A MABR composite membrane with high oxygen selectivity and its preparation method

Abstract

This invention discloses a highly oxygen-selective permeable MABR composite membrane and its preparation method, belonging to the field of MABR technology. The highly oxygen-selective MABR composite membrane includes a support layer, an intermediate layer, and an outer layer arranged sequentially from the inside out. The support layer is a polyimide gas separation membrane, the intermediate layer is a superhydrophobic coating composed of a high-fluorine-content polymer, and the outer layer is a hydrophilic rough surface composed of polyester short fibers and organic polymer materials. The highly oxygen-selective MABR composite membrane and its preparation method of this invention can achieve high-efficiency, low-energy-consumption bubble-free aeration and stable biodegradation functions in MABR water treatment processes.

Description

Technical Field

[0001] This invention belongs to the field of MABR technology, and particularly relates to a MABR composite membrane with high oxygen selectivity and its preparation method. Background Technology

[0002] In wastewater treatment, aerobic treatment is a crucial step. Its principle involves introducing air or oxygen into the water to maintain a high dissolved oxygen concentration, allowing activated sludge to undergo aerobic respiration. This promotes the rapid growth and reproduction of aerobic microorganisms, decomposing organic matter into inorganic matter and thus degrading pollutants in the water. The introduction of gas into the water is achieved through an aeration device. The traditional aeration process is as follows: air enters the pipes through a blower and then reaches the aeration device, where it is broken into bubbles of varying sizes that diffuse in the water. These bubbles rise and flow with the water for a period of time before finally bursting at the surface. During this process, some of the oxygen in the bubbles comes into contact with the water and dissolves, promoting microbial reproduction and metabolism. However, traditional aeration processes require high-powered blowers to continuously compress air, resulting in high energy consumption. Furthermore, the bubbles broken by the aeration device are of varying sizes; large bubbles create high-pressure airflow in the water, which diffuses and bursts randomly, disrupting microbial reproduction and metabolism, thus hindering the degradation of organic matter in the water. Most bubbles eventually burst at the surface and return to the air, with only a small portion of the oxygen dissolving in the water, resulting in very low oxygen utilization.

[0003] MABR, short for Membrane Aeration Bio-Reactor, is a novel water treatment technology that combines membrane technology and biotechnology. Unlike traditional bubble aeration, this technology utilizes a gas membrane for bubble-free aeration. Air or oxygen is introduced into the membrane while maintaining the gas pressure below the membrane's bubble point pressure. Oxygen selectively permeates through the MABR membrane, diffusing into the water in molecular form and dissolving rapidly, thus increasing the oxygen content of the water. Compared to traditional aeration processes, the MABR process has lower energy consumption, requires less floor space, is simpler to operate, allows for automated process control, provides a favorable environment for aerobic microbial metabolism and reproduction, and boasts high oxygen utilization (theoretically 100%).

[0004] The core of the MABR process is the MABR membrane. The MABR membrane is not used for filtration. It has two main functions: firstly, it delivers oxygen to the biolayer on the membrane surface. The volume of oxygen delivered is extremely small (theoretically a single molecule of oxygen), which cannot be observed with the naked eye. This is called bubble-free aeration. Secondly, it provides attachment points for microorganisms, promoting their rapid reproduction and metabolism to degrade organic matter in the water. Traditional MABR membranes mainly fall into two categories: one is a microporous membrane made of hydrophobic materials (PTFE, PP, PMP, etc.). Although the surface of this type of membrane has pores, it is highly hydrophobic, so water cannot enter the membrane through the micropores. Gas inside the membrane can be cut into tiny bubbles under extremely low pressure and enter the water on the other side. Although this type of membrane is low in cost and has high gas transfer efficiency, it has poor biocompatibility. Over long-term use, the membrane surface will be contaminated by the metabolic products of microorganisms. Furthermore, this type of membrane lacks gas selectivity; when aerated with air, the microbubbles produced are still composed of air with a relatively low oxygen content. The other type is a homogeneous dense membrane. This type of membrane is mainly made of some silicon-containing hydrophobic polymer materials (PDMS, etc.). The membrane surface is dense and has no pores, so water cannot enter the membrane through the surface. Oxygen inside the membrane "dissolves" upon contact with the membrane and diffuses into the water on the other side under the driving force, a process similar to that of a pervaporation membrane. This type of membrane has good biocompatibility and a dense surface that is not easily contaminated, but its oxygen transfer efficiency is extremely low, and the membrane manufacturing cost is high.

