A method for post-treatment, modification or repair of a polyamide composite membrane

Abstract

The application relates to a polyamide composite membrane post-treatment, modification or repair method, which comprises the following steps: (1) activation treatment: soaking the pretreated polyamide composite membrane by using an addition reaction oxidant, and then cleaning; (2) grafting treatment: soaking the membrane after the activation treatment by using a functional monomer solution, and then cleaning. The application can be used not only in the grafting modification process of commercial polyamide nanofiltration membranes and polyamide reverse osmosis membranes, the repair process of deteriorated polyamide nanofiltration membranes and polyamide reverse osmosis membranes, but also in the post-treatment process of the preparation stage of the polyamide nanofiltration membranes and the polyamide reverse osmosis membranes, and the process is simple and easy to be applied in industrialization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, in particular to a method for post-treatment, modification or repair of a polyamide composite membrane, and belongs to the technical field of post-treatment modification of a polyamide composite membrane and recycling of a waste membrane after repair. BACKGROUND

[0002] With the rapid development of industry, water resource shortage has become a global problem. Membrane separation technology has gradually become an important technical means to cope with water resource crisis due to its simple operation, high efficiency and other advantages, and has been widely used in water purification, seawater desalination, industrial wastewater treatment and wastewater resource utilization. However, the separation effect of existing commercial membranes still needs to be improved, and in actual application, about hundreds of thousands of membrane modules are scrapped every year due to performance degradation, generating a large amount of membrane waste, which not only causes resource waste, but also damages the natural environment. Therefore, in order to promote the sustainable development of membrane technology, it is of great research and application value to develop post-treatment modification technology of polyamide composite membrane and repair technology of waste membrane, which has become a new research hotspot.

[0003] CN114749029A discloses a method for repairing a polyamide composite reverse osmosis membrane, which first performs a membrane surface diazotization reaction on a performance-degraded polyamide reverse osmosis membrane with an acid solution containing nitrite, then performs 365nm ultraviolet light irradiation treatment on the membrane surface treated by diazotization, to improve the sodium ion permeation resistance of the separation layer and achieve the effect of repairing the desalination performance of the membrane.

[0004] CN114307686A discloses a method for high-flux modification of a polyamide composite membrane based on ether radical, which uses a modification solution containing ether radical generated by an oxidizing agent and a hydrophilic ether organic matter to graft a hydrophilic and electrically neutral ether small molecule on the membrane surface under heating or ultraviolet irradiation, to finally realize the synchronous improvement of membrane water flux and anti-fouling ability.

[0005] CN111437729A discloses a method for repairing and modifying a waste reverse osmosis membrane, which first degrades the surface polyamide separation layer of the waste reverse osmosis membrane with sodium hypochlorite, then physically coats tannic acid onto the membrane surface, and finally performs chemical cross-linking with glutaraldehyde and heat treatment, to finally obtain a repaired and modified reverse osmosis membrane.

[0006] The three methods are all aimed at repairing and modifying reverse osmosis membrane sheets, and in the process of repair or modification, ultraviolet light treatment or secondary chemical cross-linking is also required, so whether the membrane modules or nanofiltration membrane sheets in actual industrial application can be modified and repaired remains to be discussed. Therefore, a new method for post-treatment, modification or repair of a polyamide composite membrane is urgently needed to realize the synchronous improvement of water flux and salt rejection. SUMMARY

[0007] To solve the above technical problems, the present application provides a method for post-processing, modification or repair of a polyamide composite membrane. The present application uses an addition reaction oxidant to activate the membrane surface, and then grafts functional monomers. Under the premise of increasing the average effective pore size of the polyamide composite membrane and improving the pore size uniformity, the negative charge density of the membrane surface is further increased, thereby realizing the simultaneous improvement of the water flux and the salt rejection rate of the polyamide composite membrane.

[0008] To achieve this purpose, the present application uses the following technical solutions:

[0009] The present application provides a method for post-processing, modification or repair of a polyamide composite membrane, which comprises the following steps:

[0010] (1) Activation treatment: using an addition reaction oxidant to soak the pretreated polyamide composite membrane, and then washing;

[0011] (2) Grafting treatment: using a functional monomer solution to soak the activated membrane, and then washing.

[0012] It should be noted that the polyamide composite membrane in the present application includes a self-made polyamide composite membrane, a commercial polyamide composite membrane or a waste polyamide composite membrane.

