Post-treatment, modification or repair method for polyamide composite membrane

Abstract

The invention relates to a polyamide composite membrane post-treatment, modification or repair method which comprises the following steps: (1) activating treatment: soaking a pretreated polyamide composite membrane by adopting an addition reaction oxidant, and then cleaning; and (2) grafting treatment: soaking the activated membrane with a functional monomer solution, and then cleaning. The method not only can be used for the grafting modification process of commercial polyamide nanofiltration membranes and polyamide reverse osmosis membranes and the repair process of degraded polyamide nanofiltration membranes and polyamide reverse osmosis membranes, but also can be used for the post-treatment process in the preparation stage of the polyamide nanofiltration membranes and polyamide reverse osmosis membranes, and the method is simple in process and easy to industrially apply.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to a method for post-processing, modifying or repairing a polyamide composite membrane, belonging to the technical field of post-processing modification of polyamide composite membranes and recycling of abandoned membranes after repair. Background Art

[0002] With the rapid development of industry, water shortage has become a global problem. Membrane separation technology has gradually become an important technical means to cope with the water crisis due to its advantages such as simple operation, economic efficiency, etc., 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 has room for improvement, and in actual applications, about hundreds of thousands of membrane components are scrapped every year due to performance degradation, resulting in a large amount of membrane waste, which not only causes waste of resources, but also damages the natural environment. Therefore, in order to promote the sustainable development of membrane technology, the development of post-treatment modification technology of polyamide composite membranes and repair technology of waste membranes has important research and application value and has become a new research hotspot.

[0003] CN114749029A discloses a method for repairing a polyamide composite reverse osmosis membrane. First, a polyamide reverse osmosis membrane with deteriorated performance is subjected to a diazotization reaction on the membrane surface with an acidic solution containing nitrite. Then, the diazotized membrane surface is irradiated with 365nm ultraviolet light to increase the separation layer's resistance to sodium ion penetration, thereby achieving the effect of repairing the membrane's desalination performance.

[0004] CN114307686A discloses a high-flux modification method for a polyamide composite membrane based on ether free radicals, which utilizes a modified solution containing ether free radicals generated by an oxidant and a hydrophilic ether organic substance to graft hydrophilic, electrically neutral ether small molecules on the membrane surface under heating or ultraviolet irradiation conditions, ultimately achieving a simultaneous improvement in the membrane water flux and anti-pollution ability.

[0005] CN111437729A discloses a method for repairing and modifying a discarded reverse osmosis membrane. First, sodium hypochlorite is used to degrade the surface polyamide separation layer of the discarded reverse osmosis membrane, and then tannic acid is physically coated on the membrane surface. Finally, glutaraldehyde is used for chemical crosslinking and heat treatment to finally obtain a repaired and modified reverse osmosis membrane.

[0006] These three methods are all for repairing and modifying reverse osmosis membranes, and ultraviolet light treatment or chemical agent secondary cross-linking is required during the repair or modification process. Whether they can be used to modify and repair membrane components or nanofiltration membranes in actual industrial applications remains to be discussed. Therefore, a new method for post-treatment, modification or repair of polyamide composite membranes is urgently needed to achieve a simultaneous increase in water flux and salt separation rate. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for post-treatment, modification or repair of a polyamide composite membrane. The present invention uses an addition reaction oxidant to activate the membrane surface, and then grafts functional monomers to further increase the negative charge density on the membrane surface while increasing the average effective pore size of the polyamide composite membrane and improving the pore size uniformity, thereby achieving a simultaneous increase in the water flux and salt separation rate of the polyamide composite membrane.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0010] (1) Activation treatment: soaking the pretreated polyamide composite membrane in an addition reaction oxidant and then washing it;

[0011] (2) Grafting treatment: The activated membrane is soaked in a functional monomer solution and then washed.

[0012] It should be noted that the polyamide composite membrane in the present invention includes a homemade polyamide composite membrane, a commercial polyamide composite membrane or a waste polyamide composite membrane.

