A method for preparing a hollow fiber membrane with a variable pore size and a coagulation bath used in the method

Abstract

The present invention relates to a method for preparing a hollow fiber membrane, and in particular to a method for preparing a hollow fiber membrane with a variable pore size and a coagulation bath tank used in the method. A coagulation bath tank for preparing a hollow fiber membrane with a variable pore size comprises a main tank body for storing a coagulation bath, a concentration adjustment box for adjusting the concentration of the coagulation bath in the box, and a wire guide component for introducing and leading out hollow fiber membrane filaments, wherein the wire guide component is arranged at the bottom of the main tank body, the concentration adjustment box cover is arranged outside the wire guide component and connected to the bottom of the main tank body, and the top of the concentration adjustment box is located below the liquid level of the coagulation bath in the main tank body. The present invention has a simple structure and is easy to process. On the basis of various equipments in conventional processes, only the coagulation bath tank needs to be added to make a hollow fiber membrane with a variable pore size, which greatly improves the filtering effect of the hollow fiber membrane in sewage treatment with complex pollutant composition. The preparation method of the present invention has a simple process and is easy to operate.

Description

Technical Field

[0001] The invention relates to a method for preparing a hollow fiber membrane, in particular to a method for preparing a hollow fiber membrane with a variable pore size and a coagulation bath tank used in the method. Background Art

[0002] Hollow fiber membrane is a key component in the application of membrane separation technology, which is widely used in water treatment, seawater desalination, biomedicine and other fields. The conventional preparation method of hollow fiber membrane is solution phase transformation method, and its process is as follows: the casting liquid composed of polymer, solvent and pore-forming agent is squeezed into the spinneret under pressure, and the pretreated braided tube is passed through the center of the spinneret at the same time. Under the combined effect of the carrying of the braided tube and pressure, the casting liquid and the braided tube are co-extruded from the spinneret, and the casting liquid is evenly coated on the outer surface of the fiber braided tube. After a period of air bath, the casting liquid and the braided tube are immersed in the coagulation bath for double diffusion: the solvent in the casting liquid diffuses into the coagulation bath and the coagulant in the coagulation bath diffuses into the casting liquid. The gelation process occurs simultaneously on the inside and outside of the membrane. As the double diffusion proceeds, the composition inside the casting liquid changes continuously, the membrane is completely solidified, and microporous through holes are formed on the membrane surface, and finally a hollow fiber membrane is obtained.

[0003] Conventional preparation methods mostly consider aspects such as the stability and uniformity of the coagulation bath of the hollow fiber membrane. Some preparation methods consider ensuring the quality of the hollow fiber membrane molding or improving the quality of the hollow fiber membrane. The pores of the hollow fiber membranes made by these preparation methods are through holes with uniform pore sizes. Such membrane materials are effective in general water treatment applications, but for sewage treatment with more complex pollutant composition, hollow fiber membranes with pore sizes that vary along the axial direction of the hole (i.e., through holes with a cross-section similar to a trumpet mouth) can achieve better filtration effects. Hollow fiber membranes with this microporous structure cannot be prepared by existing conventional equipment and require special preparation equipment and methods. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a hollow fiber membrane with a variable pore size to solve the problems described in the background technology.

[0005] The present invention also aims to provide a coagulation bath for preparing hollow fiber membranes with variable pore sizes.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A coagulation bath tank for preparing a variable pore size hollow fiber membrane comprises a main tank body for storing a coagulation bath liquid, a concentration adjustment box for adjusting the concentration of the coagulation bath liquid in the box, and a wire guide component for introducing and leading out hollow fiber membrane filaments, wherein the wire guide component is arranged at the bottom of the main tank body, the concentration adjustment box cover is arranged outside the wire guide component and connected to the bottom of the main tank body, and the top of the concentration adjustment box is located below the liquid level of the coagulation bath liquid in the main tank body. In the present invention, the coagulation bath liquid adopts a solvent system of an organic solvent and water, specifically N,N-dimethylformamide (DMF) and water, or dimethylacetamide (DMAC) and water, wherein DMF and DMAC are hydrophilic.

[0008] Preferably, the height ratio between the concentration adjustment box and the main tank body is in the range of 1:2 to 2:3.

[0009] Preferably, the concentration adjustment box includes an adjustment box body, a water inlet pipe and a concentration controller. The adjustment box body is a closed box body. The top of the adjustment box body is provided with a thread opening for the hollow fiber membrane to pass through. The side of the adjustment box body is provided with a plurality of through holes for connecting the inside and outside of the adjustment box body. The bottom of the adjustment box body is fixedly connected to the bottom of the main tank body. The water inlet end of the water inlet pipe is arranged at the bottom of the adjustment box body, the water diversion end of the water inlet pipe is arranged outside the adjustment box body, and the concentration controller is arranged on the side of the main tank body.