[0005] In summary, high-quality MABR membranes must possess the following excellent properties: First, they need excellent oxygen selective permeability. If oxygen cannot selectively permeate, then aeration can only be done with pure oxygen, which is very costly. When using air for aeration, the oxygen content in the bubbles is very low because the oxygen content in air is only 21%. Second, they need good biocompatibility. Aerobic microorganisms can easily attach to the membrane surface, metabolize and reproduce, and their metabolic products will not contaminate the membrane. Therefore, the outer surface of the membrane needs appropriate hydrophilicity, roughness, and biocompatibility. Third, they need appropriate cost. Too high a cost will hinder the industrial application of MABR membranes. To achieve this goal, many studies have begun to explore the coupling of different materials to prepare MABR composite membranes, combining the advantages of hydrophobic microporous membranes and homogeneous dense membranes, maintaining high gas selective permeability while also possessing good biocompatibility and a certain degree of mechanical strength. Patent CN 110064309 B discloses a composite membrane for MABR and its preparation method. This method uses PVDF as the membrane material, which is mixed with a diluent at high temperature to form a homogeneous membrane liquid. The liquid membrane is then spun into a liquid membrane, cooled in an extractant, and the diluent is extracted. After solidification, a pure PVDF MABR membrane is obtained. This preparation method is simple and easy to implement, but the prepared MABR membrane lacks biocompatibility and does not achieve oxygen selective permeability. Patent CN103182254 B discloses a MABR composite membrane and its preparation method. This method first prepares a L-DOPA solution, then uniformly coats it onto the outer surface of a porous membrane, and finally heat-treats and dries it to obtain the MABR membrane. This method is simple and easy to implement, and the prepared membrane has good oxygen permeability and biocompatibility. However, L-DOPA is unstable and easily oxidized and degraded or detached from the membrane surface, resulting in poor membrane stability. Patent CN 111408278 A discloses a MABR-supported composite oxygenation membrane, its preparation method, and its application. The preparation method involves first treating a matrix to obtain a mesoporous supporting matrix, then preparing a filler with high-efficiency oxygen permeation and transport properties, coating the filler onto the surface of the mesoporous supporting matrix for cross-linking or curing, and finally immersing it in a hydrophilic biomimetic modifier solution for fixation to obtain the composite oxygenation MABR membrane. The membrane prepared by this method exhibits stable performance and excellent results in MABR wastewater treatment processes, but the preparation method is complex, environmentally unfriendly, and the membrane cost is high. Patent CN 111482091 A discloses a high-performance MABR hollow fiber composite membrane preparation method. First, a base membrane is pretreated, then a coating solution is prepared, followed by coating the pretreated base membrane with the solution, and finally, heating and curing to obtain the MABR membrane. This method is simple and easy to implement and can transform microporous membranes of various materials into MABR membranes. However, the membrane prepared by this method only has oxygen permeability without selectivity, and the prepared membrane lacks biocompatibility.Patent CN 111744370 A discloses a hollow fiber composite membrane, its preparation method, and its application. This membrane possesses excellent mechanical strength, oxygen transport performance, and biocompatibility, making it highly suitable for bubble-free aeration MABR processes. However, its manufacturing involves complex processes such as curing, paste extrusion, stretching, sintering, coating, and phase inversion, making it unsuitable for industrial production. Similar patents include CN 113731194 A: A MABR hollow fiber composite membrane, its preparation method, and its application; CN 113368711 A: A high-performance MABR hollow fiber composite membrane preparation method, etc., which will not be elaborated upon here. With the increasing application of MABR technology in wastewater treatment, the manufacture of novel MABR membranes with high oxygen selective permeability, biocompatibility, and low cost is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to provide a MABR composite membrane with high oxygen selectivity and its preparation method, so as to overcome at least one of the above-mentioned defects in the prior art.

[0007] To achieve this objective, the present invention adopts the following technical solution: The present invention provides a MABR composite membrane with high oxygen selectivity, comprising a support layer, an intermediate layer and an outer layer arranged sequentially from the inside to the outside. The support layer is a polyimide gas separation membrane, the intermediate layer is a superhydrophobic coating composed of a high fluorine content polymer, and the outer layer is a hydrophilic rough surface composed of polyester short fibers and organic polymer materials.

[0008] Preferably, under a pressure of 0.1 MPa, the oxygen permeation flux P(O2) of the polyimide gas separation membrane is greater than 1 GPU, the nitrogen permeation flux P(N2) is less than 0.3 GPU, the separation coefficient of oxygen and nitrogen is α, α is greater than 5, and the orientation index is less than 1.3.

[0009] Preferably, the reagents used in the synthesis of the high-fluorine polymer include the following components by mass parts: 95-105 parts of pure water, 0.5-1 part of emulsifier, 20-25 parts of high-fluorine hydrophobic monomer A, 3-5 parts of comonomer B, and 1-2 parts of initiator.