[0013] The present invention first uses an addition reaction oxidant such as sodium hypochlorite to activate the membrane while cleaning the membrane, and then utilizes the conjugated diene structure obtained by activation to graft functional monomers through a diene synthesis reaction, thereby further increasing the negative charge density on the membrane surface while increasing the average effective pore size of the polyamide composite membrane and improving the pore size uniformity, and ultimately achieving the simultaneous improvement of the water flux, divalent salt retention rate and salt separation rate of the polyamide composite membrane.

[0014] As a preferred technical solution of the present invention, the pretreatment in step (1) specifically comprises: cleaning the polyamide composite membrane with a cleaning agent;

[0015] Preferably, the cleaning agent includes one of a neutral cleaning agent, an acidic cleaning agent or an alkaline cleaning agent;

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

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

[0018] Preferably, the alkaline cleaning agent comprises any one of sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution or sodium dodecyl sulfate solution, or a combination of at least two thereof. Typical but non-limiting examples include: sodium hydroxide solution and sodium carbonate solution, sodium hydroxide solution and sodium bicarbonate solution, sodium hydroxide solution and sodium dodecyl sulfate solution, sodium carbonate solution and sodium bicarbonate solution, sodium carbonate solution and sodium dodecyl sulfate solution, and sodium bicarbonate solution and sodium dodecyl sulfate solution.

[0019] As a preferred technical solution of the present invention, the addition reaction oxidant in step (1) comprises any one of potassium permanganate solution, hydrogen peroxide solution, chlorine aqueous solution, sodium chlorate solution, sodium hypochlorite solution, and sodium chlorite aqueous solution, or a combination of at least two thereof. Typical but non-limiting examples include potassium permanganate solution and hydrogen peroxide solution, chlorine aqueous solution and sodium chlorate solution, sodium hypochlorite solution and sodium chlorite aqueous 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 membrane in an oxidative addition reaction, and generally does not involve free radical intermediates in the reaction process.

[0021] In the present invention, the organic matter on the surface of the polyamide composite membrane is oxidized by an addition reaction oxidant, and 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 invention, the mass concentration of the addition reaction oxidant in step (1) is 0.1%-25%, for example 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

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

[0024] Preferably, the time for soaking the pretreated polyamide composite membrane in the addition reaction oxidant 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 is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

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

[0026] It should be noted that the polyamide composite membrane pretreated by immersion in the addition reaction oxidant refers to completely immersing the polyamide composite membrane sheet (nanofiltration membrane sheet or reverse osmosis membrane sheet) in the addition reaction oxidant solution.

[0027] It should be noted that the circulation of the addition reaction oxidant through the pretreated polyamide composite membrane means that the membrane element is installed in the membrane tube of the membrane assembly, the prepared addition reaction oxidant solution is continuously passed through the membrane tube to activate the membrane element, and the prepared addition reaction oxidant solution is circulated during the treatment process.

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

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

[0030] Preferably, the negatively charged groups include carboxyl groups and / or sulfonic acid groups;

[0031] It should be noted that the negatively charged group refers to a chemical group that can lose protons (H+) or gain electrons under specific conditions (usually in a solution) and thus has a net negative charge.

[0032] Preferably, the functional monomer is any one or at least two of butenoic acid, pentenoic acid, heptenoic acid, hexenoic acid, octenic acid, nonenoic acid, dodecenoic acid, hexadecenoic acid, octadecenoic acid, 3-propyl sulfonate potassium salt, sodium p-styrene sulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-sulfonic acid disodium, and 4,4-dinitrostilbene-2,2-disulfonic acid disodium. The invention relates to a combination of olefinic acid and butylene sulfonate, wherein the olefinic acid and butylene sulfonate are olefinic acid, butylene sulfonate and butylene sulfonate. The olefinic acid and butylene sulfonate are olefinic acid, butylene sulfonate and butylene sulfonate. The olefinic acid and butylene sulfonate are olefinic acid, butylene sulfonate and butylene sulfonate.

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

[0034] Preferably, the functional monomer solution is used to soak the activated membrane for 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 is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0035] As a preferred technical solution of the present invention, the soaking in step (2) includes soaking the activated membrane with a functional monomer solution or circulating the functional monomer solution through the activated membrane.

