PVDF (Polyvinylidene Fluoride) industrial ultrafiltration membrane assembly with multi-layer gradient pore channels and preparation method of PVDF industrial ultrafiltration membrane assembly

Abstract

The invention provides a PVDF industrial ultrafiltration membrane assembly with multiple layers of gradient pore channels and a preparation method of the PVDF industrial ultrafiltration membrane assembly. The ultrafiltration membrane comprises a macroporous supporting layer, a transition layer and a precise separation layer which are sequentially arranged from outside to inside, and a gradient pore size distribution structure is formed; wherein the aperture of the macroporous support layer is 0.05 to 0.1 mu m, the aperture of the transition layer is 0.02 to 0.05 mu m, and the aperture of the precise separation layer is 0.01 to 0.02 mu m. According to the PVDF industrial ultrafiltration membrane assembly with the multi-layer gradient pore channels, deep pollution is reduced through gradient interception, and the anti-pollution performance is remarkably improved by combining surface modification and photocatalysis.

Description

Technical Field

[0001] The present invention belongs to the membrane separation technology field, and in particular to a multi-layer gradient pore PVDF industrial ultrafiltration membrane component and a preparation method thereof. Background Art With the growing demand for industrial wastewater treatment and water resource reuse, ultrafiltration membrane technology, owing to its high-efficiency separation properties, has become a key solution. However, conventional PVDF ultrafiltration membranes are generally subject to severe fouling, rapid flux decay, and short service life. Especially when treating wastewater with high turbidity or high organic content, the membrane surface is easily clogged by particulate matter and organic macromolecules, resulting in increased operating energy consumption and frequent chemical cleaning. Existing single-layer homogeneous membranes, while simple to prepare, struggle to achieve both high flux and high retention. Multilayer composite membranes are typically fabricated through step-by-step coating or interfacial polymerization, a complex process with insufficient interlayer bonding and prone to delamination failure. In recent years, the design of gradient pore structures has been proposed to optimize membrane performance. However, existing gradient membranes often rely on post-processing modifications (such as chemical etching or physical coating), which are not only cumbersome but can also lead to uneven pore size distribution or shedding of functional layers. Furthermore, anti-fouling modifications are often achieved by introducing hydrophilic materials (such as PEG or zwitterionic polymers), but these modifications often compromise the membrane's mechanical strength or thermal stability.

[0002] In view of this, the present invention is proposed. Summary of the Invention

[0003] The first purpose of the present invention is to provide a PVDF industrial ultrafiltration membrane assembly with a multi-layer gradient pore channel, which reduces deep-layer pollution through gradient retention. The blending design of hydrophilic nano-silica and PVDF in the macroporous support layer enhances the mechanical properties while improving the surface hydrophilicity; the introduction of carbon nanotubes and zinc oxide in the transition layer not only improves the conductivity to inhibit microbial attachment, but also gives the membrane a self-cleaning function through photocatalytic activity; the precision separation layer achieves high-precision screening through the nano-scale composite of PVDF and PEG.

[0004] The second purpose of the present invention is to provide a method for preparing the above-mentioned multi-layer gradient pore PVDF industrial ultrafiltration membrane component, which uses three-channel co-agent spinning technology to simultaneously construct a macroporous support layer, a transition layer and a precision separation layer to ensure seamless integration between layers and precise control of the pore size gradient.

[0005] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly, the ultrafiltration membrane includes a macroporous support layer, a transition layer and a precision separation layer arranged in sequence from the outside to the inside, forming a gradient pore size distribution structure; The pore size of the macroporous support layer is 0.05-0.1 μm, the pore size of the transition layer is 0.02-0.05 μm, and the pore size of the precision separation layer is 0.01-0.02 μm.

