A dense polyamide Janus membrane distillation membrane and its preparation method and application

Abstract

The present invention proposes a dense polyamide Janus membrane distillation membrane and its preparation method and application, which belong to the field of membrane preparation technology. The dense polyamide Janus membrane distillation membrane of the present invention includes a hydrophilic modified hydrophobic membrane, a hydrophilic intermediate layer and a polyamide layer arranged in sequence from bottom to top, wherein the hydrophilic intermediate layer is a polyvinyl alcohol layer or an aramid nanofiber layer, and the hydrophilic intermediate layer solution is uniformly coated on the surface of one side of the hydrophilic modified hydrophobic membrane to obtain a hydrophilic intermediate layer, and then a polyamide layer is formed on the surface of the hydrophilic intermediate layer by interfacial polymerization reaction, thereby obtaining the dense polyamide Janus membrane distillation membrane. By constructing a continuous and uniform PVA or ANF hydrophilic intermediate layer on a hydrophilic modified hydrophobic substrate, the storage capacity of amine monomers in the aqueous phase is increased and a complete interfacial polymerization reaction is promoted. The obtained polyamide Janus membrane distillation membrane can maintain a stable steam flux and permeate water with very low conductivity during long-term continuous operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane preparation, and relates to a dense polyamide Janus membrane distillation membrane and a preparation method and application thereof, and in particular to a dense polyamide Janus membrane distillation membrane based on a polyvinyl alcohol or aramid nanofiber intermediate layer and a preparation method and application thereof. Background Art

[0002] Membrane distillation (MD) is a desalination technology that uses the vapor pressure difference across the membrane as a driving force for mass transfer, allowing water vapor to pass through a porous, hydrophobic membrane material while simultaneously intercepting liquids and non-volatile components (such as ions). MD is a hybrid of membrane and thermal processes, combining the advantages of both membrane and distillation technologies. It can achieve near-100% removal of salt ions from solutions, offering significant advantages in treating highly concentrated, highly contaminated brine and utilizing low-grade heat such as industrial waste heat, as well as solar and geothermal energy. Furthermore, compared to traditional membrane and thermal desalination processes (reverse osmosis (RO), forward osmosis (FO), multi-effect distillation (MED), and multi-stage flash (MSF)), MD technology offers simpler equipment and operation, and the flexibility to build large-scale production systems. Therefore, MD holds considerable competitive potential and promise as a sustainable, low-energy technology for seawater desalination and brine desalination. However, conventional polymer hydrophobic MD membranes face significant challenges, such as membrane fouling and membrane infiltration, which severely limit the further promotion and application of membrane distillation technology.

[0003] Generally, membrane fouling caused by hydrophobic organic pollutants (such as oil droplets) and membrane wetting caused by amphiphilic organic compounds (such as surfactants) greatly limit the applicability of MD, which seriously affects the performance of MD membranes (such as permeability and salt rejection), increases the cleaning frequency, shortens the membrane life, and even causes irreversible membrane damage. In order to solve the above problems, various advanced MD membranes, such as superhydrophobic membranes, fully hydrophobic membranes and Janus membranes, have been developed through spraying, surface fluorination and polymer coating methods. However, the current methods still have the following problems: when the feed brine contains both oil and surfactant pollutants, it cannot simultaneously meet the high permeation flux and long-term stability of the membrane; it involves a series of difficult-to-control and complex procedures, which are difficult to produce and prepare in large quantities. Therefore, the preparation of a high-performance and easily scalable membrane distillation membrane is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a dense polyamide Janus membrane distillation membrane and a preparation method and application thereof.

[0005] To achieve the above objectives, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] A dense polyamide Janus membrane distillation membrane comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic middle layer and a polyamide (PA) layer arranged in sequence from bottom to top, wherein the hydrophilic middle layer is a polyvinyl alcohol (PVA) layer or an aramid nanofiber (ANF) layer.

[0008] Furthermore, the hydrophilically modified hydrophobic membrane includes one of a hydrophilically modified polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane, a polypropylene membrane, and a composite membrane thereof.

[0009] Furthermore, the hydrophilic modification method includes one or any combination of polydopamine deposition, polydopamine / polyethyleneimine deposition, tannic acid / 3-aminopropyltriethoxysilane adhesion, sodium hydroxide solution immersion, and plasma treatment.

[0010] The second technical solution of the present invention:

[0011] A method for preparing the dense polyamide Janus membrane distillation membrane comprises uniformly coating a hydrophilic intermediate layer solution on one surface of a hydrophobic membrane that has been hydrophilically modified to obtain a hydrophilic intermediate layer, and then sequentially infiltrating the surface of the hydrophilic intermediate layer with an aqueous phase monomer solution and an oil phase monomer solution by interfacial polymerization to form a polyamide (PA) layer, thereby obtaining the dense polyamide Janus membrane distillation membrane;

[0012] The hydrophilic intermediate layer solution is a polyvinyl alcohol (PVA) solution or an aramid nanofiber (ANF) solution.

[0013] Furthermore, the polyvinyl alcohol solution is obtained by uniformly mixing polyvinyl alcohol and deionized water at 90° C. for 6-10 hours;

[0014] The aramid nanofiber solution is prepared by dissolving potassium hydroxide in deionized water, then magnetically stirring the solution for 48-96 hours and adding dimethyl sulfoxide and aramid nanofiber.

[0015] Furthermore, the mass concentration of the polyvinyl alcohol solution is 6-12%, the usage ratio of potassium hydroxide to deionized water is 0.5-2 g / mL, the mass ratio of potassium hydroxide to aramid nanofiber is (0.5-2):1, and the usage ratio of aramid nanofiber to dimethyl sulfoxide is 0.01-0.04 g / mL.