[0013] The present application first uses an addition reaction oxidant such as sodium hypochlorite to activate the membrane while washing the membrane, and then uses the conjugated diene structure obtained by activation to graft functional monomers through diene synthesis reaction. Under the premise of increasing the average effective pore size of the polyamide composite membrane and improving the pore size uniformity, the negative charge density of the membrane surface is further increased, and finally the water flux, the divalent salt rejection rate and the salt rejection rate of the polyamide composite membrane are simultaneously improved.

[0014] As a preferred technical solution of the present application, the pretreatment in step (1) is specifically: using a cleaning agent to clean the polyamide composite membrane.

[0015] Preferably, the cleaning agent comprises one of a neutral cleaning agent, an acidic cleaning agent or a basic cleaning agent.

[0016] Preferably, the neutral cleaning agent comprises deionized water and / or ethanol.

[0017] Preferably, the acidic cleaning agent comprises any one or a combination of at least two of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution or a phosphoric acid solution. The typical but non-limiting examples are: a citric acid solution and a hydrochloric acid solution, a citric acid solution and a sulfuric acid solution, a citric acid solution and a phosphoric acid solution, a hydrochloric acid solution and a sulfuric acid solution, a hydrochloric acid solution and a phosphoric acid solution, a sulfuric acid solution and a phosphoric acid solution.

[0018] Preferably, the alkaline cleaning agent comprises any one or a combination of at least two of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution or a sodium dodecyl sulfate solution, such as a sodium hydroxide solution and a sodium carbonate solution, a sodium hydroxide solution and a sodium bicarbonate solution, a sodium hydroxide solution and a sodium dodecyl sulfate solution, a sodium carbonate solution and a sodium bicarbonate solution, a sodium carbonate solution and a sodium dodecyl sulfate solution, a sodium bicarbonate solution and a sodium dodecyl sulfate solution.

[0019] As a preferred technical solution of the present application, the addition reaction oxidant in step (1) comprises any one or a combination of at least two of a potassium permanganate solution, a hydrogen peroxide solution, an aqueous chlorine solution, a sodium chlorate solution, a sodium hypochlorite solution, and an aqueous sodium chlorite solution, such as a potassium permanganate solution and a hydrogen peroxide solution, an aqueous chlorine solution and a sodium chlorate solution, a sodium hypochlorite solution and an aqueous sodium chlorite solution, etc.

[0020] It should be noted that the addition reaction oxidant refers to an oxidant that can directly attack the functional groups on the surface of the polyamide composite membrane in the oxidation addition reaction, and the oxidant usually does not involve free radical intermediates in the reaction process.

[0021] In the present application, the organic matter on the surface of the polyamide composite membrane is treated by the addition reaction oxidant, and at the same time, the addition reaction occurs with the groups on the surface of the polyamide composite membrane, thereby obtaining a conjugated diene structure, which is helpful for the subsequent grafting reaction.

[0022] As a preferred technical solution of the present application, the mass concentration of the addition reaction oxidant in step (1) is 0.1% to 25%, such as 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0023] Preferably, the pH of the addition reaction oxidant is 7 to 14, such as 7, 8, 9, 10, 11, 12, 13, 14, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0024] Preferably, the time for the addition reaction oxidant to soak the pretreated polyamide composite membrane is 10 minutes to 12 hours, such as 10 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0025] As a preferred technical solution of the present application, the soaking in step (1) comprises soaking the pretreated polyamide composite membrane in the addition reaction oxidant or circulating the addition reaction oxidant through the pretreated polyamide composite membrane.

[0026] It should be noted that the soaking of the polyamide composite membrane after the addition reaction oxidant pre-treatment refers to the complete immersion of the polyamide composite membrane (nanofiltration membrane or reverse osmosis membrane) in the addition reaction oxidant solution.

[0027] It should be noted that the circulation of the addition reaction oxidant through the pre-treated polyamide composite membrane refers to the installation of the membrane element in the membrane tube of the membrane module, the uninterrupted passage of the prepared addition reaction oxidant solution through the membrane tube, the activation pre-treatment of the membrane element, and the recycling of the prepared addition reaction oxidant solution during the treatment process.

[0028] Preferably, the cleaning in step (1) is specifically flushing the addition reaction oxidant with deionized water.

[0029] As a preferred technical solution of the present application, the functional monomer in step (2) is an organic compound containing a double bond and a negatively charged group.

[0030] Preferably, the negatively charged group includes a carboxyl group and / or a sulfonic acid group.

