An enhanced chlorine-resistant reverse osmosis membrane and its preparation method

Abstract

This invention provides an enhanced chlorine-resistant reverse osmosis membrane, comprising a base layer, a polyamide layer, and a polymeric protective layer. The polyamide layer is disposed on the base layer, and the polymeric protective layer is disposed on the polyamide layer. The polyamide layer is formed by interfacial polymerization of a diamine aqueous phase and a polyacrylamide oil phase. The solute in the diamine aqueous phase includes common amines and specific diamines, and the specific diamine includes at least one selected from 2-methyl-p-phenylenediamine, 4-methyl-1,3-phenylenediamine, 2,6-diaminotoluene, and 2,4,6-trimethyl-1,3-phenylenediamine. The polymeric protective layer is connected to the surface of the polyamide layer through polyaldehyde molecules. This invention, through the combination of the base layer, the polyamide layer, and the polymeric protective layer, enables the enhanced chlorine-resistant reverse osmosis membrane to achieve both a high desalination rate and excellent chlorine resistance.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, and specifically to an enhanced chlorine-resistant reverse osmosis membrane and its preparation method. Background Technology

[0002] Currently, reverse osmosis membrane separation technology holds a dominant position in wastewater treatment. However, the desalination layer of existing reverse osmosis membranes is basically a common polyamide structure. During contact with oxidizing substances, the molecular bonds in the polyamide structure are unstable and easily broken by oxides such as residual chlorine (e.g., sodium hypochlorite, hypochlorous acid). Therefore, it performs poorly in terms of chlorine resistance and oxidation resistance. Moreover, commercially available chlorine-resistant and oxidation-resistant reverse osmosis membrane products also have the problem of low chlorine resistance and oxidation resistance, resulting in problems such as shortened service life and decreased desalination rate of reverse osmosis membranes.

[0003] In summary, there is an urgent need for an enhanced chlorine-resistant reverse osmosis membrane to address the problems existing in the current technology. Summary of the Invention

[0004] The purpose of this invention is to provide an enhanced chlorine-resistant reverse osmosis membrane, aiming to solve the problems of poor chlorine resistance and easy oxidation of existing reverse osmosis membranes, which leads to shortened service life and decreased desalination rate. The specific technical solution is as follows:

[0005] An enhanced chlorine-resistant reverse osmosis membrane includes a base layer, a polyamide layer, and a polymeric protective layer. The polyamide layer is disposed on the base layer, and the polymeric protective layer is disposed on the polyamide layer. The polyamide layer is formed by interfacial polymerization of a diamine aqueous phase and a polyacrylamide chloride oil phase. The solute in the diamine aqueous phase includes common amines and specific diamines. The specific diamines include at least one selected from 2-methyl-p-phenylenediamine, 4-methyl-1,3-phenylenediamine, 2,6-diaminotoluene, and 2,4,6-trimethyl-1,3-phenylenediamine. The polymeric protective layer is connected to the surface of the polyamide layer through polyaldehyde molecules.

[0006] Preferably, the aqueous phase of the diamine comprises 1-6 wt% of a common amine, 0.5 wt% to 2 wt% of a specific diamine, and the balance being water; the common amine comprises at least one of p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, diethylenetriamine, and triethylenetetramine.

[0007] Preferably, the polyacrylamide chloride oil phase comprises 0.1 to 0.5 wt% polyacrylamide chloride and the balance being an organic solvent, wherein the polyacrylamide chloride is at least one selected from isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, and trimesoyl chloride, and the organic solvent is at least one selected from Isopar G solvent, cyclohexane, n-hexane, and heptane.

[0008] Preferably, the polyaldehyde includes at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, phenylglyoxal, o-phenylenedialdehyde, trialdehyde-resorcinol, and 3,4,5-trialdehyde-1,1-biphenyl.

[0009] A method for preparing the above-mentioned enhanced chlorine-resistant reverse osmosis membrane includes the following steps:

[0010] S1: Treatment of the initial membrane

[0011] The substrate was sequentially immersed in a diamine aqueous phase and a polyacryl chloride oil phase, and the resulting cleansing process yielded a nascent reverse osmosis membrane.

[0012] S2: Polymer protective layer setup

[0013] A multi-element aldehyde solution was coated onto a nascent reverse osmosis membrane, followed by a polymer solution, to obtain an enhanced chlorine-resistant reverse osmosis membrane.

[0014] Preferably, the polyaldehyde solution comprises 1 wt% to 10 wt% of a polyaldehyde, 0.1 wt% to 1 wt% of a strong acid catalyst, and the balance being water.

[0015] Preferably, the polymer solution comprises 0.5wt% to 5wt% of a polymer compound, 0.1wt% to 1wt% of a crosslinking agent, 0.05wt% to 0.5wt% of a weak acid catalyst, and the balance being water.