[0010] Preferably, the concentration controller comprises an online liquid concentration meter, a control cabinet and an electrically controlled valve. The liquid contact port of the online liquid concentration meter is arranged in the concentration adjustment box. The online liquid concentration meter is electrically connected to the electrically controlled valve through the control cabinet. The electrically controlled valve is arranged on the water inlet end of the water inlet pipe.

[0011] Preferably, the wire guide component includes a wire guide main wheel, a main wheel fixing frame, a magnetic fixing block, a wire guide auxiliary wheel and an auxiliary wheel bracket. The wire guide main wheel is hinged to the main wheel fixing frame, the bottom of the main wheel fixing frame is connected to the bottom of the main trough body, the magnetic fixing block is arranged on the outside of the bottom of the main trough body and opposite to the bottom of the main wheel fixing frame, the wire guide auxiliary wheel is hinged to the auxiliary wheel bracket, and the auxiliary wheel bracket is arranged on the main wheel fixing frame.

[0012] Preferably, the magnetic fixing block is an electromagnet.

[0013] Preferably, a horizontal guide wheel component is provided on the top of the main tank body, and the horizontal guide wheel component includes a first guide wheel and a second guide wheel, the first guide wheel and the second guide wheel are arranged horizontally, and the first guide wheel is arranged directly above the wire guide component. The first guide wheel cooperates with the wire guide component to vertically lead out the hollow fiber membrane, and the horizontal guide wheel component allows the hollow fiber membrane to undergo an air bath.

[0014] Preferably, an auxiliary wire guide component is provided at the bottom of the main trough body, and the auxiliary wire guide component includes an auxiliary guide wheel and an auxiliary guide wheel bracket, the auxiliary guide wheel is hinged to the auxiliary guide wheel bracket, and the auxiliary guide wheel bracket is fixed to the bottom of the main trough body and arranged parallel to the wire guide component.

[0015] A method for preparing a hollow fiber membrane with a variable pore size, wherein the method adopts the coagulation bath of the present invention to prepare the hollow fiber membrane, and the method comprises the following steps:

[0016] (1) The coagulation bath liquid is injected into the main tank so that the concentration of the organic solvent in the coagulation bath liquid reaches the original concentration A;

[0017] (2) adjusting the coagulation bath tank so that the wire guide component is located directly below the external spinneret, and vertically introducing the hollow fiber membrane formed by the casting liquid into the coagulation bath liquid of the main tank through the wire guide component, so that the pore-forming agent in the casting liquid is dissolved in the coagulation bath liquid, so that a large-diameter micropore upper portion is formed on the surface of the hollow fiber membrane;

[0018] (3) The concentration of the organic solvent in the coagulation bath in the chamber is reduced to concentration B by controlling the concentration adjustment chamber, so that a concentration difference is generated between the main tank and the concentration adjustment chamber;

[0019] (4) The hollow fiber membrane is vertically introduced into the concentration adjustment box through the wire guide component, so that the pore-forming agent in the casting solution continues to dissolve in the coagulation bath in the concentration adjustment box, so that the lower part of the micropores with small diameters is formed on the surface of the hollow fiber membrane, forming micropores with variable apertures;

[0020] (5) The hollow fiber membrane is vertically led out of the concentration adjustment box through the wire guide component, and then vertically led into the bath tank so that the wire guide component is located out of the main tank body to obtain a variable pore size hollow fiber membrane.

[0021] Preferably, the concentration B of the organic solvent in the coagulation bath is less than half of the original concentration A. At this time, the pore shape of the variable pore size hollow fiber membrane is optimal. Further, the original concentration A is 1-40%.

[0022] The beneficial effects of the present invention are:

[0023] The coagulation bath tank for preparing hollow fiber membranes with variable pore size of the present invention has a simple structure and is easy to process. On the basis of various equipments in conventional processes, only the coagulation bath tank needs to be added to prepare hollow fiber membranes with variable pore size, thereby greatly improving the filtering effect of hollow fiber membranes in sewage treatment with complex pollutant composition. The preparation method of the present invention has a simple process and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the main structure of the present invention;

[0026] Figure 2 It is a schematic diagram of the top view of the structure of the present invention;

[0027] Figure 3 It is a structural schematic diagram of the concentration adjustment box of the present invention;

[0028] Figure 4 It is a structural schematic diagram of the guide wire component of the present invention;

[0029] Figure 5 It is a process principle diagram of the present invention.

