Composition for preparing ultrafiltration and / or microfiltration membranes and method for preparing composite ultrafiltration membranes

Abstract

The application relates to the field of material science, and discloses a composition for preparing an ultrafiltration and / or microfiltration membrane and a method for preparing a composite ultrafiltration membrane. In the composition, polyvinyl alcohol and a hydrophilic porous material are used to modify the ultrafiltration and / or microfiltration membrane, the dispersibility of the hydrophilic material is improved by the synergistic effect between the components, and the compatibility between the modified components such as the hydrophilic material and the membrane material is improved, so that the composite ultrafiltration membrane prepared by the method has the advantages of good hydrophilicity and good anti-pollution effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material science, in particular, to a composition for preparing ultrafiltration and / or microfiltration membrane and a method for preparing composite ultrafiltration membrane. BACKGROUND

[0002] Membrane separation technology is widely used in biology, medicine, environmental protection and other fields. In water treatment, membrane separation technology has become a research hotspot in the field of materials and environmental protection due to its small footprint, simple operation, high separation efficiency and good separation effect. The common membrane separation sewage treatment methods include ultrafiltration membrane separation, nanofiltration membrane separation treatment and liquid membrane separation treatment. Among them, the ultrafiltration membrane separation technology can effectively remove particulate matter, microorganisms, colloidal substances and other organic matter, and is an important technology in membrane separation water treatment application. However, during use, the pollutants in the wastewater are adsorbed and deposited on the membrane surface or in the pores, causing membrane pollution, which not only reduces the service life of the membrane, but also causes the membrane flux to continuously decrease with the increase of use time, affecting the treatment effect. Therefore, improving the anti-pollution property of the ultrafiltration membrane has become a research focus in membrane water treatment technology.

[0003] Studies have shown that the hydrophilicity of the membrane is related to the anti-pollution property. The common methods for improving the hydrophilicity of the ultrafiltration membrane include surface modification and blending modification. Among them, the surface modification is to cover a hydrophilic layer on the surface of the ultrafiltration membrane by surface coating or grafting, so as to improve the hydrophilicity. However, the hydrophilic coating on the surface of the modified ultrafiltration membrane obtained by coating method is easy to fall off, and the stability is poor. The operation method of the grafting method is complex, and the grafting rate is difficult to control. The stability of the product is also difficult to control. The blending modification is to directly mix the modified material in the membrane preparation process, which has the advantages of simple operation, low cost and stable modification effect. For example, CN105457510A discloses a hydrophilic polyether sulfone ultrafiltration membrane and a preparation method thereof. The polyether sulfone and the hydrophilic polymer are blended and scraped to form an ultrafiltration membrane, and then a crosslinking agent is grafted on the surface of the ultrafiltration membrane, so as to improve the hydrophilicity of the ultrafiltration membrane. CN102512998A discloses a preparation method of a molecular sieve modified polysulfone ultrafiltration membrane. The molecular sieve and the polysulfone are blended, and then a microporous membrane is prepared by phase inversion method, so as to obtain an ultrafiltration membrane with good hydrophilicity. However, the anti-pollution ability of the ultrafiltration membrane prepared by the current blending modification is limited, and the hydrophilicity still needs to be further improved. SUMMARY

[0004] The purpose of the present application is to overcome the problems of the prior art, such as the unsatisfactory anti-pollution effect of the ultrafiltration membrane and the need to improve the hydrophilicity, and to provide a composition for preparing ultrafiltration and / or microfiltration membrane and a method for preparing composite ultrafiltration membrane. The composite ultrafiltration membrane provided by the present application has the advantages of good hydrophilicity, good anti-pollution effect and high mechanical strength.

[0005] In order to achieve the above object, the present application provides a composition for preparing an ultrafiltration and / or microfiltration membrane, containing, based on the total weight of the composition, 10-20 wt% of a membrane material, 0.5-5 wt% of polyvinyl alcohol, 0.5-5 wt% of a porous material, and 5-15 wt% of an additive.

[0006] The second aspect of the present application provides a method for preparing a composite ultrafiltration membrane, comprising mixing the composition as described above to form a casting solution, then using a blade to form an ultrafiltration membrane semi-product from the casting solution, immersing the ultrafiltration membrane semi-product in a coagulation bath to perform immersion precipitation phase inversion membrane preparation, and then performing desolventization and pore preservation treatment to obtain the composite ultrafiltration membrane.