[0031] It should be noted that the negatively charged group refers to a chemical group that can lose a proton (H+) or gain an electron under certain conditions (usually in solution), thereby carrying a net negative charge.

[0032] Preferably, the functional monomer is any one of butenolic acid, pentenolic acid, heptenolic acid, hexenolic acid, octenolic acid, nonenolic acid, sunflower acid, dodecenolic acid, hexadecenolic acid, octadecenolic acid, 3-sulfopropyl potassium salt, p-styrene sulfonic acid sodium, allyl sulfonic acid sodium, methacryl sulfonic acid sodium, vinyl sulfonic acid sodium, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-disulfonic acid disodium, 4,4-dinitrostilbene-2,2-disulfonic acid disodium, or a combination of at least two thereof, and the typical but non-limiting examples are: butenolic acid and pentenolic acid, heptenolic acid and hexenolic acid, octenolic acid and nonenolic acid, sunflower acid and dodecenolic acid, hexadecenolic acid and octadecenolic acid, 3-sulfopropyl potassium salt and p-styrene sulfonic acid sodium, allyl sulfonic acid sodium and methacryl sulfonic acid sodium, vinyl sulfonic acid sodium and 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-disulfonic acid disodium and 4,4-dinitrostilbene-2,2-disulfonic acid disodium, etc.

[0033] Preferably, the concentration of the functional monomer solution in step (2) is 0.0001 mol / L-0.08 mol / L, for example, 0.0001 mol / L, 0.001 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, etc., but not limited to the listed values, and other values not listed in the above range are also applicable.

[0034] Preferably, the time for the functional monomer solution to soak the activated film is 10 min-12 h, for example, 10 min, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, etc., but not limited to the listed values, and other values not listed in the above range are also applicable.

[0035] Preferably, the soaking in step (2) includes soaking the activated film in the functional monomer solution or circulating the functional monomer solution through the activated film.

[0036] It should be noted that the soaking of the activated film in the functional monomer solution means that the polyamide composite membrane (nanofiltration membrane or reverse osmosis membrane) is completely soaked in the functional monomer solution.

[0037] It should be noted that the circulation of the functional monomer solution through the activated film means that the membrane element is installed in the membrane tube of the membrane module, and the prepared functional monomer solution is continuously passed through the membrane tube to graft the membrane element for post-treatment or repair, and the prepared functional monomer solution is recycled during the treatment process.

[0038] Preferably, the washing in step (2) is soaking the grafted film in deionized water.

[0039] Preferably, the time for the ionized water to soak the grafted film is 10 min-12 h, for example, 10 min, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, etc., but not limited to the listed values, and other values not listed in the above range are also applicable.

[0040] Preferably, the method comprises the following steps:

[0041] (1) Activation treatment: soaking the pretreated polyamide composite membrane in an addition reaction oxidant with a mass concentration of 0.1%-25% and a pH of 7-14 for 10 min-12 h, and then rinsing the addition reaction oxidant with deionized water;

[0042] The pre-treatment is specifically cleaning the polyamide composite membrane with a cleaning agent; the cleaning agent comprises one of a neutral cleaning agent, an acidic cleaning agent or a basic cleaning agent; the neutral cleaning agent comprises deionized water and / or ethanol; the acidic cleaning agent comprises any one or a combination of at least two of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution or a phosphoric acid solution; the basic cleaning agent comprises any one or a combination of at least two of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution or a sodium dodecyl sulfate solution;

[0043] The addition reaction oxidant comprises any one or a combination of at least two of a potassium permanganate solution, a hydrogen peroxide solution, a chloric water solution, a sodium chlorate solution, a sodium hypochlorite solution and a sodium chlorite solution; the soaking comprises soaking the pre-treated polyamide composite membrane with the addition reaction oxidant or circulating the addition reaction oxidant through the pre-treated polyamide composite membrane;

[0044] (2) Grafting treatment: soaking the activated membrane with a solution of the functional monomer at a concentration of 0.0001 mol / L-0.08 mol / L for 10 min-12 h, and then soaking the grafted membrane with deionized water for 10 min-12 h;

[0045] The functional monomer is an organic compound containing a double bond and a negatively charged group; the negatively charged group comprises a carboxyl group and / or a sulfonic acid group;

[0046] The functional monomer is any one or a combination of at least two of butenyl acid, pentenyl acid, heptenyl acid, hexenyl acid, octenyl acid, nonenyl acid, decenyl acid, hexadecenyl acid, octadecenyl acid, 3-sulfopropyl potassium salt, sodium p-styrenesulfonate, sodium allylsulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, disodium 4-amino-4-nitrostilbene-2,2-disulfonate and disodium 4,4-dinitrostilbene-2,2-disulfonate; the soaking comprises soaking the activated membrane with the functional monomer solution or circulating the functional monomer solution through the activated membrane.

