Anti-pollution PTFE hollow fiber composite membrane and preparation method thereof

Abstract

The invention relates to an anti-pollution PTFE (Polytetrafluoroethylene) hollow fiber composite membrane and a preparation method thereof, the anti-pollution PTFE hollow fiber composite membrane comprises a PTFE hollow fiber membrane main body framework and a PVDF (Polyvinylidene Fluoride) inlaying body embedded in a membrane pore of the main body framework, the main body framework is of a PTFE macroporous hollow fiber membrane structure, the pore diameter of the macroporous hollow fiber membrane is 50-100mu m, the inlaying body is a PVDF asymmetric porous membrane, and the pore diameter of the PVDF asymmetric porous membrane is 0.01-0.1 mu m. The prepared PTFE hollow fiber membrane composite membrane is of an asymmetric structure and has the advantages of being high in filtering precision, porosity, flux and strength and high in anti-pollution performance.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to an anti-pollution PTFE hollow fiber composite membrane and a preparation method thereof. Background Art

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

[0003] However, PTFE is difficult to process. Currently, commercial PTFE hollow fiber membranes are mostly prepared by a paste extrusion and stretching process. The pore structure is a stretched long strip symmetrical structure. Compared with the asymmetric round hole hollow fiber membrane, the stretched strip symmetrical pore structure has a larger pore size and strong hydrophobicity. It has the disadvantages of poor anti-pollution and poor treatment effect during use.

[0004] In the prior art, a Chinese patent (application number: 201010504784.3, publication number: CN101961608) discloses a method for controlling the pore size of a polytetrafluoroethylene hollow fiber membrane by dipping in a fluorine-containing concentrated solution. The steps of the method are as follows: (1) preparing a coating impregnation solution using a water-dispersible fluorine-containing dispersed concentrated solution; (2) dipping the polytetrafluoroethylene hollow fiber membrane into the above-mentioned coating impregnation solution; (3) drying the impregnated polytetrafluoroethylene hollow fiber membrane, but the membrane needs to be frequently washed with water and chemicals.

[0005] In the prior art, a Chinese patent (application number: 201980030485.X, publication number: CN112088041) discloses a hollow fiber membrane and a method for manufacturing a hollow fiber membrane. The method is to prepare an asymmetric PTFE hollow fiber membrane by winding a porous filter layer outside a support layer, but the membrane has weak anti-pollution ability. Summary of the invention

[0006] In view of the above deficiencies in the prior art, the present invention provides an anti-pollution PTFE hollow fiber composite membrane and a preparation method thereof. The prepared PTFE hollow fiber membrane composite membrane has an asymmetric structure and has the advantages of high filtration accuracy, high porosity, high flux, high strength and strong anti-pollution performance.

[0007] In order to achieve the above-mentioned purpose and other related purposes, the technical solution provided by the present invention is as follows: A pollution-resistant PTFE hollow fiber composite membrane comprises a PTFE hollow fiber membrane main frame and a PVDF insert embedded in the membrane pores of the main frame, wherein the main frame 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.

[0008] Furthermore, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 50-100 μm.

[0009] Furthermore, the pore size of the membrane of the PVDF insert gradually increases from the outside to the inside, and the outer layer is a high-precision filter layer, which plays a major role in interception and filtration.

[0010] Furthermore, the PVDF insert fills up the membrane pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, adhering tightly and not easily separated.

[0011] In order to achieve the above-mentioned object and other related objects, the present invention also provides a method for preparing any one of the anti-pollution PTFE hollow fiber composite membranes, comprising 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. 25-45% PVDF powder, 40-70% diluent, 0.3-3% dispersant, 0.5-5% hydrophilic nano-silica, added to the reactor in a certain proportion, heated, stirred and mixed to form a PVDF emulsion, the heating temperature is 40-80 degrees, the stirring time is 8-24 hours; S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is immersed in a PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores for a soaking time of 10-60 minutes; S4. The soaked and wetted PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone with a temperature of 140-200 degrees. After the temperature rises and the PVDF is dissolved, it is passed through a temperature zone of 5-20 degrees and rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane filament is extracted and removed to form a porous membrane insert. After drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

[0012] Furthermore, the diluent is one or two of DOP, DBP and triacetin.

[0013] Furthermore, the PVDF powder is prepared by an emulsion method and has a particle size of less than 10 microns.

