High-strength MBR (Membrane Bioreactor) ultrafiltration membrane, preparation system and method thereof and spinning stock solution

Abstract

The invention relates to a high-strength MBR (Membrane Biological Reactor) ultrafiltration membrane, a preparation system and method thereof and a spinning solution. According to the invention, a composite nano reinforcing agent composed of modified silicon dioxide and graphene oxide is innovatively introduced into a membrane solution. The two nano materials form a rigid-flexible synergistic enhanced network in a polymer matrix; the graphene oxide is used as a two-dimensional nanosheet layer, so that stress is effectively transmitted and dispersed; and the silicon dioxide nanoparticles are used as stress concentration points to prevent the propagation of microcracks. Meanwhile, the invention provides a set of composite reinforcement solution. The core of the scheme is that a polyester / polyamide high-density composite braided tube subjected to plasma surface treatment is adopted as a mechanical skeleton of the membrane, and main operation stress is borne from the macroscopic scale. The multi-stage synergistic enhancement mechanism from the macroscopic braided tube to the nanoscale endows the membrane filament with mechanical strength far beyond the conventional level and fatigue and filament breaking resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a membrane technology for separation, in particular to a high-strength MBR ultrafiltration membrane with improved membrane performance by modifying the woven tube with a spinning dope, and a preparation system and method thereof. BACKGROUND

[0002] In the field of membrane bioreactor (MBR) technology, the practical application of hollow fiber ultrafiltration membranes still faces a series of severe challenges. First, the insufficient mechanical strength of the membrane is a key factor that leads to the shortening of its service life. The existing technology, especially the membranes prepared by the non-solvent induced phase separation method, are prone to form macroscopic finger-like pore structures inside. Such structures are very fragile when subjected to mechanical stress caused by water flow and long-term aeration of the membrane bioreactor, resulting in membrane filament breakage, or even if a woven tube is used to increase the composite membrane, because the weaving density of the selected woven tube and the rigidity of the used formula are insufficient, the separation layer of the membrane filament will also be broken after a long period of use, seriously affecting the stable operation of the system and the water quality.

[0003] In the field of MBR ultrafiltration membrane technology, although there have been a large number of researches and applications, there are still several key technical bottlenecks to be broken through. These deficiencies seriously restrict the further popularization and application effect of MBR technology.

[0004] First, the mechanical strength and anti-fracture ability of the membrane are key factors that restrict the long-term stable operation of the MBR system. The homogeneous membrane prepared by the traditional non-solvent induced phase separation method has limited intrinsic mechanical properties due to its intrinsic unsupported structure, while the partially reinforced membrane is difficult to effectively resist the comprehensive stress brought by the continuous water flow shear, severe aeration shaking and frequent physical cleaning in the MBR operating environment due to the insufficient weaving density of the support tube, resulting in membrane filament breakage, which seriously affects the operation reliability and service life of the system. SUMMARY

[0005] To solve the above problems, the present application improves the spinning dope, membrane structure, preparation system and preparation method from multiple dimensions, thereby forming a multi-scale composite reinforced solution.

[0006] At the microscale, a composite nano-reinforcing agent composed of modified silicon dioxide and graphene oxide is innovatively introduced into the membrane liquid. Both of them construct a synergistic reinforcing network in the polymer matrix, not only effectively refining the membrane pore structure, but more importantly, greatly improving the toughness, density and bonding strength of the separation layer itself, thereby fundamentally preventing the membrane separation layer from producing micro-cracks or leaks due to stress concentration in long-term dynamic operation, and comprehensively improving the durability and reliability of the membrane filament.

[0007] At the macro scale, the plasma treated polyester / polyamide composite high-density braided tube is selected as the core mechanical skeleton, which significantly improves the overall load-bearing capacity and fatigue resistance of the membrane filament.

[0008] Secondly, the balance of membrane performance has long plagued the industry. The existing technology is difficult to achieve high strength, high precision and high flux at the same time, and the strengthening measures often lead to increased mass transfer resistance or uneven pore size distribution, and it is difficult to balance sufficient mechanical strength when pursuing high precision. The present invention solves this problem through the innovative design of a composite formulation system and a three-stage gradient coagulation process. The synergistic effect of PVDF / PES (polyvinylidene fluoride / polyether sulfone) composite polymer and PVP / PAA (polyvinylpyrrolidone / polyacrylic acid) composite additive enhances the material performance while maintaining porosity.

[0009] The specially designed three-stage gradient coagulation bath system precisely controls the solvent concentration and temperature of each coagulation bath to regulate the bidirectional diffusion rate of solvent and non-solvent, guiding the formation of a membrane with gradient structure and achieving the synergistic optimization of various performances.

[0010] Furthermore, the long-term anti-pollution and stability of the membrane is also a key problem affecting practical application. Traditional hydrophobic membrane materials easily adsorb pollutants, and conventional hydrophilic modification methods have the problem of easy loss of modifier, leading to rapid decay of hydrophilic performance with running time. To this end, the present invention provides a solution for building a durable composite hydrophilic layer. PAA and PVA are selected as composite hydrophilic agents, and during subsequent gradient heat setting, cross-linking reactions between functional groups form a stable hydrophilic layer anchored on the surface and inside the pores of the membrane, significantly improving the durability of the hydrophilic effect and the anti-pollution recovery ability of the membrane.

[0011] The present invention provides a kind of spinning dope for high-strength MBR ultrafiltration membrane, which comprises polyvinylidene fluoride, polyether sulfone, composite additive, composite nano-enhancing agent and organic solvent.

[0012] Preferably, the polyvinylidene fluoride content is 10% to 25%, the polyether sulfone content is 2% to 8%, the composite additive content is 8% to 25%, the composite nano-enhancing agent content is 0.5% to 3%, and the organic solvent content is 49% to 75%.

[0013] Preferably, the composite additive comprises polyvinylpyrrolidone and polyacrylic acid, and the mass ratio of polyvinylpyrrolidone to polyacrylic acid is 4:1 to 1:1; The composite nano-enhancing agent is a mixture of modified silicon dioxide and graphene oxide, and the mass ratio of modified silicon dioxide to graphene oxide is 3:1 to 1:1; The organic solvent is one or a mixture of N-methylpyrrolidone and N,N-dimethylacetamide, wherein when it is a mixture, the mass ratio of N-methylpyrrolidone to N,N-dimethylacetamide is 2:1 to 1:4.

[0014] The present invention provides a high-strength MBR ultrafiltration membrane, which includes a braided tube and a spinning solution coated on the braided tube. The spinning solution is the aforementioned spinning solution, and the braided tube coated with the spinning solution undergoes curing and heat setting treatment.