[0016] Furthermore, the aqueous monomer solution is a polyamine aqueous solution with a mass concentration of 0.5-2%, and the polyamine is one of piperazine, m-phenylenediamine or polyethyleneimine.

[0017] Furthermore, the oil phase monomer solution is a mixed solution of a polyacyl chloride and an organic solvent, the mass concentration of the polyacyl chloride in the oil phase monomer solution is 0.02-0.3%, the polyacyl chloride is one of trimesoyl chloride, isophthalic acid chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanoyl chloride or glutaryl chloride, and the organic solvent is one of n-hexane, n-heptane, dodecane or tetradecane.

[0018] Furthermore, the coating amount of the hydrophilic intermediate layer solution is 0.01-0.02 mL / cm 2 The amount of the aqueous monomer solution used during infiltration is 0.15-0.25 mL / cm 2 The coating amount of the oil phase monomer solution during infiltration is 0.15-0.25 mL / cm 2 .

[0019] Furthermore, the uniform coating is performed using a scraper with a gap of 50 microns.

[0020] Furthermore, the following steps are included:

[0021] (1) uniformly coating the hydrophilic intermediate layer solution on one surface of the hydrophilic modified hydrophobic membrane, and drying to obtain a hydrophilic modified hydrophobic membrane carrying the hydrophilic intermediate layer;

[0022] (2) Fixing the hydrophilic modified hydrophobic membrane carrying the hydrophilic intermediate layer, then dripping the aqueous monomer solution onto the surface of the hydrophilic intermediate layer for infiltration, letting it stand and then drying, then continuing to drip the oily monomer solution for infiltration, letting it stand and then drying, to obtain the dense polyamide Janus membrane distillation membrane.

[0023] Furthermore, in step (1), the drying is air-drying or drying at 25-35°C.

[0024] Furthermore, in step (2), the aqueous monomer solution is added dropwise and then allowed to stand for 3-10 minutes, excess aqueous monomer solution is removed, and then the mixture is dried at 30°C for 30 minutes; the oily monomer solution is added dropwise and then allowed to stand for 1-2 minutes, excess oily monomer solution is removed, and then the mixture is dried at 60°C for 5-10 minutes.

[0025] The third technical solution of the present invention:

[0026] The application of the dense polyamide Janus membrane distillation membrane in membrane distillation.

[0027] Furthermore, during application, the side of the dense polyamide Janus membrane distillation membrane on which the PA / PVA composite layer or the PA / ANF composite layer is loaded is brought into contact with the feed liquid.

[0028] The reaction principle involved in the technical solution of the present invention is:

[0029] PVA has the advantages of strong film-forming ability, good hydrophilicity, and excellent biocompatibility. It can be used as an antifouling material to prepare high-performance Janus membrane distillation membranes. The present invention uses a PVA solution cast on the surface of a hydrophilically modified hydrophobic membrane. Then, through a drying, shrinkage, and rehydration process, a hydrogel-like PVA intermediate coating is constructed in a simpler and greener manner. ANF is derived from Kevlar, which is known for its excellent mechanical properties. It has a high aspect ratio and symmetrical aromatic rings in the main chain units, which will help enhance the mechanical strength of the Janus membrane distillation membrane. The present invention uses a hydrophilically modified hydrophobic microporous membrane to facilitate the loading of the PVA or ANF coating, thereby ensuring the formation of a uniform and hydrophilic intermediate coating on the hydrophobic membrane surface.

[0030] The construction of the hydrophilic PVA and ANF intermediate coating increases the storage capacity of amine monomers in the aqueous phase and accelerates the interfacial polymerization reaction, thereby forming a complete and defect-free polyamide (PA) layer. Since the PA-PVA and PA-ANF composite layers are hydrophilic and thin, the flux of the obtained membrane is comparable to that of the unmodified hydrophobic membrane. At the same time, thanks to the formation of a complete and defect-free PA layer on the constructed intermediate layer, the obtained dense polyamide Janus membrane distillation membrane has a stable steam flux and a low conductivity permeate. Therefore, the scalable preparation process and robust membrane distillation performance of the dense polyamide Janus membrane distillation membrane based on the PVA and ANF intermediate layer have great potential in the practical application of desalination of oily and high-salt wastewater.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The present invention constructs a continuous and uniform PVA or ANF hydrophilic interlayer on a hydrophilically modified hydrophobic substrate, and performs interfacial polymerization on this basis. Compared with interfacial polymerization directly on the hydrophobic substrate, the PVA or ANF hydrophilic interlayer increases the storage capacity of amine monomers in the aqueous phase and promotes a complete interfacial polymerization reaction, thereby forming a dense and defect-free polyamide Janus membrane distillation membrane, which can maintain stable steam flux and permeate water with very low conductivity during long-term continuous operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0034] Figure 1 is a scanning electron microscope image of the original polytetrafluoroethylene membrane surface of Example 1;

[0035] Figure 2This is a scanning electron microscope image of the dense PA / PVA Janus membrane distillation membrane obtained in Example 1;

[0036] Figure 3 This is a scanning electron microscope image of the dense PA / ANF Janus membrane distillation membrane obtained in Example 2;

[0037] Figure 4 Graphs showing the water contact angle in air and the oil contact angle underwater of the polytetrafluoroethylene membrane and the dense PA / PVA and PA / ANF Janus membrane distillation membranes in Examples 3 and 4;

[0038] Figure 5 Graphs showing the flux and effluent conductivity of the polytetrafluoroethylene membrane and the dense PA / PVA and PA / ANF Janus membrane distillation membranes in Examples 3 and 4;

