A conductive hollow fiber membrane, its preparation method and membrane module

Abstract

The present invention provides a method for preparing a conductive hollow fiber membrane, which comprises the following steps: adding a functional monomer into a solvent, mixing to obtain a functional monomer solution, adding a vinylimidazole-based ionic liquid into the functional monomer solution, and stirring evenly under heating conditions to obtain a modified solution; immersing a lining support layer into the modified solution, incubating at room temperature, then transferring the lining support layer to a weak acid buffer solution for in-situ polymerization, and after the reaction is completed, washing and drying to obtain a conductive lining support layer; performing spinning, obtaining membrane filaments through coagulation bath phase inversion, and successively soaking the membrane filaments in pure water and glycerol, and drying to obtain the product. The conductive hollow fiber membrane of the present invention has high conductivity, high flux and high mechanical strength. By using it to construct a membrane module assisted by a weak electric field and applying it to water treatment, membrane fouling can be greatly alleviated.

Description

Technical Field

[0001] The present invention belongs to the field of hollow fiber membranes, and in particular relates to a conductive hollow fiber membrane, a preparation method thereof, and a membrane module. Background Art

[0002] Membrane separation technology has been widely used in water treatment fields such as drinking water purification, industrial water treatment, wastewater treatment and reuse, and seawater desalination because of its functions of separation, concentration, purification, etc., as well as the characteristics of energy conservation, high efficiency, and environmental protection. It is an important technology to solve problems such as water resource shortage and environmental pollution. However, traditional membrane separation technology still has problems such as serious membrane fouling, resulting in a decline in separation efficiency, and cannot effectively exert its performance. Electrochemical technology has been widely used in the water treatment field because of its ability to efficiently remove pollutants. Coupling electrochemical technology with membrane separation and utilizing electrostatic repulsion, electrochemical oxidation and other effects is expected to alleviate the membrane fouling problem in the application process of membrane separation technology, and it is a new type of membrane separation technology that is environmentally friendly and has great practical application potential. At present, the method of constructing a conductive membrane usually modifies the outer layer of the membrane with conductive materials (such as polypyrrole, polyaniline, carbon nanotubes, etc.) to improve its conductivity, but it is easy to cause membrane pore blockage, resulting in a significant decrease in water production flux. Summary of the Invention

[0003] In view of this, the present invention aims to overcome the defects in the prior art and provides a conductive hollow fiber membrane, a preparation method thereof, and a membrane module.

[0004] To achieve the above object, the technical solution of the present invention is realized as follows:

[0005] A preparation method of a conductive hollow fiber membrane includes the following steps:

[0006] Step 1: Add a functional monomer to a solvent, mix to obtain a functional monomer solution, add a vinylimidazole-based ionic liquid to the functional monomer solution, and stir evenly under heating conditions to obtain a modified solution;

[0007] Step 2: Immerse the inner lining support layer in the modified solution, incubate at room temperature, then transfer the inner lining support layer to a weak acid buffer solution for in-situ polymerization, and after the reaction is completed, wash and dry to obtain a conductive inner lining support layer;

[0008] Step 3: Spin the conductive inner lining support layer, obtain membrane filaments through coagulation bath phase inversion, and soak the membrane filaments in pure water and glycerol in sequence, and dry to obtain a conductive hollow fiber membrane with an inner lining structure.

[0009] The preparation principle of the conductive hollow fiber membrane mainly lies in: using functional monomers to form a layer of conductive polymer on the inner lining support layer through in-situ polymerization deposition by an oxidant (ferric chloride or ammonium persulfate) under weak acid conditions. The incorporation of ionic liquid, on the one hand, acts as a green solvent to improve the dispersion degree of functional monomers; on the other hand, it acts as a comonomer to copolymerize with pyrrole to form a conductive cross-linked structure, and at the same time, the ions in the ionic liquid further promote conductivity. Subsequently, through wet spinning technology, a hollow fiber membrane with an inner lining of conductivity is prepared.

[0010] Furthermore, the functional monomer in the functional monomer solution in Step 1 is pyrrole; the concentration of the functional monomer solution in Step 1 is 10 - 50 g / L; the temperature of the heating step in Step 1 is 10 - 50 °C.