[0010] Preferably, the emulsifier is sodium dodecyl sulfate (SDS) or octadecyltrimethylammonium chloride (STAC), the high-fluorine-content hydrophobic monomer A is perfluorohexyl ethyl acrylate (PFHEA) or perfluorooctyl ethyl acrylate (PFREA), the comonomer B is methyl methacrylate (MMA) or methyl acrylate (MA), and the initiator is ammonium persulfate (APS) or potassium persulfate (K2S2O8).

[0011] Preferably, the organic polymer material comprises, by mass parts, the following components: 98-102 parts of N,N-dimethylacetamide (DMAC), 20-25 parts of polyvinylidene fluoride (PVDF), 3-5 parts of amphiphilic material, and 3-5 parts of polyvinylpyrrolidone (PVP).

[0012] Preferably, the polyester staple fiber is polyester (PET) or nylon (PA), the polyester staple fiber length is 0.8-1.5 mm, the fineness is 0.5-1D, and the mass ratio of polyester staple fiber to organic polymer material is 1-2:50.

[0013] Preferably, the amphiphilic material is Pluronic or Hydropalat.

[0014] This invention also provides a method for preparing a MABR composite membrane with high oxygen selectivity, comprising the following steps: S1: using pure water as a dispersion medium, an emulsifier is added to the pure water and mixed evenly. Then, under stirring, a hydrophobic monomer A with high fluorine content, a comonomer B, and an initiator are added to form a uniform emulsion. The mixture is then heated under stirring to initiate an emulsion polymerization reaction. After a period of reaction, heating and stirring are stopped, and the mixture is cooled to room temperature to obtain a high-fluorine content polymer emulsion. S2: a polyimide gas separation membrane is selected as a support layer. The outer surface of the membrane is uniformly coated with the high-fluorine content polymer emulsion prepared in step S1, and then dried to form an intermediate layer, resulting in a polyimide gas separation membrane with a hydrophobic outer surface. S3: Polyvinylidene fluoride, amphiphilic material, and polyvinylpyrrolidone are dissolved in N,N-dimethylacetamide to prepare a casting solution. Then, polyester short fibers are added to the casting solution under rapid stirring. After the polyester short fibers are evenly dispersed in the casting solution, they are suspended in the membrane solution. Stirring is stopped and the membrane is allowed to stand to degas, resulting in a hydrophilic organic polymer casting solution with polyester short fibers suspended in it. S4: The hydrophilic organic polymer casting solution with polyester short fibers suspended in step S3 is applied to the hydrophobic outer surface of the polyimide gas separation membrane prepared in step S2 through a spinneret. Then, it is cured in pure water. After a solution phase inversion process, a hydrophilic rough surface is formed. The solvent in the membrane is washed away with clean water, and finally, it is air-dried to obtain a MABR composite membrane with high oxygen selectivity.

[0015] Preferably, in step S1, the emulsion polymerization reaction temperature is 70℃-90℃, and the reaction time is 4-8h.

[0016] Preferably, in step S2, the drying temperature is 60℃-70℃ and the drying time is 5-10 min.

[0017] The beneficial effects of this invention are as follows: The unique feature of the MABR composite membrane of this invention lies in its support layer, which is a polyimide gas separation membrane with a high O2 / N2 separation coefficient. When air is introduced into the inner side of the support layer, oxygen preferentially passes through this layer, thereby achieving the separation of oxygen and nitrogen in the air. The middle layer of the MABR composite membrane is a superhydrophobic coating composed of a high-fluorine-content polymer. This coating is air-permeable but water-permeable, which can both break down the oxygen passing through the support layer into tiny bubbles and transport them to the outside, and prevent external water from contacting the inner polyimide gas separation membrane. The outer layer of the MABR membrane is a hydrophilic rough surface composed of polyester short fibers and organic polymer materials. This surface has good biocompatibility, and microorganisms can easily attach to it for metabolism and reproduction. The preparation method of this MABR membrane can be divided into four steps: synthesis of a high-fluorine-content polymer emulsion, hydrophobic treatment of the outer surface of the polyimide hollow fiber gas separation membrane, preparation of a short fiber suspended hydrophilic organic polymer casting solution, and preparation of the MABR hollow fiber membrane. The MABR composite membrane prepared by this method not only has extremely high oxygen selectivity and permeability internally, but also good biocompatibility externally. Therefore, this membrane can achieve high-efficiency, low-energy-consumption bubble-free aeration and stable biodegradation functions in MABR water treatment processes. The preparation method of this MABR composite membrane is simple and easy to implement, and suitable for industrial production. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the MABR hollow fiber composite membrane in Embodiment 1 of the present invention.