[0039] Figure 6 Graphs showing the flux and effluent conductivity of the polytetrafluoroethylene membrane in Examples 5 and 6 when treating an oil-containing salt solution as the feed liquid;

[0040] Figure 7 Graphs showing the flux and effluent conductivity of the dense PA / PVA and PA / ANF Janus membrane distillation membranes in Examples 5 and 6 when treating an oil-containing salt solution as the feed liquid;

[0041] Figure 8 Graphs showing the flux and effluent conductivity of the polytetrafluoroethylene membrane in Examples 5 and 6 when treating a feed solution containing a surfactant-containing salt solution;

[0042] Figure 9 Graphs showing the flux and effluent conductivity of the dense PA / PVA and PA / ANF Janus membrane distillation membranes in Examples 5 and 6 when treating a surfactant-containing salt solution as the feed liquid;

[0043] Figure 10 Graphs showing the flux and effluent conductivity of the polytetrafluoroethylene membrane in Examples 7 and 8 when treating a salt solution containing an oil-water emulsion stabilized by a surfactant as the feed liquid;

[0044] Figure 11 Graphs showing the flux and effluent conductivity of the dense PA / PVA and PA / ANF Janus membrane distillation membranes in Examples 7 and 8 when treating a salt solution containing a surfactant-stabilized oil-water emulsion as the feed liquid.

[0045] Figure 12 Graph showing the liquid entry pressure values ​​of the PA / PVA Janus membrane distillation membrane and polytetrafluoroethylene membrane of Example 1, the PA / ANFJanus membrane distillation membrane of Example 2, and the PAJanus membrane distillation membrane of Comparative Example 1. DETAILED DESCRIPTION

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0048] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0049] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0050] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0051] An embodiment of the present invention proposes a dense polyamide Janus membrane distillation membrane, which includes a hydrophilic-modified hydrophobic membrane, a hydrophilic intermediate layer and a polyamide (PA) layer arranged in sequence from bottom to top, wherein the hydrophilic intermediate layer is a polyvinyl alcohol (PVA) layer or an aramid nanofiber (ANF) layer.

[0052] In a preferred embodiment of the present invention, the hydrophilically modified hydrophobic membrane comprises one of a hydrophilically modified polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane, a polypropylene membrane and a composite membrane thereof, preferably a polytetrafluoroethylene membrane.

[0053] The use of a hydrophilically modified hydrophobic microporous membrane facilitates the loading of the PVA and ANF coatings, thereby ensuring the formation of a uniform and hydrophilic intermediate coating on the hydrophobic membrane surface. The construction of the hydrophilic PVA and ANF intermediate coating increases the storage capacity of amine monomers in the aqueous phase and accelerates the interfacial polymerization reaction, thereby forming a complete and defect-free polyamide (PA) layer. Due to the hydrophilicity and thin PA / PVA and PA / ANF composite layers, the flux of the obtained membrane is comparable to that of the unmodified hydrophobic membrane. At the same time, thanks to the complete and defect-free PA layer formed on the intermediate layer, the resulting dense polyamide Janus membrane distillation membrane has a stable vapor flux and a low conductivity permeate.

[0054] In a preferred embodiment of the present invention, the hydrophilic modification method includes one or any combination of polydopamine deposition, polydopamine / polyethyleneimine deposition, tannic acid / 3-aminopropyltriethoxysilane adhesion, sodium hydroxide solution immersion, and plasma treatment, preferably polydopamine deposition and 3-aminopropyltriethoxysilane adhesion.

[0055] The embodiment of the present invention also provides a method for preparing the dense polyamide Janus membrane distillation membrane, wherein a hydrophilic intermediate layer solution is uniformly coated on one surface of a hydrophilically modified hydrophobic membrane to obtain a hydrophilic intermediate layer, and then an aqueous phase monomer solution and an oil phase monomer solution are sequentially de-infiltrated into the surface of the hydrophilic intermediate layer by interfacial polymerization to form a polyamide (PA) layer, thereby obtaining the dense polyamide Janus membrane distillation membrane;

[0056] The hydrophilic intermediate layer solution is a polyvinyl alcohol (PVA) solution or an aramid nanofiber (ANF) solution.

[0057] More specifically, the following steps are included:

[0058] (1) uniformly coating the hydrophilic intermediate layer solution on one surface of the hydrophilically modified hydrophobic membrane, and drying (naturally drying or drying at 25-35° C.) to obtain a hydrophilically modified hydrophobic membrane carrying the hydrophilic intermediate layer;

[0059] (2) The hydrophilic modified hydrophobic membrane carrying the hydrophilic intermediate layer is fixed on a membrane mold made of polytetrafluoroethylene material, and then the hydrophilic intermediate layer is uniformly infiltrated with an aqueous monomer solution, allowed to stand for 3-10 minutes and excess aqueous monomer solution is removed, and dried at 30°C for 30 minutes. Thereafter, the membrane is infiltrated with an oily monomer solution, allowed to stand for 1-2 minutes and excess oily monomer solution is removed, and dried at 60°C for 5-10 minutes to obtain the dense polyamide Janus membrane distillation membrane.

[0060] In a preferred embodiment of the present invention, the polyvinyl alcohol solution is obtained by uniformly mixing polyvinyl alcohol and deionized water at 90° C., with the stirring time being 6-10 hours.

[0061] In a preferred embodiment of the present invention, the aramid nanofiber solution is obtained by dissolving potassium hydroxide in deionized water, followed by magnetic stirring for 48-96 hours and adding dimethyl sulfoxide and aramid nanofibers.