[0016] Preferably, the polymeric compound includes at least one selected from polyethylene glycol, polyvinyl alcohol, tannic acid, chitosan, polyaspartic acid, and polylysine.

[0017] Preferably, the crosslinking agent includes at least one selected from diisocyanate, phthalic anhydride, maleic anhydride, and pyromellitic anhydride.

[0018] Preferably, the weak acid catalyst includes at least one of formic acid, acetic acid, propionic acid, benzoic acid, and salicylic acid.

[0019] The application of the technical solution of the present invention has the following beneficial effects:

[0020] The enhanced chlorine-resistant reverse osmosis membrane prepared by this invention firstly constructs a polyamide layer using diamines and polyacrylamide chlorides. This introduces more functional groups into the polyamide layer, increasing the steric hindrance of the amide bonds and reducing their susceptibility to chlorine attack. This allows the polyamide layer to maintain high separation performance while improving its chlorine resistance. Secondly, through an aldehyde-amine condensation reaction, nucleophilic substitution of the NH groups on the amide bonds, which are susceptible to residual chlorine attack, is performed, reducing their reactivity and improving the stability of the amino groups, further enhancing the chlorine resistance of the polyamide layer. Finally, a polymer compound is crosslinked onto the polyamide layer, and the unreacted aldehyde groups firmly fix the polymer compound to the surface of the polyamide layer, forming a stable chlorine-resistant layer. Therefore, the enhanced chlorine-resistant reverse osmosis membrane possesses both high desalination efficiency and excellent chlorine resistance.

[0021] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The present invention will now be described in further detail. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0024] Example 1:

[0025] Example 1:

[0026] A method for preparing an enhanced chlorine-resistant reverse osmosis membrane includes the following steps:

[0027] S1: Treatment of the initial membrane

[0028] The substrate (a polysulfone porous membrane in this embodiment) was sequentially immersed in a diamine aqueous phase consisting of 3 wt% m-phenylenediamine, 1 wt% 2-methyl-p-phenylenediamine and the remainder water, and a polyacrylamide oil phase consisting of 0.3 wt% trimesoyl chloride and the remainder organic solvent (cyclohexane in this embodiment). Interfacial polymerization was carried out (reaction temperature was 35°C). After washing with an aqueous acetic acid solution with a concentration of 10 wt% and a temperature of 45°C, a nascent reverse osmosis membrane was obtained.

[0029] S2: Polymer protective layer setup

[0030] A polyaldehyde aqueous solution consisting of 2 wt% glyoxal, 0.2 wt% hydrochloric acid, and the remainder water was coated onto a nascent reverse osmosis membrane. Then, a polymer aqueous solution consisting of 1 wt% polyethylene glycol, 0.2 wt% diisocyanate, 0.1 wt% formic acid, and the remainder water was coated onto the membrane. After a high-temperature (60°C) reaction, a chlorine-resistant protective layer was obtained, and an enhanced chlorine-resistant reverse osmosis membrane was prepared.

[0031] Example 2:

[0032] A method for preparing an enhanced chlorine-resistant reverse osmosis membrane includes the following steps:

[0033] S1: Treatment of the initial membrane

[0034] The substrate (a polysulfone porous membrane in this embodiment) was sequentially immersed in a diamine aqueous phase consisting of 1 wt% diethylenetriamine, 0.5 wt% 4-methyl-1,3-phenylenediamine and the balance water, and a polyacrylamide oil phase consisting of 0.1 wt% trimesoyl chloride and the balance organic solvent (cyclohexane in this embodiment). Interfacial polymerization was carried out (reaction temperature was 40°C). After washing with an oxalic acid aqueous solution with a concentration of 15 wt% and a temperature of 45°C, a nascent reverse osmosis membrane was obtained.

[0035] S2: Polymer protective layer setup

[0036] A polyaldehyde aqueous solution consisting of 1 wt% glyoxal, 0.1 wt% hydrochloric acid, and the remainder water was coated onto a nascent reverse osmosis membrane. Then, a polymer aqueous solution consisting of 0.5 wt% polyethylene glycol, 0.1 wt% diisocyanate, 0.05 wt% formic acid, and the remainder water was coated onto the membrane. After a high-temperature (70°C) reaction, a chlorine-resistant protective layer was obtained, and an enhanced chlorine-resistant reverse osmosis membrane was prepared.

