Preparation method of loose nanofiltration membrane, nanofiltration membrane and application

Abstract

The invention provides a preparation method of a loose nanofiltration membrane, the nanofiltration membrane and application, and relates to the technical field of water treatment. The preparation method comprises the steps of membrane casting solution preparation, coating and phase separation, interfacial polymerization reaction, electrostatic layer self-assembly, nano silicon dioxide addition, post-treatment and the like. By performing electrostatic layer self-assembly on the surface of the polyamide composite supporting layer and introducing nano silicon dioxide, a multi-layer separation layer with a special structure is formed, so that the separation performance and the surface charge density of the membrane are remarkably improved. The prepared loose nanofiltration membrane has a molecular weight retention value of about 1000 Daltons and relatively abundant surface negative charges, has a retention rate of more than 70% for natural organic matters (NOM) and a retention rate of less than 30% for salts, can be used in the fields of drinking water treatment, industrial wastewater treatment, seawater desalination and the like, and has wide application prospects. The problems that a traditional nanofiltration membrane is low in surface charge density, wide in pore size distribution, poor in selectivity, complex in preparation process and the like are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, in particular to a preparation method of loose nanofiltration membrane, nanofiltration membrane and application. BACKGROUND

[0002] With the global water resource shortage and water pollution problems, people's demand for high-performance water treatment technology is growing. As a kind of efficient separation technology, nanofiltration membrane shows great application potential in the fields of drinking water purification, industrial wastewater treatment and seawater desalination. However, the preparation method of traditional nanofiltration membrane mainly depends on interfacial polymerization and non-solvent induced phase separation technology, which has many limitations. On the one hand, the surface charge density of traditional nanofiltration membrane is low, and the electrostatic repulsion of organic matter is insufficient, resulting in low rejection rate of natural organic matter (NOM); on the other hand, the pore size distribution of the membrane is wide, and the selectivity is poor, which cannot realize the effective separation of small molecule organic matter and salt substances, seriously affecting the application effect in the field of drinking water treatment.

[0003] The preparation method of nanofiltration membrane in the prior art also has some problems. CN119746656A proposes a preparation method of positively charged nanofiltration membrane and nanofiltration membrane, which is mainly aimed at the application in specific fields, such as metal ion separation in lithium ion battery recycling, and does not fully consider the selective separation demand of natural organic matter and salt substances in drinking water treatment. Therefore, a new preparation method of loose nanofiltration membrane is urgently needed to effectively solve the above problems and break through the technical bottleneck of traditional nanofiltration membrane. The present application combines non-solvent induced phase separation, interfacial polymerization and electrostatic layer self-assembly technology, and introduces nano-silicon dioxide to optimize the membrane structure, which significantly improves the performance of nanofiltration membrane, makes it have higher surface charge density, narrower pore size distribution and excellent selective separation performance, and at the same time, the process is simple, the cost is controllable, and it is easy to realize industrial large-scale production, which can meet the urgent demand of modern water treatment industry for high-performance nanofiltration membrane. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In view of the deficiencies of the prior art, the present application provides a preparation method of loose nanofiltration membrane, nanofiltration membrane and application, which solves the problems proposed in the above background technology.

[0006] (II) Technical scheme

[0007] In order to achieve the above purpose, the present application is realized by the following technical scheme: a preparation method of loose nanofiltration membrane, comprising the following steps:

[0008] Step 1: Prepare a casting solution by dissolving piperazine (PIP) monomer in dimethyl sulfoxide (DMSO), adding polyethersulfone (PES) powder, and stirring until completely dissolved, wherein the weight percentage of PIP in the casting solution is 0.4% to 1.2%, and the weight percentage of PES in the casting solution is 13% to 17%;

[0009] Step 2: Coating and phase separation: coating the degassed casting solution on the surface of the non-woven fabric to a thickness of 200 μm, and then immersing it in deionized water at 25°C for phase separation to form a primary support layer;

[0010] Step 3: interfacial polymerization reaction: pouring a 0.1% by weight solution of trimesoyl chloride (TMC) in n-hexane onto the surface of the primary support layer loaded with PIP and reacting for 1 minute to form a polyamide composite support layer;

[0011] Step 4: Electrostatic layer self-assembly, using polyacrylic acid (PAA) and polyethyleneimine (PEI) as raw materials, a multilayer structure is formed on the surface of the polyamide composite support layer by electrostatic layer self-assembly technology. The specific operation is to alternately immerse the membrane in PAA aqueous solution and PEI aqueous solution, each immersion time is 10 to 30 minutes, and the immersion is repeated 3 to 5 times;

[0012] Step 5: Adding nano-silica. During the self-assembly process of the electrostatic layer, nano-silica (SiO2) is added to the PAA aqueous solution. The amount of nano-silica added is 0.1% to 1% of the mass of the PAA aqueous solution.

