High-chlorine-resistance hydrophilic film and preparation process thereof

Abstract

The invention relates to the technical field of reverse osmosis membranes, and discloses a high chlorine-resistant hydrophilic membrane and a preparation process thereof.The hydrophilic membrane comprises a membrane body, a first chlorine-resistant layer and a second chlorine-resistant layer, the first chlorine-resistant layer and the second chlorine-resistant layer are sequentially arranged on the surface of the membrane body, the first chlorine-resistant layer is prepared from laccase, dopamine, 5, 5-dimethylethylhydantoin and a stabilizer, the laccase concentration is 0.1-0.3 wt%, the dopamine concentration is 0.1-0.3 wt%, and the stabilizer concentration is 0.1-0.3 wt%. The concentration of the dopamine ranges from 0.8 wt% to 1.2 wt%, the concentration of the 5, 5-dimethylethyl hydantoin ranges from 0.3 wt% to 0.6 wt%, and the concentration of the stabilizer ranges from 0.2 wt% to 0.4 wt%; the second chlorine-resistant layer is obtained by crosslinking first carboxymethyl dextran and second carboxymethyl dextran, the molecular weight of the first carboxymethyl dextran is smaller than that of the second carboxymethyl dextran, and the weight ratio of the first carboxymethyl dextran to the second carboxymethyl dextran is (1-5): 1. According to the invention, the durability of chlorine resistance can be improved, and good water flux can be maintained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of reverse osmosis membranes, in particular to a high-chlorine-resistant hydrophilic membrane and a preparation process. BACKGROUND

[0002] A reverse osmosis membrane is an artificial semi-permeable membrane simulating a biological semi-permeable membrane and is a core component of a reverse osmosis technology. Its principle is to separate water from other substances by means of the semi-permeable membrane, under the action of a higher solution osmotic pressure. The membrane pore of the reverse osmosis membrane is very small, and can effectively remove dissolved salts, colloids, microorganisms and organic matter in water, so as to obtain high-quality pure water. The active layer of most commercial reverse osmosis membranes is prepared by interfacial combination of m-phenylenediamine and trimesoyl chloride, and the bottom material is a microporous polysulfone layer for providing support and a non-woven fabric layer for providing mechanical strength. The active layer has a dense crosslinked structure, so that the active layer has a very small pore size and excellent mechanical strength, thereby achieving the purpose of desalination.

[0003] In order to deal with the membrane pollution caused by organisms in the reverse osmosis unit, a bactericide of active chlorine is often added to the water. Although the water is subjected to dechlorination treatment before contacting the reverse osmosis membrane, there is still residual active chlorine that reacts with the active layer of the reverse osmosis membrane. The adverse effects of active chlorine on the polyamide active layer can easily lead to a decrease in the separation performance of the membrane, thereby greatly affecting the desalination effect.

[0004] Currently, there are many methods to improve the chlorine resistance of reverse osmosis membranes, such as developing new interfacial polymerization monomers to improve the chlorine resistance of the active layer. This method has high research and development costs, a long research and development cycle and great difficulty. The commonly used method is to modify the surface of the reverse osmosis membrane by surface coating, so as to form a protective layer on the surface of the reverse osmosis membrane to reduce the damage of active chlorine to the active layer. However, the stability between the protective layer and the membrane surface is poor, and the protective layer can be easily detached due to the action of water flow shear force, so that the stability of the chlorine resistance is easily affected. Therefore, it is still an important research direction to develop a persistent chlorine-resistant performance. SUMMARY

[0005] In a first aspect, the application provides a high-chlorine-resistant hydrophilic membrane.

[0006] The application adopts the following technical solution: The application discloses a high-chlorine-resistant hydrophilic membrane, which comprises a membrane body and a first chlorine-resistant layer and a second chlorine-resistant layer arranged on the surface of the membrane body in sequence, wherein the first chlorine-resistant layer is prepared from raw material components including laccase, dopamine, 5,5-dimethylhydantoin and a stabilizer, the concentration of the laccase is 0.1-0.3 wt%, the concentration of the dopamine is 0.8-1.2 wt%, the concentration of the 5,5-dimethylhydantoin is 0.3-0.6 wt%, and the concentration of the stabilizer is 0.2-0.4 wt%; and the second chlorine-resistant layer is obtained by cross-linking of a first carboxymethyl dextran and a second carboxymethyl dextran, the molecular weight of the first carboxymethyl dextran is smaller than that of the second carboxymethyl dextran, and the weight ratio of the first carboxymethyl dextran to the second carboxymethyl dextran is (1-5):1.

