Organic tubular membrane as well as preparation method and application thereof

Abstract

The invention discloses an organic tubular membrane and a preparation method and application thereof, and belongs to the technical field of membrane separation. The organic tubular membrane comprises a membrane separation layer and a non-woven fabric supporting layer, and the membrane separation layer is formed by membrane casting liquid coating the inner surface of the non-woven fabric supporting layer through a phase inversion method; wherein the membrane casting solution is prepared from the following components in percentage by mass: 20 to 25 percent of polyvinylidene fluoride, 0.5 to 0.7 percent of modified halloysite, 1.5 to 2 percent of poly (propylene glycol)-block-poly (ethylene glycol)-block-poly (propylene glycol) and the balance of solvent. The organic tubular membrane disclosed by the invention has the characteristics of good separation effect and high mechanical strength, and has important significance for solving the problem of separation of fermentation liquor with complex components and relieving membrane pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to an organic tubular membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The organic tubular membrane is a new type of separation membrane. Due to its advantages such as simple process flow, stable operation, and good separation effect, it has been widely used in the fields of high-concentration sewage treatment, special chemical wastewater treatment, oil-water separation, material separation, food, and filtration of biopharmaceutical fermentation broth. In the field of biopharmaceutical fermentation broth, due to the complex composition of the fermentation broth, membrane materials, pore sizes, structures, operating conditions (temperature, pressure, pH, etc.), and membrane cleaning methods all affect selectivity, flux, membrane fouling degree, membrane service life, and overall cost.

[0003] At present, the organic tubular membrane mainly consists of a support structure and an active separation layer. The support structure of the organic tubular membrane is generally non-woven fabric. As a support layer, it not only provides mechanical support for the membrane separation layer, but also its own structural characteristics, such as pore size, surface roughness, etc., are also important factors affecting membrane separation performance. The active separation layer is generally an ultrafiltration membrane or a microfiltration membrane structure, which is generally obtained by the phase separation method of polymer casting solution. The main preparation method is to coat the inner wall or outer wall of the support tube with the organic polymer casting solution to form a membrane. The current organic tubular membrane has problems of uneven thickness of the membrane coating and local defect pores, resulting in differences in membrane permeability and local leakage, which affect the application of the organic tubular membrane.

[0004] Patent CN115463553A discloses a non-woven fabric support layer with a double-layer structure. By setting the bottom layer and the surface layer with different linear densities, the problem of the casting solution penetrating to the reverse side of the non-woven fabric is solved. However, this patent has technical problems such as low mechanical strength, easy to break under pressure, and the membrane is easily fouled and cannot be used for a long time. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an organic tubular membrane, a preparation method thereof, and an application thereof. The organic tubular membrane has the characteristics of good separation effect and high mechanical strength, and is of great significance for solving the separation problem of complex fermentation broth and alleviating membrane fouling.

[0006] To achieve the above purpose, according to one aspect of the present invention, there is provided an organic tubular membrane, including a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by the phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, calculated by mass percentage, includes the following components: 20-25% of polyvinylidene fluoride, 0.5-0.7% of modified halloysite, 1.5-2% of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance of solvent.

[0007] In the present invention, the non-woven fabric support layer is made of polyester non-woven fabric or polypropylene non-woven fabric.

[0008] In the present invention, the modified halloysite is halloysite composite-modified with tannic acid and amino-silane coupling agent. Preferably, the mass ratio of tannic acid to amino-silane coupling agent is 1:1. More preferably, the mass ratio of halloysite, tannic acid and amino-silane coupling agent is 1:1:1. Further preferably, the amino-silane coupling agent is γ-aminopropyltriethoxysilane.

[0009] In the present invention, in the casting solution, the mass percentage of polyvinylidene fluoride is 20-25%. It can be understood that its mass percentage can be any specific value among 20%, 21%, 22%, 23%, 24%, 25% or any value within the range of 20-25%.

[0010] In the present invention, in the casting solution, the mass percentage of modified halloysite is 0.5-0.7%. It can be understood that its mass percentage can be any specific value among 0.5%, 0.6%, 0.7% or any value within the range of 0.5-0.7%.