[0062] In a preferred embodiment of the present invention, the mass concentration of the polyvinyl alcohol solution is 6-12%, preferably 8-10%.

[0063] In a preferred embodiment of the present invention, the dosage ratio of potassium hydroxide to deionized water is 0.5-2 g / mL, preferably 1 g / mL, the mass ratio of potassium hydroxide to aramid nanofiber is (0.5-2):1, preferably (0.8-1):1, and the dosage ratio of aramid nanofiber to dimethyl sulfoxide is 0.01-0.04 g / mL, preferably 0.02-0.025 g / mL.

[0064] In a preferred embodiment of the present invention, the aqueous monomer solution is a polyamine aqueous solution with a mass concentration of 0.5-2%, and the polyamine is one of piperazine, m-phenylenediamine or polyethyleneimine, preferably a m-phenylenediamine aqueous solution or a piperazine aqueous solution with a mass concentration of 1-2%.

[0065] In a preferred embodiment of the present invention, the oil phase monomer solution is a mixed solution of a polyacyl chloride and an organic solvent, the mass concentration of the polyacyl chloride in the oil phase monomer solution is 0.02-0.3%, preferably 0.02-0.1%, the polyacyl chloride is one of trimesoyl chloride, isophthalic acid chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanoyl chloride or glutaryl chloride, preferably trimesoyl chloride, and the organic solvent is one of n-hexane, n-heptane, dodecane or tetradecane, preferably n-hexane.

[0066] In a preferred embodiment of the present invention, the coating amount of the hydrophilic intermediate layer solution is 0.01-0.02 mL / cm 2 The amount of the aqueous monomer solution used during infiltration is 0.15-0.25 mL / cm 2 The amount of the oil phase monomer solution used during infiltration is 0.15-0.25 mL / cm 2 .

[0067] In a preferred embodiment of the present invention, the uniform coating is performed using a scraper with a gap of 50 microns.

[0068] The embodiment of the present invention also proposes the application of the dense polyamide Janus membrane distillation membrane in membrane distillation.

[0069] During application, the side of the dense polyamide Janus membrane distillation membrane on which the PA / PVA composite layer or the PA / ANF composite layer is loaded is brought into contact with the feed liquid.

[0070] The two sides of the membrane distillation membrane are the feed liquid on the hot side and the permeate on the cold side, wherein the feed liquid is a salt solution, more preferably a salt solution with the addition of a surfactant and an oil-water emulsion stabilized by the surfactant, and the permeate is deionized water.

[0071] The purpose of adding oil to the feed liquid is to test the anti-fouling performance of dense polyamide Janus membrane distillation; the purpose of adding surfactant to the feed liquid is to test the anti-wetting performance of dense polyamide Janus membrane distillation; the purpose of adding surfactant-stabilized oil-water emulsion to the feed liquid is to test the simultaneous anti-fouling and anti-wetting performance of dense polyamide Janus membrane distillation membrane.

[0072] The raw materials used in the examples of the present invention are all commercially available.

[0073] The technical solution of the present invention is further illustrated by the following examples.

[0074] Example 1

[0075] A dense polyamide Janus membrane distillation membrane comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic polyvinyl alcohol (PVA) layer, and a polyamide (PA) layer arranged sequentially from bottom to top. The preparation method comprises the following steps:

[0076] (1) 0.1 g dopamine and 0.1 g polyethyleneimine were dissolved in 50 mL of 50 mmol / L Tris-HCl buffer solution (pH = 8) to obtain an activation solution. The upper surface of the polytetrafluoroethylene membrane was then immersed in the activation solution. After standing for 12 h, the membrane surface was rinsed and naturally dried to obtain a polytetrafluoroethylene membrane with one side hydrophilically modified.

[0077] (2) 8 g of PVA powder was added to 92 g of deionized water and stirred under magnetic stirring at 90° C. for 8 h to form a uniform PVA solution. The obtained PVA solution was poured onto one side of the hydrophilically modified polytetrafluoroethylene membrane prepared in step (1) and evenly coated with a scraper with a gap of 50 μm. The coating amount was 0.012 mL / cm 2 After being evenly coated, the film was dried at 35°C for 30 min to obtain a hydrophilic-modified hydrophobic membrane loaded with PVA film;

[0078] (3) dissolving m-phenylenediamine in deionized water and stirring to mix uniformly to obtain an aqueous monomer solution, wherein the concentration of m-phenylenediamine in the aqueous monomer solution is 2 wt %, and dissolving trimesoyl chloride in n-hexane and ultrasonically mixing to obtain an oily monomer solution, wherein the concentration of trimesoyl chloride in the oily monomer solution is 0.2 wt %;

[0079] (4) The hydrophilic-modified hydrophobic membrane loaded with PVA film prepared in step (2) was fixed on a polytetrafluoroethylene mold, and then the aqueous monomer solution prepared in step (3) was used to uniformly infiltrate the surface of the PVA film at a dosage of 0.16 mL / cm 2 After standing for 5 minutes, remove the excess aqueous monomer solution, dry it naturally, and then continue to use the oil phase monomer solution prepared in step (3) to evenly infiltrate the mixture. The amount used is 0.16 mL / cm 2 After evenly spreading, it was allowed to stand for 2 minutes, the excess oil phase monomer solution was removed, and it was dried at 60°C for 10 minutes to obtain a dense polyamide Janus membrane distillation membrane, which was recorded as a dense PA / PVA Janus membrane distillation membrane.