[0007] By adopting the technical scheme, the dopamine is oxidized into catechol into a quinone structure by catalysis of the laccase, then self-polymerization is triggered, so that a polydopamine layer is formed on the surface of the membrane body; and the amino group (-NH2) existing on the surface of the membrane body can react with the quinone structure in the dopamine to form a covalent bond, so that the polydopamine layer is stably connected to the surface of the membrane body; and the carbonyl group in the membrane body can also form a coordination bond with the catechol group of the dopamine, so as to further enhance the binding force with the membrane body, thereby forming a stable protective layer on the surface of the membrane body. The phenolic hydroxyl group in the polydopamine can construct a hydrophilic channel to maintain water flux, and the stabilizer can inhibit the homopolymerization of dopamine into large particles, so that the protective layer is more uniform and has good water permeability.

[0008] Secondly, the 5,5-dimethylhydantoin is embedded in the polydopamine layer, the imino group (-NH-) in the 5,5-dimethylhydantoin can actively capture active chlorine to generate stable N-Cl, so as to block the diffusion of active chlorine to the membrane body, thereby playing a role in protecting the membrane body. The second chlorine-resistant layer is obtained by cross-linking of the first carboxymethyl dextran and the second carboxymethyl dextran, the multi-hydroxyl structure of which forms a hydration layer, which can effectively block the penetration of ClO - , and the hydroxyl group (-OH) of the dextran can be oxidized into aldehyde / carboxyl by hypochlorous acid, so as to further consume the penetrated free chlorine, thereby endowing the membrane body with chlorine resistance.

[0009] Optionally, the first chlorine-resistant layer is obtained by the following steps: 5,5-dimethylhydantoin, a stabilizer, dopamine and laccase are sequentially added into a Tris-HCl buffer solution, the pH of the buffer solution is controlled to be 8-8.5, and the reaction solution is obtained by uniformly mixing; the membrane body is immersed in the reaction solution and reacted at 4 DEG C for 110-120 min, then the temperature is increased to 25 DEG C for reaction for 50-60 min, and then the temperature is increased to 40 DEG C for reaction for 20-30 min; after the reaction is completed, the membrane body is rinsed with deionized water and dried at 50 DEG C.

[0010] By adopting the technical scheme, the laccase can be selected from spore laccase and the like, the temperature in the reaction process is divided into three stages, first, slow nucleation at 4℃, the activity of laccase is also reduced at low temperature, in this process, 5, 5-dimethyl hydantoin can be adsorbed on the surface of the nascent polydopamine nucleus, then the temperature is raised, the activity of laccase is improved, the quinone group is accelerated to generate, the polydopamine accumulation extends the chain length, and the chain segment can also coat 5, 5-dimethyl hydantoin, after the temperature continues to rise, the imino group of 5, 5-dimethyl hydantoin nucleophilic attack on the quinone group of polydopamine is promoted, thereby forming a cross-linked network structure, forming a structure similar to a core-shell structure, thereby reducing the loss of 5, 5-dimethyl hydantoin and improving the chlorine resistance durability.

[0011] Optionally, the stabilizer is selected from a mixture of polyethylene glycol and cysteine, and the weight ratio of the polyethylene glycol to the cysteine is (1-3):1.

[0012] By adopting the technical scheme, the steric hindrance effect of polyethylene glycol prevents excessive aggregation of dopamine, thereby adjusting the hydrophilicity of the coating and the dispersion stability of 5, 5-dimethyl hydantoin; the quinone group generated by oxidation of dopamine can undergo a Michael addition reaction with the thiol group of cysteine to form a more stable C-S bond, thereby significantly improving the oxidation resistance.

[0013] Optionally, the molecular weight of the first carboxymethyl dextran is 5-10 kDa, and the molecular weight of the second carboxymethyl dextran is 60-70 kDa.