[0037] Example 3:

[0038] The substrate (a polysulfone porous membrane in this embodiment) was sequentially immersed in a diamine aqueous phase consisting of 6 wt% m-phenylenediamine, 2 wt% 2,6-diaminotoluene and the remainder water, and a polyacrylamide oil phase consisting of 0.5 wt% trimesoyl chloride and the remainder organic solvent (cyclohexane in this embodiment). Interfacial polymerization was carried out (reaction temperature was 45°C). After washing with a citric acid aqueous solution with a concentration of 20 wt% and a temperature of 55°C, a nascent reverse osmosis membrane was obtained.

[0039] S2: Polymer protective layer setup

[0040] A polyaldehyde aqueous solution consisting of 10 wt% glutaraldehyde, 1 wt% phosphoric acid and the balance water was coated onto a nascent reverse osmosis membrane. Then, a polymer aqueous solution consisting of 5 wt% polyaspartic acid, 1 wt% pyromellitic anhydride, 0.5 wt% benzoic acid and the balance water was coated onto the membrane. After a high-temperature (65°C) reaction, a chlorine-resistant protective layer was obtained, and an enhanced chlorine-resistant reverse osmosis membrane was prepared.

[0041] Comparative Example 1: Unlike Example 1, only 2-methyl-p-phenylenediamine was not added to the diamine aqueous phase.

[0042] Comparative Example 2: Unlike Example 1, it was not washed with an aqueous oxalic acid solution.

[0043] Comparative Example 3: Unlike Example 1, only the polyaldehyde solution was not coated.

[0044] Comparative Example 4: Unlike Example 1, only the polymer solution was not coated.

[0045] Comparative Example 5: Unlike Example 1, 2-methyl-p-phenylenediamine was not added to the aqueous phase, and the polyaldehyde solution and polymer solution were not coated.

[0046] The enhanced chlorine-resistant reverse osmosis membranes prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to desalination rate and chlorine resistance tests, respectively. The specific test procedures are as follows:

[0047] 1) Desalination rate test:

[0048] The above-mentioned enhanced chlorine-resistant reverse osmosis membrane was tested for its desalination rate in an aqueous solution of 2000 mg / L NaCl at 25 °C and 1.55 MPa operating pressure.

[0049] Desalination rate is the most commonly used indicator for evaluating the separation performance of reverse osmosis membranes, denoted by R0, and its expression is as follows:

[0050]

[0051] Where C0 represents the influent conductivity, μs / cm; C f The conductivity of the produced water is expressed in μs / cm.

[0052] 2) Chlorine resistance test:

[0053] Prepare a 1000 ppm NaClO solution and adjust the pH to 7.0 with 1 mol / L HCl or 1 mol / L NaOH. Immerse the enhanced chlorine-resistant reverse osmosis membrane in the NaClO solution for 24 hours. After 24 hours, remove the membrane, rinse the surface with pure water, and then soak it in pure water for 1 hour. Then, test the desalination rate of the enhanced chlorine-resistant reverse osmosis membrane according to 1).

[0054] The test results for 1)-2) above are shown in Table 1.

[0055] Table 1 shows the changes in desalination performance of the enhanced chlorine-resistant reverse osmosis membranes prepared in Examples 1-3 and Comparative Examples 1-5 before and after the chlorine resistance test.

[0056]

[0057] From the data in Table 1, we know that:

[0058] The enhanced chlorine-resistant reverse osmosis membranes prepared in Examples 1-3 maintained high desalination rates before and after chlorine resistance tests, indicating their excellent chlorine resistance and antioxidant properties. The main mechanism behind this result is as follows: the addition of a specific diamine (with multiple functional groups) to the aqueous phase increases the steric hindrance of the formed polyamide bonds, reducing the likelihood of attack by residual chlorine. Then, through an aldehyde-amine condensation reaction, nucleophilic substitution of the NH groups on the amide bonds reduces their reactivity and improves the stability of the amino groups, giving them preliminary chlorine resistance. Finally, by coating a protective layer onto the polyamide layer, unreacted aldehyde groups and crosslinking agents firmly fix the preferred polymer onto the polyamide surface, forming a stable protective layer. This allows the enhanced chlorine-resistant reverse osmosis membrane to maintain both a high desalination rate and excellent chlorine resistance.

[0059] The reverse osmosis membrane prepared in Comparative Example 1 showed a significantly lower desalination rate after the chlorine resistance test compared to before the test. This phenomenon is partly due to the absence of a specific diamine, which prevented the formation of sterically hindered chemical bonds around the polyamide bonds, thus failing to reduce the attack of residual chlorine on the amide bonds. Consequently, the membrane's chlorine resistance was lower than that of Examples 1-3.

[0060] The reverse osmosis membrane prepared in Comparative Example 2 showed a significantly lower desalination rate after the chlorine resistance test compared to before the test. This phenomenon was due to the lack of cleaning treatment of the initial ecological membrane. The unreacted monomers remaining on the membrane surface affected the effective binding of subsequent polyaldehydes with free amino groups on the polyamide layer surface, resulting in a reduction in the amount of polymer adhering to the polyamide layer surface, thus reducing the membrane's chlorine resistance.

