Modified microfiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of microfiltration membranes, and discloses a modified microfiltration membrane and a preparation method and application thereof, and the preparation method comprises the following steps: S1, carrying out hydrophilic modification on a basement membrane by using a hydrophilic modifier to obtain a hydrophilic basement membrane; s2, carrying out hydrophobic modification on the hydrophilic substrate membrane by adopting a hydrophobic modifier to obtain a heterogeneous modified microfiltration membrane; wherein the preparation process of the hydrophilic modifier comprises the following steps: adding a free radical initiator into a mixed solution containing a hydroxyl monomer, a silane monomer X and an alkaline buffer solution, and carrying out condensation reaction to obtain the hydrophilic modifier; the preparation process of the hydrophobic modifier comprises the following steps: adding a silicon source into a mixed solution containing a silane monomer Y, an alkaline substance and a solvent B, and carrying out condensation polymerization to obtain the hydrophobic modifier. According to the micro-filtration membrane, through the design of combining hydrophilic modification and hydrophobic modification, the risks of membrane structure damage and wettability failure are greatly reduced, membrane pollution can be stably resisted for a long time, and continuous and efficient separation performance is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microfiltration membranes, in particular to a modified microfiltration membrane and a preparation method and application thereof BACKGROUND

[0002] Membrane separation technology has significant advantages in the stable separation of oil-water emulsion due to its high efficiency and environmental protection. Membrane fouling is one of the key factors limiting membrane separation technology. Membrane fouling is mainly caused by the adhesion of organic pollutants such as oil droplets and concentrated emulsions in the feed liquid on the surface and in the pores of the hydrophobic membrane, which blocks the membrane pores and causes a rapid decrease in water flux. Currently, the membrane surface is often chemically modified, such as grafting hydrophilic groups, to make the membrane repel the oil phase in the water environment and reduce the risk of membrane fouling.

[0003] For example, the Chinese patent application with publication number CN118663088A discloses a positively charged and hydrophilic-hydrophobic composite distillation membrane and its preparation method and application. The hydrophobic membrane surface is modified by a polydopamine adhesive to form a positively charged hydrophilic coating on the surface of the hydrophobic base membrane, thereby preventing oil stains from entering the hydrophobic membrane base and improving the anti-pollution performance of the composite distillation membrane for emulsified oil. However, in this scheme, long-term use of the membrane can cause damage to the membrane structure and surface wettability, and the anti-pollution design of the membrane can also be damaged, resulting in increased pollution. SUMMARY

[0004] To solve the above technical problems, the present application provides a modified microfiltration membrane and a preparation method and application thereof. The microfiltration membrane is designed by combining hydrophilic and hydrophobic modification, which greatly reduces the risk of membrane structure damage and wettability failure, can resist membrane fouling stably and effectively for a long time, and ensures the sustained and efficient separation performance.

[0005] The specific technical scheme of the present application is as follows: a preparation method of a modified microfiltration membrane, comprising the following steps: S1: hydrophilic modification of the base membrane using a hydrophilic modifier to obtain a hydrophilic base membrane; S2: hydrophobic modification of the hydrophilic base membrane using a hydrophobic modifier to obtain a heterogeneously modified microfiltration membrane; The preparation process of the hydrophilic modifier is as follows: a free radical initiator is added to a mixed solution containing a hydroxyl monomer and a silane monomer X and an alkaline buffer, and a condensation reaction is carried out to obtain the hydrophilic modifier. The preparation process of the hydrophobic modifier is as follows: a silicon source is added to a mixed solution containing a silane monomer Y, an alkaline substance and a solvent B, and a polycondensation reaction is carried out to obtain the hydrophobic modifier.

[0006] The modified microfiltration membrane of the present invention is constructed by first subjecting the base membrane to hydrophilic modification and then to hydrophobic modification, forming a heterogeneous, wettable, antifouling coating with coexisting hydrophilic and hydrophobic regions. The combination of hydrophilic and hydrophobic modifications facilitates the entry of both the oil and water phases in the emulsion into the membrane, reducing penetration pressure. The hydrophilic modification facilitates high permeability of the continuous aqueous phase in the emulsified oil through the membrane. The bridging of silane particles with hydrophilic silanes grafts hydrophobic particles onto the hydrophilic matrix, allowing the hydrophobic particles to capture and aggregate oil droplets in the emulsion, forming a continuous oil phase. During the separation process, the oil phase, based on the shearing effect of the continuous water phase in the emulsion, enters the filtrate together with the continuous water phase under the flushing of continuous water flow, forming stratified water phase and oil phase, thereby enhancing the separation performance. In this process, the oil droplets are not simply screened by the membrane pores, but flow in coordination with the water phase on the membrane surface through coalescence and other means, reducing the direct impact and blockage of the oil droplets on the membrane pores, reducing the risk of damage to the membrane structure and wettability due to large-scale contact of the oil phase with the membrane pores, and reducing membrane pollution caused by the clogging of the membrane pores by the retained oil phase. At the same time, the simultaneous recovery of the oil and water phases is achieved based on coalescence and demulsification separation.

