Separation membrane, preparation method for separation membrane, and filtering device using separation membrane

Abstract

A separation membrane, a preparation method for a separation membrane, and a filtering device using a separation membrane. The preparation method for the separation membrane comprises the following steps: dissolving a polymer membrane-forming material and an additive in an organic solvent to prepare a casting solution; scrape coating the casting solution on a flat substrate; and transferring the substrate into an environment with the temperature of -20 degrees Celsius to 4 degrees Celsius for cooling; and placing the cooled substrate into a coagulating bath for phase inversion to form a membrane, and finally obtaining a polymer porous membrane. The additive is a mixture of polyvinylpyrrolidone and a block copolymer. The preparation method greatly improves the pure water flux of the separation membrane.

Description

Separation membrane, method for preparing separation membrane, and filtering device using separation membrane Technical Field

[0001] The present invention relates to the technical field of filter membranes and membrane assemblies, and in particular to a separation membrane with high flux and high hydrophilicity, a preparation method thereof, and a filtering device using the membrane, in particular a hemodialyzer, a blood purification filter, a tangential flow filter, or a water purification filter. Background Art

[0002] Separation membranes have many advantages over traditional separation technologies, especially high separation efficiency, low cost, and environmental friendliness. They are widely used in various industries, such as biopharmaceuticals, seawater desalination, wastewater treatment, food and beverages, battery separators, petrochemicals, etc. Phase inversion method is an important preparation method for separation membranes. Phase inversion method mainly includes non-solvent induced phase separation, heat induced phase separation, solvent evaporation induced phase separation and gas phase induced phase separation. The non-solvent induced phase separation method for preparing polymer separation membranes is simple and easy to operate, and the prepared separation membranes usually have an asymmetric structure. This method uses a reagent that can dissolve the polymer as a solvent. After the solvent dissolves the polymer, it will form a uniform casting liquid. The casting liquid is then coated on a substrate such as a glass sheet and quickly immersed in a coagulation bath. During this process, the solvent and the non-solvent in the coagulation bath will undergo a strong exchange, forming a structure with a dense surface and a finger-like pore support layer on the lower layer.

[0003] During the phase inversion process, additives are often added to slow the phase inversion time to increase the porosity of the separation membrane, reduce the appearance of macropores, and improve separation efficiency. For example, a certain weight ratio of DMAc, NMP, NaCl, or HCl is added to the coagulation bath. Prolonging the phase inversion time reduces ineffective macropores, increases sponge pores, and improves separation efficiency. However, the addition of these additives increases the subsequent membrane cleaning process and the need for coagulation bath recycling, significantly increasing industrial costs. Furthermore, the increased porosity still contains a high number of ineffective pores.

[0004] Chun et al. [Chun KY, Jang SH, Kim HS, Kim YW, Han HS and Joe YI, “Effects of solvent on the pore formation in asymmetric 6FDA–4,4'ODA polyimide membrane: terms of thermodynamics, precipitation kinetics, and physical factors”, Journal of Membrane Science, 2000, 169(2), 197–214] found that increasing the DMAc content in the coagulation bath delayed the phase inversion time. However, the pore structure of the membrane support remained finger-like and did not change with increasing DMAc content.

[0005] Chinese patent application CN116712869A discloses a technical solution that replaces a conventional coagulation bath (e.g., aqueous ethanol or tetrahydrofuran) with aqueous methanol, and then controls the methanol concentration to control the phase separation rate. However, this method suffers from the following issues: methanol is highly toxic and flammable, and its volatilization during the phase inversion process can easily pose a risk. Furthermore, the subsequent use and recovery of the coagulation bath are difficult and expensive.

[0006] Chinese patent application CN116422158A discloses a method for controlling the phase separation rate by adjusting the viscosity of the casting solution by adding sulfonated polyethersulfone. However, this method suffers from the problem that the mechanical strength of the resulting sulfonated polyethersulfone separation membrane is inferior to that of pure polyethersulfone separation membranes.

