A cationic electrodialysis membrane and its preparation method

Abstract

The present invention belongs to the technical field of electrodialysis membranes, and specifically relates to a cationic electrodialysis membrane and a preparation method thereof. The preparation method comprises the following steps: (1) preparing pre-treated nanomaterials by weight; (2) preparing PVC resin; (3) 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; (4) adding a cation exchange resin and a modified PVC resin to N,N-dimethylacetamide, oscillating evenly, and obtaining a casting liquid; (5) pouring the casting liquid onto a smooth flat plate and scraping it into a film, drying, cooling, and placing it in deionized water, the film automatically peels off from the smooth flat plate, and then soaking it in a NaCl solution to obtain a cationic electrodialysis membrane. The cationic electrodialysis membrane prepared by the present invention has excellent performance and can achieve Li + Mg 2+ selective separation.

Description

Technical Field

[0001] The present 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 for anions and cations. Under the action of a DC electric field at both ends, the anions and cations in the feed solution undergo directional movement, thereby achieving the purpose of separating, purifying and concentrating 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 primarily include surface resistance, energy consumption, current efficiency, and mechanical strength. 1. Surface resistance reflects the membrane's electrical conductivity and directly affects the energy consumption and efficiency of the electrodialysis process. Higher surface resistance means higher resistive losses, leading to increased energy consumption. High surface resistance may be caused by low conductivity of the membrane material itself or by contamination or deposits on the membrane surface, which increase resistance. 2. Energy consumption during the electrodialysis process is related to multiple factors, including membrane resistance, current density, and solution concentration differences. High energy consumption generally indicates low system efficiency, possibly due to poor membrane selectivity, which leads to the migration of non-target ions and unnecessary energy consumption. 3. Current efficiency is an important metric that measures the ratio of the actual amount of ions migrated to the theoretically predicted value. Low current efficiency can be caused by a variety of factors, including membrane fouling, scaling, and the occurrence of side reactions. These factors can cause some current to be used for the migration or consumption of non-target substances, thereby reducing current efficiency. 4. Mechanical strength (such as tensile strength) is related to the durability and stability of the membrane during 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 too 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 with different electrical properties, but cannot achieve Li + Mg 2+ selective separation.

[0004] Conventional electrodialysis membranes are typically produced by immersing a porous film substrate in a solution containing a crosslinking monomer, an ionic monomer, and a monofunctional nonionic monomer for a period of time, then removing the substrate and subjecting it to polymerization. Alternatively, a porous polyolefin film substrate is immersed in a solution containing a crosslinking monomer and a monofunctional nonionic monomer for a period of time, then removed and subjecting the substrate to polymerization, followed by ionization. However, existing electrodialysis membranes have relatively high electrical resistance.

[0005] Therefore, there is an urgent need for a cationic electrodialysis membrane and a preparation method. 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 nanomaterial 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 nanomaterial; the nanomaterial 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 to N,N-dimethylacetamide to obtain a casting solution;

[0012] (5) The casting solution is formed into a membrane to obtain a cationic electrodialysis membrane.

[0013] Further, by weight,

[0014] The step (1) comprises dispersing 5 parts of a nanomaterial in 60 to 80 parts of ethanol, adding 7 to 9 parts of a 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) comprises mixing 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 an initiator, and 0.3 to 0.5 parts of a surfactant, reacting the mixture at 50 to 60° C. for 5 to 8 hours, adding 0.015 to 0.017 parts of diethylhydroxylamine, removing unreacted vinyl chloride, centrifuging, and drying to obtain a PVC resin;

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

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

[0018] The step (5) comprises pouring the casting solution onto a smooth flat plate, scraping the film, drying the film, 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 the film 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] By adding pretreated carboxylated carbon nanotube nanomaterials to PVC membranes, this invention improves the Li-Mg selectivity of cationic electrodialysis membranes while simultaneously reducing electrical resistance. The high conductivity and uniform dispersion of the nanomaterials form an effective conductive network, reducing resistance in the ion transport path and, consequently, lowering membrane resistance.

[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 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 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 improves current efficiency by modifying PVC with maleic anhydride grafted onto PE. Maleic anhydride groups react with functional groups such as hydroxyl or carboxyl groups on the PVC surface, forming covalent bonds or strong physical adsorption, thereby enhancing interfacial bonding. This enhanced interfacial bonding helps improve the overall strength and toughness of the composite material. The uniform microstructure and reduced defects reduce membrane resistance and increase ion migration rates.

[0027] Furthermore, in step (5), the mixture is immersed in a 1-1.2 mol / L NaCl solution for 15-18 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 by adding pretreated nanomaterials into the PVC membrane, and at the same time reduce the resistance.

[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 following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts 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 commodities:

[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 the nanomaterial in 70 parts of ethanol, adding 8 parts of a silane coupling agent KH570, and reacting the mixture under the conditions of heating at 60°C for 7 hours, filtering the mixture after the reaction, washing the mixture three times with water, and vacuum drying the mixture to obtain the pretreated nanomaterial;

[0039] The nanomaterial is carboxylated carbon nanotubes with a length of 0.5-2 μm and a carboxyl content of 0.49 wt%. The raw material carbon nanotubes were 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 peroxyneodecanoate and 0.4 parts of surfactant Span 20 were mixed and reacted at 55°C for 7 hours, and then 0.016 parts of diethylhydroxylamine were added. Unreacted vinyl chloride was removed by vacuum rotary evaporation, and the mixture was centrifuged and dried to obtain PVC resin;

