A method for producing a hollow fiber desalination membrane

Abstract

This invention provides a method for preparing a hollow fiber desalination membrane, comprising the following steps: adding benzophenone to a solvent and ultrasonically mixing to obtain a dispersion; heating the solvent and adding a pore-forming agent while stirring, adding a hydrophilic agent while stirring, adding the dispersion while stirring, and adding resin while stirring to form a casting solution; vacuum degassing the casting solution and core solution, followed by spinning and coagulation to form a hollow fiber base membrane; subjecting the hollow fiber base membrane to an interfacial polymerization reaction using an aqueous solution and an organic solution to obtain a hollow fiber desalination membrane; and hydrophilic modification of the hollow fiber desalination membrane. By using benzophenone to prepare the hollow fiber desalination membrane, the permeability and tensile strength of the hollow fiber desalination membrane are increased, avoiding the easy breakage of the membrane fibers during practical applications.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, and in particular to a method for preparing a hollow fiber desalination membrane. Background Technology

[0002] With the increasing prominence of global water scarcity and the continuous strengthening of efforts in domestic and industrial wastewater treatment, membrane technology is being widely applied in fields such as domestic wastewater treatment and industrial water recycling.

[0003] The separation membrane is the key to membrane separation technology, and the membrane material itself, as the core component, has received widespread attention. Among them, polyvinylidene fluoride (PVDF) has advantages such as small pore size, high mechanical strength, and wide application range, but it also has disadvantages such as easy clogging and high price. Polyethersulfone (PES) has advantages such as strong stability, corrosion resistance, and strong creep resistance, but it is prone to fiber breakage. The reason for the fiber breakage is the low compressive strength of the membrane fibers. Moreover, as the contaminants trapped in the membrane accumulate on the inner surface and in the pores of the separation membrane, the water flux and separation capacity of the separation membrane gradually decrease. Backwashing can partially restore the water flux of the membrane, but it cannot achieve 100% recovery. Therefore, when the water flux of the separation membrane drops by more than 30%, chemical cleaning must be performed to remove contaminants adhering to the ultrafiltration membrane wall and pores in a timely manner to prevent the ultrafiltration membrane from forming irreversible clogging.

[0004] In membrane separation, desalination membranes are commonly used in the treatment of high-salinity wastewater. Currently, the most widely used desalination membranes are reverse osmosis and nanofiltration membranes, with structures including hollow fiber, spiral wound, plate and frame, and tubular types. Spiral wound membranes are the most common type on the market. Hollow fiber membranes have advantages such as high specific surface area, high packing density, and ease of encapsulation. Although membrane technology researchers have conducted extensive research on hollow fiber reverse osmosis and hollow fiber nanofiltration membranes in recent years, the tensile strength, fouling resistance, and water flux of most hollow fiber membranes are still not ideal.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing hollow fiber desalination membranes. This method has low requirements for equipment and reaction conditions, uses readily available raw materials, is inexpensive, and is safe and environmentally friendly during the preparation process. Due to the excellent dispersibility, hydrophilicity, and mechanical properties of the introduced benzophenone, the prepared hollow fiber desalination membrane has high water flux, good antifouling performance, good mechanical properties, and good pressure resistance. It also has biomimetic characteristics and selective salt separation characteristics, making it suitable for treating high-salt wastewater. Furthermore, it increases the tensile strength of the hollow fiber desalination membrane and can effectively reduce the membrane fiber breakage rate during use.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] This invention provides a method for preparing a hollow fiber desalination membrane, which includes the following steps:

[0009] Benzophenone was added to a solvent and ultrasonically mixed to obtain a dispersion.

[0010] After heating the solvent, add the pore-forming agent and stir, add the hydrophilic agent and stir, add the dispersion and stir, and add the resin and stir to form a casting solution;

[0011] After vacuum degassing of the casting solution and core solution, hollow fiber base membrane is formed by spinning and solidification.

[0012] Hollow fiber membranes were subjected to interfacial polymerization reactions with aqueous and organic phase solutions to obtain hollow fiber desalination membranes.

