A method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane

Abstract

The present invention discloses a method for in-situ construction of a multi-component modified layer on the surface of an anion exchange membrane: step (1), coupling electrodeposition and co-deposition method to deposit and construct a first negatively charged modified layer on the surface of the anion exchange membrane; step (2), coupling electrodeposition and co-deposition method to deposit and construct a first positively charged modified layer on the surface of the first negatively charged modified layer; step (3), repeating step (1) to construct a second negatively charged modified layer on the surface of the first positively charged modified layer; ... step (2n), repeating step (2) to construct an nth positively charged modified layer on the surface of the nth negatively charged modified layer; step (2n+1), repeating step (1) to construct an n+1th negatively charged modified layer on the surface of the nth positively charged modified layer; n is greater than or equal to 1. The present invention can solve the problem that the existing anion exchange membrane cannot take into account good anti-pollution performance, stable modified layer and in-situ construction of modified layer.

Description

Technical Field

[0001] The present invention relates to the technical field of anion exchange membranes. Specifically, it is a method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane. Background Art

[0002] Electrodialysis utilizes the selective permeability of ion exchange membranes to cations and anions. Under the action of a direct current electric field, cations and anions migrate directionally, thereby achieving the purposes of separating, purifying, and concentrating electrolyte solutions. Compared with reverse osmosis technology, electrodialysis has the advantages of a high concentration multiple of concentrated water (the salt content of concentrated water can reach 15% - 20%), the desalination rate of fresh water can be artificially controlled, and membrane fouling can be significantly reduced by frequent electrode reversal. Therefore, it has also attracted much attention in the field of industrial wastewater desalination. When this technology is used for industrial wastewater desalination, organic substances and other impurity components in the wastewater will cause membrane fouling, thereby affecting the desalination performance. The prevention and control of electrodialysis membrane fouling is of great significance for promoting the application of electrodialysis in industrial wastewater treatment. Compared with cation exchange membranes, anion exchange membranes are more easily adsorbed by negatively charged organic substances in the wastewater to form membrane fouling, and the membrane fouling is more serious. Therefore, the development of anion exchange membranes with good anti-fouling performance is of great significance for promoting the popularization and application of this technology in the field of industrial wastewater desalination.

[0003] So far, there have been many studies on membrane modification to improve the anti-fouling performance of anion exchange membranes. For example, SriMulyati et al. (Journal of Membrane Science. 2012, 417 / 418: 137-143.) deposited anionic polyelectrolyte sodium polystyrene sulfonate on the surface of the anion exchange membrane by electrodeposition to improve its anti-fouling performance. The study found that the modified layer effectively improved the negative charge density and hydrophilicity of the surface, thus effectively inhibiting the fouling of sodium dodecylbenzenesulfonate on the anion membrane. However, the modified layer and the membrane surface are only combined by electrostatic force, so the stability of the modified layer is poor. Li Yujiao et al. (Journal of Membrane Science, 2018, 566: 44-53.) first constructed a graphene oxide modified layer on the surface of the anion exchange membrane by electrodeposition, and then used dopamine self-polymerization encapsulation to improve the stability of the modified layer; the study found that the stability and compactness of the modified layer of the composite modified membrane are better than those of the conventional electrodeposition modified membrane, so its anti-fouling performance is better; however, this modification method has the defects of requiring step-by-step operation and being unable to complete the modification in-situ. Once the modified layer is damaged during long-term actual operation, the reconstruction of the modified layer will be very cumbersome. Shen Jiangnan et al. (CN 105709607 A) constructed a self-polymerized modified layer on the surface of the anion exchange membrane by the method of dopamine self-polymerization, and improved the uniformity of the modified layer by adding stirring and aeration, thus effectively improving the ability of the anion membrane to inhibit the pollution of the anionic surfactant sodium dodecylbenzenesulfonate. Subsequently, the same researcher (CN 11473356 A) further grafted a gentamicin-based polymer on the surface of the dopamine-modified anion exchange membrane to improve its ability to inhibit biological fouling. However, these two modification methods still have the problems of requiring off-site operation and being unable to perform directional modification.