[0011] The inventors of the present application found that adding a certain amount of halloysite composite-modified with tannic acid and amino-silane coupling agent to the system of the present application can significantly improve the separation efficiency and mechanical strength of the organic tubular membrane. During the modification process, the phenolic hydroxyl groups of tannic acid are oxidized to benzoquinone under weak alkaline conditions and react with the amino groups in the amino-silane coupling agent. After the alkoxy groups of the amino-silane coupling agent form hydrogen bonds with the phenolic hydroxyl groups of tannic acid and hydrolyze, they self-condense to form oligomers, and a hydrophilic coating is formed on the surface of halloysite through this complex cross-linked structure. On the one hand, the long-chain structure enables the modified halloysite to entangle with the hydrophobic poly(propylene glycol) chain segments at both ends of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and the polyvinylidene fluoride chain segments, increasing the compatibility among the three. On the other hand, during the phase inversion process, a large number of hydrophilic groups will promote the migration of the modified halloysite to the surface, improving the surface wettability of the membrane, thereby improving the separation efficiency of the membrane. The inventors also found that it is necessary to strictly control the addition amount of the modified halloysite in the system. When the addition amount is too high, secondary aggregation will occur in the polyvinylidene fluoride-based membrane, thereby blocking the membrane pores, being unfavorable for the transmission of the solution, and thus affecting the separation performance of the membrane; when the addition amount is too low, it will also affect the mechanical strength and separation effect of the membrane.

[0012] In the present invention, in the casting solution, the mass percentage of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 1.5-2%. It can be understood that the mass percentage can be any specific value among 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or any value within the range of 1.5-2%.

[0013] In the present invention, the number-average molecular weight of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3000-3500. In the present invention, in poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the mass content of the poly(ethylene glycol) block is 10-15%. It can be understood that the mass content can be any specific value among 10%, 11%, 12%, 13%, 14%, 15% or any value within the range of 10-15%. The present invention further regulates the interaction between the hydrophobic segment, the hydrophilic segment and the polyvinylidene fluoride-based membrane by controlling the mass content of the poly(ethylene glycol) block, thereby regulating the pore size on the membrane surface and improving the pore structure of the membrane, and enhancing the separation effect of the membrane. If the mass content of the poly(ethylene glycol) block is too high, the anchoring effect of the hydrophobic segment is weakened, and the poly(ethylene glycol) segment is likely to be lost from the membrane, thus affecting the separation effect and anti-pollution property. In addition, the hydrophilic poly(ethylene glycol) block with low surface energy forms a hydration layer on the surface of the organic tubular membrane through hydrogen bonds, inhibiting the adhesion caused by the direct interaction between the pollutants and the membrane surface, thereby improving the anti-pollution property of the tubular organic membrane. The poly(propylene glycol) hydrophobic segments at both ends can be fully wound with the polyvinylidene fluoride-based membrane to form a firm and stable structure.

[0014] Surprisingly, to the inventors of the present application, adding a certain amount of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and modified halloysite in the system of the present application, the two acting synergistically, significantly improves the separation effect and mechanical strength of the organic tubular membrane, and at the same time improves the anti-fouling property. The modified halloysite has special structures and physicochemical properties. During the film-forming process, it will entangle with poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol). The hydrophilic groups form a hydration layer on the surface of the organic tubular membrane through hydrogen bonds, thereby affecting the morphological structure of the membrane, improving the microscopic morphological structure of the membrane, and further enhancing the separation effect and anti-fouling performance of the membrane. In addition, by further controlling the contents of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and modified halloysite and the number-average molecular mass of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the casting solution of the present application has appropriate viscosity and fluidity, thereby avoiding the problems of uneven thickness of the membrane coating and local defective pores, and at the same time being able to induce the generation of finger-like pore structures in the membrane cross-section, regulating the pore size on the membrane surface, thereby significantly improving the pore structure of the membrane and enhancing the separation effect of the membrane. If the viscosity is too low, it will cause the phenomenon that the casting solution excessively penetrates into the non-woven fabric, reducing the separation effect.

[0015] In the present invention, the solvent is selected from one or two of N,N-dimethylacetamide or N,N-dimethylformamide.