[0030] In the figure: 1. main tank body, 2. concentration adjustment box, 3. wire guide component, 4. first guide wheel, 5. second guide wheel, 6. auxiliary guide wheel, 7. auxiliary guide wheel bracket, 8. adjustment box body, 9. water inlet pipe, 10. wire through hole, 11. through hole, 12. water inlet end, 13. water diversion end, 14. online liquid concentration meter, 15. control cabinet, 16. electric control valve, 17. liquid contact port, 18. wire guide main wheel, 19. main wheel fixing frame, 20. magnetic fixing block, 21. wire guide auxiliary wheel, 22. auxiliary wheel bracket. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0032] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0033] Example:

[0034] like Figure 1 The coagulation bath tank for preparing a hollow fiber membrane with a variable pore size shown in the figure comprises a main tank body 1 for storing a coagulation bath liquid, a concentration adjustment box 2 for adjusting the concentration of the coagulation bath liquid in the box, and a wire guide component 3 for introducing and leading out hollow fiber membrane filaments. The wire guide component is arranged at the bottom of the main tank body, the concentration adjustment box cover is arranged outside the wire guide component and connected to the bottom of the main tank body, and the top of the concentration adjustment box is located below the liquid level of the coagulation bath liquid in the main tank body.

[0035] A horizontal guide wheel component is provided on the top of the main tank body, and the horizontal guide wheel component includes a first guide wheel 4 and a second guide wheel 5. The first guide wheel and the second guide wheel are arranged horizontally, and the first guide wheel is arranged directly above the wire guide component. The first guide wheel cooperates with the wire guide component to vertically lead out the hollow fiber membrane, and the horizontal guide wheel component allows the hollow fiber membrane to undergo an air bath.

[0036] An auxiliary wire guide component is provided at the bottom of the main tank body, and the auxiliary wire guide component includes an auxiliary guide wheel 6 and an auxiliary guide wheel bracket 7. The auxiliary guide wheel is hinged to the auxiliary guide wheel bracket, and the auxiliary guide wheel bracket is fixed to the bottom of the main tank body and arranged parallel to the wire guide component.

[0037] The height ratio of the concentration adjustment box to the main tank body ranges from 1:2 to 2:3. In this embodiment, the height ratio is selected to be 2:3. Figure 2 and Figure 3 As shown, the concentration adjustment box includes an adjustment box body 8, a water inlet pipe 9 and a concentration controller. The adjustment box body is a closed box body. The top of the adjustment box body is provided with a thread opening 10 for the hollow fiber membrane to pass through. The side of the adjustment box body is provided with a plurality of through holes 11 for connecting the inside and outside of the adjustment box body. The bottom of the adjustment box body is fixedly connected to the bottom of the main tank body. The bottom of the adjustment box body is not provided with a bottom plate, and the bottom of the adjustment box body can be directly welded to the bottom of the main tank body. The water inlet end 12 of the water inlet pipe is provided at the bottom of the adjustment box body, and the water inlet end 13 of the water inlet pipe is provided outside the adjustment box body. The concentration controller is provided on the side of the main tank body. The concentration controller includes an online liquid concentration meter 14, a control cabinet 15 and an electric control valve 16. The liquid contact port 17 of the online liquid concentration meter is provided in the concentration adjustment box. The online liquid concentration meter is electrically connected to the electric control valve through the control cabinet, and the electric control valve is provided on the water inlet end of the water inlet pipe. The contact port of the online liquid concentration meter monitors the concentration of the coagulation bath liquid in the concentration adjustment box in real time. As the solvent in the hollow fiber membrane casting liquid continuously dissolves into the coagulation bath liquid, the concentration of the coagulation bath liquid in the concentration adjustment box continuously increases. The online liquid concentration meter converts the concentration signal into an electrical signal and transmits it to the control cabinet. The control cabinet is set to control the concentration of the coagulation bath liquid in the concentration adjustment box to be within a certain range. The control cabinet controls the electric control valve to open the water supply pipe according to the electrical signal to allow water to enter, thereby reducing the concentration of the coagulation bath liquid in the concentration adjustment box to maintain its concentration within a certain range.