[0015] This invention provides a method for preparing a high-strength MBR ultrafiltration membrane, which includes the following steps: Step 1: Mix polyvinylidene fluoride, polyethersulfone, composite additives, composite nano-reinforcing agents and organic solvents according to the formula ratio, and stir at 45℃ to 85℃ for 8 to 20 hours to form a uniform spinning solution. Step 2: Degas the spinning solution obtained in Step 1 under a vacuum of -0.065 MPa to -0.088 MPa and a temperature of 45°C to 75°C for 8 to 20 hours. Step 3: The deaerated spinning solution is coated onto the braided tube at the adjustable spinneret using a spinning metering pump. The output speed of the spinning metering pump is controlled between 18 r / min and 55 r / min, and the coating thickness is adjusted in real time using an infrared real-time monitoring device. Step 4: The coated nascent membrane is formed by passing through a primary coagulation bath, a secondary coagulation bath, and a tertiary coagulation bath in sequence. The temperature of the coagulation bath is controlled between 25℃ and 70℃, and the traction speed is between 5m / min and 30m / min. Step 5: Soak the formed membrane fibers in deionized water for 6 to 24 hours, treat them with a solution of composite hydrophilic agent for 6 to 24 hours, and finally perform gradient heat setting at 20°C to 100°C indoors for 1 to 5 hours to obtain the finished MBR ultrafiltration membrane.

[0016] The method for preparing a high-strength MBR ultrafiltration membrane provided by the present invention uses the above-mentioned spinning solution in step 1.

[0017] Preferably, the braided tube in step 3 is a polyester and polyamide composite braided tube that has undergone plasma treatment, and the surface energy of the braided tube is ≥45mN / m; The braided tube is pretreated with plasma before use to remove organic pollutants from the surface through physical bombardment and to introduce hydroxyl and carboxyl polar active groups on the fiber surface through chemical reaction, thereby improving the wettability and interfacial bonding strength with the spinning solution. The power of the plasma treatment device is 100 W-1000 W and the treatment time is 10 seconds to 1200 seconds. The control accuracy of the infrared real-time monitoring device is ±5μm; The primary coagulation bath in step 4 is a primary mixture of water and N,N-dimethylacetamide, the mass content of N,N-dimethylacetamide in the primary mixture is 15% to 35%, and the temperature is 35-55 DEG C; the secondary coagulation bath is a secondary mixture of water and N-methyl pyrrolidone, the content of N-methyl pyrrolidone in the secondary mixture is 8% to 18%, and the temperature is 35 DEG C to 55 DEG C; the tertiary coagulation bath is pure water, and the temperature is 45 DEG C to 58 DEG C; The composite hydrophilic agent in step 5 is a composite solution of glycerol and polyvinyl alcohol in water, the mass ratio of glycerol to polyvinyl alcohol is 2:1 to 1:1, and the total mass concentration of glycerol and polyvinyl alcohol in the composite solution is 12-48%; the gradient heat setting includes three stages: the first stage is treated at 60 DEG C to 70 DEG C for 1 hour, the second stage is treated at 70 DEG C to 80 DEG C for 1 hour, and the third stage is treated at 80 DEG C to 90 DEG C for 1 hour-2 hours; The finished MBR ultrafiltration membrane is a hollow fiber membrane with a gradient change structure, and the gradient change structure refers to that the pore size and structure of the membrane separation layer present a gradient change in the cross section perpendicular to the length of the hollow fiber membrane, that is, a gradient change structure with an outer layer of ultra-thin dense separation layer and an inner layer of highly interconnected sponge-like support layer is formed; the outer diameter of the hollow fiber membrane is 0.9 mm to 3.5 mm, and the inner diameter is 0.5 to 2.8 mm; the tensile strength of the membrane filament is greater than or equal to 100 MPa, the pure water flux is greater than or equal to 450 L / (m²·h), the surface pore size is 0.02 μm to 0.1 μm, and the porosity is greater than or equal to 70%.

[0018] The application provides a preparation system for a high-strength MBR ultrafiltration membrane, which comprises, which is sequentially connected, a stirring tank, a stirring tank outlet valve, a defoaming tank, a spinning metering pump, an adjustable spinneret, a multi-stage coagulation bath device, a yarn collecting wheel and a yarn collecting wheel water tank. It also comprises a braided tube pay-off device, which supplies the braided tube to the adjustable spinneret; the spinning metering pump sprays the spinning dope to the braided tube supplied to the adjustable spinneret, and the spinning dope is the spinning dope described above.

[0019] Preferably, the multi-stage coagulation bath device has a primary coagulation bath, a secondary coagulation bath and a tertiary coagulation bath connected in sequence. It also comprises a nitrogen system, which has a nitrogen tank, a nitrogen valve, a stirring tank nitrogen valve and a defoaming tank nitrogen valve, the nitrogen tank is connected to the stirring tank nitrogen valve and the defoaming tank nitrogen valve through the nitrogen valve, the downstream of the stirring tank nitrogen valve is connected to the stirring tank, and the downstream of the defoaming tank nitrogen valve is connected to the defoaming tank. It also comprises a computer control system, which is connected to the stirring tank through a stirring tank temperature and pressure control circuit to control the temperature and pressure of the stirring tank. The computer control system is connected with the defoaming tank through a defoaming tank temperature and pressure control circuit for controlling the temperature and pressure of the defoaming tank; The computer control system is connected with the spinning metering pump through a spinning pump control circuit; The computer control system is connected with the adjustable spinneret through a spinneret regulation circuit for controlling the spinning temperature and rate of the adjustable spinneret; The computer control system is connected with the braided tube pay-off device through a braided tube pay-off device control circuit for controlling the pay-off rate of the braided tube pay-off device; The computer control system is connected with the infrared real-time monitoring device through an infrared real-time monitoring device signal feedback circuit for controlling the coating thickness; The computer control system is connected with the primary coagulation bath through a primary coagulation bath temperature and concentration feedback circuit for controlling the temperature and concentration of the primary coagulation bath; The computer control system is connected with the secondary coagulation bath through a secondary coagulation bath temperature and concentration feedback circuit for controlling the temperature and concentration of the secondary coagulation bath; The computer control system is connected with the tertiary coagulation bath through a tertiary coagulation bath temperature and concentration feedback circuit for controlling the temperature and concentration of the tertiary coagulation bath; The computer control system is connected with the receiving wheel through a receiving wheel receiving speed control circuit for controlling the receiving speed of the receiving wheel; The primary coagulation bath is connected with a primary coagulation bath discharge electromagnetic valve and a primary coagulation bath inlet electromagnetic valve, respectively; The secondary coagulation bath is connected with a secondary coagulation bath inlet electromagnetic control valve and a secondary coagulation bath discharge electromagnetic control valve, respectively; The tertiary coagulation bath is connected with a tertiary coagulation bath inlet electromagnetic control valve and a tertiary coagulation bath discharge electromagnetic control valve, respectively; The computer control system is connected with the tertiary coagulation bath discharge electromagnetic control valve through a tertiary coagulation bath discharge control circuit; The computer control system is connected with the tertiary coagulation bath inlet electromagnetic control valve through a tertiary coagulation bath inlet control circuit; The computer control system is connected with the primary coagulation bath discharge electromagnetic valve through a primary coagulation bath discharge control circuit; The computer control system is connected with the primary coagulation bath inlet electromagnetic valve through a primary coagulation bath inlet control circuit; The computer control system is connected with the secondary coagulation bath discharge electromagnetic control valve through a secondary coagulation bath discharge control circuit; The computer control system is connected with the secondary coagulation bath inlet electromagnetic control valve through a secondary coagulation bath inlet control circuit.

