Conductive hollow fiber membrane, preparation method thereof and membrane module

Abstract

The present invention provides a conductive hollow fiber membrane preparation method, which comprises: adding a functional monomer to a solvent, mixing to obtain a functional monomer solution, adding a vinyl imidazole ionic liquid to the functional monomer solution, and uniformly stirring under a heating condition to obtain a modified liquid; immersing a lining support layer into the modification liquid, incubating at room temperature, then transferring the lining support layer into a weak acid buffer solution for in-situ polymerization, and after the reaction is completed, cleaning and drying to obtain a conductive lining support layer; and spinning, carrying out coagulating bath phase inversion to obtain membrane filaments, sequentially soaking the membrane filaments in pure water and glycerol, and drying to obtain the membrane. The conductive hollow fiber membrane disclosed by the invention has high conductivity, high flux and high mechanical strength, and membrane pollution can be greatly relieved when a weak electric field assisted membrane assembly constructed by the conductive hollow fiber membrane is applied to water treatment.

Description

Technical Field

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

[0002] Membrane separation technology is widely used in water treatment fields such as drinking water purification, industrial water treatment, wastewater treatment and reuse, and seawater desalination because of its separation, concentration, purification and other functions as well as its energy-saving, high efficiency and environmental protection. It is an important technology to solve problems such as water shortage and environmental pollution. However, traditional membrane separation technology still has serious membrane pollution, resulting in reduced separation efficiency and other problems, and cannot effectively exert its performance. Electrochemical technology is widely used in the field of water treatment 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 pollution problem in the application of membrane separation technology. It is an environmentally friendly and new membrane separation technology with 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 proposes a conductive hollow fiber membrane and a preparation method and a membrane assembly thereof.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows: A method for preparing a conductive hollow fiber membrane comprises the following steps: 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.

[0005] The preparation principle of the conductive hollow fiber membrane is mainly to use the functional monomer to form a conductive polymer layer on the inner lining support layer through in-situ polymerization under weak acid conditions of an oxidant (ferric chloride or ammonium persulfate). The addition of ionic liquid, on the one hand, acts as a green solvent to improve the dispersion of the functional monomer; on the other hand, it copolymerizes with pyrrole as a comonomer to form a conductive cross-linked structure, and the ions in the ionic liquid further promote conductivity. Subsequently, a conductive hollow fiber membrane with an inner lining is prepared through wet spinning technology.

[0006] 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; and the temperature of the heating step in step 1 is 10-50°C.

[0007] Furthermore, 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.

[0008] Furthermore, the incubation time in step 2 is 30-60 minutes.

[0009] Furthermore, the weak acid buffer solution in step 2 contains an oxidant, and the concentration of the oxidant is 10-50 g / L; the oxidant is ferric chloride and / or ammonium persulfate; and the time of the in-situ polymerization step in step 2 is 30-60 min.

[0010] Furthermore, 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.

[0011] A conductive hollow fiber membrane prepared by using the preparation method.

[0012] A weak electric field auxiliary membrane component constructed using the conductive hollow fiber membrane comprises a metal mesh and a conductive hollow fiber membrane bundle, wherein the metal mesh and the conductive hollow fiber membrane bundle are connected to an external 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; and the conductive hollow fiber membrane bundle is composed of a plurality of the conductive hollow fiber membranes.

[0013] Furthermore, the metal mesh is located outside the conductive hollow fiber membrane bundle; the metal mesh is made of titanium or stainless steel.

[0014] Furthermore, 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 pipes at the upper end are provided with a water outlet. The bottom of the conductive hollow fiber membrane bundle is sealed with epoxy resin.

[0015] The present invention uses a conductive polymer doped with vinylimidazole ionic liquid as a modified material to modify the inner lining support layer of the hollow fiber membrane, prepares a conductive hollow fiber membrane through a wet spinning process, and performs conductive packaging and assembly to construct a membrane component that can realize the combination of weak electric field assistance and membrane separation function, which is used to alleviate membrane pollution in the water treatment process and enhance the pollutant removal efficiency; the conductive polymer is a copolymer formed by oxidative polymerization of functional monomers to jointly deposit an inner lining support layer, which is used to improve the conductivity of the hollow fiber membrane.

[0016] Compared with the prior art, the present invention has the following advantages: The conductive hollow fiber membrane described in the present invention utilizes low-cost, easily available, and environmentally friendly functional monomers through a one-step simple oxidative polymerization reaction to form a conductive polymer (such as polypyrrole, polyaniline, etc.) which is in situ deposited on the 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 lining support layer, and the modification has little effect on the morphology and size of the lining support layer, and can be well connected with the existing wet spinning membrane making process.