[0036] It should be noted that the said membrane after immersion activation treatment in the functional monomer solution refers to completely immersing the polyamide composite membrane (nanofiltration membrane or reverse osmosis membrane) in the functional monomer solution.

[0037] It should be noted that the functional monomer solution circulates through the activated membrane means that the membrane element is installed in the membrane tube of the membrane assembly, the prepared functional monomer solution is continuously passed through the membrane tube, the membrane element is subjected to post-grafting treatment or grafting repair, and the prepared functional monomer solution is circulated during the treatment process.

[0038] As a preferred technical solution of the present invention, the cleaning in step (2) specifically comprises: soaking the grafted membrane in deionized water.

[0039] Preferably, the time for soaking the grafted membrane in ion water 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 is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0040] As a preferred technical solution of the present invention, the method comprises the following steps:

[0041] (1) Activation treatment: soak 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 rinse the addition reaction oxidant with deionized water;

[0042] The pretreatment is specifically as follows: the polyamide composite membrane is cleaned with a cleaning agent; the cleaning agent includes one of a neutral cleaning agent, an acidic cleaning agent or an alkaline cleaning agent; the neutral cleaning agent includes deionized water and / or ethanol; the acidic cleaning agent includes any one of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution or a phosphoric acid solution or a combination of at least two; the alkaline cleaning agent includes any one of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution or a sodium dodecyl sulfate solution or a combination of at least two;

[0043] The addition reaction oxidant includes any one of potassium permanganate solution, hydrogen peroxide solution, chlorine aqueous solution, sodium chlorate solution, sodium hypochlorite solution, sodium chlorite aqueous solution, or a combination of at least two thereof; the soaking includes soaking the pretreated polyamide composite membrane in the addition reaction oxidant or circulating the addition reaction oxidant through the pretreated polyamide composite membrane;

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

[0045] Wherein, the functional monomer is an organic substance containing a double bond and a negatively charged group; the negatively charged group includes a carboxyl group and / or a sulfonic acid group;

[0046] The functional monomer is any one of butenoic acid, pentenoic acid, heptenoic acid, hexenoic acid, octenic acid, nonenoic acid, hempenoic acid, dodecenoic acid, hexadecenoic acid, octadecenoic acid, 3-propyl sulfonate potassium salt, sodium p-styrene sulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-sulfonic acid disodium, and 4,4-dinitrostilbene-2,2-disulfonic acid disodium, or a combination of at least two thereof; the soaking comprises soaking the activated membrane in a functional monomer solution or circulating the functional monomer solution through the activated membrane.

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

[0048] (1) The present invention first uses an addition reaction oxidant such as sodium hypochlorite to activate the membrane while cleaning the membrane, and then uses the conjugated diene structure obtained by activation to graft functional monomers through a diene synthesis reaction, thereby increasing the average effective pore size of the separation membrane and improving the pore size uniformity, and further increasing the negative charge density on the membrane surface, thereby ultimately achieving a simultaneous increase in the water flux, divalent salt rejection rate, and salt separation rate of the polyamide composite membrane;

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

[0050] (3) The addition reaction oxidant and grafting monomer used in the present invention are easy to obtain, the preparation method is simple, and they can be used at room temperature, and are easy to promote and use on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 and 1 , which are scanning electron microscope images of the post-treatment modified membrane of Example 1, wherein (a) is a surface image of the post-treatment modified membrane, and (b) is a cross-sectional image of the post-treatment modified membrane.

[0052] Figure 2 This is the 72-hour filtration result of the sodium chloride / sodium sulfate mixed salt solution of the post-treated modified membrane in Example 3. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0054] Example 1

[0055] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0056] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0057] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0058] (3) The activated membrane was immersed in 0.03 mol / L 4,4-dinitrostilbene-2,2-disulfonic acid disodium salt (MW = 474.32) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane. The scanning electron microscope image is shown in FIG. Figure 1 shown.

