is a PVDF asymmetric porous membrane, and the pore diameter thereof is 0.01-0.1 μm. The PTFE hollow-fiber composite membrane prepared in the present invention has an asymmetric structure and has the advantages of high filtering precision, a high porosity, high flux, high strength and strong anti-fouling property.

Description

A pollution-resistant PTFE hollow fiber composite membrane and its preparation method Technical Field

[0001] This invention relates to the field of environmental protection technology, and in particular to an anti-pollution PTFE hollow fiber composite membrane and its preparation method. Background Technology

[0002] PTFE (polytetrafluoroethylene) is a membrane material with properties such as heat resistance, acid and alkali resistance, microbial erosion resistance, solvent resistance, and high strength, and can be used for the treatment of special industrial wastewater.

[0003] However, PTFE is difficult to process. Currently, most commercial PTFE hollow fiber membranes are prepared by extruding and stretching paste to form pores. The pore structure is a stretched elongated symmetrical structure. Compared with the asymmetrical circular hole hollow fiber membrane, the stretched elongated symmetrical pore structure has the disadvantages of larger pore size, strong hydrophobicity, poor anti-fouling properties and poor treatment effect during use.

[0004] In the prior art, Chinese patent (application number: 201010504784.3, publication number: CN101961608) discloses a method for controlling the pore size of polytetrafluoroethylene hollow fiber membrane by impregnation with fluorine-containing concentrate. The steps of the method are as follows: (1) preparing a coating impregnation solution using a water-dispersible fluorine-containing concentrate; (2) impregnating the polytetrafluoroethylene hollow fiber membrane in the above coating impregnation solution; (3) drying the impregnated polytetrafluoroethylene hollow fiber membrane. However, the membrane requires frequent water washing and chemical washing.

[0005] In the prior art, Chinese patent (application number: 201980030485.X, publication number: CN112088041) discloses hollow fiber membranes and methods for manufacturing hollow fiber membranes. The method is to prepare asymmetric PTFE hollow fiber membranes by winding a porous filter layer around the support layer. However, the membranes have weak antifouling ability. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides an antifouling PTFE hollow fiber composite membrane and its preparation method. The prepared PTFE hollow fiber composite membrane has an asymmetric structure and has the advantages of high filtration accuracy, high porosity, high flux, high strength, and strong antifouling performance.

[0007] To achieve the above and other related objectives, the present invention provides the following technical solution:

[0008] A pollution-resistant PTFE hollow fiber composite membrane includes a PTFE hollow fiber membrane main skeleton and a PVDF insert embedded in the membrane pores of the main skeleton. The main skeleton is a PTFE macroporous hollow fiber membrane structure with a macropore diameter of 50-100 μm, and the insert is a PVDF asymmetric porous membrane with a pore diameter of 0.01-0.1 μm.

[0009] Furthermore, the pore size of the PTFE hollow fiber membrane backbone is 50-100 μm.

[0010] Furthermore, the pore size of the PVDF insert gradually increases from the outside to the inside, and the outer layer is a high-precision filter layer, which plays the main role in interception and filtration.

[0011] Furthermore, the PVDF insert fills the pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, adhering tightly and not easily separated.

[0012] To achieve the above and other related objectives, the present invention also provides a method for preparing an antifouling PTFE hollow fiber composite membrane according to any one of the claims, comprising the following steps:

[0013] S1. A PTFE macroporous hollow fiber membrane with a pore size of 50-100 μm was prepared by controlling the stretching ratio process;

[0014] S2. Add 25-45% PVDF powder, 40-70% diluent, 0.3-3% dispersant, and 0.5-5% hydrophilic nano silica to a reaction vessel in a certain proportion. Heat, stir and mix to prepare a PVDF emulsion. The heating temperature is 40-80 degrees Celsius and the stirring time is 8-24 hours.

[0015] S3. Immerse the PTFE macroporous hollow fiber membrane obtained in step S1 in PVDF emulsion. The PVDF emulsion permeates into the PTFE membrane pores. The immersion time is 10-60 minutes.

[0016] S4. The PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone with a temperature of 140-200 degrees Celsius. After the PVDF dissolves at the increased temperature, it is then passed through a zone with a temperature of 5-20 degrees Celsius. The membrane is then rapidly cooled to allow the PVDF to separate into two phases. After cooling and phase separation, the diluent in the membrane fibers is removed by extraction to form a porous membrane insert. After drying, an antifouling PTFE hollow fiber composite membrane is obtained.

[0017] Furthermore, the diluent is one or two of DOP, DBP, and triacetin.

[0018] Furthermore, the PVDF powder is prepared by an emulsion method and has a particle size of less than 10 micrometers.

[0019] Furthermore, the dispersant is sodium polyphosphate or sodium hexametaphosphate.

[0020] Furthermore, the hydrophilic nano-silica particles have a particle size of 10-20 nanometers.