[0019] Figure 2 This is a flowchart illustrating the preparation process of the MABR hollow fiber composite membrane according to Embodiment 1 of the present invention.

[0020] Figure 3 This is a schematic diagram of the structure of the MABR flat panel composite membrane according to Embodiment 1 of the present invention.

[0021] Figure 4 This is a flowchart illustrating the preparation process of the MABR flat panel composite membrane according to Embodiment 1 of the present invention.

[0022] The labels in the attached diagram are: 1-support layer, 2-intermediate layer, 3-outer layer. Detailed Implementation

[0023] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0024] Contents not described in detail in this specification are prior art known to those skilled in the art. In the description of this invention, it should be understood that terms such as "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, terms such as "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] Example 1: like Figures 1 to 2 As shown, this embodiment provides a MABR composite membrane with high oxygen selectivity, comprising a support layer 1, an intermediate layer 2, and an outer layer 3 arranged sequentially from the inside out. The support layer 1 is a polyimide gas separation membrane, the intermediate layer 2 is a superhydrophobic coating composed of a high-fluorine-content polymer, and the outer layer 3 is a hydrophilic rough surface composed of polyester short fibers and organic polymer materials. The MABR composite membrane with high oxygen selectivity in this embodiment is a MABR hollow fiber composite membrane.

[0026] The special feature of the MABR composite membrane of the present invention is that the support layer 1 is a polyimide gas separation membrane with a high O2 / N2 separation coefficient. When air is introduced into the inside of the support layer 1, oxygen will preferentially pass through this layer, thereby achieving the separation of oxygen and nitrogen in the air. The middle layer 2 of the MABR composite membrane is a superhydrophobic coating composed of a polymer with high fluorine content. This coating is breathable but not water-permeable. It can both break the oxygen passing through the support layer 1 into tiny bubbles and transport it to the outside, and prevent external water from contacting the internal polyimide gas separation membrane. The outer layer 3 of the MABR membrane is a hydrophilic rough surface composed of polyester short fibers and organic polymer materials. This surface has good biocompatibility, and microorganisms can easily attach to it for metabolism and reproduction.

[0027] In this process, gas at 20°C passes through a polyimide gas separation membrane at a pressure of 0.1 MPa. The oxygen permeation flux of the polyimide gas separation membrane is P(O2) = 1.2 GPU, the nitrogen permeation flux is P(N2) = 0.2 GPU, the separation coefficient of oxygen and nitrogen (i.e. the ratio of oxygen to nitrogen permeation rates) is α, α = 5, and the orientation index is 1.1.

[0028] The reagents used in the synthesis of the high-fluorine polymer in this embodiment include the following components by mass parts: 100 parts pure water, 0.5 parts emulsifier (SDS), 20 parts high-fluoride hydrophobic monomer A (PFHEA), 5 parts comonomer B (MMA), and 1 part initiator (APS).

[0029] The organic polymer material in this embodiment includes the following components by mass parts: 100 parts N,N-dimethylacetamide, 20 parts polyvinylidene fluoride, 3 parts Pranic, and 3 parts polyvinylpyrrolidone.

[0030] In this embodiment, the polyester staple fiber is polyester, the length of the polyester staple fiber is 1 mm, the fineness is 0.5D, and the mass ratio of polyester staple fiber to organic polymer material is 1:50.

[0031] This embodiment also provides a method for preparing an oxygen-selective MABR composite membrane, which includes the following steps: S1: Using pure water as the dispersion medium, add 5 g SDS to 1000 g pure water and mix well. Then, while stirring, add 200 g PFHEA, 50 g MMA, and 10 g APS to form a uniform emulsion. Then, while stirring, heat to 70°C to start the emulsion polymerization reaction. After reacting for 8 hours, stop heating and stirring, and cool to room temperature to obtain a high-fluorine content polymer emulsion.

[0032] S2: A commercially available polyimide hollow fiber gas separation membrane with P(O2) of 1.2 GPU, P(N2) of 0.2 GPU, separation coefficient α = 6, and orientation index of 1.1 is selected as the base membrane support layer 1. The outer surface of the membrane is uniformly coated with the high-fluorine content polymer emulsion prepared in step S1, and then dried at 60°C for 10 min as the intermediate layer 2. After drying, a hydrophobic polyimide gas separation membrane is obtained for later use.

[0033] S3: Dissolve 200 g PVDF, 30 g Pluronic, and 30 g PVP in 1000 g DMAC to prepare a casting solution. Then, under rapid stirring, add 2% of the casting solution mass of PET short fibers with a length of 1 mm and a fineness of 0.5 D to the casting solution. After dispersing evenly, suspend the fibers in the casting solution, stop stirring, and allow them to stand to degas, thus obtaining a hydrophilic organic polymer casting solution of polyester short fiber suspension.

