A gradient wicking microporous membrane, its preparation method and application

Abstract

The application provides a gradient-infiltration microporous membrane and a preparation method and application thereof, and belongs to the field of separation membrane materials. The gradient-infiltration microporous membrane comprises a lower hydrophobic layer and an upper hydrophilic layer, and the hydrophilicity of the gradient-infiltration microporous membrane gradually decreases from the upper surface to the lower surface. The contact angle of the upper surface of the upper hydrophilic layer is less than 90 degrees, and the water drop infiltration time is less than 10 seconds. The contact angle of the lower surface of the lower hydrophobic layer is greater than 90 degrees and less than 160 degrees. Compared with the prior art, the application innovatively constructs a microporous membrane sponge structure and gradient-infiltration modification, that is, the gas is preliminarily cut through the regulation of the membrane pore structure, the gas permeability is improved, and the gas inlet pressure is reduced, and then through the gradient-infiltration modification, a single-sided thin hydrophilic layer interface is formed on the surface of the bulk membrane, the bubble size is reduced, and the membrane surface contamination capacity is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of separation membrane materials, and particularly relates to a gradient wettability microporous membrane and a preparation method and application thereof. BACKGROUND

[0002] Industrial activities, oil exploration and oil-containing wastewater discharge in daily life pose a serious challenge to the environment, not only threatening the health of the ecosystem, but also directly endangering human well-being. Traditional oil-water separation methods, such as centrifugation, air flotation, flocculation and adsorption, are effective under certain conditions, but generally face problems such as high energy consumption, secondary pollution and failure after material adsorption saturation.

[0003] In recent years, membrane separation technology has attracted widespread attention due to its high selectivity and relatively low operating cost. However, traditional polymer separation membranes based on pore size screening mechanism are easily affected by membrane fouling, which not only reduces the service life of the membrane, but also increases the maintenance cost, limiting its long-term operation ability in practical applications. With the increasing awareness of environmental protection worldwide, there is an increasing demand for oil-water separation solutions that can operate continuously and stably, with excellent anti-fouling performance.

[0004] Currently, the anti-fouling performance is improved mainly by preventing oil pollution from contacting the membrane surface, and removing strategies such as pyrolysis and catalytic degradation, but there are still problems such as poor long-term anti-fouling performance and discontinuous separation process. Coalescence demulsification is a process in which emulsion is separated into oil and water phases by passing through a membrane, although it can remove some oil pollution, but the increase in pressure and affinity can easily cause the deformation of the coalesced oil phase and adhere to the membrane pores, causing membrane fouling. The reason is that the existing oil-water separation process is to make the single or double phase of the emulsion pass through the membrane, causing the oil pollution to adhere to the membrane surface and cause membrane fouling. Therefore, how to prevent oil pollution from adhering to the membrane surface is the key to anti-fouling separation. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and proposes a gradient wettability microporous membrane for generating micro-nano bubbles, and a micro-nano bubble generating device is designed, in which gas diffuses from the hydrophobic side of the gradient wettability microporous membrane into the liquid inlet area and disperses into micro-nano bubbles, based on the affinity of micro-nano bubbles and oil phase in the emulsion, the micro-nano bubbles interact with the oil phase, achieving demulsification effect, in addition, the rising micro-nano bubbles continuously collide with the emulsion, accelerating the demulsification of the emulsion, finally, the demulsified oil phase is transported to the top of the liquid inlet area by the buoyancy and rupture of the bubbles, obtaining the separated water phase and oil phase, realizing a long-lasting separation process and simultaneous recovery of oil and water phases.

[0006] The present application provides a gradient wettability microporous membrane, the gradient wettability microporous membrane comprises a lower hydrophobic layer and an upper hydrophilic layer, and the hydrophilicity of the gradient wettability microporous membrane gradually decreases from the upper surface to the lower surface, the contact angle of the upper surface of the upper hydrophilic layer is < 90° and the water drop wetting time is < 10s, and the contact angle of the lower surface of the lower hydrophobic layer is > 90° and < 160°.

[0007] In some embodiments, the thickness ratio of the upper hydrophilic layer and the lower hydrophobic layer is (1-20):(99-80).

[0008] In some embodiments, the gradient wettability microporous membrane has a multi-level pore structure, the porosity of the gradient wettability microporous membrane is 50-90% and the average pore size is 50-1000nm.