[0047] Compared with the prior art, the present application has at least the following beneficial effects:

[0048] (1) The present application first uses an addition reaction oxidant such as sodium hypochlorite to activate the membrane while cleaning the membrane, and then grafts the functional monomer through the diene synthesis reaction by using the conjugated diene structure obtained by activation, which can increase the average effective pore size of the separation membrane, improve the pore size uniformity, further increase the negative charge density on the surface of the membrane, and ultimately realize the synchronous improvement of the water flux, the divalent salt retention rate and the salt separation rate of the polyamide composite membrane;

[0049] (2) The present application can be used not only in the repair process of deteriorated polyamide nanofiltration membranes and polyamide reverse osmosis membranes, the graft modification process of commercial polyamide nanofiltration membranes and polyamide reverse osmosis membranes, but also in the post-treatment process in the preparation stage of polyamide nanofiltration membranes and polyamide reverse osmosis membranes.

[0050] (3) The addition reaction oxidant and the graft monomer used in the present application are easy to obtain, the configuration method is simple, and the present application can be used at room temperature, and is easy to be used on a large scale. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 Figure 1 is a scanning electron microscope picture of the post-treatment modified membrane of Example 1, (a) is a surface picture of the post-treatment modified membrane, and (b) is a cross-section picture of the post-treatment modified membrane.

[0052] Figure 2 Figure 3 is the filtration result of the sodium chloride / sodium sulfate mixed salt solution of the post-treatment modified membrane of Example 3 for 72 hours. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be further described below by combining the drawings and through specific embodiments. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0054] Example 1

[0055] The present embodiment provides a method for post-treatment, modification or repair of a polyamide composite membrane, which comprises the following steps:

[0056] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) is cut to an appropriate size, and the surface of the nanofiltration membrane is rinsed with anhydrous ethanol solution to remove impurities;

[0057] (2) A sodium hypochlorite solution with an active chlorine concentration of 6%-14% is selected to soak the pretreated membrane for 6 hours, and then the sodium hypochlorite solution is rinsed clean with deionized water;

[0058] (3) A 0.03 mol / L 4,4-dinitrostilbene-2,2 disodium disulfonate (molecular weight MW = 474.32) solution is used to soak the activated treated membrane for 6 hours, and then the post-treatment modified membrane is obtained by rinsing with deionized water, and the scanning electron microscope picture thereof is shown in Figure 1. Figure 1

[0059] Example 2

[0060] The present embodiment provides a method for post-treatment, modification or repair of a polyamide composite membrane, which comprises the following steps:

[0061] ​(1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to the appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0062] (2) The pre-processed membrane was soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution was rinsed clean with deionized water;

[0063] (3) The activated treated membrane was soaked in a 0.06mol / L 4,4-dinitrostilbene-2,2 disodium sulfonate (molecular weight MW=474.32) solution for 6h, and then rinsed with deionized water to obtain the post-processed modified membrane.

[0064] Example 3

[0065] The present embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, which comprises the following steps:

[0066] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to the appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0067] (2) The pre-processed membrane was soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution was rinsed clean with deionized water;

[0068] (3) The activated treated membrane was soaked in a 0.015mol / L sodium p-styrenesulfonate (molecular weight MW=206.19) solution for 6h, and then rinsed with deionized water to obtain the post-processed modified membrane.

[0069] Example 4

[0070] The present embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, which comprises the following steps:

[0071] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to the appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0072] (2) The pre-processed membrane was soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution was rinsed clean with deionized water;

[0073] (3) The activated treated membrane was soaked in a 0.015mol / L sodium p-styrenesulfonate (molecular weight MW=206.19) solution for 6h, and then rinsed with deionized water to obtain the post-processed modified membrane.