[0034] S4: The hydrophilic organic polymer casting solution of polyester short fiber suspension prepared in step S3 is applied to the hydrophobic outer surface of the polyimide gas separation membrane prepared in step S2 through a spinneret, and then cured in pure water. After the solution phase inversion process, a hydrophilic rough surface is formed. The solvent in the membrane is cleaned with water and finally air-dried to obtain the MABR composite membrane with high oxygen selectivity.

[0035] The test results are as follows: The water contact angle of the polyimide support layer 1 on the inner surface of the MABR composite membrane is 65°, the water contact angle of the superhydrophobic coating in the middle is 144°, the water contact angle of the outer surface is 20°, the root mean square roughness of the outer surface is 130 nm, and the oxygen permeation flux through the membrane at 20℃ and 0.1MPa pressure is 1 GPU. When a 1 square meter membrane is made into a module and placed in pure water for aeration with air at 20℃, the oxygen aeration efficiency is 11 Kg / KWh, and the oxygen utilization rate is >99%. When a 1 square meter module is placed in ordinary domestic sewage and the aeration power is controlled at 0.1 KWh per hour, the degradation of ammonia nitrogen organic matter reaches 8 g / d.

[0036] Example 2: This embodiment also provides a method for preparing a MABR composite membrane with high oxygen selectivity, including the following steps: S1: Using pure water as the dispersion medium, add 10 g STAC to 1000 g pure water and mix well. Then, under stirring, add 250 g PFREA, 30 g MA, and 20 g K2S2O8 to form a uniform emulsion. Then, under stirring, heat to 90℃ to start the emulsion polymerization reaction. After reacting for 4 hours, stop heating and stirring, and cool to room temperature to obtain a high-fluorine content polymer emulsion.

[0037] S2: A commercially available polyimide hollow fiber gas separation membrane with P(O2) of 1.8 GPU, P(N2) of 0.3 GPU, separation coefficient α = 6, and orientation index of 1.0 is selected as the base membrane support layer 1. The outer surface of the membrane is uniformly coated with the high-fluorine content polymer emulsion prepared in step S1, and then dried at 70°C for 5 min as the intermediate layer 2. After drying, a hydrophobic polyimide gas separation membrane is obtained for later use.

[0038] S3: Dissolve 250 g PVDF, 50 g Hydropalat, and 50 g PVP in 1000 g DMAC to prepare a casting solution. Then, under rapid stirring, add 3% of the casting solution mass of PA short fibers with a length of 1 mm and a fineness of 0.1 D to the casting solution. After dispersing evenly, suspend the fibers in the casting solution, stop stirring, and allow them to stand to degas, thus obtaining a hydrophilic organic polymer casting solution with polyester short fiber suspension.

[0039] S4: The hydrophilic organic polymer casting solution of polyester short fiber suspension prepared in step S3 is applied to the hydrophobic outer surface of the polyimide gas separation membrane prepared in step S2 through a spinneret, and then cured in pure water. After the solution phase inversion process, a hydrophilic rough surface is formed. The solvent in the membrane is cleaned with water and finally air-dried to obtain the MABR composite membrane with high oxygen selectivity.

[0040] The test results are as follows: The water contact angle of the polyimide support layer 1 on the inner surface of the MABR composite membrane is 62°, the water contact angle of the superhydrophobic coating in the middle is 151°, the water contact angle of the outer surface is 17°, and the root mean square roughness of the outer surface is 144 nm. When oxygen passes through the membrane at 20°C and 0.1 MPa pressure, the oxygen permeation flux is 1.2 GPU. When a 1-square-meter membrane is made into a module and placed in pure water for aeration with air at 20°C, the oxygen aeration efficiency is 12.5 Kg / KWh, and the oxygen utilization rate is >99%. When a 1-square-meter module is placed in ordinary domestic sewage and the aeration power is controlled at 0.1 KWh per hour, the degradation of ammonia nitrogen organic matter reaches 8.5 g / d.

[0041] Example 3: This embodiment also provides a method for preparing a MABR composite membrane with high oxygen selectivity, including the following steps: S1: Using pure water as the dispersion medium, add 6 g STAC to 1000 g pure water and mix well. Then, under stirring, add 220 g PFHEA, 40 g MA, and 15 g K2S2O8 to form a uniform emulsion. Then, under stirring, heat to 80℃ to start the emulsion polymerization reaction. After reacting for 6 hours, stop heating and stirring, and cool to room temperature to obtain a high-fluorine content polymer emulsion.