[0007] The third aspect of the present application provides a composite ultrafiltration membrane prepared by the method as described above.

[0008] Through the above technical solution, the present application can achieve the following beneficial effects:

[0009] (1) The composite ultrafiltration membrane provided by the present application uses polyvinyl alcohol and a hydrophilic porous material to modify the ultrafiltration membrane, and utilizes the synergistic effect between the components, especially the synergistic effect between the polyvinyl alcohol and the hydrophilic porous material, to improve the hydrophilicity and anti-fouling performance of the ultrafiltration membrane, improve the compatibility between the hydrophilic material and the membrane material, and improve the dispersibility of the components in the casting solution, especially the hydrophilic material, so that the hydrophilicity and anti-fouling performance of the ultrafiltration membrane are better and more stable.

[0010] (2) The addition of the porous material in the composite ultrafiltration membrane provided by the present application not only affects the permeability of the ultrafiltration membrane through its own pore structure, but also increases the mechanical strength and stability of the ultrafiltration membrane, so that the composite ultrafiltration membrane is more durable and has a longer service life.

[0011] (3) The composite ultrafiltration membrane provided by the present application further adds a crosslinking agent during the preparation process, which chemically crosslinks the polyvinyl alcohol during phase separation and membrane formation, improves the water resistance of the composite ultrafiltration membrane, and further improves the service life. DETAILED DESCRIPTION

[0012] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The endpoints of the ranges and any values should be considered to be open-ended ranges, unless the context clearly indicates the closed-ended nature of the range. Thus, the endpoints of the ranges should be considered to be approximate values, and thus, the disclosure should be understood to encompass any and all ranges contained within the described ranges, including end points between the stated ranges and, when appropriate, single values within those ranges. It is also understood that the disclosure will encompass ranges using any and all specific, non-endpoint values that fall within the stated ranges.

[0013] The inventors of the present application have ingeniously found in the course of research that, when a blending method is used for preparing an ultrafiltration membrane, simultaneously adding a porous material and polyvinyl alcohol can not only improve the hydrophilicity and anti-fouling performance of the ultrafiltration membrane, but also the compatibility and dispersibility of the porous material in the membrane matrix are also good. By selecting and optimizing the components, the anti-fouling performance and mechanical stability of the ultrafiltration membrane can be further improved.

[0014] The present application provides a composition for preparing an ultrafiltration and / or microfiltration membrane, containing, based on the total weight of the composition, 10-20 wt% of a membrane material, 0.5-5 wt% of polyvinyl alcohol, 0.5-5 wt% of a porous material, and 5-15 wt% of an additive. The "ultrafiltration and / or microfiltration membrane" can be any form of membrane material used in the process of ultrafiltration or microfiltration treatment in the art, for example, it can be a (flat plate) ultrafiltration membrane, a hollow fiber membrane, etc.

[0015] The porous material used in the composition provided by the present application can be any existing hydrophilic porous material used in the preparation of ultrafiltration and / or microfiltration membranes in the art. According to a preferred embodiment of the present application, the porous material is selected from at least one of microporous molecular sieves, mesoporous inorganic materials, and organic framework structure materials.

[0016] In order to obtain better hydrophilicity while ensuring the mechanical properties of the membrane, preferably, the particle size of the porous material is 0.1-1 μm.

[0017] Any microporous molecular sieve with the above-mentioned particle size can be suitable for the present application. Preferably, the microporous molecular sieve is selected from microporous zeolite molecular sieves. Any microporous zeolite molecular sieve that can be used in the preparation of ultrafiltration and / or microfiltration membranes in the art can be suitable for the present application, for example, 4A molecular sieve, ZSM-5 molecular sieve, Y-type molecular sieve, etc.

[0018] Any mesoporous inorganic material with the above-mentioned particle size and pore structure characteristics can be suitable for the present application. Preferably, the mesoporous inorganic material is selected from mesoporous carbon and / or mesoporous SiO2.

[0019] Any organic framework structure material with the above-mentioned particle size and pore structure characteristics can be suitable for the present application. Preferably, the organic framework structure material is selected from metal-organic framework materials (MOFs) and / or covalent organic framework materials (COFs).