[0021] The present invention has the following positive effects:

[0022] 1. The PTFE hollow fiber composite membrane of the present invention consists of a main skeleton and an insert. The main skeleton is prepared by sintering and stretching to form a PTFE macroporous hollow fiber membrane structure, and the insert is a PVDF porous membrane structure. The main skeleton provides support, and the PVDF porous membrane provides filtration. The PVDF porous membrane is prepared based on the principle of phase separation. The pore size and structure can be adjusted by adjusting the phase separation process parameters. The prepared membrane has a progressively larger pore size from the outside to the inside, exhibiting an asymmetric structure. During filtration, contaminants larger than the outer pore size are trapped on the surface of the membrane fibers and cannot enter the interior, thus preventing contamination of the membrane pores. During operation, backwashing with water easily removes contaminants from the membrane pores, thus eliminating the need for frequent water and chemical washing.

[0023] 2. The PTFE hollow fiber composite membrane of this invention not only possesses the high strength of PTFE hollow fiber membranes but also the high porosity and high precision of PVDF thermally induced phase separation, and its membrane structure is asymmetric. Because the PVDF membrane-forming solution is an emulsion before dissolution that first enters the pores of the PTFE membrane, followed by phase separation, the PVDF membrane fills the PTFE pores and coats the fibers, resulting in a tight adhesion that is difficult to separate. This solves the problem of the difficulty in preparing asymmetric pore structures for PTFE stretched membranes, and also provides higher porosity and filtration precision, while exhibiting higher strength compared to PVDF hollow fiber membranes.

[0024] 3. The PTFE hollow fiber composite membrane preparation method of the present invention greatly increases the ways to control membrane pore size and pore structure by introducing a phase separation preparation process, thus broadening the ideas for PTFE membrane hydrophilic modification process. Attached Figure Description

[0025] Figure 1 is a schematic flowchart of the preparation method of the anti-fouling PTFE hollow fiber composite membrane of the present invention. Detailed Implementation

[0026] 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.

[0027] Example 1: As shown in Figure 1, a PTFE hollow fiber membrane with a pore size of 70 μm was prepared by controlling the stretching ratio and other processes.

[0028] 37% PVDF powder, 60% DOP, 2% sodium polyphosphate, and 1% hydrophilic nano silica were added to a reaction vessel in a weight ratio. After heating, stirring and mixing, a PVDF emulsion was prepared. The heating temperature was 50 degrees Celsius and the stirring time was 12 hours.

[0029] The PTFE macroporous hollow fiber membrane was immersed in PVDF emulsion, and the PVDF emulsion permeated into the PTFE membrane pores for 30 minutes.

[0030] The PTFE hollow fiber membrane, after being soaked and moistened, is first passed through a heating zone at a temperature of 160 degrees Celsius. After the PVDF dissolves, it is then passed through a zone at a temperature of 10 degrees Celsius. The membrane is then rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane fibers is removed by ethanol extraction to form a porous membrane insert. After drying, an antifouling PTFE hollow fiber composite membrane is obtained.

[0031] In this embodiment, the pore size of the PTFE hollow fiber membrane backbone is 50 μm.

[0032] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.02 μm.

[0033] In this embodiment, the PVDF insert is an asymmetric porous membrane with pore size gradually increasing from the outside to the inside. The outer layer is a high-precision filter layer, which plays the main role in interception and filtration.

[0034] In this embodiment, the PVDF insert fills the pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, adhering tightly and not easily separated.

[0035] Example 2: An anti-fouling PTFE hollow fiber composite membrane, which differs from Example 1 in that the diluent is DBP.

[0036] In this embodiment, the pore size of the PTFE hollow fiber membrane backbone is 60 μm.

[0037] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.03 μm.

[0038] Example 3: An anti-fouling PTFE hollow fiber composite membrane, which differs from Example 1 in that the soaked and wetted PTFE hollow fiber membrane first passes through a heating zone at a temperature of 150 degrees Celsius, and after the PVDF dissolves at a higher temperature, it then passes through a zone at a temperature of 5 degrees Celsius.

[0039] In this embodiment, the pore size of the PTFE hollow fiber membrane backbone is 70 μm.

[0040] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.04 μm.

[0041] Example 4: As shown in Figure 1, a method for preparing the antifouling PTFE hollow fiber composite membrane includes the following steps:

[0042] S1. A PTFE macroporous hollow fiber membrane with a pore size of 80 μm was prepared by controlling the stretching ratio.

[0043] S2. Add 45% PVDF powder, 60% diluent, 3% dispersant, and 5% hydrophilic nano silica to a reaction vessel in a certain proportion. Heat, stir and mix to prepare a PVDF emulsion. The heating temperature is 80 degrees and the stirring time is 10 hours.

[0044] S3. Immerse the PTFE macroporous hollow fiber membrane obtained in step S1 in PVDF emulsion. The PVDF emulsion permeates into the PTFE membrane pores. The immersion time is 30 minutes.

