Post-treatment method of polyamide desalination membrane material

Abstract

The invention relates to a post-treatment method of a polyamide desalination membrane material. The method comprises the following steps: dissolving a certain amount of transition metal salt and a small amount of citric acid in pure water to prepare a water solution with a certain concentration as a post-treatment solution A; dissolving a certain amount of hydrogen peroxide in pure water to prepare a hydrogen peroxide aqueous solution with a certain concentration, adjusting the pH value with diluted hydrochloric acid, and taking the hydrogen peroxide aqueous solution as a post-treatment solution B; the method comprises the following steps of: soaking the surface of a membrane by using a post-treatment solution A at room temperature, soaking the surface of the membrane treated by the post-treatment solution A by using a post-treatment solution B, draining the post-treatment solution after a certain time, cleaning the membrane by using a citric acid aqueous solution with a certain concentration, and cleaning the membrane by using pure water. The method disclosed by the invention is simple to operate and low in treatment cost, can effectively improve the desalination performance of the polyamide membrane material, and has a very good industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membrane preparation, and specifically refers to a post-treatment method for polyamide desalination membrane materials, specifically a method for utilizing hydroxyl radicals to reconstruct the microstructure of a separation layer of a polyamide desalination membrane material to improve the desalination performance of the membrane material. Technical Background

[0002] The global shortage of fresh water resources has become a problem of great concern to the world. In the past two decades, polyamide technology has developed rapidly. The membrane method can use less energy consumption (about 3-6kW·h / m 3 ), simpler operation and environmentally friendly characteristics to achieve seawater desalination. Therefore, membrane method gradually replaced thermal method and became the main technology for seawater desalination. Polyamide membrane has become a key material in these fields with its excellent separation performance, high selectivity and relatively stable performance.

[0003] Although polyamide membranes have many advantages, they still face some challenges and problems in practical applications, mainly including: (1) Balance between flux and rejection rate (trade-off effect): There is a mutually restrictive relationship between the flux and salt ion rejection rate of polyamide membranes, that is, increasing the flux tends to reduce the rejection rate, and vice versa; this balance relationship limits the performance of polyamide membranes in certain specific applications. (2) Membrane fouling: Membrane fouling is one of the main problems faced by polyamide membranes in practical applications. Pollutants such as suspended matter, colloids, organic matter and microorganisms in water are easily deposited on the membrane surface or in the membrane pores, resulting in a decrease in membrane flux and rejection rate, and even affecting the service life of the membrane. (3) Chlorine resistance: In some applications, such as sewage resource utilization and seawater desalination, the membrane needs to withstand the erosion of chlorine-containing water. Polyamide membranes have poor tolerance to chlorine and are easily damaged by chlorine oxidation.

[0004] In the application process of polyamide membranes, better desalination performance is required in some specific fields. However, due to the limitations of the production process, some polyamide membranes do not meet their performance requirements or the desalination performance of the membranes decreases during long-term operation. If polyamide membranes that meet the requirements are re-produced to address these problems, the economic cost will be greatly increased. If the polyamide desalination membrane material can be post-treated with a cheap and efficient method to give the membrane better separation performance, this will be of great significance to improving the desalination performance of polyamide desalination membrane materials, expanding the application field, promoting environmental protection and sustainable development, and promoting technological progress and industrial upgrading. Summary of the invention

[0005] The present invention provides a post-treatment method for improving the desalination performance of a polyamide desalination membrane material.

[0006] The technical problem to be solved by the present invention is how to quickly and effectively reconstruct the microstructure of the separation layer of the polyamide desalination membrane material to improve the desalination performance of the membrane material. The present invention cleverly utilizes the complexation between transition metal ions and functional groups such as carboxyl groups on the surface of the membrane material to achieve the enrichment of iron ions at the functional groups and play a molecular target role, and utilizes the hydroxyl radicals generated by the reaction of iron ions with hydrogen peroxide to trigger the further oxidation synthesis of the terminal amino groups on the membrane surface to form a phenazine structure, thereby increasing the cross-linking density of the membrane surface. At the same time, the hydroxyl radicals generated near the carboxyl groups can partially decompose the amide bonds to generate new terminal amino groups to continue to undergo oxidation synthesis. The formed phenazine structure can also undergo protonation reaction with the terminal carboxyl groups on the membrane surface, adjust the charge on the membrane surface, and finally achieve the improvement of the desalination performance of the polyamide membrane material.