[0061] The reverse osmosis membrane prepared in Comparative Example 3 showed a significantly lower desalination rate after the chlorine resistance test compared to before the test. This phenomenon was due to the absence of a polyaldehyde solution, which reduced the amount of subsequent polymer adhering to the polyamide layer surface, making the amide bonds more susceptible to attack by residual chlorine.

[0062] The reverse osmosis membrane prepared in Comparative Example 4 showed a significantly lower desalination rate after the chlorine resistance test compared to before the test. This phenomenon is due to the absence of a polymer protective layer, which exposes the amide bonds to the residual chlorine solution, making them highly susceptible to attack by the high concentration of residual chlorine solution. This damages the incompletely protected amide bonds, resulting in a decrease in chlorine resistance.

[0063] The reverse osmosis membrane prepared in Comparative Example 5 showed a significantly lower desalination rate after the chlorine resistance test compared to before the test, indicating that the method of the present invention can significantly improve the chlorine resistance of the reverse osmosis membrane.

[0064] In summary, the components and preparation steps used in this invention have a synergistic effect on improving the chlorine resistance of the reverse osmosis membrane. The absence of any step or component will lead to a decrease in the chlorine resistance of the reverse osmosis membrane.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An enhanced chlorine-tolerant reverse osmosis membrane, characterized by, The device comprises a base layer, a polyamide layer, and a polymer protective layer. The polyamide layer is disposed on the base layer, and the polymer protective layer is disposed on the polyamide layer. The polyamide layer is formed by interfacial polymerization of a diamine aqueous phase and a polyacrylamide oil phase. The solute in the diamine aqueous phase includes a common amine and a specific diamine. The specific diamine includes at least one selected from 2-methyl-p-phenylenediamine, 4-methyl-1,3-phenylenediamine, 2,6-diaminotoluene, and 2,4,6-trimethyl-1,3-phenylenediamine. The diamine aqueous phase comprises 1-6 wt% of a common amine, 0.5 wt% to 2 wt% of a specific diamine, and the balance being water. The polymer protective layer is connected to the surface of the polyamide layer through polyaldehyde molecules.

2. The reinforced chlorine-tolerant reverse osmosis membrane according to claim 1, wherein The common amine includes at least one of p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, diethylenetriamine, and triethylenetetramine.

3. The reinforced chlorine-tolerant reverse osmosis membrane according to claim 1, wherein The polyacryl chloride oil phase comprises 0.1 to 0.5 wt% polyacryl chloride and the balance being an organic solvent; the polyacryl chloride is at least one of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, and trimesoyl chloride, and the organic solvent is at least one of Isopar G solvent, cyclohexane, n-hexane, and heptane.

4. The reinforced chlorine-tolerant reverse osmosis membrane according to claim 1, wherein The polyaldehydes include at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, phenylglyoxal, o-phenylenedialdehyde, trialdehyde-resorcinol, and 3,4,5-trialdehyde-1,1-biphenyl.

5. A method for preparing the reinforced chlorine-tolerant reverse osmosis membrane according to any one of claims 1 to 4, characterized by, Includes the following steps: S1: Treatment of the initial membrane The substrate was sequentially immersed in a diamine aqueous phase and a polyacryl chloride oil phase, and the resulting cleansing process yielded a nascent reverse osmosis membrane. S2: Polymer protective layer setup A multi-element aldehyde solution was coated onto a nascent reverse osmosis membrane, followed by a polymer solution, to obtain an enhanced chlorine-resistant reverse osmosis membrane.

6. The preparation method according to claim 5, characterized in that, The polyaldehyde solution comprises 1 wt% to 10 wt% polyaldehyde, 0.1 wt% to 1 wt% strong acid catalyst, and the balance being water.

7. The preparation method according to claim 5, characterized in that, The polymer solution comprises 0.5wt% to 5wt% of a polymer compound, 0.1wt% to 1wt% of a crosslinking agent, 0.05wt% to 0.5wt% of a weak acid catalyst, and the balance being water.

8. The preparation method according to claim 7, characterized in that, The polymeric compound includes at least one of polyethylene glycol, polyvinyl alcohol, tannic acid, chitosan, polyaspartic acid, and polylysine.

9. The preparation method according to claim 7, characterized in that, The crosslinking agent includes at least one of diisocyanate, phthalic anhydride, maleic anhydride, and pyromellitic anhydride.

10. The preparation method according to claim 7, characterized in that, The weak acid catalyst includes at least one of formic acid, acetic acid, propionic acid, benzoic acid, and salicylic acid.

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