A super-hydrophobic pressure-driven distillation membrane and its preparation method

Abstract

The present invention relates to the field of pressure-driven distillation technology, and in particular to a super-hydrophobic pressure-driven distillation membrane and a method for preparing the same. The method comprises the following steps: preparing a first suspension containing a porous material, a siloxane monomer, a chelating agent, and an organic solvent; pouring or coating the first suspension on the surface of a support membrane, reacting, and drying to obtain a hydrophobic porous layer; preparing a second suspension containing nanoparticles, a fluorinated alkoxysilane monomer, and an organic solvent; pouring the second suspension on the surface of the hydrophobic porous layer, reacting, and drying to obtain a fluorinated nano-super-hydrophobic layer, i.e., a super-hydrophobic pressure-driven distillation membrane. The present invention utilizes the above-mentioned steps to produce a super-hydrophobic pressure-driven distillation membrane and a method for preparing the same, thereby obtaining a high-throughput, anti-scaling, and oxidation-resistant pressure-driven distillation membrane.

Description

Technical Field

[0001] The present 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. Background Art

[0002] Pressure-driven distillation (PD) technology has emerged as a potential alternative to current RO technology due to its near-perfect selectivity, comparable energy efficiency to RO, and excellent antioxidant properties. During PD, sufficient hydraulic pressure is applied to the feed solution, creating a vapor partial pressure gradient across the membrane that acts as a driving force for mass transfer, driving the evaporation of water molecules and the subsequent transport of vapor molecules. Therefore, PD holds significant potential for producing freshwater 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 selectivity, pressure-driven distillation shows significant advantages, especially for low molecular weight neutral solutes (such as boron, urea and disinfection by-products). It has a high removal efficiency. In addition, polyamide-based reverse osmosis membranes are susceptible to active chlorine due to the amide group, so a series of expensive pretreatment steps, such as disinfection and dechlorination, are required to control biological fouling and membrane oxidation. In comparison, the pressure-driven distillation membrane process has a water flux comparable to that of the reverse osmosis membrane, can efficiently intercept non-volatile solutes, and exhibits good oxidation resistance. However, the pressure-driven distillation process currently lacks suitable polymer membrane materials, and there is an urgent need 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:

[0006] S1. preparing a suspension comprising a porous material, a siloxane monomer, a chelating agent and an organic solvent;

[0007] 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;

[0008] S3, preparing a second suspension containing nanoparticles, a fluorinated alkoxysilane monomer, and an organic solvent;

[0009] 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.

[0010] 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 balance of organic solvent.

[0011] Preferably, in S3, the second suspension comprises, by mass fraction, 0.1-1% of nanoparticles, 1-10% of fluorine-containing alkoxysilane monomer, and the balance an organic solvent.

[0012] 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.

[0013] Preferably, in S1, the siloxane monomer includes one or more of polymethylphenylsiloxane, polyvinylsiloxane, polyhydrogensiloxane, polyepoxysiloxane, and polyacryloxysiloxane.

[0014] 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.

[0015] Preferably, in S3, the nanoparticles include one or more of zinc oxide, titanium dioxide, and silicon dioxide.

[0016] More preferably, in S3, the particle size of the nanoparticles is 10 nm to 1 μm.

[0017] 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.

[0018] Preferably, the organic solvents in S1 and S3 include one or more of n-hexane, n-heptane, acetonitrile, ethyl acetate, toluene, and mesitylene.

[0019] Preferably, the support membrane in S2 is a porous polymer membrane with a molecular weight cut-off of 10 kDa to 100 kDa.

[0020] More preferably, the material of the polymer porous membrane is one or more of polyvinylidene fluoride, polyamide, polyacrylonitrile, polysulfone, polyethersulfone, and polyimide.

[0021] Preferably, the reaction time in S2 is in the range of 0.5 to 10 hours, and the reaction temperature is in the range of 20 to 70°C.

[0022] 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.

[0023] The super-hydrophobic pressure-driven distillation membrane is prepared by the above-mentioned method for preparing a super-hydrophobic pressure-driven distillation membrane.

[0024] Mechanism of the present invention:

[0025] The pressure-driven distillation membrane in the present invention is composed of a support layer, a hydrophobic porous layer and a fluorinated nano-superhydrophobic layer; the support layer allows liquid water to enter from the permeation side, thereby reducing mass transfer resistance and increasing vapor permeation flux; the porous material has a stable pore structure and high porosity, which promotes rapid transmission of water vapor; the fluorinated alkoxysilane monomer undergoes a condensation reaction with the hydroxyl group on the surface of the nanoparticles, directionally grafting the fluorine chain to the surface of the nanoparticles, reducing the surface energy and imparting superhydrophobicity. The superhydrophobic state can effectively prevent liquid infiltration and promote the water evaporation process. At the same time, the hydrophobic porous layer acts as a confined gas phase transmission channel to achieve ultrafast diffusion of water molecules; the fluorinated nano-superhydrophobic layer is used to construct a superhydrophobic state and a gas-liquid interface, realizing water evaporation and transmembrane transmission of steam molecules driven by the transmembrane vapor partial pressure difference.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention adopts the above-mentioned super-hydrophobic pressure-driven distillation membrane to achieve solute retention through the volatility difference between the solute and the solvent. It has a high retention rate for non-volatile solutes such as salt, boron, and urea, and can be applied to the removal, desalination, concentration or enrichment of neutral small molecules.

