Preparation method and device of inner and outer layer regulated hollow fiber double-layer membrane

Abstract

The application relates to a preparation method and device of a hollow fiber double-layer membrane with inner and outer layer regulation, and comprises the following preparation steps: 15-20 parts of a polymer, 1-40 parts of a macromolecular additive and 50-80 parts of a solvent are mixed according to weight fractions, and after uniform stirring, an inner layer polymer casting solution is obtained; 20-30 parts of a polymer, 10-40 parts of a macromolecular additive, 1-10 parts of a small molecular additive and 40-70 parts of a solvent are mixed according to weight fractions, and after uniform stirring, an outer layer polymer casting solution is obtained; the inner and outer layer polymer casting solutions are respectively connected to the inner layer and the outer layer of a double-layer spinneret, the inner and outer layer polymer casting solutions are uniformly coated on the surface of a hollow support tube in sequence, the thicknesses of the inner and outer layer polymer castings are controlled, and a nascent hollow fiber double-layer membrane is obtained; solidification is carried out in a coagulation bath, and after solidification, the hollow fiber double-layer membrane is wound, arranged, tied into a bundle, soaked, taken out and dried, so that the technical problem that the pore structure of a prepared membrane is limited and the skin layer and the sublayer structure cannot be regulated respectively is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of hollow fiber double-layer membranes, and in particular to a preparation method and device of a hollow fiber double-layer membrane with inner and outer layers regulated. Background Art

[0002] Membrane separation technology has excellent performance and a wide range of uses, involving all aspects of social life. For example, separation membranes are usually used as the core separation technology in fields such as industrial wastewater treatment, seawater desalination, and material separation. There are many forms of separation membranes. The more common form of separation membrane microfiltration products on the market is lined hollow fiber membranes. The membrane layer structure is mainly composed of a relatively dense epidermis layer and a sublayer support layer with a gradient network pore structure. The main function of the epidermis layer is separation, and the sublayer plays the role of supporting the membrane and having good permeability. The flux of the membrane and the filtration accuracy of the membrane are jointly determined by the dense epidermis layer and the porous sublayer support layer. The preparation of hollow fiber membranes usually adjusts the membrane pore structure through the casting formula to achieve the separation effect. However, the existing preparation methods are relatively limited in adjusting the membrane pore structure, especially when it comes to the difficulty of regulating the epidermis and sublayer structures separately.

[0003] Patent CN 105214526 A discloses a method for preparing a double-layer hollow fiber ultrafiltration membrane using polyvinylidene fluoride-g-POEM as a hydrophilic modified material. The patent mentions that combining the inner and outer layers can improve the mechanical strength of the membrane, increase the porosity and hydrophilicity, and further increase the membrane flux. However, the patent does not consider whether the membrane accuracy will decrease while increasing the membrane flux. Patent CN103285740 A discloses a method for preparing an antibacterial double-layer hollow fiber membrane, mentioning that the outer layer is passed through a silver ion sieve and the inner layer is a porous support layer to achieve improved membrane separation and antibacterial efficiency. However, a common problem with the load is that as the membrane runs for a long time, the load will be lost, and the long-term effectiveness of the antibacterial effect cannot be guaranteed; Patent CN106621866A discloses a polyethersulfone hollow fiber ultrafiltration membrane and its processing device and preparation method, mentioning that the organic macromolecules, organic small molecules, and inorganic salts in the additives in the formula for preparing the polyethersulfone hollow fiber ultrafiltration membrane can be used to adjust the pore size, but the pore size distribution of the obtained membrane is uniform, and it is impossible to separate the membranes with larger pores and the membranes with smaller pores, and it is impossible to simultaneously guarantee the water flux and accuracy of the hollow fiber membrane.

[0004] Therefore, in order to solve the above problems, the present invention urgently needs to provide a method and device for preparing a hollow fiber double-layer membrane with inner and outer layers regulated. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for preparing a hollow fiber double-layer membrane with inner and outer layers regulated, so as to solve the technical problem in the prior art that the existing preparation methods are limited in regulating the membrane pore structure, especially the difficulty in separately regulating the epidermal layer and sublayer structure.