[0011] Furthermore, the vinylimidazole-based ionic liquid in Step 1 is at least one of 1-butyl-3-vinylimidazole chloride, 1-butyl-3-vinylimidazole, or 1-butyl-3-vinylimidazole tetrafluoroborate; the mass ratio of the vinylimidazole-based ionic liquid to the functional monomer is 1:1 - 5.

[0012] Furthermore, the time of the incubation step in Step 2 is 30 - 60 min.

[0013] Furthermore, the weak acid buffer solution in Step 2 contains an oxidant, the concentration of the oxidant is 10 - 50 g / L; the oxidant is ferric chloride and / or ammonium persulfate; the time of the in-situ polymerization step in Step 2 is 30 - 60 min.

[0014] Furthermore, the spinning solution used in the spinning step in Step 3 is a polyvinylidene fluoride spinning solution, the injection pump speed of the spinning solution is 1 - 50 rpm / min, and the winding roller traction speed of the inner lining is 1 - 30 m / min.

[0015] A conductive hollow fiber membrane prepared by using the above preparation method.

[0016] A weak electric field-assisted membrane module constructed by using the conductive hollow fiber membrane, including a metal mesh and a conductive hollow fiber membrane filament bundle. The metal mesh and the conductive hollow fiber membrane filament bundle are connected to a DC power supply to form a weak electric field; wherein, the anode of the weak electric field is the metal mesh, and the cathode is the conductive hollow fiber membrane; the conductive hollow fiber membrane filament bundle is composed of a plurality of the conductive hollow fiber membranes.

[0017] Furthermore, the metal mesh is located outside the conductive hollow fiber membrane filament bundle; the material of the metal mesh is titanium or stainless steel.

[0018] Furthermore, the bottom of the conductive hollow fiber membrane filament bundle is a closed structure; water collection pipe fittings are arranged at both ends of the conductive hollow fiber membrane filament bundle, and a water outlet is provided on the water collection pipe fitting located at the upper end. The bottom of the conductive hollow fiber membrane filament bundle is sealed with epoxy resin.

[0019] In the present invention, a conductive polymer doped with a vinylimidazole-based ionic liquid is used as a modification material to modify the inner lining support layer of the hollow fiber membrane filament. A conductive hollow fiber membrane is prepared through a wet spinning process, and is conductively encapsulated and assembled into a component to construct a membrane component capable of combining weak electric field assistance and membrane separation functions, which is used to alleviate membrane fouling during the water treatment process and enhance the pollutant removal efficiency; the conductive polymer is formed by oxidative polymerization of functional monomers to form a copolymer, which is co-deposited on the inner lining support layer to improve the conductivity of the hollow fiber membrane.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The conductive hollow fiber membrane described in the present invention uses low-cost, easily obtainable, and environmentally friendly functional monomers to form a conductive polymer (such as polypyrrole, polyaniline, etc.) through a simple one-step oxidative polymerization reaction, and in-situ deposits it on the inner lining support layer to make it conductive; the incorporation of ionic liquid further promotes the polymerization reaction to form a copolymer of pyrrole and ionic liquid, forming a stable conductive coating on the surface of the inner lining support layer, and the modification has little influence on the morphology and size of the inner lining support layer, and can be well connected with the existing wet spinning membrane preparation process.

[0022] The conductive hollow fiber membrane of the present invention has good conductivity and high water production flux because the conductive coating is modified on the inner lining support layer with large pores instead of the external membrane surface, and the water production flux is better maintained, breaking through the "trade-off effect" between conductivity and permeability; in addition, the internal conductive coating is not interfered by pollutants in the external water body and can maintain long-term conductive stability.

[0023] The conductive hollow fiber membrane described in the present invention has high conductivity, high flux, and high mechanical strength. Using it to construct a membrane component assisted by a weak electric field and applying it to water treatment will greatly alleviate membrane fouling, reduce the number of membrane cleanings, extend the membrane service life, and improve the separation and removal efficiency.

