Montmorillonite nanosheet modified cation exchange membrane, preparation method thereof and electrodialysis device for reducing salt of fermented food

Abstract

The invention relates to a montmorillonite nanosheet modified cation exchange membrane, a preparation method thereof and an electrodialysis device for reducing salt of fermented food, and belongs to the technical field of membrane materials for food processing. According to the cation exchange membrane, montmorillonite nanosheets are adopted as a modifier, the montmorillonite nanosheets are prepared through freezing-unfreezing circulation and ultrasonic stripping, then the montmorillonite nanosheets and a polymer matrix are blended to prepare a membrane casting solution, and the modified electrodialysis membrane is obtained after membrane scraping and drying. The membrane has excellent sodium ion selective permeability and amino acid interception capability, and can effectively realize efficient removal of sodium ions in fermented food and retention of flavor substances. The invention further provides an electrodialysis device comprising the montmorillonite nanosheet modified cation exchange membrane, a multi-cavity structure is adopted, a transition chamber and barrier liquid are arranged, concentration polarization and extreme water pollution are effectively inhibited, and the desalination efficiency and the product quality are improved.

Description

Technical Field

[0001] This invention belongs to the field of membrane materials and technology for food processing, specifically relating to montmorillonite nanosheet modified cation exchange membranes, their preparation methods, and electrodialysis devices for reducing salt content in fermented foods. Background Technology

[0002] Fermented foods, such as soy sauce, soybean paste, and oyster sauce, are indispensable condiments in global culinary cultures. However, these foods produced using traditional fermentation processes typically contain high levels of salt (sodium chloride). Excessive sodium intake is a major risk factor for health problems such as high blood pressure and cardiovascular disease. Therefore, developing technologies that can effectively reduce the salt content of fermented foods while preserving their original flavor has become an important challenge for the food industry.

[0003] Among existing salt reduction technologies, electrodialysis is widely used due to its advantages such as high efficiency, energy saving, and mild processing conditions. However, current electrodialysis technology used for salt reduction in fermented foods still has significant drawbacks. Firstly, the insufficient selectivity of the core component—the electrodialysis membrane (especially the cation exchange membrane)—is a key issue. Fermentation broth has a complex composition, containing not only sodium ions (Na+) that need to be removed... + It is also rich in amino acids, small molecule peptides, and other nutrients that give the product its umami and characteristic flavor. Traditional electrodialysis membranes, under the influence of an electric field, have difficulty efficiently distinguishing sodium... + Along with these positively charged amino acid molecules (such as glutamic acid), valuable flavor compounds are lost during the desalination process, seriously affecting the sensory quality and nutritional value of fermented foods after salt reduction.

[0004] Secondly, traditional electrodialysis devices are prone to concentration polarization during operation, which reduces ion migration efficiency, increases energy consumption, and may cause precipitation and scaling. Furthermore, the wastewater generated by the electrode reactions may contaminate materials in the product chamber, affecting food safety.

[0005] Therefore, there is an urgent need in this field to develop a highly selective ion exchange membrane that can preferentially allow Na+ to pass through. + It can effectively retain flavor substances such as amino acids. At the same time, it is necessary to design a high-efficiency electrodialysis device that can overcome concentration polarization and avoid water pollution, so as to achieve the industrial production goal of reducing salt and preserving flavor in fermented foods. Summary of the Invention

[0006] The purpose of this invention is to provide a montmorillonite nanosheet modified cation exchange membrane and its electrodialysis device to solve the problems of easy loss of flavor substances, low salt reduction efficiency and easy product contamination in existing fermented food salt reduction technologies.

[0007] On the one hand, the present invention provides a method for preparing a montmorillonite nanosheet modified cation exchange membrane, which adopts the following technical solution: The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Add montmorillonite to deionized water, stir and disperse to obtain montmorillonite suspension; S2. The montmorillonite suspension obtained in step S1 is placed in a sealed bottle, frozen and then thawed, and ultrasonically treated to prepare montmorillonite nanosheets. S3. Take the polymer matrix and the montmorillonite nanosheets obtained in step S2 and mix them with an organic solvent. Heat and stir in an oil bath until the polymer is completely dissolved. Let stand to obtain a uniformly dispersed casting solution. S4. Pour the casting solution obtained in step S3 onto the surface of a glass plate, spread it evenly with a scraper, place the glass plate in a vacuum drying oven to dry, and after evaporating the solvent, obtain the montmorillonite nanosheet modified cation exchange membrane.