[0006] The present invention provides a method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers, comprising the following preparation steps:

[0007] S1: Mix 15-20 parts of polymer, 1-40 parts of macromolecular additive and 50-80 parts of solvent according to weight parts, and stir evenly to obtain inner layer polymer casting solution;

[0008] S2: Mix 20-30 parts of polymer, 10-40 parts of macromolecular additive, 1-10 parts of micromolecular additive and 40-70 parts of solvent according to weight parts, and stir evenly to obtain an outer layer polymer casting solution;

[0009] S3: connecting the inner polymer casting liquid to the inner layer of the double-layer spinneret, connecting the outer polymer casting liquid to the outer layer of the double-layer spinneret, and uniformly coating the inner polymer casting liquid and the outer polymer casting liquid on the surface of the hollow support tube in sequence, while controlling the thickness of the inner and outer polymer casting films to obtain a nascent hollow fiber double-layer membrane;

[0010] S4: The prepared nascent hollow fiber double-layer membrane is pulled into a coagulation bath containing dimethylacetamide and water through a winding wheel for coagulation. After coagulation, it is rolled up, sorted, tied into bundles in a fiber collection trough, soaked for a period of time, taken out and dried to obtain a hollow fiber double-layer membrane.

[0011] Preferably, in step S1, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyether sulfide resin or polymethyl methacrylate;

[0012] The macromolecular additive is at least one of polyvinyl pyrrolidone or polyethylene oxide;

[0013] The solvent is at least one of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone;

[0014] After the polymer, macromolecular additive and solvent are mixed, they are stirred at a temperature of 40-80° C. for 4-24 hours.

[0015] Preferably, in step S2, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyether sulfide resin or polymethyl methacrylate;

[0016] The macromolecular additive is at least one of polyvinyl pyrrolidone or polyethylene oxide;

[0017] The small molecule additive is at least one of polyethylene glycol, glycerol, Tween 80, lithium chloride, sodium chloride or acetone;

[0018] The solvent is at least one of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone;

[0019] The polymer, the macromolecular additive, the small molecule additive and the solvent are mixed and stirred at a temperature of 40-80° C. for 4-24 hours.

[0020] Preferably, in step S3, the hollow support tube is made of at least one of nylon, polyester or polyurethane fiber.

[0021] Preferably, in step S3, the thickness of the inner polymer cast film is controlled to be 20-100 μm, and the thickness of the outer polymer cast film is controlled to be 10-50 μm.

[0022] Preferably, in step S4, the pulling speed of the winding wheel is 10-70 m / min.

[0023] Preferably, in step S4, the mass ratio of dimethylacetamide to water in the coagulation bath is (0-20):(80-100), and the coagulation bath temperature is 10-70°C.

[0024] Preferably, in step S4, the newly formed hollow fiber double-layer membrane is fully soaked in pure water for 24 hours.

[0025] The present invention also provides an inner and outer layer regulated hollow fiber double-layer membrane obtained based on the preparation method of the inner and outer layer regulated hollow fiber double-layer membrane as described in any one of the above.

[0026] The present invention also provides a preparation device for preparing the above-mentioned inner and outer layer regulated hollow fiber double-layer membrane, comprising a first feeding pump and a second feeding pump, the first feeding pump being connected to the first feeding port of the double-layer spinneret through a liquid guide tube, the second feeding pump being connected to the second feeding port of the double-layer spinneret through a liquid guide tube, a hollow support tube passing through the center of the double-layer spinneret as an inner lining, a gel tank being provided below the silk outlet of the double-layer spinneret, a plurality of silk winding wheels being provided in the gel tank, the silk winding wheels at the end being connected to a membrane silk collector, and the membrane silk collector being detachably mounted on the silk collecting tank;

[0027] The double-layer spinneret includes an inner spinneret and an outer spinneret.

[0028] The present invention provides a method and apparatus for preparing a hollow fiber double-layer membrane with regulated inner and outer layers, which has the following improvements compared to the prior art:

[0029] 1. The present invention provides a method and device for preparing a hollow fiber double-layer membrane with inner and outer layers regulated. The additives in the inner layer polymer casting liquid are composed of commonly used low-priced macromolecular additives. After mixing with polymers and solvents, the inner layer membrane pore structure obtained is a gradient network of large pores, ensuring a higher membrane flux; the additives in the outer layer polymer casting liquid are composed of macromolecular additives and small molecule additives. After mixing with polymers and solvents, the outer layer membrane pore structure obtained is a sponge-like uniform small pore, ensuring a higher membrane precision; the thickness of the inner and outer polymer casting membranes is controlled during the preparation process, and the cost of double-layer membrane production is lower when the membrane wall thickness is similar.