[0013] Step 6: Post-treatment: drain or purge with nitrogen to remove excess liquid on the surface, dry at room temperature for 5 minutes, and rinse with deionized water.

[0014] Preferably, the weight percentage of the PIP in the casting solution is 0.8%, and the weight percentage of the PES in the casting solution is 15%.

[0015] Preferably, the phase separation time is set to 10-30 seconds.

[0016] Preferably, the interfacial polymerization reaction time is 1-2 minutes.

[0017] Preferably, the weight percentage of the TMC in the n-hexane solution is 0.1%.

[0018] Preferably, the particle size of the nano-silicon dioxide is 10 to 50 nanometers.

[0019] Preferably, the loose nanofiltration membrane has a molecular weight cutoff value of about 1000 Daltons and relatively abundant surface negative charge, a rejection rate for natural organic matter (NOM) greater than 70%, and a rejection rate for salt less than 30%.

[0020] Preferably, the loose nanofiltration membrane is used in the fields of drinking water treatment, industrial wastewater treatment, seawater desalination and the like.

[0021] (III) Beneficial Effects

[0022] The present application provides a preparation method of a loose nanofiltration membrane, a nanofiltration membrane and application, which has the following beneficial effects:

[0023] 1. By combining non-solvent induced phase separation, interfacial polymerization and electrostatic layer self-assembly technology, and introducing nano-silicon dioxide to optimize the membrane structure, the loose nanofiltration membrane of the present application has higher surface charge density and narrower pore size distribution. This makes the membrane rejection rate of natural organic matter (NOM) significantly improved, more than 70%, while the salt rejection rate is controlled to be less than 30%, realizing effective separation of small molecule organic matter and salt substances, solving the problems of low surface charge density, wide pore size distribution and poor selectivity of traditional nanofiltration membranes, and significantly improving the application effect of nanofiltration membranes in the field of drinking water treatment.

[0024] 2. The preparation method of the present application is simple, easy to operate and control, without the need for complex equipment and harsh conditions, thereby reducing the production cost. At the same time, the method has good repeatability and stability, and can stably produce loose nanofiltration membrane products with consistent performance, solving the problems of complex preparation process, high cost and difficult large-scale industrial application in the prior art, and providing the possibility for large-scale production and application of nanofiltration membranes. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The present application is a preparation process schematic diagram. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] Embodiment one:

[0028] As shown in Figure 1 The present application provides a preparation method of a loose nanofiltration membrane, which comprises the following steps:

[0029] Step one, preparation of casting solution, in a glass reactor with stirring paddle, add a certain amount of dimethyl sulfoxide (DMSO), then add piperazine (PIP) monomer and polyether sulfone (PES) powder in turn. Turn on the stirring paddle, stir at 500 rpm for 12 hours to ensure that PIP and PES are completely dissolved to form a uniform casting solution. Among them, the weight percentage of PIP in the casting solution is 0.8%, and the weight percentage of PES in the casting solution is 15%.

[0030] Step two, coating and phase separation, pour the degassed casting solution into the coating tank, use the coating knife to evenly coat the casting solution on the surface of the non-woven fabric, the coating thickness is 200 microns. Then quickly immerse the coated non-woven fabric into deionized water at 25℃, the phase separation time is 15 seconds, forming the nascent support layer.

[0031] Step three, interfacial polymerization reaction, pour 0.1% of trimesoyl chloride (TMC) in n-hexane solution onto the surface of the nascent support layer loaded with PIP, react for 1 minute to form a polyamide composite support layer.

[0032] Step four, electrostatic layer self-assembly, prepare 0.1 mol / L aqueous solution of polyacrylic acid (PAA) and polyethyleneimine (PEI) respectively. The polyamide composite support layer is alternately soaked in PAA aqueous solution and PEI aqueous solution, each soaking time is 20 minutes, and the soaking is repeated 4 times to form a multilayer structure.