[0080] Example 2

[0081] A dense polyamide Janus membrane distillation membrane comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic aramid nanofiber (ANF) layer, and a polyamide (PA) layer arranged sequentially from bottom to top. The preparation method comprises the following steps:

[0082] (1) 0.1 g dopamine and 0.1 g polyethyleneimine were dissolved in 50 mL of 50 mmol / L Tris-HCl buffer solution (pH = 8) to obtain an activation solution. The upper surface of the polytetrafluoroethylene membrane was then immersed in the activation solution. After standing for 12 h, the membrane surface was rinsed and naturally dried to obtain a polytetrafluoroethylene membrane with one side hydrophilically modified.

[0083] (2) 0.4 g of KOH was completely dissolved in 0.4 mL of deionized water, and then 20 mL of dimethyl sulfoxide and 0.4 g of aramid nanofiber were added under magnetic stirring. After uniform stirring for 50 h, a deep red ANF solution was obtained. The obtained ANF solution was poured onto one side of the hydrophilically modified polytetrafluoroethylene membrane prepared in step (1) and evenly coated with a scraper with a gap of 50 μm. The amount of the drop was 0.02 mL / cm 2 The coated membrane was slowly immersed in deionized water and allowed to stand for 30 min, and then naturally dried to obtain a hydrophilic-modified hydrophobic membrane loaded with ANF membrane;

[0084] (3) dissolving m-phenylenediamine in deionized water and stirring to mix uniformly to obtain an aqueous monomer solution, wherein the concentration of m-phenylenediamine in the aqueous monomer solution is 2 wt %, and dissolving trimesoyl chloride in n-hexane and ultrasonically mixing to obtain an oily monomer solution, wherein the concentration of trimesoyl chloride in the oily monomer solution is 0.2 wt %;

[0085] (4) The hydrophilic-modified hydrophobic membrane loaded with ANF membrane prepared in step (2) was fixed on a polytetrafluoroethylene membrane, and then the aqueous monomer solution prepared in step (3) was used to uniformly infiltrate the surface of the PVA membrane at a dosage of 0.16 mL / cm 2 After standing for 5 minutes, remove the excess aqueous monomer solution, dry it naturally, and then continue to use the oil phase monomer solution prepared in step (3) to evenly infiltrate the mixture. The amount used is 0.16 mL / cm 2 After evenly spreading, the mixture was allowed to stand for 2 minutes, the excess oil phase monomer solution was removed, and the mixture was dried at 60°C for 10 minutes to obtain a dense polyamide Janus membrane distillation membrane, which was recorded as a dense PA / ANF Janus membrane distillation membrane.

[0086] The polytetrafluoroethylene membranes in Examples 1 and 2 and the obtained dense PA / PVA Janus membrane distillation membranes and dense PA / ANF Janus membrane distillation membranes were characterized by scanning electron microscopy. The scanning electron micrographs of the polytetrafluoroethylene membranes are shown in FIG. Figure 1 , the scanning electron microscope image of the dense PA / PVA Janus membrane distillation membrane is shown in Figure 2 , the scanning electron microscope image of the dense PA / ANF Janus membrane distillation membrane is shown in Figure 3 .

[0087] Depend on Figure 1-3 It can be seen that the surface of the polytetrafluoroethylene membrane presents a porous network structure composed of nanofibers, while the surfaces of the obtained PA / PVA and PA / ANF Janus membrane distillation membranes show a dense and relatively flat structure.

[0088] Example 3

[0089] A dense polyamide Janus membrane distillation membrane (dense PA / PVAJanus membrane distillation membrane) comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic polyvinyl alcohol (PVA) layer, and a polyamide (PA) layer, which are sequentially arranged from bottom to top. The preparation method is the same as that of Example 1, except that, in step (1), 0.1 g of dopamine and 0.1 g of 3-aminopropyltriethoxysilane are dissolved in 50 mmol / L, 50 mL of a Tris-HCl buffer solution (pH=8) to obtain an activation solution, and then the upper surface of a polytetrafluoroethylene membrane is immersed in the activation solution. After standing for 10 hours, the membrane surface is rinsed and naturally dried to obtain a polytetrafluoroethylene membrane with a hydrophilic modified surface. The other process steps and parameters are the same as those of Example 1.

[0090] Example 4

[0091] A dense polyamide Janus membrane distillation membrane (dense PA / ANF Janus membrane distillation membrane) comprises a hydrophilically modified hydrophobic membrane, a hydrophilic aramid nanofiber (ANF) layer, and a polyamide (PA) layer, which are sequentially arranged from bottom to top. The preparation method is the same as that of Example 2, except that, in step (1), 0.1 g of dopamine and 0.1 g of 3-aminopropyltriethoxysilane are dissolved in 50 mL of a 50 mmol / L Tris-HCl buffer solution (pH=8) to obtain an activation solution, and then the upper surface of a polytetrafluoroethylene membrane is immersed in the activation solution. After standing for 10 hours, the membrane surface is rinsed and naturally dried to obtain a polytetrafluoroethylene membrane with a hydrophilically modified surface. The other process steps and parameters are the same as those of Example 2.

[0092] The surface wetting properties of the dense PA / PVA and PA / ANF Janus membrane distillation membranes obtained in Examples 3 and 4 were tested. The results are as follows: Figure 4 shown.