[0007] Preferably, the hydroxyl-containing monomer is selected from one or more of proanthocyanidins, dopamine hydrochloride, and lignin; the silane monomer X is selected from one or more of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, 3-[(2,3)-epoxypropyloxy]propylmethyldimethoxysilane, aminoethylaminoisobutylmethyldimethoxysilane, and 3-aminopropyldimethoxymethylsilane; the silane monomer Y is selected from one or more of ethyl silicate, diphenyldimethoxysilane, tris(trimethylsiloxy)silane, and tert-butyldiphenylmethoxysilane; the alkaline substance is selected from one or more of ammonia water and sodium hydroxide; and the solvent B is selected from one or more of ethanol, n-hexane, isopropanol, toluene, and chloroform.

[0008] Preferably, based on weight, the hydroxyl-containing monomer is 0.2-0.4 parts, and the silane monomer X is 0.5-0.7 parts; or, based on weight, the silane monomer Y is 0.7-1.1 parts, the alkaline substance is 9-11 parts, and the solvent B is 24-40 parts.

[0009] Preferably, the pH value of the alkaline buffer solution is 8-9.

[0010] Preferably, in step S1, the base membrane is hydrophilically modified by dipping or grafting, and the reaction temperature of the hydrophilic modification is 20-40° C., and the reaction time is 4-6 hours.

[0011] Preferably, in step S2, the hydrophobic modifier is distributed on the hydrophilic base membrane by spraying to perform hydrophobic modification, and the reaction time of the hydrophobic modification is 20-100 minutes.

[0012] As preferred, in step S1, the preparation of the base membrane comprises the following steps: i: dissolving the polymer and the crosslinking agent in solvent A to obtain a casting solution; ii: treating the casting solution by phase inversion method or electrospinning method to form a solidified film; iii: heat-crosslinking the solidified film to obtain the base membrane.

[0013] The base membrane is crosslinked and modified in the application, which improves the tolerance of the membrane substrate in harsh environments such as strong acid, strong base, high temperature and organic solvent.

[0014] As preferred, in step i, the polymer is selected from one or more of poly(vinylidene fluoride-trifluoroethylene) and polyvinylidene fluoride; the crosslinking agent is selected from maleic anhydride, p-phenylenediamine, polyoxyethylene diamine, pentaethylene hexamine and other reagents containing two or more amino functional groups; the solvent A is selected from one or more of cyclohexanone, DMF (dimethylformamide), DMAC (dimethylacetamide), TEP (triethyl phosphate) and NMP (N-methyl pyrrolidone); or, the polymer is 10-20 parts, the crosslinking agent is 1-2 parts, and the solvent A is 130-160 parts by weight.

[0015] As preferred, in step iii, the temperature of the heat-crosslinking is 230-250℃.

[0016] The second specific technical solution of the application is a modified microfiltration membrane prepared by the above preparation method.

[0017] The third specific technical solution of the application is the application of a modified microfiltration membrane in treating emulsified oil in harsh environments, wherein the modified microfiltration membrane is the above modified microfiltration membrane, and the harsh environment includes strong acid, strong base, salt and organic solvent environment.