[0033] Step five, adding nano-silicon dioxide, add nano-silicon dioxide (Si O2) to the PAA aqueous solution, the addition amount of nano-silicon dioxide is 0.5% of the mass of the PAA aqueous solution.

[0034] Step six, post-processing, take the membrane out of the solution, blow off the excess liquid on the surface with nitrogen, dry at room temperature for 5 minutes, then wash with deionized water to obtain a loose nanofiltration membrane.

[0035] Example two

[0036] The same as example one, the difference is that in the coating and phase separation step, the phase separation time is 20 seconds. By adjusting the phase separation time, the influence of the phase separation time on the structure and performance of the membrane is investigated.

[0037] Example three

[0038] The same as example one, the difference is that in the interfacial polymerization reaction step, the reaction time is 2 minutes. The influence of the interfacial polymerization reaction time on the performance of the membrane is studied.

[0039] Example four

[0040] The difference between the embodiment one and the embodiment two is that the number of repeated immersion in the electrostatic layer self-assembly step is 5 times.

[0041] Comparative example one

[0042] The nanofiltration membrane is prepared by the traditional method, and the steps of electrostatic layer self-assembly and adding nano-silicon dioxide are omitted, and the remaining steps are the same as those of the embodiment one.

[0043] The nanofiltration membranes prepared in the embodiment one to four and the comparative example one are tested for performance, and the test results are shown in the following table:

[0044] Sample Water flux (L / m 2 / h / bar) NOM rejection (%) Salt rejection (%) Example One 25.3±1.2 78.6±2.3 22.1±1.5 Example Two 23.8±1.0 75.2±1.8 24.5±1.2 Example Three 22.5±0.8 73.1±2.0 26.3±1.0 Example Four 26.1±1.5 80.5±2.5 21.0±1.3 Comparative Example One Comparative Example Two 18.2±0.9 65.4±1.7 35.6±2.1

[0045] The test results show that the loose nanofiltration membranes prepared in the embodiment one to four have significant advantages in multiple key performance indicators, highlighting the advancement and practicality of the preparation method of the present application.

[0046] In terms of water flux, the water fluxes of the embodiments one to four are all more than 22 L / m 2 / h / bar, and the water flux of the embodiment four reaches 26.1 L / m 2 / h / bar. This index reflects the amount of water that can pass through the membrane per unit time, and the higher the value, the higher the filtration efficiency of the membrane, which can process more water in the same time, which means that the processing efficiency can be effectively improved and the processing cost can be reduced for the actual water treatment application scenario.

[0047] Focusing on the natural organic matter (NOM) rejection rate, the NOM rejection rates of the embodiments one to four are all greater than 70%, and the highest can reach 80.5% (embodiment four). This shows that the loose nanofiltration membrane prepared by the present application can efficiently block the natural organic matter in water and prevent it from entering the product water side. In the treatment of drinking water, the presence of natural organic matter may cause problems such as color and odor of water, and may also react with disinfectants to generate harmful disinfection by-products, which poses a threat to water quality safety. The loose nanofiltration membrane of the present application can significantly reduce the content of natural organic matter in water and improve the quality and safety of drinking water due to its high NOM rejection rate.

[0048] Looking at the salt rejection rate, the salt rejection rates of the embodiments one to four are all less than 30%, and the lowest can reach 21.0% (embodiment four). This shows that the loose nanofiltration membrane of the present application can effectively separate natural organic matter and salt substances while effectively rejecting macromolecular organic matter, allowing small-molecule salt to partially pass through, thereby realizing selective separation. This selective separation capability is of great significance for drinking water treatment, as it not only removes harmful organic impurities but also appropriately retains beneficial mineral components in water, avoiding problems such as poor water quality taste and insufficient mineral intake in the human body caused by excessive desalination.

[0049] Compared with Comparative Example 1, the performance of Examples 1 to 4 is more obvious. Comparative Example 1 omits the steps of electrostatic layer self-assembly and adding nano-silica, and its water flux is only 18.2 L / m 2 / h / bar, the NOM rejection rate is 65.4%, and the salt rejection rate is as high as 35.6%. This fully illustrates the key role of the steps of electrostatic layer self-assembly and adding nano-silica in the preparation method of the application. The electrostatic layer self-assembly technology constructs a multi-layer separation layer with a special structure on the membrane surface, significantly improves the separation performance and surface charge density of the membrane, enhances the electrostatic repulsion of the organic matter, and thus improves the NOM rejection rate. The addition of nano-silica optimizes the microstructure of the separation layer, further improves the selectivity and flux of the membrane.