[0030] 2. The preparation method and device of the hollow fiber double-layer membrane with inner and outer layers provided by the present invention, through the control of the double-layer membrane making formula, preparation method and device, the inner layer regulates the membrane water flux to 3000-5000LMH, and the outer layer regulates the membrane pore accuracy to 0.02-0.1μm, so that the hollow fiber membrane can have both high precision and high flux performance. Under constant operating flux, the operating pressure of the double-layer membrane is lower than that of the standard sample, and the pollution resistance effect is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 Schematic diagram of the structure of the processing device for regulating the inner and outer layers of the hollow fiber double-layer membrane of the present invention;

[0033] Figure 2 Schematic diagram (cross-sectional view) of the internal structure of the double-layer spinneret of the present invention;

[0034] Figure 3 This is an electron microscope image of Example 1 of the present invention;

[0035] Figure 4 This is an electron microscope image of Example 2 described in the present invention;

[0036] Figure 5 This is an electron microscope image of Example 3 described in the present invention;

[0037] Figure 6 This is an electron microscope image of the comparative example described in the present invention;

[0038] Figure 7 This is a diagram showing the evaluation data of the membrane's anti-fouling operation in the present invention.

[0039] Description of reference numerals:

[0040] 1. First feed pump; 2. Second feed pump; 3. Double-layer spinneret; 301. First feed port; 302. Second feed port; 303. Inner spinneret; 304. Outer spinneret; 4. Hollow support tube; 5. Gel tank; 6. Winding wheel; 7. Membrane yarn collector; 8. Wire collecting tank. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0043] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0044] The present invention provides a preparation method of an inner and outer layer regulated hollow fiber double-layer membrane, comprising the following preparation steps: S1, according to parts by weight, 15-20 parts of a polymer, 1-40 parts of a macromolecular additive and 50-80 parts of a solvent are mixed, and after stirring evenly, an inner layer polymer casting solution is obtained; S2, according to parts by weight, 20-30 parts of a polymer, 10-40 parts of a macromolecular additive, 1-10 parts of a small molecule additive and 40-70 parts of a solvent are mixed, and after stirring evenly, an outer layer polymer casting solution is obtained; S3, the inner layer polymer is mixed, and the outer layer polymer casting solution is obtained. The casting liquid is connected to the inner layer of the double-layer spinneret, and the outer layer polymer casting liquid is connected to the outer layer of the double-layer spinneret. The inner layer polymer casting liquid and the outer layer polymer casting liquid are uniformly coated on the surface of the hollow support tube in turn, and the thickness of the inner and outer layers of polymer casting films are controlled to obtain a nascent hollow fiber double-layer membrane; S4 pulls the prepared nascent hollow fiber double-layer membrane through a winding wheel into a coagulation bath containing dimethylacetamide and water for coagulation. After coagulation, it is rolled up, sorted, tied into bundles in a wire collection trough, soaked for a period of time, taken out and dried to obtain a hollow fiber double-layer membrane.

[0045] Specifically, in step S1, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyether sulfone resin or polymethyl methacrylate; the macromolecular additive is at least one of polyvinyl pyrrolidone or polyethylene oxide; the solvent is at least one of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone; after the polymer, macromolecular additive and solvent are mixed, they are stirred at a temperature of 40-80°C for 4-24 hours.

[0046] Specifically, in step S2, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyether sulfone resin or polymethyl methacrylate; the macromolecular additive is at least one of polyvinyl pyrrolidone or polyethylene oxide; the small molecule additive is at least one of polyethylene glycol, glycerol, Tween 80, lithium chloride, sodium chloride or acetone; the solvent is at least one of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone; after the polymer, macromolecular additive, small molecule additive and solvent are mixed, they are stirred at a temperature of 40-80°C for 4-24 hours.

[0047] Specifically, in step S3, the hollow support tube is made of at least one of nylon, polyester or polyurethane fiber.

[0048] Specifically, in step S3, the thickness of the inner polymer cast film is controlled to be 20-100 μm, and the thickness of the outer polymer cast film is controlled to be 10-50 μm.

[0049] Specifically, in step S4, the pulling speed of the winding wheel is 10-70 m / min.

[0050] Specifically, in step S4, the mass ratio of dimethylacetamide to water in the coagulation bath is (0-20):(80-100), and the coagulation bath temperature is 10-70°C.

[0051] Specifically, in step S4, the newly formed hollow fiber double-layer membrane is fully soaked in pure water for 24 hours.