[0016] According to another aspect of the present invention, there is also provided a method for preparing the above-mentioned organic tubular membrane, the method comprising the following steps: (1) Prepare a casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and a solvent in proportion, and stir evenly at a constant temperature of 65-70 °C in a water bath for 4-6 h to obtain a casting solution; (2) Let the casting solution stand for defoaming under vacuum for 10-48 h, and place it together with the non-woven fabric on an integral tubular scraping film machine for tube-coiling film coating to obtain a primary organic tubular membrane; (3) Prepare the organic tubular membrane by the phase inversion method: Immerse the primary organic tubular membrane in a deionized water coagulation bath for 48-60 h, change the deionized water every 6 h, and air-dry at room temperature to obtain the organic tubular membrane.

[0017] In some embodiments, in step (1), a casting solution is prepared: polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and a solvent are mixed in proportion, and stirred uniformly at a constant temperature of 65 - 70 °C in a water bath for 4 - 6 h to obtain the casting solution. In the present invention, the modified halloysite in step (1) is obtained through the following steps: halloysite is dispersed in Tris buffer solution, an amino silane coupling agent and tannic acid are added, the pH value of the system is controlled at 7.6 - 7.8, stirred at room temperature for 24 - 36 h, centrifuged, washed, and dried to obtain the modified halloysite. Preferably, the washing is performed using anhydrous ethanol and deionized water. More preferably, the drying temperature is 50 - 60 °C.

[0018] In some embodiments, in step (2), the casting solution is allowed to stand and defoam under vacuum for 10 - 48 h, and then placed on an integrated tubular scraping film machine together with non-woven fabric to roll tube and coat the film, obtaining a primary organic tubular membrane. Preferably, the coating pressure is 0.1 - 2 MPa, and the coating speed is 5 - 100 cm / min.

[0019] In some embodiments, in step (3), an organic tubular membrane is prepared by a phase inversion method: the primary organic tubular membrane is immersed in a deionized water coagulation bath and soaked for 48 - 60 h, and the deionized water is changed every 6 h, and then air-dried at room temperature to obtain the organic tubular membrane.

[0020] According to another aspect of the present invention, there is also provided an application of the above-mentioned organic tubular membrane or the organic tubular membrane prepared by the above method in a fermentation broth.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention creatively designs an organic tubular membrane. By using a casting solution with specific components, the separation effect, mechanical strength and anti-pollution property of the obtained organic tubular membrane are significantly improved. Specifically, a certain amount of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and modified halloysite are added to the casting solution, and the two act synergistically to significantly improve the separation effect and mechanical strength of the organic tubular membrane, and at the same time improve the anti-pollution property.

[0022] (2) The present invention further uses halloysite modified by a composite of tannic acid and an amino silane coupling agent, which can significantly improve the separation efficiency and mechanical strength of the tubular organic membrane. On the one hand, the long-chain structure enables the modified halloysite to entangle with the polyvinylidene fluoride chain segments, increasing its compatibility with the polyvinylidene fluoride-based membrane. On the other hand, during the phase inversion process, a large number of hydrophilic groups will promote the migration of the modified halloysite to the surface, improving the surface wettability of the membrane, thereby improving the separation efficiency of the membrane.

[0023] (3)The present invention also provides a method for preparing an organic tubular membrane, which is simple and easy to operate and suitable for large-scale production. Detailed Embodiments

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art regarding the present invention. In case of conflict, the definition in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether right or wrong, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0026] In this article, when describing embodiments or examples, it should be understood that it is not used to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described in the present invention can be covered within the scope defined by the claims.

[0027] In this article, for the sake of brevity of description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0028] The present invention provides an organic tubular membrane, which is characterized in that it includes a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by a phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, by mass percentage, includes the following components: 20-25% of polyvinylidene fluoride, 0.5-0.7% of modified halloysite, 1.5-2% of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance of solvent.

[0029] In some embodiments, the non-woven fabric support layer is made of polyester non-woven fabric or polypropylene non-woven fabric.

[0030] In some embodiments, the modified halloysite is halloysite composite-modified with tannic acid and amino-silane coupling agent.