[0009] The second object of the present application is to provide a preparation method of the above-mentioned gradient wettability microporous membrane, which specifically comprises the following steps:

[0010] S1, dissolving a film-forming polymer in a first organic solvent to obtain a casting solution after stirring treatment;

[0011] S2, after the deaeration treatment of the casting solution prepared in step S1, coating on a non-woven fabric to obtain a nascent film;

[0012] S3, after the nascent film prepared in step S2 is treated in a coagulation bath and then taken out for soaking treatment and air drying;

[0013] S4, after the microporous membrane is subjected to wettability treatment, the upper surface of the microporous membrane is faced to a hydrophilic modification liquid and floated on the surface of the hydrophilic modification liquid for modification reaction, and then taken out for air drying to obtain a gradient wettability microporous membrane.

[0014] Compared with the prior art, in the preparation process of the present application, a microporous polymer membrane is first prepared by a blade coating technique, and then the surface of the membrane is modified by a hydrophilic polymer to obtain a gradient wettability microporous membrane.

[0015] In some embodiments, in step S1, the film-forming polymer is selected from at least one of polyvinylidene fluoride, polyacrylonitrile, polylactic acid, acrylate, polyether sulfone and polysulfone; the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, tripropyl phosphate, acetone and chloroform; and the concentration of the casting solution is 10-30wt%.

[0016] In some embodiments, in step S1, the stirring treatment temperature is 20-100℃.

[0017] Compared with the prior art, proper temperature control (such as 20-100℃) can prevent local supersaturation of the solution during stirring, and ensure uniformity of the whole solution system; and by adjusting the temperature, the viscosity of the solution can be accurately controlled at different stages, and the casting solution has ideal flowability and coating performance.

[0018] In some embodiments, in the step S2, the thickness of the nascent film is 50-300 μm.

[0019] In some embodiments, in the step S3, the temperature of the coagulation bath is 10-50℃, the coagulation bath is composed of water and the second organic solvent in a mass ratio of (9:1)-(1:9), and the treatment time in the coagulation bath is 5-60 s.

[0020] In some embodiments, in the step S4, the second organic solvent is at least one selected from the group consisting of ethanol, methanol, N, N-dimethylformamide, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N, N-dimethylformamide, and N, N-dimethylacetamide.

[0021] In some embodiments, in the step S4, the temperature of the soaking treatment is 20-100℃, the soaking liquid is pure water, and the time is 6-48 h.

[0022] In some embodiments, in the step S5, the organic solvent used in the soaking treatment is at least one selected from the group consisting of methanol, n-hexane, toluene, and ethanol; the concentration of the hydrophilic modification liquid is 0.1-90 g / L, and the hydrophilic modification liquid is at least one selected from the group consisting of amino acid, allyl group, hydroxyl group, block copolymer of polyethylene oxide and polyethylene terephthalate, polyether type polyester block copolymer, polysiloxane type hydrophilic finishing agent, polyurethane type polymer, and surfactant.

[0023] A third object of the present application is to provide a micro-nano bubble generating device, comprising

[0024] The separation unit comprises a containing cavity, a gradient micro-wetting film is arranged in the containing cavity, the containing cavity is divided into a liquid inlet area and a gas inlet area by the gradient micro-wetting film, the liquid inlet area is located above the gas inlet area in the vertical direction, the upper layer of the gradient micro-wetting film is a hydrophobic layer and faces the liquid inlet area, the lower layer of the gradient micro-wetting film is a hydrophilic layer and faces the gas inlet area, a liquid inlet is arranged on the liquid inlet area, and a gas inlet is arranged on the gas inlet area.

[0025] The gas supply unit is used for providing gas pressure and is connected with the gas inlet.

[0026] The emulsion supply unit is used for providing the emulsion to be separated and is connected with the liquid inlet.

[0027] In some embodiments, the gas supply unit comprises a gas cylinder, the gas outlet of the gas cylinder is connected with the gas inlet, and a pressure gauge and a flow meter are further arranged on the gas cylinder; the emulsion supply unit comprises an emulsion tank, and the emulsion tank is connected with the liquid inlet through a peristaltic pump.

[0028] In some embodiments, an oil phase storage area is arranged above the liquid inlet area, and the liquid inlet is located below the oil phase storage area in the vertical direction.

[0029] In some embodiments, a liquid outlet is further arranged on the liquid inlet area, and the liquid outlet is connected with the emulsion tank, and the liquid inlet is located above the liquid outlet in the vertical direction.

[0030] In addition, the method for preparing the gradient-infiltration microporous membrane and designing the micro-nano bubble generator has the following advantages:

[0031] 1. The microporous membrane sponge structure is innovatively constructed, and gradient-infiltration modification is performed, that is, the gas is preliminarily cut through the regulation of the membrane pore structure, the gas permeation rate is improved, and the gas inlet pressure is reduced, and then a single-sided thin layer of a hydrophilic layer interface is formed on the surface of the body membrane through gradient-infiltration modification, so that the bubble size is reduced, and the pollution capacity of the membrane surface is improved.