[0014] By adopting the technical scheme, the combination of high molecular weight and low molecular weight can balance the comprehensive performance of water permeability and chlorine resistance.

[0015] Optionally, the second chlorine-resistant layer is obtained by the following steps: adding the first carboxymethyl dextran and the second carboxymethyl dextran into the MES buffer solution, adding an activator, and uniformly mixing to obtain a mixed solution; the total mass concentration of the first carboxymethyl dextran and the second carboxymethyl dextran is 2-3 wt%, and the mass concentration of the activator is 0.1-0.12 wt%; immersing the membrane body loaded with the first chlorine-resistant layer into the mixed solution, constant-temperature reaction, then rinsing clean, then immersing into a crosslinking agent solution, crosslinking the first carboxymethyl dextran and the second carboxymethyl dextran, and then rinsing and drying after crosslinking.

[0016] By adopting the technical scheme, the first carboxymethyl dextran and the second carboxymethyl dextran are grafted on the surface of the membrane body and crosslinked by the crosslinking agent, thereby forming the second chlorine-resistant layer. The activator can be selected from a combination of (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS).

[0017] Optionally, the crosslinking agent is selected from one of glutaraldehyde or genipin.

[0018] Optionally, the reaction solution further comprises a modified filler with a mass fraction of 0.1-0.2wt%, wherein the modified filler is obtained by the following method: dissolving 5,5-dimethylhydantoin in ethanol, then adding nano-silica modified by an amino silane coupling agent, stirring for 6-8h, and then filtering and drying to obtain the modified filler.

[0019] Optionally, the average particle size of the nano-silica is 10-20nm.

[0020] Optionally, the amino silane coupling agent is selected from 3-aminopropyl triethoxysilane.

[0021] By using the above technical solution, the silica modified by the amino silane coupling agent has better hydrophilicity and is not easy to agglomerate, and the surface and internal pores of the silica can adsorb part of the 5,5-dimethylhydantoin in the 5,5-dimethylhydantoin solution, so that the 5,5-dimethylhydantoin can be released slowly in the first chlorine-resistant layer, thereby further improving the chlorine resistance. The amino group on the surface of the modified silica can react with the carboxyl group between the dextran, thereby improving the stability of the connection between the second chlorine-resistant layer and the first chlorine-resistant layer.

[0022] In a second aspect, the application provides a preparation process of a high-chlorine-resistant hydrophilic membrane.

[0023] The preparation process of the high-chlorine-resistant hydrophilic membrane comprises the following steps: (1) pretreating the membrane body to remove impurities on the surface of the membrane body; (2) adding 5,5-dimethylhydantoin, a stabilizer, dopamine, a porous filler, and laccase into Tris-HCl buffer solution in sequence, mixing uniformly, then immersing the membrane body into the reaction solution, and reacting at 4℃, 25℃, and 40℃ respectively, and then cleaning with deionized water and drying.

[0024] In summary, the application has at least one of the following beneficial effects: 1. The outermost layer of the membrane body forms a second chlorine-resistant layer by cross-linking of dextran, and the multi-hydroxyl structure of the dextran forms a hydration layer by cross-linking, which can effectively block the penetration of ClO - , and the hydroxyl (-OH) of the dextran can be oxidized to aldehyde / carboxyl by hypochlorous acid, further consuming the penetrated free chlorine, thereby imparting chlorine resistance to the membrane body; 2. The first chlorine-resistant layer is formed by polymerizing a polydopamine layer on the surface of the membrane body, and 5,5-dimethylhydantoin is embedded therein. The polydopamine layer is reacted at multiple gradient temperatures to enable the polydopamine segments to better coat the 5,5-dimethylhydantoin, and the 5,5-dimethylhydantoin imino group can actively capture active chlorine to block the damage of active chlorine to the membrane body. In addition, the quinone group (C=O) generated by the oxidation of dopamine can capture free chlorine to generate non-active chloranil complex, thereby consuming active chlorine that penetrates the first chlorine-resistant layer, thereby achieving the effect of protecting the membrane body. DETAILED DESCRIPTION

[0025] The present application is further described below.