[0031] In some embodiments, the mass ratio of tannic acid to amino-silane coupling agent is 1:1.

[0032] In some embodiments, the solvent is selected from one or two of N,N-dimethylacetamide or N,N-dimethylformamide.

[0033] In some embodiments, the number-average molecular weight of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3000 - 3500.

[0034] In some embodiments, in the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the mass content of the poly(ethylene glycol) block is 10 - 15%.

[0035] The present invention also provides a method for preparing the above-mentioned organic tubular membrane, and the method includes the following steps: (1) Prepare a casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and a solvent in proportion, and stir evenly at a constant temperature of 65 - 70 °C in a water bath for 4 - 6 h to obtain a casting solution; (2) Let the casting solution stand for defoaming under vacuum for 10 - 48 h, and place it together with non-woven fabric on an integrated tubular film scraping machine to roll and coat the film to obtain a primary organic tubular membrane; (3) Prepare the organic tubular membrane by the phase inversion method: Immerse the primary organic tubular membrane in a deionized water coagulation bath for 48 - 60 h, change the deionized water every 6 hours, and dry it at room temperature to obtain the organic tubular membrane.

[0036] In some embodiments, the modified halloysite in step (1) is obtained through the following steps: Disperse halloysite in Tris buffer solution, add an amino silane coupling agent and tannic acid, control the pH value of the system at 7.6 - 7.8, stir at room temperature for 24 - 36 h, centrifuge, wash, and dry to obtain the modified halloysite.

[0037] The present invention also provides an application of the above-mentioned organic tubular membrane or the organic tubular membrane prepared according to the above method in a fermentation broth.

[0038] The present invention will be described in detail below through examples. It should be understood that the following examples are only used to further explain and illustrate the content of the present invention exemplarily, and are not used to limit the present invention.

[0039] Example 1 is the best example.

[0040] The chemical auxiliaries used in the examples and comparative examples of the present invention are all commercially available, and the specific information is as follows: Polyvinylidene fluoride: weight-average molecular weight of 400,000, purchased from Aladdin Reagent Co., Ltd.; Poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol): number-average molecular weight of 3,300, poly(ethylene glycol) block content of 10 wt%, purchased from Merck Chemical; Tannic acid, N,N-dimethylacetamide, N,N-dimethylformamide: purchased from Aladdin Reagent Co., Ltd.; Amino silane coupling agent: γ-aminopropyltriethoxysilane, purchased from Aladdin Reagent Co., Ltd.; Halloysite: diameter of 50 - 300 nm, length of 1 - 10 μm, purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.; Polyester non-woven fabric: purchased from Toray; Polypropylene non-woven fabric: purchased from Zhejiang Naisite Non-woven Fabric Co., Ltd.; Pure water: self-made in the laboratory.

[0041] Example 1 An organic tubular membrane described in this example includes a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by the phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, by mass percentage, includes the following components: 22% of polyvinylidene fluoride, 0.6% of modified halloysite, 1.8% of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance of solvent. The modified halloysite is halloysite compound-modified with tannic acid and amino silane coupling agent in a mass ratio of 1:1. The non-woven fabric is polyester non-woven fabric. The solvent is N,N-dimethylacetamide.

[0042] The preparation method of the organic tubular membrane described in this example includes the following steps: (1) Prepare the casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the solvent in proportion, and stir evenly at a constant temperature of 65 °C in a water bath for 6 h to obtain the casting solution. The modified halloysite is obtained through the following steps: Disperse 1 g of halloysite in 500 mL of Tris buffer solution, add 1 g of amino silane coupling agent and 1 g of tannic acid, control the pH value of the system at 7.8, stir at room temperature for 24 h, centrifuge, wash with absolute ethanol and deionized water, and dry at 60 °C to obtain the modified halloysite. (2) Let the casting solution stand and defoam under vacuum for 48 h, and place it on an integrated tubular scraping film machine together with the non-woven fabric to roll and coat the film to obtain a primary organic tubular membrane. The coating pressure is 2 MPa, and the coating speed is 100 cm / min. (3) Prepare the organic tubular membrane by the phase inversion method: Immerse the primary organic tubular membrane in a deionized water coagulation bath and soak for 60 h, change the deionized water every 6 h, and air-dry at room temperature to obtain the organic tubular membrane.