[0020] Any metal-organic framework material that can be used in the preparation of ultrafiltration and / or microfiltration membranes in the art can be suitable for the present application. For example, ZIFs series metal-organic framework materials, UiO series metal-organic framework materials, etc.

[0021] Any covalent organic framework material that can be used in the preparation of ultrafiltration and / or microfiltration membranes in the art can be used in the present application. For example, TpPa-1, TpPa-2, and the like.

[0022] According to a preferred embodiment of the present application, the additive comprises an organic additive and / or an inorganic additive.

[0023] In the present application, the additive serves to improve the interaction between the components in the composition and to reduce the solvation in the polymer solution, thereby effectively adjusting the pore size, porosity, and hydrophilicity of the membrane. Any organic and / or inorganic additive that can play the above-mentioned roles can be used in the present application.

[0024] Preferably, the organic additive is selected from at least one of polyethylene glycol, ethyl acetate, polymaleic anhydride, cyclohexanol, glycerol, triethyl phosphate, tributyl phosphate, and polyvinylpyrrolidone.

[0025] Preferably, the inorganic additive is selected from at least one of sodium chloride, lithium chloride, calcium chloride, lithium nitrate, calcium nitrate, magnesium chloride, and zinc chloride.

[0026] Any polyvinyl alcohol that is currently used in the art for the modification of ultrafiltration and / or microfiltration membranes (hydrophilic) can be used in the present application. According to a preferred embodiment of the present application, the weight average molecular weight of the polyvinyl alcohol is 100000-200000.

[0027] Preferably, the alcoholysis degree of the polyvinyl alcohol is more than 85%.

[0028] Any membrane material that is currently used in the art for the preparation of ultrafiltration and / or microfiltration membranes can be used in the present application. Preferably, the membrane material is selected from at least one of polysulfone, polyethersulfone (preferably polyethersulfone having a weight average molecular weight of 40000-60000), and fluorine-containing polymer (for example, polyvinylidene fluoride, and the like, preferably polyvinylidene fluoride having a weight average molecular weight of 300000-450000).

[0029] The composition provided in the present application further comprises a solvent. In order to optimize the structure and performance of the membrane prepared using the composition, according to a preferred embodiment of the present application, the content of the solvent is 60-80% by weight based on the total weight of the composition.

[0030] Any solvent that is currently used in the art for the preparation of ultrafiltration and / or microfiltration membranes can be used in the composition provided in the present application. According to a preferred embodiment of the present application, the solvent is selected from at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl pyrrolidone.

[0031] According to a preferred embodiment of the present application, the composition further comprises a cross-linking agent. Preferably, the cross-linking agent is glutaraldehyde. The "independent existence" means that the cross-linking agent is packaged and used separately from the composition.

[0032] The ultrafiltration and / or microfiltration membrane prepared by using the composition as described above also belongs to the present application.

[0033] The second aspect of the present application provides a method for preparing a composite ultrafiltration membrane, which comprises mixing the composition as described above to form a casting solution, then using the casting solution to prepare an ultrafiltration membrane semi-product by means of blade coating, and then immersing the ultrafiltration membrane semi-product in a coagulation bath for immersion precipitation phase inversion membrane preparation, followed by desolventization and pore maintenance treatment to obtain a composite ultrafiltration membrane.

[0034] According to a preferred embodiment of the present application, the mixing conditions include a temperature of 80-100°C, a stirring speed of 150-400 rpm, and a time of 12-24 h.

[0035] According to a preferred embodiment of the present application, the casting solution needs to be defoamed and homogenized before being subjected to blade coating.

[0036] Any defoaming method for preparing an ultrafiltration membrane in the prior art can be applied to the method provided by the present application. Preferably, the defoaming method includes a temperature of 20-30°C and a standing time of 12-24 h.

[0037] Any homogenization method for improving the dispersity and compatibility of components in a mixture (especially a casting solution for an ultrafiltration membrane) in the prior art can be applied to the present application. Preferably, the homogenization method includes a temperature of 20-30°C and ultrasonic treatment for 2-6 h.

[0038] According to a preferred embodiment of the present application, the coagulation bath contains a cross-linking agent.

[0039] Preferably, the cross-linking agent is selected from glutaraldehyde.