[0024] Using the conductive hollow fiber membrane filament described in the present invention as an electrode to construct a conductive membrane component, a weak electric field is formed by applying an external DC power supply, and electrostatic repulsion and electro-oxidation of pollutants can occur on the membrane surface, significantly alleviating membrane fouling, reducing the number of membrane cleanings, and extending the membrane service life; the structure of the conductive membrane component is reasonable and compact, easy to modularize and assemble, and can realize membrane separation under the assistance of a weak electric field, and is applicable to different specifications and different water treatment operation modes.

[0025] The preparation process of the conductive hollow fiber membrane described in the present invention is simple, with low production cost, capable of large-scale industrial production, and suitable for various water treatment scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagrams of the membrane module according to the embodiments of the present invention: Among them, Figure a is the structural diagram of the membrane module, Figure b is the internal structural diagram of the membrane module, and Figure c is the cross-sectional structural diagram of the membrane module;

[0027] Figure 2 Schematic diagram of the conductive hollow fiber membrane according to the embodiments of the present invention;

[0028] Figure 3 Scanning electron microscope images of the conductive hollow fiber membrane according to the embodiments of the present invention: Among them, Figure a is the surface of the unmodified inner liner, Figure b is the surface of the modified inner liner, and Figure c is the cross-section of the conductive hollow fiber membrane;

[0029] Figure 4 Schematic diagrams of the conductive inner liner support layer according to the embodiments of the present invention: Among them, Figure a is the original inner liner support layer, and Figure b is the conductive inner liner support layer;

[0030] Figure 5 Comparison diagrams of the conductivity and flux of the conductive hollow fiber membranes according to the embodiments and comparative examples of the present invention.

[0031] Description of the reference numerals:

[0032] 1, water outlet; 2, collecting pipe fitting; 3, metal mesh; 4, conductive hollow fiber membrane filament bundle; 5, wire; 6, inner liner support layer; 7, conductive modification layer; 8, spinning solution layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0034] The present invention will be described in detail below with reference to the embodiments.

[0035] Embodiment 1

[0036] A method for preparing a conductive hollow fiber membrane, comprising the following steps:

[0037] (1) Add 1-butyl-3-vinylimidazolium tetrafluoroborate ionic liquid (the mass ratio of pyrrole to ionic liquid is 3) to the 50 g / L aqueous pyrrole solution respectively, and stir and mix evenly at room temperature to obtain a modification solution;

[0038] (2) Immerse the inner lining support layer 6 in the above-mentioned modified liquid for 3 h to fully contact it with the mixed liquid. Then, immerse the soaked inner lining support layer 6 in a ferric chloride solution containing 30 g / L. After fully reacting at room temperature for 1 h, rinse the unreacted reagents with water and air-dry naturally to form a conductive modification layer 7 on the outer side of the inner lining support layer 6, thus obtaining a conductive inner lining support layer 6;

[0039] (3) Wind the dried conductive inner lining around a winding roller for spinning. Use a wet spinning machine for spinning. The spinning solution is polyvinylidene fluoride. Control the speed of the feed pump at 10 mL / min and the traction speed of the winding roller at 20 m / min. Obtain membrane filaments through phase inversion in a coagulation bath, and form a spinning solution layer 8 on the outer side of the conductive modification layer 7. Immerse the membrane filaments in pure water for 48 h, and change the water several times in the middle to wash away the residual organic solvents. Then transfer them to glycerol and immerse for 72 h, and then dry at room temperature to finally obtain a conductive hollow fiber membrane.

[0040] As Figure 1-2 shown, a weak electric field-assisted membrane module constructed using the above-mentioned conductive hollow fiber membrane includes a titanium metal mesh and a conductive hollow fiber membrane filament bundle 4. A weak electric field is formed by connecting the titanium metal mesh and the conductive hollow fiber membrane filament bundle 4 to a DC power supply; wherein, the anode of the weak electric field is the titanium metal mesh, and the cathode is the conductive hollow fiber membrane; the conductive hollow fiber membrane filament bundle 4 is composed of a plurality of the above-mentioned conductive hollow fiber membranes.