[0007] The present invention is achieved through the following technical solutions:

[0008] A post-treatment method for a polyamide desalination membrane material, characterized in that it comprises the following steps:

[0009] S1. Dissolve a certain amount of transition metal salt and a small amount of citric acid in pure water to prepare an aqueous solution of a certain concentration as post-treatment solution A;

[0010] S2, dissolving a certain amount of 30% by mass percent hydrogen peroxide aqueous solution in pure water to prepare a certain concentration of hydrogen peroxide aqueous solution, and adjusting the pH value with dilute hydrochloric acid to prepare a post-treatment solution B;

[0011] S3. At room temperature, soak the membrane surface with post-treatment solution A, and drain the solution on the membrane surface after a certain period of time;

[0012] S4. At room temperature, the membrane treated with the post-treatment solution A is soaked with the post-treatment solution B. After a certain period of time, the post-treatment solution is drained, and then the membrane is cleaned with a citric acid aqueous solution of a certain concentration, and then the membrane is cleaned with pure water.

[0013] Preferably, the transition metal salt in the above-mentioned post-treatment method of a polyamide desalination membrane material is one or more of ferrous chloride, ferrous sulfate, cupric chloride, ferric chloride, or ferric sulfate.

[0014] Preferably, the mass percentage concentration of the transition metal salt in the above-mentioned post-treatment method of polyamide desalination membrane material is 0.5%-2%.

[0015] Preferably, in the above-mentioned post-treatment method for polyamide desalination membrane materials, the mass percentage concentration of hydrogen peroxide in the post-treatment solution B is 0.5%-2%.

[0016] Preferably, the pH value of the post-treatment solution B in the above-mentioned post-treatment method for polyamide desalination membrane materials is in the range of 3-7.

[0017] Preferably, in the above-mentioned post-treatment method for polyamide desalination membrane material, the time for soaking the surface of the polyamide membrane with the post-treatment solution A is 1-10 minutes.

[0018] Preferably, in the above-mentioned post-treatment method for polyamide desalination membrane material, the surface of the membrane sheet treated with the post-treatment solution A is immersed in the post-treatment solution B for 10-30 minutes.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The post-treatment method of the polyamide desalination membrane material provided by the present invention can effectively reconstruct the microstructure of the membrane surface, and utilize the amino groups on the membrane surface and the amino groups formed by the cleavage of the amide bonds to undergo oxidation synthesis under the action of hydroxyl radicals to form a phenazine structure, thereby improving the desalination performance of the membrane material. The polyamide membrane after post-treatment can be applied to more fields.

[0021] 2. The post-treatment method of the polyamide desalination membrane material provided by the present invention uses a cheap and easily available post-treatment agent, has a low treatment cost, and can be adapted to the post-treatment of various polyamide desalination membrane materials.

[0022] 3. The post-treatment method of the polyamide desalination membrane material provided by the present invention can be used to repair the performance of the degraded polyamide desalination membrane material, effectively extend the service life of the polyamide desalination membrane material, and reduce the waste of the desalination membrane material.

[0023] Instruction Manual

[0024] Figure 1 AFM image of the commercially available LP-RO polyamide desalination membrane (Ra = 32.9 ± 0.6 nm) in Comparative Example 1;

[0025] Figure 2 AFM images of commercially available LP-RO polyamide desalination membrane (Ra=32.9±0.6nm) and post-treated polyamide desalination membrane (Ra=33.4±0.8nm) in Example 1;

[0026] Figure 3 SEM image of the commercially available LP-RO polyamide desalination membrane in Comparative Example 1;

[0027] Figure 4 The commercially available LP-RO polyamide desalination membrane in Example 4 was post-treated, and the SEM image

[0028] Figure 5 The membrane surface N1S high-resolution XPS spectrum of the commercially available LP-RO polyamide desalination membrane in Comparative Example 1;

[0029] Figure 6The N1S high-resolution XPS spectrum of the membrane surface of the commercially available LP-RO polyamide desalination membrane after post-treatment in Example 8; DETAILED DESCRIPTION

[0030] The implementation of the present invention is specifically described below:

[0031] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the scheme of the present invention is further described. Obviously, the described embodiments are only provided as illustrations rather than limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Polyamide desalination membrane: LP-RO polyamide desalination membrane purchased from the market is soaked in 20-30℃ deionized water for 30min, then rinsed with pure water and set aside.