[0004] In summary, the currently obtained modified membranes still have the problems of being unable to take into account good anti-fouling performance, stable modified layers, and the ability to construct modified layers in-situ, and it is difficult to completely solve the membrane fouling problem in the electrodialysis system. Therefore, there is an urgent need for a technology that can construct a stable modified layer with good anti-fouling performance on the surface of the anion exchange membrane in-situ without disassembling the membrane stack. Summary of the Invention

[0005] For this reason, the technical problem to be solved by the present invention is to provide a method for in-situ constructing a multi-component modified layer on the surface of an anion exchange membrane to solve the problem that the existing anion exchange membranes cannot take into account good anti-fouling performance, stable modified layers, and the ability to construct modified layers in-situ.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for in-situ constructing a multi-component modified layer on the surface of an anion exchange membrane, comprising the following steps:

[0008] Step (1), using coupled electrodeposition and co - deposition methods to deposit and construct the first negatively charged modification layer on the surface of the anion - exchange membrane;

[0009] Step (2), using coupled electrodeposition and co - deposition methods to deposit and construct the first positively charged modification layer on the surface of the first negatively charged modification layer;

[0010] Step (3), repeating Step (1) to construct the second negatively charged modification layer on the surface of the first positively charged modification layer;

[0011] ……

[0012] Step (2n), repeating Step (2) to construct the nth positively charged modification layer on the surface of the nth negatively charged modification layer;

[0013] Step (2n + 1), repeating Step (1) to construct the (n + 1)th negatively charged modification layer on the surface of the nth positively charged modification layer;

[0014] n is greater than or equal to 1 and n is an integer; after the construction of the (n + 1)th negatively charged modification layer is completed, the anion - exchange membrane with a multi - component modification layer in - situ constructed on its surface is obtained. In the present invention, Step (1) is finally repeated to ensure that the outermost layer is a negatively charged modification layer, and at the same time, according to needs, by adjusting the number of layers of the modification layer, the anti - fouling performance can be improved as much as possible on the basis of not significantly affecting the desalination performance of the modified anion - exchange membrane. This in - situ construction method of the present invention can deposit anionic polyelectrolyte and dopamine and cationic polyelectrolyte and dopamine alternately on the surface of the anion - exchange membrane under the action of electric field force without disassembling the membrane stack, and in - situ construct a multi - component modification layer to improve the anti - fouling performance of the membrane surface.

[0015] For the method of in - situ constructing a multi - component modification layer on the surface of the anion - exchange membrane described above, in Step (1), anionic polyelectrolyte and dopamine are used as modifiers to construct a negatively charged modification layer on the surface of the anion - exchange membrane; in Step (2), cationic polyelectrolyte and dopamine are used as modifiers to construct a positively charged modification layer on the surface of the negatively charged modification layer.

[0016] For the method of in - situ constructing a multi - component modification layer on the surface of the anion - exchange membrane described above, in Step (1), the method of using coupled electrodeposition and co - deposition methods to deposit and construct a negatively charged modification layer on the surface of the anion - exchange membrane includes the following steps:

[0017] Step (1 - 1), preparing a mixed solution A of anionic polyelectrolyte, dopamine and sodium chloride;

[0018] Step (1-2): Circulate sodium chloride solution through the concentrated chamber of the electrodialysis device, and circulate mixed solution A through the dilute chamber. Under the action of a direct current electric field, a negatively charged modification layer is deposited on the side of the anion exchange membrane facing the dilute chamber.

[0019] Step (1-3): After the deposition is completed, circulate deionized water through the dilute chamber to wash the surface of the anion exchange membrane, the membrane stacking compartment, and the infusion pipeline.