[0040] More preferably, the coagulation bath is a mixed aqueous solution of hydrochloric acid and glutaraldehyde, wherein the concentration of HCl in the mixed aqueous solution is 0.015-0.045 M, and the concentration of glutaraldehyde is 2-5 wt%.

[0041] According to a preferred embodiment of the present application, the blade coating conditions include a temperature of 20-30°C, a blade coating speed of 5-15 cm / s, and a blade coating thickness of 100-250 μm.

[0042] According to a preferred embodiment of the present application, the immersion precipitation phase inversion membrane preparation method includes immersing the blade coating product in a coagulation bath at a temperature of 20-60°C and standing for 0.5-3 h.

[0043] Any desolventization method available in the art for the preparation of ultrafiltration membranes can be applied to the method provided by the present application. According to a preferred embodiment of the present application, the desolventization method comprises: standing in water at a temperature of 20-30℃ for 24-72h.

[0044] Any conventional pore-keeping method available in the art for the preparation of ultrafiltration membranes can be applied to the method provided by the present application.

[0045] The third aspect of the present application provides a composite ultrafiltration membrane prepared by the method as described above.

[0046] In addition, the present application also provides the use of the composite ultrafiltration membrane as described above in sewage treatment. For example, the use in the treatment of domestic sewage, industrial sewage and the like.

[0047] The present application will be described in detail below by way of examples. It should be understood that the following examples are only used to further explain and illustrate the present application, and are not intended to limit the present application.

[0048] In the following examples, the weight average molecular weight of polyvinyl alcohol is 145000, and the alcoholysis degree is 98±1%. Unless otherwise specified, other chemical reagents used are purchased from regular chemical suppliers, and the purity is analytical pure.

[0049] In the following examples, the specific method of pore-keeping treatment is: soaking with 0.2wt% sodium dodecyl sulfate for 5-6 days, and then drying at a humidity of 88% and room temperature.

[0050] In the following examples, unless otherwise specified, all operations are carried out at room temperature (25±5℃).

[0051] Example 1

[0052] (1) Preparation of casting solution

[0053] Components: 15wt% polyether sulfone (weight average molecular weight 58000), 1wt% polyvinyl alcohol, 0.5wt% 4A molecular sieve (particle size 500nm), 10wt% polyethylene glycol (PEG400), 73.5wt% dimethyl sulfoxide.

[0054] After mixing the above components, heat to 80℃, stir at 200rpm for 24h. Stand for 24h to defoam, and then ultrasonic treatment for 2h to obtain casting solution-1.

[0055] (2) Membrane scraping

[0056] The casting solution-1 was uniformly coated onto a glass plate by using a doctor blade, the doctor blade speed was 15 cm / s, the doctor blade thickness was 150 μm, and the ultrafiltration membrane semi-product-1 was obtained.

[0057] (3) Coagulation, desolventization and pore-keeping treatment

[0058] The coagulation bath-1 was an aqueous solution of HCl and glutaraldehyde, wherein the concentration of HCl was 0.02 M and the concentration of glutaraldehyde was 4 wt%.

[0059] The ultrafiltration membrane semi-product-1 was immersed in the coagulation bath-1 at 20 °C for 3 h. Then the coagulated ultrafiltration membrane semi-product-1 was immersed in deionized water for 72 h for desolventization treatment, and after pore-keeping treatment, the composite ultrafiltration membrane A1 was obtained.

[0060] Example 2

[0061] (1) Preparation of casting solution

[0062] Components: 18 wt% polyethersulfone (weight average molecular weight 58000), 1 wt% polyvinyl alcohol, 1 wt% 4A molecular sieve (particle size 500 nm), 5 wt% polyethylene glycol (PEG400), 75 wt% dimethyl sulfoxide.

[0063] After mixing the above components, heating to 80 °C, stirring at 300 rpm for 12 h. Defoaming for 24 h, and then ultrasonic treatment for 4 h, the casting solution-2 was obtained.

[0064] (2) Doctor blade coating

[0065] The casting solution-2 was uniformly coated onto a glass plate by using a doctor blade, the doctor blade speed was 10 cm / s, the doctor blade thickness was 150 μm, and the ultrafiltration membrane semi-product-2 was obtained.