[0038] like Figure 4As shown, the wire guide component includes a wire guide main wheel 18, a main wheel fixing frame 19, a magnetic fixing block 20, a wire guide auxiliary wheel 21 and an auxiliary wheel bracket 22. The wire guide main wheel is hinged on the main wheel fixing frame, the bottom of the main wheel fixing frame is connected to the bottom of the main tank body, the magnetic fixing block is arranged outside the bottom of the main tank body and opposite to the bottom of the main wheel fixing frame, the wire guide auxiliary wheel is hinged on the auxiliary wheel bracket, and the auxiliary wheel bracket is arranged on the main wheel fixing frame. The magnetic fixing block is an electromagnet. When the coagulation bath is in the working state, the electromagnet is energized to work and the wire guide component is firmly fixed to the bottom of the concentration adjustment box. When the coagulation bath is not in the working state and needs to be repaired, the electromagnet circuit is turned off, and the wire guide component can be moved to the top of the coagulation bath main tank body for repair.

[0039] A method for preparing a hollow fiber membrane with a variable pore size, wherein the method adopts the coagulation bath to prepare the hollow fiber membrane, and the specific steps of the method are as follows:

[0040] (1) The coagulation bath is injected into the main tank so that the concentration of DMF or DMAC in the coagulation bath reaches the original concentration A;

[0041] (2) adjusting the coagulation bath tank so that the wire guide component is located directly below the external spinneret, and vertically introducing the hollow fiber membrane formed by the casting liquid into the coagulation bath liquid of the main tank through the wire guide component, so that the pore-forming agent in the casting liquid is dissolved in the coagulation bath liquid, so that a large-diameter micropore upper portion is formed on the surface of the hollow fiber membrane;

[0042] (3) The concentration of DMF or DMAC in the coagulation bath in the control box is reduced to concentration B by using the concentration adjustment box, so that a concentration difference is generated between the main tank and the concentration adjustment box;

[0043] (4) The hollow fiber membrane is vertically introduced into the concentration adjustment box through the wire guide component, so that the pore-forming agent in the casting solution continues to dissolve in the coagulation bath in the concentration adjustment box, so that the lower part of the micropores with small diameters is formed on the surface of the hollow fiber membrane, forming micropores with variable apertures;

[0044] (5) The hollow fiber membrane fibers are vertically led out of the concentration adjustment box through the wire guide component, and then vertically led out of the main tank body to obtain a hollow fiber membrane with a variable pore size.

[0045] In the above method, the original concentration A and concentration B of DMF or DMAC in the coagulation bath can be selected according to actual product needs. The original concentration A can be 1-40%, and the concentration B can be lower than the original concentration A to produce a concentration difference.

[0046] As another embodiment, a further preferred solution is that the concentration B of DMF or DMAC in the coagulation bath is less than half of the original concentration A. At this time, the concentration difference of the coagulation bath between the main tank and the concentration adjustment box is large, and the pore shape of the variable pore size hollow fiber membrane is optimal.

[0047] The process principle of the present invention is that a braided tube coated with casting liquid enters a coagulation bath tank filled with coagulation bath liquid for phase transformation into a membrane, or the casting liquid is directly entered into a coagulation bath tank filled with coagulation bath liquid through an air bath for phase transformation into a membrane. When the immersion coagulation method is used for phase transformation, the membrane is formed by the mutual diffusion of the solvent in the casting liquid and the non-solvent in the coagulation bath liquid. The mutual diffusion rate of the two determines the performance of the membrane to a large extent. Therefore, the solvent in the coagulation bath liquid can control the mass transfer rate in the membrane formation process. The increase of solvent in the coagulation bath can reduce the chemical potential change of diffusion and mass transfer exchange between the casting liquid and the coagulation bath, thereby reducing the mutual diffusion rate. On the one hand, this reduces the polymer concentration at the interface between the membrane and the coagulation bath, promoting the formation of a porous membrane skin layer, and on the other hand, it delays the time for the phase separation of the casting liquid, tending to form a thick and dense skin layer. Therefore, the coagulation bath with a higher solvent content will form a larger pore size portion of the micropores, while the coagulation bath with a lower solvent content will form a smaller pore size portion of the micropores. The diffusion pore-forming process of the casting liquid in the main tank and the concentration adjustment box with different solvent concentrations is shown in FIG. Figure 5 shown.