[0052] The present invention also provides an inner-and-outer layer regulated hollow fiber double-layer membrane obtained based on the preparation method of the inner-and-outer layer regulated hollow fiber double-layer membrane as described in any one of the above.

[0053] like Figure 1 、 Figure 2 As shown, the present invention also provides a preparation device for preparing the above-mentioned inner and outer layer regulated hollow fiber double-layer membrane, including a first feeding pump 1 and a second feeding pump 2. The first feeding pump 1 is connected to the first feed port 301 of the double-layer spinneret 3 through a liquid guide tube, and the second feeding pump 2 is connected to the second feed port 302 of the double-layer spinneret 3 through a liquid guide tube. A hollow support tube 4 is passed through the center of the double-layer spinneret 3 as an inner lining, and a gel tank 5 is provided below the silk outlet of the double-layer spinneret 3. A plurality of winding wheels 6 are provided in the gel tank 5. The winding wheel 6 at the end is connected to the membrane silk collector 7, and the membrane silk collector 7 is detachably mounted on the silk collecting tank 8; wherein, the double-layer spinneret 3 includes an inner spinneret 303 and an outer spinneret 304.

[0054] The present invention provides a method and device for preparing a hollow fiber double-layer membrane with inner and outer layers regulated. The additives in the inner layer polymer casting liquid are composed of commonly used low-cost macromolecular additives. After mixing with polymers and solvents, the inner layer membrane pore structure obtained is a gradient network of large pores, ensuring a higher membrane flux; the additives in the outer layer polymer casting liquid are composed of macromolecular additives and small molecule additives. After mixing with polymers and solvents, the outer layer membrane pore structure obtained is a sponge-like uniform small pore, ensuring a higher membrane precision; the thickness of the inner and outer polymer casting membranes is controlled during the preparation process, and the cost of double-layer membrane production is lower when the membrane wall thickness is similar.

[0055] The present invention provides a method and device for preparing a hollow fiber double-layer membrane with inner and outer layers regulated. Through the control of the double-layer membrane formulation, preparation method and device, the inner layer regulates the membrane water flux to 3000-5000LMH, and the outer layer regulates the membrane pore accuracy to 0.02-0.1μm, thereby achieving the hollow fiber membrane with both high precision and high flux performance. Under constant operating flux, the operating pressure of the double-layer membrane is lower than that of the standard sample, and the pollution resistance effect is better.

[0056] Example 1

[0057] First, the polymer, additives and solvent are prepared to prepare the inner and outer layer casting solutions, where:

[0058] The composition of the inner layer casting solution is as follows: 15.4 parts of polyvinylidene fluoride, 14.5 parts of polyvinyl pyrrolidone, 7.3 parts of polyethylene oxide, and 62.8 parts of dimethylacetamide;

[0059] The outer layer casting solution consists of: 20.7 parts of polyvinylidene fluoride, 10.8 parts of polyvinyl pyrrolidone, 7.2 parts of polyethylene glycol, 1 part of lithium chloride, 0.5 parts of Tween 80, and 59.8 parts of dimethylacetamide.

[0060] After the two casting polymer solutions are evenly stirred, they are degassed separately and then connected to the inner casting liquid outlet and outer casting liquid outlet of the two feed ports of the double-layer spinneret through the feed pump outlet respectively. A hollow support tube is passed through the center of the spinneret as an inner lining. The winding wheel is turned on, and the pump feeding is turned on to control the membrane thickness of the inner and outer double layers to be 35 μm for the inner layer and 45 μm for the outer layer respectively. The inner and outer layers of the liquid are evenly coated on the surface of the hollow support tube; the nascent hollow fiber coated inside and outside is pulled into the gel tank by the winding wheel at a speed of 30 m / min, solidified into a hollow fiber membrane in the gel tank, wound up by the winding wheel, and cut into a fixed length, and then fully soaked for 24 hours and dried.

[0061] The membrane performance was tested and the pure water flux was 4200LMH. Figure 3 The membrane pore size test is 0.08 μm, and the rejection rate of 400,000 molecular weight polyethylene oxide (PEO) is 91%. Figure 7 As shown in the figure, under constant operating flux, the operating pressure does not change significantly with the increase of operating time, the maximum operating pressure is less than 3kPa, and the membrane has good anti-fouling effect.

