Anti-fouling ptf hollow fiber composite membrane and its preparation method

Abstract

The application relates to an anti-pollution PTFE hollow fiber composite membrane and a preparation method thereof, which comprises a PTFE hollow fiber membrane main framework and a PVDF inlay embedded in the membrane holes of the main framework, the main framework is a PTFE macroporous hollow fiber membrane structure, the macroporous pore diameter is 50-100 mu m, and the inlay is a PVDF asymmetric porous membrane with a pore diameter of 0.01-0.1 mu m. The prepared PTFE hollow fiber membrane composite membrane has an asymmetric structure, high filtration precision, high porosity, high flux, high strength and strong anti-pollution performance.

Description

TECHNICAL FIELD

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

[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, and currently commercialized PTFE hollow fiber membranes are mostly prepared by a paste extrusion and stretching process to form holes, and the hole structure is a stretched long strip-shaped symmetrical structure. Compared with a round hole hollow fiber membrane with an asymmetric structure, the stretched long strip-shaped symmetrical hole structure has the disadvantages of larger hole diameter, stronger hydrophobicity, poor anti-pollution property, and poor treatment effect during use.

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

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

[0006] In view of the deficiencies of the above prior art, the present application 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 precision, high porosity, high flux, high strength, and strong anti-pollution performance.

[0007] In order to achieve the above-mentioned purposes and other related purposes, the technical solutions provided by the present application are as follows:

[0008] An anti-pollution PTFE hollow fiber composite membrane comprises a PTFE hollow fiber membrane main framework and a PVDF inlay body embedded in the membrane holes of the main framework. The main framework is a PTFE macroporous hollow fiber membrane structure, the macropore diameter is 50-100 pm, and the inlay body is a PVDF asymmetric porous membrane with a pore diameter of 0.01-0.1 pm.

[0009] Further, the membrane pore size of the PTFE hollow fiber membrane body framework is 50-100 μm.

[0010] Further, the membrane pore size of the PVDF inlay gradually increases from outside to inside, the outer layer is a high-precision filter layer, which plays a main interception filtering role.

[0011] Further, the PVDF inlay fills the membrane pores of the PTFE macroporous hollow fiber membrane structure and is coated on the fibers of the body framework, and is tightly adhered and not easy to separate.

[0012] In order to achieve the above-mentioned purpose and other related purposes, the application also provides a preparation method of the anti-pollution PTFE hollow fiber composite membrane.

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

[0014] S2. PVDF powder 25-45%, diluent 40-70%, dispersing agent 0.3-3%, hydrophilic nano-silicon dioxide 0.5-5% are added to a reaction kettle in a certain proportion, and after heating, stirring and mixing, a PVDF emulsion is prepared, the heating temperature is 40-80 degrees, and the stirring time is 8-24 hours;

[0015] S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is soaked in the PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores, and the soaking time is 10-60 minutes;

[0016] S4. The PTFE hollow fiber membrane soaked and wetted in step S3 is first passed through a heating area with a temperature of 140-200 degrees, and after the temperature rises and the PVDF is dissolved, it is passed through a region with a temperature of 5-20 degrees, and the PVDF is rapidly cooled to cause phase separation, and after cooling and phase separation, the diluent in the membrane is removed by extraction to form a porous membrane inlay, and after drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

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

[0018] Further, the PVDF powder is prepared by emulsion method, and the particle size is less than 10 microns.

[0019] Further, the dispersing agent is polyphosphoric acid sodium or sodium hexametaphosphate.

[0020] Further, the particle size of the hydrophilic nano-silicon dioxide is 10-20 nanometers.