[0007] In summary, the existence of the above problems has, to a certain extent, limited the development speed of large-scale industrial production of high water flux separation membranes. How to effectively improve the pore structure of separation membranes without significantly increasing production costs is a problem that needs to be solved.

[0008] Summary of the Invention

[0009] In order to solve the problems of insufficient separation membrane performance and complicated subsequent cleaning process in the above-mentioned manufacturing process, the present invention provides a separation membrane with high flux and high hydrophilicity, a method for preparing the separation membrane, and a filtration device using the separation membrane.

[0010] The preparation method of the present invention can rapidly cool the casting liquid that has not undergone phase transformation in a short period of time by adding a rapid cooling operation before entering the coagulation bath, thereby slowing down the phase transformation speed when it enters the coagulation bath. A large number of sponge pore structures can be formed during the film formation process, thereby avoiding the problem of a large number of invalid pores caused by phase transformation directly entering the coagulation bath, thereby improving the water flux and hydrophilicity of the porous membrane.

[0011] Based on the above working principle, the present invention provides a method for preparing a separation membrane, which comprises the following steps:

[0012] (1) dissolving a polymer film-forming material and an additive in an organic solvent to prepare a casting solution, and applying the casting solution on a flat substrate;

[0013] (2) moving the substrate into an environment with a temperature of -20°C to 4°C to cool it down;

[0014] (3) placing the cooled substrate into a coagulation bath for phase transformation into a membrane, and finally obtaining a polymer porous membrane.

[0015] Wherein, the additive in step (1) is a mixture of polyvinyl pyrrolidone (PVP) and block copolymers.

[0016] The membrane-forming materials in step (1) of the present invention are all high molecular polymers, which are suitable for polymer membrane materials in different separation membrane fields. These polymers can be selected from: polysulfones, polyvinylidene fluoride, polyacrylonitrile, polystyrene, including copolymers containing styrene (such as acrylonitrile-styrene copolymers, styrene-butadiene copolymers and styrene-vinyl benzyl halide copolymers), polysulfates, cellulose polymers (such as cellulose acetate, cellulose acetate butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc.), polyamides and polyimides, including aromatic polyamides and aromatic polyimides, polyethers, polyarylene ethers (such as polyphenylene ether and polyxylene ether), polyesteramide diisocyanate, polyurethanes, polyesters (including polyarylates) such as polyethylene terephthalate, polyalkyl methacrylate, polyalkyl acrylate, polyphenylene terephthalate, etc., polysulfides, monomers with α-olefin unsaturation other than the above. Polymers obtained from the present invention include polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, polyvinyl polymers (such as polyvinyl chloride, polyvinyl fluoride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl alcohol, polyvinyl esters such as polyvinyl acetate and polyvinyl propionate, polyvinyl pyridine, polyvinyl pyrrolidone, polyvinyl ethers, polyvinyl ketones, polyvinyl aldehydes such as polyvinyl formal and polyvinyl butyral, polyvinyl amides, polyvinyl amines, polyvinyl carbamates, polyvinyl ureas, polyvinyl phosphates and polyvinyl sulfates), polyallyls, polybenzbenzimidazoles, polyhydrazides, polyoxadiazoles, polytriazoles, polybenzimidazoles, polycarbodiimides, polyphosphazenes, and the like, as well as copolymers, including terpolymers containing the above repeating units (such as a terpolymer of acrylonitrile-vinyl bromide-p-sulfophenyl methallyl ether sodium salt) and graft copolymers and blends containing any of the above. Typical substituents for providing substituted polymers include halogen (such as fluorine, chlorine and bromine), hydroxyl, lower alkyl, lower alkoxy, monocyclic aromatic, lower acyl, etc. All of the above polymers and other polymers that can be thought of by those skilled in the art are included in the scope of the polymers described in the present invention, but this does not constitute a limitation on the scope of the present invention.

[0017] Preferably, the polymer film-forming material in step (1) can be selected from one or a mixture of two or more of polysulfone polymers, cellulose polymers, polyvinylidene fluoride polymers, and polyacrylonitrile polymers.