[0059] Example 2

[0060] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0061] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0062] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

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

[0064] Example 3

[0065] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0066] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0067] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

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

[0069] Example 4

[0070] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0071] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0072] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0073] (3) The activated membrane was soaked in 0.015 mol / L sodium vinyl sulfonate (molecular weight MW = 130.09) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane.

[0074] Example 5

[0075] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0076] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0077] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

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

[0079] Example 6

[0080] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0081] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0082] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

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

[0084] Example 7

[0085] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0086] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0087] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0088] (3) The activated membrane was immersed in a 0.015 mol / L 4,4-diaminobenzene-2,2-disulfonic acid (molecular weight MW = 370.04) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane.

[0089] Example 8

[0090] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0091] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0092] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0093] (3) The activated membrane was soaked in 0.015 mol / L 4-amino-4-nitrostilbene-2,2-sulfonic acid disodium (molecular weight MW = 400.38) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane.

[0094] Example 9

[0095] This embodiment provides a method for post-processing, modifying or repairing a polyamide composite membrane, the method comprising the following steps:

[0096] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0097] (2) Soak the pretreated membrane in a sodium hypochlorite solution with an active chlorine concentration of 6% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0098] (3) The activated membrane was soaked in 0.015 mol / L 0.0075 mol / L pentenoic acid (molecular weight MW = 100.12) solution for 6 h, and then rinsed with deionized water to obtain a post-treated modified membrane.

[0099] Example 10

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

[0101] Embodiment 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 a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable 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% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0105] (3) soaking the activated membrane in a 0.015 mol / L sodium p-styrene sulfonate (molecular weight MW = 206.19) solution for 6 h, and then rinsing with deionized water to obtain a post-treated modified membrane;

[0106] Repeat steps (1)-(2) twice to obtain a three-time 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 a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable 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% to 14% for 6 hours, and then rinse the sodium hypochlorite solution with deionized water;

[0111] (3) soaking the activated membrane in a 0.015 mol / L sodium p-styrene sulfonate (molecular weight MW = 206.19) solution for 6 h, and then rinsing 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, which is different from Example 1 only in that the step of grafting functional monomers is omitted, and only sodium hypochlorite is used to activate the polyamide nanofiltration membrane, and the rest is the same as Example 1.

[0115] Comparative Example 2

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

[0117] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

[0118] (2) Soak the pretreated membrane in a 0.015 mol / L potassium persulfate solution for 6 h, and then rinse the sodium hypochlorite solution with deionized water;

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

[0120] Comparative Example 3

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

[0122] (1) Cut a polyamide nanofiltration membrane (NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.) into a suitable size, and rinse the surface of the nanofiltration membrane with anhydrous ethanol solution to remove impurities;

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

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

[0125] Comparative Example 4

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

[0127] Comparative Example 5

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

[0129] Comparative Example 6

[0130] The comparative example is DK commercial nanofiltration membrane purchased from Suez Company.

[0131] Comparative Example 7

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

[0133] Comparative Example 8

[0134] The comparative example is NF270 commercial nanofiltration membrane purchased from Dow Chemical Company of the United States.

[0135] Performance Testing

[0136] The pure water permeation flux, sodium sulfate retention rate (2000 ppm) and sodium chloride retention rate (2000 ppm) of the polyamide nanofiltration membranes of Examples 1-12 and Comparative Examples 1-8 at 25° C. were tested. The specific process is as follows:

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

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

[0139]

[0140] Where PWP is the pure water permeation flux (Lm -2 h -1 bar -1 );V p A is the volume of permeate collected in time t (L); 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 retention rate is calculated according to the following formula:

[0142]

[0143] Among them C p and C f Represent the concentration of solute in the permeate and 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 is calculated according to the following formula:

[0145]

[0146] Where R NaCl is the retention rate of sodium chloride, R Na2SO4 is the retention rate of sodium sulfate.

[0147] In addition, the polyamide nanofiltration membrane of Example 3 was tested for salt water permeation flux, sodium sulfate retention rate and sodium chloride retention rate in a sodium chloride / sodium sulfate mixed salt solution (total concentration 2000 ppm, mass ratio 1:1) at 25° C. The specific process is as follows:

[0148] The mixed salt solution was tested using a low-pressure cross-flow device (purchased from Hangzhou Saifei Membrane Separation Technology Co., Ltd.). The effective area of ​​the tested membrane is 7 cm 2 .