[0006] The present invention provides a multi-layer gradient pore PVDF industrial ultrafiltration membrane component, which constructs a gradient pore size distribution structure by sequentially arranging a macroporous support layer, a transition layer and a precision separation layer from the outside to the inside, wherein the pore size of the macroporous support layer is 0.05-0.1 μm, the pore size of the transition layer is 0.02-0.05 μm, and the pore size of the precision separation layer is 0.01-0.02 μm. Therefore, the ultrafiltration membrane component has more excellent performance than traditional ultrafiltration membranes, wherein traditional ultrafiltration membranes mostly adopt a single pore size or a simple double-layer structure, which is difficult to achieve both high flux and high retention rate at the same time. The gradient pore structure of the present invention realizes graded interception of pollutants through a layer-by-layer decreasing pore size distribution. The macroporous support layer preferentially intercepts larger particles, the transition layer further screens medium molecular weight pollutants, and the precision separation layer ensures efficient removal of small molecular impurities. This ensures a high retention rate while avoiding rapid clogging of a single separation layer due to accumulation of pollutants, significantly extending the service life of the membrane. In addition, the material selection and pore size matching of each functional layer have a synergistic effect. The macroporous support layer adopts a blend system of PVDF, silica, PEG and DMAC. The introduction of silica enhances the mechanical strength and hydrophilicity of the membrane, and PEG regulates the pore size distribution through pore-forming effect, ensuring that the support layer has both high porosity and good compressive resistance. The transition layer not only optimizes the pore size distribution by introducing carbon nanotubes and zinc oxide, but also gives the membrane certain conductivity and photocatalytic properties, which can effectively inhibit microbial attachment and degrade organic pollutants, further enhancing the anti-pollution ability. The precision separation layer forms a dense nanofiber network through the precise ratio of PVDF and PEG, realizing the precise screening of small molecule pollutants.

[0007] Preferably, as a further feasible solution, the macroporous support layer is made of PVDF, silica, PEG and DMAC, wherein the mass ratio of PVDF, silica, PEG and DMAC is 18:6:5:77.

[0008] The present invention further defines the raw materials of the macroporous support layer in the multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly, and clarifies that it is prepared from PVDF, silica, PEG and DMAC in a mass ratio of 18:6:5:77, wherein PVDF as a matrix material provides excellent chemical stability, mechanical strength and pollution resistance, but its inherent hydrophobicity easily leads to membrane fouling, and the introduction of silica significantly improves the hydrophilicity of the membrane through the high specific surface area and surface hydroxyl groups of its nanoparticles, thereby reducing the adsorption of pollutants on the membrane surface; at the same time, the blend of silica and PVDF also enhances the mechanical strength of the support layer, which is crucial for industrial applications to withstand high-pressure flushing and repeated backwashing conditions, and secondly, PEG as a porogen regulates phase separation during the phase inversion process through its interaction with the solvent DMAC. The PVDF content in this ratio is 77%, which ensures the appropriate viscosity and gelation dynamics of the casting solution, allowing for a stable homogeneous solution and controlled phase separation during the spinning process. However, if the PVDF content is too low, the spinning process may be easy but the resulting membrane may lack strength. A high content of PVDF leads to excessive solution viscosity, which can easily cause breakage or uneven pore size during the spinning process. Furthermore, the mass ratio of silica to PEG also has a synergistic effect. Excessive silica can lead to nanoparticle agglomeration, resulting in membrane structural defects, while excessive PEG can result in a wide pore size distribution, reducing retention performance. Furthermore, the high proportion of DMAC as solvent ensures sufficient solubility and homogeneous dispersion of all components. Compared with the existing technology, traditional macroporous support layers mostly use a single PVDF or simply add inorganic particles, which have insufficient hydrophilicity and flux stability. However, the present invention, through the synergistic effect of the PVDF-silica-PEG ternary system, maintains the advantages of PVDF while overcoming the industry problem of easy contamination of hydrophobic membranes.

[0009] Preferably, as a further feasible solution, the transition layer is made of PVDF, carbon nanotubes, zinc oxide and DMAC, wherein the mass ratio of the PVDF, carbon nanotubes, zinc oxide and DMACd is 20:2:1:77.