[0026] The reverse osmosis membrane in the embodiment is selected from a commercially available reverse osmosis membrane prepared by interfacial combination of m-phenylenediamine and trimesoyl chloride, the support layer of which is composed of non-woven fabric and polysulfone layer, and the active layer is an amide layer formed by interfacial polymerization. In the present application, a first chlorine-resistant layer and a second chlorine-resistant layer are formed on the surface of the membrane body, i.e., on one side surface of the active layer of the membrane body, and active chlorine is captured and consumed by the protective layer, thereby reducing the damage of active chlorine to the active layer and imparting good chlorine resistance to the membrane body.

[0027] Preparation Example 1: Preparation of modified filler The nano-silicon dioxide was heated at 500°C with a heating rate of 2°C / min. After heating, it was cooled to room temperature, then added to a 30% H2O2 solution (60°C, 2 hours) to increase the surface adsorption sites, washed with deionized water until neutral, and finally vacuum dried at 100°C for 10 hours. The average particle size of the nano-silicon dioxide was 10-20 nm.

[0028] Two parts of nano-silicon dioxide and 100 parts of anhydrous ethanol were added to a three-necked flask, ultrasonically dispersed, and heated to 80°C. Then, 0.1 part of 3-aminopropyl triethoxysilane was added, and the stirring was continued for 8 hours. After the reaction was completed, centrifugal separation was performed, and the product was washed with deionized water several times and dried to obtain the amino-silane coupling agent surface-modified nano-silicon dioxide.

[0029] One part of 5,5-dimethylhydantoin was added to 100 parts of ethanol, heated to 60°C, and after the dissolution of 5,5-dimethylhydantoin was completed, two parts of amino-silane coupling agent surface-modified nano-silicon dioxide was added, ultrasonically dispersed, and then magnetically stirred continuously for 8 hours. After centrifugal separation, the product was washed with anhydrous ethanol several times and vacuum dried to obtain the modified filler.

[0030] Example 1: A preparation process of a high-chlorine-resistant hydrophilic membrane, comprising the following steps: (1) Pretreatment of the membrane body, first immerse the membrane body in 1wt% sodium hydroxide solution for cleaning 5min to remove grease and other impurities on the surface of the membrane body, then immerse the membrane body in 0.5M hydrochloric acid solution for activation 5min, then rinse with deionized water until neutral.

[0031] (2) Preparation of the first chlorine-resistant layer; prepare Tris-HCl buffer solution, adjust the pH to 8.5, then add 5,5-dimethylhydantoin, dopamine, stabilizer and laccase in turn, avoid light and magnetic stirring (300rpm) for 10min to obtain the reaction solution. Among them, the concentration of 5,5-dimethylhydantoin is 0.3wt%, the concentration of dopamine is 1wt%, the concentration of stabilizer is 0.2wt%, the stabilizer is a mixture of polyethylene glycol-400 and cysteine with a weight ratio of 1:1, and the concentration of laccase is 0.1wt%.

[0032] Immerse the membrane body in the reaction solution and keep it oscillating (80rpm) at 4℃ for 2h, then transfer it to the condition of 25℃ and oscillate (150rpm) for 1h, then heat it to 40℃ at a heating rate of 1℃ / min and oscillate (rpm100) for 0.5h. After the reaction is completed, rinse with deionized water and dry in a 50℃ oven to form the first chlorine-resistant layer on the surface of the membrane body.

[0033] (3) Preparation of the second chlorine-resistant layer: dissolve the first carboxymethyl dextran and the second carboxymethyl dextran in the MES buffer solution with pH 6.0, then add the activator and mix uniformly to obtain the mixed solution; the total mass concentration of the first carboxymethyl dextran and the second carboxymethyl dextran is 2wt%, and the concentration of the activator is 0.1wt%; the molecular weight of the first carboxymethyl dextran is 10kDa, the molecular weight of the second carboxymethyl dextran is 70kDa, and the weight ratio of the first carboxymethyl dextran to the second carboxymethyl dextran is 1:1; the activator is a combination of EDC and NHS, and the weight ratio of EDC to NHS is 4:1; Immerse the membrane body obtained in step (2) into the mixed solution, oscillate at 40℃ for 4h, then take it out and rinse with water to remove the physically adsorbed dextran, then immerse it in a glutaraldehyde solution with a concentration of 0.5wt%, and crosslink at 25℃ for 2h, then rinse with water and dry under vacuum at 40℃ to obtain the high chlorine-resistant hydrophilic membrane.