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

[0150]

[0151] PWP 盐水 is the saline permeate flux (L m -2 h -1 bar -1 );V p A is the volume of permeate collected in time t (L); 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 retention rate is calculated according to the following formula:

[0153]

[0154] Among them C pi and C fi Represent the concentration of solute in the permeate and retentate respectively, obtained by ion chromatography test.

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

[0156]

[0157] Where R NaCl is the retention rate of sodium chloride, R Na2SO4 is the retention rate of sodium sulfate.

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

[0159] Table 1

[0160]

[0161]

[0162] from Figure 1 It can be seen that the surface of the post-treatment modified membrane obtained in Example 1 is smooth and flat without obvious protruding structures, indicating that functional monomers are grafted onto 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] By comparing 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, increase the retention rate of sodium chloride, but also ultimately reduce the salt retention rate and salt separation rate of the polyamide nanofiltration membrane.

[0165] By comparing Example 3 with Examples 11 and 12, it can be seen that the method for post-treatment, modification or repair of the polyamide composite membrane provided by the present invention can be repeatedly used in the repair process of discarded polyamide composite membranes, and after multiple repairs, a relatively high pure water permeation flux and salt retention rate can still be maintained.

[0166] By comparing Example 1 with Comparative Example 1, it can be seen that treating the polyamide composite membrane with only the addition reaction oxidant sodium hypochlorite solution can increase the pure water permeation flux of the membrane, but will reduce the retention rate of sodium chloride and sodium sulfate and cannot effectively improve the salt separation rate of the membrane.

[0167] By comparing Example 6 with Comparative Examples 2 and 3, it can be seen that the use of free radical oxidant potassium persulfate to activate the membrane will reduce the pure water permeation flux and salt separation rate of the polyamide nanofiltration membrane. This is mainly because the free radical oxidant potassium persulfate triggers a chain reaction by generating free radicals, resulting in the formation of a thicker resistance layer on the membrane surface, thereby reducing the water flux, increasing the retention rate of sodium chloride, and further reducing the salt separation rate of the polyamide nanofiltration membrane; in addition, the use of free radical oxidant potassium persulfate and reducing agent sodium metabisulfite to activate the membrane will also reduce the salt separation rate of the polyamide nanofiltration membrane.

[0168] By comparing Example 1 with 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 present invention, the pure water permeation flux and salt separation rate of the obtained post-treatment modified membrane are better than most commercially available polyamide nanofiltration membranes on the market.

[0169] In summary, the present invention 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 to obtain a conjugated diene structure, and then grafting functional monomers through a diene synthesis reaction. While 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 achieving a simultaneous increase in the water flux, divalent salt retention rate and salt separation rate of the polyamide composite membrane.

[0170] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

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 in an addition reaction oxidant and then washing it; (2) Grafting treatment: The activated membrane is soaked in a functional monomer solution and then washed.

2. The method according to claim 1, characterized in that The pretreatment in step (1) specifically comprises: cleaning the polyamide composite membrane with a cleaning agent; Preferably, the cleaning agent includes one of a neutral cleaning agent, an acidic cleaning agent or an alkaline cleaning agent; Preferably, the neutral cleaning agent comprises deionized water and / or ethanol; Preferably, the acid cleaning agent comprises any one of citric acid solution, hydrochloric acid solution, sulfuric acid solution or phosphoric acid solution, or a combination of at least two thereof; Preferably, the alkaline cleaning agent includes any one of sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution or sodium dodecyl sulfate solution, or a combination of at least two thereof.

3. The method according to claim 1 or 2, characterized in that: The addition reaction oxidant in step (1) comprises any one of potassium permanganate solution, hydrogen peroxide solution, chlorine aqueous solution, sodium chlorate solution, sodium hypochlorite solution, and sodium chlorite aqueous solution, or a combination of at least two thereof.

