An organic tubular membrane, its preparation method and use

Abstract

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

Description

TECHNICAL FIELD

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

[0002] The organic tubular membrane is a new type of separation membrane, and has the advantages of simple process flow, stable operation and good separation effect, and is widely used in the fields of high-concentration sewage treatment, special chemical wastewater treatment, oil-water separation, material separation, food, and fermentation broth of biological pharmaceuticals. In the field of fermentation broth of biological pharmaceuticals, the composition of the fermentation broth is complex, and the membrane material, pore size, structure, operating conditions (temperature, pressure, pH, etc.), and membrane cleaning method all affect the selectivity, flux, membrane pollution degree, service life of the membrane, 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 a non-woven fabric, which not only provides mechanical support for the membrane separation layer, but also has structural characteristics such as pore size and surface roughness, which are important factors affecting the separation performance of the membrane. The active separation layer is generally a structure of ultrafiltration membrane or microfiltration membrane, which is generally obtained by phase separation of a high-molecular polymer casting solution, and the main preparation method is to coat the organic high-molecular polymer casting solution on the inner wall or outer wall of the support tube to prepare a membrane. The current organic tubular membrane has the problems of uneven thickness and local defect holes of the membrane coating, which leads to differences in permeation performance of the membrane and local leakage, affecting the application of the organic tubular membrane.

[0004] Patent CN115463553A discloses a double-layer structure of a non-woven fabric support layer, which solves the problem of penetration of the casting solution to the reverse side of the non-woven fabric by setting a bottom layer and a surface layer with different linear densities, but the patent has the technical problems of low mechanical strength, easy to break under pressure, and the membrane is easily polluted and cannot be used for a long time. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide an organic tubular membrane and a preparation method and application thereof, which has the characteristics of good separation effect and high mechanical strength, and is of great significance to solve the problem of separation of complex fermentation broth and alleviate membrane pollution.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, an organic tubular membrane is provided, which comprises a membrane separation layer and a non-woven fabric support layer, the membrane separation layer is formed by a casting solution coated on the inner surface of the non-woven fabric support layer by phase inversion method; wherein the casting solution comprises the following components in mass percentage: polyvinylidene fluoride 20-25%, modified halloysite 0.5-0.7%, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) 1.5-2%, and the balance is a solvent.

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

[0008] In the present application, the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent. Preferably, the mass ratio of tannic acid and 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-aminopropyl triethoxysilane.

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

[0010] In the present application, the mass percentage of modified halloysite in the casting solution is 0.5-0.7%. It can be understood that the mass percentage can be any specific value of 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 the addition of a certain amount of halloysite modified by tannic acid and amino silane coupling agent in 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 group of tannic acid is oxidized to benzoquinone under weak alkaline conditions and reacts with the amino group in the amino silane coupling agent. The alkoxyl group of the amino silane coupling agent forms a hydrogen bond with the phenolic hydroxyl group of tannic acid after hydrolysis, and then condenses to form an oligomer. A hydrophilic coating layer is formed on the surface of the halloysite through this complex cross-linking structure. On the one hand, the long-chain structure enables the modified halloysite to entangle with the polypropylene glycol hydrophobic segment and the polyvinylidene fluoride segment at both ends of polypropylene glycol)-block-poly(ethylene glycol)-block-polypropylene glycol), thereby 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, thereby improving the wettability of the membrane surface and thus 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. If the addition amount is too high, it will cause secondary agglomeration in the polyvinylidene fluoride-based membrane, thereby blocking the membrane pores and affecting the transmission of the solution, thereby affecting the separation performance of the membrane. If the addition amount is too low, it will also affect the mechanical strength and separation effect of the membrane.

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

[0013] In the application, the number average molecular mass of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3000-3500. In the application, the mass content of poly(ethylene glycol) block in poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 10-15%, which can be understood as any specific value of 10%, 11%, 12%, 13%, 14%, 15% or any value within the range of 10-15%. The application further regulates the interaction between the hydrophobic segment and the hydrophilic segment and the polyvinylidene fluoride-based membrane by controlling the mass content of the poly(ethylene glycol) block, thereby regulating the membrane surface pore size and improving the pore structure of the membrane to improve 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 easily lost from the membrane, thereby 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 bonding, which inhibits 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 segment at both ends can fully entangle with the polyvinylidene fluoride-based membrane to form a firm and stable structure.