[0093] Figure 4 The water contact angle in air and the oil contact angle underwater of the polytetrafluoroethylene membrane of Examples 3 and 4 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes are shown in FIG. Figure 4 As can be seen, the PTFE membrane is highly hydrophobic, with a water contact angle of 145.7° in air, and oleophilic underwater, with an oil contact angle of only 13.5°. This is mainly attributed to the strong hydrophobic-hydrophobic interaction between the oil droplet and the PTFE membrane surface. In contrast, the surfaces of the dense PA / PVA and PA / ANF Janus membrane distillation membranes are hydrophilic in air (water contact angles of 75.8° and 69.5° in air) and oleophobic underwater (oil contact angles of 136.2° and 135° underwater). This is mainly attributed to the hydration layer formed on the surface of the dense PA / PVA and PA / ANF composite layers, which inhibits the adhesion of oil droplets. This shows that the dense PA / PVA and PA / ANF Janus membrane distillation membranes have excellent anti-oil fouling potential.

[0094] Application Example 1

[0095] Basic performance tests were conducted on the polytetrafluoroethylene membranes of Examples 3 and 4 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes using a direct contact membrane distillation apparatus:

[0096] Using a 3.5 wt% sodium chloride aqueous solution as the feed liquid, with the dense PA / PVA and PA / ANF composite layers facing the feed liquid, the feed side temperature was set to 65°C, and the condensation side temperature was set to 20°C, the permeability and salt rejection of the polytetrafluoroethylene membranes of Examples 3 and 4 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes were tested. The results are shown in Figure 2. Figure 5As shown, the permeation flux of the original polytetrafluoroethylene membrane is 21.0 kg·m -2 ·h -1 Since the PVA and ANF coatings exhibit hydrogel-like properties, which ensure sufficient liquid water supply, the introduction of micron-thick coatings will not damage or sacrifice the membrane permeation flux. Therefore, when the dense ultra-thin PA layer is further introduced, the vapor flux of PA / PVA and PA / ANF Janus membrane distillation membranes (19.6 kg·m -2 ·h -1 and 19.4 kg·m -2 ·h -1 ) is only slightly lower than that of the original polytetrafluoroethylene membrane, and the salt rejection rate is as high as 99.99%.

[0097] Example 5

[0098] A dense polyamide Janus membrane distillation membrane (dense PA / PVA Janus membrane distillation membrane) comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic polyvinyl alcohol (PVA) layer, and a polyamide (PA) layer, arranged sequentially from bottom to top. The preparation method is the same as that of Example 1, except that, in step (2), 10 g of PVA powder is added to 90 g of deionized water, and magnetic stirring is performed at 90° C. for 8 h to form a uniform PVA solution. The obtained PVA solution is poured onto one side of the hydrophilic-modified polytetrafluoroethylene membrane prepared in step (1), and is uniformly coated with a scraper with a gap of 50 μm, and the coating amount is 0.012 mL / cm 2 After uniform coating, the mixture was placed at 35° C. and dried for 30 minutes to obtain a hydrophilic-modified hydrophobic membrane carrying a PVA film, wherein the thickness of the PVA film was about 1 μm. The other process steps and parameters were the same as those in Example 1.

[0099] Example 6

[0100] A dense polyamide Janus membrane distillation membrane (dense PA / ANF Janus membrane distillation membrane) comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic aramid nanofiber (ANF) layer, and a polyamide (PA) layer, which are sequentially arranged from bottom to top. The preparation method is the same as that of Example 2, except that, in step (2), 0.4 g of KOH is completely dissolved in 0.4 mL of deionized water, and then 20 mL of dimethyl sulfoxide and 0.5 g of aramid nanofiber are added under magnetic stirring. After uniform stirring for 50 h, a deep red ANF solution is obtained. The obtained ANF solution is poured onto one side of the hydrophilic-modified polytetrafluoroethylene membrane prepared in step (1), and is evenly coated with a scraper with a gap of 50 μm, and the coating amount is 0.02 mL / cm 2The coated membrane was slowly immersed in deionized water and allowed to stand for 30 minutes, and then naturally dried to obtain a hydrophilic-modified hydrophobic membrane carrying an ANF membrane, wherein the thickness of the ANF membrane was about 1 micron. The other process steps and parameters were the same as those in Example 2.

[0101] Application Example 2

[0102] Basic performance tests were conducted on the polytetrafluoroethylene membranes of Examples 5 and 6 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes using a direct contact membrane distillation apparatus:

[0103] (1) Anti-pollution performance

[0104] An aqueous solution containing 3.5 wt% sodium chloride and 1000 mg / L mineral oil was used as the feed liquid. The dense PA / PVA and PA / ANF composite layers faced the feed liquid. The feed side temperature was set to 65°C and the condensation side temperature was set to 20°C. The anti-fouling performance of the polytetrafluoroethylene membranes of Examples 5 and 6 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes was tested. The results are shown in FIG. Figure 6 and Figure 7 .

[0105] Depend on Figure 6 、 Figure 7 It can be seen that due to the strong hydrophobic-hydrophobic interaction, the original polytetrafluoroethylene membrane is easily contaminated by oil, resulting in its steam flux decreasing from 22.4 kg·m -2 ·h -1 The dense PA / PVA and PA / ANF Janus membranes maintained a stable steam flux (20.0 kg·m -2 ·h -1 ) and very low permeate conductivity, indicating that both membranes possess excellent anti-fouling capabilities. The defect-free, hydrophilic PA / PVA and PA / ANF composite layers possess good hydration capacity. The resulting hydration layer prevents the adhesion and wetting of oil droplets, thereby preventing contact between the hydrophobic substrate and the oil droplets.

[0106] (2) Anti-wetting performance

[0107] A salt solution containing 3.5 wt% sodium chloride and 0.4 mM sodium dodecyl sulfate was used as the feed liquid. The dense PA / PVA and PA / ANF composite layers faced the feed liquid. The feed side temperature was set to 65°C and the condensation side temperature was set to 20°C. The anti-wetting properties of the polytetrafluoroethylene membranes of Examples 5 and 6 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes were tested. The results are shown in FIG. Figure 8 and Figure 9 .