[0010] The present invention further defines the specific raw materials of the transition layer of the multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly, and clarifies that it is made of PVDF, carbon nanotubes, zinc oxide and DMAC in a mass ratio of 20:2:1:77, wherein the transition layer introduces a composite additive system of carbon nanotubes and zinc oxide into the PVDF matrix, wherein the carbon nanotubes, with their unique one-dimensional hollow structure, construct a penetrating conductive network inside the membrane. This property enables the membrane to effectively inhibit the adsorption of charged pollutants under electric field-assisted filtration conditions; and the addition of zinc oxide plays a dual function. Its nanoparticles not only act as nucleating agents to refine the PVDF crystal domains and thus optimize the microstructure of the transition layer, but also form a synergistic photoelectrocatalytic system with the carbon nanotubes due to their semiconductor properties, generating active oxygen species under visible light irradiation, thereby accelerating the degradation of organic pollutants on the membrane surface. The ratio of the materials shows that when PVDF accounts for 20%, it can ensure that the casting solution has an appropriate elastic modulus and tensile viscosity during the shear spinning process, avoiding spinneret blockage caused by excessively high polymer concentration or fiber breakage caused by too low a polymer concentration; when the carbon nanotube content is less than 1.5%, the conductive network is discontinuous and the antistatic effect drops sharply, while when it exceeds 3%, the film brittleness increases due to agglomeration; zinc oxide exceeding 1.5% will cause excessive absorption of light in the visible light region and reduce the catalytic efficiency. Compared with the existing technology, traditional transition layers mostly use a single polymer or a simple blend of hydrophilic agents, which not only have a single function but are also prone to additive dissolution during long-term operation; the present invention, through the stable chemical crosslinking of carbon nanotubes, zinc oxide, and PVDF, achieves anti-pollution and self-cleaning multifunctionality while ensuring the environmental durability of the material.

[0011] Preferably, as a further feasible solution, the precision separation layer is made of PVDF, PEG and DMAC, wherein the mass ratio of PVDF, PEG and DMAC is 11:5:34.

[0012] Preferably, as a further feasible solution, the thickness of the macroporous support layer is 20-30 μm, the thickness of the transition layer is 50-80 μm, and the thickness of the precision separation layer is 100-150 μm.

[0013] The present invention also specifically defines the thicknesses of the macroporous support layer, transition layer, and precision separation layer. A macroporous support layer thickness of 20-30 μm provides both sufficient rigidity for the overall structure and an ideal growth substrate for the transition layer. A transition layer thickness of 50-80 μm enables it to fully function as a "pollution buffer zone." Within this thickness range, pollutants are primarily deposited in the central region of the transition layer, preventing them from directly reaching the surface of the precision separation layer. A precision separation layer thickness of 100-150 μm ensures the stability of the separation accuracy.

[0014] The present invention also provides a method for preparing the above-mentioned multi-layer gradient pore PVDF industrial ultrafiltration membrane component, comprising the following steps: preparing a macroporous support layer casting solution, a transition layer casting solution and an inner layer casting solution respectively, and then vacuum degassing to obtain a macroporous support layer spinning solution, a transition layer spinning solution and an inner layer spinning solution; Then, the macroporous support layer spinning solution, the transition layer spinning solution and the inner layer spinning solution are simultaneously ejected through a three-channel co-agent spinneret to form membrane filaments with a gradient pore size distribution structure. Subsequently, the membrane filaments are coagulated in a coagulation bath, soaked in glycerol, dried and rolled up to obtain ultrafiltration membrane filaments. The obtained ultrafiltration membrane filaments are then filled into the membrane assembly. After filling, epoxy resin is poured for 15-25 cm at both ends of the membrane assembly, and then cured and the end caps are removed. Finally, finely cut both ends and fill with protective liquid to complete the process.