[0074] Example 5

[0075] The embodiment provides a polyamide composite membrane post-treatment, modification or repair method, and the method comprises the following steps:

[0076] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) is cut to an appropriate size, the surface of the nanofiltration membrane is rinsed with anhydrous ethanol solution, and impurities are removed;

[0077] (2) The pretreated membrane is soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution is rinsed clean with deionized water;

[0078] (3) The activated treated membrane is soaked in a 0.015mol / L sodium allyl sulfonate (molecular weight MW=144.1) solution for 6h, and then rinsed with deionized water to obtain a post-treatment modified membrane.

[0079] Example 6

[0080] The embodiment provides a polyamide composite membrane post-treatment, modification or repair method, and the method comprises the following steps:

[0081] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) is cut to an appropriate size, the surface of the nanofiltration membrane is rinsed with anhydrous ethanol solution, and impurities are removed;

[0082] (2) The pretreated membrane is soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution is rinsed clean with deionized water;

[0083] (3) The activated treated membrane is soaked in a 0.015mol / L 3-sulfopropyl methacrylate potassium salt (molecular weight MW=246.32) solution for 6h, and then rinsed with deionized water to obtain a post-treatment modified membrane.

[0084] Example 7

[0085] The embodiment provides a polyamide composite membrane post-treatment, modification or repair method, and the method comprises the following steps:

[0086] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) is cut to an appropriate size, the surface of the nanofiltration membrane is rinsed with anhydrous ethanol solution, and impurities are removed;

[0087] (2) The pretreated membrane is soaked in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6h, and then the sodium hypochlorite solution is rinsed clean with deionized water;

[0088] (3) 0.015 mol / L 4,4-diaminostilbene-2,2-disulfonic acid (molecular weight MW = 370.04) solution was used to soak the activated membrane for 6 h, and then the membrane was washed with deionized water to obtain the post-treatment modified membrane.

[0089] Example 8

[0090] The present example provides a method for post-treatment, modification or repair of a polyamide composite membrane, which comprises the following steps:

[0091] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to an appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0092] (2) A sodium hypochlorite solution with an active chlorine concentration of 6%-14% was used to soak the pretreated membrane for 6 h, and then the sodium hypochlorite solution was washed clean with deionized water;

[0093] (3) 0.015 mol / L 4-aminostilbene-2,2-sulfonic acid disodium salt (molecular weight MW = 400.38) solution was used to soak the activated membrane for 6 h, and then the membrane was washed with deionized water to obtain the post-treatment modified membrane.

[0094] Example 9

[0095] The present example provides a method for post-treatment, modification or repair of a polyamide composite membrane, which comprises the following steps:

[0096] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to an appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0097] (2) A sodium hypochlorite solution with an active chlorine concentration of 6%-14% was used to soak the pretreated membrane for 6 h, and then the sodium hypochlorite solution was washed clean with deionized water;

[0098] (3) 0.015 mol / L 0.0075 mol / L pentenoic acid (molecular weight MW = 100.12) solution was used to soak the activated membrane for 6 h, and then the membrane was washed with deionized water to obtain the post-treatment modified membrane.

[0099] Example 10

[0100] The present example provides a method for post-treatment, modification or repair of a polyamide composite membrane, which is different from Example 1 only in that the concentration of 4,4-dinitrostilbene-2,2-disulfonic acid disodium salt (molecular weight MW = 474.32) is adjusted to 0.1 mol / L, and the rest is the same as Example 1.

[0101] Example 11

[0102] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0103] (1) Cut the polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into appropriate size and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0104] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0105] (3) The activated membrane was soaked in a 0.015 mol / L sodium p-styrenesulfonate (molecular weight MW = 206.19) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane;

[0106] Repeat steps (1)-(2) twice to obtain a three-step post-treatment modified membrane.

[0107] Example 12

[0108] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0109] (1) Cut the polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into appropriate size and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0110] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6%-14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0111] (3) The activated membrane was soaked in a 0.015 mol / L sodium p-styrenesulfonate (molecular weight MW = 206.19) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane;

[0112] Repeat steps (1)-(2) four times to obtain five post-treatment modified membranes.

[0113] Comparative Example 1

[0114] This comparative example provides a method for post-treatment, modification or repair of a polyamide composite membrane. The only difference from Example 1 is that the step of grafting functional monomers is omitted, and only sodium hypochlorite is used to activate the polyamide nanofiltration membrane. The rest is the same as Example 1.