[0066] (3) Coagulation, desolventization and pore-keeping treatment

[0067] The coagulation bath-2 was an aqueous solution of HCl and glutaraldehyde, wherein the concentration of HCl was 0.015 M and the concentration of glutaraldehyde was 2 wt%.

[0068] The ultrafiltration membrane semi-product-2 was immersed in the coagulation bath-2 at 40 °C for 2 h. Then the coagulated ultrafiltration membrane semi-product-2 was immersed in deionized water for 72 h for desolventization treatment, and after pore-keeping treatment, the composite ultrafiltration membrane A2 was obtained.

[0069] Example 3

[0070] Components: 15 wt% polyethersulfone (weight average molecular weight 58000), 1 wt% polyvinyl alcohol, 0.5 wt% mesoporous SiO2 (particle size 200 nm), 10 wt% glycerol, 73.5 wt% dimethyl sulfoxide.

[0071] After mixing the above components, heat to 80°C, stir at 300 rpm for 24 h. Defoam for 12 h, then ultrasonic treatment for 6 h to obtain casting solution-3.

[0072] (2) Blade casting

[0073] The casting solution-3 is uniformly coated onto the glass plate by using a doctor blade, the casting speed is 10 cm / s, the casting thickness is 150 pm, and the ultrafiltration membrane semi-finished product-3 is obtained.

[0074] (3) Coagulation, desolventization and pore preservation

[0075] The coagulation bath-2 in Example 2 is used for coagulation.

[0076] The ultrafiltration membrane semi-finished product-3 is immersed in the coagulation bath-2 for coagulation at 60°C for 1 h. Then the coagulated ultrafiltration membrane semi-finished product-3 is immersed in deionized water for desolventization treatment for 36 h, and after pore preservation treatment, the composite ultrafiltration membrane A3 is obtained.

[0077] Example 4

[0078] Components: 15 wt% polyvinylidene fluoride (weight average molecular weight 400000), 2 wt% polyvinyl alcohol, 1 wt% mesoporous carbon (particle size 100 nm), 10 wt% polyethylene glycol (PEG 400), 72 wt% dimethyl sulfoxide.

[0079] After mixing the above components, heat to 90°C, stir at 350 rpm for 18 h. Defoam for 12 h, then ultrasonic treatment for 2 h to obtain casting solution-4.

[0080] (2) Blade casting

[0081] The casting solution-4 is uniformly coated onto the glass plate by using a doctor blade, the casting speed is 5 cm / s, the casting thickness is 100 pm, and the ultrafiltration membrane semi-finished product-4 is obtained.

[0082] (3) Coagulation, desolventization and pore preservation

[0083] Coagulation bath-3: an aqueous solution of HCl and glutaraldehyde, wherein the concentration of HCl is 0.02 M and the concentration of glutaraldehyde is 2 wt%.

[0084] The ultrafiltration membrane semi-finished product-4 is immersed in the coagulation bath-3 for coagulation at 60°C for 0.5 h. Then the coagulated ultrafiltration membrane semi-finished product-4 is immersed in deionized water for desolventization treatment for 24 h, and after pore preservation treatment, the composite ultrafiltration membrane A4 is obtained.

[0085] Example 5

[0086] Components: 20 wt% polyether sulfone (weight average molecular weight 58000), 0.5 wt% polyvinyl alcohol, 0.5 wt% 4A molecular sieve (particle size 500 nm), 10 wt% polyvinyl pyrrolidone (PVP K30), 69 wt% dimethyl sulfoxide.

[0087] After mixing the above components, heat to 80°C, stir at 350 rpm for 24 h. Stand for 24 h for defoaming, and then ultrasonic treatment for 2 h to obtain casting solution-5.

[0088] (2) Blade coating

[0089] The casting solution-5 is uniformly coated onto a glass plate using a doctor blade at a coating speed of 15 cm / s and a coating thickness of 150 μm to obtain ultrafiltration membrane semi-product-5.

[0090] (3) Coagulation film formation, desolventization and pore preservation treatment

[0091] Coagulation bath-4: an aqueous mixture of HCl and glutaraldehyde, wherein the concentration of HCl is 0.03 M and the concentration of glutaraldehyde is 4 wt%.