[0013] Hydrophilic modification of hollow fiber desalination membranes.

[0014] Preferably, the aqueous phase solution is prepared by mixing and stirring pure water and / or ethanol, benzophenone, piperazine, and pH adjuster, and the organic phase solution is prepared by dissolving polyacrylamide chloride in n-hexane and / or n-heptane;

[0015] Preferably, the pH adjuster is one of hydrochloric acid and sulfuric acid, and the pH is adjusted to 7-10;

[0016] Preferably, the pH adjuster is hydrochloric acid with a pH adjusted to 8;

[0017] Preferably, the concentration of benzophenone is 0.5-2.5 wt%, and the concentration of piperazine is 0.05-3.0 wt%.

[0018] Preferably, the concentration of benzophenone is 2.0 wt%, and the concentration of piperazine is 2.0 wt%.

[0019] In this invention, benzophenone is added to both the casting solution and the aqueous solution. Benzophenone itself has good dispersibility and hydrophilicity. When benzophenone is added to the casting solution, it can be fully dispersed in the casting solution, which can greatly increase the permeability of the base film. Moreover, benzophenone itself has good mechanical properties, which can increase the tensile strength of the base film. The prepared base film has the advantages of uniformity, strong hydrophilicity, high flux, and high strength.

[0020] When a desalination layer is formed on the surface of a base membrane by interfacial polymerization of an aqueous solution and an organic solution, the aqueous solution also contains benzophenone. In combination with the benzophenone in the base membrane, the benzophenone in the base membrane can improve the membrane strength, while the benzophenone in the desalination layer can improve the water flux of the desalination membrane. The desalination membrane prepared in this way not only has good water flux, but also its mechanical properties and pressure resistance are greatly improved.

[0021] Preferably, the base membrane can be divided into two forms: internal pressure and external pressure. Before the interfacial polymerization reaction is carried out using aqueous solution and organic solution, two DN25 PVC pipes are connected by a tee. Then, a hollow fiber tube is inserted into the pipe, and the ends are cut off by casting epoxy resin. When the internal pressure is used for cutting, the side tee is the water outlet. However, when the external pressure is used for cutting, the side tee is the water inlet.

[0022] Preferably, the concentration of the solvent is 56-80 wt%, and the solvent is one or a combination of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0023] Preferably, the concentration of the solvent is 75 wt%, and the solvent is dimethylformamide.

[0024] Preferably, the concentration of the porogen is 0.5-2 wt%, and the porogen is one or a combination of several of sodium chloride, calcium chloride, lithium chloride, and polyvinylpyrrolidone.

[0025] Preferably, the concentration of the porogen is 1.0 wt%, and the porogen is polyvinylpyrrolidone.

[0026] Preferably, the concentration of the hydrophilic agent is 5-17 wt%, and the hydrophilic agent is one or a combination of two of polyethylene glycol and anhydrous ethanol;

[0027] The concentration of the hydrophilic agent is 8 wt%, and the hydrophilic agent is anhydrous ethanol.

[0028] Preferably, the concentration of the resin is 14-25 wt%, and the resin is one or a combination of several of polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyethersulfone, polyarylethersulfone, and sulfonated polysulfone.

[0029] Preferably, the resin concentration is 16 wt%, and the resin is polyvinylidene fluoride.

[0030] Preferably, the core fluid is selected from one of pure water with a conductivity of less than 10 μS / cm, or a mixture of pure water and a solvent;

[0031] Preferably, the core fluid is pure water with a conductivity of less than 10 μS / cm.

[0032] Preferably, the hydrophilic modification includes the following steps: adding the hollow fiber desalination membrane to an ethanol solution of 20% by volume of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, irradiating it at 25°C with a 300W lamp at a lamp distance of 20cm for 20 minutes, and then cleaning it with deionized water and ethanol.

[0033] By using 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to hydrophilically modify the desalination membrane, its hydrophilicity can be increased. When used in combination with introduced benzophenone, the water flux of the desalination membrane can be significantly improved.

