Cationic electrodialysis membrane and preparation method thereof

Abstract

The invention belongs to the technical field of electrodialysis membranes, and particularly relates to a cationic electrodialysis membrane and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a pretreated nano material in parts by weight; (2) preparing PVC resin; (3) mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, mixing, and crushing in a crusher to obtain modified PVC resin; (4) adding cation exchange resin and modified PVC resin into N, N-dimethylacetamide, and uniformly oscillating to obtain a membrane casting solution; and (5) pouring the membrane casting solution on a smooth flat plate, scraping to form a membrane, drying, cooling, putting into deionized water, automatically stripping the membrane from the smooth flat plate, and soaking in a NaCl solution to obtain the cationic electrodialysis membrane. The prepared cationic electrodialysis membrane is excellent in performance, and selective separation of Li < + > and Mg < 2 + > can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrodialysis membranes, and in particular relates to a cationic electrodialysis membrane and a preparation method thereof. Background Art

[0002] Electrodialysis utilizes the selective permeability of ion exchange membranes to anions and cations. Under the action of the DC electric field at both ends, the anions and cations in the feed solution are directed to move, thereby achieving the purpose of separation, purification and concentration of the electrolyte solution. The ion exchange membrane is the main core component of the electrodialysis process.

[0003] The technical challenges faced by cationic electrodialysis membranes in practical applications mainly include problems such as surface resistance, energy consumption, current efficiency, and mechanical strength. 1. Surface resistance reflects the conductivity of the membrane, which directly affects the energy consumption and efficiency of the electrodialysis process. Higher surface resistance means higher resistance loss, resulting in increased energy consumption. The reasons for high surface resistance may include low conductivity of the membrane material itself, or contamination or sediment on the membrane surface, which increases resistance. 2. Energy consumption in the electrodialysis process is related to multiple factors, including membrane resistance, current density, solution concentration difference, etc. Higher energy consumption usually indicates low system efficiency, which may be due to poor membrane selectivity, resulting in non-target ions also participating in the migration, increasing unnecessary energy consumption. 3. Current efficiency is an important indicator to measure the ratio between the actual amount of migrated ions and the theoretical predicted value. Low current efficiency may be caused by a variety of factors, including membrane fouling, scaling, and the occurrence of side reactions. These will cause part of the current to be used for the migration or consumption of non-target substances, thereby reducing the current efficiency. 4. Mechanical strength (such as tensile strength) is related to the durability and stability of the membrane in long-term operation. If the mechanical strength of the membrane is insufficient, it may break or be damaged during actual operation, affecting the separation effect. This is usually related to the physical properties of the membrane material and its manufacturing process. 5. As the main component of batteries, the efficient acquisition and stable supply of lithium resources are the top priorities for the development of the new energy industry. Among the existing methods of obtaining lithium resources, lithium extraction from salt lakes has a natural cost advantage. How to extract high-purity lithium from salt lakes with excessively high impurity content is one of the difficulties that need to be overcome in the current lithium extraction from salt lakes. Ordinary ion exchange membranes have a good separation effect between ions of different electrical properties, but cannot achieve Li + Mg 2+ selective separation.

[0004] In the prior art, electrodialysis membranes are usually obtained by immersing a porous film substrate in a solution containing a cross-linking monomer, an ionic monomer and a monofunctional non-ionic monomer for a period of time, then taking it out and polymerizing it, or by immersing a porous polyolefin film substrate in a solution containing a cross-linking monomer and a monofunctional non-ionic monomer for a period of time, then taking it out and polymerizing it and then ionizing it. However, the existing electrodialysis membranes have a high resistance.

[0005] Therefore, there is an urgent need for a cationic electrodialysis membrane and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a cationic electrodialysis membrane and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a cationic electrodialysis membrane comprises the following steps: (1) dispersing a nano material in an organic solvent, then adding a silane coupling agent, reacting, and after the reaction is completed, removing the organic solvent to obtain a pretreated nano material; the nano material is a carboxylated carbon nanotube;

[0009] (4) dispersing vinyl chloride, pretreated nanomaterials, initiators and surfactants in water, reacting at 50-60° C. for 5-8 hours, then adding diethylhydroxylamine to remove unreacted vinyl chloride, and drying to obtain PVC resin;

[0010] (5) mixing and crushing the PVC resin, zinc stearate and maleic anhydride grafted PE to obtain a modified PVC resin;

[0011] (4) adding a cation exchange resin and a modified PVC resin into N,N-dimethylacetamide to obtain a casting solution;

[0012] (5) Forming the casting solution into a membrane to obtain a cationic electrodialysis membrane.