[0033] Prepare post-treatment solution A: a certain amount of transition metal salt and a small amount of citric acid are dissolved in pure water to prepare a post-treatment solution A with a mass percentage concentration of 0.5%-4%. The transition metal salt is one or more of ferrous chloride, ferrous sulfate, cupric chloride, ferric chloride, ferric sulfate, etc.

[0034] Preparation of post-treatment solution B: Dissolve a certain amount of 30% hydrogen peroxide aqueous solution in pure water to prepare a post-treatment solution B with a concentration of 0.5%-2%, wherein the pH value of solution B ranges from 3 to 7.

[0035] Soaking the membrane surface in post-treatment solution A: Use post-treatment solution A to soak the cleaned polyamide membrane surface for 5-10 minutes at room temperature and pressure, and drain the post-treatment solution after a certain period of time.

[0036] The membrane surface is soaked in solution B: At room temperature, after solution A is drained, the membrane treated with post-treatment solution A is immediately soaked in post-treatment solution B for 10-30 minutes, and the post-treatment solution is drained after a certain period of time. Then, it is soaked and cleaned with a certain concentration of citric acid aqueous solution, and then the membrane is washed with pure water.

[0037] The present invention evaluates the separation performance (salt rejection (R) and water flux (F)) of the polyamide membrane material: a cross-flow experiment is adopted, with 500 mg / l NaCl aqueous solution as the feed liquid, and the test is carried out under the conditions of 0.5 MPa, 25° C., and pH 7.0±0.2.

[0038] The separation performance test results of polyamide membrane are shown in the following table

[0039]

[0040]

[0041]

[0042] From the data in the above table, it can be found that post-treatment of the polyamide desalination membrane under appropriate conditions can improve the desalination performance of the membrane. When tested with 500 mg / l NaCl aqueous solution as the feed liquid, at 0.5 MPa, 25°C, and pH 7.0±0.2, the desalination rate reached a maximum of 99.4, and the flux reached a maximum of 25.53 (l / m 2 h), under certain conditions, the flux and desalination rate of polyamide desalination membrane materials can be improved simultaneously.

Claims

1. A post-treatment method for a polyamide desalination membrane material, characterized in that: The steps include: S1. Dissolving a certain amount of transition metal salt and a small amount of citric acid in pure water to prepare an aqueous solution of a certain concentration as post-treatment solution A; the transition metal salt is one or more of ferrous chloride, ferrous sulfate, cupric chloride, ferric chloride, or ferric sulfate; S2. Dissolve a certain amount of 30% hydrogen peroxide aqueous solution in pure water to prepare a certain concentration of hydrogen peroxide aqueous solution, and adjust the pH value to 3-7 with dilute hydrochloric acid to prepare a post-treatment solution B; the mass percentage concentration of hydrogen peroxide is 0.5%-2%; S3. At room temperature, soak the membrane surface with post-treatment solution A, and drain the solution on the membrane surface after a certain period of time; S4. At room temperature, the membrane treated with the post-treatment solution A is soaked with the post-treatment solution B. After a certain period of time, the post-treatment solution is drained, and then the membrane is cleaned with a citric acid aqueous solution of a certain concentration, and then the membrane is cleaned with pure water.

2. The post-treatment method of a polyamide desalination membrane material according to claim 1, characterized in that: The mass percentage concentration of the transition metal salt is 0.5%-2%.

3. The post-treatment method of a polyamide desalination membrane material according to claim 1, characterized in that: The time for soaking the membrane surface with the post-treatment solution A is 1-10 minutes.

4. The post-treatment method of a polyamide desalination membrane material according to claim 1, characterized in that: The time for soaking the membrane treated with the post-treatment solution A with the post-treatment solution B is 10-30 minutes.

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