[0017] The conductive hollow fiber membrane of the present invention has good conductivity and high water flux. This is because the conductive coating is modified on the inner lining support layer with large pores rather than the external membrane surface, so the water flux is better maintained, breaking through the "trade-off effect" between conductivity and permeability; in addition, the internal conductive coating is not affected by pollutants in the external water body and can maintain long-term conductive stability.

[0018] The conductive hollow fiber membrane described in the present invention has high conductivity, high flux and high mechanical strength. Using it to construct a weak electric field-assisted membrane assembly for use in water treatment will greatly alleviate membrane pollution, reduce the number of membrane cleaning times, extend the membrane service life and improve separation and removal efficiency.

[0019] By using the conductive hollow fiber membrane filaments described in the present invention as electrodes to construct a conductive membrane assembly, a weak electric field is formed by applying an external DC power supply, which can cause electrostatic repulsion and electro-oxidation of pollutants on the membrane surface, significantly alleviating membrane pollution, reducing the number of membrane cleaning times, and extending the service life of the membrane; the conductive membrane assembly has a reasonable and compact structure and is easy to assemble in a modular manner, and can achieve membrane separation under the assistance of a weak electric field, and is suitable for different specifications and different water treatment operation modes.

[0020] The conductive hollow fiber membrane of the present invention has a simple preparation process, low production cost, can be industrially mass-produced, and is suitable for application in various water treatment scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the membrane assembly according to the embodiment of the present invention: wherein, Figure a is a structural diagram of the membrane assembly, Figure b is an internal structural diagram of the membrane assembly, and Figure c is a cross-sectional structural diagram of the membrane assembly; Figure 2 is a schematic diagram of a conductive hollow fiber membrane according to an embodiment of the present invention; Figure 3 The scanning electron microscope images of the conductive hollow fiber membrane according to the embodiment of the present invention are shown in FIG. a, FIG. b is the surface of the unmodified inner liner, FIG. c is the cross section of the conductive hollow fiber membrane; Figure 4 Schematic diagram of the conductive lining support layer according to an embodiment of the present invention: wherein, Figure a is the original lining support layer, and Figure b is the conductive lining support layer; Figure 5 It is a comparison chart of the conductivity and flux of the conductive hollow fiber membrane described in the embodiment of the present invention and the comparative example.

[0022] Description of reference numerals: 1. Water outlet; 2. Water collecting pipe; 3. Metal mesh; 4. Conductive hollow fiber membrane bundle; 5. Conducting wire; 6. Lining support layer; 7. Conductive modified layer; 8. Spinning liquid layer. DETAILED DESCRIPTION

[0023] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0024] The present invention will be described in detail below with reference to the embodiments.

[0025] Example 1 A method for preparing a conductive hollow fiber membrane comprises the following steps: (1) adding 1-butyl-3-vinylimidazolium tetrafluoroborate ionic liquid (the mass ratio of pyrrole to ionic liquid is 3) to 50 g / L pyrrole aqueous solution, stirring and mixing at room temperature to obtain a modified solution; (2) soaking the inner lining support layer 6 in the modified solution for 3 hours to make it fully contact with the mixed solution, then soaking the inner lining support layer 6 in a 30g / L ferric chloride solution, and fully reacting it at room temperature for 1 hour, then washing the unreacted reagent with water and naturally drying it, forming a conductive modified layer 7 on the outer side of the inner lining support layer 6, and obtaining a conductive inner lining support layer 6; (3) The dried conductive lining is wound on a winding roller for spinning, and the spinning is carried out using a wet bionic machine. The spinning solution is polyvinylidene fluoride, the feed pump speed is controlled at 10 mL / min, and the winding roller pulling speed is controlled at 20 m / min. After phase transformation in a coagulation bath, membrane filaments are obtained, and a spinning solution layer 8 is formed on the outside of the conductive modified layer 7. The membrane filaments are immersed in pure water for 48 hours, and the water is changed several times in the middle to wash away the residual organic solvent. Subsequently, the membrane filaments are immersed in glycerol for 72 hours and then dried at room temperature to finally obtain a conductive hollow fiber membrane.

[0026] like Figure 1-2 As shown, a weak electric field auxiliary membrane component constructed using the conductive hollow fiber membrane comprises a metal titanium mesh and a conductive hollow fiber membrane bundle 4, wherein the metal titanium mesh and the conductive hollow fiber membrane bundle 4 are connected to an external DC power supply to form a weak electric field; wherein the anode of the weak electric field is the metal titanium mesh, and the cathode is the conductive hollow fiber membrane; the conductive hollow fiber membrane bundle 4 is composed of a plurality of the conductive hollow fiber membranes.

