A post-treatment method for a polyamide desalination membrane material

Abstract

The application relates to a post-treatment method of a polyamide desalination membrane material. A certain amount of transition metal salt and a small amount of citric acid are dissolved in pure water to prepare an aqueous solution with a certain concentration as post-treatment solution A; a certain amount of hydrogen peroxide is dissolved in pure water to prepare a hydrogen peroxide aqueous solution with a certain concentration, and the pH value is adjusted by using dilute hydrochloric acid as post-treatment solution B; at room temperature, the membrane surface is soaked and treated by using the post-treatment solution A, and then the membrane surface treated by using the post-treatment solution A is soaked and treated by using the post-treatment solution B; after a certain time, the post-treatment solution is drained, then the membrane is cleaned by using an aqueous citric acid solution with a certain concentration, and finally the membrane is washed by using pure water. The method is simple in operation, low in treatment cost, can effectively improve the desalination performance of the polyamide membrane material, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of separation membrane preparation, and particularly relates to a post-processing method of a polyamide desalination membrane material, and particularly relates to a method for improving the desalination performance of a polyamide desalination membrane material by using hydroxyl radicals to reconstruct the microstructure of a separation layer of the polyamide desalination membrane material. TECHNICAL BACKGROUND

[0002] The global shortage of fresh water resources has become a problem that the world is very concerned about. In the past two decades, polyamide technology has developed rapidly. Membrane method can realize seawater desalination with smaller energy consumption (about 3-6 kW·h / m 3 ), simpler operation and environment-friendly characteristics. Therefore, membrane method has gradually replaced thermal method and become the main technology for seawater desalination. Polyamide membrane has become a key material in these fields due to 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 application, mainly including: (1) trade-off effect between flux and rejection rate: there is a mutual limiting relationship between the flux and the salt ion rejection rate of the polyamide membrane, that is, increasing the flux will reduce the rejection rate, and vice versa; this balance relationship limits the performance of the polyamide membrane in some specific applications. (2) membrane fouling: membrane fouling is one of the main problems faced by polyamide membranes in practical application. Suspended solids, colloids, organic matter and microorganisms in water are easy to deposit 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 application fields, such as wastewater resource utilization and seawater desalination process, the membrane needs to withstand the erosion of chlorine-containing water. The polyamide membrane has poor resistance to chlorine and is easy to be 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 production process, some polyamide membranes do not meet the performance requirements or the desalination performance of the membrane decreases during long-term operation. If the polyamide membrane that meets the requirements is produced again to cope with these problems, the economic cost will be greatly increased. If a cheap and efficient method can be used to post-process the polyamide desalination membrane material to give the membrane better separation performance, it is of great significance to improve the desalination performance of the polyamide desalination membrane material, expand the application field, promote environmental protection and sustainable development, and promote technological progress and industrial upgrading. SUMMARY

[0005] The application provides a post-processing method for improving the desalination performance of a polyamide desalination membrane material.

[0006] The technical problem to be solved by the present application is how to quickly and effectively restructure the microstructure of the separation layer of the polyamide desalination membrane material and improve the desalination performance of the membrane material. The present application ingeniously utilizes the complexation of transition metal ions with functional groups such as carboxyl groups on the surface of the membrane material, realizes the enrichment of iron ions at the functional groups and the molecular target effect, utilizes the hydroxyl radicals generated by the reaction of iron ions with hydrogen peroxide to initiate the further oxidation of the terminal amino groups on the membrane surface to form phenazine structures, and further improves the crosslinking density of the membrane surface. Meanwhile, the hydroxyl radicals generated near the carboxyl groups can partially decompose the amide bonds to generate new terminal amino groups for further oxidation and synthesis, the formed phenazine structures can further undergo protonation reaction with the terminal carboxyl groups on the membrane surface to adjust the charge on the membrane surface, and finally the desalination performance of the polyamide membrane material is improved.

[0007] The present application is realized by the following technical scheme:

[0008] A post-treatment method for a polyamide desalination membrane material, characterized by comprising the following steps:

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

[0010] S2. A certain amount of 30% mass percentage hydrogen peroxide aqueous solution is dissolved in pure water to prepare a hydrogen peroxide aqueous solution with a certain concentration, and the pH value is adjusted with dilute hydrochloric acid as post-treatment solution B;

[0011] S3. The membrane surface is soaked with the post-treatment solution A at room temperature, and the solution on the membrane surface is drained after a certain time;

[0012] S4. The membrane sheet treated by the post-treatment solution A is soaked with the post-treatment solution B at room temperature, the post-treatment solution is drained after a certain time, then the membrane sheet is washed with a citric acid aqueous solution with a certain concentration, and finally the membrane sheet is washed with pure water.

[0013] As a preferred, the transition metal salt in the post-treatment method for the polyamide desalination membrane material is one or more of ferrous chloride, ferrous sulfate, copper chloride, ferric chloride, or iron sulfate.

[0014] As a preferred, the mass percentage concentration of the transition metal salt in the post-treatment method for the polyamide desalination membrane material is 0.5%-2%.