[0020] In the above method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (1-1), the anionic polyelectrolyte in mixed solution A is sodium polystyrene sulfonate [since the ionization degree of the sulfonic acid group is better than that of the carboxyl and hydroxyl groups, compared with polyvinyl alcohol and sodium polyacrylate, sodium polystyrene sulfonate is more likely to deposit on the surface of the anion exchange membrane to obtain a modification layer with better modification effect]. The mass concentration of sodium polystyrene sulfonate is 0.05 - 2.0 g / L (if the concentration of sodium polystyrene sulfonate is too low, the deposition amount will decrease and affect the effect of the modification layer; if the concentration is too high, the membrane surface area with hydrophobic segments will increase, thus affecting the modification effect); the molar concentration of sodium chloride in mixed solution A is 0.05 - 2.0 mol / L (the presence of the supporting electrolyte sodium chloride can not only reduce the energy consumption during the in-situ modification process, but also assist the modified components to deposit on the membrane surface to construct a modification layer; when the concentration of the supporting electrolyte NaCl is too high, chloride ions will preferentially migrate to the surface of the anion membrane and aggregate, and there is an electrostatic repulsion effect between the aggregated chloride ions and the negatively charged modified components; therefore, too high a concentration of the supporting electrolyte is not conducive to the construction of the in-situ modification layer); the mass ratio of dopamine to sodium polystyrene sulfonate in mixed solution A is 1:(1 - 10) (the ionization degree of the negatively charged group of sodium polystyrene sulfonate is significantly better than that of dopamine and its derivatives, so too small a mass ratio will affect the negative charge density of the electro-modification layer; during the co-deposition of sodium polystyrene sulfonate and dopamine, the polymerization reaction process will be delayed or hindered due to electrostatic interaction, so too high a mass ratio may affect the stability of the in-situ modification layer); use hydrochloric acid or sodium hydroxide to adjust the pH of mixed solution A to 7 - 11.

[0021] In the above method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (1-2), the flow rates of the sodium chloride solution in the concentrated chamber and mixed solution A in the dilute chamber are both 90 - 5000 mL / min; on the one hand, an aerobic environment is required during the in-situ modification process to ensure the progress of the polymerization reaction, and on the other hand, due to the limited volume of the compartment, most of the feed liquid is stored in the feed liquid tank; therefore, it is necessary to continuously update the solution in the compartment to ensure the aerobic environment in the compartment and the supply of modified components; at the same time, too high a flow rate will also form a turbulent zone on the membrane surface, which is not conducive to the construction of the in-situ modification layer.

[0022] In the method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (1-2), the molar concentration of the sodium chloride solution in the concentrated chamber is 0.05 - 2.0 mol / L; the constant current density of the direct current electric field is 3 - 20 mA / cm 2 , the deposition time is 30 - 600 min; the electric field is the key to ensuring the directional migration of the modification components and minimizing the influence on the cation exchange membrane; however, when the current density is too high (exceeding 20 mA / cm 2 ), the modification components will agglomerate on the membrane surface due to the existence of electro-convection and gravity-convection effects, which is not conducive to constructing a uniform and dense modification layer; too short deposition time will lead to limited deposition amount of the modification components and affect the modification effect; the positively charged groups on the surface of the anion exchange membrane are limited, so the deposition amount of the in-situ single layer is limited, and thus the deposition time should not be too long.

[0023] In the method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (2), the method for depositing and constructing a positively charged modification layer on the surface of the anion exchange membrane by coupling electrodeposition and co-deposition method includes the following steps:

[0024] Step (2-1): Prepare a mixed solution B of a cationic polyelectrolyte, dopamine, and sodium chloride;

[0025] Step (2-2): Reverse the positive and negative connections of the membrane stack, circulate sodium chloride solution in the dilute chamber of the electrodialysis device, and circulate the mixed solution B in the concentrated chamber. Use the action of the direct current electric field to deposit a negatively charged modification layer on the side of the anion exchange membrane facing the dilute chamber;

[0026] Step (2-3): After the deposition, circulate deionized water in the concentrated chamber to wash the surface of the anion exchange membrane, the membrane stack compartments, and the infusion pipelines.

[0027] In the method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (2-1), the cationic polyelectrolyte in the mixed solution B is polyethyleneimine, and the mass concentration of polyethyleneimine is 0.05 - 2.0 g / L; the molar concentration of sodium chloride in the mixed solution B is 0.05 - 2.0 mol / L; the mass ratio of dopamine to polyethyleneimine in the mixed solution B is 1:(1 - 10); use hydrochloric acid or sodium hydroxide to adjust the pH of the mixed solution B to 7 - 11.

[0028] In the method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (2-2), the molar concentration of the sodium chloride solution in the dilute chamber is 0.05 - 1.0 mol / L; the constant current density of the direct current electric field is 3 - 20 mA / cm 2 , the deposition time is 30 - 600 min.

[0029] In the method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane, in step (2-2), the flow rates of the sodium chloride solution in the dilute chamber and the mixed solution B in the concentrated chamber are both 90 to 5000 mL / min.