[0027] The metal mesh 3 is located outside the conductive hollow fiber membrane bundle 4. Water collecting pipes 2 are provided at both ends of the conductive hollow fiber membrane bundle 4, and a water outlet 1 is provided on the water collecting pipe 2 at the upper end. The bottom of the conductive hollow fiber membrane bundle 4 is sealed with epoxy resin.

[0028] The inner and outer sides of the root of the conductive hollow fiber membrane bundle 4 are modified with polypyrrole at the same time, so that the conductive layer of the membrane lining is connected to the outer layer of the root membrane, and then the lead wire 5 is connected through a conductive glue. The conductive hollow fiber bundle is used as the cathode, and the metal titanium mesh fixed outside the membrane assembly is used as the anode, which is connected to the negative and positive electrodes of the external power supply respectively to provide a DC voltage for the entire conductive membrane assembly. The schematic diagram of the conductive membrane assembly structure is shown in FIG. Figure 1 shown.

[0029] The lining support layer 6 before and after modification is as follows Figure 4 As shown, a black coating is formed on the surface of the modified liner support layer 6, which 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.

[0030] like Figure 3 As shown in the figure, the surface of the modified liner is rougher and covered with a layer of clustered polymer, which indicates that the synthesis of conductive polypyrrole and the formation of composite polymer with ionic liquid are deposited on the surface of the liner. The cross section of the conductive hollow fiber membrane shows an obvious stratified interface, with the outermost layer being the polyvinylidene fluoride membrane layer and the inner layer being the hollow liner support layer 6, with the conductive polymer layer located in the middle.

[0031] Example 2 The only difference from Example 1 is that the concentration of the pyrrole aqueous solution is 25 g / L.

[0032] Comparative Example 1 The only difference from Example 1 is that the concentration of the pyrrole aqueous solution is 5 g / L.

[0033] Comparative Example 2 The only difference from Example 1 is that the functional monomer is aniline.

[0034] Comparative Example 3 The only difference from Example 1 is that the functional monomer is thiophene.

[0035] Comparative Example 4 The only difference from Example 1 is that the ionic liquid is a 1-ethyl-3-methylimidazole ionic liquid.

[0036] Comparative Example 5 The only difference from Example 1 is that the conductive modified layer 7 is modified on the outside of the membrane fiber surface (ie, the outside of the spinning solution layer 8).

[0037] The conductivity of the conductive hollow fiber membranes prepared in each embodiment and comparative example was tested, and the results are as follows: Figure 5 As shown, the conductivity of the blank membrane filament is 0, indicating that the blank membrane filament is not conductive, while the hollow fiber membrane filaments modified by polypyrrole and ionic liquid are conductive, and the conductivity increases with the increase of pyrrole concentration. When the pyrrole concentration is 50g / L, the conductivity is 3.6S / m, indicating that more pyrrole participates in the polymerization reaction to form conductive polypyrrole, and no matter it is modified on the membrane surface or the lining support layer 6, the conductivity is not much different; compared with aniline and thiophene functional monomers to form conductive polymers, their conductivity is lower than that of pyrrole monomers, indicating that polypyrrole has better conductivity; similarly, when non-vinyl ionic liquids are selected to participate in the reaction, the conductivity decreases significantly, indicating that vinyl ionic liquids participate in the reaction during the polymerization process and are oxidized together with functional monomers to form conductive copolymers, thereby proving the feasibility of using polypyrrole modified linings to prepare conductive hollow fiber membranes.

[0038] The flux test of the membrane assembly constructed by the conductive hollow fiber membrane prepared in each embodiment and comparative example was carried out. The results are as follows: Figure 5As shown, it was found that the water production flux of the blank membrane component was relatively high. After the inner lining support layer was modified with 6 polypyrrole, the flux decreased, and with the increase of pyrrole concentration, the flux decreased more significantly, indicating that the formed conductive polymer would affect the pore size of the inner lining layer to a certain extent, 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 conductive coating was modified on the membrane surface and the membrane pores were completely blocked. Compared with aniline and thiophene functional monomers, the flux was also significantly weaker than pyrrole. Aniline and thiophene also copolymerized with ionic liquids in the presence of oxidants. Similarly, using non-vinyl ionic liquids, high flux was also shown, indicating that complete polymerization did not occur.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in 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.

2. The method for preparing a conductive hollow fiber membrane according to claim 1, characterized in that: 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.

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 weak acid buffer solution in step 2 contains an oxidant, and the concentration of the oxidant is 10-50 g / L; the oxidant is ferric chloride and / or ammonium persulfate; and 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 or stainless steel.

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.

Images