[0018] More preferably, the polymer membrane-forming material can be selected from one or a mixture of two or more of polyethersulfone (PES), polysulfone (PSF) and a series of polymers thereof with different sulfonation degrees.

[0019] In practice, modifying additives used in the film-forming process are also classified into different categories. These additives can be selected from mixtures of polyvinyl pyrrolidone (PVP) and block copolymers. Polyvinyl pyrrolidone (PVP) additives contain N-vinyl pyrrolidone (NVP) units as the primary structural unit and may also contain other copolymerizable units. All additives in the above categories, as well as other additives that can be imagined by those skilled in the art, are encompassed by the additives described in the present invention, but this does not constitute a limitation on the scope of the present invention.

[0020] Preferably, the polyvinyl pyrrolidone (PVP) additive is polyvinyl pyrrolidone (PVP).

[0021] Preferably, the block copolymer additive is poloxamer.

[0022] In addition, based on the mechanism of action of the present invention (the rapid cooling operation before the coagulation bath can slow down the phase conversion rate of the non-phase-converted casting liquid entering the coagulation bath later), the time of the rapid cooling process from -20°C to 4°C can be adjusted according to the requirements of the final product.

[0023] Preferably, the cooling time in the low temperature environment in step (2) is 5 seconds to 5 minutes.

[0024] More preferably, the cooling time in the low temperature environment in step (2) is 15 seconds to 1 minute.

[0025] The technical solution of the present invention also relates to a separation membrane prepared according to the above preparation method.

[0026] The technical solution of the present invention also relates to a filtration device, which includes the above-mentioned separation membrane.

[0027] Preferably, the filtration device is a hemodialyzer, a blood purification filter, a tangential flow filter, or a water purification filter. However, the above four devices do not limit the scope of the present invention. Those skilled in the art can easily imagine that the separation membrane involved in this technical solution can be applied to other filtration equipment. These various filtration devices suitable for different separation fields are all included in the scope of the additive described in the present invention.

[0028] The separation membrane obtained by the present invention has high water flux and hydrophilicity. Apart from the addition of a rapid cooling step before the substrate is placed in the coagulation bath, no other production steps are changed. The method is simple and easy to operate, with a short freezing time and low process costs. Furthermore, the present invention can simplify the cleaning process during production. Compared with existing technologies, the present invention reduces production costs while improving the water flux and hydrophilicity of the separation membrane, making it suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] FIG1 is a schematic diagram of a separation membrane preparation process in which a rapid cooling process is added in an embodiment;

[0031] FIG2 is a schematic diagram of the separation membrane preparation process without adding the rapid cooling process in Comparative Example 1;

[0032] Figure 3a)-c) are scanning electron micrographs of the cross-section of the separation membrane obtained in Comparative Example 1;

[0033] Figure 3d)-f) are scanning electron micrographs of the cross-section of the separation membrane of sample 2 obtained in Example. DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to specific examples. However, the following examples are only a portion of the embodiments of the present invention and do not constitute a limitation of the scope of the present invention. Any improvements and adjustments made by those skilled in the art based on the above invention without creative work are also considered to fall within the scope of protection of the present invention.

[0035] For example, according to the technical solution of the present invention, the polymer film-forming material of the present invention can be selected from one or more mixtures of polysulfone polymers, cellulose polymers, polyvinylidene fluoride polymers, polyacrylonitrile polymers and other high molecular polymers. Since the above-mentioned film-forming materials are all organic polymers, and the film-forming properties are very good, they are commonly used organic polymer membrane materials in different separation membrane fields, and all of the above-mentioned polymers are included in the scope covered by the present invention. However, for ease of explanation, polyethersulfone is selected as a polymer for reference in the following experiments, but this does not constitute a limitation on the scope of the present invention. Similarly, polyvinyl pyrrolidone (PVP) and block copolymer additives are also different due to the different use scenarios. For ease of explanation, in the following experiments, only a mixture of pore-forming agent polyvinyl pyrrolidone and poloxamer is selected as an additive, and this selection does not constitute a limitation on the scope of the present invention.

