Super-hydrophobic pressure-driven distillation membrane and preparation method thereof

Abstract

The invention relates to the technical field of pressure-driven distillation, in particular to a super-hydrophobic pressure-driven distillation membrane and a preparation method thereof.The preparation method comprises the following steps that first suspension liquid containing a porous material, a siloxane monomer, a chelating agent and an organic solvent is prepared; pouring or coating the suspension I on the surface of a support membrane, reacting and drying to obtain a hydrophobic porous layer; preparing a suspension II containing nanoparticles, a fluorine-containing alkoxy silane monomer and an organic solvent; pouring the suspension II on the surface of the hydrophobic porous layer, reacting and drying to obtain a fluorinated nano super-hydrophobic layer, namely the super-hydrophobic pressure-driven distillation membrane. According to the super-hydrophobic pressure-driven distillation membrane and the preparation method of the super-hydrophobic pressure-driven distillation membrane, the pressure-driven distillation membrane which is high in flux, resistant to scaling and resistant to oxidation is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of pressure-driven distillation, and in particular to a super-hydrophobic pressure-driven distillation membrane and a preparation method thereof. Background Art

[0002] Pressure-driven distillation technology has become a potential alternative to current reverse osmosis technology due to its near-perfect selectivity, energy efficiency comparable to reverse osmosis technology, and excellent antioxidant properties. In the process of pressure-driven distillation, sufficient hydraulic pressure is applied to the feed solution to form a vapor partial pressure gradient on both sides of the membrane as a driving force for mass transfer, thereby driving the evaporation of water molecules and the subsequent transmission of steam molecules. Therefore, pressure-driven distillation technology has great potential in producing fresh water from unconventional water sources.

[0003] Compared with temperature-driven membrane distillation technology, pressure-driven distillation successfully avoids heat loss and temperature polarization. At the same time, compared with reverse osmosis technology, which is widely used but is subject to the trade-off between water permeability and solute selection, pressure-driven distillation shows significant advantages, especially for low molecular weight neutral solutes (such as boron, urea and disinfection by-products). It has high removal efficiency. In addition, polyamide-based reverse osmosis membranes require a series of expensive pretreatment steps, such as disinfection and dechlorination, to control biofouling and membrane oxidation because the amide group is susceptible to active chlorine. In comparison, the pressure-driven distillation membrane process has a water flux comparable to that of reverse osmosis membranes, can efficiently intercept non-volatile solutes, and exhibits good oxidation resistance. However, the pressure-driven distillation process currently lacks suitable polymer membrane materials, and it is urgent to design and develop superhydrophobic pressure-driven distillation membranes to enhance the practical application value of this process. Summary of the invention

[0004] The purpose of the present invention is to provide a super hydrophobic pressure-driven distillation membrane and a preparation method thereof, so as to obtain a high-flux, anti-scaling and oxidation-resistant pressure-driven distillation membrane.

[0005] To achieve the above object, the present invention provides a method for preparing a super hydrophobic pressure-driven distillation membrane, comprising the following steps: S1, preparing a suspension containing a porous material, a siloxane monomer, a chelating agent and an organic solvent; S2, pouring or coating the suspension in S1 on the surface of the support membrane, and drying after the reaction to obtain a hydrophobic porous layer; S3, preparing a second suspension containing nanoparticles, a fluorine-containing alkoxysilane monomer and an organic solvent; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, and drying after the reaction to obtain a fluorinated nano super hydrophobic layer, namely a super hydrophobic pressure-driven distillation membrane.

[0006] Preferably, in S1, the suspension 1 comprises, by mass fraction, 0.01-0.5% of porous material, 0.1-4% of siloxane monomer, 0.1-4% of chelating agent and the remainder of organic solvent.

[0007] Preferably, in S3, the second suspension comprises, by mass fraction, 0.1-1% of nanoparticles, 1-10% of fluorine-containing alkoxysilane monomer, and the remainder of organic solvent.

[0008] Preferably, in S1, the porous material includes one or more of cyclodextrin, cucurbituril, calixarene, zeolite, carbon nanotube, diatomaceous earth, molecular sieve, carbide-derived carbon, and mesoporous silica.

[0009] Preferably, in S1, the siloxane monomer includes one or more of polymethylphenylsiloxane, polyvinylsiloxane, polyhydrogensiloxane, polyepoxysiloxane, and polyacryloxysiloxane.

[0010] Preferably, in S1, the chelating agent includes one or more of dicumyl peroxide, divinylbenzene, trimethoxysilane, triethoxysilane, maleic anhydride, dibutyltin dilaurate, triethylamine, tetramethylammonium hydroxide, ammonium persulfate, and tin chloride.