[0014] Surprisingly, the inventors of the present application found that the addition of 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 synergistically improves the separation effect and mechanical strength of the organic tubular membrane, and simultaneously improves the anti-fouling property. The modified halloysite has special structure and physicochemical properties, and will intertwine with the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) during the membrane forming process. The hydrophilic groups form a hydration layer on the surface of the organic tubular membrane through hydrogen bonding, thereby affecting the morphological structure of the membrane, improving the micro-morphology of the membrane, and further improving the separation effect and anti-fouling performance of the membrane. In addition, by further controlling the content of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and the modified halloysite and the number average molecular weight of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the casting solution of the present application has suitable viscosity and fluidity, thereby avoiding the problems of uneven thickness and local defect holes in the membrane coating, and simultaneously inducing the formation of finger-like hole structure in the membrane cross-section and regulating the pore size of the membrane surface, thereby significantly improving the pore structure of the membrane and improving the separation effect of the membrane. If the viscosity is too low, the casting solution will excessively penetrate into the non-woven fabric, thereby reducing the separation effect.

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

[0016] According to another aspect of the present application, there is also provided a preparation method of the above-mentioned organic tubular membrane, which comprises the following steps:

[0017] (1) preparing a casting solution: mixing polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and a solvent in a proportion, and stirring at a constant temperature of 65-70°C for 4-6h to obtain a casting solution;

[0018] (2) placing the casting solution under vacuum for 10-48h to remove bubbles, and coiling the non-woven fabric on an integrated tubular film coater to coat the membrane, thereby obtaining a nascent organic tubular membrane;

[0019] (3) preparing an organic tubular membrane by phase inversion: immersing the nascent organic tubular membrane in a deionized water coagulation bath for 48-60h, replacing the deionized water every 6 hours, and drying at room temperature to obtain the organic tubular membrane.

[0020] In some embodiments, in step (1), the casting solution is prepared: polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent are mixed in proportion, stirred at a constant temperature water bath 65-70℃ for 4-6h, to obtain the casting solution. In the present application, the modified halloysite in step (1) is obtained by the following steps: halloysite is dispersed in Tris buffer, 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 24-36h, centrifuged, washed, dried to obtain the modified halloysite. Preferably, the washing is using anhydrous ethanol and deionized water. More preferably, the drying temperature is 50-60℃.

[0021] In some embodiments, in step (2), the casting solution is placed under vacuum for 10-48h, and is coated on the non-woven fabric together on an integrated pipe type film applicator to obtain a nascent organic pipe type membrane. Preferably, the coating pressure is 0.1-2MPa, and the coating speed is 5-100cm / min.

[0022] In some embodiments, in step (3), the organic pipe type membrane is prepared by phase inversion method: the nascent organic pipe type membrane is immersed in a deionized water coagulation bath for 48-60h, the deionized water is replaced every 6 hours, and the membrane is air dried at room temperature to obtain the organic pipe type membrane.

[0023] According to another aspect of the present application, there is also provided a use of the above-mentioned organic pipe type membrane or the organic pipe type membrane prepared according to the above-mentioned method in fermentation broth.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] (1) The present application creatively designs an organic pipe type membrane, which has significantly improved separation effect, mechanical strength and anti-pollution by using a specific component of the casting solution. 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, which synergistically improves the separation effect and mechanical strength of the organic pipe type membrane, and also improves the anti-pollution.

[0026] (2) The present application can significantly improve the separation efficiency and mechanical strength of the pipe type organic membrane by further using tannic acid and amino silane coupling agent to modify the halloysite. On the one hand, the long chain structure makes the modified halloysite entangle with the polyvinylidene fluoride segment, 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.

[0027] (3) The application further provides a preparation method of the organic tubular membrane, which is simple and easy to operate and suitable for large-scale production. DETAILED DESCRIPTION

[0028] To enable those skilled in the art to better understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings to those skilled in the art of the present application, and in case of conflict, the definition in the specification shall prevail.

[0029] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the present application, i.e., the present application can be practiced without regard to any particular theory or mechanism.

[0030] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present application to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the described methods and materials included in the scope defined by the claims are intended to be covered.

[0031] Herein, for the sake of brevity, all possible combinations of the various technical features described in the various embodiments or examples are not described. Therefore, any combination of the various technical features in the various embodiments or examples can be made as long as there is no contradiction, and all possible combinations should be considered as the scope of the present disclosure.