[0032] 2. The micro-nano bubble generating device is designed, in which the gas diffuses from the hydrophobic side of the gradient-infiltration microporous membrane to the liquid inlet area from bottom to top and is dispersed into micro-nano bubbles, based on the affinity between the micro-nano bubbles and the oil phase in the emulsion, the micro-nano bubbles interact with the oil phase, and the demulsification effect is achieved, in addition, the rising micro-nano bubbles continuously collide with the emulsion, accelerate the demulsification of the emulsion, and finally the demulsified oil phase is transmitted to the top of the liquid inlet area through the bubble buoyancy and rupture effect, so that the layered water phase and oil phase are obtained, and a long-term separation process and synchronous oil-water recovery are realized.

[0033] 3. Compared with the existing oil-water separation mechanism: the single phase or double phase in the emulsion is allowed to pass through the membrane, and the emulsion and the filtrate inevitably contact the membrane surface, once the oil stain is not removed from the membrane surface in time, the oil stain will be attached to the membrane surface, forming a continuous oil film, and causing membrane pollution. The microporous membrane in the oil-water separation device obtained by the method has gradient infiltration, the hydrophilic side contacts the emulsion, the bubbles from bottom to top further carry away the oil stain on the membrane surface, in addition, the filtrate does not pass through the membrane in the separation process, which can effectively prevent membrane pollution, realize long-term separation, and achieve the purpose of synchronous oil-water recovery.

[0034] 4. The micro-nano bubble generating device provided by the method has a water-oil emulsion permeation flux of more than 1500 Lm -2 h -1 bar -1, the separation rate is as high as 99.5% or more, and the oil and water recovery rate is greater than 95%, which is difficult to achieve by conventional oil and water separation membranes. The micro-nano bubble generating device is expected to be applied to actual oily wastewater treatment to cope with key environmental and industrial challenges. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Schematic diagram of hydrophilic and hydrophobic membrane bubbling;

[0036] Figure 2 Cross-sectional morphology of the gradient wetting microporous membrane of the present application;

[0037] Figure 3 Structure schematic diagram of the micro-nano bubble generating device;

[0038] The drawings show that: 1-gas cylinder, 2-pressure gauge, 3-flow meter, 4-gas inlet area, 5-gradient wetting microporous membrane, 6-liquid inlet area, 7-peristaltic pump, 8-emulsion tank, 9-oil phase storage area. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present application, and are not used to limit the parameter range described in the present application, and the reasonable changes derived therefrom are still within the protection scope of the claims of the present application.

[0040] It should be noted that the endpoints of the ranges and any values disclosed herein are not limited to the exact values recited, and the ranges or values should be interpreted as including values approximating the recited ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] Unless otherwise defined, all terms, symbols and other scientific and technical terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. In some cases, terms having conventional meanings are defined herein for the purposes of clarification or ease of reference, and such definitions herein should not be understood as indicating significant differences from the conventional meanings. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available kits and reagents, instruments is carried out according to the protocols and parameters given by the manufacturer.

[0042] The embodiment of the present application provides a gradient-infiltration microporous membrane, the gradient-iniltration microporous membrane comprises a lower hydrophobic layer and an upper hydrophilic layer, and the hydrophilicity of the gradient-infiltration microporous membrane gradually decreases from the upper surface to the lower surface, the contact angle of the upper surface of the upper hydrophilic layer is < 90° and the water drop infiltration time is < 10s, the contact angle of the lower surface of the lower hydrophobic layer is > 90° and < 160°, the thickness ratio of the upper hydrophilic layer and the lower hydrophobic layer is (1-20):(99-80), the gradient-infiltration microporous membrane has a multi-stage pore structure, the porosity of the gradient-infiltration microporous membrane is 50-90% and the average pore size is 50-1000nm.

[0043] The embodiment of the present application further provides a preparation method of the gradient-infiltration microporous membrane, and the preparation method specifically comprises the following steps:

[0044] S1, dissolving a film-forming polymer in a first organic solvent to obtain a casting solution after stirring treatment;

[0045] S2, performing defoaming treatment on the casting solution prepared in the step S1, and coating on a non-woven fabric to obtain a nascent membrane;

[0046] S3, after the nascent membrane prepared in the step S2 is treated in a coagulation bath and taken out for soaking treatment and air drying;

[0047] S4, after the microporous membrane is subjected to infiltration treatment, the upper surface of the microporous membrane is faced to a hydrophilic modification liquid and floats on the surface of the hydrophilic modification liquid to perform a modification reaction, and then the microporous membrane is taken out and air dried to obtain the gradient-infiltration microporous membrane.