[0015] As a preferred, the mass percentage concentration of hydrogen peroxide in the post-treatment solution B in the post-treatment method for the polyamide desalination membrane material is 0.5%-2%.

[0016] As a preferred, the pH value of the post-treatment solution B in the post-treatment method for the polyamide desalination membrane material is in the range of 3-7.

[0017] As preferred, the soaking time of the polyamide membrane in the post-processing solution A in the post-processing method of the polyamide desalination membrane material is 1-10 minutes.

[0018] As preferred, the soaking time of the polyamide membrane in the post-processing solution B in the post-processing method of the polyamide desalination membrane material is 10-30 minutes.

[0019] Compared with the prior art, the polyamide desalination membrane material provided by the application has the following advantages:

[0020] 1. The post-processing method of the polyamide desalination membrane material can effectively reconstruct the microstructure of the membrane surface, and the amino groups formed by the breaking of the amino groups and amide bonds on the membrane surface are oxidized to form phenazine structures under the action of hydroxyl radicals, thereby improving the desalination performance of the membrane material, and the post-processed polyamide membrane can be applied to more fields.

[0021] 2. The post-processing method of the polyamide desalination membrane material uses a cheap and easily available post-processing agent, has low processing cost, and can be used for the post-processing of various polyamide desalination membrane materials.

[0022] 3. The post-processing method of the polyamide desalination membrane material can be used for the performance repair of performance-deteriorated polyamide desalination membrane materials, effectively prolongs the service life of the polyamide desalination membrane materials, and reduces the waste of the desalination membrane materials.

[0023] Drawings of the specification

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

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

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

[0027] Figure 4 SEM image of the commercially available LP-RO polyamide desalination membrane sheet in Example 4 after post-processing

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

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

[0030] The following will be specifically described for the implementation of the present application:

[0031] In order to enable the above-mentioned objects, features and advantages of the present application to be more clearly understood, the scheme of the present application will be further described. Obviously, the described embodiments are only provided as illustration but not limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts, all belong to the scope of protection of the present application.

[0032] Polyamide desalination membrane: commercially available LP-RO polyamide desalination membrane, soaked in 20-30℃ deionized water for 30min, and then washed with pure water, ready for use.

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

[0034] Post-treatment solution B is configured: a certain amount of 30% mass percentage hydrogen peroxide aqueous solution is dissolved in pure water to configure post-treatment solution B with a mass percentage of 0.5%-2%, and the pH value of the B solution is in the range of 3-7.

[0035] Membrane surface immersion post-treatment solution A: the post-treatment solution A is used to soak and treat the surface of the cleaned polyamide membrane at room temperature and normal pressure for 5-10min, and the post-treatment solution is drained after a certain time.

[0036] Membrane surface immersion solution B: immediately after the solution A is drained, the post-treatment solution B is used to soak and treat the membrane surface treated by the post-treatment solution A at room temperature for 10min-30min, and the post-treatment solution is drained after a certain time. Then the membrane is soaked and cleaned with a certain concentration of citric acid aqueous solution, and then washed with pure water.

[0037] The separation performance (desalination rate (R) and water flux (F)) of the polyamide membrane material is evaluated: cross-flow experiment is adopted, 500mg / l NaCl aqueous solution is used as feed liquid, and the test is carried out under the conditions of 0.5MPa, 25℃, and pH 7.0±0.2.

[0038] The separation performance test results of the polyamide membrane membrane are as follows

[0039]

[0040]

[0041]

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

Claims

1. A method of post-treatment of a polyamide desalination membrane material, characterized by, It comprises the following steps: S1, a certain amount of transition metal salt and a small amount of citric acid are dissolved in pure water to prepare a certain concentration of aqueous solution as post-processing solution A; the transition metal salt is one or more of ferrous chloride, ferrous sulfate, copper chloride, iron chloride, or iron sulfate; S2, a certain amount of 30% mass percentage concentration of hydrogen peroxide aqueous solution is dissolved in pure water to prepare a certain concentration of hydrogen peroxide aqueous solution, and the pH value is adjusted to 3-7 with dilute hydrochloric acid as post-processing solution B; the mass percentage concentration of hydrogen peroxide is 0.5%-2%; S3, at room temperature, the membrane surface is soaked with post-processing solution A for a certain time, and then the membrane surface solution is drained; S4, at room temperature, the membrane treated by post-processing solution A is soaked with post-processing solution B for a certain time, then the post-processing solution is drained, then the membrane is cleaned with a certain concentration of citric acid aqueous solution, and then the membrane is washed with pure water.

2. The method of claim 1, wherein the polyamide desalination membrane material is post-treated by: The mass percentage concentration of the transition metal salt is 0.5%-2%.

3. The method of claim 1, wherein the polyamide desalination membrane material is post-treated by: The soaking time of the membrane surface with post-processing solution A is 1-10 minutes.

4. The method of claim 1, wherein the polyamide desalination membrane material is post-treated by: The soaking time of the membrane treated by post-processing solution A with post-processing solution B is 10-30 minutes.

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