[0030] The technical solution of the present invention has achieved the following beneficial technical effects:

[0031] 1. Aiming at the problem that the anion exchange membrane is seriously polluted when the electrodialysis technology is used for industrial wastewater desalination, but there is currently a lack of anti-pollution anion exchange membrane materials, the present invention provides a method for in-situ constructing a multi-component modification layer on the surface of the anion exchange membrane to improve the anti-pollution performance. In this method, an induced polymerization reaction is introduced during the electrodeposition of polyelectrolytes to form chemical bonds between the modified components and the base membrane, so as to improve the stability of the modification layer. The hydrophilic and negatively charged functional groups in the modified components are used to improve the hydrophilicity and negative charge density of the membrane surface, thereby improving the ability of the anion exchange membrane to resist organic pollution. The present invention uses in-situ alternating deposition of modification layers with different charges to construct a modification layer with adjustable thickness and good stability on the surface of the anion exchange membrane without disassembling the membrane stack, effectively improving the anti-pollution performance of the anion exchange membrane.

[0032] 2. The present invention uses the strongly ionized functional groups of polyelectrolytes to achieve in-situ directional construction of the modification layer. Utilizing the strong adhesion of the self-polymerization product polydopamine of dopamine, the covalent bonds formed by Michael addition reaction between dopamine and its product and the styrene-divinylbenzene copolymer type anion exchange membrane with quaternary ammonium groups, and the covalent / non-covalent bonds formed by Michael addition and Schiff base reaction between dopamine and polyelectrolytes to enhance the stability of the modification layer. In addition, the electrostatic interaction between dopamine and polyelectrolytes can inhibit the aggregation of dopamine during the self-polymerization process, thereby improving the smoothness of the surface of the in-situ modified membrane, which in turn helps to improve its anti-pollution performance.

[0033] 3. The present invention can effectively improve the anti-pollution performance of the anion exchange membrane without significantly affecting the desalination performance of the anion exchange membrane itself. At the same time, the number of anion exchange membranes can be increased according to actual needs to achieve the construction of modification layers on the surfaces of multiple anion exchange membranes simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic structural diagram of the electrodialysis device in the embodiment of the present invention; wherein, the electrode plates of the electrodialysis device are both titanium-coated ruthenium electrode plates; C - cation exchange membrane; A - anion exchange membrane; ① and ② are the cathode and anode respectively, which need to be converted according to different steps during the modification process; 1 and 4 are the electrode chambers respectively; 2 and 3 are the dilute chamber or the concentrated chamber respectively, which need to be converted according to different steps during the modification process;

[0035] Figure 2Schematic diagram of possible reaction mechanisms in the in-situ modification in the embodiments of the present invention;

[0036] Figure 3a Influence curve of the pH of mixed solution A in the embodiments of the present invention on the Zeta potential of the in-situ constructed modification layer on the surface of the anion exchange membrane;

[0037] Figure 3b Influence curve of the pH of mixed solution A in the embodiments of the present invention on the surface contact angle of the in-situ constructed modification layer on the surface of the anion exchange membrane;

[0038] Figure 4 Influence curve of the number of layers of the in-situ constructed modification layer in the embodiments of the present invention on the change of the conductivity in the dilute chamber with time in the electrodialysis fouling experiment (PM represents the electrodialysis desalination experiment without the pollutant sodium dodecylbenzenesulfonate SDBS using the original anion exchange membrane; PM - 50mg / L SDBS represents the electrodialysis desalination experiment with 50mg / L sodium dodecylbenzenesulfonate SDBS using the original anion exchange membrane; Co1layer - 50mg / L SDBS, Co3layer - 50mg / L SDBS, and Co5layer - 50mg / L SDBS respectively represent the electrodialysis desalination experiments with 50mg / L sodium dodecylbenzenesulfonate SDBS using the anion exchange membrane modified with 1 layer, 3 layers, and 5 layers of in-situ modification layer);

[0039] Figure 5a Influence curve of the change of the conductivity in the dilute chamber with time in the electrodialysis fouling experiment before and after the desalination experiment for 300 min of the anion exchange membrane solely modified by 5 layers of polyelectrolytes in the embodiments of the present invention ("5layer - M" represents the anion exchange membrane solely modified by 5 layers of polyelectrolytes; "5layer - M (after 300 min desalination)" represents the anion exchange membrane solely modified by 5 layers of polyelectrolytes after being rinsed);