[0108] Depend on Figure 8 and Figure 9 It can be seen that in the initial stage, the permeate flux and permeate conductivity of the polytetrafluoroethylene membrane increased significantly; after 30 minutes of the experiment, the permeate flux increased from 22.4 kg·m -2 ·h -1 Increased to 133.4 kg·m -2 ·h -1 The permeate conductivity increased from 3.2 μS / cm to 5895.5 μS / cm, indicating that the PTFE membrane was severely wetted, allowing the feed solution to pass directly through the hydrophobic membrane into the permeate side. In contrast, the dense PA / PVA and PA / ANF Janus membranes exhibit excellent wetting resistance. After 24 hours of the experiment, the permeate side still maintained very low conductivity of 25.2 μS / cm and 2.2 μS / cm, respectively.

[0109] Example 7

[0110] A dense polyamide Janus membrane distillation membrane (dense PA / PVA Janus membrane distillation membrane) comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic polyvinyl alcohol (PVA) layer, and a polyamide (PA) layer, arranged sequentially from bottom to top. The preparation method is the same as that of Example 3, except that, in step (3), piperazine is dissolved in deionized water and ultrasonically mixed to obtain an aqueous monomer solution, wherein the piperazine concentration in the aqueous monomer solution is 1 wt %; and trimesoyl chloride is dissolved in n-hexane and ultrasonically mixed to obtain an oily monomer solution, wherein the trimesoyl chloride concentration in the oily monomer solution is 0.1 wt %. The other process steps and parameters are the same as those of Example 3.

[0111] Example 8

[0112] A dense polyamide Janus membrane distillation membrane (dense PA / ANF Janus membrane distillation membrane) comprises a hydrophilic-modified hydrophobic membrane, a hydrophilic aramid nanofiber (ANF) layer, and a polyamide (PA) layer, arranged sequentially from bottom to top. The preparation method is the same as that of Example 4, except that, in step (3), piperazine is dissolved in deionized water and ultrasonically mixed to obtain an aqueous monomer solution, wherein the piperazine concentration in the aqueous monomer solution is 1 wt %; and trimesoyl chloride is dissolved in n-hexane and ultrasonically mixed to obtain an oily monomer solution, wherein the trimesoyl chloride concentration in the oily monomer solution is 0.1 wt %. The other process steps and parameters are the same as those of Example 4.

[0113] Application Example 3

[0114] Basic performance tests were conducted on the polytetrafluoroethylene membranes of Examples 7 and 8 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes using a direct contact membrane distillation apparatus:

[0115] A saline solution containing 3.5 wt% sodium chloride, 1000 mg / L mineral oil, and 0.4 mM sodium dodecyl sulfate (SDS) was used as the feed liquid. The dense PA / PVA and PA / ANF composite layers faced the feed liquid. The feed side temperature was set to 65°C and the condensation side temperature was set to 20°C. The anti-fouling and anti-wetting properties of the polytetrafluoroethylene membranes of Examples 7 and 8 and the dense PA / PVA and PA / ANF Janus membrane distillation membranes were tested. The results are shown in Table 1. Figure 10 、 Figure 11 .

[0116] Depend on Figure 10 、 Figure 11 It can be seen that for the PTFE membrane, the steam flux increased fourfold within the initial 15 minutes, indicating that SDS caused severe membrane pore wetting. As the oil contamination intensified, the steam flux decreased significantly and the conductivity increased significantly to 6468.0μS / cm. Compared with the original PTFE membrane, the dense PA / PVA and PA / ANF Janus membrane distillation membranes have better resistance to both contamination and wetting. During the 100h membrane distillation test, the flux of the PA / PVA Janus membrane distillation membrane slowly decreased (by 10.3kg·m -2 ·h -1 ), the conductivity of the distillate increased slightly. The PA / ANF Janus membrane distillation membrane has a more stable evaporation flux (~20.5kg·m -2 ·h -1 ) and lower effluent conductivity. The dense and complete PA / ANF composite layer, with its high capillary pressure and hydration capacity, inhibits surfactant diffusion and intercepts oil contaminants within the hydration layer, thereby preventing direct contact between SDS and oil and the hydrophobic substrate. This enables long-term, robust, and efficient membrane distillation treatment of high-salinity emulsions containing surfactant-stabilized oil.

[0117] Comparative Example 1

[0118] A polyamide Janus membrane distillation membrane comprises a hydrophilic-modified hydrophobic membrane and a polyamide (PA) layer arranged sequentially from bottom to top, and a preparation method comprises the following steps:

[0119] (1) 0.1 g dopamine and 0.1 g polyethyleneimine were dissolved in 50 mL of 50 mmol / L Tris-HCl buffer solution (pH = 8) to obtain an activation solution. The upper surface of the polytetrafluoroethylene membrane was then immersed in the activation solution. After standing for 12 h, the membrane surface was rinsed and naturally dried to obtain a polytetrafluoroethylene membrane with one side hydrophilically modified.

[0120] (2) dissolving m-phenylenediamine in deionized water and stirring to mix uniformly to obtain an aqueous monomer solution, wherein the concentration of m-phenylenediamine in the aqueous monomer solution is 2 wt %, and dissolving trimesoyl chloride in n-hexane and ultrasonically mixing to obtain an oily monomer solution, wherein the concentration of trimesoyl chloride in the oily monomer solution is 0.2 wt %;

[0121] (3) The hydrophilically modified polytetrafluoroethylene membrane prepared in step (1) is fixed on a polytetrafluoroethylene membrane, and then the aqueous monomer solution prepared in step (2) is evenly added dropwise to one side of the hydrophilically modified polytetrafluoroethylene membrane. After standing for 5 minutes, the excess aqueous monomer solution is removed and the membrane is naturally dried. Then, the oily monomer solution prepared in step (3) is continued to be added dropwise to the surface of the membrane, spread evenly, and then stood for 2 minutes to remove the excess oily monomer solution. The membrane is dried at 60°C for 10 minutes to obtain a polyamide Janus membrane distillation membrane, which is referred to as a PAJanus membrane distillation membrane.