[0011] Preferably, in S3, the nanoparticles include one or more of zinc oxide, ferric oxide, carbon nanotubes, graphene, quantum dots, titanium dioxide, and silicon dioxide.

[0012] More preferably, in S3, the particle size of the nanoparticles is 10 nm to 1 μm.

[0013] Preferably, in S3, the fluorine-containing alkoxysilane monomer includes one or more of perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorododecyltriethoxysilane, perfluorohexyltrimethoxysilane, perfluorotridecyltriethoxysilane, perfluorononadecyltrimethoxysilane, perfluorohexadecyltriethoxysilane, perfluorobutyltrimethoxysilane, perfluoropentadecyltriethoxysilane, perfluorooctadecyltriethoxysilane, and perfluoropropyltrimethoxysilane.

[0014] Preferably, the organic solvents in S1 and S3 include one or more of n-hexane, n-heptane, acetonitrile, ethyl acetate, toluene and mesitylene.

[0015] Preferably, the support membrane in S2 is a polymer porous membrane with a molecular weight cutoff of 10 kDa to 100 kDa.

[0016] More preferably, the material of the polymer porous membrane is one or more of polyvinylidene fluoride, polyamide, polyacrylonitrile, polysulfone, polyethersulfone, and polyimide.

[0017] Preferably, the reaction time in S2 ranges from 0.5 to 10 hours, and the reaction temperature ranges from 20 to 70°C.

[0018] Preferably, the reaction time in S4 is in the range of 0.5 to 10 hours, and the reaction temperature is in the range of 20 to 70°C.

[0019] The super-hydrophobic pressure-driven distillation membrane is prepared by the above-mentioned method for preparing a super-hydrophobic pressure-driven distillation membrane.

[0020] Mechanism of the present invention: The pressure-driven distillation membrane in the present invention is composed of a support layer, a hydrophobic porous layer and a fluorinated nano super-hydrophobic layer; the support layer allows liquid water to enter from the permeation side, thereby reducing mass transfer resistance and increasing steam permeation flux; the porous material has a stable pore structure and high porosity, which promotes rapid transmission of water vapor; the fluorinated alkoxysilane monomer reacts with the hydroxyl groups on the surface of the nanoparticles to directional graft the fluorine chain to the surface of the nanoparticles, reducing the surface energy and imparting super-hydrophobicity, and the super-hydrophobic state can effectively prevent liquid infiltration and promote the water evaporation process. At the same time, the hydrophobic porous layer serves as a confined gas phase transmission channel to achieve ultra-fast diffusion of water molecules; the fluorinated nano super-hydrophobic layer is used to construct a super-hydrophobic state and a gas-liquid interface, and realizes water evaporation and trans-membrane transmission of steam molecules under the drive of the trans-membrane steam partial pressure difference.

[0021] Beneficial effects of the present invention: (1) The present invention adopts the above-mentioned super-hydrophobic pressure-driven distillation membrane to achieve the interception of solutes by the difference in volatility between the solute and the solvent. It has a high interception rate for non-volatile solutes such as salt, boron, urea, etc., and can be applied to the removal, desalination, concentration or enrichment process of neutral small molecules.

[0022] (2) The present invention adopts the above-mentioned super-hydrophobic pressure-driven distillation membrane, the separation layer is stable and firm, the permeation flux is large, and it has good long-term operation stability.

[0023] (3) The present invention adopts the above-mentioned method for preparing a super-hydrophobic pressure-driven distillation membrane, which has a simple preparation process, mild preparation conditions, a wide range of applications, and is easy to scale up and promote.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a surface scanning electron microscope image of the polysulfone support membrane in Example 4 of the present invention; Figure 2 is a water contact angle diagram of the superhydrophobic pressure-driven distillation membrane in Example 1 of the present invention; Figure 3 This is a surface scanning electron microscope image of the superhydrophobic pressure-driven distillation membrane in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and embodiments. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs. The above-mentioned features or features mentioned in the specific examples mentioned in the present invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0027] Materials used in the present invention: There is no particular limitation on the sources of all raw materials in the present invention and the following examples, and any raw materials may be commercially available.

[0028] Water flux detection method of pressure-driven distillation membrane: The water permeation flux and solute retention rate of the membrane are tested using a membrane permeation selectivity performance evaluation system. The evaluation system consists of a gas cylinder, a membrane pool, a pipeline, a regulating valve, a water bath, a buffer tank, and a pressure detector. The effective membrane area is 14.5 cm 2 , the test pressure is 6-10bar, the test temperature is 60±0.5℃. The solution concentrations for testing the retention rates of sodium chloride, boron and urea are 1000ppm, 5ppm and 500ppm respectively.