[0018] Compared with the prior art, the application has at least the following advantages: (1) The present application constructs a heterogeneous anti-fouling coating layer with coexistence of hydrophilic and hydrophobic regions on the substrate membrane. The combination of hydrophilic and hydrophobic modification is conducive to the easy entry of oil and water phases in the emulsion into the membrane, reducing the breakthrough pressure; the hydrophilic modification is conducive to the continuous water phase in the emulsified oil passing through the membrane at a high permeation flux; the hydrophobic particles grafted on the hydrophilic matrix can capture and coalesce the oil droplets in the emulsion, forming a continuous oil phase. In the separation process, the oil phase is sheared based on the continuous water phase in the emulsion, and under the scouring of the continuous water flow, it enters the filtrate together with the continuous water phase, forming a layered water phase and oil phase, enhancing the separation performance. In this process, the oil droplets do not simply rely on membrane pore size screening, but flow cooperatively with the water phase on the membrane surface through coalescence and other methods, reducing the direct impact and blockage of oil droplets on the membrane pores, reducing the risk of membrane structure and wettability damage caused by a large amount of oil phase contacting the membrane pores, and reducing the membrane pollution caused by the blockage of the membrane pores by the trapped oil phase. At the same time, based on the coalescence demulsification separation, the oil and water phases are simultaneously recovered; (2) The present application crosslinks the substrate membrane to improve the resistance of the membrane substrate to harsh environments such as strong acid, strong base, salt and organic solvent; (3) The modified microfiltration membrane prepared by the present application has high resistance to harsh environments, an oil-in-water emulsion permeation flux of more than 1000 Lm - 2 h -1 bar -1 , a separation rate of more than 99.5%, a continuous operation time of more than 100h, an oil recovery rate of >80%, and a water recovery rate of nearly 100%. It has a broad application prospect in the treatment of oil-water separation and other industrial wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a scanning electron microscope image of the modified microfiltration membrane of Example 1; Figure 2 is a contact angle test result graph of the modified microfiltration membrane of Example 1. DETAILED DESCRIPTION

[0020] The present application will be described below through specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. Any changes and advantages that can be thought of by those skilled in the art without departing from the spirit and scope of the present application are included in the present application, and the appended claims and any equivalents thereof are the scope of protection of the present application.

[0021] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified, which can be obtained from conventional commercial channels; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0022] In the following examples, the water-in-D5 emulsion is an emulsion system with decamethylcyclopentasiloxane (D5) as the dispersed phase and water as the continuous phase.

[0023] Example 1 A method for preparing a modified microfiltration membrane comprises the following steps: 1) Dissolve 15 g of poly(vinylidene fluoride-trifluoroethylene) and 1.5 g of polyoxyethylene diamine in 150 mL of cyclohexanone solution, stir at 60° C. for 4 h, and then allow to stand and evacuate to remove small bubbles in the solvent to obtain a casting solution; 2) Pour the casting solution onto a smooth, clean glass substrate, scrape the film with a 150 μm scraper, and place it in a coagulation bath of water and ethanol (volume ratio 1:1) for 5 seconds. Then, transfer it to pure water at 60°C for 24 hours to form a solidified film. 3) The cured film was placed in a vacuum oven and dried at 50°C for 6 hours, and then heated to 240°C for cross-linking for 1 hour to obtain a base film; 4) preparing 150 mL of 50 mM tris (hydroxymethyl)aminomethane hydrochloride buffer at a pH of 8.5, dissolving 0.3 g of proanthocyanidin and 0.6 g of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane in the buffer, and then adding 0.3 g of ammonium persulfate to undergo a condensation reaction to obtain a hydrophilic modifier; 5) placing the basement membrane in a hydrophilic modifier, reacting at 30°C and 120 rpm for 5 hours, then removing the membrane, washing it with deionized water, and drying it in a 60°C oven for 3 hours to obtain a hydrophilic basement membrane for later use; 6) Prepare a mixed solution by mixing 10 ml of ammonia water and 40 ml of ethanol, add 1 ml of ethyl silicate, and then disperse 0.5 g of SiO2 in the mixed solution. Stir and react for 6 hours to obtain a hydrophobic modifier by polycondensation. 7) Spraying the hydrophobic modifier onto the hydrophilic base membrane and reacting for 30 minutes, removing the membrane and rinsing the unreacted hydrophobic modifier with deionized water, and drying the membrane in an oven at 80° C. for 6 hours to obtain a heterogeneously modified microfiltration membrane.

[0024] The microstructure of the prepared heterogeneous modified microfiltration membrane was observed using scanning electron microscopy (SEM). Figure 1 As shown, the heterogeneously modified microfiltration membrane has a micro-nanoporous structure: a sponge-like porous structure with numerous raised structures on the membrane surface. The sponge-like porous structure provides a large specific surface area, increasing the contact area between the membrane and the oil-water emulsion, allowing the oil droplets and water in the emulsion to more fully contact the membrane. The raised structures further disrupt the fluid flow state and promote the coalescence of oil droplets.

[0025] The prepared heterogeneous modified microfiltration membrane was subjected to contact angle test. When testing water contact angle, 4 μL of deionized water droplet was added on the surface of the heterogeneous modified microfiltration membrane by using a syringe. When testing oil contact angle, the heterogeneous modified microfiltration membrane was immersed in a quartz tank filled with deionized water, and 4 μL of oil droplet was added on the surface of the membrane by using a syringe. The results are shown in Figure 2 FIG. 1. The water contact angle is 0°, and the oil contact angle under water is 116°, indicating that the heterogeneous modified microfiltration membrane has superhydrophilicity and superoleophobicity under water. In addition, the oil droplet slowly penetrates into the membrane for about 30 s, indicating that the membrane has good permeability.