[0020] Preferably, the following steps are included: First step: raw material preparation and pretreatment: According to the formula, weigh each component: polyvinylidene fluoride 10% to 25%, polyether sulfone 2% to 8%, polyvinylpyrrolidone 5% to 15%, polyacrylic acid 2% to 8%, modified silica 0.2% to 1.5%, graphene oxide 0.3% to 1.5%, and N-methylpyrrolidone and N,N-dimethylacetamide complex organic solvent 49% to 75%, and the braided tube is subjected to plasma pretreatment, the surface energy is increased to ≥45 mN / m, and good interfacial bonding is ensured; Second step: intelligent spinning dope preparation: Add the raw materials to the stirring tank: set the stirring parameters through the computer control system: temperature 45°C to 85°C, rotation speed 40 r / min to 140 r / min, add the substances in the first step in order, ensure sufficient dissolution and dispersion, stirring time 8-20 hours, until a uniform transparent spinning dope is formed; Vacuum degassing treatment: transfer the spinning dope to the degassing tank, degassing at a vacuum degree of -0.065 MPa to -0.088 MPa and a temperature of 45°C to 85°C for 8-20 hours; Third step: precision spinning and online monitoring: Parameter setting: the spinning metering pump rotation speed: 18 r / min to 55 r / min; the drawing speed: 5 m / min to 30 m / min; the adjustable spinneret temperature: 30-60°C; Real-time monitoring and adjustment: the infrared real-time monitoring device measures the coating thickness in real time, with an accuracy of ±5 μm; the computer control system dynamically adjusts the adjustable spinneret and the spinning metering pump rotation speed according to the coating thickness data, and the braided tube pay-off device ensures constant tension to avoid fluctuations; Fourth step: multi-stage gradient coagulation molding: In the first coagulation bath, the solvent content is 15% to 35%, the temperature is 35°C to 55°C, and the residence time is 10 seconds to 30 seconds; the first coagulation bath is used to complete the preliminary phase separation and form the basic skeleton of the membrane; In the second coagulation bath, the solvent content is 8% to 18%, the temperature is 35°C to 55°C, and the residence time is 20 seconds to 50 seconds, further promoting phase separation, i.e., guiding the formation of an outer phase ultra-thin dense separation layer and an inner phase highly interconnected sponge-like support layer. Because the solvent concentration in the second coagulation bath is significantly reduced, the water intrusion speed increases, driving the phase separation to proceed deeper and more thoroughly, refining the pore structure and promoting the formation of a sponge-like structure at the fracture surface; The third coagulation bath is pure water, the temperature is 45°C to 58°C, and the residence time is 30 seconds to 60 seconds, completing the final phase separation and solidifying the membrane structure; Fifth step: post-treatment and performance optimization: Cleaning treatment: soak in deionized water for 8 to 20 hours to completely remove residual solvents; water temperature is controlled at 25 to 40°C; Hydrophilic treatment: the concentration of the composite solution formed by glycerol and polyvinyl alcohol in water is 12% to 48%; treatment time is 8 to 20 hours, and treatment temperature is 30 to 50°C; Gradient heat setting: first stage: 60 to 70°C, 1 hour; second stage: 70 to 80°C, 1 hour; third stage: 80 to 90°C, 1 to 2 hours.

[0021] The beneficial effects of the present application are: First, the present application innovatively introduces a composite nano-reinforcing agent composed of modified silicon dioxide and graphene oxide into the membrane solution. These two kinds of nanomaterials form a synergistic reinforcing network in the polymer matrix: graphene oxide as a two-dimensional nanosheet layer effectively transmits and disperses stress; and silicon dioxide nanoparticles act as stress concentration points to prevent the propagation of microcracks.

[0022] At the same time, the present application proposes a "composite reinforcement" solution. The core of this solution is to use a polyester / polyamide high-density composite braided tube treated by plasma surface treatment as the mechanical skeleton of the membrane, which bears the main operating stress from the macroscopic scale. This multi-level synergistic reinforcement mechanism from the macroscopic braided tube to the nanoscale together gives the membrane filament mechanical strength and anti-fatigue breaking ability far beyond the conventional level.

[0023] Second, the existing technology is difficult to break through the "trade-off phenomenon" of membrane performance, i.e., the balance between performance indicators, i.e., increasing the mechanical strength of the membrane often accompanies the decrease in permeation flux and the deterioration of pore size distribution, and vice versa. In order to break this performance bottleneck, the present application starts from the thermodynamic and kinetic processes of membrane formation and designs a new composite formula and a multi-stage gradient coagulation process. In terms of formula, a composite polymer system of polyvinylidene fluoride (PVDF) and polyether sulfone (PES) is used, and a composite additive of polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) is used to precisely control the phase separation behavior by using the interaction between different molecules.

[0024] In the preferred solution, in terms of process, the membrane filament successively passes through three gradient coagulation baths with different solvent concentrations and temperatures during the forming process. This process precisely controls the exchange rate of solvent and non-solvent to guide the membrane to form a gradient structure with an ultra-thin and dense separation layer and a highly interconnected sponge-like support layer, thereby successfully realizing the unification of high strength, high filtration precision, and high flux.

[0025] Furthermore, the long-term anti-fouling performance and operation stability of the membrane material are insufficient. The traditional hydrophobic PVDF membrane is easily blocked by adsorption of pollutants, and the conventional physical blending hydrophilic modifier also has the problem of easy elution and loss, which leads to rapid decay of hydrophilic performance with running time. In view of this, the application constructs a "long-lasting" hydrophilic treatment scheme. In the post-treatment stage, the membrane is soaked with a composite hydrophilic agent of glycerol and polyvinyl alcohol (PVA), and then a gradient heating heat setting process is carried out. In this process, through the esterification cross-linking reaction between the carboxyl groups (-COOH) on the PAA molecular chain and the hydroxyl groups (-OH) on the PVA molecular chain, a stable hydrophilic layer is formed and anchored on the membrane surface and the pore, so as to firmly "anchor" the hydrophilic component on the membrane surface and the pore, significantly improve the durability of the hydrophilic effect, and ensure the stability of the flux and excellent anti-fouling recovery ability of the membrane in long-term operation.

[0026] Finally, in view of the problem of poor batch consistency of products caused by rough control of key parameters in the existing production process, the application integrates the intelligent process control concept into the preparation system. In particular, in the spinning coating link, an infrared online thickness monitoring device is integrated, which can measure and feedback control the coating thickness of the membrane liquid on the braided tube in real time and non-contact, thereby ensuring the uniformity of the structure of each membrane filament at the source. In addition, the entire coagulation bath system is equipped with independent temperature control and concentration automatic compensation device, which ensures the absolute stability of the process conditions. Through these precise process control means, the application realizes the high-quality transformation from laboratory to industrial production, and guarantees the large-scale and consistent manufacturing of high-performance membrane products.

[0027] In summary, through a set of systematic and multi-level innovation schemes from material formula, reinforced structure, forming process to process control, the application solves the four core problems of mechanical strength, performance balance, long-term stability and production consistency in the field for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a component connection relationship diagram of the preparation system of the high-strength MBR ultrafiltration membrane of the application.