[0040] Figure 5b Change of the anti - fouling performance of the in-situ modified anion exchange membrane in the electrodialysis fouling experiment before and after the desalination experiment for 300 min ("Co5layer - M" represents the 5 - layer in-situ modified anion exchange membrane; "Co5layer - M (after 300 min desalination)" represents the 5 - layer in-situ modified anion exchange membrane after being rinsed). Detailed implementation manners

[0041] The method for in-situ constructing a multi - component modification layer on the surface of the anion exchange membrane in this embodiment includes the following steps:

[0042] Step (1), depositing and constructing the first negatively charged modification layer on the surface of the anion exchange membrane by coupling electrodeposition and co - deposition method; specifically including the following steps:

[0043] Step (1-1): Prepare a mixed solution A of 500 mL of sodium polystyrene sulfonate, dopamine, and sodium chloride; in the mixed solution A, the mass concentration of sodium polystyrene sulfonate is 0.6 g / L, the mass concentration of dopamine is 0.3 g / L, and the molar concentration of sodium chloride is 0.1 mol / L; adjust the pH of the mixed solution A to 7-10 using hydrochloric acid or sodium hydroxide;

[0044] Step (1-2): In this embodiment, the in-situ construction of the multi-component modification layer of the anion exchange membrane is carried out in a small-scale electrodialysis device at the laboratory scale. As Figure 1 shown, 500 mL of 0.1 mol / L Na2SO4 solution circulates through the electrode chambers 1 and 4; the electrode plates are all titanium-coated ruthenium electrode plates; C is a cation exchange membrane; A is an anion exchange membrane; ① and ② are the cathode and anode respectively, and need to be converted into each other according to different steps during the modification process; 1 and 4 are both electrode chambers; 2 and 3 are the dilute chamber or the concentrated chamber respectively, and need to be converted into each other according to different steps during the modification process.

[0045] Using electrode ① as the anode and electrode ② as the cathode, 500 mL of 0.1 mol / L sodium chloride solution is driven by a peristaltic pump and flows through the concentrated chamber 2 of the electrodialysis membrane stack, and the mixed solution A is driven by a peristaltic pump and flows through the dilute chamber 3 of the electrodialysis membrane stack, and their flow rates are both 100 mL / min; during this modification process, the constant current density of the DC electric field of the membrane stack is given by a DC regulated voltage of 5 mA / cm 2 , and a negatively charged modification layer is deposited on the side of the anion exchange membrane facing the dilute chamber under the action of the DC electric field. The modification deposition time is 60 min, which can effectively improve the hydrophilicity and negative charge density of the membrane surface;

[0046] Step (1-3): After the deposition, deionized water is circulated in the dilute chamber 3 to wash the surface of the anion exchange membrane, the membrane stacking compartment, and the infusion pipeline.

[0047] As Figure 2 shown, in this process, the in-situ directional construction of the modification layer is realized by using the strongly ionized functional groups of the polyelectrolyte. The strong adhesion of the self-polymerization product polydopamine of dopamine, the covalent bond formed by the Michael addition reaction between dopamine and its product and the styrene-divinylbenzene copolymer type anion exchange membrane with quaternary ammonium groups, and the non-covalent bond formed by the Michael addition reaction between dopamine and sodium polystyrene sulfonate are used to enhance the stability of the modification layer.

[0048] Step (2): Deposit and construct the first positively charged modification layer on the surface of the first negatively charged modification layer by coupling electrodeposition and co-deposition methods; specifically, it includes the following steps:

[0049] Step (2-1): Prepare a mixed solution B of 500 mL of polyethyleneimine, dopamine, and sodium chloride; in the mixed solution B, the mass concentration of polyethyleneimine is 1.0 g / L, the mass concentration of dopamine is 0.4 g / L, and the molar concentration of sodium chloride is 0.1 mol / L; adjust the pH of the mixed solution B to 8 using hydrochloric acid or sodium hydroxide;

[0050] Step (2-2): Reverse the positive and negative connections of the membrane stack, that is, change the positive and negative connections of the power supply to exchange the electrodes of the membrane stack, with electrode ① as the cathode and electrode ② as the anode. Circulate 500 mL of 0.1 mol / L NaCl solution through the dilute chamber 2 and circulate the mixed solution B (sodium chloride solution of dopamine and polyethyleneimine) through the concentrated chamber 3, both with a flow rate of 100 mL / min; the constant current density of the DC electric field is 5 mA / cm 2 , and the deposition time is 60 min, so that the modified components are deposited on the side of the anion exchange membrane facing the concentrated chamber under the action of the DC electric field to improve the hydrophilicity of the membrane surface;

[0051] Step (2-3): After the deposition, circulate deionized water through the concentrated chamber 3 to wash the surface of the anion exchange membrane, the membrane stack compartments, and the infusion pipeline.