[0045] S4. The PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone at a temperature of 200 degrees Celsius. After the PVDF dissolves at the increased temperature, it is then passed through a zone at a temperature of 20 degrees Celsius. The membrane is then rapidly cooled to allow the PVDF to undergo phase separation. After cooling and phase separation, the diluent in the membrane fibers is removed by extraction to form a porous membrane insert. After drying, an antifouling PTFE hollow fiber composite membrane is obtained.

[0046] In this embodiment, the diluent is DOP and triacetin.

[0047] In this embodiment, the PVDF powder is prepared by emulsion method and has a particle size of less than 10 micrometers.

[0048] In this embodiment, the dispersant is sodium hexametaphosphate.

[0049] In this embodiment, the pore size of the PTFE hollow fiber membrane backbone is 80 μm.

[0050] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.06 μm.

[0051] Example 5: As shown in Figure 1, a method for preparing the antifouling PTFE hollow fiber composite membrane includes the following steps:

[0052] S1. A PTFE macroporous hollow fiber membrane with a pore size of 90 μm was prepared by controlling the stretching ratio.

[0053] S2. Add 25% PVDF powder, 50% diluent, 2% dispersant, and 3% hydrophilic nano silica to a reaction vessel in a certain proportion. Heat, stir and mix to prepare a PVDF emulsion. The heating temperature is 70 degrees and the stirring time is 9 hours.

[0054] S3. Immerse the PTFE macroporous hollow fiber membrane obtained in step S1 in PVDF emulsion. The PVDF emulsion permeates into the PTFE membrane pores. The immersion time is 20 minutes.

[0055] S4. The PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone at a temperature of 150 degrees Celsius. After the temperature rises and the PVDF dissolves, it is then passed through a zone at a temperature of 15 degrees Celsius. The membrane is then rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane fibers is removed by extraction to form a porous membrane insert. After drying, an antifouling PTFE hollow fiber composite membrane is obtained.

[0056] In this embodiment, the diluent is DBP and triacetin.

[0057] In this embodiment, the PVDF powder is prepared by emulsion method and has a particle size of less than 10 micrometers.

[0058] In this embodiment, the dispersant is sodium polyphosphate.

[0059] In this embodiment, the pore size of the PTFE hollow fiber membrane backbone is 90 μm.

[0060] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.09 μm.

[0061] Membrane fiber performance test results

[0062] The test results show that the modified PTFE composite membrane has an asymmetric pore structure, which has high filtration accuracy, high porosity, high flux, and high strength. This structure of the membrane has better antifouling performance.

[0063] In summary, the PTFE hollow fiber membrane composite membrane prepared by this invention has an asymmetric structure and has the advantages of high filtration accuracy, high porosity, high flux, high strength, and strong anti-fouling performance.

[0064] 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 pollution-resistant PTFE hollow fiber composite membrane, characterized in that: The membrane includes a PTFE hollow fiber membrane main skeleton and a PVDF insert embedded in the membrane pores of the main skeleton. The main skeleton is a PTFE macroporous hollow fiber membrane structure with a macropore diameter of 50-100 μm, and the PVDF insert is a PVDF asymmetric porous membrane with a pore diameter of 0.01-0.1 μm.

2. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The pore size of the PTFE hollow fiber membrane backbone is 50-100μm.

3. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The pore size of the PVDF insert gradually increases from the outside to the inside, and the outer layer is a high-precision filter layer, which plays the main role in interception and filtration.

4. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The PVDF insert fills the pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, adhering tightly and not easily separated.

5. A method for preparing the antifouling PTFE hollow fiber composite membrane according to any one of claims 1-4, characterized in that, Includes the following steps: S1. A PTFE macroporous hollow fiber membrane with a pore size of 50-100 μm was prepared by controlling the stretching ratio process; S2. Add 25-45% PVDF powder, 40-70% diluent, 0.3-3% dispersant, and 0.5-5% hydrophilic nano silica to a reaction vessel in a certain proportion. Heat, stir and mix to prepare a PVDF emulsion. The heating temperature is 40-80 degrees Celsius and the stirring time is 8-24 hours. S3. Immerse the PTFE macroporous hollow fiber membrane obtained in step S1 in PVDF emulsion. The PVDF emulsion permeates into the PTFE membrane pores. The immersion time is 10-60 minutes. S4. The PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone with a temperature of 140-200 degrees Celsius. After the PVDF dissolves at the increased temperature, it is then passed through a zone with a temperature of 5-20 degrees Celsius. The membrane is then rapidly cooled to allow the PVDF to separate into two phases. After cooling and phase separation, the diluent in the membrane fibers is removed by extraction to form a porous membrane insert. After drying, an antifouling PTFE hollow fiber composite membrane is obtained.

6. The preparation method according to claim 5, characterized in that: The diluent is any one or two of DOP, DBP, and triacetin.

7. The preparation method according to claim 5, characterized in that: The PVDF powder is prepared by emulsion method and has a particle size of less than 10 micrometers.

8. The preparation method according to claim 5, characterized in that: The dispersant is sodium polyphosphate or sodium hexametaphosphate.

9. The preparation method according to claim 5, characterized in that: The hydrophilic nano-silica particles have a particle size of 10-20 nanometers.

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