[0029] Explanation of reference signs: 1-nitrogen tank, 2-nitrogen valve, 3-stirring tank nitrogen valve, 4-stirring tank, 5-stirring tank outlet valve, 6-deaeration tank nitrogen valve, 7-deaeration tank, 8-spinning metering pump, 9-infrared real-time monitoring device, 10-adjustable spinneret, 11-woven tube pay-off device, 12-first-stage coagulation bath, 13-second-stage coagulation bath, 14-third-stage coagulation bath, 15-filleting wheel, 16-filleting wheel water tank, 17-stirring tank temperature and pressure control circuit, 18-deaeration tank temperature and pressure control circuit, 19-spinning pump control circuit, 20-computer control system, 21-spinneret control circuit, 22-woven tube pay-off device control circuit, 23-infrared real-time monitoring device signal feedback circuit, 24-first-stage coagulation bath temperature and concentration feedback circuit, 25-second-stage coagulation bath temperature and concentration feedback circuit, 26-third-stage coagulation bath temperature and concentration feedback circuit, 27-filleting wheel spinning speed control circuit, 28-first-stage coagulation bath discharge solenoid valve, 29-first-stage coagulation bath inlet solenoid valve, 30-second-stage coagulation bath inlet solenoid control valve, 31-second-stage coagulation bath discharge solenoid control valve, 32-third-stage coagulation bath inlet solenoid control valve, 33-third-stage coagulation bath discharge solenoid control valve, 34-third-stage coagulation bath discharge control circuit, 35-first-stage coagulation bath discharge control circuit, 36-first-stage coagulation bath inlet control circuit, 37-second-stage coagulation bath discharge control circuit, 38-second-stage coagulation bath inlet control circuit, 39-third-stage coagulation bath inlet control circuit. DETAILED DESCRIPTION

[0030] Example 1 The embodiment provides a spinning dope for high-strength MBR ultrafiltration membranes, which comprises polyvinylidene fluoride, polyether sulfone, a composite additive, a composite nano reinforcing agent and an organic solvent.

[0031] In a preferred embodiment, the polyvinylidene fluoride (PVDF) content is 10% to 25%, the polyether sulfone (PES) content is 2% to 8%, the composite additive content is 8% to 25%, the composite nano reinforcing agent content is 0.5% to 3%, and the organic solvent content is 49% to 75%.

[0032] In a preferred embodiment, the composite additive comprises polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA), and the mass ratio of the polyvinylpyrrolidone to the polyacrylic acid is 4:1 to 1:1. The composite nano reinforcing agent is a mixture of modified silicon dioxide and graphene oxide, and the mass ratio of the modified silicon dioxide to the graphene oxide is 3:1 to 1:1.

[0033] The modified silica is fumed silica treated with a silane coupling agent (such as γ-aminopropyl triethoxysilane, KH-550) on the surface, with a primary particle size of 10-30 nm. The fumed silica can be commercially available, such as the corresponding model in the Evonik AEROSIL ® series; the graphene oxide is a single-layer or few-layer graphene oxide water dispersion that can be commercially available, with a sheet size of 0.5 μm-5 μm, such as the relevant product provided by Xianfeng Nanometer Technology Co., Ltd.; The organic solvent is one or a mixture of N-methyl pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc), and when it is a mixture, the mass ratio of NMP to DMAc is 2:1 to 1:4.

[0034] In a specific implementation ratio, the raw material ratio of the spinning dope is: PVDF: 18%, PES: 4%, PVP-K17 (K17 is the molecular weight level): 12%, PAA: 4%, modified silica: 0.4%, graphene oxide: 0.6%, DMAc: 45%, NMP: 16%.

[0035] Preparation process of MBR ultrafiltration membrane: the raw materials in Example 1 were added to stirring tank 4 in a proportion, stirred at 65°C and 90 r / min for 15 hours to form a uniform spinning dope. The spinning dope was transferred to a defoaming tank 7, and defoaming was carried out at a vacuum degree of -0.075 MPa and a temperature of 62°C for 16 hours. After defoaming, the spinning dope was transported to an adjustable spinneret 10 at a speed of 32 r / min through a spinning metering pump 8, coated on a plasma-treated polyester and polyamide braided tube, and an infrared real-time monitoring device 9 was used for online monitoring to control the thickness at 250±5 μm.

[0036] The coated nascent membrane successively passed through: a primary coagulation bath (DMAc content 25%, temperature 48°C), a secondary coagulation bath (NMP content 12%, temperature 48°C), and a tertiary coagulation bath (pure water, temperature 52°C), with a drawing speed of 14 m / min. After spinning, the membrane filaments were immersed in deionized water for 15 hours, and then treated in a water solution of 20% glycerol and PVA composite hydrophilic agent (mass ratio 1:1) for 15 hours.

[0037] Finally, gradient heat setting was carried out: successively at 65°C for 1 h, 75°C for 1 h, and 85°C for 2 h.

[0038] Performance test results: tensile strength: 118 MPa; pure water flux: 480 L / (m²·h); surface pore size: 0.03 μm; porosity: 70%; bubble point pressure: 0.23 MPa.

[0039] Another set of specific spinning dope raw material ratio: PVDF: 14%, PES: 5%, PVP-K30: 10%, PAA: 3%, modified silica: 0.8%, graphene oxide: 0.7%, DMAc: 50%, NMP: 16.5%; The preparation process of the MBR ultrafiltration membrane: the raw materials are stirred at 70℃ and 100r / min for 12 hours to form a spinning dope. The degassing conditions are: vacuum degree-0.08MPa, temperature 65℃, time 14 hours. The spinning metering pump 8 rotates at 28r / min, and the drawing speed is 16m / min. The coagulation bath parameters are: first stage (DMAc content 30%, temperature 45℃), second stage (NMP content 15%, temperature 45℃), and third stage (pure water, temperature 55℃). Post-processing: soaked in deionized water for 12 hours, treated with 18% glycerol / PVA composite hydrophilic agent (mass ratio 1.5:1) for 18 hours.

[0040] Gradient heat setting: 60℃ for 1h, 70℃ for 1h, 80℃ for 2h.

[0041] Performance test results: tensile strength: 115MPa; pure water flux: 560L / (m²·h); surface pore size: 0.028μm; porosity: 75%; bubble point pressure: 0.25MPa; the above examples prove that the MBR ultrafiltration membrane prepared by the method of the present application has excellent comprehensive performance and completely achieves the expected technical effect.

[0042] As can be seen, the present embodiment also provides a high-strength MBR ultrafiltration membrane, which comprises a woven tube and a spinning dope coated on the woven tube. The woven tube coated with the spinning dope is subjected to solidification and heat setting treatment to obtain the MBR ultrafiltration membrane.