[0041] (3) PVC resin, zinc stearate and maleic anhydride grafted PE were mixed in an internal mixer at a mass ratio of 50:6:13, mixed at 165° C., and then crushed 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 in a weight ratio of 4:11:87, and oscillating the mixture to obtain a casting solution;

[0043] (5) The casting solution was poured onto a smooth flat plate and scraped to form a membrane, which was then placed in a vacuum drying oven and dried at 65°C for 20 h. The membrane was then taken out of the oven and cooled to room temperature in air. The cooled membrane was placed in deionized water for 15 h, and the membrane automatically peeled off from the smooth flat plate. The membrane was then immersed in a 1 mol / L NaCl solution for 16 h 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 a silane coupling agent KH570, and reacting the mixture under the conditions of heating at 60°C for 6 hours, filtering the mixture after the reaction, washing it with water three times, and vacuum drying the mixture to obtain the pretreated nanomaterial;

[0047] The nanomaterial is carboxylated carbon nanotubes with a length of 0.5-2 μm and a carboxyl content of 0.49 wt%. The raw material carbon nanotubes were 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 isopropyl peroxyneodecanoate and 0.5 parts of surfactant Span 20 were mixed and reacted at 50°C for 8 hours, and then 0.015 parts of diethylhydroxylamine were added. Unreacted vinyl chloride was removed by vacuum rotary evaporation, and the mixture was centrifuged and dried to obtain PVC resin;

[0049] (3) PVC resin, zinc stearate and maleic anhydride grafted PE were mixed in an internal mixer at a mass ratio of 50:7:15, mixed at 165° C., and then crushed 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 in a weight ratio of 3:12:90, and oscillating the mixture to obtain a casting solution;

[0051] (5) The casting solution was poured onto a smooth flat plate and scraped to form a membrane, which was then placed in a vacuum drying oven and dried at 65°C for 20 h. The membrane was then taken out of the oven and cooled to room temperature in air. The cooled membrane was placed in deionized water for 15 h, and the membrane automatically peeled off from the smooth flat plate. The membrane was then immersed in a 1.2 mol / L NaCl solution for 18 h 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 during the preparation of the PVC resin.

[0054] Mix 100 parts of vinyl chloride, 145 parts of deionized water, 0.05 parts of initiator isopropyl peroxyneodecanoate and 0.4 parts of surfactant Span 20, react at 55°C for 7 hours, then add 0.016 parts of diethylhydroxylamine to remove unreacted vinyl chloride, centrifuge and dry 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 membrane's surface resistance was measured using the following apparatus: it consists of two electrode chambers, two intermediate chambers, and a membrane-mounting clamp. Before testing, the membrane to be tested was equilibrated in a 0.5 mol / L NaCl solution for 12 hours. During the measurement, the equilibrated membrane was secured within the clamp, and a 0.3 mol / L Na₂SO₄ solution was pumped into the two electrode chambers and circulated continuously. A 0.5 mol / L NaCl solution was then pumped into the two intermediate chambers. The current was maintained constant at 0.05 A, and the inter-electrode potential, U, was read using a digital multimeter. The membrane resistance was calculated using the formula R = S × [(U - U₀) / I]. Here, U₀ is the blank voltage (V), i.e., the voltage reading when no membrane is in place; I is the applied current (A); and S is the membrane's effective area.

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

[0065] Tensile strength test: CTM2050 automatic mechanical strength tester was used to test the cationic electrodialysis membrane. The membrane was cut into 2×10cm 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] From the above performance test results, it can be seen that the electrodialysis membranes of Examples 1 and 2 have excellent comprehensive performance, especially the comprehensive performance of Example 1 is the most outstanding.

[0070] In Comparative Example 1, where no pre-treated nanomaterials were added, the cationic electrodialysis membrane exhibited decreased selectivity for positive ions of varying valences and increased resistance. In Comparative Example 2, where the PVC resin was unmodified, the membrane's mechanical properties and current efficiency decreased. In Comparative Examples 3 and 4, varying amounts of maleic anhydride-grafted PE were added, resulting in decreased current efficiency. These experimental results further demonstrate the importance of the technical solutions defined in the present invention for its effectiveness.

[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 within 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 nanomaterial 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 nanomaterial; the nanomaterial is a carboxylated carbon nanotube; (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 to N,N-dimethylacetamide to obtain a casting solution; (5) The casting solution is formed into a membrane to obtain a cationic electrodialysis membrane.

2. The method for preparing a cationic electrodialysis membrane according to claim 1, wherein: By weight, The step (1) comprises dispersing 5 parts of a nanomaterial in 60 to 80 parts of ethanol, adding 7 to 9 parts of a 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) comprises mixing 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 an initiator, and 0.3 to 0.5 parts of a surfactant, reacting the mixture at 50 to 60° C. for 5 to 8 hours, adding 0.015 to 0.017 parts of diethylhydroxylamine, removing unreacted vinyl chloride, centrifuging, and drying to obtain a PVC resin; The step (3) comprises mixing PVC resin, zinc stearate and maleic anhydride grafted PE in an internal mixer, kneading the mixture, and then crushing the mixture in a crusher to obtain a modified PVC resin; The step (4) includes adding a cation exchange resin and a modified PVC resin into N,N-dimethylacetamide and shaking the mixture to obtain a casting solution; The step (5) comprises pouring the casting solution onto a smooth flat plate, scraping the film, drying the film, 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 the film in a NaCl solution to obtain a cationic electrodialysis membrane.

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

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

8. The method for preparing a cationic electrodialysis membrane according to claim 1, wherein 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, wherein: In the step (5), the sample is immersed in a 1-1.2 mol / L NaCl solution for 15-18 hours.

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

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