[0048] In the step S1, the film-forming polymer is at least one selected from polyvinylidene fluoride, polyacrylonitrile, polylactic acid, acrylate, polyether sulfone and polysulfone; the first organic solvent is at least one selected from N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, tripropyl phosphate, acetone and chloroform; and the concentration of the casting solution is 10-30wt%.

[0049] In the step S1, the temperature of the stirring treatment is 20-100℃.

[0050] In the step S2, the thickness of the nascent membrane is 50-300μm.

[0051] In the step S3, the temperature of the coagulation bath is 10-50℃, the coagulation bath is composed of water and a second organic solvent with a mass ratio of (9:1)-(1:9), and the treatment time in the coagulation bath is 5-60s.

[0052] The second organic solvent in the step S4 is selected from at least one of ethanol, methanol, N, N-dimethylformamide, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N, N-dimethylformamide, and N, N-dimethylacetamide.

[0053] In the step S4, the temperature of the soaking treatment is 20-100 DEG C, the soaking liquid is pure water, and the time is 6-48h.

[0054] In the step S5, the organic solvent used in the infiltration treatment is selected from at least one of methanol, n-hexane, toluene, and ethanol; the concentration of the hydrophilic modification liquid is 0.1-90 g / L, and the hydrophilic modification liquid is selected from at least one of amino acid, allyl group, hydroxyl group, block copolymer of polyethylene oxide and polyethylene terephthalate, polyether type polyester block copolymer, polysiloxane type hydrophilic finishing agent, polyurethane type polymer, and surfactant.

[0055] The embodiment of the present application further provides a micro-nano bubble generating device, which comprises

[0056] The separation unit comprises a containing cavity, wherein a gradient micro-infiltration film 5 is arranged in the containing cavity, and the gradient micro-infiltration film 5 divides the containing cavity into a liquid inlet area 6 and a gas inlet area 4, and in the vertical direction, the liquid inlet area 6 is located above the gas inlet area 4, the upper layer of the gradient micro-infiltration film 5 is a hydrophobic layer facing the liquid inlet area 6, and the lower layer of the gradient micro-infiltration film 5 is a hydrophilic layer facing the gas inlet area 4, and the liquid inlet area 6 is provided with a liquid inlet, and the gas inlet area 4 is provided with a gas inlet.

[0057] The gas supply unit comprises a gas cylinder 1, wherein the gas outlet of the gas cylinder 1 is connected with the gas inlet, and the gas cylinder 1 is further provided with a pressure gauge 2 and a flow meter 3.

[0058] The emulsion supply unit comprises an emulsion tank 8, wherein the emulsion tank 8 is connected with the liquid inlet through a peristaltic pump 7.

[0059] Specifically, the liquid inlet area 6 is provided with an oil phase storage area 9 above, and in the vertical direction, the liquid inlet is located below the oil phase storage area 9.

[0060] Specifically, the liquid inlet area 6 is further provided with a liquid outlet, and the liquid outlet is connected with the emulsion tank 8, and in the vertical direction, the liquid inlet is located above the liquid outlet.

[0061] The gas operating pressure is 0.01-10 MPa, and the bubble size is 100 nm-1 mm.

[0062] The technical effects of the present application are described below in combination with specific embodiments.

[0063] Example 1

[0064] This example provides a preparation of a gradient-infiltration microporous membrane:

[0065] Dissolve 15 g of polyvinylidene fluoride powder in 85 g of triethyl phosphate, and stir at a temperature of 80°C to obtain a casting solution with a concentration of 15%;

[0066] After defoaming, coat the casting solution on a non-woven fabric to form a nascent membrane with a thickness of 50 μm;

[0067] After placing the prepared nascent membrane in a mixed coagulation bath (1:9) of water and ethanol at 10°C for 5 s, take out the membrane and immerse it in pure water at 60°C for 6 h, and then take it out and dry;

[0068] Infiltrate the microporous membrane with n-hexane, and make the upper surface of the membrane face a 50% amino acid type hydrophilic modification liquid and float on the liquid surface, and react at room temperature for 24 h, and then take out and dry.