[0092] The ultrafiltration membrane semi-product-5 is placed in the coagulation bath-4 and soaked at 20°C for 3 h for coagulation. Then the coagulated ultrafiltration membrane semi-product-5 is soaked in deionized water for 48 h for desolventization treatment, and after pore preservation treatment, the composite ultrafiltration membrane A5 is obtained.

[0093] Example 6

[0094] Components: 20 wt% polyether sulfone (weight average molecular weight 58000), 0.5 wt% polyvinyl alcohol, 0.5 wt% UiO-66 (average particle size 400 nm), 10 wt% polyvinyl pyrrolidone (PVP K30), 69 wt% dimethylacetamide.

[0095] After mixing the above components, heat to 80°C, stir at 300 rpm for 24 h. Stand for 24 h for defoaming, and then ultrasonic treatment for 2 h to obtain casting solution-6.

[0096] (2) Blade coating

[0097] The casting solution-6 is uniformly coated onto a glass plate using a doctor blade at a coating speed of 15 cm / s and a coating thickness of 150 μm to obtain ultrafiltration membrane semi-product-6.

[0098] (3) Coagulation film formation, desolventization and pore preservation treatment

[0099] The coagulation film formation is carried out using the coagulation bath-3 in Example 4.

[0100] The ultrafiltration membrane semi-product-6 was placed in the coagulation bath-3 and soaked for coagulation at 20°C for 3h. Then the coagulated ultrafiltration membrane semi-product-6 was soaked in deionized water for 72h for desolventizing treatment, and after pore maintaining treatment, the composite ultrafiltration membrane A6 was obtained.

[0101] Example 7

[0102] Components: 20wt% polyether sulfone (weight average molecular weight 58000), 0.5wt% polyvinyl alcohol, 0.5wt% 4A molecular sieve (particle size 500nm), 10wt% lithium chloride, 69wt% dimethyl sulfoxide.

[0103] After mixing the above components, heating to 90°C, stirring at 250rpm for 24h. Standing for 12h for defoaming, and then ultrasonic treatment for 4h, the casting solution-7 was obtained.

[0104] (2) Film scraping

[0105] The casting solution-7 was uniformly coated onto the glass plate with a doctor blade, the film scraping speed was 5cm / s, the film scraping thickness was 100μm, and the ultrafiltration membrane semi-product-7 was obtained.

[0106] (3) Coagulation film forming, desolventizing and pore maintaining treatment

[0107] The coagulation bath-2 in Example 2 was used for coagulation film forming.

[0108] The ultrafiltration membrane semi-product-7 was placed in the coagulation bath-2 and soaked for coagulation at 20°C for 3h. Then the coagulated ultrafiltration membrane semi-product-7 was soaked in deionized water for 72h for desolventizing treatment, and after pore maintaining treatment, the composite ultrafiltration membrane A7 was obtained.

[0109] Example 8

[0110] Components: 18wt% polyether sulfone (weight average molecular weight 58000), 1wt% polyvinyl alcohol, 1wt% COF-TpPa-1 (particle size 1μm), 5wt% polyethylene glycol (PEG400), 75wt% dimethyl sulfoxide.

[0111] After mixing the above components, heating to 80°C, stirring at 300rpm for 12h. Standing for 24h for defoaming, and then ultrasonic treatment for 4h, the casting solution-8 was obtained.

[0112] (2) Film scraping

[0113] The casting solution-8 was uniformly coated onto the glass plate with a doctor blade, the film scraping speed was 10cm / s, the film scraping thickness was 150μm, and the ultrafiltration membrane semi-product-8 was obtained.

[0114] (3) Coagulation film forming, desolventizing and pore maintaining treatment

[0115] Coagulation bath-5: an aqueous solution of HCl and glutaraldehyde, wherein the concentration of HCl is 0.04 M and the concentration of glutaraldehyde is 2 wt%.

[0116] The ultrafiltration membrane semi-product-8 was immersed in the coagulation bath-5 at 40 °C for 2 h. Then the coagulated ultrafiltration membrane semi-product-8 was immersed in deionized water for 72 h for desolventizing treatment, and after pore maintaining treatment, the composite ultrafiltration membrane A8 was obtained.