[0014] Furthermore, the dispersant is sodium polyphosphate or sodium hexametaphosphate.

[0015] Furthermore, the hydrophilic nano-silica has a particle size of 10-20 nanometers.

[0016] The present invention has the following positive effects: 1. The PTFE hollow fiber composite membrane of the present invention is composed of a main skeleton and an insert body. The main skeleton adopts a sintering and stretching method to prepare a PTFE macroporous hollow fiber membrane structure. The insert body is a PVDF porous membrane structure. The main skeleton plays a supporting role, and the PVDF porous membrane plays a filtering role. The PVDF porous membrane is prepared according to the phase separation principle. The membrane pore size and structure can be adjusted by the phase separation process parameters. The prepared membrane pore size increases from the outside to the inside, and has an asymmetric structure. When filtering, pollutants larger than the outer layer interception pore size are trapped on the surface of the membrane silk and cannot enter the interior, thereby not easily polluting the membrane pores. During operation, it is also easy to wash pollutants in the membrane pores when backwashing with water, so there is no need for frequent water washing and drug washing.

[0017] 2. The PTFE hollow fiber composite membrane of the present invention not only has the high strength of the PTFE hollow fiber membrane, but also has the high porosity and high precision of the thermally induced phase separation of PVDF, and the membrane structure is an asymmetric structure. Since the PVDF membrane-making liquid is an emulsion before dissolution, it first enters the membrane pores of PTFE and then dissolves and separates. The PVDF membrane fills the membrane pores of PTFE and is coated on the fiber, adhering tightly and not easy to separate. The problem that the PTFE stretch membrane is difficult to prepare an asymmetric pore structure is solved, and it has higher porosity and filtration accuracy, and has higher strength than the PVDF hollow fiber membrane.

[0018] 3. The preparation method of the PTFE hollow fiber composite membrane of the present invention introduces a phase separation preparation process, which greatly increases the ways to control the membrane pore size and pore structure, and broadens the process ideas for hydrophilic modification of PTFE membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of the process of preparing the anti-pollution PTFE hollow fiber composite membrane. DETAILED DESCRIPTION

[0020] The following is a description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, including various details of the embodiments of the present disclosure to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0021] Example 1: Figure 1 As shown, a PTFE hollow fiber membrane with a pore size of 70 μm and a PTFE macroporous hollow fiber membrane were prepared by controlling the stretching ratio and other processes; 37% PVDF powder, 60% DOP, 2% sodium polyphosphate and 1% hydrophilic nano-silicon dioxide were added into the reactor according to weight ratio, heated, stirred and mixed to form PVDF emulsion, the heating temperature was 50 degrees and the stirring time was 12 hours; The PTFE macroporous hollow fiber membrane was immersed in PVDF emulsion, and the PVDF emulsion penetrated into the pores of the PTFE membrane for 30 minutes; The soaked and wetted PTFE hollow fiber membrane is first passed through a heating area with a temperature of 160 degrees. After the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 10 degrees and rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane filament is removed by ethanol extraction to form a porous membrane insert. After drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

[0022] In this embodiment, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 50 μm.

[0023] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.02 μm.

[0024] In this embodiment, the PVDF insert is an asymmetric porous membrane, the pore size of which increases gradually from the outside to the inside, and the outer layer is a high-precision filter layer, which plays a major role in interception and filtration.

[0025] In this embodiment, the PVDF insert fills up the membrane pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, adhering tightly and not easily separated.

[0026] Example 2: An anti-pollution PTFE hollow fiber composite membrane, which is different from Example 1 in that the diluent is DBP.

[0027] In this embodiment, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 60 μm.

[0028] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.03 μm.

[0029] Example 3: An anti-pollution PTFE hollow fiber composite membrane. The difference from Example 1 is that the soaked wet PTFE hollow fiber membrane first passes through a heating area with a temperature of 150 degrees, and then passes through an area with a temperature of 5 degrees after the temperature rises and the PVDF is dissolved.

[0030] In this embodiment, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 70 μm.

[0031] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.04 μm.