[0034] Example 2: The process steps and components of this example and example 1 are the same, the difference is that in the reaction solution of step (2), the concentration of 5,5-dimethylhydantoin is 0.6wt%, the concentration of dopamine is 1.2wt%, the concentration of stabilizer is 0.4wt%, and the concentration of laccase is 0.3wt%.

[0035] Example 3: The process steps and components of this example and Example 1 are the same, except that in step (2), the stabilizer is composed of polyethylene glycol-400 and cysteine in a weight ratio of 3:1.

[0036] Example 4: The process steps and components of this example and Example 1 are the same, except that in step (3), the weight ratio of the first carboxymethyl dextran and the second carboxymethyl dextran is 5:1.

[0037] Example 5: The process steps and components of this example and Example 1 are the same, except that in step (2), the modified filler in Preparation Example 1 is also added in a mass fraction of 0.1wt%.

[0038] Comparative Example 1 The process steps and components of this comparative example and Example 1 are the same, except that the membrane body does not have a second chlorine-resistant layer loaded.

[0039] Comparative Example 2 The process steps and components of this comparative example and Example 1 are the same, except that the first chlorine-resistant layer is not loaded, and the membrane body in step (1) is directly loaded with the second chlorine-resistant layer through step (3).

[0040] Comparative Example 3 The process steps and components of this comparative example and Example 1 are the same, except that in step (2), no stabilizer is added.

[0041] Comparative Example 4 The process steps and components of this comparative example and Example 1 are the same, except that in step (2), after the membrane body is immersed in the reaction solution, it is oscillated (150 rpm) at 25°C for 3h, then heated to 40°C at a heating rate of 1°C / min, oscillated (rpm 100) for 0.5h, after the reaction is completed, it is rinsed with deionized water, and dried in an oven at 50°C.

[0042] Comparative Example 5 The process steps and components of this comparative example and Example 1 are the same, except that in step (3), an equal amount of the first carboxymethyl dextran is used instead of the second carboxymethyl dextran.

[0043] Comparative Example 6 The process steps and components of this comparative example and Example 1 are the same, except that in step (3), an equal amount of the second carboxymethyl dextran is used instead of the first carboxymethyl dextran.

[0044] Performance Test: The prepared reverse osmosis membrane was used to test the water flux and desalination rate of 5000 mg / L NaCl aqueous solution at 25℃, pH 7.5-8, and an operating pressure of 1.55 MPa.

[0045] Chlorine resistance test: The membrane was continuously operated under 800 ppm active chlorine for 96 h, and deionized water was used for cleaning after each test. The desalination rate was tested after cleaning.

[0046] Table 1 Examples 1-5 and Comparative Examples 1-6

[0047] By comparing the data of Example 1 and Comparative Example 1 and Comparative Example 2, it can be seen that the membrane of Example 1 can maintain good water flux, and after the chlorine resistance test, the desalination rate can maintain a high level, which shows that the first chlorine-resistant layer and the second chlorine-resistant layer can synergistically block and consume active chlorine, thereby reducing the oxidation of the membrane by active chlorine, thereby improving the chlorine resistance of the prepared hydrophilic membrane.

[0048] By comparing Example 1 and Comparative Example 3, it can be seen that the stabilizer can mainly limit the polydopamine layer to form large particles through steric hindrance effect, thereby maintaining good water flux, and the stable C-S bond formed by cysteine can significantly improve the oxidation resistance, thereby improving the stability of the polydopamine layer. By comparing Example 1 and Comparative Example 4, it can be seen that the reaction of polydopamine is controlled by multiple temperature stages, which can better wrap the polydopamine in 5,5-dimethyl hydantoin, improve the durability of chlorine resistance, and the generated chain segment better maintains the water passage. By comparing Example 1 and Comparative Examples 5 and 6, the second chlorine-resistant layer formed by low molecular weight carboxymethyl dextran has a smaller impact on water flux, but the chlorine resistance is also poor, and the second layer formed by high molecular weight carboxymethyl dextran has better chlorine resistance, but has a greater impact on water flux.