[0034] Preferably, the vacuum degassing of the casting solution and core solution includes the following steps:

[0035] The casting solution is vacuum degassed at 50-80℃ for 10-16 hours, and the core solution is vacuum degassed at 30-60℃ for 4-8 hours.

[0036] Preferably, the casting solution is vacuum degassed at 60°C for 12 hours, and the core solution is vacuum degassed at 40°C for 5 hours.

[0037] Preferably, after forming the hollow fiber base membrane, the hollow fiber base membrane is rinsed and soaked in pure water for 8-16 hours, and then soaked in glycerol water for 4-10 hours;

[0038] Preferably, the soaking time in pure water is 10 hours, and the soaking time in glycerin water is 8 hours.

[0039] Compared with the prior art, the present invention has at least the following advantages:

[0040] (1) This invention increases the permeability of the base membrane by adding benzophenone to the casting solution, increases the tensile strength of the membrane by its hydrophilicity, increases the water flux when the desalination layer is formed by adding benzophenone to the aqueous solution, and increases the hydrophilicity of the desalination membrane by hydrophilic modification. The hollow fiber desalination membrane prepared in this way has high water flux, good antifouling performance, good mechanical properties and pressure resistance, and also has biomimetic characteristics and selective salt separation characteristics, which can be well applied in the treatment of high salinity wastewater.

[0041] (2) The preparation method provided by the present invention is simple, the raw materials are readily available, the cost is low, the preparation process is safe and environmentally friendly, and the membrane fibers of the prepared membrane are not easily broken, which can effectively reduce the membrane fiber breakage rate during field application. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0043] Example 1

[0044] This embodiment provides a method for preparing a hollow fiber desalination membrane, which includes the following steps:

[0045] 1) Add benzophenone to dimethylformamide, and then put it into an ultrasonic mixer for ultrasonic mixing to obtain a dispersion containing benzophenone;

[0046] 2) Pour the solvent into the reaction vessel, heat it to 70°C, then add the pore-forming agent, stir thoroughly for 50 min, then add the hydrophilic agent and continue stirring for 20 min, then add the dispersion prepared in 1), stir for 20 min, then add the resin, and continue stirring for 10 h to form a homogeneous casting solution.

[0047] In this embodiment, the solvent concentration is 75%, and the solvent is dimethylformamide; the porogen concentration is 1.0 wt%, and the porogen is polyvinylpyrrolidone; the hydrophilic agent concentration is 8 wt%, and the hydrophilic agent is anhydrous ethanol; the resin concentration is 16 wt%, and the resin is polyvinylidene fluoride.

[0048] 3) The casting solution prepared in 2) is vacuum degassed at 60°C for 12 hours. Then the core solution (pure water with conductivity less than 10 μS / cm) is vacuum degassed at 40°C for 6 hours. After the casting solution and core solution are vacuum degassed, they are spun into fine streams through a spinneret. After passing through the air bath between the spinneret and the coagulation bath, they are immersed in the coagulation bath to form an externally pressurized hollow fiber base membrane. The hollow fiber base membrane is then rinsed and soaked in pure water for 10 hours, and then soaked in glycerol water for 8 hours.

[0049] In this embodiment, the temperature of the coagulation bath is 24°C, the air bath is 5cm, the glycerol content in the glycerol water is 25wt%, the ambient temperature is 25°C, and the ambient humidity is 50%RH.

[0050] 4) After ultrasonically cleaning the hollow fiber base membrane prepared in 3) for 10 minutes, two DN25 PVC pipes with a length of 15cm are bonded together with a T-joint. Take 25 hollow fiber base membranes with a length of 40cm and put them into the pipes. Cast the ends with epoxy resin and cut off the ends to obtain the base membrane assembly.