[0032] Example 4: Figure 1 As shown, a method for preparing the anti-pollution PTFE hollow fiber composite membrane comprises the following steps: S1. A PTFE macroporous hollow fiber membrane with a pore size of 80 μm was prepared by controlling the stretching ratio process; S2. 45% PVDF powder, 60% diluent, 3% dispersant, 5% hydrophilic nano-silica were added to the reactor in a certain proportion, heated, stirred and mixed to form a PVDF emulsion, the heating temperature was 80 degrees, and the stirring time was 10 hours; S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is immersed in a PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores for 30 minutes; S4. The soaked and wetted PTFE hollow fiber membrane obtained in step S3 is first passed through a heating area with a temperature of 200 degrees. After the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 20 degrees and rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane filaments is extracted and removed to form a porous membrane insert. After drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

[0033] In this embodiment, the diluents are DOP and triacetin.

[0034] In this embodiment, the PVDF powder is prepared by an emulsion method, and the particle size is less than 10 microns.

[0035] In this embodiment, the dispersant is sodium hexametaphosphate.

[0036] In this embodiment, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 80 μm.

[0037] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.06 μm.

[0038] Example 5: Figure 1 As shown, a method for preparing the anti-pollution PTFE hollow fiber composite membrane comprises the following steps: S1. A PTFE macroporous hollow fiber membrane with a pore size of 90 μm was prepared by controlling the stretching ratio process; S2. 25% PVDF powder, 50% diluent, 2% dispersant, 3% hydrophilic nano-silica were added to the reactor in a certain proportion, heated, stirred and mixed to form a PVDF emulsion, the heating temperature was 70 degrees, and the stirring time was 9 hours; S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is immersed in a PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores for 20 minutes; S4. The soaked and wetted PTFE hollow fiber membrane obtained in step S3 is first passed through a heating area with a temperature of 150 degrees. After the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 15 degrees and rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane filament is extracted and removed to form a porous membrane insert. After drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

[0039] In this embodiment, the diluents are DBP and triacetin.

[0040] In this embodiment, the PVDF powder is prepared by an emulsion method, and the particle size is less than 10 microns.

[0041] In this embodiment, the dispersant is sodium polyphosphate.

[0042] In this embodiment, the membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 90 μm.

[0043] In this embodiment, the PVDF insert is a PVDF asymmetric porous membrane with a pore size of 0.09 μm.

[0044] Membrane fiber performance test results:

[0045] From the test results, it can be seen that the pore structure of the modified PTFE composite membrane is an asymmetric structure with high filtration accuracy, high porosity, high flux and high strength. The membrane with this structure has better anti-pollution performance.

[0046] In summary, the PTFE hollow fiber membrane composite membrane prepared by the present invention has an asymmetric structure and has the advantages of high filtration accuracy, high porosity, high flux, high strength and strong anti-pollution performance.

[0047] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

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

2. The anti-pollution PTFE hollow fiber composite membrane according to claim 1, characterized in that: The membrane pore diameter of the PTFE hollow fiber membrane main body skeleton is 50-100 μm.

3. The anti-pollution PTFE hollow fiber composite membrane according to claim 1, characterized in that: The membrane 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 a major role in interception and filtration.

4. The anti-pollution PTFE hollow fiber composite membrane according to claim 1, characterized in that: The PVDF insert fills up the membrane pores of the PTFE macroporous hollow fiber membrane structure and covers the fibers of the main skeleton, and is tightly adhered and difficult to separate.

5. A method for preparing the anti-pollution PTFE hollow fiber composite membrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. A PTFE macroporous hollow fiber membrane with a pore size of 50-100 μm was prepared by controlling the stretching ratio process; S2. 25-45% PVDF powder, 40-70% diluent, 0.3-3% dispersant, 0.5-5% hydrophilic nano-silica, added to the reactor in a certain proportion, heated, stirred and mixed to form a PVDF emulsion, the heating temperature is 40-80 degrees, the stirring time is 8-24 hours; S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is immersed in a PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores for a soaking time of 10-60 minutes; S4. The soaked and wetted PTFE hollow fiber membrane obtained in step S3 is first passed through a heating zone with a temperature of 140-200 degrees. After the temperature rises and the PVDF is dissolved, it is passed through a temperature zone of 5-20 degrees and rapidly cooled to cause phase separation of the PVDF. After cooling and phase separation, the diluent in the membrane filament is extracted and removed to form a porous membrane insert. After drying, an anti-pollution 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 an emulsion method and has a particle size of less than 10 microns.

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-silicon dioxide particle size is 10-20 nanometers.

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