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

[0022] 1. The PTFE hollow fiber composite membrane of the present application is composed of a main skeleton and an inlay. The main skeleton is prepared by sintering and stretching to form a PTFE macroporous hollow fiber membrane structure, and the inlay is a PVDF porous membrane structure. The main skeleton serves as a support, and the PVDF porous membrane serves as a filter. The PVDF porous membrane is prepared by phase separation principle, and the membrane pore size and structure can be adjusted by phase separation process parameters. The prepared membrane has a gradually increasing pore size from outside to inside, and has an asymmetric structure. During filtration, pollutants larger than the outer layer retention pore size are retained on the surface of the membrane filament and cannot enter the interior, so the membrane pores are not easily contaminated. During water backwashing, the pollutants in the membrane pores are also easily washed out, so frequent water washing and chemical washing are not needed.

[0023] 2. The PTFE hollow fiber composite membrane of the present application not only has the high strength of PTFE hollow fiber membrane, but also has the high porosity and high precision of PVDF thermally induced phase separation, and the membrane structure is asymmetric. Since the emulsion before dissolution is first introduced into the membrane pores of PTFE, and then dissolved and phase separated, the PVDF membrane fills the membrane pores of PTFE and is tightly adhered to the fiber, and is not easy to separate. The problem of difficult preparation of asymmetric pore structure of PTFE stretched membrane is solved, and the membrane has higher porosity and filtration precision, and has higher strength than PVDF hollow fiber membrane.

[0024] 3. The preparation method of the PTFE hollow fiber composite membrane of the present application greatly increases the control method of membrane pore size and pore structure by introducing the phase separation preparation process, and widens the hydrophilic modification process idea of PTFE membrane. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a flowchart of the preparation method of the anti-pollution PTFE hollow fiber composite membrane of the present application. DETAILED DESCRIPTION

[0026] Exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, which include various details of the embodiments of the present disclosure to assist in understanding, and should be considered as merely exemplary. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Also, in order to be clear and concise, descriptions of well-known functions and structures are omitted in the following description.

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

[0028] ​PVDF powder 37%, DOP 60%, sodium polyphosphate 2%, hydrophilic nano-silica 1% by weight ratio into the reaction kettle, heated and stirred with mixed into PVDF emulsion, heating temperature is 50 degrees, stirring time is 12 hours;

[0029] The PTFE macroporous hollow fiber membrane is soaked in the PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane holes, and the soaking time is 30 minutes.

[0030] The soaked PTFE hollow fiber membrane is first passed through a heating area with a temperature of 160 degrees, and after the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 10 degrees to rapidly cool and cause the PVDF to phase separate. After cooling and phase separation, the diluent in the membrane filament is extracted with ethanol to remove it, forming a porous membrane inlay. After drying, an anti-pollution PTFE hollow fiber composite membrane is obtained.

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

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

[0033] In this embodiment, the PVDF inlay is an asymmetric porous membrane, and the membrane pore size gradually increases from the outside to the inside. The outer layer is a high-precision filtration layer that plays a major role in retention and filtration.

[0034] In this embodiment, the PVDF inlay fills the membrane pores of the PTFE macroporous hollow fiber membrane structure and is coated on the fibers of the main body framework, adhering tightly and not easily separating.

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

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

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

[0038] Example 3: An anti-pollution PTFE hollow fiber composite membrane, which differs from Example 1 in that the soaked PTFE hollow fiber membrane is first passed through a heating area with a temperature of 150 degrees, and after the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 5 degrees.

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

[0040] In the embodiment, the PVDF inlay is a PVDF asymmetric porous membrane, and the pore size is 0.04 μm.

[0041] Embodiment 4: As shown in the figure, a preparation method of the anti-fouling PTFE hollow fiber composite membrane comprises the following steps: Figure 1

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

[0043] S2. PVDF powder 45%, diluent 60%, dispersant 3%, and hydrophilic nanosilica 5% are added into a reaction kettle in a certain proportion, and after heating, stirring and mixing, a PVDF emulsion is prepared, the heating temperature is 80 degrees, and the stirring time is 10 hours;

[0044] S3. The PTFE macroporous hollow fiber membrane obtained in step S1 is soaked in the PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores, and the soaking time is 30 minutes;

[0045] S4. The PTFE hollow fiber membrane soaked and wetted in step S3 is first passed through a heating area with a temperature of 200 degrees, and after the temperature rises and the PVDF is dissolved, it is passed through a region with a temperature of 20 degrees, and the PVDF is rapidly cooled to cause phase separation. After cooling and phase separation, the diluent in the membrane is removed by extraction to form a porous membrane inlay, and after drying, an anti-fouling PTFE hollow fiber composite membrane is obtained.