[0026] Under a pressure of 0.1 bar, the initial permeation flux of the heterogeneous modified microfiltration membrane for water-in-D5 emulsion was measured to be 4000 L m -2 h -1 bar -1 , the stable permeation flux reached 1000 L m -2 h -1 bar -1 , the separation efficiency reached more than 99.5%, the membrane had excellent antifouling performance, could continuously and stably separate for more than 100 h, the oil recovery rate was 90.0%, and the water recovery rate was 100%.

[0027] It should be noted that in step 1) of the embodiment, cyclohexanone is used as solvent A only as an example. Solvent A is used to dissolve the polymer and the crosslinking agent, and therefore a suitable solvent A should be selected according to the type of the polymer and the crosslinking agent. Solvent A is selected from common solvents in the art such as cyclohexanone, DMF, DMAC, TEP, NMP, etc. In step 1) of the embodiment, ethanol is used as solvent B only as an example. Solvent B is used to dissolve the silane-containing monomer Y and the basic substance, and therefore a suitable solvent B should be selected according to the type of the silane-containing monomer Y and the basic substance. Solvent B is selected from common solvents in the art such as ethanol, n-hexane, isopropyl alcohol, toluene, chloroform, etc.

[0028] Example 2 A method for preparing a modified microfiltration membrane, comprising the following steps: 1) 10 g of poly(vinylidene fluoride-trifluoroethylene) and 1.0 g of polyoxyethylene diamine were dissolved in 130 mL of cyclohexanone solution, stirred at 60°C for 4 h, and then vacuumed to remove small air bubbles in the solvent to obtain a casting solution; 2) The casting solution was poured onto a smooth and clean glass substrate, a 150 μm doctor blade was used to scrape the membrane, and the membrane was placed in a coagulation bath of water and ethanol (volume ratio 1:1) for 5 s, and then transferred into pure water at 60°C for 24 h to form a solidified membrane; 3) The solidified membrane was placed in a vacuum box and dried at 50°C for 6 h, and then heated to 230°C for crosslinking for 1 h to obtain a base membrane; 4) Prepare 150 mL of 50 mM, pH 8.0 tris-hydroxymethyl aminomethane hydrochloride buffer, dissolve 0.2 g of procyanidins, 0.5 g of N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane in the above buffer, and then add 0.3 g of ammonium persulfate to obtain a hydrophilic modifier through condensation reaction; 5) Put the base film into the hydrophilic modifier, take it out after 4 h of reaction at 20 °C and 120 rpm, wash it with deionized water, and then put it into a 60 °C oven for 3 h to obtain a hydrophilic base film for use; 6) Prepare a mixed solution by mixing 10 mL of ammonia water with 30 mL of ethanol, mix 0.8 mL of ethyl silicate into the mixed solution, and then disperse 0.5 g of SiO2 in the mixed solution, stir for 6 h, and then perform polycondensation reaction to obtain a hydrophobic modifier; 7) Spray the hydrophobic modifier on the hydrophilic base film, take the film out after 20 min of reaction, wash the unreacted hydrophobic modifier with deionized water, and then put it into an 80 °C oven for drying for 6 h to obtain a heterogeneously modified microfiltration membrane.

[0029] Perform microscopic structure observation and contact angle test on the obtained heterogeneously modified microfiltration membrane by using scanning electron microscopy (SEM) technology, and the test method is as in Example 1. The results are as follows: the heterogeneously modified microfiltration membrane has a micro-nano-pore structure and a sponge porous structure, and the membrane surface is composed of many protruding structures; oil droplets slowly penetrate into the membrane over time, and it takes about 30 s.

[0030] Test the heterogeneously modified microfiltration membrane by using a cross-flow microfiltration device under a pressure of 0.1 bar. The initial permeation flux of the heterogeneously modified microfiltration membrane for water-in-D5 emulsion is 4100 L m -2 h -1 bar -1 , the stable permeation flux reaches 1070 L m -2 h -1 bar -1 , the separation efficiency reaches more than 99.7%, the membrane has excellent antifouling performance, can continuously and stably separate for more than 100 h, the oil recovery rate is 90.4%, and the water recovery rate is 100%.