[0052] As Figure 2 shown, in this process, the strong adhesion of the self-polymerization product polydopamine of dopamine, the non-covalent bonds formed by the Michael addition reaction between dopamine and its product to construct the modification layer in step 2, and the non-covalent bonds / covalent bonds formed by the Michael addition and Schiff base reactions between dopamine and polyethyleneimine are used to enhance the stability of the modification layer.

[0053] Step (3): Repeat step (1) to construct a second negatively charged modification layer on the surface of the first positively charged modification layer; repeat step (2) to construct a second positively charged modification layer on the surface of the second negatively charged modification layer; repeat step (1) to construct a third negatively charged modification layer on the surface of the second positively charged modification layer; thus, an anion exchange membrane with a multi-component modification layer in-situ constructed on the surface is obtained.

[0054] In this embodiment, there is 1 pair of membranes in the electrodialysis device, but in actual applications, the number of membrane pairs can be increased to 2 pairs, 3 pairs, 4 pairs, 5 pairs, 6 pairs, 7 pairs... according to requirements to achieve the in-situ construction of stable modification layers on the surfaces of multiple anion exchange membranes simultaneously.

[0055] To study the effect of the pH of the mixed solution A on the anti-pollution performance of the anion exchange membrane with an in-situ constructed modification layer, in this embodiment, using the same method as above, change the pH of the mixed solution A to 7, 7.8, 8.8, and 9.8 respectively. Denote the anion exchange membranes with a single-layer in-situ constructed modification layer as M1, M2, M3, and M4, and denote the original anion exchange membrane as M0;

[0056] As Figure 3a and Figure 3b shown, the contact angles and Zeta potentials on the surfaces of different anion exchange membranes have decreased significantly compared to the original anion exchange membrane, indicating that both the hydrophilicity and negative charge density on the surface of the anion exchange membrane after constructing the modification layer have been significantly enhanced, thereby effectively improving the anti-fouling performance of the anion exchange membrane. Among them, the hydrophilicity of the anion exchange membrane surface improves significantly with the increase of the pH of the modification solution, which is mainly caused by the acceleration of the self-polymerization process of dopamine and the increase of the negative charge density of the modification components by appropriately increasing the pH. The negative charge density on the surface of the anion exchange membrane shows a trend of first weakening and then strengthening, which may be due to the shielding effect of polydopamine on the strong ionization of sulfonic acid groups.

[0057] In this example, a total of 5 layers of modification layers, namely a negatively charged modification layer - a positively charged modification layer - a negatively charged modification layer - a positively charged modification layer - a negatively charged modification layer, were in-situ constructed on the surface of the anion exchange membrane, denoted as Co5layer-PM.

[0058] To study the effect of the number of in-situ constructed modification layers on the anti-fouling performance of the anion exchange membrane, in this example, anion exchange membranes with 1 layer and 3 layers of odd-numbered modification layers were in-situ constructed using the same method as above, denoted as Co1layer-PM and Co3layer-PM respectively, and the desalination performance of anion exchange membranes with different numbers of in-situ constructed modification layers in the electrodialysis fouling experiment was investigated.

[0059] In this example, the electrodialysis fouling experiment was carried out on a laboratory-scale small electrodialysis device. The effective area of each ion exchange membrane is 50 cm 2 , the anode chamber uses a 500 mL 0.1 mol / L sodium sulfate solution, and a 500 mL 0.1 mol / L sodium chloride solution is driven by a peristaltic pump and flows through the concentrated chamber of the electrodialysis membrane stack. A 500 mL 0.1 mol / L sodium chloride and 50 mg / L sodium dodecylbenzenesulfonate (SDBS) mixed solution is driven by a peristaltic pump and flows through the dilute chamber of the electrodialysis membrane stack. The solution flow rate is 100 mL / min for all.