[0043] Example 2: The present embodiment provides a preparation method of a high-strength MBR ultrafiltration membrane, which comprises the following steps: Step 1: mix polyvinylidene fluoride, polyether sulfone, composite additive, composite nano reinforcing agent and organic solvent according to the formula proportion; stir at 45℃ to 85℃ for 8 hours to 20 hours to form a uniform spinning dope; Step 2: degas the spinning dope obtained in step 1 at a vacuum degree of-0.065 MPa to-0.088 Mpa and a temperature of 45℃ to 75℃ for 8 hours to 20 hours; Step 3: coat the degassed spinning dope on the woven tube at the adjustable spinneret 10 through the spinning metering pump 8, the discharge speed of the spinning metering pump 8 is controlled at 18r / min to 55r / min, and the coating thickness is real-time adjusted and controlled through the infrared real-time monitoring device 9; Step 4: The coated nascent membrane is shaped by passing through a first coagulation bath 12, a second coagulation bath 13 and a third coagulation bath 14 in sequence, the temperature of the coagulation baths being controlled at 25-70°C, and the drawing speed being 5-30 m / min; Step 5: The shaped membrane filament is soaked in deionized water for 6-24 hours, treated with a solution of a composite hydrophilic agent for 6-24 hours, and finally gradient heat set at 20-100°C for 1-5 hours in a room, to obtain a finished product of MBR ultrafiltration membrane.

[0044] The composition of the spinning dope in Step 1 is the spinning dope in Example 1.

[0045] In a preferred embodiment, the braided tube in Step 3 is a polyester and polyamide composite braided tube treated by plasma, and the braided tube is pretreated by plasma before use, to remove surface organic contaminants by physical bombardment, and to introduce polar active groups such as hydroxyl (-OH) and carboxyl (-COOH) on the fiber surface by chemical reaction. After plasma treatment, the braided tube is stably grafted with oxygen-containing polar functional groups mainly including hydroxyl (-OH) and carboxyl (-COOH) on the fiber surface. The mechanism of plasma treatment belongs to the prior art. More detailed explanations are given below: In a plasma field, active particles are generated by ionization of oxygen-containing gas (such as oxygen or air), and the basic process of surface chemical modification of polymer fibers is as follows: initiation: high-energy particles break the C-H bond of the molecular chain of the fiber surface polymer, generating surface macromolecular radicals (R•). Oxidation: the radical rapidly combines with oxygen (O2) in the atmosphere to generate a peroxide radical (R-O-O•). Transformation: the peroxide radical forms unstable peroxide by hydrogen abstraction reaction, and further decomposes to generate an alkoxy radical (R-O•). This radical is stabilized by hydrogen abstraction, i.e. forming a surface hydroxyl group (R-OH). Deep oxidation: the alkoxy radical or intermediate oxidation product (such as aldehyde) can further react with active oxygen species, and finally generate a carboxyl group (R-COOH) at the chain end. By introducing hydroxyl (-OH) and carboxyl (-COOH), the wettability and interfacial bonding strength with the spinning dope are improved. The above explanation of the mechanism belongs to the common general knowledge in the art, and can be implemented by referring to the prior art.

[0046] The device for plasma treatment has a power of 100-1000 W or 300-700 W, and a treatment time of 10-1200 seconds or preferably 30-800 seconds; the surface energy of the braided tube is ≥45 mN / m; and the control accuracy of the infrared real-time monitoring device 9 is ±5 μm.

[0047] The primary coagulation bath 12 in step 4 is a primary mixture of water and N,N-dimethylacetamide, the mass content of N,N-dimethylacetamide in the primary mixture is 15% to 35%, and the temperature is 35-55℃; the secondary coagulation bath 13 is a secondary mixture of water and N-methylpyrrolidone, the content of N-methylpyrrolidone in the secondary mixture is 8% to 18%, and the temperature is 35℃ to 55℃; the tertiary coagulation bath 14 is pure water, and the temperature is 45℃ to 58℃.

[0048] The composite hydrophilic agent in step 5 is a composite solution of glycerol and polyvinyl alcohol in water, the mass ratio of glycerol to polyvinyl alcohol is 2:1 to 1:1, and the total mass concentration of glycerol and polyvinyl alcohol in the composite solution is 12-48%; the gradient heat setting includes three stages: the first stage is treated at 60℃ to 70℃ for 1 hour, the second stage is treated at 70℃ to 80℃ for 1 hour, and the third stage is treated at 80℃ to 90℃ for 1 hour-2 hours.

[0049] The finished MBR ultrafiltration membrane is a hollow fiber membrane with a gradient change structure, that is, the pore size and structure of the membrane separation layer present a gradient change in the cross section perpendicular to the length of the hollow fiber membrane, that is, a gradient change structure with an outer layer of ultra-thin dense separation layer and an inner layer of highly interconnected sponge-like support layer; the outer diameter of the hollow fiber membrane is 0.9mm to 3.5mm, and the inner diameter is 0.5 to 2.8mm; the tensile strength of the membrane filament is ≥100MPa, the pure water flux is ≥450L / (m²·h), the surface pore size is 0.02μm to 0.1μm, and the porosity is ≥70%.

[0050] Example 3: As Figure 1 shown, the embodiment provides a preparation system for high-strength MBR ultrafiltration membrane, which includes a stirring tank 4, a stirring tank outlet valve 5, a defoaming tank 7, a spinning metering pump 8, an adjustable spinneret 10, a multi-stage coagulation bath device, a yarn collecting wheel 15 and a yarn collecting wheel water tank 16 connected in sequence; It also includes a braided tube pay-off device 11 which supplies a braided tube to the adjustable spinneret 10; the spinning metering pump 8 supplies a spinning dope to the braided tube of the adjustable spinneret 10, and the spinning dope uses the spinning dope of example 1.