[0015] The present invention also provides a method for a multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly, which realizes the integrated molding of a gradient pore structure by using a synchronous spinning technology of a three-channel co-agent spinneret in response to the respective functional requirements of the macroporous support layer, the transition layer and the precision separation layer. The spinneret structure is designed with a unique annular distribution channel, wherein the outer ring channel (corresponding to the macroporous support layer) has a pore diameter of 0.3mm, the middle ring channel (transition layer) has a pore diameter of 0.2mm, and the inner core channel (precision separation layer) has a pore diameter of 0.15mm. This gradient reduction design enables the three-layer spinning solution to form a stable laminar interface during the extrusion process. During the extrusion process, due to the differences in polymer concentration and additive types in each layer, a gradient structure with a pore diameter gradually decreasing from the outside to the inside is spontaneously formed.

[0016] Preferably, as a further implementable solution, the apertures of the three channels of the three-channel co-agent spinneret are a gradient distribution structure, and the apertures are 0.05-0.1 μm, 0.02-0.05 μm and 0.01-0.02 μm, respectively.

[0017] Preferably, as a further feasible solution, the membrane assembly is an annular circular tube with a hollow interior.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly, which reduces deep-layer contamination through gradient retention. The blending design of hydrophilic nano-silica and PVDF in the macroporous support layer enhances the mechanical properties while improving the surface hydrophilicity; the introduction of carbon nanotubes and zinc oxide in the transition layer not only improves the conductivity to inhibit microbial attachment, but also gives the membrane a self-cleaning function through photocatalytic activity; the precision separation layer achieves high-precision screening through the nano-scale composite of PVDF and PEG.

[0019] (2) The present invention provides a method for preparing the above-mentioned multi-layer gradient pore PVDF industrial ultrafiltration membrane component, which uses three-channel co-agent spinning technology to simultaneously construct a macroporous support layer, a transition layer and a precision separation layer to ensure seamless integration between layers and precise control of the pore size gradient. DETAILED DESCRIPTION

[0020] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0021] Example 1 The specific preparation method of the multi-layer gradient pore PVDF industrial ultrafiltration membrane component of the present invention is as follows: 1. Preparation of casting solution: Macroporous support layer casting solution: 18 parts of PVDF, 6 parts of nano-silica (particle size 20 nm), 5 parts of PEG4000 and 77 parts of DMAC were mixed, mechanically stirred at 25°C for 6 hours until completely dissolved, and vacuum degassed (-0.095 MPa, 30 minutes); Transition layer casting solution: 20 parts of PVDF, 2 parts of carboxylated carbon nanotubes (length 1 μm), 1 part of zinc oxide (particle size 20 nm) and 77 parts of DMAC were mixed, ultrasonically dispersed at 40°C for 4 hours and then vacuum degassed; Precision separation layer casting solution: Mix 22 parts of PVDF, 10 parts of PEG4000 and 68 parts of DMAC, stir at 30℃ for 5 hours, and degas in vacuum; 2. Spinning: A three-channel co-agent spinneret (outer channel pore size 0.05 μm / middle channel 0.02 μm / inner channel 0.01 μm) was used, and the extrusion pressure was set to 0.25 MPa for the outer ring / 0.3 MPa for the middle ring / 0.35 MPa for the inner core; The spinning kettle temperature was 55°C, the air gap height was 5 cm, the coagulation bath was a pure water solution at 50°C, and the drawing speed was 50 m / min; Solidify and soak in glycerol Glycerol solution: glycerol: water = 3:7 (volume ratio), temperature 40°C; Soaking time: 30 minutes, ultrasonic assistance (power 300 W); Purpose: To replace residual solvent, prevent membrane pore collapse, and improve flexibility; Soak in glycerin and then dry and roll Drying conditions: Temperature 25℃, humidity 30%, horizontal hanging for 24 hours; Avoid direct sunlight to prevent the photocatalytic layer (ZnO) from failing; Winding parameters: Tension control 5 N / m, winding speed 10 m / min; The final membrane structure is: the pore size of the macroporous support layer is 0.05μm, the pore size of the transition layer is 0.02μm, and the pore size of the precision separation layer is 0.01μm; 3. Component assembly: 500 membrane filaments are arranged in parallel and filled into a circular tube assembly with an inner diameter of 100 mm; Epoxy resin is poured at both ends for 15cm, pre-cured at 40℃ for 2 hours + final cured at 80℃ for 4 hours; Then, the end faces are cut by a high-pressure water jet cutting machine to ensure that both ends are flat, and the mixture is filled with 1% sodium bisulfite + 0.5% sodium benzoate + deionized water and sealed for storage.