[0060] In the electrodialysis fouling experiment, a conductivity tester was used to record the change curve of the conductivity of the feed liquid in the dilute chamber with time online to investigate the anti-fouling performance of anion exchange membranes with different numbers of in-situ modified layers. A constant voltage of 4 V was applied to the membrane stack system through a precision DC regulated power supply. After continuous testing for 180 min, the results are as Figure 4As shown. When the feed solution in the dilute chamber contains 50 mg / L SDBS, the desalination rate of the electrodialysis fouling experiment using the original membrane starts to decline rapidly after 20 min of operation. Compared with the case without SDBS, the desalination rate after 180 min of operation is 14.84%, indicating that the anionic surfactant SDBS is easily adsorbed on the surface of the original membrane to form a fouling layer, resulting in a decrease in the electrodialysis desalination rate. When the feed solution in the dilute chamber contains 50 mg / L SDBS, during the electrodialysis fouling experiment using three modified membranes with 1, 3, and 5 in-situ modification layers, the desalination rates in the dilute chamber after 180 min are 19.04%, 21.53%, and 24.32% respectively, all higher than the desalination rate of the electrodialysis fouling experiment using the original membrane. This shows that the anti-fouling performance of the in-situ modified membranes has been improved, and the anti-fouling performance increases with the increase in the number of modification layers.

[0061] In this example, an anion exchange membrane composed solely of 5 layers of polyelectrolyte as the modification layer was also prepared by the above method, that is, neither mixed solution A nor mixed solution B contained dopamine; the prepared anion exchange membrane was denoted as 5layer-M; a 300-minute desalination experiment was carried out with it and the anion exchange membrane with a polyelectrolyte modification layer containing dopamine (denoted as Co5layer-M) to compare their anti-fouling performance.

[0062] The desalination test in this example was carried out on a laboratory-scale small electrodialysis device. The effective area of each ion exchange membrane in the desalination experiment was 50 cm 2 , the anode chamber used 500 mL of 0.1 mol / L sodium sulfate solution, and 500 mL of 0.1 mol / L sodium chloride solution was driven by a peristaltic pump and flowed through the concentrated chamber and the dilute chamber of the electrodialysis membrane stack, and the solution flow rate was 100 mL / min. During the desalination process, a constant voltage of 4 V was applied to the membrane stack system by a precision DC regulated power supply, and a 300-minute desalination experiment (similar to rinsing) was carried out. Then the rinsed anion exchange membrane was applied to the electrodialysis fouling experiment (the experimental conditions in this part were the same as those in the above electrodialysis fouling experiment). By comparing the difference in the desalination rate of the anion exchange membrane in the anti-fouling experiment of the electrodialysis system before and after rinsing, the difference in the anti-fouling performance of the modified membrane before and after rinsing was investigated and the stability of its modification layer was analyzed.

[0063] As shown in Figure 5, when the 5layer-M before being rinsed was used in the electrodialysis fouling experiment with 50 mg / L SDBS in the dilute chamber solution, after the desalination system operated for 180 min, the conductivity of the dilute chamber decreased from 10.30 mS / cm to 7.795 mS / cm (i.e., the desalination rate was 24.32%). When the 5layer-M was used in the electrodialysis fouling experiment again after undergoing a 300-min rinsing test, its desalination rate decreased by 3.54% after 180 min. This shows that the anti-fouling performance of the 5layer-M suffered certain losses during the 300-min rinsing experiment, which may be due to the polyelectrolyte adsorbed on the membrane surface by electrostatic interaction being washed off during the rinsing process. For Co5layer-M, before and after the rinsing experiment, the change trend of the conductivity of the dilute chamber solution was almost the same, and the desalination rate showed no obvious attenuation. Thus, it can be seen that the anti-fouling performance of the Co5layer-M anion exchange membrane is better than that of the 5layer-M anion exchange membrane.

[0064] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. The obvious changes or modifications derived therefrom are still within the protection scope of the claims of this patent application.