[0043] Example 2 An organic tubular membrane according to this embodiment includes a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by a phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, by mass percentage, includes the following components: 20% polyvinylidene fluoride, 0.5% modified halloysite, 1.5% poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance is solvent; the modified halloysite is halloysite composite-modified with tannic acid and amino silane coupling agent in a mass ratio of 1:1; the non-woven fabric is polypropylene non-woven fabric; the solvent is N,N-dimethylformamide.

[0044] The preparation method of the organic tubular membrane according to this embodiment includes the following steps: (1) Prepare the casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent in proportion, and stir evenly at 70 °C in a constant temperature water bath for 4 h to obtain the casting solution; the modified halloysite is obtained through the following steps: Disperse 1 g of halloysite in 500 mL of Tris buffer solution, add 1 g of amino silane coupling agent and 1 g of tannic acid, control the pH value of the system at 7.6, stir at room temperature for 36 h, centrifuge, wash with absolute ethanol and deionized water, and dry at 50 °C to obtain the modified halloysite; (2) Let the casting solution stand and defoam under vacuum for 10 h, and place it on an integrated tubular scraping coater together with the non-woven fabric to roll the tube and coat the film to obtain a primary organic tubular membrane; the coating pressure is 0.1 MPa, and the coating speed is 5 cm / min; (3) Prepare the organic tubular membrane by the phase inversion method: Immerse the primary organic tubular membrane in a deionized water coagulation bath and soak for 48 h, change the deionized water every 6 h, and air dry at room temperature to obtain the organic tubular membrane.

[0045] Example 3 An organic tubular membrane according to this embodiment includes a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by a phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, by mass percentage, includes the following components: 25% polyvinylidene fluoride, 0.7% modified halloysite, 2% poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance is solvent; the modified halloysite is obtained by using tannic acid and amino silane coupling agent for composite modification; the non-woven fabric is polyester non-woven fabric; the solvent is N,N-dimethylacetamide.

[0046] The preparation method of the organic tubular membrane according to this embodiment includes the following steps: (1) Prepare the casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and a solvent in proportion, and stir evenly for 6 h under the condition of a constant temperature water bath at 65 °C to obtain the casting solution; the modified halloysite is obtained through the following steps: Disperse halloysite in Tris buffer solution, add an amino-silane coupling agent and tannic acid with a mass ratio of 1:1, control the pH value of the system at 7.8, stir at room temperature for 30 h, centrifuge, wash with absolute ethanol and deionized water, and dry at 50 °C to obtain the modified halloysite; (2) Let the casting solution stand and defoam under vacuum for 30 h, and place it together with the non-woven fabric on an integrated tubular film scraping machine to wind the tube and coat the film to obtain a primary organic tubular membrane; the coating pressure is 1 MPa, and the coating speed is 50 cm / min; (3) Prepare the organic tubular membrane by the phase inversion method: Immerse the primary organic tubular membrane in a deionized water coagulation bath and soak for 60 h, change the deionized water every 6 h, and air-dry at room temperature to obtain the organic tubular membrane.

[0047] Comparative Example 1 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the mass content of the poly(ethylene glycol) block in the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 30%.

[0048] Comparative Example 2 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the number average molecular mass of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 2000.

[0049] Comparative Example 3 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the mass percentage content of the modified halloysite is 0.9%.

[0050] Comparative Example 4 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the mass percentage content of the modified halloysite is 0.2%.

[0051] Comparative Example 5 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the mass percentage content of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3%.

[0052] Comparative Example 6 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the mass percentage content of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 1%.

[0053] Comparative Example 7 The preparation method of the organic tubular membrane in this comparative example is exactly the same as that in Example 1, except that the modified halloysite used is obtained only by modification with an amino-silane coupling agent; specifically, the modified halloysite is obtained through the following steps: 1 g of halloysite is dispersed in 500 mL of Tris buffer solution, 1 g of amino-silane coupling agent is added, the pH value of the system is controlled at 7.8, stirred at room temperature for 24 h, centrifuged, washed with absolute ethanol and deionized water, and dried at 60 °C to obtain the modified halloysite.