[0013] Further, by weight,

[0014] The step (1) comprises dispersing 5 parts of nanomaterial in 60-80 parts of ethanol, adding 7-9 parts of silane coupling agent, reacting, filtering after the reaction, washing with water, and vacuum drying to obtain a pretreated nanomaterial, wherein the nanomaterial is a carboxylated carbon nanotube;

[0015] The step (2) is as follows: 100 parts of vinyl chloride, 1 to 3 parts of pretreated nanomaterials, 140 to 150 parts of deionized water, 0.04 to 0.06 parts of initiator and 0.3 to 0.5 parts of surfactant are mixed, reacted at 50 to 60° C. for 5 to 8 hours, and then 0.015 to 0.017 parts of diethylhydroxylamine are added to remove unreacted vinyl chloride, centrifuged and dried to obtain PVC resin;

[0016] The step (3) comprises mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, kneading, and then crushing in a crusher to obtain a modified PVC resin;

[0017] The step (4) is as follows: adding a cation exchange resin and a modified PVC resin into N,N-dimethylacetamide, and shaking the mixture evenly to obtain a casting solution;

[0018] The step (5) is as follows: pouring the casting liquid onto a smooth flat plate and scraping it into a film, drying it, and then cooling the film to room temperature; placing the cooled film in deionized water, allowing the film to automatically peel off from the smooth flat plate, and then immersing it in a NaCl solution to obtain a cationic electrodialysis membrane.

[0019] The silane coupling agent in step (1) is γ-methacryloxypropyltrimethoxysilane.

[0020] Furthermore, the length of the carboxylated carbon nanotubes is 0.1-10 μm, and the carboxyl content is 0.1-5 wt %.

[0021] The present invention can improve the Li-Mg selectivity coefficient of the cationic electrodialysis membrane and reduce the resistance by adding pre-treated carboxylated carbon nanotube nanomaterials into the PVC membrane. The high conductivity and uniform dispersion of the nanomaterials form an effective conductive network, reduce the resistance in the ion transmission path, and thus reduce the resistance of the membrane.

[0022] Furthermore, the reaction conditions in step (1) are heating at 80-90° C. for 6-8 hours.

[0023] Furthermore, the surfactant in step (2) is sorbitan monolaurate; and / or the initiator in step (2) is cumyl peroxyneodecanoate.

[0024] Furthermore, in the step (4), the weight ratio of the cation exchange resin, the modified PVC resin and N,N-dimethylacetamide is (3-5): (10-12): (85-90).

[0025] Furthermore, in the step (3), the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:(5-7):(10-15).

[0026] The present invention can improve the current efficiency by modifying PVC by grafting PE with maleic anhydride. The maleic anhydride group reacts with functional groups such as hydroxyl or carboxyl on the surface of PVC to form a covalent bond or strong physical adsorption, thereby enhancing the interface bonding force. This enhanced interface bonding force helps to improve the overall strength and toughness of the composite material. The uniform microstructure and fewer defects reduce the resistance of the membrane and improve the ion migration rate.

[0027] Furthermore, in step (5), the mixture is immersed in a 1 to 1.2 mol / L NaCl solution for 15 to 18 hours.

[0028] The invention provides a cationic electrodialysis membrane prepared by the preparation method.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0030] 1. The present invention can improve the selectivity coefficient of positive ions of different valence states of the cationic electrodialysis membrane and reduce the resistance by adding pretreated nanomaterials into the PVC membrane.

[0031] 2. The present invention can improve the mechanical properties of the dialysis membrane and the current efficiency by modifying PVC by grafting PE with maleic anhydride. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The raw materials used in the following examples of the present invention are all commercially available products:

[0034] The cation exchange resin was purchased from Bengbu Sanyi Technology Co., Ltd., brand 001X8H.

[0035] Maleic anhydride grafted PE, Dongguan Xinrui New Materials Co., Ltd., brand PE~14L.

[0036] Example 1

[0037] This embodiment provides a cationic electrodialysis membrane, and the preparation method thereof comprises the following steps: by weight:

[0038] (1) dispersing 5 parts of nanomaterial in 70 parts of ethanol, adding 8 parts of silane coupling agent KH570, and reacting. The reaction conditions are heating at 60° C. for 7 hours. After the reaction is completed, the mixture is filtered, washed with water three times, and vacuum dried to obtain the pretreated nanomaterial;

[0039] The nano material is carboxylated carbon nanotubes, the length of the carboxylated carbon nanotubes is 0.5-2 μm, the carboxyl content is 0.49 wt%, and the raw material carbon nanotubes are purchased from Xianfeng Nano.