[0069] After testing, the gradient-infiltration microporous membrane prepared in this example has a gradual change in infiltration from hydrophilic to hydrophobic from the upper surface to the lower surface, a hydrophilic contact angle of 40°, a hydrophobic contact angle of 130°, a hydrophilic contact angle infiltration time of 20 s, a hydrophilic-hydrophobic ratio of 2:98, a porosity of 90%, and an average pore size of 500 nm.

[0070] In addition, use the gradient-infiltration microporous membrane 5 prepared in this example to separate oil and water, prepare a 1% water-in-D5 emulsion, pump the emulsion into the liquid inlet area 6 through a peristaltic pump 7, and at the same time, introduce nitrogen gas into the gas inlet area 4, so that the gas diffuses from the hydrophobic side of the gradient-infiltration microporous membrane 5 into the hydrophilic side, and the nitrogen gas is separated into micro-bubbles with a diameter of about 10 μm through the gradient-infiltration microporous membrane 5, and the gas pressure is 0.01 MPa. The micro-bubbles collide with the oil droplets in the water-in-D5 emulsion in the liquid inlet area 6, and are aggregated to form large gas bubbles coated with oil films through hydrophobic interaction, and the aggregated oil phase is broken by the buoyancy of the gas bubbles and sent to the top end of the liquid inlet area 6, and a layered water phase and oil phase are obtained, and after multiple cycles, a water phase can be obtained in the liquid inlet area 6 and the emulsion tank 8.

[0071] After testing, the separation flux is 2039 L m 2 h -1 bar -1 , the separation efficiency is greater than 99.5%, the oil recovery rate is greater than 95%, the water recovery rate is close to 100%, and the process can be operated stably for a long time.

[0072] Example 2

[0073] This example provides a preparation of a gradient-infiltration microporous membrane:

[0074] 20 g of polyacrylonitrile powder was dissolved in 80 g of N,N-dimethylacetamide to obtain a casting solution with a concentration of 20% at a temperature of 60°C;

[0075] After defoaming, the casting solution was coated on the non-woven fabric to form a nascent film with a thickness of 150 μm;

[0076] The prepared nascent film was placed in a mixed coagulation bath of water and methanol (5:5) at 30°C for 30 s, then the film was taken out and soaked in pure water at 20°C for 12 h, and then dried;

[0077] The microporous membrane was infiltrated with methanol, and the upper surface of the membrane was facing a 0.1% polyethylene oxide and polyethylene terephthalate block copolymer hydrophilic modification liquid and floating on the liquid surface, and the reaction was carried out at room temperature for 48 h, and then the film was taken out and dried.

[0078] After testing, the gradient infiltration microporous membrane prepared in this embodiment had a hydrophilic to hydrophobic transition from the upper surface to the lower surface, a hydrophilic contact angle of 10°, a hydrophobic contact angle of 110°, a hydrophilic contact angle infiltration time of 10 s, a hydrophilic to hydrophobic ratio of 30:70, a porosity of 90%, and an average pore size of 500 nm.

[0079] In addition, the gradient infiltration microporous membrane 5 prepared in this embodiment was used for oil-water separation, a 1% water-in-hexadecane emulsion was prepared, the emulsion was pumped into the liquid inlet area 6 by a peristaltic pump 7, nitrogen gas was introduced into the gas inlet area 4, and the gas diffused from the hydrophobic side of the gradient infiltration microporous membrane 5 into the hydrophilic side, and the nitrogen gas was separated into micro-bubbles with a diameter of about 60 μm through the gradient infiltration microporous membrane 5, and the gas pressure was 0.05 MPa. The micro-bubbles collided with the oil droplets in the water-in-hexadecane emulsion in the liquid inlet area 6, and gathered to form large gas bubbles coated with oil film through hydrophobic interaction, and the gathered oil phase was broken by the buoyancy of the gas bubbles and sent to the top of the liquid inlet area 6, and a layered water phase and oil phase were obtained, and after multiple cycles, a water phase was obtained in the liquid inlet area 6 and the emulsion tank 8.

[0080] After testing, the separation flux was 4500 L m 2 h -1 bar -1 , the separation efficiency was greater than 99.6%, the oil recovery rate was greater than 96%, and the water recovery rate was nearly 100%, and the process could be operated stably for a long time.