[0115] Comparative Example 2

[0116] The present comparative example provides a method for post-treatment, modification or repair of a polyamide composite membrane, comprising the following steps:

[0117] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to an appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0118] (2) The pretreated membrane was soaked in 0.015 mol / L potassium persulfate solution for 6 h, and then the sodium hypochlorite solution was rinsed clean with deionized water;

[0119] (3) The activated treated membrane was soaked in 0.015 mol / L 3-sulfopropyl methacrylate potassium salt (molecular weight MW = 246.32) solution for 6 h, and then rinsed with deionized water to obtain a post-treatment modified membrane.

[0120] Comparative Example 3

[0121] The present comparative example provides a method for post-treatment, modification or repair of a polyamide composite membrane, comprising the following steps:

[0122] (1) The polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) was cut to an appropriate size, and the surface of the nanofiltration membrane was rinsed with anhydrous ethanol solution to remove impurities;

[0123] (2) The pretreated membrane was soaked in 0.015 mol / L potassium persulfate and sodium metabisulfite solution for 6 h, and then the sodium hypochlorite solution was rinsed clean with deionized water;

[0124] (3) The activated treated membrane was soaked in 0.015 mol / L 3-sulfopropyl methacrylate potassium salt (molecular weight MW = 246.32) solution for 6 h, and then rinsed with deionized water to obtain a post-treatment modified membrane.

[0125] Comparative Example 4

[0126] The present comparative example is a NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.

[0127] Comparative Example 5

[0128] The present comparative example is a NF30 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.

[0129] Comparative Example 6

[0130] The present comparative example is a DK commercial nanofiltration membrane, purchased from Suez.

[0131] Comparative Example 7

[0132] This comparative example is XC-N commercial nanofiltration membrane, purchased from Suez.

[0133] Comparative Example 8

[0134] This comparative example is NF270 commercial nanofiltration membrane, purchased from Dow Chemical Company, USA.

[0135] Performance test

[0136] The pure water permeate flux, sodium sulfate rejection (2000 ppm) and sodium chloride rejection (2000 ppm) of the polyamide nanofiltration membranes of Test Examples 1-12 and Comparative Examples 1-8 at 25°C were tested according to the following procedure:

[0137] The low-pressure cross-flow device (purchased from Hangzhou Saifi Membrane Separation Technology Co., Ltd.) was used to test the pure water permeate flux and inorganic salt rejection. The effective area of the membrane was 7 cm 2 The filtration process was carried out in a full circulation mode at a pressure of 5 bar and a cross-flow flow rate of 40 L / H.

[0138] (1) The pure water permeate flux was calculated according to the following formula:

[0139]

[0140] Where PWP is the pure water permeate flux (Lm -2 h -1 bar -1 ); V p is the volume of permeate collected in t time (L); A m is the effective membrane area (m 2 ); t is the running time (h); and TMP is the transmembrane pressure (bar).

[0141] (2) The inorganic salt rejection was calculated according to the following formula:

[0142]

[0143] Where C p and C f represent the concentration of solute in the permeate and the retentate, respectively: for inorganic salt solutions, the concentration ratio can be replaced by the conductivity ratio.

[0144] (3) The sodium chloride / sodium sulfate separation factor was calculated according to the following formula:

[0145]

[0146] Where R NaCl is the sodium chloride rejection, and R Na2SO4 is the sodium sulfate rejection.

[0147] In addition, the salt water permeate flux, sodium sulfate rejection and sodium chloride rejection of the polyamide nanofiltration membrane of Example 3 in a sodium chloride / sodium sulfate mixed salt solution (total concentration 2000 ppm, mass ratio 1:1) at 25°C were also tested, in particular as follows:

[0148] A low pressure cross-flow device (purchased from Hangzhou Saifi Membrane Separation Technology Co., Ltd.) was used to test the mixed salt solution. The effective area of the tested membrane was 7 cm 2 .

[0149] (1 ') The salt water permeate flux was calculated according to the following formula:

[0150]

[0151] Where PWP 盐水 is the salt water permeate flux (L m -2 h -1 bar -1 ); V p is the volume of permeate collected in t time (L); A m is the effective membrane area (m 2 ); t is the running time (h); and TMP is the transmembrane pressure (bar).

[0152] (2 ') The inorganic salt rejection was calculated according to the following formula:

[0153]

[0154] Where C pi and C fi represent the concentrations of solutes in the permeate and the retained liquid, respectively, obtained by ion chromatography testing.

[0155] (3 ') The sodium chloride / sodium sulfate separation factor was calculated according to the following formula:

[0156]

[0157] Where R NaCl is the sodium chloride rejection, and R Na2SO4 is the sodium sulfate rejection.