[0040] (2) 100 parts of vinyl chloride, 2 parts of pretreated nanomaterials, 145 parts of deionized water, 0.05 parts of initiator isopropyl peroxy neodecanoate and 0.4 parts of surfactant Span 20 are mixed, reacted at 55° C. for 7 hours, and then 0.016 parts of diethylhydroxylamine are added, unreacted vinyl chloride is removed by vacuum rotary evaporation, centrifuged and dried to obtain PVC resin;

[0041] (3) mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, wherein the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:6:13, kneading at 165° C., and then crushing in a crusher to obtain a modified PVC resin;

[0042] (4) adding a cation exchange resin and a modified PVC resin to N,N-dimethylacetamide, wherein the weight ratio of the cation exchange resin, the modified PVC resin and the N,N-dimethylacetamide is 4:11:87, and oscillating the mixture evenly to obtain a casting solution;

[0043] (5) The casting liquid is poured onto a smooth flat plate and scraped to form a film, which is then placed in a vacuum drying oven and dried at 65°C for 20 hours. The film is then taken out of the oven and cooled to room temperature in air. The cooled film is placed in deionized water for 15 hours, and the film automatically peels off from the smooth flat plate. The film is then immersed in a 1 mol / L NaCl solution for 16 hours to obtain a cationic electrodialysis membrane.

[0044] Example 2

[0045] This embodiment provides a cationic electrodialysis membrane, and the preparation method thereof comprises the following steps: by weight:

[0046] (1) dispersing 5 parts of the nanomaterial in 60 parts of ethanol, adding 7 parts of silane coupling agent KH570, and reacting. The reaction conditions are heating at 60° C. for 6 hours. After the reaction is completed, the mixture is filtered, washed with water three times, and vacuum dried to obtain the pretreated nanomaterial;

[0047] The nano material is carboxylated carbon nanotubes, the length of the carboxylated carbon nanotubes is 0.5-2 μm, and the carboxyl content is 0.49 wt%. The raw material carbon nanotubes are purchased from Xianfeng Nano, item number 100298.

[0048] (2) 100 parts of vinyl chloride, 3 parts of pretreated nanomaterials, 150 parts of deionized water, 0.04 parts of initiator cumyl peroxy neodecanoate and 0.5 parts of surfactant Span 20 were mixed, reacted at 50° C. for 8 h, and then 0.015 parts of diethylhydroxylamine were added. Unreacted vinyl chloride was removed by vacuum rotary evaporation, centrifuged and dried to obtain PVC resin;

[0049] (3) mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, wherein the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:7:15, kneading at 165° C., and then crushing in a crusher to obtain a modified PVC resin;

[0050] (4) adding a cation exchange resin and a modified PVC resin to N,N-dimethylacetamide, wherein the weight ratio of the cation exchange resin, the modified PVC resin and the N,N-dimethylacetamide is 3:12:90, and oscillating the mixture evenly to obtain a casting solution;

[0051] (5) The casting liquid is poured onto a smooth flat plate and scraped to form a film, which is then placed in a vacuum drying oven and dried at 65°C for 20 hours. The film is then taken out of the oven and cooled to room temperature in air. The cooled film is placed in deionized water for 15 hours, and the film automatically peels off from the smooth flat plate. The film is then immersed in a 1.2 mol / L NaCl solution for 18 hours to obtain a cationic electrodialysis membrane.

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 1 is that no pre-treated nanomaterial is added in the preparation of PVC resin.

[0054] 100 parts of vinyl chloride, 145 parts of deionized water, 0.05 parts of initiator isopropyl peroxy neodecanoate and 0.4 parts of surfactant Span 20 were mixed, reacted at 55°C for 7 hours, and then 0.016 parts of diethylhydroxylamine were added to remove unreacted vinyl chloride, centrifuged and dried to obtain PVC resin.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that there is no step (3), and the PVC resin prepared in step (2) is used to replace the modified PVC resin to prepare the casting solution.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 1 is that the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:6:5.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 1 is that the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:6:21.

[0061] Performance Testing

[0062] The performance of the electrodialysis membranes prepared in Examples 1-2 and Comparative Examples 1-4 was tested.

[0063] The following device is used to measure the surface resistance of the membrane: the device consists of two electrode chambers, two intermediate chambers and a membrane fixing clamp. Before the test, the membrane to be tested is placed in a 0.5mol / LNaCl solution for 12 hours of equilibrium; during the measurement, the balanced membrane to be tested is fixed in the clamp, and a 0.3mol / L Na2SO4 solution is pumped into the two electrode chambers and circulated continuously; a 0.5mol / LNaCl solution is fed and pumped into the two intermediate chambers; the current is kept constant at 0.05A, and the inter-electrode potential U is read with a digital multimeter. The membrane resistance is obtained by the calculation formula R=S×[(U-U0) / I]. Among them, U0 is the blank voltage (V), that is, the voltage reading when the membrane is not placed; I is the current used (A); S is the effective area of ​​the membrane.