[0117] Example 9

[0118] Components: 15 wt% polyether sulfone (weight average molecular weight 58000), 1.5 wt% polyvinyl alcohol, 0.5 wt% 4A molecular sieve (particle size 500 nm), 10 wt% magnesium chloride, 73 wt% dimethyl sulfoxide.

[0119] After mixing the above components, heating to 80 °C, stirring at 200 rpm for 24 h. Standing for 24 h for defoaming, and then ultrasonic treatment for 2 h, the casting solution-9 was obtained.

[0120] (2) Blade coating

[0121] The casting solution-9 was uniformly coated onto a glass plate by a doctor blade, the blade coating speed was 15 cm / s, and the blade coating thickness was 150 μm, and the ultrafiltration membrane semi-product-9 was obtained.

[0122] (3) Coagulation, desolventizing and pore maintaining treatment

[0123] Coagulation bath-6: an aqueous solution of HCl and glutaraldehyde, wherein the concentration of HCl is 0.04 M and the concentration of glutaraldehyde is 4 wt%.

[0124] The ultrafiltration membrane semi-product-9 was immersed in the coagulation bath-6 at 20 °C for 3 h. Then the coagulated ultrafiltration membrane semi-product-9 was immersed in deionized water for 72 h for desolventizing treatment, and after pore maintaining treatment, the composite ultrafiltration membrane A9 was obtained.

[0125] Example 10

[0126] The method in Example 1 was adopted, except that no glutaraldehyde was added in the coagulation bath, but the concentration of HCl therein was kept the same as that in the coagulation bath-1. The remaining steps and conditions were the same as in Example 1. The composite ultrafiltration membrane A10 was obtained.

[0127] Comparative Example 1

[0128] The method in Example 1 was adopted, except that the content of polyvinyl alcohol in the casting solution was adjusted to 10 wt%, and the content of dimethyl sulfoxide was adjusted to 64.5 wt%. The remaining steps and conditions were the same as in Example 1. The composite ultrafiltration membrane D1 was obtained.

[0129] Comparative Example 2

[0130] The method in Example 1 was adopted, except that 4A molecular sieve was replaced by nano-SiO2 (particle size 500 nm). The remaining steps and conditions were the same as in Example 1. Composite ultrafiltration membrane D2 was obtained.

[0131] Comparative Example 3

[0132] The method in Example 1 was adopted, except that no 4A molecular sieve was added, and the content of dimethyl sulfoxide in the casting solution was adjusted to 74 wt.%. The remaining steps and conditions were the same as in Example 1.

[0133] Composite ultrafiltration membrane D3 was obtained.

[0134] Comparative Example 4

[0135] The method in Example 1 was adopted, except that no polyvinyl alcohol was added, and the content of dimethyl sulfoxide in the casting solution was adjusted to 74.5 wt.%. The remaining steps and conditions were the same as in Example 1. Composite ultrafiltration membrane D4 was obtained.

[0136] Test Example 1

[0137] The properties of the composite ultrafiltration membranes obtained in the above examples and comparative examples were tested by the following methods, respectively. The results are shown in Table 1.

[0138] (1) Tensile strength: tested by an electronic tensile tester (Instron 3342, USA) at a tensile rate of 40 mm / min.

[0139] (2) Water contact angle: tested by a contact angle measuring instrument (EasyDrop Standard, KRUSS, Germany), in which the ambient temperature was controlled at 20℃±5℃, and the contact angle was tested at 5 different test points on each membrane and averaged.

[0140] (3) Water resistance test: after the membrane was immersed in deionized water for 72 hours (deionized water was replaced every 12 hours), the membrane was taken out and rinsed, dried at room temperature, and the contact angle was measured. The water resistance of the membrane was judged by comparing the change in the initial contact angle and the contact angle after immersion, and the greater the change, the worse the water resistance.

[0141] (4) Pure water flux: tested by a cup-type ultrafiltration system, in which high-purity nitrogen was used for pressure driving, the driving pressure was 0.1 MPa, and an electronic balance was used to continuously monitor the cumulative volume change of the permeate water online, and the water flux J of the membrane was calculated according to the following formula:

[0142]

[0143] In the formula, V is the volume of the permeate, A is the effective filtration area of the membrane, and t is the filtration time.