[0041] The above-mentioned metal mesh 3 is located on the outer side of the conductive hollow fiber membrane filament bundle 4. Water collecting pipe fittings 2 are arranged at both ends of the conductive hollow fiber membrane filament bundle 4, and a water outlet 1 is provided on the water collecting pipe fitting 2 at the upper end. The bottom of the conductive hollow fiber membrane filament bundle 4 is sealed with epoxy resin.

[0042] Modify the inner and outer sides of the root of the conductive hollow fiber membrane filament bundle 4 simultaneously with polypyrrole to connect the conductive layer of the inner lining of the membrane filament with the outer layer of the root membrane filament, and then connect and lead out a wire 5 through a conductive adhesive. Using the conductive hollow fiber filament bundle as the cathode and the metal titanium mesh fixed outside the membrane module as the anode, connect them to the negative and positive poles of an external power supply respectively to provide a DC voltage for the entire conductive membrane module. The structural schematic diagram of the conductive membrane module is as Figure 1 shown.

[0043] The inner lining support layer 6 before and after modification is as Figure 4 shown, in which a black coating is formed on the surface of the modified inner lining support layer 6. This is because pyrrole and ionic liquid are rapidly oxidized by ferric chloride under weak acid to generate a black conductive copolymer of pyrrole and ionic liquid.

[0044] As Figure 3As shown, the surface of the modified inner lining is rougher, and a layer of clustered polymers covers the surface, indicating that the synthesis of conductive polypyrrole and the formation of a composite polymer with ionic liquid are deposited on the surface of the inner lining. From the cross-section of the conductive hollow fiber membrane, an obvious layered interface can be seen. The outermost layer is the polyvinylidene fluoride membrane layer, and the inner part is the hollow inner lining support layer 6, with the conductive polymer layer in the middle.

[0045] Example 2

[0046] The difference from Example 1 is only that: the concentration of the pyrrole aqueous solution is 25 g / L.

[0047] Comparative Example 1

[0048] The difference from Example 1 is only that: the concentration of the pyrrole aqueous solution is 5 g / L.

[0049] Comparative Example 2

[0050] The difference from Example 1 is only that: the functional monomer is aniline.

[0051] Comparative Example 3

[0052] The difference from Example 1 is only that: the functional monomer is thiophene.

[0053] Comparative Example 4

[0054] The difference from Example 1 is only that: the ionic liquid is 1-ethyl-3-methylimidazolium ionic liquid.

[0055] Comparative Example 5

[0056] The difference from Example 1 is only that: the conductive modification layer 7 is modified on the outer side of the membrane filament surface (i.e., the outer side of the spinning solution layer 8).

[0057] The conductivity of the conductive hollow fiber membranes prepared in each example and comparative example was tested, and the results are as Figure 5 shown. The conductivity of the blank membrane filament is 0, indicating that the blank membrane filament is non-conductive. The hollow fiber membrane filaments modified with polypyrrole and ionic liquid all have conductivity, and the conductivity increases with the increase of the pyrrole concentration. When the pyrrole concentration is 50 g / L, the conductivity is 3.6 S / m, indicating that more pyrrole participates in the polymerization reaction to form conductive polypyrrole, and whether it is modified on the membrane surface or the inner lining support layer 6, the conductivity difference is not significant; compared with the conductive polymers formed by aniline and thiophene functional monomers, their conductivities are both lower than that of the pyrrole monomer, indicating that polypyrrole has better conductivity; similarly, when a non-vinyl ionic liquid is selected to participate in the reaction, the conductivity decreases significantly, indicating that the vinyl ionic liquid participates in the reaction during the polymerization process and co-oxidizes with the functional monomer to form a conductive copolymer, thus proving the feasibility of preparing conductive hollow fiber membranes by modifying the inner lining with polypyrrole.