[0054] Application Example The feed liquid to be treated used in the application example is a simulated feed liquid with a composition similar to that of a microbial fermentation broth. The composition of the simulated feed liquid includes: 106 inactivated Escherichia coli per mL, 20 g / L of bovine serum albumin (BSA), 0.1 mol / L of NaCl, 0.02 mol / L of MgCl2, 0.02 mol / L of CaCl2, 20 g / L of 1,3-propanediol, 5 g / L of glycerol, 5 g / L of glucose, 5 g / L of 2,3-butanediol, 2 g / L of ethanol, 4 g / L of acetic acid, 4 g / L of butyric acid, 4 g / L of succinic acid; 2 L, pH = 7.0.

[0055] The organic tubular membranes obtained in Examples 1-3 and Comparative Examples 1-7 were respectively installed in a tubular membrane module, and then assembled with a booster pump, a frame, a pressure gauge, a pipeline flowmeter, and an electric control system into a membrane separation device. The simulated feed liquid was added to the membrane separation device, the operating pressure was set at 3 bar, the operating temperature was 30 °C, the flow rate was 3 m / s, the membrane separation device was started for separation operation, and the permeate was collected.

[0056] Performance Test The organic tubular membranes obtained in Examples 1-3 and Comparative Examples 1-7 and the permeate obtained in the application example were subjected to performance tests according to the following methods, and the specific results are shown in Table 1.

[0057] (1) Average pore size: Tested using a bubble point method pore size analyzer.

[0058] (2) Porosity: The porosity was determined by the dry-wet weight method.

[0059] (3) Tensile strength at break: Specimens with a length of 240 mm were prepared, and the tensile strength at break of the specimens was tested using a tensile machine.

[0060] (4) Initial pure water flux: the volume of pure water passing through the membrane per unit time, per unit area, and per unit transmembrane pressure at a temperature of 25 °C and a pressure of 0.1 MPa.

[0061] (5) Water flux recovery rate: After passing pure water through the membrane separation equipment that has processed the simulated feed liquid in the application example for cleaning, measure the pure water flux after cleaning. The test conditions are: temperature 25 °C, pressure 0.1 MPa. According to the formula: Water flux recovery rate = (pure water flux after cleaning / initial pure water flux) × 100%, calculate the water flux recovery rate. The larger the water flux recovery rate, the better the anti-fouling property.

[0062] (6) BSA rejection rate: It is measured using an ultraviolet-visible spectrophotometer. Select an appropriate wavelength to measure the absorbance values of the permeate and the simulated feed liquid. BSA rejection rate = (1 - concentration of BSA in the permeate / concentration of BSA in the simulated feed liquid) × 100%.

[0063] Table 1 Performance data of Examples 1-3 and Comparative Examples 1-7 。

[0064] It can be seen from Table 1 that the average pore size and porosity of the organic tubular membranes described in Examples 1-3 are relatively large, the breaking tensile strength is relatively high, and at the same time, the water flux recovery rate and BSA rejection rate are relatively high, indicating that the separation effect, mechanical strength, and anti-fouling property of the organic tubular membranes obtained using the casting solution of the present invention are good. By comparing Example 1 with Comparative Example 1, it can be seen that the mass content of the poly(ethylene glycol) block in the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) described in Comparative Example 1 is relatively high, the anchoring effect of the hydrophobic chain segment is weakened, and the poly(ethylene glycol) chain segment is easily lost from the membrane, resulting in a decrease in the water flux recovery rate and BSA rejection rate of the membrane. By comparing Example 1 with Comparative Example 2, it can be seen that the number-average molecular weight of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) described in Comparative Example 2 is relatively low, the viscosity of the casting solution is relatively low, and the casting effect is not good, resulting in a decrease in the water flux recovery rate and BSA rejection rate of the membrane and a deterioration of the separation effect. By comparing Example 1 with Comparative Examples 3 and 4, it can be seen that the mass percentage content of the modified halloysite in Comparative Examples 3 and 4 is relatively high or low, and the breaking tensile strength and separation effect of the obtained tubular membranes are both deteriorated. By comparing Example 1 with Comparative Examples 5 and 6, it can be seen that the mass percentage content of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) in Comparative Examples 5 and 6 is relatively high or low, resulting in a relatively high or low viscosity of the casting solution, affecting the casting effect, and thus resulting in a deterioration of the separation effect and anti-fouling property of the membrane. By comparing Example 1 with Comparative Example 7, it can be seen that the modification method of the modified halloysite used in Comparative Example 7 is different, and the separation effect and anti-fouling property of the obtained tubular membranes are also significantly deteriorated.