[0081] Example 3

[0082] This embodiment provides a preparation of a gradient infiltration microporous membrane:

[0083] 30 g of polyether sulfone powder was dissolved in 70 g of N-methyl pyrrolidone to obtain a casting solution with a concentration of 30% at a temperature of 70°C;

[0084] After defoaming, the casting solution was coated on the non-woven fabric to form a nascent film with a thickness of 300 μm;

[0085] After being placed in a mixed coagulation bath of water and dimethyl sulfoxide (3:7) at 60 °C for 60 s, the nascent film was taken out and soaked in pure water at 80 °C for 18 h, and then taken out and air-dried;

[0086] The microporous film was immersed in methanol, and the upper surface of the film was made to face a 30% surfactant hydrophilic modification liquid and float on the liquid surface, and reacted at room temperature for 0.5 h, and then taken out and air-dried.

[0087] After testing, the gradient wettability microporous film 5 prepared in this embodiment had a wettability gradually changing from hydrophilic to hydrophobic from the upper surface to the lower surface, a hydrophilic contact angle of 0°, a hydrophobic contact angle of 140°, a hydrophilic contact angle immersion time of 5 s, a hydrophilic / hydrophobic ratio of 10:90, a porosity of 60%, and an average pore size of 100 nm.

[0088] In addition, the gradient wettability microporous film 5 prepared in this embodiment was used for oil-water separation, a 1% water-in-isooctane emulsion was prepared, the emulsion was pumped into the liquid inlet area 6 by a peristaltic pump 7, and oxygen was introduced into the gas inlet area 4, the oxygen diffused from the hydrophobic side of the gradient wettability microporous film into the hydrophilic side, and the oxygen was divided into micro-bubbles with a diameter of about 100 nm through the gradient wettability microporous film 5, and the gas pressure was 2 MPa. The micro-bubbles collided with the oil droplets in the water-in-hexadecane emulsion in the liquid inlet area 6, and gathered to form large bubbles coated with oil film through hydrophobic interaction, and the gathered oil phase was broken by the buoyancy of the bubbles and sent to the top of the liquid inlet area 6, and a layered water phase and oil phase were obtained, and after multiple cycles, a water phase was obtained in the liquid inlet area 6 and the emulsion tank 8.

[0089] After testing, the separation flux was 6000 L m 2 h -1 bar -1 , the separation efficiency was greater than 99.9%, the oil recovery rate was greater than 98%, the water recovery rate was close to 100%, and the process could be operated stably for a long time.

[0090] Example 4

[0091] This embodiment provides a preparation of a gradient wettability microporous film:

[0092] 10 g of polyether sulfone powder was dissolved in 90 g of chloroform to obtain a casting solution with a concentration of 10%, and the solution was stirred at a temperature of 50 °C;

[0093] After defoaming, the casting solution was coated on the non-woven fabric to form a nascent film with a thickness of 200 μm;

[0094] After the prepared nascent membrane is placed in a mixed coagulation bath of water and acetone (8:2) at 25°C for 15 s, the membrane is taken out and soaked in pure water at 40°C for 10 h, and then taken out and air-dried;

[0095] The microporous membrane is infiltrated with ethanol, and the upper surface of the membrane is made to face a 30% polyether polyester block copolymer, polysiloxane hydrophilic finishing agent mixed hydrophilic modification liquid and float on the liquid surface, and react at room temperature for 2 h, and then taken out and air-dried.

[0096] After testing, the gradient infiltrating microporous membrane 5 has a hydrophilic gradually changing to hydrophobic from the upper surface to the lower surface, a hydrophilic contact angle of 0°, a hydrophobic contact angle of 120°, a hydrophilic contact angle infiltration time of 3 s, a hydrophilic-hydrophobic ratio of 13:887, a porosity of 75%, and an average pore size of 800 nm.

[0097] In addition, the gradient infiltrating microporous membrane 5 prepared in this embodiment is used for oil-water separation. A 1% water-in-soybean oil emulsion is prepared, the emulsion is pumped into the liquid inlet area 6 by a peristaltic pump 7, and a mixed gas of carbon dioxide and oxygen is introduced into the gas inlet area 4. The mixed gas diffuses from the hydrophobic side of the gradient infiltrating microporous membrane into the hydrophilic side. Oxygen is separated into microporous bubbles with a diameter of about 500 microns through the gradient infiltrating microporous membrane 5, and the gas pressure is 0.3 MPa. The microporous bubbles collide with the oil droplets in the water-in-hexadecane emulsion in the liquid inlet area 6, and are aggregated to form large bubbles coated with an oil film through hydrophobic interaction. The aggregated oil phase is broken by the buoyancy of the bubbles and sent to the top of the liquid inlet area 6, and a layered water phase and oil phase are obtained. After multiple cycles, a water phase is obtained in the liquid inlet area 6 and the emulsion tank 8.