[0050] From the dispersion degree of experimental data, the error range of each index of Examples 1 to 4 is small, which indicates that the experimental results have high repeatability and stability, which is a positive signal for actual industrial production, indicating that the preparation method of the application has strong controllability and can stably produce loose nanofiltration membrane products with consistent performance.

[0051] In summary, the preparation method of the application successfully prepares a loose nanofiltration membrane with superior performance by skillfully combining non-solvent induced phase separation, interfacial polymerization and electrostatic layer self-assembly technologies, and innovatively introducing nano-silica. The membrane has great application potential in the field of drinking water treatment, can efficiently remove harmful organic matter in water, and at the same time allow appropriate minerals to pass through, providing high-quality and safe drinking water for people. In addition, in the fields of industrial wastewater treatment and seawater desalination, the loose nanofiltration membrane of the application can also play an important role, helping to achieve the goals of efficient use of water resources and environmental protection.

[0052] Although embodiments of the application have been shown and described, it is to be understood that for the purpose of the present application, the embodiments change, modify, replace and vary in many ways without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a loose nanofiltration membrane, characterized in that: The following steps are involved: Step 1: Prepare a casting solution by dissolving piperazine (PIP) monomer in dimethyl sulfoxide (DMSO), adding polyethersulfone (PES) powder, and stirring until completely dissolved, wherein the weight percentage of PIP in the casting solution is 0.4% to 1.2%, and the weight percentage of PES in the casting solution is 13% to 17%; Step 2: Coating and phase separation: coating the degassed casting solution on the surface of the non-woven fabric to a thickness of 200 μm, and then immersing it in deionized water at 25°C for phase separation to form a primary support layer; Step 3: interfacial polymerization reaction: pouring a 0.1% by weight solution of trimesoyl chloride (TMC) in n-hexane onto the surface of the primary support layer loaded with PIP and reacting for 1 minute to form a polyamide composite support layer; Step 4: Electrostatic layer self-assembly, using polyacrylic acid (PAA) and polyethyleneimine (PEI) as raw materials, a multilayer structure is formed on the surface of the polyamide composite support layer by electrostatic layer self-assembly technology. The specific operation is to alternately immerse the membrane in PAA aqueous solution and PEI aqueous solution, each immersion time is 10 to 30 minutes, and the immersion is repeated 3 to 5 times; Step 5: Adding nano-silica. During the self-assembly process of the electrostatic layer, nano-silica (SiO2) is added to the PAA aqueous solution. The amount of nano-silica added is 0.1% to 1% of the mass of the PAA aqueous solution. Step 6: Post-treatment: drain or purge with nitrogen to remove excess liquid on the surface, dry at room temperature for 5 minutes, and rinse with deionized water.

2. The method for preparing a loose nanofiltration membrane according to claim 1, wherein: The weight percentage of the PIP in the casting solution is 0.8%, and the weight percentage of the PES in the casting solution is 15%.

3. The method for preparing a loose nanofiltration membrane according to claim 1, wherein: The phase separation time is set to 10-30 seconds.

4. The method for preparing a loose nanofiltration membrane according to claim 1, wherein: The interfacial polymerization reaction time is 1-2 minutes.

5. The method for preparing a loose nanofiltration membrane according to claim 1, wherein: The weight percentage of the TMC in the n-hexane solution is 0.1%.

6. The method for preparing a loose nanofiltration membrane according to claim 1, wherein: The particle size of the nano-silicon dioxide is 10 to 50 nanometers.

7. The loose nanofiltration membrane prepared by the method for preparing a loose nanofiltration membrane according to any one of claims 1 to 6, characterized in that: The loose nanofiltration membrane has a molecular weight cutoff value of about 1000 Daltons and relatively abundant surface negative charges, a retention rate of more than 70% for natural organic matter (NOM), and a retention rate of less than 30% for salt.

8. Use of a loose nanofiltration membrane prepared by the method for preparing a loose nanofiltration membrane according to any one of claims 1 to 6, characterized in that: The loose nanofiltration membrane is used in the fields of drinking water treatment, industrial wastewater treatment and seawater desalination.

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