[0042] S2: A commercially available polyimide hollow fiber gas separation membrane with P(O2) of 2.1 GPU, P(N2) of 0.3 GPU, separation coefficient α = 7, and orientation index of 1.1 is selected as the base membrane support layer 1. The outer surface of the membrane is uniformly coated with the high-fluorine content polymer emulsion prepared in step S1, and then dried at 65°C for 8 min as the intermediate layer 2. After drying, a hydrophobic polyimide gas separation membrane is obtained for later use.

[0043] S3: Dissolve 220 g PVDF, 40 g Pluronic, and 40 g PVP in 1000 g DMAC to prepare a casting solution. Then, under rapid stirring, add 4% of the casting solution mass of PA short fibers with a length of 1 mm and a fineness of 0.6 D to the casting solution. After dispersing evenly, suspend the fibers in the casting solution, stop stirring, and allow the solution to stand to degas, thus obtaining a hydrophilic organic polymer casting solution of polyester short fiber suspension.

[0044] S4: The hydrophilic organic polymer casting solution of polyester short fiber suspension prepared in step S3 is applied to the hydrophobic outer surface of the polyimide gas separation membrane prepared in step S2 through a spinneret, and then cured in pure water. After the solution phase inversion process, a hydrophilic rough surface is formed. The solvent in the membrane is cleaned with water and finally air-dried to obtain the MABR composite membrane with high oxygen selectivity.

[0045] The test results are as follows: The water contact angle of the polyimide support layer 1 on the inner surface of the MABR composite membrane is 68°, the water contact angle of the superhydrophobic coating in the middle is 157°, the water contact angle of the outer surface is 19°, and the root mean square roughness of the outer surface is 148 nm. When oxygen passes through the membrane at 20°C and 0.1 MPa pressure, the oxygen permeation flux is 1.5 GPU. When a 1-square-meter membrane is made into a module and placed in pure water for aeration with air at 20°C, the oxygen aeration efficiency is 12 Kg / KWh, and the oxygen utilization rate is >99%. When a 1-square-meter module is placed in ordinary domestic sewage and the aeration power is controlled at 0.1 KWh per hour, the degradation of ammonia nitrogen organic matter reaches 9.5 g / d.

[0046] Comparative Example 1: The difference from Example 3 is that Pluronic was not added to the organic polymer casting solution; otherwise, they are exactly the same.

[0047] The test results are as follows: The water contact angle of the polyimide support layer 1 on the inner surface of the MABR composite membrane is 68°, the water contact angle of the superhydrophobic coating in the middle is 157°, the water contact angle of the outer surface is 89°, and the root mean square roughness of the outer surface is 124 nm. When oxygen passes through the membrane at 20°C and 0.1 MPa pressure, the oxygen permeation flux is 0.8 GPU. When a 1 square meter membrane is made into a module and placed in pure water for aeration with air at 20°C, the oxygen aeration efficiency is 5 kg / kWh, and the oxygen utilization rate is >99%. When a 1 square meter module is placed in ordinary domestic sewage and the aeration power is controlled at 0.1 kWh per hour, the degradation of ammonia nitrogen organic matter reaches 3.5 g / d. The test results clearly show that without Pluronic in the casting solution, the contact angle of the MABR membrane surface increases significantly, hydrophobicity is enhanced, roughness decreases, and the biocompatibility of the membrane decreases. This is not conducive to the metabolism and reproduction of microorganisms on the membrane surface, and microbial metabolites are more likely to accumulate on the membrane surface, causing membrane fouling. Ultimately, this leads to a decrease in oxygen permeation flux, aeration efficiency, and the degradation of organic matter.

[0048] Comparative Example 2: The difference from Example 3 is that no comonomer MA was added during the emulsion polymerization process; otherwise, they are exactly the same.

[0049] The test results are as follows: The water contact angle of the polyimide support layer 1 on the inner surface of the MABR composite membrane is 68°, the water contact angle of the superhydrophobic coating in the middle is 165°, the water contact angle of the outer surface is 19°, and the root mean square roughness of the outer surface is 148 nm. When oxygen passes through the membrane at 20°C and 0.1 MPa pressure, the oxygen permeation flux is 1.5 GPU. When a 1-square-meter membrane is made into a module and placed in pure water for aeration with air at 20°C, the oxygen aeration efficiency is 6 kg / kWh, and the oxygen utilization rate is 71%. When a 1-square-meter module is placed in ordinary domestic sewage and the aeration power is controlled at 0.1 kWh per hour, the degradation of ammonia nitrogen organic matter reaches 5.5 g / d. The test results clearly show that without the addition of comonomer MA, the emulsion polymerization process produces a homopolymer composed of hydrophobic monomers. The contact angle of the hydrophobic coating composed of this homopolymer is significantly increased. Under the condition that the oxygen permeation flux remains unchanged, the oxygen aeration efficiency is significantly reduced, and the degradation of ammonia nitrogen organic matter is also significantly reduced. This is because the homopolymer cannot achieve single-molecule permeation of oxygen, and some oxygen permeates through the membrane in the form of microbubbles.