[0098] After testing, the separation flux is 1000 L m 2 h -1 bar -1 , the separation efficiency is greater than 99.5%, and the oil recovery rate is greater than 95% and the water recovery rate is close to 100%. The process can be operated stably for a long time.

[0099] Comparative Example 1

[0100] This comparative example provides a preparation of a polyvinylidene fluoride polymer microporous membrane:

[0101] 15 g of polyvinylidene fluoride powder is dissolved in 85 g of triethyl phosphate, and a casting solution with a concentration of 15% is obtained by stirring at a temperature of 80°C;

[0102] After degassing, the casting solution is coated on a non-woven fabric to form a nascent membrane with a thickness of 50 μm;

[0103] After the prepared nascent membrane is placed in a mixed coagulation bath of water and ethanol (1:9) at 10°C for 5 s, the membrane is taken out and soaked in pure water at 60°C for 6 h, and then taken out and air-dried.

[0104] The contact angle of the polyvinylidene fluoride polymer microporous membrane was 130°, the porosity was 90%, and the average pore size was 500 nm after detection.

[0105] In addition, the polyvinylidene fluoride polymer microporous membrane prepared by the present comparative example was used for oil-water separation, a water-in-D5 emulsion with a concentration of 1% was prepared, the emulsion was pumped into the liquid inlet area 6 by a peristaltic pump 7, nitrogen was introduced into the gas inlet area 4, and the gas was diffused from the hydrophobic side of the gradient wicking microporous membrane into the hydrophilic side. The nitrogen gas was separated into micro-bubbles with a diameter of about 2 mm by the gradient wicking microporous membrane 5, and the gas pressure was 0.01 MPa.

[0106] However, due to the generation of large and sparse bubbles, the process cannot effectively separate the water-in-D5 emulsion.

[0107] Comparative Example 2

[0108] The present comparative example provides a preparation of a polyvinylidene fluoride polymer microporous membrane:

[0109] 15 g of polyvinylidene fluoride powder was dissolved in 85 g of triethyl phosphate, and a casting solution with a concentration of 15% was obtained by stirring at a temperature of 80°C;

[0110] After degassing, the casting solution was coated on a non-woven fabric to form a nascent membrane with a thickness of 50 μm;

[0111] The prepared nascent membrane was placed in a mixed coagulation bath of water and ethanol (1:9) at 10°C for 5 s, then the membrane was taken out and soaked in pure water at 60°C for 6 h, and then taken out and dried;

[0112] The microporous membrane was immersed in n-hexane, and the whole membrane was immersed in a 50% amino acid hydrophilic modification solution, and reacted at room temperature for 24 h, and then taken out and dried.

[0113] The contact angle of the polyvinylidene fluoride polymer microporous membrane was 0°, the whole membrane showed hydrophilic, the porosity was 90%, and the average pore size was 500 nm after detection.

[0114] In addition, the polyvinylidene fluoride microporous membrane prepared by the present comparative example is used for oil-water separation, a water-in-oil emulsion with a concentration of 1% is prepared, the emulsion is pumped into the liquid inlet area 6 by a peristaltic pump 7, and nitrogen gas is introduced into the gas inlet area 4, the gas diffuses into the hydrophilic side from the hydrophobic side of the gradient wicking microporous membrane 5, and the nitrogen gas is separated into micro-bubbles with a diameter of about 10 μm by the gradient wicking microporous membrane 5, and the gas pressure is 10 MPa. The micro-bubbles collide with the oil droplets in the water-in-oil emulsion in the liquid inlet area 6, and are aggregated to form large bubbles coated with oil film by hydrophobic interaction, and the aggregated oil phase is broken by the buoyancy of the bubbles at the top of the liquid inlet area 6, and a layered water phase and oil phase are obtained, and after multiple cycles, a water phase is obtained in the liquid inlet area 6 and the emulsion tank 8.

[0115] After detection, the separation flux is 2000 L m 2 h -1 bar -1 The separation efficiency is greater than 99.5%, and the oil recovery rate is greater than 95% and the water recovery rate is close to 100%, and the process can be operated stably for a long time, but the gas pressure used is high and the cost is high.

[0116] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present disclosure.

Claims

1. A gradient wettability microporous membrane characterized in that, The gradient-infiltration microporous membrane comprises a lower hydrophobic layer and an upper hydrophilic layer, and the hydrophilicity of the gradient-infiltration microporous membrane gradually decreases from the upper surface to the lower surface, the contact angle of the upper surface of the upper hydrophilic layer is < 90° and the water drop infiltration time is < 10 s, and the contact angle of the lower surface of the lower hydrophobic layer is > 90° and < 160°.