[0048] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A coagulation bath for preparing a hollow fiber membrane with a variable pore size, characterized in that: The coagulation bath tank for preparing variable-pore-size hollow fiber membranes comprises a main tank body for storing coagulation bath liquid, a concentration adjustment box for adjusting the concentration of the coagulation bath liquid in the box, and a wire guide component for introducing and leading out hollow fiber membrane filaments, wherein the wire guide component is arranged at the bottom of the main tank body, the concentration adjustment box cover is arranged outside the wire guide component and connected to the bottom of the main tank body, and the top of the concentration adjustment box is located below the liquid level of the coagulation bath liquid in the main tank body; a horizontal guide wheel component is arranged at the top of the main tank body, and the horizontal guide wheel component comprises a first guide wheel and a second guide wheel, the first guide wheel and the second guide wheel are arranged horizontally, the first guide wheel is arranged directly above the wire guide component, and the first guide wheel cooperates with the wire guide component to vertically lead out the hollow fiber membrane filaments, and the horizontal guide wheel component enables the hollow fiber membrane The silk takes an air bath; the concentration adjustment box includes an adjustment box body, a water inlet pipe and a concentration controller, the adjustment box body is a closed box body, the top of the adjustment box body is provided with a thread opening for the hollow fiber membrane silk to pass through, the side of the adjustment box body is provided with a plurality of through holes for connecting the inside and outside of the adjustment box body, the bottom of the adjustment box body is fixedly connected to the bottom of the main tank body, the water inlet end of the water inlet pipe is arranged at the bottom of the adjustment box body, the water inlet end of the water inlet pipe is arranged outside the adjustment box body, and the concentration controller is arranged on the side of the main tank body; the concentration controller includes an online liquid concentration meter, a control cabinet and an electric control valve, the liquid contact port of the online liquid concentration meter is arranged in the concentration adjustment box, the online liquid concentration meter is electrically connected to the electric control valve through the control cabinet, and the electric control valve is arranged on the water inlet end of the water inlet pipe.

2. The coagulation bath according to claim 1, characterized in that: The height ratio of the concentration adjustment box to the main tank body ranges from 1:2 to 2:

3.

3. The coagulation bath according to claim 1, characterized in that: The wire guide component includes a wire guide main wheel, a main wheel fixing frame, a magnetic fixing block, a wire guide auxiliary wheel and an auxiliary wheel bracket. The wire guide main wheel is hinged to the main wheel fixing frame, the bottom of the main wheel fixing frame is connected to the bottom of the main trough body, the magnetic fixing block is arranged on the outside of the bottom of the main trough body and opposite to the bottom of the main wheel fixing frame, the wire guide auxiliary wheel is hinged to the auxiliary wheel bracket, and the auxiliary wheel bracket is arranged on the main wheel fixing frame.

4. The coagulation bath according to claim 3, characterized in that: The magnetic fixing block is an electromagnet.

5. The coagulation bath according to claim 1, characterized in that: An auxiliary wire guide component is provided at the bottom of the main tank body, and the auxiliary wire guide component includes an auxiliary guide wheel and an auxiliary guide wheel bracket. The auxiliary guide wheel is hinged on the auxiliary guide wheel bracket, and the auxiliary guide wheel bracket is fixed to the bottom of the main tank body and arranged parallel to the wire guide component.

6. A method for preparing a hollow fiber membrane with a variable pore size, characterized in that: The method uses the coagulation bath described in any one of claims 1 to 5 to prepare a hollow fiber membrane, and the method comprises the following steps: (1) The coagulation bath liquid is injected into the main tank so that the concentration of the organic solvent in the coagulation bath liquid reaches the original concentration A; (2) adjusting the coagulation bath tank so that the wire guide component is located directly below the external spinneret, and vertically introducing the hollow fiber membrane formed by the casting liquid into the coagulation bath liquid of the main tank through the wire guide component, so that the pore-forming agent in the casting liquid is dissolved in the coagulation bath liquid, so that a large-diameter micropore upper portion is formed on the surface of the hollow fiber membrane; (3) The concentration of the organic solvent in the coagulation bath in the chamber is reduced to concentration B by controlling the concentration adjustment chamber, so that a concentration difference is generated between the main tank and the concentration adjustment chamber; (4) The hollow fiber membrane is vertically introduced into the concentration adjustment box through the wire guide component, so that the pore-forming agent in the casting solution continues to dissolve in the coagulation bath in the concentration adjustment box, so that the lower part of the micropores with small diameters is formed on the surface of the hollow fiber membrane, forming micropores with variable apertures; (5) The hollow fiber membrane is vertically led out of the concentration adjustment box through the wire guide component, and then vertically led into the bath tank so that the wire guide component is located out of the main tank body to obtain a variable pore size hollow fiber membrane.

7. The method according to claim 6, characterized in that: The concentration B of the organic solvent in the coagulation bath is less than half of the original concentration A.

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