[0050] Example 4: like Figures 3 to 4 As shown, the difference between this embodiment and Embodiment 1 is that: In this embodiment, the oxygen-selective permeable MABR composite membrane is a MABR flat sheet composite membrane.

[0051] The preparation method of this MABR membrane can be divided into four steps: synthesis of a high-fluorine-content polymer emulsion, hydrophobication treatment of the outer surface of the polyimide hollow fiber gas separation membrane, preparation of a short-fiber suspended hydrophilic organic polymer casting solution, and preparation of the MABR hollow fiber membrane. The MABR composite membrane prepared by this method not only exhibits extremely high oxygen selectivity and permeability internally, but also good biocompatibility externally. Therefore, this membrane can achieve high-efficiency, low-energy-consumption bubble-free aeration and stable biodegradation in MABR water treatment processes. The preparation method of this MABR composite membrane is simple and easy to implement, and suitable for industrial production.

[0052] This invention starts with commercially available gas separation membranes, selecting a suitable gas separation membrane as the base membrane and support layer 1 to simplify the membrane fabrication process and reduce costs. In the field of gas separation membranes, polyimide, due to its excellent physicochemical properties, has become one of the ideal materials for gas separation membrane preparation. However, ordinary polyimide molecules have high rigidity and strong intermolecular interactions, making it difficult to process into membranes and resulting in poor gas permeability after membrane formation. Commercially available polyimide gas separation membranes are all modified membranes; different modification methods and membrane fabrication methods can yield gas separation membranes with vastly different performance characteristics, suitable for various gas separation applications. The performance of a gas separation membrane is determined by two parameters: the permeability coefficient (P) and the selectivity coefficient (α). A higher permeability coefficient indicates that the gas permeates more easily through the membrane. The selectivity coefficient (α) is the ratio of the permeability coefficients of the two gases, i.e., α = P. A / P B P A P represents the permeability coefficient of gases that more easily pass through the membrane. B The permeability coefficient of gases that are more difficult to permeate through the membrane is α. The larger the α, the stronger the selectivity of the membrane for gases that are easier to permeate. The gases used in the MABR process are generally pure oxygen or air. Pure oxygen is expensive. The membrane prepared in this invention uses air aeration, which is inexpensive. The main components of air are O2 and N2. Therefore, using a polyimide hollow fiber gas separation membrane with a high O2 / N2 separation coefficient as the base membrane and support layer 1 can easily achieve high selective permeability of oxygen while greatly simplifying the membrane manufacturing process and reducing the membrane manufacturing cost.

[0053] In this invention, a high-fluorine-content polymer emulsion is prepared by emulsion polymerization using pure water as the dispersion medium. This ensures that the emulsion will not swell and damage the polyimide film during coating. PFHEA and PFREA are used as hydrophobic monomers because they have suitable molecular weights, high fluorine content, and are relatively easy to polymerize. Adding comonomers MMA and MA to the hydrophobic monomers not only increases the polymer's molecular weight but also enhances its adhesion to the polyimide film, ensuring the high-fluorine-content polymer adheres firmly to the film surface without detachment. APS and K2S2O8 are used as initiators because they are water-soluble and do not interact with the emulsifier, making them ideal for the emulsion polymerization reaction in this invention. One of the technical challenges of this invention lies in the emulsion polymerization, requiring precise control of reaction conditions, the proportions of each substance, and the order of addition. Otherwise, the resulting emulsion will not be a copolymer of hydrophobic and comonomers but a blend of hydrophobic and comonomer homopolymers, which cannot form a superhydrophobic coating that only allows oxygen molecules to permeate.