[0051] In a preferred embodiment, the multi-stage coagulation bath device has a primary coagulation bath 12, a secondary coagulation bath 13 and a tertiary coagulation bath 14 connected in sequence; Also includes a nitrogen system, the nitrogen system has nitrogen tank 1, nitrogen valve 2, stirring tank nitrogen valve 3 and nitrogen valve 6 of defoaming tank, the nitrogen tank 1 is connected with stirring tank nitrogen valve 3 and nitrogen valve 6 of defoaming tank respectively through the nitrogen valve 2, the stirring tank nitrogen valve 3 is connected with the stirring tank 4 downstream;The defoaming tank nitrogen valve 6 is connected with the defoaming tank 7 downstream; Also includes computer control system 20, the computer control system 20 is connected with the stirring tank 4 through stirring tank temperature and pressure control line 17, to control the temperature and pressure of the stirring tank 4; The computer control system 20 is connected with the defoaming tank 7 through defoaming tank temperature and pressure control line 18, to control the temperature and pressure of the defoaming tank 7; The computer control system 20 is connected with the spinning metering pump 8 through spinning pump control line 19; The computer control system 20 is connected with the adjustable spinneret 10 through spinneret control line 21, to control the spinning rate of the adjustable spinneret 10; The computer control system 20 is connected with the braided tube pay-off device 11 through braided tube pay-off device control line 22, to control the pay-off rate of the braided tube pay-off device 11; The computer control system 20 is connected with the infrared real-time monitoring device 9 through infrared real-time monitoring device signal feedback line 23, to control the coating thickness; The computer control system 20 is connected with the primary coagulation bath 12 through primary coagulation bath temperature and concentration feedback line 24, to control the temperature and concentration of the primary coagulation bath 12; The computer control system 20 is connected with the secondary coagulation bath 13 through secondary coagulation bath temperature and concentration feedback line 25, to control the temperature and concentration of the secondary coagulation bath 13; The computer control system 20 is connected with the tertiary coagulation bath 14 through tertiary coagulation bath temperature and concentration feedback line 26, to control the temperature and concentration of the tertiary coagulation bath 14; The computer control system 20 is connected with the receiving wheel 15 through receiving wheel receiving speed control line 27, to control the receiving speed of the receiving wheel 15; The primary coagulation bath 12 is connected with primary coagulation bath discharge electromagnetic valve 28 and primary coagulation bath inlet electromagnetic valve 29 respectively; The secondary coagulation bath 13 is connected with secondary coagulation bath inlet electromagnetic control valve 30 and secondary coagulation bath discharge electromagnetic control valve 31 respectively; The tertiary coagulation bath 14 is connected with tertiary coagulation bath inlet electromagnetic control valve 32 and tertiary coagulation bath discharge electromagnetic control valve 33 respectively; The computer control system 20 is connected with the third coagulation bath discharge electromagnetic control valve 33 through a third coagulation bath discharge control line 34; The computer control system 20 is connected with the third coagulation bath discharge electromagnetic control valve 33 through a third coagulation bath discharge control line 34; The computer control system 20 is connected with the first coagulation bath discharge electromagnetic valve 28 through a first coagulation bath discharge control line 35; The computer control system 20 is connected with the first coagulation bath discharge electromagnetic valve 28 through a first coagulation bath discharge control line 35; The computer control system 20 is connected with the second coagulation bath discharge electromagnetic control valve 31 through a second coagulation bath discharge control line 37; The computer control system 20 is connected with the second coagulation bath discharge electromagnetic control valve 31 through a second coagulation bath discharge control line 37.

[0052] As to the control mode of the computer control system 20, the specific feedback and control technology adopts the prior art. For example, the control of pressure and temperature adopts the feedback of sensors and the control of heating and pressurizing equipment, the control of wheel speed is realized by adjusting the motor speed, the control of concentration is realized by the existing automatic feeding system, and the flow regulation is realized by valves or pressure control.

[0053] The use method of the system comprises the following steps: First step: raw material preparation and pretreatment: According to the formula, the components are weighed: polyvinylidene fluoride is 10% to 25%, polyether sulfone is 2% to 8%, polyvinylpyrrolidone is 5% to 15%, polyacrylic acid is 2% to 8%, modified silicon dioxide is 0.2% to 1.5%, graphene oxide is 0.3% to 1.5%, and the organic solvent of N-methylpyrrolidone and N,N-dimethylacetamide is 49% to 75%, and the braided tube is subjected to plasma pretreatment, the power of the device for plasma treatment is 100 W -1000W, and the treatment time is 10 seconds to 1200 seconds; the surface energy is increased to ≥45mN / m, and good interface bonding is ensured; Second step: intelligent spinning dope preparation: The raw materials are added into the stirring tank 4: the stirring parameters are set by the computer control system 20: temperature 45℃ to 85℃, rotation speed 40 r / min to 140 r / min, the substances in the first step are added in turn, and the stirring time is 8-20 hours, until a uniform transparent spinning dope is formed; Vacuum defoaming treatment: the spinning dope is transferred to the defoaming tank 7, and defoaming is performed at a vacuum degree of -0.065 MPa to -0.088 MPa and a temperature of 45 DEG C to 85 DEG C for 8-20 hours, and the defoaming process is monitored in real time by a pressure sensor; Third step: precision spinning and online monitoring: Parameter setting: the rotation speed of the spinning metering pump 8 is 18 r / min to 55 r / min, the drawing speed is 5 m / min to 30 m / min, and the temperature of the adjustable spinneret 10 is 30-60 DEG C; Real-time monitoring and adjustment: the infrared real-time monitoring device 9 measures the coating thickness in real time with an accuracy of ±5 μm, and the computer control system 20 dynamically adjusts the rotation speed of the adjustable spinneret 10 and the spinning metering pump 8 according to the coating thickness data, and the braided tube pay-off device 11 ensures constant tension to avoid fluctuations; Fourth step: multi-stage gradient coagulation forming: In the first coagulation bath, the solvent content is 15% to 35%, the temperature is 35 DEG C to 55 DEG C, and the residence time is 10 seconds to 30 seconds; the first coagulation bath is used to complete the preliminary phase separation and form the basic skeleton of the membrane; In the second coagulation bath, the solvent content is 8% to 18%, the temperature is 35 DEG C to 55 DEG C, and the residence time is 20 seconds to 50 seconds, further promoting phase separation, that is, guiding the formation of an outer phase ultra-thin dense separation layer and an inner phase highly interconnected sponge-like support layer. Because the solvent concentration in the second coagulation bath is significantly reduced, the water intrusion speed is accelerated, driving the phase separation to a deeper and more thorough direction, refining the pore structure and promoting the formation of a sponge-like structure on the cross section; The third coagulation bath is pure water, the temperature is 45 DEG C to 58 DEG C, and the residence time is 30 seconds to 60 seconds, to complete the final phase separation and solidify the membrane structure; Fifth step: post-treatment and performance optimization: Cleaning treatment: immersion in deionized water for 8 hours to 20 hours to completely remove residual solvents; the water temperature is controlled at 25 DEG C to 40 DEG C; Hydrophilic treatment: the concentration of the composite solution of glycerol and polyvinyl alcohol in water is 12% to 48%; the treatment time is 8 hours to 20 hours, and the treatment temperature is 30 DEG C to 50 DEG C; Gradient heat setting: first stage: 60 DEG C to 70 DEG C, 1 hour; second stage: 70 DEG C to 80 DEG C, 1 hour; third stage: 80 DEG C to 90 DEG C, 1 hour to 2 hours.

[0054] Compared with the prior art, the MBR ultrafiltration membrane prepared by the present application exhibits breakthrough comprehensive performance: the tensile strength reaches more than 110 MPa, the pure water flux exceeds 450 L / (m²·h), and at the same time, the accurate surface pore size of 0.02 μm to 0.03 μm and excellent long-term running stability are maintained.

[0055] This technology not only solves the problems of broken wire, pollution and performance degradation in MBR application for a long time, but also provides a reliable technical path for the industrial production of high-performance ultrafiltration membrane, which has important engineering application value.

[0056] In summary, the fundamental difference between the product of the present application and the existing product is the change from "single material modification" to "multi-scale composite system design".

[0057] Specifically: Difference one: adopt the composite structure of "woven tube skeleton + nano reinforced separation layer".

[0058] Prior art: mostly use homogeneous membrane (no support, poor strength) or simple support tube (insufficient density, easy to peel off).

[0059] The product: uses high-density woven tube as a macroscopic skeleton to bear the main stress, and introduces composite nano reinforcing agent (modified silicon dioxide + graphene oxide) for micro toughening in the separation layer.

[0060] The problem solved: fundamentally solves the problem of broken wire due to insufficient strength of the membrane wire, and prevents cracks or leaks in the separation layer during long-term use, greatly improving the service life and operation reliability of the membrane.