[0051] 5) Preparation of aqueous solution: Pure water, 2.0 wt% benzophenone, 2.0 wt% piperazine and hydrochloric acid with pH adjusted to 8 are mixed evenly and stirred for 30 min to prepare an aqueous solution;

[0052] 6) Preparation of organic phase solution: Dissolve 2 wt% isophthaloyl chloride in n-hexane to obtain organic phase solution;

[0053] 7) Feed the aqueous phase solution prepared in 5) into the three-way port on the side of the base membrane module, let it stand for 5 minutes, and then feed the organic phase solution prepared in 6) into the same three-way port, let it stand for 45 seconds. In this way, a desalination layer can be formed on the surface of the base membrane to obtain a hollow fiber desalination membrane.

[0054] 8) The hollow fiber base membrane prepared in 7) was added to an ethanol solution of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester with a volume fraction of 20%, and irradiated at 25°C with a 300W high-pressure mercury lamp with a lamp distance of 20 cm for 20 min. After that, it was washed 4 times with deionized water and ethanol respectively to obtain a hydrophilic modified hollow fiber desalination membrane.

[0055] In this embodiment, the stirring frequency is 20Hz.

[0056] The prepared hollow fiber desalination membrane was tested, and the results were as follows: the membrane's molecular weight cutoff of 20,000 was 90%, and the pure water flux was 311.4 L / m³. 2 Magnesium sulfate solution flux: 19.2 L / m³ 2 .h, Magnesium sulfate solution retention rate: 95%.

[0057] Examples 2-5

[0058] The specific implementation method is the same as that in Example 1, with the differences shown in Table 1 below:

[0059] Table 1. The effect of different reagent selections on test results

[0060]

[0061]

[0062] Examples 6-7

[0063] The specific implementation method is the same as that in Example 1, with the differences shown in Table 2 below:

[0064] Table 2. Effects of reaction conditions on test results

[0065]

[0066] Example 8

[0067] The specific implementation method is the same as in Example 1, except that the concentration of benzophenone is 3.0 wt% when preparing the aqueous solution in step 5). The prepared hollow fiber desalination membrane is then tested, and the results are as follows:

[0068] The membrane's molecular weight cutoff for 20,000 molecules was 89%, and its pure water flux was 308.4 L / m³. 2 Magnesium sulfate solution flux: 21.4 L / m³ 2 .h, Magnesium sulfate solution retention rate: 93.1%.

[0069] Comparative Example 1

[0070] The specific implementation method is the same as in Example 1, except that no dispersion is added to the casting solution. Specifically, when preparing the casting solution in step 2), the benzophenone-containing dispersion prepared in step 1) is not added. The hollow fiber desalination membrane prepared was then tested, and the test results are as follows:

[0071] The membrane's molecular weight cutoff for 20,000 molecules was 80%, its pure water flux was 204.3 L / m².h, its magnesium sulfate solution flux was 23.5 L / m².h, and its magnesium sulfate solution cutoff was 89.5%.

[0072] Comparative Example 2

[0073] The specific implementation method is the same as in Example 1, the only difference being that benzophenone is not added when preparing the aqueous solution in step 5). The prepared hollow fiber desalination membrane is then tested, and the results are as follows:

[0074] The membrane's molecular weight cutoff for 20,000 molecules was 81%, its pure water flux was 206.2 L / m².h, its magnesium sulfate solution flux was 25.4 L / m².h, and its magnesium sulfate solution cutoff was 88.2%.

[0075] Comparative Example 3

[0076] The specific implementation method is the same as in Example 1, the only difference being that hydrophilic modification (8) is not performed. The prepared hollow fiber desalination membrane was tested, and the results are as follows:

[0077] The membrane's molecular weight cutoff for 20,000 molecules was 82%, its pure water flux was 200.4 L / m².h, its magnesium sulfate solution flux was 24.8 L / m².h, and its magnesium sulfate solution cutoff was 89.0%.