4. The method according to any one of claims 1 to 3, characterized in that: The mass concentration of the addition reaction oxidant in step (1) is 0.1%-25%; Preferably, the pH of the addition reaction oxidant is 7-14; Preferably, the pretreated polyamide composite membrane is immersed in the addition reaction oxidant for 10 minutes to 12 hours.

5. The method according to any one of claims 1 to 4, characterized in that: The soaking in step (1) includes soaking the pretreated polyamide composite membrane in an addition reaction oxidant or circulating the addition reaction oxidant through the pretreated polyamide composite membrane; Preferably, the cleaning in step (1) specifically comprises: flushing the addition reaction oxidant with deionized water.

6. The method according to any one of claims 1 to 5, characterized in that: The functional monomer in step (2) is an organic substance containing a double bond and a negatively charged group; Preferably, the negatively charged groups include carboxyl groups and / or sulfonic acid groups; Preferably, the functional monomer is any one of butenoic acid, pentenoic acid, heptenoic acid, hexenoic acid, octenoic acid, nonenoic acid, dodecenoic acid, hexadecenoic acid, octadecenoic acid, 3-propyl sulfonate potassium salt, sodium p-styrene sulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-sulfonic acid disodium, and 4,4-dinitrostilbene-2,2-disulfonic acid disodium, or a combination of at least two thereof.

7. The method according to any one of claims 1 to 6, characterized in that: The concentration of the functional monomer solution in step (2) is 0.0001 mol / L-0.08 mol / L; Preferably, the activation treated membrane is immersed in the functional monomer solution for 10 min-12 h.

8. The method according to any one of claims 1 to 7, characterized in that: The soaking in step (2) includes soaking the activated membrane with the functional monomer solution or circulating the functional monomer solution through the activated membrane.

9. The method according to any one of claims 1 to 8, characterized in that: The cleaning in step (2) specifically comprises: soaking the grafted membrane in deionized water; Preferably, the time for soaking the grafted membrane in the ion water is 10 min-12 h.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) Activation treatment: soak 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 rinse the addition reaction oxidant with deionized water; The pretreatment is specifically as follows: the polyamide composite membrane is cleaned with a cleaning agent; the cleaning agent includes one of a neutral cleaning agent, an acidic cleaning agent or an alkaline cleaning agent; the neutral cleaning agent includes deionized water and / or ethanol; the acidic cleaning agent includes any one of a citric acid solution, a hydrochloric acid solution, a sulfuric acid solution or a phosphoric acid solution or a combination of at least two; the alkaline cleaning agent includes any one of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution or a sodium dodecyl sulfate solution or a combination of at least two; The addition reaction oxidant includes any one of potassium permanganate solution, hydrogen peroxide solution, chlorine aqueous solution, sodium chlorate solution, sodium hypochlorite solution, sodium chlorite aqueous solution, or a combination of at least two thereof; the soaking includes soaking the pretreated polyamide composite membrane in the addition reaction oxidant or circulating the addition reaction oxidant through the pretreated polyamide composite membrane; (2) Grafting treatment: The activated membrane is soaked in a solution with a functional monomer concentration of 0.0001 mol / L-0.08 mol / L for 10 min-12 h, and then the grafted membrane is soaked in deionized water for 10 min-12 h; Wherein, the functional monomer is an organic substance containing a double bond and a negatively charged group; the negatively charged group includes a carboxyl group and / or a sulfonic acid group; The functional monomer is any one of butenoic acid, pentenoic acid, heptenoic acid, hexenoic acid, octenic acid, nonenoic acid, hempenoic acid, dodecenoic acid, hexadecenoic acid, octadecenoic acid, 3-propyl sulfonate potassium salt, sodium p-styrene sulfonate, sodium allyl sulfonate, sodium methacrylate sulfonate, sodium vinyl sulfonate, 4,4-diaminostilbene-2,2-disulfonic acid, 4-amino-4-nitrostilbene-2,2-sulfonic acid disodium, and 4,4-dinitrostilbene-2,2-disulfonic acid disodium, or a combination of at least two thereof; the soaking comprises soaking the activated membrane in a functional monomer solution or circulating the functional monomer solution through the activated membrane.

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