[0064] The current efficiency is calculated as follows: the actual number of cations that migrate / the theoretical number of cations that migrate*100%.

[0065] Tensile strength test: CTM2050 automatic mechanical strength tester was used to test the cationic electrodialysis membrane. The membrane was cut into 2×10 cm 2 Then place the small piece vertically into the clamp and tighten the screws, input the thickness value of the small piece, set the tensile speed to 2mm / min, terminate the test after the membrane breaks, record the tensile strength of the membrane, repeat the measurement 3 times and take the average value.

[0066] The method for determining the selectivity coefficients of lithium and magnesium refers to the determination method in Chinese Patent 202411383030.5.

[0067] Table 1 Performance test results

[0068]

[0069] It can be seen from the above performance test results that the electrodialysis membranes of Examples 1 to 2 have excellent comprehensive performance, especially the comprehensive performance of Example 1 is the most outstanding.

[0070] In comparative example 1, no pre-treated nanomaterials were added, and the selectivity coefficient of positive ions of different valence states of the cationic electrodialysis membrane decreased, and the resistance increased; in comparative example 2, the PVC resin was not modified, the mechanical properties of the dialysis membrane decreased, and the current efficiency decreased; in comparative examples 3-4, the amount of maleic anhydride grafted PE added was different, and the current efficiency decreased. The above experimental results further prove the importance of the technical solution defined in the present invention for its technical effect.

[0071] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a cationic electrodialysis membrane, characterized in that: The method comprises the following steps: (1) dispersing a nano material in an organic solvent, then adding a silane coupling agent, reacting, and after the reaction is completed, removing the organic solvent to obtain a pretreated nano material; the nano material is a carboxylated carbon nano tube; (2) dispersing vinyl chloride, pretreated nanomaterials, initiators and surfactants in water, reacting at 50-60° C. for 5-8 hours, then adding diethylhydroxylamine to remove unreacted vinyl chloride, and drying to obtain PVC resin; (3) mixing and crushing the PVC resin, zinc stearate and maleic anhydride grafted PE to obtain a modified PVC resin; (4) adding a cation exchange resin and a modified PVC resin into N,N-dimethylacetamide to obtain a casting solution; (5) Forming the casting solution into a membrane to obtain a cationic electrodialysis membrane.

2. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: By weight, The step (1) comprises dispersing 5 parts of nanomaterial in 60-80 parts of ethanol, adding 7-9 parts of silane coupling agent, reacting, filtering after the reaction, washing with water, and vacuum drying to obtain a pretreated nanomaterial, wherein the nanomaterial is a carboxylated carbon nanotube; The step (2) is as follows: 100 parts of vinyl chloride, 1 to 3 parts of pretreated nanomaterials, 140 to 150 parts of deionized water, 0.04 to 0.06 parts of initiator and 0.3 to 0.5 parts of surfactant are mixed, reacted at 50 to 60° C. for 5 to 8 hours, and then 0.015 to 0.017 parts of diethylhydroxylamine are added to remove unreacted vinyl chloride, centrifuged and dried to obtain PVC resin; The step (3) comprises mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, kneading, and then crushing in a crusher to obtain a modified PVC resin; The step (4) is as follows: adding a cation exchange resin and a modified PVC resin into N,N-dimethylacetamide, and shaking the mixture evenly to obtain a casting solution; The step (5) is as follows: pouring the casting liquid onto a smooth flat plate and scraping it into a film, drying it, and then cooling the film to room temperature; placing the cooled film in deionized water, allowing the film to automatically peel off from the smooth flat plate, and then immersing it in a NaCl solution to obtain a cationic electrodialysis membrane.

3. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: The silane coupling agent in step (1) is γ-methacryloxypropyltrimethoxysilane.

4. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: The length of the carboxylated carbon nanotubes is 0.1-10 μm, and the carboxyl content is 0.1-5 wt %.

5. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: The reaction conditions in step (1) are heating at 80-90° C. for 6-8 hours.

6. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: The surfactant in step (2) is sorbitan monolaurate; and / or the initiator in step (2) is cumyl peroxyneodecanoate.

7. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: In the step (4), the weight ratio of the cation exchange resin, the modified PVC resin and N,N-dimethylacetamide is (3-5): (10-12): (85-90).

8. The method for preparing a cationic electrodialysis membrane according to claim 1, characterized in that: In the step (3), the mass ratio of PVC resin, zinc stearate and maleic anhydride grafted PE is 50:(5-7):(10-15).

9. The method for preparing a cationic electrodialysis membrane according to claim 2, characterized in that: In the step (5), the mixture is immersed in a 1 to 1.2 mol / L NaCl solution for 15 to 18 hours.

10. A cationic electrodialysis membrane obtained by the preparation method according to any one of claims 1 to 9.

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