[0078] The data from Examples 1-8 and Comparative Examples 1-3 show that, in Examples 1-8, the hollow fiber desalination membranes prepared according to the preparation method provided by this invention can increase the pure water flux to 302.5-311.4 L / m³.2 The magnesium sulfate solution rejection rate was increased to 93.1-95%, while the pure water flux and magnesium sulfate solution rejection rate of Comparative Examples 1-3 were significantly lower than those of Example 1 of this invention. This is because in Comparative Example 1, benzophenone was not added to the casting solution, resulting in the hollow fiber desalination membrane not containing benzophenone. Benzophenone can greatly improve the permeability of the prepared hollow fiber desalination membrane. When benzophenone was not added to the casting solution of Comparative Example 1, the permeability of the hollow fiber membrane prepared was much lower than that of Example 1, which also resulted in its pure water flux being less than that of Example 1 of this invention. In Comparative Example 2, benzophenone was not added to the aqueous phase solution, resulting in poor flux and hydrophilicity when forming the desalination layer, which also resulted in its effect being less than that of Example 1. In Comparative Example 3, no hydrophilic modification was performed, resulting in the performance of the desalination membrane prepared being less than that of Example 1.

[0079] Therefore, when preparing hollow fiber desalination membranes, it is important to ensure that the amount of each component and the preparation conditions comply with the scope of this invention. Only in this way can a uniform, highly hydrophilic, high-flux, and high-strength hollow fiber desalination membrane be prepared.

[0080] Finally, it is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the principles and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow fiber desalination membrane, characterized in that, Includes the following steps: Benzophenone was added to a solvent and ultrasonically mixed to obtain a dispersion. After heating the solvent, add the pore-forming agent and stir, add the hydrophilic agent and stir, add the dispersion and stir, and add the resin and stir to form a casting solution; After vacuum degassing of the casting solution and core solution, hollow fiber base membrane is formed by spinning and solidification. Hollow fiber membranes were subjected to interfacial polymerization reactions with aqueous and organic phase solutions to obtain hollow fiber desalination membranes. Hydrophilic modification of hollow fiber desalination membranes; The hydrophilic modification includes the following steps: adding the hollow fiber desalination membrane to an ethanol solution of 20% by volume of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, and irradiating it at 25°C with a 300W lamp at a lamp distance of 20cm for 20 minutes, and then cleaning it with deionized water and ethanol. The aqueous solution is prepared by mixing and stirring pure water, benzophenone, piperazine, and pH adjuster. The organic solution is prepared by dissolving a polyacrylamide chloride in n-hexane and / or n-heptane.

2. The preparation method according to claim 1, characterized in that, The pH adjuster is either hydrochloric acid or sulfuric acid, and the pH is adjusted to 7-10. The concentration of benzophenone is 0.5-2.5 wt%, and the concentration of piperazine is 0.05-3.0 wt%. The concentration of benzophenone is 2.0 wt%, and the concentration of piperazine is 2.0 wt%.

3. The preparation method according to claim 1, characterized in that, The concentration of the solvent is 56-80 wt%, and the solvent is one or a combination of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

4. The preparation method according to claim 1, characterized in that, The concentration of the porogen is 0.5-2 wt%, and the porogen is one or a combination of several of sodium chloride, calcium chloride, lithium chloride, and polyvinylpyrrolidone.

5. The preparation method according to claim 1, characterized in that, The concentration of the hydrophilic agent is 5-17 wt%, and the hydrophilic agent is one or a combination of two of polyethylene glycol and anhydrous ethanol.

6. The preparation method according to claim 1, characterized in that, The concentration of the resin is 14-25 wt%, and the resin is one or a combination of several of the following: polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyethersulfone, polyarylethersulfone, and sulfonated polysulfone.

7. The preparation method according to claim 1, characterized in that, The core fluid is selected from one of the following: pure water with a conductivity of less than 10 μS / cm, or a mixture of pure water and a solvent.

8. The preparation method according to claim 1, characterized in that, The vacuum degassing of the casting solution and core solution includes the following steps: The casting solution is vacuum degassed at 50-80℃ for 10-16 hours, and the core solution is vacuum degassed at 30-60℃ for 4-8 hours.

9. The preparation method according to claim 1, characterized in that, After the hollow fiber base membrane is formed, it is rinsed and soaked in pure water for 8-16 hours, and then soaked in glycerol water for 4-10 hours.

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