[0061] Difference two: use "composite formula + three-stage gradient coagulation" synergistic process.

[0062] Prior art: formula is relatively simple (such as single polymer or additive), process is mostly single or two-stage coagulation, and it is difficult to accurately control the membrane structure.

[0063] The product of the present application: adopts PVDF / PES composite polymer and PVP / PAA composite additive, and is matched with three-stage gradient coagulation bath process to accurately control the film forming process.

[0064] The problem solved: successfully breaks the "trade-off phenomenon" of membrane performance, and realizes high strength, high precision (small pore size) and high flux, solving the contradiction of traditional membrane "one strong, one weak".

[0065] Difference three: introduce "persistent hydrophilic layer" construction technology.

[0066] Prior art: often modified by physically blending a single hydrophilic agent (such as PVP), but it is easy to lose and the hydrophilic effect is not persistent.

[0067] The product: through the composite hydrophilic agent (glycerol + PVA) and gradient heat setting process, a stable cross-linked hydrophilic network is formed in the membrane.

Claims

1. A spinning solution for high-strength MBR ultrafiltration membranes, characterized in that, It includes polyvinylidene fluoride, polyethersulfone, composite additives, composite nano-reinforcing agents, and organic solvents.

2. The spinning solution for high-strength MBR ultrafiltration membranes according to claim 1, characterized in that, According to the mass percentage: the polyvinylidene fluoride content is 10% to 25%, the polyethersulfone content is 2% to 8%, the composite additive content is 8% to 25%, the composite nano-reinforcing agent content is 0.5% to 3%, and the organic solvent content is 49% to 75%.

3. The spinning solution for high-strength MBR ultrafiltration membranes according to claim 1, characterized in that, The composite additive includes polyvinylpyrrolidone and polyacrylic acid, wherein the mass ratio of polyvinylpyrrolidone to polyacrylic acid is 4:1 to 1:

1. The composite nano-reinforcing agent is a mixture of modified silica and graphene oxide, wherein the mass ratio of modified silica to graphene oxide is 3:1 to 1:

1. The organic solvent is one or a mixture of N-methylpyrrolidone and N,N-dimethylacetamide, wherein if it is a mixture, the mass ratio of N-methylpyrrolidone to N,N-dimethylacetamide is 2:1 to 1:

4.

4. A high-strength MBR ultrafiltration membrane, characterized in that, The device includes a braided tube and a spinning solution coated on the braided tube, wherein the spinning solution is the spinning solution as described in any one of claims 1 to 3, and the braided tube coated with the spinning solution is subjected to curing and heat setting treatment.

5. A method for preparing a high-strength MBR ultrafiltration membrane, characterized in that, Includes the following steps: Step 1: Mix polyvinylidene fluoride, polyethersulfone, composite additives, composite nano-reinforcing agents and organic solvents according to the formula ratio, and stir at 45℃ to 85℃ for 8 to 20 hours to form a uniform spinning solution. Step 2: Degas the spinning solution obtained in Step 1 under a vacuum of -0.065 MPa to -0.088 MPa and a temperature of 45°C to 75°C for 8 to 20 hours. Step 3: The defoamed spinning solution is coated onto the braided tube at the adjustable spinneret (10) by the spinning metering pump (8). The output speed of the spinning metering pump (8) is controlled between 18 r / min and 55 r / min, and the coating thickness is adjusted in real time by the infrared real-time monitoring device (9). Step 4: The coated nascent membrane is formed by passing through a primary coagulation bath (12), a secondary coagulation bath (13), and a tertiary coagulation bath (14) in sequence. The temperature of the coagulation bath is controlled between 25°C and 70°C, and the traction speed is between 5m / min and 30m / min. Step 5: Soak the formed membrane fibers in deionized water for 6 to 24 hours, treat them with a solution of composite hydrophilic agent for 6 to 24 hours, and finally perform gradient heat setting at 20°C to 100°C indoors for 1 to 5 hours to obtain the finished MBR ultrafiltration membrane.

6. The method for preparing a high-strength MBR ultrafiltration membrane according to claim 5, characterized in that: The spinning solution in step 1 is composed of the spinning solution as described in claim 2 or 3.

7. The method for preparing a high-strength MBR ultrafiltration membrane according to claim 5, characterized in that: The braided tube in step 3 is a polyester and polyamide composite braided tube that has been plasma treated, and the surface energy of the braided tube is ≥45mN / m; The braided tube is pretreated with plasma before use to remove organic pollutants from the surface through physical bombardment and to introduce hydroxyl and carboxyl polar active groups on the fiber surface through chemical reaction, thereby improving the wettability and interfacial bonding strength with the spinning solution. The power of the plasma treatment device is 100 W-1000 W and the treatment time is 10 seconds to 1200 seconds. The control accuracy of the infrared real-time monitoring device (9) is ±5μm; The primary coagulation bath (12) in step 4 is a primary mixture of water and N,N-dimethylacetamide, wherein the mass content of N,N-dimethylacetamide in the primary mixture is 15% to 35%, and the temperature is 35-55℃; the secondary coagulation bath (13) is a secondary mixture of water and N-methylpyrrolidone, wherein the N-methylpyrrolidone content in the secondary mixture is 8% to 18%, and the temperature is 35℃ to 55℃; the tertiary coagulation bath (14) is pure water, and the temperature is 45℃ to 58℃; The composite hydrophilic agent in step 5 is a composite solution of glycerol and polyvinyl alcohol in water, with a mass ratio of glycerol to polyvinyl alcohol of 2:1 to 1:1, and a total mass concentration of glycerol and polyvinyl alcohol in the composite solution of 12-48%. The gradient heat setting includes three stages: the first stage is treatment at 60°C to 70°C for 1 hour, the second stage is treatment at 70°C to 80°C for 1 hour, and the third stage is treatment at 80°C to 90°C for 1-2 hours. The finished MBR ultrafiltration membrane is a hollow fiber membrane with a gradient structure. The gradient structure refers to the gradient change in pore size and structure of the membrane separation layer along a cross-section perpendicular to the length of the hollow fiber membrane, forming a gradient structure with an outer ultrathin dense separation layer and an inner highly permeable sponge-like support layer. The outer diameter of the hollow fiber membrane is 0.9 mm to 3.5 mm, and the inner diameter is 0.5 mm to 2.8 mm. The membrane fiber tensile strength is ≥100 MPa, the pure water flux is ≥450 L / (m²·h), the surface pore size is 0.02 μm to 0.1 μm, and the porosity is ≥70%.

8. A system for preparing a high-strength MBR ultrafiltration membrane, characterized in that, It includes a mixing tank (4), a mixing tank outlet valve (5), a degassing tank (7), a spinning metering pump (8), an adjustable spinneret (10), a multi-stage coagulation bath device, a take-up wheel (15), and a take-up wheel water tank (16) connected in sequence. It also includes a braided tube feeding device (11) that supplies braided tubes to the adjustable spinneret (10); the spinning metering pump (8) sprays spinning solution onto the braided tubes supplied to the adjustable spinneret (10), the spinning solution being the spinning solution as described in any one of claims 1 to 3.