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

[0047] In the embodiment, the PVDF powder is prepared by emulsion method, and the particle size is less than 10 microns.

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

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

[0050] In the embodiment, the PVDF inlay is a PVDF asymmetric porous membrane, and the pore size is 0.06 μm.

[0051] Embodiment 5: As shown in the figure, a preparation method of the anti-fouling PTFE hollow fiber composite membrane comprises the following steps: Figure 1

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

[0053] ​​S2. Put PVDF powder 25%, diluent 50%, dispersant 2%, and hydrophilic nano-silica 3% into a reaction kettle in a certain proportion, and prepare a PVDF emulsion after heating, stirring and mixing, the heating temperature is 70 degrees, and the stirring time is 9 hours;

[0054] S3. Soak the PTFE macroporous hollow fiber membrane obtained in step S1 in the PVDF emulsion, and the PVDF emulsion penetrates into the PTFE membrane pores, and the soaking time is 20 minutes;

[0055] 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, and after the temperature rises and the PVDF is dissolved, it is passed through an area with a temperature of 15 degrees, and the PVDF is rapidly cooled to cause phase separation, and after cooling and phase separation, the diluent in the membrane filaments is removed by extraction to form a porous membrane inlay, and after drying, an anti-pollution 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 the particle size is less than 10 microns.

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

[0059] In this embodiment, the membrane pore size of the PTFE hollow fiber membrane main framework is 90 microns.

[0060] In this embodiment, the PVDF inlay is a PVDF asymmetric porous membrane, and the pore size is 0.09 microns.

[0061] The performance test results of the membrane filaments are as follows:

[0062]

[0063] From the test results, it can be seen that the modified PTFE composite membrane has an asymmetric structure, high filtration precision, high porosity, high flux, high strength, and better anti-pollution performance.

[0064] In summary, the PTFE hollow fiber membrane composite membrane prepared by the application has an asymmetric structure, high filtration precision, high porosity, high flux, high strength, and strong anti-pollution performance.

[0065] The above detailed description does not limit the scope of the disclosure. Various modifications, combinations, sub-combinations and alternatives can be made to the detailed description. Any modification, equivalent replacement and improvement etc. made within the spirit and principle of the disclosure shall be included in the scope of the disclosure.

Claims

1. A pollution-resistant PTFE hollow fiber composite membrane, characterized in that: The membrane comprises a PTFE hollow fiber membrane main skeleton and PVDF inserts embedded in the membrane pores of the main skeleton. The main skeleton is a PTFE macroporous hollow fiber membrane structure with macropores having a diameter of 50-100 μm. The PVDF inserts are PVDF asymmetric porous membranes with a pore size of 0.01-0.1 μm. The pore size of the PVDF inserts gradually increases from the outside to the inside, and the outer layer is a high-precision filter layer that plays the main role in interception and filtration. The preparation method of the antifouling PTFE hollow fiber composite membrane 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 according to the weight ratio. 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 at a temperature of 140-200 degrees Celsius. After the PVDF dissolves at the increased temperature, it is then passed through a zone at a temperature of 5-20 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.

2. 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.

3. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The diluent is any one or two of DOP, DBP, and triacetin.

4. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The dispersant is sodium polyphosphate or sodium hexametaphosphate.

5. The antifouling PTFE hollow fiber composite membrane according to claim 1, characterized in that: The hydrophilic nano-silica particles have a particle size of 10-20 nanometers.

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