[0058] Flux tests were conducted on the membrane modules constructed from the conductive hollow fiber membrane filaments prepared in each example and comparative example. The results are as Figure 5 shown. It was found that the water production flux of the blank membrane module was relatively high. After the polypyrrole modification of the inner lining support layer 6, the flux decreased. Moreover, as the pyrrole concentration increased, the flux decreased more significantly, indicating that the formed conductive polymer would, to a certain extent, affect the pore size of the inner lining layer, resulting in a decrease in water production capacity. When the pyrrole concentration was 25 g / L, the flux could reach 60% of the original flux, which was within an acceptable range. However, when the conductive layer was coated on the membrane surface, the flux was almost 0, indicating that the modification of the conductive coating on the membrane surface completely blocked the membrane pores. Comparing the aniline and thiophene functional monomers, the flux was also significantly weaker than that of pyrrole. Aniline and thiophene also underwent copolymerization with the ionic liquid under the oxidant. Similarly, the use of non-vinyl ionic liquids also showed a high flux, indicating that complete polymerization did not occur.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a conductive hollow fiber membrane, characterized in that: The steps include: Step 1 is to add a functional monomer into a solvent, mix to obtain a functional monomer solution, add a vinyl imidazole ionic liquid into the functional monomer solution, and stir evenly under heating conditions to obtain a modified solution; Step 2 is to immerse the lining support layer in the modified solution, incubate at room temperature, then transfer the lining support layer to a weak acid buffer solution for in-situ polymerization, and after the reaction is completed, wash and dry to obtain a conductive lining support layer; Step 3 is to spin the conductive lining support layer, obtain membrane fibers through phase transformation in a coagulation bath, soak the membrane fibers in pure water and glycerol in turn, and obtain a conductive hollow fiber membrane with a lining structure after drying; The functional monomer in the functional monomer solution in step 1 is pyrrole; and the weak acid buffer solution in step 2 contains an oxidant.

2. The method for preparing a conductive hollow fiber membrane according to claim 1, characterized in that: The concentration of the functional monomer solution in step 1 is 10-50 g / L; the temperature of the heating step in step 1 is 10-50°C.

3. The method for preparing a conductive hollow fiber membrane according to claim 2, characterized in that: The vinyl imidazole ionic liquid in step 1 is at least one of 1-butyl-3-vinylimidazole chloride, 1-butyl-3-vinylimidazole or 1-butyl-3-vinylimidazole tetrafluoroborate; the mass ratio of the vinyl imidazole ionic liquid to the functional monomer is 1:1-5.

4. The method for preparing a conductive hollow fiber membrane according to claim 1, characterized in that: The incubation time in step 2 is 30-60 minutes.

5. The method for preparing a conductive hollow fiber membrane according to claim 1, characterized in that: The concentration of the oxidant is 10-50 g / L; the oxidant is ferric chloride and / or ammonium persulfate; the time of the in-situ polymerization step in step 2 is 30-60 min.

6. The method for preparing a conductive hollow fiber membrane according to claim 1, characterized in that: The spinning solution used in the spinning step in step 3 is polyvinylidene fluoride spinning solution, the speed of the spinning solution injection pump is 1-50rpm / min, and the speed of the winding roller pulling the lining is 1-30m / min.

7. A conductive hollow fiber membrane prepared by the preparation method according to any one of claims 1 to 6.

8. A weak electric field assisted membrane assembly constructed using the conductive hollow fiber membrane according to claim 7, characterized in that: It comprises a metal mesh and a conductive hollow fiber membrane bundle, wherein the metal mesh and the conductive hollow fiber membrane bundle form a weak electric field by an external DC power supply; wherein the anode of the weak electric field is the metal mesh, and the cathode is the conductive hollow fiber membrane; the conductive hollow fiber membrane bundle is composed of a plurality of conductive hollow fiber membranes as described in claim 7.

9. The weak electric field auxiliary membrane assembly according to claim 8, characterized in that: The metal mesh is located outside the conductive hollow fiber membrane bundle; the material of the metal mesh is titanium.

10. The weak electric field auxiliary membrane assembly according to claim 8, characterized in that: The bottom of the conductive hollow fiber membrane bundle is a closed structure; both ends of the conductive hollow fiber membrane bundle are provided with water collecting pipes, and the water collecting pipe located at the upper end is provided with a water outlet.

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