[0031] Example 3 A method for preparing a modified microfiltration membrane, comprising the following steps: 1) Dissolve 20 g of poly(vinylidene fluoride-trifluoroethylene) and 2.0 g of polyoxyethylene diamine in 160 mL of cyclohexanone solution, stir at 60 °C for 4 h, and then perform vacuum extraction to remove small gas bubbles in the solvent to obtain a casting solution; 2) Pour the casting solution onto a smooth and clean glass substrate, use a 150 μm doctor blade to scrape the film, and then put it into a coagulation bath of water and ethanol (volume ratio 1:1) for 5 s, and then transfer it into pure water at 60 °C for 24 h to form a solidified film; 3) The solidified film was placed in a vacuum box and dried at 50°C for 6 h, then heated to 250°C for crosslinking for 1 h to obtain a base film; 4) A 150 mL 50 mM, pH 9.0 tris-hydroxymethyl aminomethane hydrochloride buffer was prepared, 0.4 g of procyanidins and 0.7 g of N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane were dissolved in the above buffer, and 0.3 g of ammonium persulfate was added to obtain a hydrophilic modifier by condensation reaction; 5) The base film was placed in the hydrophilic modifier, and after reaction at 40°C and 120 rpm for 6 h, it was taken out, washed with deionized water, and then placed in a 60°C oven for 3 h to obtain a hydrophilic base film for use; 6) A mixed solution was prepared by mixing 12 mL of ammonia water with 50 mL of ethanol, 1.2 mL of ethyl silicate was mixed in, and 0.5 g of SiO2 was dispersed in the mixed solution, and the mixture was stirred for 6 h to obtain a hydrophobic modifier by polycondensation reaction; 7) The hydrophobic modifier was sprayed on the hydrophilic base film, and after reaction for 40 min, the film was taken out and washed with deionized water to remove the unreacted hydrophobic modifier, and then placed in an 80°C oven for drying for 6 h to obtain a heterogeneously modified microfiltration membrane.

[0032] The heterogeneously modified microfiltration membrane was observed by scanning electron microscopy (SEM) and tested for contact angle, and the test method was as in Example 1. The results were as follows: the heterogeneously modified microfiltration membrane had a micro-nano-porous structure and a sponge-like porous structure, and the surface of the membrane was composed of many protruding structures; oil droplets slowly penetrated into the membrane over time, about 30 s.

[0033] The heterogeneously modified microfiltration membrane was tested by a cross-flow microfiltration device under a pressure of 0.1 bar. The initial permeation flux of the heterogeneously modified microfiltration membrane for a water-in-D5 emulsion was 4050 L m -2 h -1 bar -1 , the stable permeation flux reached 1100 L m -2 h -1 bar -1 , the separation efficiency reached more than 99.6%, and the membrane had excellent antifouling performance, with continuous and stable separation for more than 100 h, an oil recovery rate of 90.2%, and a water recovery rate of 100%.

[0034] Example 4 A method for preparing a modified microfiltration membrane, comprising the following steps: 1) 15 g of polyvinylidene fluoride and 1.5 g of p-phenylenediamine were dissolved in 150 mL of DMF solution, stirred at 60°C for 4 h, and then vacuumed to remove small gas bubbles in the solvent to obtain a casting solution; 2) Transfer the casting solution to a syringe with a stainless steel needle, install the syringe on the electrospinning device, set the electrospinning parameters: voltage 15 kV, receiving distance 15 cm, push speed 0.5 mL / h, turn on the electrospinning device, the casting solution forms fibers under the action of high-voltage electric field, and is collected on the grounded receiving device, continue spinning until a certain thickness of the solidified film is obtained; 3) Put the solidified film into a vacuum box, dry at 50°C for 6 h, then heat to 240°C for crosslinking for 1 h, to obtain the base film; 4) Prepare 150 mL of 50 mM, pH 8.5 tris-hydroxymethyl aminomethane hydrochloride buffer, dissolve 0.3 g of dopamine hydrochloride and 0.6 g of 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane in the above buffer, then add 0.3 g of ammonium persulfate, and condensation reaction to obtain a hydrophilic modifier; 5) Put the base film into the hydrophilic modifier, react at 30°C, 120 rpm for 5 h, then take it out, wash with deionized water, and then put it into a 60°C oven for 3 h to dry, to obtain a hydrophilic base film for use; 6) Prepare a mixed solution of 10 mL of ammonia and 40 mL of n-hexane, mix in 1 mL of diphenyldimethoxysilane, and then disperse 0.5 g of SiO2 in the above mixed solution, stir for 6 h, and condensation reaction to obtain a hydrophobic modifier; 7) Spray the hydrophobic modifier on the hydrophilic base film, react for 100 min, take out the film and wash with deionized water to remove the unreacted hydrophobic modifier, and then put it into an 80°C oven to dry for 6 h, to obtain a heterogeneously modified microfiltration membrane.