[0049] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, therefore: any equivalent changes made on the basis of the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A high-chlorine-resistant hydrophilic membrane, characterized by: The film body is provided with a first chlorine-resistant layer and a second chlorine-resistant layer in sequence on the surface of the film body, the first chlorine-resistant layer is prepared from raw materials including laccase, dopamine, 5,5-dimethylhydantoin, and stabilizer, the concentration of the laccase is 0.1-0.3wt%, the concentration of the dopamine is 0.8-1.2wt%, the concentration of the 5,5-dimethylhydantoin is 0.3-0.6wt%, and the concentration of the stabilizer is 0.2-0.4wt%; the second chlorine-resistant layer is obtained by cross-linking of first carboxymethyl dextran and second carboxymethyl dextran, the molecular weight of the first carboxymethyl dextran is less than that of the second carboxymethyl dextran, and the weight ratio of the first carboxymethyl dextran to the second carboxymethyl dextran is (1-5):

1.

2. The high chlorine tolerant hydrophilic membrane according to claim 1, wherein: The first chlorine-resistant layer is obtained by the following steps: 5,5-dimethylhydantoin, stabilizer, dopamine and laccase are sequentially added into Tris-HCl buffer solution, the pH of the buffer solution is controlled to be 8-8.5, and the reaction solution is obtained by uniformly mixing, the film body is immersed in the reaction solution, and reacted at 4℃ for 110-120min, then the temperature is raised to 25℃ for reaction for 50-60min, and then the temperature is raised to 40℃ for reaction for 20-30min, after the reaction is completed, the film body is rinsed with deionized water and dried at 50℃.

3. The high chlorine tolerant hydrophilic membrane according to claim 1, wherein: The stabilizer is selected from a mixture of polyethylene glycol and cysteine, and the weight ratio of the polyethylene glycol to the cysteine is (1-3):

1.

4. The high chlorine tolerant hydrophilic membrane according to claim 2, wherein: The molecular weight of the first carboxymethyl dextran is 5-10kDa, and the molecular weight of the second carboxymethyl dextran is 60-70kDa.

5. The high chlorine tolerant hydrophilic membrane according to claim 4, wherein: The second chlorine-resistant layer is obtained by the following steps: the first carboxymethyl dextran and the second carboxymethyl dextran are added into MES buffer solution, and an activating agent is added, and the mixture is uniformly mixed to obtain a mixed solution; the total mass concentration of the first carboxymethyl dextran and the second carboxymethyl dextran is 2-3wt%, and the mass concentration of the activating agent is 0.1-0.12wt%; the film body loaded with the first chlorine-resistant layer is immersed in the mixed solution, and reacted at a constant temperature, then rinsed, then immersed in a cross-linking agent solution, and the first carboxymethyl dextran and the second carboxymethyl dextran are cross-linked, and after cross-linking, rinsing and drying are performed.

6. The high chlorine tolerant hydrophilic membrane according to claim 5, wherein: The cross-linking agent is selected from one of glutaraldehyde or genipin.

7. The high chlorine tolerant hydrophilic membrane according to claim 5, wherein: The reaction solution further contains a modified filler with a mass fraction of 0.1-0.2wt%, and the modified filler is obtained by the following method: 5,5-dimethylhydantoin is dissolved in ethanol, then nano-silicon dioxide modified by a surface of an amino silane coupling agent is added, stirred for 6-8h, filtered and dried to obtain the modified filler.

8. The high chlorine tolerant hydrophilic membrane according to claim 7, wherein: The average particle size of the nano-silicon dioxide is 10-20nm.

9. The high chlorine tolerant hydrophilic membrane according to claim 7, wherein: The amino silane coupling agent is selected from 3-aminopropyl triethoxysilane.

10. The process for preparing a high chlorine-tolerant hydrophilic membrane according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) the film body is pretreated to remove impurities on the surface of the film body; (2) the first chlorine-resistant layer is loaded on the surface of the film body to obtain a first modified film body; (3) the second chlorine-resistant layer is loaded on the surface of the first chlorine-resistant layer to obtain the high chlorine-resistant and hydrophilic film.

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