[0032] The present application provides an organic tubular membrane, characterized in that it comprises a membrane separation layer and a non-woven fabric support layer, the membrane separation layer is formed by a casting solution coated on the inner surface of the non-woven fabric support layer by phase inversion method; wherein the casting solution comprises the following components by mass percentage: polyvinylidene fluoride 20-25%, modified halloysite 0.5-0.7%, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) 1.5-2%, and the balance is solvent.

[0033] In some embodiments, the non-woven fabric support layer is made of polyester non-woven fabric or polypropylene non-woven fabric.

[0034] In some embodiments, the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent.

[0035] In some embodiments, the mass ratio of tannic acid and amino silane coupling agent is 1:1.

[0036] In some embodiments, the solvent is selected from one or both of N,N-dimethylacetamide or N,N-dimethylformamide.

[0037] In some embodiments, the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) has a number average molecular weight of 3000-3500.

[0038] In some embodiments, in the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol), the poly(ethylene glycol) block has a mass content of 10-15%.

[0039] The present application also provides a preparation method of the above organic tubular membrane, comprising the following steps:

[0040] (1) preparing a casting solution: mixing polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent in proportion, stirring at a constant speed in a constant-temperature water bath at 65-70℃ for 4-6h to obtain a casting solution;

[0041] (2) placing the casting solution in a vacuum condition for 10-48h to remove bubbles, and coiling a tube to coat a film on an integrated tubular film applicator together with a non-woven fabric to obtain a nascent organic tubular membrane;

[0042] (3) preparing an organic tubular membrane by phase inversion: immersing the nascent organic tubular membrane in a deionized water coagulation bath for 48-60h, replacing the deionized water every 6 hours, and drying at room temperature to obtain the organic tubular membrane.

[0043] In some embodiments, the modified halloysite in step (1) is obtained by the following steps: dispersing halloysite in Tris buffer, adding amino silane coupling agent and tannic acid, controlling the pH value of the system at 7.6-7.8, stirring at room temperature for 24-36h, centrifuging, washing, and drying to obtain the modified halloysite.

[0044] The present application also provides an application of the above organic tubular membrane or the organic tubular membrane prepared according to the above method in fermentation broth.

[0045] The present application will be described in detail through the following examples. It should be understood that the following examples are only used to exemplarily further explain and illustrate the content of the present application, and are not used to limit the present application.

[0046] Example 1 is the best mode of the present application.

[0047] The chemical additives used in the examples and comparative examples of the present application are all commercially available, and the specific information is as follows:

[0048] Polyvinylidene fluoride: weight average molecular mass 400000, purchased from Aldrich Reagent Co., Ltd.; poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol): number average molecular weight 3300, poly(ethylene glycol) block content 10 wt%, purchased from Merck Chemical; tannic acid, N,N-dimethylacetamide, N,N-dimethylformamide: purchased from Aldrich Reagent Co., Ltd.; amino silane coupling agent: γ-aminopropyl triethoxysilane, purchased from Aldrich Reagent Co., Ltd.; halloysite: diameter 50-300 nm, length 1-10 μm, purchased from Jiangsu Xianfeng Nanometer Material 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 laboratory.

[0049] Example 1

[0050] The organic tubular membrane described in this example comprises a membrane separation layer and a non-woven fabric support layer, and the membrane separation layer is formed by phase inversion method from casting solution coated on the inner surface of the non-woven fabric support layer; wherein the casting solution comprises the following components in terms of mass percentage: polyvinylidene fluoride 22%, modified halloysite 0.6%, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) 1.8%, and the balance solvent; the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent at a mass ratio of 1:1; the non-woven fabric is polyester non-woven fabric; and the solvent is N,N-dimethylacetamide.