9. The high-strength MBR ultrafiltration membrane preparation system according to claim 8, characterized in that, The multi-stage coagulation bath device has a first-stage coagulation bath (12), a second-stage coagulation bath (13) and a third-stage coagulation bath (14) connected in sequence. It also includes a nitrogen system, which has a nitrogen tank (1), a nitrogen valve (2), a stirring tank nitrogen valve (3), and a degassing tank nitrogen valve (6). The nitrogen tank (1) is connected to the stirring tank nitrogen valve (3) and the degassing tank nitrogen valve (6) respectively through the nitrogen valve (2). The stirring tank nitrogen valve (3) is connected downstream to the stirring tank (4). The degassing tank nitrogen valve (6) is connected downstream to the degassing tank (7). It also includes a computer control system (20), which is connected to the mixing tank (4) via a mixing tank temperature and pressure control line (17) to control the temperature and pressure of the mixing tank (4); The computer control system (20) is connected to the degassing tank (7) via the degassing tank temperature and pressure control line (18) to control the temperature and pressure of the degassing tank (7); The computer control system (20) is connected to the spinning metering pump (8) through the spinning pump control line (19). The computer control system (20) is connected to the adjustable spinneret (10) via the spinneret control line (21) to control the filament output temperature and rate of the adjustable spinneret (10). The computer control system (20) is connected to the braided tube pay-off device (11) via the braided tube pay-off device control line (22) to control the pay-off rate of the braided tube pay-off device (11). The computer control system (20) is connected to the infrared real-time monitoring device (9) through the infrared real-time monitoring device signal feedback line (23) for controlling the coating thickness; The computer control system (20) is connected to the primary coagulation bath (12) through the primary coagulation bath temperature and concentration feedback line (24) to control the temperature and concentration of the primary coagulation bath (12); The computer control system (20) is connected to the secondary coagulation bath (13) through the secondary coagulation bath temperature and concentration feedback line (25) to control the temperature and concentration of the secondary coagulation bath (13); The computer control system (20) is connected to the three-stage coagulation bath (14) through the three-stage coagulation bath temperature and concentration feedback line (26) to control the temperature and concentration of the three-stage coagulation bath (14); The computer control system (20) is connected to the take-up wheel (15) via the take-up wheel take-up speed control line (27) to control the take-up speed of the take-up wheel (15); The primary coagulation bath (12) is connected to the primary coagulation bath discharge solenoid valve (28) and the primary coagulation bath inlet solenoid valve (29), respectively. The secondary coagulation bath (13) is connected to the secondary coagulation bath inlet solenoid control valve (30) and the secondary coagulation bath outlet solenoid control valve (31), respectively. The three-stage coagulation bath (14) is connected to the three-stage coagulation bath inlet solenoid control valve (32) and the three-stage coagulation bath outlet solenoid control valve (33), respectively. The computer control system (20) is connected to the three-stage coagulation bath discharge electromagnetic control valve (33) through the three-stage coagulation bath discharge control line (34). The computer control system (20) is connected to the three-stage coagulation bath induction solenoid control valve (32) through the three-stage coagulation bath induction control line (39). The computer control system (20) is connected to the primary coagulation bath discharge solenoid valve (28) through the primary coagulation bath discharge control line (35). The computer control system (20) is connected to the primary coagulation bath inlet solenoid valve (29) through the primary coagulation bath inlet control line (36). The computer control system (20) is connected to the secondary coagulation bath discharge electromagnetic control valve (31) through the secondary coagulation bath discharge control line (37). The computer control system (20) is connected to the secondary coagulation bath solenoid control valve (30) via the secondary coagulation bath entry control line (38).

10. The method of using the high-strength MBR ultrafiltration membrane preparation system according to claim 9, characterized in that, Includes the following steps: Step 1: Raw material preparation and pretreatment: Weigh the following components according to the formula: 10% to 25% polyvinylidene fluoride, 2% to 8% polyethersulfone, 5% to 15% polyvinylpyrrolidone, 2% to 8% polyacrylic acid, 0.2% to 1.5% modified silica, 0.3% to 1.5% graphene oxide, and 49% to 75% organic solvent of N-methylpyrrolidone and N,N-dimethylacetamide composite. Pre-treat the braided tube with plasma. The plasma treatment device has a power of 100 W to 1000 W and a treatment time of 10 seconds to 1200 seconds. The surface energy is increased to ≥45 mN / m to ensure good interfacial bonding. Step 2: Intelligent preparation of spinning solution: Add the raw materials into the mixing tank (4): Set the mixing parameters through the computer control system (20): temperature 45℃ to 85℃, rotation speed 40 r / min to 140 r / min, add the substances in the first step in sequence, ensure full dissolution and dispersion, and stir for 8-20 hours until a uniform and transparent spinning solution is formed. Vacuum degassing treatment: The spinning solution is transferred to the degassing tank (7) and degassed for 8-20 hours under vacuum conditions of -0.065 MPa to -0.088 MPa and temperature of 45°C to 85°C; Step 3: Precision spinning and online monitoring: Parameter settings: The spinning metering pump (8) speed: 18r / min to 55r / min; traction speed: 5m / min to 30m / min; the adjustable spinneret (10) temperature: 30-60℃; Real-time monitoring and adjustment: The infrared real-time monitoring device (9) measures the coating thickness in real time with an accuracy of ±5μm; the computer control system (20) dynamically adjusts the speed of the adjustable spinneret (10) and the spinning metering pump (8) according to the coating thickness data; the braided tube feeding device (11) ensures constant tension and avoids fluctuations. Step 4: Multi-level gradient solidification and molding: In the primary coagulation bath, the solvent content is 15% to 35%, the temperature is 35°C to 55°C, and the residence time is 10 to 30 seconds; the primary coagulation bath is used to complete the initial phase separation and form the basic framework of the membrane. In the secondary coagulation bath, the solvent content is 8% to 18%; the temperature is 35°C to 55°C; and the residence time is 20 to 50 seconds. This further promotes phase separation, that is, it guides the formation of an ultra-thin and dense separation layer of the outer phase and a highly interconnected sponge-like support layer of the inner phase. Because the solvent concentration is significantly reduced in the secondary coagulation bath, the intrusion rate of water is accelerated, driving phase separation to a deeper and more thorough direction, refining the pore structure and promoting the formation of the sponge-like structure. The three-stage coagulation bath is pure water, with a temperature of 45℃ to 58℃ and a residence time of 30 to 60 seconds, to complete the final phase separation and solidify the membrane structure. Step 5: Post-processing and performance optimization: Cleaning treatment: Soak in deionized water for 8 to 20 hours to completely remove residual solvent; water temperature should be controlled between 25°C and 40°C. Hydrophilic treatment: The concentration of the composite solution formed by glycerol and polyvinyl alcohol in water is 12% to 48%; the treatment time is 8 to 20 hours and the treatment temperature is 30°C to 50°C. Gradient heat setting: First stage: 60℃ to 70℃, 1 hour; Second stage: 70℃ to 80℃, 1 hour; Third stage: 80℃ to 90℃, 1 to 2 hours.

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