[0036] In order to effectively illustrate the present invention, separation membranes subjected to a rapid cooling process at a temperature of -20°C to 4°C (6 groups of samples) were selected for water flux testing and cross-sectional structure comparison with separation membranes without the rapid cooling process. The experimental settings for Example 1 and Comparative Example 1 are as follows:

[0037] Example

[0038] This embodiment provides a method for preparing a separation membrane as shown in FIG1 , and prepares 6 groups of samples according to different temperatures and times in the rapid cooling process. The specific preparation method is as follows:

[0039] (1) Casting solution preparation: 16 g polyethersulfone, 6 g polyvinylpyrrolidone, 4 g poloxamer, and 74 g dimethylacetamide were mixed to prepare 6 groups of 100 g casting solution each;

[0040] (2) Stir the above 6 sets of casting solutions at 60°C for 10 hours until they are completely dissolved and transparent, and then degas for 8 hours. Then, pour the 6 sets of casting solutions onto 6 scraping boards at room temperature of 25°C;

[0041] (3) Then, the six groups of coated glass plates were placed in a low-temperature environment as shown in Table 1 for the corresponding time;

[0042] (4) The six groups of glass plates that had undergone the rapid cooling process were placed in a coagulation bath of deionized water at a temperature of 20°C and immersed for 48 hours. The water was changed three times during the process, and then naturally dried, finally obtaining six groups of separation membrane samples.

[0043] Among them, polyethersulfone was purchased from Sumitomo Chemical Co., Ltd. of Japan (SUMIKAEXCEL PES, 4800p), dimethylacetamide was purchased from Zhangqiu Mingyue Chemical Co., Ltd. (DMAc, purity 100%), polyvinylpyrrolidone was purchased from Nippon Shokubai Co., Ltd. (PVP, K-85N), and poloxamer was purchased from BASF China Shanghai Branch ( P 407 Geismar).

[0044] Table 1 Low temperature environment temperature and storage time of 6 groups of samples

[0045] The present invention also provides a comparative example 1, which is a method for preparing a separation membrane as shown in FIG2 . The specific preparation method is as follows:

[0046] (1) Casting solution preparation: 16 g polyethersulfone, 6 g polyvinylpyrrolidone, 4 g poloxamer, and 74 g dimethylacetamide were mixed to prepare 100 g casting solution;

[0047] (2) Stir the above components at 60°C for 10 hours until they are completely dissolved and transparent. After degassing for 8 hours, pour the casting solution onto a scraping board at room temperature of 25°C and apply;

[0048] (3) The coated glass plate was then placed in a coagulation bath of deionized water at a temperature of 20°C and immersed for 48 hours, with the water changed three times in the middle, and then naturally dried to finally obtain a separation membrane.

[0049] The present invention also provides two separation membrane performance testing methods, which can be used to test the performance of the separation membrane provided in the technical solution of the present invention and any one of Comparative Example 1.

[0050] (1) Water flux test

[0051] Flux is the volume of fluid passing through the membrane per unit time and per unit area. The pure water flux was measured using a membrane performance evaluation instrument (Hangzhou Saifei Membrane Separation Technology Co., Ltd., effective area 22cm 2 ) cross-flow filtration device, and the permeability was tested at an ambient temperature of 20°C and an operating pressure of 0.1 MPa.

[0052] In the pure water flux test, the separation membrane without the accelerated cooling process and the six groups of separation membrane samples in the embodiment of the accelerated cooling process were immersed in deionized water for 3 hours, then placed in a membrane tank and pre-pressed with a pressure of 0.1 MPa for 30 minutes until the water flux stabilized. The water flux was then tested at an inlet water pressure of 0.1 MPa, and the pure water flux value was recorded every 10 minutes for 1 hour. The pure water flux (J) was calculated using the formula (as shown below): W ).

[0053] Where V(L) is the volume of infiltrated water, S(m 2 ) is the effective area of ​​the membrane, and t(h) is the operation time. The test results are shown in Table 2 below.