[0051] The preparation method of the organic tubular membrane described in this example comprises the following steps:

[0052] (1) Preparation of casting solution: polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent are mixed in proportion, and stirred at a constant speed in a constant temperature water bath at 65℃ for 6h to obtain the casting solution; the modified halloysite is obtained by the following steps: 1g of halloysite is dispersed in 500mL of Tris buffer, 1g of amino silane coupling agent and 1g of tannic acid are added, the pH value of the system is controlled at 7.8, and stirring is carried out at room temperature for 24h, followed by centrifugation, washing with anhydrous ethanol and deionized water, and drying at 60℃ to obtain the modified halloysite;

[0053] (2) The casting solution is placed under vacuum for 48h to remove bubbles, and is wound with non-woven fabric on an integrated tubular film coater to coat the film, to obtain a nascent organic tubular membrane; the coating pressure is 2MPa, and the coating speed is 100cm / min;

[0054] (3) Preparation of organic tubular membrane by phase inversion method: the nascent organic tubular membrane is immersed in a deionized water coagulation bath for 60h, and the deionized water is replaced every 6h, and the organic tubular membrane is obtained after air drying at room temperature.

[0055] Example 2

[0056] The organic tubular membrane described in this embodiment comprises a membrane separation layer and a non-woven fabric support layer, and the membrane separation layer is formed by a phase inversion method using a casting solution coated on the inner surface of the non-woven fabric support layer; wherein the casting solution comprises the following components by mass percentage: polyvinylidene fluoride 20%, modified halloysite 0.5%, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) 1.5%, and the balance solvent; the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent at a mass ratio of 1:1; the non-woven fabric is polypropylene non-woven fabric; and the solvent is N,N-dimethylformamide.

[0057] The preparation method of the organic tubular membrane described in this embodiment comprises the following steps:

[0058] (1) Preparation of casting solution: polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and solvent are mixed in proportion, and stirred uniformly at 70°C in a constant temperature water bath for 4h to obtain the casting solution; the modified halloysite is obtained by the following steps: 1g of halloysite is dispersed in 500mL of Tris buffer, 1g of amino silane coupling agent and 1g of tannic acid are added, the pH value of the system is controlled at 7.6, and stirring is performed at room temperature for 36h, followed by centrifugation, washing with anhydrous ethanol and deionized water, and drying at 50°C to obtain the modified halloysite;

[0059] (2) The casting solution is placed under vacuum for 10h to remove bubbles, and is wound on a non-woven fabric to coat a film on a one-piece tubular film coater to obtain a nascent organic tubular membrane; the coating pressure is 0.1MPa, and the coating speed is 5cm / min;

[0060] (3) Preparation of organic tubular membrane by phase inversion method: the nascent organic tubular membrane is immersed in a deionized water coagulation bath for 48h, and the deionized water is replaced every 6 hours, and the organic tubular membrane is obtained after air drying at room temperature.

[0061] Example 3

[0062] The organic tubular membrane described in this embodiment comprises a membrane separation layer and a non-woven fabric support layer, and the membrane separation layer is formed by a phase inversion method using a casting solution coated on the inner surface of the non-woven fabric support layer; wherein the casting solution comprises the following components by mass percentage: polyvinylidene fluoride 20%, modified halloysite 0.5%, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) 1.5%, and the balance solvent; the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent at a mass ratio of 1:1; the non-woven fabric is polypropylene non-woven fabric; and the solvent is N,N-dimethylformamide.

[0063] The preparation method of the organic tubular membrane in the embodiment comprises the following steps:

[0064] (1) preparing a casting solution: mixing polyvinylidene fluoride, modified halloysite, poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) and a solvent at a proportion, stirring at a constant speed for 6 hours under the condition of a constant-temperature water bath at 65°C, to obtain the casting solution; the modified halloysite is obtained by the following steps: dispersing halloysite in Tris buffer, adding amino silane coupling agent and tannic acid at a mass ratio of 1:1, controlling the pH value of the system at 7.8, stirring at room temperature for 30 hours, centrifuging, washing with anhydrous ethanol and deionized water, and drying at 50°C to obtain the modified halloysite;

[0065] (2) placing the casting solution under vacuum for 30 hours of static defoaming, and winding the tube for coating on an integrated tubular film coater together with non-woven fabric to obtain a nascent organic tubular membrane; the coating pressure is 1 MPa, and the coating speed is 50 cm / min;

[0066] (3) preparing the organic tubular membrane by phase inversion: immersing the nascent organic tubular membrane in a deionized water coagulation bath for 60 hours, replacing the deionized water every 6 hours, and drying at room temperature to obtain the organic tubular membrane.

[0067] Comparative Example 1

[0068] The preparation method of the organic tubular membrane in the comparative example is completely same as that in Example 1, and the only difference is 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%.