[0158] Table 1 is the test result of the post-treatment modified membranes of Examples 1-12 and Comparative Examples 1-8, Figure 2 is the 72-hour filtration result of the sodium chloride / sodium sulfate mixed salt solution of the post-treatment modified membrane of Example 3.

[0159] Table 1

[0160]

[0161]

[0162] From Figure 1 It can be seen that the post-treatment modified membrane obtained in Example 1 has a smooth surface without obvious protruding structures, indicating that the functional monomer is grafted on the membrane surface.

[0163] From Figure 2 It can be seen that the post-treatment modified membrane obtained in Example 3 has good long-term stability.

[0164] From the comparison of Example 1, Example 2 and Example 10, it can be seen that increasing the concentration of the functional monomer solution will not only reduce the pure water permeation flux of the polyamide nanofiltration membrane, but also increase the sodium chloride rejection rate, and finally reduce the salt rejection rate and the salt separation rate of the polyamide nanofiltration membrane.

[0165] From the comparison of Example 3, Example 11 and Example 12, it can be seen that the method for post-treatment, modification or repair of the polyamide composite membrane provided by the application can be repeatedly used in the repair process of the waste polyamide composite membrane, and after multiple repairs, the polyamide composite membrane can still maintain a high pure water permeation flux and a high salt rejection rate.

[0166] From the comparison of Example 1 and Comparative Example 1, it can be seen that only using the addition reaction oxidant sodium hypochlorite solution to treat the polyamide composite membrane can increase the pure water permeation flux of the membrane, but will reduce the sodium chloride and sodium sulfate rejection rates, and cannot effectively improve the salt separation rate of the membrane.

[0167] From the comparison of Example 6 and Comparative Examples 2 and 3, it can be seen that the activation treatment process of the membrane using the free radical oxidant potassium persulfate will reduce the pure water permeation flux and the salt separation rate of the polyamide nanofiltration membrane. This is mainly because the free radical oxidant potassium persulfate generates free radicals to initiate a chain reaction, resulting in the formation of a relatively thick resistance layer on the membrane surface, thereby reducing the water flux, increasing the sodium chloride rejection rate, and further reducing the salt separation rate of the polyamide nanofiltration membrane. In addition, the activation treatment of the membrane using the free radical oxidant potassium persulfate and the reducing agent sodium pyrosulfite will also reduce the salt separation rate of the polyamide nanofiltration membrane.

[0168] From the comparison of Example 1 and Comparative Examples 4-8, it can be seen that the method for post-treatment, modification or repair of the polyamide composite membrane provided by the application has a pure water permeation flux and a salt separation rate that are superior to those of most commercially available polyamide nanofiltration membranes on the market.

[0169] In summary, the application provides a method for post-treatment, modification or repair of a polyamide composite membrane. By using an addition reaction oxidant to activate the membrane while cleaning the membrane, a conjugated diene structure is obtained, and then a functional monomer is grafted through a diene synthesis reaction. Under the premise of increasing the average effective pore size of the separation membrane and improving the pore size uniformity, the negative charge density on the membrane surface is further increased, thereby realizing the simultaneous improvement of the water flux, the divalent salt rejection rate and the salt separation rate of the polyamide composite membrane.

[0170] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application, which can be easily thought of by any person skilled in the art, falls within the protection scope and disclosure scope of the present application.

Claims

1. A method for post-treatment, modification or repair of a polyamide composite membrane, characterized in that, The method comprises the following steps: (1) Activation treatment: soaking the pretreated polyamide composite membrane with an addition reaction oxidant, and then cleaning; the addition reaction oxidant in step (1) comprises any one or a combination of at least two of a potassium permanganate solution, a hydrogen peroxide solution, a chlorine water solution, a sodium chlorate solution, a sodium hypochlorite solution, and a sodium chlorite aqueous solution; (2) Grafting treatment: soaking the membrane after the activation treatment with a functional monomer solution, and then cleaning; The functional monomer in step (2) is an organic substance containing a double bond and a negatively charged group; the negatively charged group comprises a carboxyl group and / or a sulfonic acid group.

2. The method of claim 1, wherein, The pretreatment in step (1) specifically comprises: cleaning the polyamide composite membrane with a cleaning agent.

3. The method of claim 2, wherein, The cleaning agent comprises one of a neutral cleaning agent, an acidic cleaning agent, or a basic cleaning agent.