[0062] Example 2

[0063] First, the polymer, additives and solvent are prepared to prepare the inner and outer layer casting solutions, where:

[0064] The composition of the inner layer casting solution is as follows: 18 parts of polyvinylidene fluoride, 16.3 parts of polyvinyl pyrrolidone, 5.8 parts of polyethylene oxide, and 59.9 parts of dimethyl sulfoxide;

[0065] The outer layer casting solution consists of: 22.3 parts of polyvinylidene fluoride, 12.7 parts of polyvinyl pyrrolidone, 6.5 parts of polyethylene glycol, 1.5 parts of sodium chloride, 0.8 parts of Tween 80, and 56.2 parts of dimethyl sulfoxide.

[0066] After the two casting polymer solutions are evenly stirred, they are degassed separately and then connected to the inner casting liquid outlet and outer casting liquid outlet of the two feed ports of the double-layer spinneret through the feed pump outlet respectively. A hollow support tube is passed through the center of the spinneret as an inner lining. The winding wheel is turned on, and the pump feeding is turned on to control the thickness of the inner and outer double layers of the membrane to be 50 μm for the inner layer and 50 μm for the outer layer respectively. The inner and outer layers of the liquid are evenly coated on the surface of the hollow support tube; the nascent hollow fiber coated inside and outside is pulled into the gel tank by the winding wheel at a speed of 20 m / min, solidified into a hollow fiber membrane in the gel tank, wound up by the winding wheel, and cut into a fixed length, and then fully soaked for 24 hours and dried.

[0067] Test membrane performance, the membrane pure water flux is 3500LMH, such as Figure 4 The membrane pore size test is 0.07 μm, and the rejection rate of 400,000 molecular weight PEO is 93%. Figure 7 As shown in the figure, under constant operating flux, the operating pressure does not change significantly with the increase of operating time, the maximum operating pressure is less than 3kPa, and the membrane has good anti-fouling effect.

[0068] Example 3

[0069] First, the polymer, additives and solvent are prepared to prepare the inner and outer layer casting solutions, where:

[0070] The composition of the inner layer casting solution is as follows: 17.5 parts of polyvinylidene fluoride, 13.2 parts of polyvinyl pyrrolidone, 10.3 parts of polyethylene oxide, and 59 parts of solvent N-methylpyrrolidone;

[0071] The outer layer casting liquid consists of: 24.1 parts of polyvinylidene fluoride, 16.2 parts of polyvinyl pyrrolidone, 10 parts of polyethylene glycol, 2 parts of lithium chloride, 3 parts of acetone, 0.5 parts of Tween 80, and 44.2 parts of N-methylpyrrolidone.

[0072] After the two casting polymer solutions are evenly stirred, they are degassed separately and then connected to the inner casting liquid outlet and outer casting liquid outlet of the two feed ports of the double-layer spinneret through the feed pump outlet respectively. A hollow support tube is passed through the center of the spinneret as an inner lining. The winding wheel is turned on, and the pump feeding is turned on to control the thickness of the inner and outer double layers of the membrane to be 60 μm for the inner layer and 30 μm for the outer layer respectively. The inner and outer layers of the liquid are evenly coated on the surface of the hollow support tube; the nascent hollow fiber coated inside and outside is pulled into the gel tank by the winding wheel at a speed of 50 m / min, solidified into a hollow fiber membrane in the gel tank, wound up by the winding wheel, and cut into a fixed length, and then fully soaked for 24 hours and dried.

[0073] The membrane performance was tested and the pure water flux was 3200LMH. Figure 5The membrane pore size test is 0.06μm, and the rejection rate of 400,000 molecular weight PEO is 94%. Figure 7 As shown in the figure, under constant operating flux, the operating pressure gradually increases with the increase of operating time, the maximum operating pressure is less than 5kPa, and the membrane has good anti-fouling effect.

[0074] Comparative example (standard sample)

[0075] Preparation of single-layer membrane: Control the thickness of a single membrane layer to be 50-150 μm, and evenly coat the polymer liquid composed of the outer layer casting liquid in the above-mentioned Example 2 on the surface of the hollow support tube. The coated nascent hollow fiber is pulled into the gel tank by a winding wheel at a speed of 25 m / min, and solidified into a hollow fiber membrane in the gel tank. It is wound by the winding wheel, arranged into a fixed length, and then cut, fully soaked for 24 hours and then dried.

[0076] Test membrane performance, the membrane pure water flux is 1800LMH, such as Figure 6 The membrane pore size test is 0.085μm, and the rejection rate of 400,000 molecular weight PEO is 92%. Figure 7 As shown in the figure, under constant operating flux, the operating pressure increases significantly with the increase of operating time, the maximum operating pressure is greater than 10kPa, and the membrane has poor anti-fouling effect.