[0122] Application Example 4

[0123] The liquid entry pressure value test was performed on the dense PA / PVA Janus membrane distillation membrane and polytetrafluoroethylene membrane of Example 1, the PA / ANF Janus membrane distillation membrane of Example 2, and the PA Janus membrane distillation membrane of Comparative Example 1 using a pressure testing device. The results are shown in FIG. Figure 12 .

[0124] Liquid ingress pressure test is an important parameter used to evaluate the anti-wetting performance of membrane distillation membranes. Figure 12 It can be seen that the liquid entry pressure of the polytetrafluoroethylene membrane is 2.9±0.2 bar, while the liquid entry pressure of the PA Janus membrane distillation membrane of Comparative Example 1 has increased to 4.3±0.1 bar. In contrast, the liquid entry pressure of the compact PA / PVA and PA / ANF Janus membrane distillation membranes of Examples 1 and 2 has significantly increased to 9.0±0.2 bar and 9.8±0.5 bar, respectively. This is mainly attributed to the dual-layer barrier effect and capillary effect of the hydrophilic intermediate layer and the compact polyamide layer.

[0125] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A dense polyamide Janus membrane distillation membrane, characterized in that The invention comprises a hydrophilic modified hydrophobic membrane, a hydrophilic middle layer and a polyamide layer arranged in sequence from bottom to top, wherein the hydrophilic middle layer is a polyvinyl alcohol layer or an aramid nanofiber layer; The dense polyamide Janus membrane distillation membrane is obtained by uniformly coating a hydrophilic intermediate layer solution on one surface of a hydrophobic membrane that has been hydrophilically modified to obtain a hydrophilic intermediate layer, and then using an interfacial polymerization reaction to sequentially infiltrate the surface of the hydrophilic intermediate layer with an aqueous phase monomer solution and an oil phase monomer solution to form a polyamide layer, thereby obtaining the dense polyamide Janus membrane distillation membrane; The hydrophilic intermediate layer solution is a polyvinyl alcohol solution or an aramid nanofiber solution; The polyvinyl alcohol solution is obtained by uniformly mixing polyvinyl alcohol and deionized water; The aramid nanofiber solution is prepared by dissolving potassium hydroxide in deionized water and then adding dimethyl sulfoxide and aramid nanofiber under magnetic stirring; The preparation method of the dense polyamide Janus membrane distillation membrane comprises the following steps: The hydrophilic intermediate layer solution is evenly coated on one surface of the hydrophilic modified hydrophobic membrane, and after drying, a hydrophilic modified hydrophobic membrane carrying the hydrophilic intermediate layer is obtained; The hydrophilic modified hydrophobic membrane carrying the hydrophilic intermediate layer is fixed, and then uniformly infiltrated with an aqueous monomer solution, allowed to stand and then dried, and then further uniformly infiltrated with a uniform oil-phase monomer solution, allowed to stand and then dried to obtain the dense polyamide Janus membrane distillation membrane; The hydrophilic modification method comprises one or any combination of polydopamine deposition, polydopamine / polyethyleneimine deposition, tannic acid / 3-aminopropyltriethoxysilane adhesion, sodium hydroxide solution immersion, and plasma treatment.

2. The dense polyamide Janus membrane distillation membrane according to claim 1, characterized in that The hydrophilic-modified hydrophobic membrane comprises one of a hydrophilic-modified polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane, a polypropylene membrane and a composite membrane thereof.

3. The dense polyamide Janus membrane distillation membrane according to claim 1, characterized in that The mass concentration of the polyvinyl alcohol solution is 6-12%, the usage ratio of potassium hydroxide to deionized water is 0.5-2 g / mL, the mass ratio of potassium hydroxide to aramid nanofiber is (0.5-2):1, and the usage ratio of aramid nanofiber to dimethyl sulfoxide is 0.01-0.04 g / mL.

4. The dense polyamide Janus membrane distillation membrane according to claim 1, characterized in that The aqueous monomer solution is a polyamine aqueous solution with a mass concentration of 0.5-2%, and the polyamine is one of piperazine, m-phenylenediamine or polyethyleneimine.

5. The dense polyamide Janus membrane distillation membrane according to claim 1, characterized in that The oil phase monomer solution is a mixed solution of a polyacyl chloride and an organic solvent, wherein the mass concentration of the polyacyl chloride in the oil phase monomer solution is 0.02-0.3%, the polyacyl chloride is one of trimesoyl chloride, isophthalic acid chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanoyl chloride or glutaryl chloride, and the organic solvent is one of n-hexane, n-heptane, dodecane or tetradecane.

6. The dense polyamide Janus membrane distillation membrane according to claim 1, characterized in that The coating amount of the hydrophilic intermediate layer solution is 0.01-0.02 mL / cm 2 The amount of the aqueous monomer solution used during infiltration is 0.15-0.25 mL / cm 2 The amount of the oil phase monomer solution used during infiltration is 0.15-0.25 mL / cm 2 .

7. Use of the dense polyamide Janus membrane distillation membrane according to any one of claims 1 to 6 in membrane distillation.

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