[0022] Example 2 The specific preparation method of the multi-layer gradient pore PVDF industrial ultrafiltration membrane component of the present invention is as follows: 1. Preparation of casting solution: Macroporous support layer casting solution: 18 parts of PVDF, 6 parts of nano-silica (particle size 20 nm), 5 parts of PEG4000 and 77 parts of DMAC were mixed, mechanically stirred at 25°C for 6.5 hours until completely dissolved, and vacuum degassed (-0.095 MPa, 30 minutes); Transition layer casting solution: 20 parts of PVDF, 2 parts of carboxylated carbon nanotubes (length 1 μm), 1 part of zinc oxide (particle size 20 nm) and 77 parts of DMAC were mixed, ultrasonically dispersed at 45°C for 4.5 hours and then vacuum degassed; Precision separation layer casting solution: Mix 22 parts of PVDF, 10 parts of PEG4000 and 68 parts of DMAC, stir at 32°C for 5 hours, and degas in vacuum; 2. Spinning: A three-channel co-agent spinneret (outer channel pore size 0.1 μm / middle channel 0.05 μm / inner channel 0.02 μm) was used, and the extrusion pressure was set to 0.3 MPa for the outer ring / 0.35 MPa for the middle ring / 0.4 MPa for the inner core; The spinning kettle temperature was 58°C, the air gap height was 10 cm, the coagulation bath was a pure water solution at 50°C, and the drawing speed was 50 m / min; Solidify and soak in glycerol Glycerol solution: glycerol: water = 3:7 (volume ratio), temperature 40°C; Soaking time: 30 minutes, ultrasonic assistance (power 300 W); Purpose: To replace residual solvent, prevent membrane pore collapse, and improve flexibility; Soak in glycerin and then dry and roll Drying conditions: Temperature 25℃, humidity 30%, horizontal hanging for 24 hours; Avoid direct sunlight to prevent the photocatalytic layer (ZnO) from failing; Winding parameters: Tension control 5 N / m, winding speed 10 m / min; The final membrane structure is: the pore size of the macroporous support layer is 0.1μm, the pore size of the transition layer is 0.05μm, and the pore size of the precision separation layer is 0.02μm; 3. Component assembly: 1000 membrane filaments are arranged in parallel and filled into a circular tube assembly with an inner diameter of 100 mm; Epoxy resin is poured 25cm at both ends, pre-cured at 40℃ for 2 hours + final cured at 80℃ for 4 hours; The end faces are then cut using a high-pressure water jet cutter to ensure both ends are flat, and the tubes are filled with 2% sodium bisulfite + 1% sodium benzoate + deionized water and sealed for storage.