[0144] Table 1

[0145]

[0146]

[0147] From the data in Table 1, it can be seen that the ultrafiltration membrane prepared by using the composition and method provided by the present application has good hydrophilicity, high flux and strength, and the water resistance and stability of the ultrafiltration membrane are high as shown by the comparison of the initial water contact angle and the water contact angle after soaking in deionized water for 72 hours. Therefore, the service life of the ultrafiltration membrane provided by the present application can be effectively prolonged.

[0148] By comparing the detection results of ultrafiltration membranes A1 and A10, it can be seen that the water resistance of the ultrafiltration membrane can be significantly improved when a crosslinking agent is added to the coagulation bath. By comparing the detection results of ultrafiltration membranes A1 and D1-D4, it can be seen that when any one component of the composition provided by the present application is missing or other non-preferred materials of the present application are used to replace a certain component, the performance of the ultrafiltration membrane prepared by using the composition will be poor.

[0149] In addition, it is found during the preparation of ultrafiltration membranes A1-A10 that almost no agglomeration of the modified components in the casting solution can be observed, indicating that the uniformity of the casting solution is good when the composition provided by the present application is used to prepare the ultrafiltration membrane. However, during the preparation of ultrafiltration membrane D4, obvious agglomeration of the modified components in the casting solution can be observed, indicating that the compatibility of the modified components with the membrane matrix is poor, resulting in uneven distribution of the components in the casting solution.

[0150] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a composite ultrafiltration membrane, characterized in that, The method includes mixing the composition to prepare a casting solution, then using the casting solution to prepare an ultrafiltration membrane semi-finished product by a scraping method, then placing the ultrafiltration membrane semi-finished product in a coagulation bath for immersion precipitation phase inversion to form a membrane, and then undergoing solvent removal and pore preservation treatment to obtain a composite ultrafiltration membrane. Based on the total weight of the composition, the composition contains: 10-20% by weight of membrane material, 0.5-5% by weight of polyvinyl alcohol, 0.5-5% by weight of porous material, and 5-15% by weight of additives; The porous material is at least one of microporous molecular sieves, mesoporous inorganic materials, and organic framework structural materials. The porous material has a particle size of 0.1-1 μm; The microporous molecular sieve is selected from microporous zeolite molecular sieve; The mesoporous inorganic material is selected from mesoporous carbon and / or mesoporous SiO2; The organic framework material is a covalent organic framework material, and the covalent organic framework material is COF-TpPa-1; The coagulation bath is a mixed aqueous solution of hydrochloric acid and glutaraldehyde, wherein the concentration of HCl in the mixed aqueous solution is 0.015-0.045M, and the concentration of glutaraldehyde is 2-5% by weight. The method of immersion precipitation phase inversion film preparation includes: immersing the film-coated product in a coagulation bath and letting it stand at a temperature of 20-60℃ for 0.5-3 hours.

2. The method according to claim 1, wherein, The additives include organic additives and / or inorganic additives.

3. The method according to claim 2, wherein, The organic additive is selected from at least one of polyethylene glycol, ethyl acetate, polymaleic anhydride, cyclohexanol, glycerol, triethyl phosphate, tributyl phosphate, and polyvinylpyrrolidone; And / or, the inorganic additive is selected from at least one of sodium chloride, lithium chloride, calcium chloride, lithium nitrate, calcium nitrate, magnesium chloride, and zinc chloride.

4. The method according to claim 1, wherein, The weight-average molecular weight of the polyvinyl alcohol is 100,000-200,000.

5. The method according to claim 4, wherein, The degree of alcoholysis of the polyvinyl alcohol is above 85%.

6. The method according to claim 1, wherein, The membrane material is selected from at least one of polysulfone, polyethersulfone, and fluoropolymers; And / or, the composition further includes a solvent, the amount of which is 60-80% by weight of the total weight of the composition.

7. The method according to claim 6, wherein, The solvent is selected from at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

8. The method according to claim 1, wherein, The mixing conditions include: temperature 80-100℃, stirring speed 150-400rpm, and time 12-24h; And / or, the conditions for scraping the film include: temperature 20-30℃, scraping speed 5-15cm / s, and scraping thickness 100-250μm; And / or, the solvent removal method includes: soaking in water at a temperature of 20-30°C for 24-72 hours.

9. The composite ultrafiltration membrane prepared by the method according to any one of claims 1-8.

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