[0077] Table 1 Performance test results of polyvinylidene fluoride hollow fiber double-layer membrane

[0078]

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers, characterized in that: The inner and outer layers of the hollow fiber double-layer membrane have a gradient network of large pores in the inner layer and a sponge-like uniform pore structure in the outer layer, and the preparation steps include: S1: mixing 15-20 parts of a polymer, 1-40 parts of a macromolecular additive, and 50-80 parts of a solvent in parts by weight, and stirring evenly to obtain an inner layer polymer casting solution; in step S1, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyethersulfone resin, or polymethyl methacrylate; the macromolecular additive is at least one of polyvinyl pyrrolidone or polyethylene oxide; and the solvent is at least one of dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone; S2: mixing 20-30 parts of a polymer, 10-40 parts of a macromolecular additive, 1-10 parts of a small molecule additive, and 40-70 parts of a solvent in parts by weight, and stirring evenly to obtain an outer layer polymer casting solution; in step S2, the polymer is at least one of polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polyethersulfone resin, or polymethyl methacrylate; and the small molecule additive is at least one of polyethylene glycol, glycerol, Tween 80, lithium chloride, sodium chloride, or acetone; S3: connecting the inner polymer casting liquid to the inner layer of the double-layer spinneret, connecting the outer polymer casting liquid to the outer layer of the double-layer spinneret, and uniformly coating the inner polymer casting liquid and the outer polymer casting liquid on the surface of the hollow support tube in sequence, while controlling the thickness of the inner and outer polymer casting films to obtain a nascent hollow fiber double-layer membrane; In step S4, the prepared nascent hollow fiber double-layer membrane is pulled through a winding wheel into a coagulation bath containing dimethylacetamide and water for coagulation. After coagulation, it is rolled up, arranged, tied into bundles in a fiber collection trough, soaked for a period of time, taken out and dried to obtain a hollow fiber double-layer membrane. In step S4, the mass ratio of dimethylacetamide to water in the coagulation bath is (0-20): (80-100), and the coagulation bath temperature is 10-70°C.

2. The method for preparing a hollow fiber double-layer membrane with inner and outer layers regulated according to claim 1, characterized in that: In step S1, the polymer, the macromolecular additive and the solvent are mixed and stirred at a temperature of 40-80° C. for 4-24 hours.

3. The method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers according to claim 1, characterized in that: In step S2, the polymer, the macromolecular additive, the small molecule additive and the solvent are mixed and stirred at a temperature of 40-80° C. for 4-24 hours.

4. The method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers according to claim 1, characterized in that: In step S3, the hollow support tube is made of at least one of nylon, polyester or polyurethane fiber.

5. The method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers according to claim 1, characterized in that: In step S3, the thickness of the inner polymer cast film is controlled to be 20-100 μm, and the thickness of the outer polymer cast film is controlled to be 10-50 μm.

6. The method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers according to claim 1, characterized in that: In step S4, the pulling speed of the winding wheel is 10-70 m / min.

7. The method for preparing a hollow fiber double-layer membrane with regulated inner and outer layers according to claim 1, characterized in that: In step S4, the newly formed hollow fiber double-layer membrane is fully soaked in pure water for 24 hours.

8. A hollow fiber double-layer membrane with inner and outer layers regulated obtained by the method for preparing a hollow fiber double-layer membrane with inner and outer layers regulated according to any one of claims 1 to 7.

9. A device for preparing the hollow fiber double-layer membrane with regulated inner and outer layers according to claim 8, characterized in that: The invention comprises a first feeding pump (1) and a second feeding pump (2), wherein the first feeding pump (1) is connected to the first feeding port (301) of the double-layer spinneret (3) through a liquid guide tube, and the second feeding pump (2) is connected to the second feeding port (302) of the double-layer spinneret (3) through a liquid guide tube, a hollow support tube (4) is passed through the center of the double-layer spinneret (3) as an inner lining, a gel tank (5) is provided below the outlet of the double-layer spinneret (3), a plurality of winding wheels (6) are provided in the gel tank (5), the winding wheel (6) at the end is connected to a membrane yarn collector (7), and the membrane yarn collector (7) is detachably mounted on a collection tank (8); The double-layer spinneret (3) comprises an inner spinneret (303) and an outer spinneret (304).

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