[0065] It can be seen that the present invention creatively designs an organic tubular membrane. By using a casting solution with specific components, the separation effect, mechanical strength, and anti-fouling property of the obtained organic tubular membrane are significantly improved. Specifically, a certain amount of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and modified halloysite are added to the casting solution, and their synergistic effect significantly improves the separation effect and mechanical strength of the organic tubular membrane, while also enhancing the anti-fouling property. In addition, by further using halloysite composite-modified with tannic acid and amino-silane coupling agent, the separation efficiency and mechanical strength of the tubular organic membrane can be significantly improved. On the one hand, the long-chain structure enables the modified halloysite to entangle with the polyvinylidene fluoride chain segments, increasing its compatibility with the polyvinylidene fluoride base membrane. On the other hand, during the phase inversion process, a large number of hydrophilic groups will promote the migration of the modified halloysite to the surface, improving the surface wettability of the membrane, thereby enhancing the separation efficiency of the membrane.

[0066] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, based on the above description, other different forms of changes or variations can be made. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. An organic tubular membrane, characterized in that, It includes a membrane separation layer and a non-woven fabric support layer. The membrane separation layer is formed by a phase inversion method from a casting solution coated on the inner surface of the non-woven fabric support layer. Among them, the casting solution, by mass percentage, includes the following components: 20-25% of polyvinylidene fluoride, 0.5-0.7% of modified halloysite, 1.5-2% of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), and the balance of solvent.

2. The organic tubular membrane according to claim 1, characterized in that, The non-woven fabric support layer is made of polyester non-woven fabric or polypropylene non-woven fabric.

3. An organic tubular membrane according to claim 1, wherein The modified halloysite is halloysite composite modified by tannic acid and amino silane coupling agent.

4. The organic tubular membrane according to claim 3, characterized in that, The mass ratio of the tannic acid to the amino silane coupling agent is 1:

1.

5. An organic tubular membrane according to claim 1, characterized in that, The solvent is selected from one or both of N,N-dimethylacetamide or N,N-dimethylformamide.

6. An organic tubular membrane according to claim 1, wherein The number average molecular weight of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3000-3500.

7. An organic tubular membrane according to claim 1, characterized in that, In the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the mass content of the poly(ethylene glycol) block is 10-15%.

8. A method for preparing an organic tubular membrane according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) Prepare the casting solution: Mix polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent in proportion, and stir evenly for 4-6 h under the condition of a constant temperature water bath at 65-70 °C to obtain the casting solution; (2) Let the casting solution stand for defoaming for 10-48 h under vacuum conditions, and place it on an integral tube-type film scraping machine together with the non-woven fabric for tube winding and film coating to obtain a primary organic tube membrane; (3) Prepare the organic tube membrane by the phase inversion method: Immerse the primary organic tube membrane in a deionized water coagulation bath and soak it for 48-60 h, change the deionized water every 6 h, and air dry at room temperature to obtain the organic tube membrane.

9. The preparation method of an organic tubular membrane according to claim 8, characterized in that, In step (1), the modified halloysite is obtained through the following steps: Disperse halloysite in Tris buffer solution, add amino silane coupling agent and tannic acid, control the pH value of the system at 7.6-7.8, stir at room temperature for 24-36 h, centrifuge, wash, and dry to obtain the modified halloysite.

10. Application of the organic tube membrane according to any one of claims 1-7 or the organic tube membrane prepared by the method according to any one of claims 8-9 in a fermentation broth.