[0029] Water flux calculation formula: J = V / (A • Δt), where J is the water flux of the membrane (L • m -2 •h -1 ), V is the volume of water permeating the membrane (L), A is the effective area of ​​the membrane (m 2 ), Δt is the penetration time (h).

[0030] Retention rate calculation formula: R=(1-C d / C f )*100%, where C d is the distillate concentration (mg / L), C f is the stock solution concentration (mg / L).

[0031] Example 1 The present invention provides a method for preparing a super-hydrophobic pressure-driven distillation membrane, comprising the following steps: S1, preparing a suspension containing 0.03% by mass of cyclodextrin, 1.5% by mass of polyepoxysiloxane, 1.2% by mass of trimethoxysilane, 1.2% by mass of dibutyltin dilaurate and n-heptane; S2, pouring the suspension in S1 onto the surface of the polyvinylidene fluoride support membrane, reacting at 60° C. for 1 hour and then drying to obtain a hydrophobic porous layer; S3, preparing a suspension 2 containing 0.2% by mass of zinc oxide nanoparticles, 3% by mass of perfluorohexyltrimethoxysilane and n-heptane; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, reacting at 60° C. for 2 hours and then drying to obtain a fluorinated nano super hydrophobic layer, i.e., a super hydrophobic pressure-driven distillation membrane.

[0032] The test results show that the water contact angle of the superhydrophobic pressure-driven distillation membrane is 160° and the water permeation flux is 1.5 L•m -2 •h -1 , NaCl retention rate is 99%, boron retention rate is 98%, and urea retention rate is 97%.

[0033] Example 2 The present invention provides a method for preparing a super-hydrophobic pressure-driven distillation membrane, comprising the following steps: S1, preparing a suspension containing 0.03% molecular sieve, 2.0% polymethylphenylsiloxane, 1.5% trimethoxysilane, 1.5% dibutyltin dilaurate and n-heptane by mass fraction; S2, pouring the suspension in S1 onto the surface of the polyvinylidene fluoride support membrane, reacting at 50° C. for 2 hours and then drying to obtain a hydrophobic porous layer; S3, preparing a suspension containing 0.5% by mass of titanium dioxide nanoparticles, 5% by mass of perfluoropropyltrimethoxysilane and n-hexane; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, reacting at 50° C. for 4 hours and then drying to obtain a fluorinated nano super hydrophobic layer, i.e., a super hydrophobic pressure-driven distillation membrane.

[0034] The water contact angle of the superhydrophobic pressure-driven distillation membrane was tested to be 160° and the water permeation flux was 2.0 L•m -2 •h -1 , NaCl retention rate is 99%, boron retention rate is 98%, and urea retention rate is 96%.

[0035] Example 3 S1, preparing a suspension containing 0.05% by mass of carbon nanotubes, 2.0% by mass of polydimethylsiloxane, 2% by mass of ethyl orthosilicate, 2% by mass of dibutyltin dilaurate and n-heptane; S2, pouring the suspension in S1 onto the surface of the polyethersulfone support membrane, reacting at 70°C for 1 hour and then drying to obtain a hydrophobic porous layer; S3, preparing a suspension containing 0.5% by mass of titanium dioxide nanoparticles, 4% by mass of perfluorododecyltriethoxysilane and n-hexane; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, reacting at 70°C for 1 hour and then drying to obtain a fluorinated nano super hydrophobic layer, i.e., a super hydrophobic pressure-driven distillation membrane.

[0036] The water contact angle of the superhydrophobic pressure-driven distillation membrane was tested to be 158° and the water permeation flux was 2.0 L•m -2 •h -1 , NaCl retention rate is 98%, boron retention rate is 97%, and urea retention rate is 95%.

[0037] Example 4 S1, preparing a suspension containing 0.05% by mass of carbide-derived carbon, 3% by mass of polyvinylsiloxane, 2% by mass of dicumyl peroxide, 2% by mass of tin chloride and n-heptane; S2, pour the suspension in S1 into Figure 1 The surface of the polysulfone support membrane shown was reacted at 20°C for 10 hours and then dried to obtain a hydrophobic porous layer; S3, preparing a suspension 2 containing 0.6% by mass of silica nanoparticles, 6% by mass of perfluorononayltrimethoxysilane and n-hexane; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, reacting at 20°C for 10 hours and then drying to obtain a fluorinated nano super hydrophobic layer, i.e., a super hydrophobic pressure-driven distillation membrane.