2. The gradient wettability microporous membrane of claim 1, wherein, The thickness ratio of the upper hydrophilic layer and the lower hydrophobic layer is (1-20):(99-80); And / or, the gradient-infiltration microporous membrane has a multi-level pore structure, the porosity of the gradient-infiltration microporous membrane is 50-90% and the average pore size is 50-1000 nm.

3. A method of making a gradient wicking microporous membrane as claimed in any one of claims 1-2, characterized in that, The preparation method specifically comprises the following steps: S1, dissolving the film-forming polymer in a first organic solvent, and obtaining a casting solution after stirring treatment; S2, after the casting solution prepared in step S1 is subjected to defoaming treatment, it is coated on a non-woven fabric to obtain a nascent film; S3, after the nascent film prepared in step S2 is treated in a coagulation bath, it is taken out, subjected to immersion treatment, and then dried; S4, after the microporous membrane is subjected to infiltration treatment, the upper surface of the microporous membrane is faced towards a hydrophilic modification liquid and floated on the surface of the hydrophilic modification liquid to perform a modification reaction, and then the microporous membrane is taken out and dried to obtain a gradient-infiltration microporous membrane.

4. The production method according to claim 3, wherein In step S1, the film-forming polymer is selected from at least one of polyvinylidene fluoride, polyacrylonitrile, polylactic acid, acrylate, polyether sulfone, and polysulfone; the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, tripropyl phosphate, acetone, and chloroform; and the concentration of the casting solution is 10-30 wt%. And / or, in step S1, the stirring treatment is performed at a temperature of 20-100°C.

5. The production method according to claim 3, wherein In step S2, the thickness of the nascent film is 50-300 μm. And / or, in step S3, the temperature of the coagulation bath is 10-50°C, the coagulation bath is composed of water and a second organic solvent in a mass ratio of (9:1)-(1:9), and the nascent film is treated in the coagulation bath for 5-60 s.

6. The production method according to claim 3, wherein In step S3, the second organic solvent is selected from at least one of ethanol, methanol, N,N-dimethylformamide, methanol, ethyl acetate, acetone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. And / or, in step S4, the immersion treatment is performed at a temperature of 20-100°C, the immersion liquid is pure water, and the immersion time is 6-48 h.

7. The production method according to claim 3, wherein In step S4, the organic solvent used for the infiltration treatment is selected from at least one of methanol, n-hexane, toluene, and ethanol; the concentration of the hydrophilic modification liquid is 0.1-90 g / L, and the hydrophilic modification liquid is selected from at least one of amino acid, allyl group, hydroxyl group, block copolymer of polyethylene oxide and polyethylene terephthalate, polyether type polyester block copolymer, polysiloxane type hydrophilic finishing agent, polyurethane type polymer, and surfactant.

8. A micro-nano bubble generating device, characterized by comprising: The gradient-infiltration microporous membrane is prepared by the method, and has the following advantages: The separation unit comprises a containing cavity, the gradient-infiltration microporous membrane (5) as claimed in any one of claims 1-2 is arranged in the containing cavity, and the gradient-infiltration microporous membrane (5) divides the containing cavity into a liquid inlet area (6) and a gas inlet area (4), and in the vertical direction, the liquid inlet area (6) is located above the gas inlet area (4), the upper hydrophobic layer of the gradient-infiltration microporous membrane (5) faces the liquid inlet area (6), the lower hydrophilic layer of the gradient-infiltration microporous membrane (5) faces the gas inlet area (4), and the liquid inlet area (6) is provided with a liquid inlet, and the gas inlet area (4) is provided with a gas inlet; The gas supply unit is used for providing gas pressure and is connected to the gas inlet; The emulsion supply unit is used for providing the emulsion to be separated and is connected to the liquid inlet.

9. The micro-nano bubble generating apparatus according to claim 8, wherein The gas supply unit comprises a gas cylinder (1), the gas outlet of the gas cylinder (1) is connected to the gas inlet, and the gas cylinder (1) is further provided with a pressure gauge (2) and a flow meter (3); the emulsion supply unit comprises an emulsion tank (8), and the emulsion tank (8) is connected to the liquid inlet through a peristaltic pump (7). 10.The micro-nano bubble generating apparatus of claim 9, wherein The liquid inlet area (6) is provided with an oil phase storage area (9) above, and in the vertical direction, the liquid inlet is located below the oil phase storage area (9); And / or, the liquid inlet area (6) is further provided with a liquid outlet, the liquid outlet is connected to the emulsion tank (8), and in the vertical direction, the liquid inlet is located above the liquid outlet.

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