[0035] Use scanning electron microscopy (SEM) to observe the microstructure of the obtained heterogeneously modified microfiltration membrane and perform contact angle testing, and the test method is as in Example 1. The results are as follows: the heterogeneously modified microfiltration membrane has a micro-nano-porous structure, a sponge porous structure, and a membrane surface composed of many protruding structures; oil droplets slowly penetrate into the membrane over time, about 30 s.

[0036] Test the heterogeneously modified microfiltration membrane by a cross-flow microfiltration device under a pressure of 0.1 bar. The initial permeation flux of the heterogeneously modified microfiltration membrane for water-in-D5 emulsion is 4190 L m -2 h -1 bar -1 , the stable permeation flux reaches 1050 L m -2 h -1 bar -1 , the separation efficiency reaches more than 99.5%, has excellent antifouling performance, can continuously and stably separate for more than 100 h, the oil recovery rate is 90.2%, and the water recovery rate is 100%.

[0037] Example 5 A method for preparing a modified microfiltration membrane, comprising the following steps: 1) 15 g of polyvinylidene fluoride and 1.5 g of polyoxyethylene diamine were dissolved in 150 mL of DMAC solution, stirred at 60°C for 4 h, and then vacuumized to remove small air bubbles in the solvent to obtain a casting solution; 2) The casting solution was poured onto a smooth and clean glass substrate, a 150 μm doctor blade was used to scrape the membrane, and it was placed in a coagulation bath of water and ethanol (volume ratio 1:1) for 5 s, and then transferred into pure water at 60°C for 24 h to form a solidified membrane; 3) The solidified membrane was placed in a vacuum box and dried at 50°C for 6 h, and then heated to 240°C for crosslinking for 1 h to obtain a base membrane; 4) 150 mL of 50 mM, pH 8.5 tris-hydroxymethyl aminomethane hydrochloride buffer solution was prepared, 0.3 g of dopamine hydrochloride and 0.6 g of aminoethyl amino isobutyl methyl dimethoxy silane were dissolved in the above buffer solution, and then 0.3 g of ammonium persulfate was added to obtain a hydrophilic modifier by condensation reaction; 5) The base membrane was placed in the hydrophilic modifier, reacted at 30°C and 120 rpm for 5 h, taken out, washed with deionized water, and then placed in a 60°C oven for 3 h to dry to obtain a hydrophilic base membrane for use; 6) 10 mL of ammonia water and 40 mL of n-hexane were prepared into a mixed solution, 1 mL of tert-butyl diphenyl methoxy silane was mixed, and then 0.5 g of SiO2 was dispersed in the mixed solution, and the mixture was stirred for 6 h to obtain a hydrophobic modifier by condensation reaction; 7) The hydrophobic modifier was sprayed on the hydrophilic base membrane, reacted for 30 min, the membrane was taken out and washed with deionized water to remove the unreacted hydrophobic modifier, and then placed in an 80°C oven to dry for 6 h to obtain a heterogeneous modified microfiltration membrane.

[0038] The prepared heterogeneous modified microfiltration membrane was observed by scanning electron microscopy (SEM) and tested for contact angle, and the test method was as in Example 1. The results were as follows: the heterogeneous modified microfiltration membrane had a micro-nano-porous structure, a sponge porous structure, and the membrane surface was composed of many protruding structures; oil droplets slowly penetrated into the membrane over time, about 30 s.

[0039] The heterogeneous modified microfiltration membrane was tested by a cross-flow microfiltration device under a pressure of 0.1 bar. The initial permeation flux of the membrane for water-in-D5 emulsion was 4120 L m -2 h -1 bar -1 , the stable permeation flux reached 1000 L m -2 h -1 bar -1 , the separation efficiency reached more than 99.5%, the membrane had excellent antifouling performance, could continuously and stably separate for more than 100 h, the oil recovery rate was 90.4%, and the water recovery rate was 100%.

[0040] Example 6 A method for preparing a modified microfiltration membrane, which differs from Example 1 in that: In step 6), the basic substance is sodium hydroxide.

[0041] Example 7 A method for preparing a modified microfiltration membrane, which differs from Example 1 in that: in step 4), the hydroxyl-containing monomer is lignin, and the silane monomer X is 3-aminopropyl dimethoxymethyl silane.

[0042] Example 8 A method for preparing a modified microfiltration membrane, which differs from Example 1 in that: in step 6), the silane monomer Y is tert-butyl diphenyl methoxysilane.