Claims

1. A method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane, characterized in that, It includes the following steps: Step (1): Deposit and construct the first negatively charged modification layer on the surface of the anion exchange membrane by coupled electrodeposition and codeposition methods; Step (2): Deposit and construct the first positively charged modification layer on the surface of the first negatively charged modification layer by coupled electrodeposition and codeposition methods; Step (3): Repeat Step (1) to construct the second negatively charged modification layer on the surface of the first positively charged modification layer; …… Step (2n): Repeat Step (2) to construct the nth positively charged modification layer on the surface of the nth negatively charged modification layer; Step (2n + 1): Repeat Step (1) to construct the (n + 1)th negatively charged modification layer on the surface of the nth positively charged modification layer; n is greater than or equal to 1 and n is an integer; after the construction of the (n + 1)th negatively charged modification layer is completed, the anion exchange membrane with a multi-component modification layer in-situ constructed on the surface is obtained; In Step (1), an anionic polyelectrolyte and dopamine are used as modifiers to construct a negatively charged modification layer on the surface of the anion exchange membrane; in Step (2), a cationic polyelectrolyte and dopamine are used as modifiers to construct a positively charged modification layer on the surface of the negatively charged modification layer; In Step (1), the method for depositing and constructing a negatively charged modification layer on the surface of the anion exchange membrane by coupled electrodeposition and codeposition methods includes the following steps: Step (1-1): Prepare a mixed solution A of an anionic polyelectrolyte, dopamine and sodium chloride; the anionic polyelectrolyte is sodium polystyrene sulfonate; Step (1-2): Circulate sodium chloride solution in the concentrated chamber of the electrodialysis device and circulate the mixed solution A in the dilute chamber, and deposit a negatively charged modification layer on the side of the anion exchange membrane facing the dilute chamber under the action of a direct current electric field; Step (1-3): After the deposition is completed, circulate deionized water in the dilute chamber to wash the surface of the anion exchange membrane, the membrane stacking chamber and the infusion pipeline.

2. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 1, characterized in that, In Step (1-1), in the mixed solution A, the mass concentration of sodium polystyrene sulfonate is 0.05 - 2.0 g / L; the molar concentration of sodium chloride in the mixed solution A is 0.05 - 2.0 mol / L; the mass ratio of dopamine to sodium polystyrene sulfonate in the mixed solution A is 1:(1 - 10); use hydrochloric acid or sodium hydroxide to adjust the pH of the mixed solution A to 7 - 11.

3. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 1, characterized in that, In Step (1-2), the flow rates of the sodium chloride solution in the concentrated chamber and the mixed solution A in the dilute chamber are both 90 - 5000 mL / min.

4. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 1, characterized in that, In step (1-2), the molar concentration of the sodium chloride solution in the concentrated chamber is 0.05 to 2.0 mol / L; the constant current density of the direct current electric field is 3 to 20 mA / cm 2 , and the deposition time is 30 to 600 min.

5. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 1, wherein In Step (2), the method for depositing and constructing a positively charged modification layer on the surface of the anion exchange membrane by coupled electrodeposition and codeposition methods includes the following steps: Step (2-1): Prepare a mixed solution B of a cationic polyelectrolyte, dopamine and sodium chloride; Step (2-2): Switch the positive and negative connections of the membrane stack, circulate sodium chloride solution in the dilute chamber of the electrodialysis device and circulate the mixed solution B in the concentrated chamber, and deposit a negatively charged modification layer on the side of the anion exchange membrane facing the dilute chamber under the action of a direct current electric field; Step (2-3): After the deposition is completed, circulate deionized water in the concentrated chamber to wash the surface of the anion exchange membrane, the membrane stacking chamber and the infusion pipeline.

6. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 5, characterized in that, In step (2-1), the cationic polyelectrolyte in the mixed solution B is polyethyleneimine, and the mass concentration of polyethyleneimine is 0.05 - 2.0 g / L; the molar concentration of sodium chloride in the mixed solution B is 0.05 - 2.0 mol / L; the mass ratio of dopamine to polyethyleneimine in the mixed solution B is 1:(1 - 10); the pH of the mixed solution B is adjusted to 7 - 11 using hydrochloric acid or sodium hydroxide.

7. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 5, characterized in that, In step (2-2), the molar concentration of the sodium chloride solution in the light chamber is 0.05 to 1.0 mol / L; the constant current density of the DC electric field is 3 to 20 mA / cm 2 , and the deposition time is 30 to 600 min.

8. The method for in-situ constructing a multi-component modification layer on the surface of an anion exchange membrane according to claim 5, characterized in that, In step (2-2), the flow rates of the sodium chloride solution in the dilute chamber and the mixed solution B in the concentrated chamber are both 90 - 5000 mL / min.

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