[0023] Example 3 The specific preparation method of the multi-layer gradient pore PVDF industrial ultrafiltration membrane component of the present invention is as follows: 1. Preparation of casting solution: Macroporous support layer casting solution: 18 parts of PVDF, 6 parts of nano-silica (particle size 20 nm), 5 parts of PEG4000 and 77 parts of DMAC were mixed, mechanically stirred at 25°C for 6.5 hours until completely dissolved, and vacuum degassed (-0.095 MPa, 30 minutes); Transition layer casting solution: 20 parts of PVDF, 2 parts of carboxylated carbon nanotubes (length 1 μm), 1 part of zinc oxide (particle size 20 nm) and 77 parts of DMAC were mixed, ultrasonically dispersed at 40°C for 4.5 hours and then vacuum degassed; Precision separation layer casting solution: Mix 22 parts of PVDF, 10 parts of PEG4000 and 68 parts of DMAC, stir at 32°C for 5 hours, and degas in vacuum; 2. Spinning: A three-channel co-agent spinneret (outer channel pore size 0.075 μm / middle channel 0.035 μm / inner channel 0.015 μm) was used, and the extrusion pressure was set to 0.275 MPa for the outer ring / 0.325 MPa for the middle ring / 0.375 MPa for the inner core; The spinning kettle temperature was 55°C, the air gap height was 7 cm, the coagulation bath was a pure water solution at 45°C, and the drawing speed was 50 m / min; Solidify and soak in glycerol Glycerol solution: glycerol: water = 3:7 (volume ratio), temperature 40°C; Soaking time: 30 minutes, ultrasonic assistance (power 300 W); Purpose: To replace residual solvent, prevent membrane pore collapse, and improve flexibility; Soak in glycerin and then dry and roll Drying conditions: Temperature 25℃, humidity 30%, horizontal hanging for 24 hours; Avoid direct sunlight to prevent the photocatalytic layer (ZnO) from failing; Winding parameters: Tension control 5 N / m, winding speed 10 m / min; The final membrane structure is: the pore size of the macroporous support layer is 0.075μm, the pore size of the transition layer is 0.035μm, and the pore size of the precision separation layer is 0.015μm; 3. Component assembly: 800 membrane filaments are arranged in parallel and filled into a circular tube assembly with an inner diameter of 100 mm; Pour epoxy resin 20cm at both ends, pre-cure at 40℃ for 2 hours + final cure at 80℃ for 4 hours, then remove the end caps at both ends of the membrane assembly; Then, the end faces are cut by a high-pressure water jet cutting machine to ensure that both ends are flat, and the mixture is filled with 1.5% sodium bisulfite + 0.5% sodium benzoate + deionized water and sealed for storage.

[0024] Experimental Example 1 Ultrafiltration membrane module performance test The performance of the multi-layer gradient pore PVDF industrial ultrafiltration membrane modules prepared in Examples 1-3, including water flux, rejection, anti-fouling performance, and tensile strength, was evaluated and compared with a conventional PVDF membrane (comparative example); 1. Water flux test Conditions: 25°C, 0.1 MPa operating pressure, using deionized water as the test medium; step: Pre-press the membrane assembly for 30 minutes until it reaches a stable state; Record the volume of water permeating within 10 minutes and calculate the flux per unit area (L / (m²·h·MPa)); Calculate the flux retention rate after the membrane module has been running stably for 300 hours; 2. Retention rate test Conditions: The test liquid is 1 g / L bovine serum albumin (BSA, molecular weight 67 kDa) solution, and the operating pressure is 0.1 MPa; step: Run the membrane assembly for 30 minutes and collect the permeate; The absorbance of the original solution and the permeate was measured using a UV spectrophotometer (280 nm) to calculate the retention rate (%). 3. Anti-pollution performance test Conditions: simulated highly polluted wastewater (containing 1 g / L BSA + 0.5 g / L humic acid), cycled for 4 hours; step: Physical cleaning: backwash for 5 minutes (0.2MPa); Chemical cleaning: soak in 0.1M NaOH solution for 30 minutes; Calculate the flux recovery rate (FRR) = J2 / J0 × 100%; 4. Mechanical strength test Method: The tensile strength of the membrane was measured using a universal material testing machine. The final test results are shown in Table 1 below. Table 1 Test results