[0043] Comparative Example 1 This comparative example prepared a hydrophilic modified microfiltration membrane, including the following steps: 1) 15 g of poly(vinylidene fluoride-trifluoroethylene) and 1.5 g of polyoxyethylene diamine were dissolved in 150 mL of cyclohexanone solution, stirred at 60°C for 4 h, and then vacuumed to remove small gas bubbles in the solvent to obtain a casting solution; 2) The casting solution was poured onto a smooth and clean glass substrate, a 150 μm doctor blade was used to scrape the membrane, and it was placed in a coagulation bath of water and ethanol (volume ratio 1:1) for 5 s, and then transferred to pure water at 60°C for 24 h to form a solidified membrane; 3) The solidified membrane was placed in a vacuum box and dried at 50°C for 6 h, then heated to 240°C for crosslinking for 1 h to obtain a base membrane; 4) 150 mL of 50 mM, pH 8.5 tris-hydroxymethyl aminomethane hydrochloride buffer was prepared, 0.3 g of procyanidin and 0.6 g of N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane were dissolved in the above buffer, and then 0.3 g of ammonium persulfate was added to obtain a hydrophilic modifier; 5) The base membrane was placed in the hydrophilic modifier, reacted at 30°C and 120 rpm for 5 h, then taken out, washed with deionized water, and then placed in a 60°C oven for 3 h to dry, to obtain a hydrophilic modified microfiltration membrane.

[0044] The prepared hydrophilic modified microfiltration membrane was observed for microstructure and tested for contact angle using scanning electron microscopy (SEM) technology, and the test method was as in Example 1. The results were that the heterogeneous modified microfiltration membrane had a micro-nano pore structure, a sponge porous structure, and the membrane surface was composed of many protruding structures; the membrane surface contact angle slowly penetrated into the membrane over time, about 30 s.

[0045] The initial permeation flux of this heterogeneous harsh environment-resistant micro-porous membrane for water-in-D5 emulsion was 4000 L m-2 h -1 bar -1 , the separation efficiency reached more than 99.5%, but its flux decayed to zero after 2h separation, and only the water phase could be recovered in a single phase.

[0046] Comparative Example 2 A modified microfiltration membrane was prepared in this comparative example, and the base membrane was not cross-linked and modified, including the following steps: 1) 15g of poly(vinylidene fluoride-trifluoroethylene) was dissolved in 150mL of cyclohexanone solution, stirred at 60°C for 4h, and then vacuumed to remove small air bubbles in the solvent to obtain a casting solution; 2) The casting solution was poured onto a smooth and clean glass substrate, a 150μm doctor blade was used to scrape the membrane, and it was placed in a coagulation bath of water and ethanol (volume ratio 1:1) for 5s, and then transferred to pure water at 60°C for 24h to obtain a base membrane; 3) 150mL of 50mM, pH 8.5 tris-hydroxymethyl aminomethane hydrochloride buffer was prepared, 0.3g of procyanidin and 0.6g of N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxy silane were dissolved in the above buffer, and then 0.3g of ammonium persulfate was added to obtain a hydrophilic modifier; 4) The base membrane was placed in the hydrophilic modifier, reacted for 5h at 30°C and 120rpm, then taken out, washed with deionized water, and then placed in a 60°C oven for 3h to dry, to obtain a hydrophilic base membrane for use; 5) 10ml of ammonia water and 40ml of ethanol were prepared into a mixed solution, 1mL of ethyl silicate was mixed in, and then 0.5g of SiO2 was dispersed in the above mixed solution, and stirred for 6h to prepare a hydrophobic modifier; 6) The hydrophobic modifier was sprayed on the hydrophilic base membrane, reacted for 30min, the unreacted hydrophobic modifier was washed off with deionized water, and then placed in an 80°C oven for 6h to obtain a heterogeneously modified microfiltration membrane.

[0047] The resistance of the heterogeneously modified microfiltration membrane prepared in Example 1 and the heterogeneously modified microfiltration membrane prepared in Comparative Example 2 to harsh environments was tested, and the test method was as follows: the heterogeneously modified microfiltration membrane prepared in Example 1 and the heterogeneously modified microfiltration membrane prepared in Comparative Example 2 were cut into small pieces of the same size, the size and mass were accurately recorded, the base membrane pieces were divided into four groups, each group was immersed in a strong acid solution, a strong base solution, a salt solution and an organic solvent (a good solvent for the base membrane without cross-linking agent) respectively, and soaked at room temperature for 24h, and the dissolution of the membrane after soaking was observed.

[0048] The test results are as follows: Table 1 Resistance test results of Example 1 and Comparative Example 2 1M: refers to the substance amount concentration of the solution is 1 mol / L.