[0028] (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.

[0029] (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.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a surface scanning electron microscope image of the polysulfone support membrane in Example 4 of the present invention;

[0032] Figure 2 is a water contact angle diagram of the superhydrophobic pressure-driven distillation membrane in Example 1 of the present invention;

[0033] 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

[0034] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0035] 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 commercially available raw materials may be used.

[0036] Water flux testing method for pressure-driven distillation membrane: The membrane permeation selectivity performance evaluation system is used to test the water permeation flux and solute retention rate of the membrane. The evaluation system consists of a gas cylinder, membrane pool, pipeline, regulating valve, water bath, buffer tank, and pressure detector. The effective membrane area is 14.5 cm 2 The test pressure is 6-10 bar and 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.

[0037] 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).

[0038] Retention rate calculation formula: R = (1-C d / C f )*100%, where C d is the distillate concentration (mg / L), C f is the concentration of the raw material solution (mg / L).

[0039] Example 1

[0040] The present invention provides a method for preparing a super-hydrophobic pressure-driven distillation membrane, comprising the following steps:

[0041] 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;

[0042] 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;

[0043] S3, preparing a suspension containing 0.2% by mass of zinc oxide nanoparticles, 3% by mass of perfluorohexyltrimethoxysilane and n-heptane;

[0044] S4. Pour the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, react at 60° C. for 2 hours, and then dry to obtain a fluorinated nano super-hydrophobic layer, i.e., a super-hydrophobic pressure-driven distillation membrane.

[0045] The water contact angle of the superhydrophobic pressure-driven distillation membrane was tested to be 160°, and the water permeation flux was 1.5 L·m -2 ·h -1 , NaCl retention rate 99%, boron retention rate 98%, urea retention rate 97%.

[0046] Example 2

[0047] The present invention provides a method for preparing a super-hydrophobic pressure-driven distillation membrane, comprising the following steps:

[0048] S1. Prepare a suspension containing 0.03% molecular sieve, 2.0% polymethylphenylsiloxane, 1.5% trimethoxysilane, 1.5% dibutyltin dilaurate and n-heptane by mass fraction;

[0049] 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;

[0050] S3, preparing a suspension containing 0.5% by mass of titanium dioxide nanoparticles, 5% by mass of perfluoropropyltrimethoxysilane and n-hexane;

[0051] S4. Pour the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, react at 50° C. for 4 hours, and then dry to obtain a fluorinated nano super-hydrophobic layer, i.e., a super-hydrophobic pressure-driven distillation membrane.

[0052] 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 99%, boron retention rate 98%, urea retention rate 96%.

[0053] Example 3

[0054] 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;

[0055] 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;

[0056] S3, preparing a suspension containing 0.5% by mass of titanium dioxide nanoparticles, 4% by mass of perfluorododecyltriethoxysilane and n-hexane;

[0057] S4. Pour the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, react at 70° C. for 1 hour, and then dry to obtain a fluorinated nano super-hydrophobic layer, i.e., a super-hydrophobic pressure-driven distillation membrane.

[0058] 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%.

[0059] Example 4

[0060] 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;

[0061] 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;

[0062] S3, preparing a suspension containing 0.6% by mass of silica nanoparticles, 6% by mass of perfluorononayltrimethoxysilane and n-hexane;

[0063] S4. Pour the second suspension in S3 onto the surface of the hydrophobic porous layer obtained in S2, react at 20° C. for 10 hours, and then dry to obtain a fluorinated nano super-hydrophobic layer, i.e., a super-hydrophobic pressure-driven distillation membrane.

[0064] 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%.

[0065] Performance Testing

[0066] 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.

[0067] 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 retention rate of the membrane remained basically unchanged, indicating that the prepared super-hydrophobic pressure-driven distillation membrane has good oxidation resistance.

[0068] Figure 2 This is a water contact angle diagram of the super-hydrophobic pressure-driven distillation membrane in Example 1. The water contact angle of the membrane is 160°, indicating that its surface is in a super-hydrophobic 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.

[0069] 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.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions 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 comprising a porous material, a siloxane monomer, a chelating agent and an organic solvent; The porous material includes one or more of cyclodextrin, carbon nanotubes, molecular sieves, and carbide-derived carbon; The siloxane monomer includes one or more of polymethylphenylsiloxane, polyvinylsiloxane, polyhydrogensiloxane, polyepoxysiloxane, and polyacryloxysiloxane; The chelating agent includes one or more of dicumyl peroxide, trimethoxysilane, dibutyltin dilaurate, and tin chloride; 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 fluorinated alkoxysilane monomer, and an organic solvent; the nanoparticles include one or more of zinc oxide, titanium dioxide, and silicon dioxide; 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, wherein: 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 balance of organic solvent.

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

5. The method for preparing a super-hydrophobic pressure-driven distillation membrane according to claim 1, wherein: The organic solvents in S1 and S3 include one or more of n-hexane, n-heptane, acetonitrile, ethyl acetate, toluene, and mesitylene. 6 . 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 5 .

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