4. The method of claim 3, wherein, The neutral cleaning agent comprises deionized water and / or ethanol.

5. The method of claim 3, wherein, The acidic cleaning agent comprises any one or a combination of at least two of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution, or a phosphoric acid solution.

6. The method of claim 3, wherein, The basic cleaning agent comprises any one or a combination of at least two of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, or a sodium dodecyl sulfate solution.

7. The method of claim 1, wherein, The mass concentration of the addition reaction oxidant in step (1) is 0.1%-25%.

8. The method of claim 1, wherein, The pH of the addition reaction oxidant is 7-14.

9. The method of claim 1, wherein, The soaking time of the addition reaction oxidant on the pretreated polyamide composite membrane is 10 min-12 h.

10. The method of claim 1, wherein, The soaking in step (1) comprises soaking the pretreated polyamide composite membrane with the addition reaction oxidant or circulating the addition reaction oxidant through the pretreated polyamide composite membrane.

11. The method of claim 1, wherein, The cleaning in step (1) specifically comprises: rinsing the addition reaction oxidant clean with deionized water.

12. The method according to claim 1, characterized in that The functional monomer is any one or a combination of at least two of butenolic acid, pentenolic acid, heptenolic acid, hexenolic acid, octenolic acid, nonenolic acid, sunflower acid, dodecenolic acid, hexadecenolic acid, octadecenolic acid, 3-sulfopropyl potassium salt, sodium p-styrenesulfonate, sodium allylsulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-disulfonic acid disodium, and 4,4-dinitrostilbene-2,2-disulfonic acid disodium.

13. The method of claim 1, wherein, The concentration of the functional monomer solution in step (2) is 0.0001 mol / L-0.08 mol / L.

14. The method of claim 1, wherein, The soaking time of the functional monomer solution on the activated membrane is 10 min-12 h.

15. The method of claim 1, wherein, The soaking in step (2) comprises soaking the activated membrane with the functional monomer solution or circulating the functional monomer solution through the activated membrane.

16. The method of claim 1, wherein, The cleaning in step (2) specifically comprises: soaking the membrane after the grafting treatment with deionized water.

17. The method of claim 16, wherein, The soaking time of the deionized water on the membrane after the grafting treatment is 10 min-12 h.

18. The method of claim 1, wherein, The method comprises the following steps: (1) Activation treatment: soaking the pretreated polyamide composite membrane with an addition reaction oxidant with a mass concentration of 0.1%-25% and a pH of 7-14 for 10 min-12 h, and then rinsing the addition reaction oxidant clean with deionized water; The pre-treatment specifically comprises: cleaning the polyamide composite membrane with a cleaning agent; the cleaning agent comprises one of a neutral cleaning agent, an acidic cleaning agent or a basic cleaning agent; the neutral cleaning agent comprises deionized water and / or ethanol; the acidic cleaning agent comprises any one or a combination of at least two of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution or a phosphoric acid solution; the basic cleaning agent comprises any one or a combination of at least two of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution or a sodium dodecyl sulfate solution; The addition reaction oxidant comprises any one or a combination of at least two of a potassium permanganate solution, a hydrogen peroxide solution, a chlorine water solution, a sodium chlorate solution, a sodium hypochlorite solution or a sodium chlorite aqueous solution; the soaking comprises soaking the pre-treated polyamide composite membrane in the addition reaction oxidant or circulating the addition reaction oxidant through the pre-treated polyamide composite membrane; (2) Grafting treatment: soaking the activated membrane in a solution of a functional monomer with a concentration of 0.0001 mol / L-0.08 mol / L for 10 min-12 h, and then soaking the grafted membrane in deionized water for 10 min-12 h; The functional monomer is an organic compound containing a double bond and a negatively charged group; the negatively charged group comprises a carboxyl group and / or a sulfonic acid group; The functional monomer is any one or a combination of at least two of butenolic acid, pentenolic acid, heptenolic acid, hexenolic acid, octenolic acid, nonenolic acid, sunflower acid, dodecenolic acid, hexadecenolic acid, octadecenolic acid, 3-sulfopropyl potassium salt, p-styrenesulfonic acid sodium, allyl sulfonic acid sodium, methacrylate sulfonic acid sodium, vinyl sulfonic acid sodium, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-disulfonic acid disodium, 4,4-dinitrostilbene-2,2-disulfonic acid disodium; the soaking comprises soaking the activated membrane in the functional monomer solution or circulating the functional monomer solution through the activated membrane.

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