[0038] The water contact angle of the superhydrophobic pressure-driven distillation membrane was tested to be 159° and the water permeation flux was 1.9 L•m -2 •h -1 , NaCl retention rate 99%, boron retention rate 97%, urea retention rate 95%.

[0039] Performance Testing The super-hydrophobic pressure-driven distillation membrane prepared in Example 1 was used to separate calcium chloride and sodium sulfate solutions with a concentration of 1000 ppm. After 24 hours of continuous separation test, the water permeation flux and retention rate of the membrane remained basically unchanged, indicating that the prepared super-hydrophobic pressure-driven distillation membrane has good anti-scaling properties.

[0040] After the super-hydrophobic pressure-driven distillation membrane prepared in Example 1 was immersed in a sodium hypochlorite solution with a concentration of 2000 ppm for 36 hours, the water permeation flux and the retention rate of the membrane remained basically unchanged, indicating that the prepared super-hydrophobic pressure-driven distillation membrane has good oxidation resistance.

[0041] Figure 2 This is a water contact angle diagram of the superhydrophobic pressure-driven distillation membrane of Example 1. The water contact angle of the membrane is 160°, indicating that its surface is in a superhydrophobic state. Figure 3 This is a surface scanning electron microscope image of the superhydrophobic pressure-driven distillation membrane of Example 1. It can be seen that the spherical nanoparticles are densely packed and firmly attached to the membrane surface. The separation layer is stable and firm, ensuring long-term operational stability.

[0042] Therefore, the present invention provides a method for preparing a super-hydrophobic pressure-driven distillation membrane, which has a simple preparation process, mild preparation conditions, a wide range of applications, and is easy to scale up and realize industrial production. The prepared super-hydrophobic pressure-driven distillation membrane achieves effective retention of non-volatile solutes, has a large permeation flux, and has good long-term stability, anti-scaling and oxidation resistance.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a super-hydrophobic pressure-driven distillation membrane, characterized in that: The following steps are included: S1, preparing a suspension containing a porous material, a siloxane monomer, a chelating agent and an organic solvent; S2, pouring or coating the suspension in S1 on the surface of the support membrane, and drying after the reaction to obtain a hydrophobic porous layer; S3, preparing a second suspension containing nanoparticles, a fluorine-containing alkoxysilane monomer and an organic solvent; S4, pouring the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, and drying after the reaction to obtain a fluorinated nano super hydrophobic layer, namely a super hydrophobic pressure-driven distillation membrane.

2. The method for preparing a super hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S1, the suspension 1 includes, by mass fraction, 0.01-0.5% of porous material, 0.1-4% of siloxane monomer, 0.1-4% of chelating agent and the remainder of organic solvent.

3. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S3, the second suspension includes, by mass fraction, 0.1-1% of nanoparticles, 1-10% of fluorine-containing alkoxysilane monomer, and the balance of organic solvent.

4. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S1, the porous material includes one or more of cyclodextrin, cucurbituril, calixarene, zeolite, carbon nanotube, diatomaceous earth, molecular sieve, carbide-derived carbon, and mesoporous silica.

5. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S1, the siloxane monomer includes one or more of polymethylphenylsiloxane, polyvinylsiloxane, polyhydrogensiloxane, polyepoxysiloxane, and polyacryloxysiloxane.

6. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S1, the chelating agent includes one or more of dicumyl peroxide, divinylbenzene, trimethoxysilane, triethoxysilane, maleic anhydride, dibutyltin dilaurate, triethylamine, tetramethylammonium hydroxide, ammonium persulfate, and tin chloride.

7. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S3, the nanoparticles include one or more of zinc oxide, ferric oxide, carbon nanotubes, graphene, quantum dots, titanium dioxide, and silicon dioxide.

8. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: In S3, the fluorine-containing alkoxysilane monomer includes one or more of perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorododecyltriethoxysilane, perfluorohexyltrimethoxysilane, perfluorotridecyltriethoxysilane, perfluorononadecyltrimethoxysilane, perfluorohexadecyltriethoxysilane, perfluorobutyltrimethoxysilane, perfluoropentadecyltriethoxysilane, perfluorooctadecyltriethoxysilane, and perfluoropropyltrimethoxysilane.

9. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, characterized in that: The organic solvents in S1 and S3 include one or more of n-hexane, n-heptane, acetonitrile, ethyl acetate, toluene, and mesitylene.

10. A super-hydrophobic pressure-driven distillation membrane prepared by the method for preparing a super-hydrophobic pressure-driven distillation membrane according to any one of claims 1 to 9.

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