[0049] As can be seen from the table: The heterogeneous modification microfiltration membrane prepared in Comparative Example 2 is dissolved, and the heterogeneous modification microfiltration membrane prepared in Example 1 maintains an intact form. The results of scanning electron microscopy of the base film small pieces before and after soaking in Example 1 show that the surface morphology of the membrane has not changed significantly. It can be proved that the heterogeneous modification microfiltration membrane prepared in Example 1 has excellent resistance in harsh environments such as strong acid / strong base, salt solution and organic solvent, and exhibits good stability and practicability.

[0050] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0051] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still belongs to the protection scope of the technical solution of the present application.

Claims

1. A method for preparing a modified microfiltration membrane, characterized in that: The following steps are involved: S1: using a hydrophilic modifier to hydrophilically modify the basement membrane to obtain a hydrophilic basement membrane; S2: hydrophobic modification of the hydrophilic basement membrane using a hydrophobic modifier to obtain a heterogeneously modified microfiltration membrane; The preparation process of the hydrophilic modifier is as follows: a free radical initiator is added to a mixture containing a hydroxyl monomer, a silane monomer X and an alkaline buffer solution, and a condensation reaction is performed to obtain the hydrophilic modifier; The preparation process of the hydrophobic modifier is as follows: a silicon source is added to a mixed solution containing a silane monomer Y, an alkaline substance and a solvent B, and the hydrophobic modifier is prepared by a condensation reaction.

2. The method for preparing a modified microfiltration membrane according to claim 1, wherein: The hydroxyl-containing monomer is selected from one or more of proanthocyanidins, dopamine hydrochloride, and lignin; the silane monomer X is selected from one or more of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, 3-[(2,3)-epoxypropyloxy]propylmethyldimethoxysilane, aminoethylaminoisobutylmethyldimethoxysilane, and 3-aminopropyldimethoxymethylsilane; the silane monomer Y is selected from one or more of ethyl silicate, diphenyldimethoxysilane, tris(trimethylsiloxy)silane, and tert-butyldiphenylmethoxysilane; the alkaline substance is selected from one or more of ammonia water and sodium hydroxide; and the solvent B is selected from one or more of ethanol, n-hexane, isopropanol, toluene, and chloroform.

3. The method for preparing a modified microfiltration membrane according to claim 1, wherein: In parts by weight, the hydroxyl-containing monomer is 0.2-0.4 parts, and the silane monomer X is 0.5-0.7 parts; or, in parts by weight, the silane monomer Y is 0.7-1.1 parts, the alkaline substance is 9-11 parts, and the solvent B is 24-40 parts.

4. The method for preparing a modified microfiltration membrane according to claim 1, wherein: In step S1, the base membrane is hydrophilically modified by dipping or grafting, and the reaction temperature of the hydrophilic modification is 20-40° C. and the reaction time is 4-6 hours.

5. The method for preparing a modified microfiltration membrane according to claim 1, wherein: In step S2, a hydrophobic modifier is distributed on the hydrophilic base membrane by spraying to perform hydrophobic modification, and the reaction time of the hydrophobic modification is 20-100 minutes.

6. The method for preparing a modified microfiltration membrane according to any one of claims 1 to 5, characterized in that: In step S1, the preparation of the basement membrane includes the following steps: i: dissolving the polymer and cross-linking agent in solvent A to obtain a casting solution; ii: The casting solution is treated by phase inversion or electrospinning to form a solidified film; iii: The cured film is thermally cross-linked to obtain a base film.

7. The method for preparing a modified microfiltration membrane according to claim 6, wherein: In step i, the polymer is selected from one or more of poly(vinylidene fluoride-trifluoroethylene) and polyvinylidene fluoride; the cross-linking agent is selected from reagents containing two or more amino functional groups such as maleic anhydride, p-phenylenediamine, polyoxyethylene diamine, pentaethylenehexamine, etc.; the solvent A is selected from one or more of cyclohexanone, DMF, DMAC, TEP, and NMP; or, in parts by weight, the polymer is 10-20 parts, the cross-linking agent is 1-2 parts, and the solvent A is 130-160 parts.

8. The method for preparing a modified microfiltration membrane according to claim 6, wherein: In step iii, the temperature of the thermal crosslinking is 230-250°C.

9. A modified microfiltration membrane, characterized in that: The method is described in any one of claims 1 to 8.

10. Application of a modified microfiltration membrane for treating emulsified oil in a harsh environment, characterized in that: The modified microfiltration membrane is the modified microfiltration membrane according to claim 9, and the harsh environment includes a strong acid, a strong base, a salt and an organic solvent environment.

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