[0054] In this invention, Pluronic and Hydropalat are used as amphiphilic materials to improve the biocompatibility of the membrane outer surface. These two materials possess both hydrophobic and hydrophilic segments. The hydrophobic segments ensure stable retention in the membrane, while the hydrophilic segments impart hydrophilicity. These materials not only exhibit good compatibility with other materials in the organic polymer casting solution but are also non-toxic and possess strong affinity for microorganisms, promoting their reproduction and metabolism on the membrane surface. This invention uses PET and PA polyester staple fibers suspended in a hydrophilic organic polymer casting solution. The resulting MABR membrane has numerous short fiber protrusions on its outer surface, significantly increasing the surface roughness and greatly facilitating the attachment of aerobic microorganisms. Another technical challenge of this invention lies in the matching of the polyester staple fibers with the hydrophilic organic polymer casting solution. Casting solutions of different viscosities and compositions require polyester staple fibers of appropriate length and fineness. The goal is to ensure that the polyester staple fibers can suspend in the membrane solution without settling, while also ensuring that the polyester staple fibers are firmly fixed to the membrane surface after film formation.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a MABR composite membrane with high oxygen selectivity, characterized in that, Includes the following steps: S1: Using pure water as the dispersion medium, add emulsifier to pure water and mix evenly. Then, add hydrophobic monomer A with high fluorine content, comonomer B and initiator under stirring to form a uniform emulsion. Then, heat up under stirring to start the emulsion polymerization reaction. After reacting for a period of time, stop heating and stirring, and cool to room temperature to obtain a high fluorine content polymer emulsion. S2: Select a polyimide gas separation membrane as the support layer. Under a pressure of 0.1 MPa, the oxygen permeation flux P(O2) of the polyimide gas separation membrane is greater than 1 GPU, the nitrogen permeation flux P(N2) is less than 0.3 GPU, the separation coefficient of oxygen and nitrogen is α, α is greater than 5, and the orientation index is less than 1.

3. The outer surface of the membrane is uniformly coated with the high fluorine content polymer emulsion prepared in step S1, and then dried as an intermediate layer to obtain a hydrophobic polyimide gas separation membrane for later use. S3: Polyvinylidene fluoride, amphiphilic materials, and polyvinylpyrrolidone are dissolved in N,N-dimethylacetamide to prepare a casting solution. Then, polyester staple fiber is added to the casting solution under rapid stirring. After the polyester staple fiber is evenly dispersed in the casting solution, it is suspended in the casting solution. Stirring is stopped and the mixture is allowed to stand to degas, resulting in a hydrophilic organic polymer casting solution with polyester staple fiber suspension. S4: The hydrophilic organic polymer casting solution of polyester short fiber suspension prepared in step S3 is applied to the hydrophobic outer surface of the polyimide gas separation membrane prepared in step S2 through a spinneret, and then cured in pure water. After the solution phase inversion process, a hydrophilic rough surface is formed. The solvent in the membrane is cleaned with water and finally air-dried to obtain the MABR composite membrane with high oxygen selectivity.

2. The method for preparing a highly oxygen-selective MABR composite membrane according to claim 1, characterized in that: In step S1, the emulsion polymerization reaction temperature is 70℃-90℃, and the reaction time is 4-8h.

3. The method for preparing a highly oxygen-selective MABR composite membrane according to claim 1, characterized in that: In step S2, the drying temperature is 60℃-70℃ and the drying time is 5-10 minutes.

4. A highly oxygen-selective MABR composite membrane, prepared by the method for preparing a highly oxygen-selective MABR composite membrane according to any one of claims 1-3, characterized in that: It includes a support layer, an intermediate layer, and an outer layer arranged sequentially from the inside out; The support layer is a polyimide gas separation membrane; The intermediate layer is a superhydrophobic coating composed of a polymer with high fluorine content; The outer layer is a hydrophilic rough surface composed of polyester staple fibers and organic polymer materials.

5. The oxygen-selective permeable MABR composite membrane according to claim 4, characterized in that, The reagents used in the synthesis of the high-fluorine polymer include, by mass parts, the following components: 95-105 parts pure water; Emulsifier 0.5-1 part; High-fluoride hydrophobic monomer A20-25 parts; Comonomer B: 3-5 parts; Initiator 1-2 parts.

6. The oxygen-selective permeable MABR composite membrane according to claim 5, characterized in that: The emulsifier is sodium dodecyl sulfate or octadecyltrimethylammonium chloride; The high-fluorine-content hydrophobic monomer A is perfluorohexyl ethyl acrylate or perfluorooctyl ethyl acrylate; Comonomer B is methyl methacrylate or methyl acrylate; The initiator is ammonium persulfate or potassium persulfate.

7. The oxygen-selective permeable MABR composite membrane according to claim 4, characterized in that, Organic polymer materials, by mass parts, include the following components: 98-102 parts of N,N-dimethylacetamide; 20-25 parts of polyvinylidene fluoride; 3-5 sets of documents from both parents; 3-5 parts of polyvinylpyrrolidone.

8. The oxygen-selective permeable MABR composite membrane according to claim 4, characterized in that: The polyester staple fiber is polyester or nylon; The polyester staple fiber has a length of 0.8-1.5 mm and a fineness of 0.5-1D; The mass ratio of the polyester staple fiber to the organic polymer material is 1-2:

50.

9. The oxygen-selective permeable MABR composite membrane according to claim 7, characterized in that: The parent materials are either Pranick or Hydrupa.

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