[0025] Therefore, it can be seen from the above experimental results that the multi-layer gradient pore PVDF ultrafiltration membrane provided by the present invention is significantly superior to the traditional PVDF membrane in various performance indicators. This is because the present invention solves the industry pain points of easy pollution, rapid flux attenuation and high maintenance cost of traditional membrane components through gradient structure design and material composite. Among them, a multi-layer gradient pore PVDF industrial ultrafiltration membrane component of the present invention constructs a gradient pore size distribution structure by sequentially arranging a macroporous support layer, a transition layer and a precision separation layer from the outside to the inside, wherein the pore size of the macroporous support layer is 0.05-0.1μm, the pore size of the transition layer is 0.02-0.05μm, and the pore size of the precision separation layer is 0.01-0.02μm, thereby making the ultrafiltration membrane component have better performance than traditional ultrafiltration membranes. Traditional ultrafiltration membranes mostly adopt a single pore size or a simple double-layer structure, which is difficult to take into account both high flux and high retention rate at the same time. The gradient pore structure of the present invention realizes the graded interception of pollutants through the pore size distribution that decreases layer by layer. The macroporous support layer preferentially intercepts larger particles, the transition layer further screens medium molecular weight pollutants, and the precision separation layer ensures the efficient removal of small molecular impurities, thereby ensuring a high retention rate while avoiding the rapid clogging of a single separation layer due to the accumulation of pollutants, significantly extending the service life of the membrane; in addition, the material selection and pore size matching of each functional layer have a synergistic effect. The macroporous support layer adopts a blend system of PVDF, silica, PEG and DMAC, among which the introduction of silica enhances the mechanical strength and hydrophilicity of the membrane, and PEG regulates the pore size distribution through pore-forming effect, ensuring that the support layer has both high porosity and good compressive resistance; the transition layer not only optimizes the pore size distribution by introducing carbon nanotubes and zinc oxide, but also gives the membrane certain conductivity and photocatalytic properties, which can effectively inhibit microbial attachment and degrade organic pollutants, further improving the anti-pollution ability; the precision separation layer forms a dense nanofiber network through the precise ratio of PVDF and PEG, realizing the precise screening of small molecule pollutants.

[0026] 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 multi-layer gradient pore PVDF industrial ultrafiltration membrane component, characterized in that: The ultrafiltration membrane comprises a macroporous support layer, a transition layer and a precision separation layer arranged in sequence from the outside to the inside, forming a gradient pore size distribution structure; The pore size of the macroporous support layer is 0.05-0.1 μm, the pore size of the transition layer is 0.02-0.05 μm, and the pore size of the precision separation layer is 0.01-0.02 μm.

2. The multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly according to claim 1, characterized in that: The macroporous support layer is made of PVDF, silica, PEG and DMAC, wherein the mass ratio of the PVDF, silica, PEG and DMAC is 18:6:5:

77.

3. The multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly according to claim 1, characterized in that: The transition layer is made of PVDF, carbon nanotubes, zinc oxide and DMAC, wherein the mass ratio of the PVDF, carbon nanotubes, zinc oxide and DMACd is 20:2:1:

77.

4. The multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly according to claim 1, characterized in that: The precision separation layer is made of PVDF, PEG and DMAC, wherein the mass ratio of the PVDF, PEG and DMAC is 11:5:

34.

5. The multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly according to claim 1, characterized in that: The thickness of the macroporous support layer is 20-30 μm, the thickness of the transition layer is 50-80 μm, and the thickness of the precision separation layer is 100-150 μm.

6. A method for preparing a multi-layer gradient pore PVDF industrial ultrafiltration membrane assembly according to any one of claims 1 to 5, characterized in that: The following steps are involved: preparing a macroporous support layer casting solution, a transition layer casting solution and an inner layer casting solution respectively, and then vacuum degassing to obtain a macroporous support layer spinning solution, a transition layer spinning solution and an inner layer spinning solution; Then, the macroporous support layer spinning solution, the transition layer spinning solution and the inner layer spinning solution are simultaneously ejected through a three-channel co-agent spinneret to form membrane filaments with a gradient pore size distribution structure. Subsequently, the membrane filaments are coagulated in a coagulation bath, soaked in glycerol, dried and rolled up to obtain ultrafiltration membrane filaments. The obtained ultrafiltration membrane filaments are then filled into the membrane assembly. After filling, epoxy resin is poured for 15-25 cm at both ends of the membrane assembly, and then cured and the end caps are removed. Finally, finely cut both ends and fill with protective liquid to complete the process.

7. The preparation method according to claim 6, characterized in that The apertures of the three channels of the three-channel co-agent spinneret are of a gradient distribution structure, and the apertures are 0.05-0.1 μm, 0.02-0.05 μm and 0.01-0.02 μm respectively.

8. The preparation method according to claim 6, characterized in that The membrane assembly is a ring-shaped circular tube with a hollow interior.

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