[0069] Comparative Example 2

[0070] The preparation method of the organic tubular membrane in the comparative example is completely same as that in Example 1, and the only difference is that the number average molecular mass of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 2000.

[0071] Comparative Example 3

[0072] The preparation method of the organic tubular membrane in the comparative example is completely same as that in Example 1, and the only difference is that the mass percentage content of the modified halloysite is 0.9%.

[0073] Comparative Example 4

[0074] The preparation method of the organic tubular membrane in the comparative example is completely same as that in Example 1, and the only difference is that the mass percentage content of the modified halloysite is 0.2%.

[0075] Comparative Example 5

[0076] The preparation method of the organic tubular membrane of the present comparative example is completely the same as that of Example 1, and the only difference is that the mass percentage content of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 3%.

[0077] Comparative Example 6

[0078] The preparation method of the organic tubular membrane of the present comparative example is completely the same as that of Example 1, and the only difference is that the mass percentage content of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) is 1%.

[0079] Comparative Example 7

[0080] The preparation method of the organic tubular membrane of the present comparative example is completely the same as that of Example 1, and the only difference is that the modified halloysite used is obtained by modification with only an amino silane coupling agent; specifically, the modified halloysite is obtained by the following steps: dispersing 1 g of halloysite in 500 mL of Tris buffer, adding 1 g of amino silane coupling agent, controlling the pH value of the system at 7.8, stirring at room temperature for 24 h, centrifuging, washing with anhydrous ethanol and deionized water, and drying at 60°C to obtain the modified halloysite.

[0081] Application Example

[0082] The feed liquid used in the application example is a simulated feed liquid with a composition similar to that of a microbial fermentation liquid, and the composition of the simulated feed liquid includes: 106 inactivated Escherichia coli / mL, bovine serum albumin (BSA) 20 g / L, NaCl 0.1 mol / L, MgCl2 0.02 mol / L, CaCl2 0.02 mol / L, 1,3-propanediol 20 g / L, glycerol 5 g / L, glucose 5 g / L, 2,3-butanediol 5 g / L, ethanol 2 g / L, acetic acid 4 g / L, butyric acid 4 g / L, succinic acid 4 g / L; 2 L, pH = 7.0.

[0083] The organic tubular membranes obtained in Examples 1-3 and Comparative Examples 1-7 are respectively installed in a tubular membrane module, and then assembled into a membrane separation device together with a booster pump, a rack, a pressure gauge, a pipeline flowmeter, and an electric control system. The simulated feed liquid is added to the membrane separation device, the operating pressure is set to 3 bar, the operating temperature is set to 30°C, the flow rate is set to 3 m / s, the membrane separation device is started to operate, and the permeate is collected.

[0084] Performance Test

[0085] The organic tubular membranes obtained in Examples 1-3 and Comparative Examples 1-7 and the permeate obtained in the application example are tested for performance according to the following method, and the specific results are shown in Table 1.

[0086] (1) Average pore size: tested using a bubble point pore size analyzer.

[0087] (2) Porosity: The porosity was measured by the dry-wet weight method.

[0088] (3) Tensile strength at break: The tensile strength at break of the sample was measured by a tensile testing machine.

[0089] (4) Initial pure water flux: The volume of pure water per unit time, per unit area and per unit transmembrane pressure passing through the membrane under the conditions of temperature 25°C and pressure 0.1 MPa.

[0090] (5) Water flux recovery rate: After the membrane separation equipment in the application example was treated with the simulated feed liquid, pure water was introduced into the membrane separation equipment for cleaning, and then the pure water flux after cleaning was measured. The test conditions were temperature 25°C and pressure 0.1 MPa. According to the formula: water flux recovery rate = (pure water flux after cleaning / initial pure water flux) x 100%, the water flux recovery rate was calculated. The greater the water flux recovery rate, the better the anti-pollution property.

[0091] (6) BSA rejection rate: The ultraviolet-visible spectrophotometer was used for measurement. The absorbance values of the permeate and the simulated feed liquid were measured at a suitable wavelength, and the BSA rejection rate = (1 - the concentration of BSA in the permeate / the concentration of BSA in the simulated feed liquid) x 100%.

[0092] Table 1 Performance data of examples 1-3 and comparative examples 1-7

[0093] .