[0054] Table 2 Pure water flux test results of 6 groups of samples in Comparative Example 1 and Example

[0055] (2) Cross-sectional structure

[0056] The cross-sectional structure was characterized using a field emission electron scanning microscope (JSM-6701F JEOL, Japan).

[0057] Because the cross-sectional appearance of the separation membranes of the six groups of samples in Example 1 is similar, for ease of illustration, only the separation membrane of Sample 2 and the separation membrane prepared in Comparative Example 1 are selected for cross-sectional morphological characterization and comparison. The cross-sectional morphology of the separation membrane prepared in Comparative Example 1 is shown in Figures 3a)-c), and the cross-sectional morphology of the separation membrane of Sample 2 is shown in Figures 3d)-e).

[0058] It is easy to see from the comparison of the two sets of figures that the visible pores on the surface of the separation membrane disappear in Figure 3d) compared with Figure 3a), and the finger-like pores in the dense layer in Figures 3b)-c) are changed into sponge pores in Figures 3e)-f).

[0059] The above two tests show that adding a rapid cooling step during the membrane formation process can improve the porosity of the membrane, form sponge pores and increase the water flux of the separation membrane.

[0060] Furthermore, to effectively demonstrate the superiority of the polyvinyl pyrrolidone and block copolymer mixtures used as additives in the present invention, various other additives were also selected for the experiment in Comparative Example 2. For the sake of brevity and effective illustration, four additive combinations were selected for comparison, and only the additives, cooling environment, and film-forming water flux were compared. All other settings in the film-forming process were the same as in the examples and are not further described here.

[0061] Table 3 Pure water flux test results of the four additive combinations in Comparative Example 2

[0062] Table 3 shows that the combination of the above four additives actually reduces the water flux of the separation membrane in a rapid cooling environment. Combined with the excellent performance of the polyvinyl pyrrolidone and block copolymer combinations in Table 2, it can be seen that although many of the additives are known materials, they cannot be arbitrarily selected or replaced in the rapid cooling environment described in the present invention. The effective additive combination, cooling temperature, and cooling time all require extensive experimentation to determine.

[0063] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, and improvements made within the scope of the present invention are intended to be included within the scope of the claims.

Claims

1. A method for preparing a separation membrane, characterized in that: The method comprises the following steps: (1) dissolving a polymer film-forming material and an additive in an organic solvent to prepare a film casting solution, and applying the film casting solution on a flat substrate by scraping; (2) moving the substrate into an environment with a temperature of -20°C to 4°C for cooling; (3) placing the cooled substrate into a coagulation bath for phase transformation into a membrane, thereby finally obtaining a polymer porous membrane. Wherein, the additive in step (1) is a mixture of polyvinyl pyrrolidone (PVP) and block copolymers.

2. The method according to claim 1, characterized in that The polymer film-forming material in step (1) is one or a mixture of two or more of polysulfone polymers, cellulose polymers, polyvinylidene fluoride polymers, and polyacrylonitrile polymers.

3. The method according to claim 2, characterized in that The polymer film-forming material is one or a mixture of two or more of polyethersulfone (PES), polysulfone (PSF) and a series of polymers with different sulfonation degrees.

4. The method according to any one of claims 1 to 3, characterized in that: The polyvinyl pyrrolidone (PVP) is polyvinyl pyrrolidone (PVP).

5. The method according to any one of claims 1 to 4, characterized in that: The block copolymers are poloxamers.

6. The method according to any one of claims 1 to 5, characterized in that The cooling time in the environment in step (2) is 5 seconds to 5 minutes.

7. The method according to any one of claims 1 to 6, characterized in that The cooling time in the environment in step (2) is 15 seconds to 1 minute.

8. A separation membrane, characterized in that: It is prepared according to the method according to any one of claims 1 to 7.

9. A filtering device, characterized in that: The filtration device comprises the separation membrane according to claim 8.

10. The filtering device according to claim 9, characterized in that The filtering device is a hemodialyzer, a blood purification filter, a tangential flow filter, or a water purification filter.

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