[0094] From Table 1, it can be seen that the organic tubular membranes described in Examples 1-3 have large average pore size and porosity, high tensile strength at break, and high water flux recovery rate and BSA rejection rate, indicating that the organic tubular membranes obtained using the casting solution described in the application have good separation effect, mechanical strength and anti-pollution property. From the comparison between Example 1 and 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 too high, the anchoring effect of the hydrophobic segment is weakened, and the poly(ethylene glycol) segment is prone to be lost from the membrane, resulting in a decrease in the water flux recovery rate and BSA rejection rate of the membrane. From the comparison between Example 1 and 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 too low, the viscosity of the casting solution is too low, and the casting effect is not good, thereby resulting in a decrease in the water flux recovery rate and BSA rejection rate of the membrane and a deterioration in the separation effect. From the comparison between Example 1 and Comparative Examples 3 and 4, it can be seen that the mass percentage of the modified halloysite in Comparative Examples 3 and 4 is too high or too low, and the tensile strength at break and separation effect of the tubular membranes obtained are poor. From the comparison between Example 1 and Comparative Examples 5 and 6, it can be seen that the mass percentage of the poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) in Comparative Examples 5 and 6 is too high or too low, resulting in a high or low viscosity of the casting solution, affecting the casting effect, and thereby resulting in a deterioration in the separation effect and anti-pollution property of the membrane. From the comparison between Example 1 and 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-pollution property of the tubular membrane obtained are also obviously poor.

[0095] It can be seen from the above that the application creatively designs an organic tubular membrane, and the separation effect, mechanical strength and anti-pollution property of the obtained organic tubular membrane are obviously improved by using a casting solution of specific components. 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 components synergistically improve the separation effect and mechanical strength of the organic tubular membrane, and also improve the anti-pollution property. In addition, the application can obviously improve the separation efficiency and mechanical strength of the tubular organic membrane by further using tannic acid and amino silane coupling agent to modify the halloysite. On the one hand, the long chain structure enables the modified halloysite to entangle with the polyvinylidene fluoride segment, increasing the compatibility of the modified halloysite 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, so that the surface wettability of the membrane is improved, thereby improving the separation efficiency of the membrane.

[0096] Obviously, the above embodiments of the present application are merely exemplary for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and here, all the implementation modes cannot be exhausted, and any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. An organic tubular membrane characterized in that, The organic tubular membrane comprises a membrane separation layer and a non-woven fabric support layer, and the membrane separation layer is formed by a phase inversion method using a casting solution coated on the inner surface of the non-woven fabric support layer; wherein the casting solution comprises the following components in terms of mass percentage: polyvinylidene fluoride 20-25%, modified halloysite 0.5-0.7%, polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol 1.5-2%, and the rest solvent; the number average molecular weight of the polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol is 3000-3500; the mass content of the polyethylene glycol block in the polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol is 10-15%; the modified halloysite is halloysite modified by tannic acid and amino silane coupling agent; and the mass ratio of the tannic acid to the amino silane coupling agent is 1:

1.

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

3. The organic tubular membrane according to claim 1, wherein The solvent is selected from one or both of N,N-dimethylacetamide or N,N-dimethylformamide.

4. A method of producing an organic tubular membrane according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: (1) preparing the casting solution: mixing polyvinylidene fluoride, modified halloysite, polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol and solvent in proportion, and stirring at a constant speed in a thermostatic water bath at 65-70°C for 4-6h to obtain the casting solution; (2) placing the casting solution in a vacuum condition for 10-48h to remove bubbles, and coiling the non-woven fabric on an integrated tubular doctor blade coater to coat the membrane to obtain a nascent organic tubular membrane; (3) preparing the organic tubular membrane by a phase inversion method: immersing the nascent organic tubular membrane in a deionized water coagulation bath for 48-60h, replacing the deionized water every 6h, and drying at room temperature to obtain the organic tubular membrane.

5. The method of claim 4, wherein the organic tubular membrane is prepared by the steps of: The modified halloysite in step (1) is obtained by the following steps: dispersing halloysite in Tris buffer, adding amino silane coupling agent and tannic acid, controlling the pH value of the system at 7.6-7.8, stirring at room temperature for 24-36h, centrifuging, washing, and drying to obtain the modified halloysite.

6. Use of the organic tubular membrane according to any one of claims 1-3 or prepared by the method according to any one of claims 4-5 in a fermentation broth.