[0008] Preferably, the freezing and thawing conditions in step S2 are as follows: first freeze at -20°C for 12 hours, then thaw at 20°C for 12 hours, and repeat 1-2 times.

[0009] Preferably, the frequency of ultrasonic treatment in step S2 is 200-450 W.

[0010] Preferably, in step S3, the montmorillonite nanosheets and polymer matrix are solid components, and the mass of the solid components accounts for 21% of the total mass of the casting solution; the mass of the montmorillonite nanosheets accounts for 7.5% of the total mass of the solid components. The polymer matrix is ​​at least one of polyethersulfone, polysulfone, sulfonated polysulfone, and sulfonated polyethersulfone.

[0011] Preferably, the organic solvent in step S3 is at least one of N,N-dimethylacetamide and N-methylpyrrolidone.

[0012] Preferably, in step S3, the heating and stirring temperature is 60-80℃ and the time is 3-4 h; The settling time in step S3 is 2 hours.

[0013] Preferably, the coating thickness in step S4 is 300-600 μm; In step S4, the drying temperature is 60-80℃ and the drying time is 8-12 h.

[0014] On the one hand, the present invention provides a montmorillonite nanosheet modified cation exchange membrane prepared by the above preparation method.

[0015] On the other hand, the present invention also provides an electrodialysis device for reducing salt content in fermented foods using a montmorillonite nanosheet-modified cation exchange membrane prepared by the above-mentioned method, employing the following technical solution: An electrodialysis device for reducing salt content in fermented foods includes an anode plate, a first electrode chamber, a first barrier chamber, a reaction module, a second barrier chamber, a second electrode chamber, and a cathode plate distributed in a horizontal direction. The reaction module is configured in multiple groups. Each group of reaction modules is provided with a soy sauce chamber, a transition chamber, and a concentrated salt chamber in sequence along the direction from the anode plate to the cathode plate. Montmorillonite nanosheet modified cation exchange membranes are respectively arranged between the soy sauce chamber, the transition chamber, and the concentrated salt chamber. A montmorillonite nanosheet modified cation exchange membrane is arranged between the first electrode chamber and the first barrier chamber. A montmorillonite nanosheet modified cation exchange membrane is arranged between the second electrode chamber and the second barrier chamber. An anion exchange membrane is arranged between each pair of adjacent reaction modules.

[0016] Preferably, the lower part of the anode plate is provided with a first raw material inlet, a first concentrated brine inlet, a first transition chamber inlet, a second raw material inlet, a second concentrated brine inlet, and a second transition chamber inlet, and the upper part of the anode plate is provided with a first transition chamber outlet, a first raw material outlet, a first concentrated brine outlet, a second transition chamber outlet, a second raw material outlet, and a second concentrated brine outlet; The first electrode chamber has a first electrode water outlet at the upper part and a first electrode water inlet at the lower part; The upper part of the second electrode chamber has a second electrode water outlet, and the lower part of the second electrode chamber has a second electrode water inlet; The upper part of the first barrier chamber is provided with a first sodium water outlet, and the lower part of the first barrier chamber is provided with a first sodium water inlet. The second barrier chamber is provided with a second sodium water outlet at the upper part and a second sodium water inlet at the lower part. Filter plates are respectively installed between the first electrode chamber, the first barrier chamber, the soy sauce chamber, the transition chamber, the concentrated salt chamber, the second barrier chamber, and the second electrode chamber; The anode plate, the first electrode chamber, the first barrier chamber, the reaction module, the second barrier chamber, the second electrode chamber, and the cathode plate are tightly connected by fixing screws.

[0017] In summary, the present invention has the following beneficial technical effects: 1. The core beneficial effect of this invention lies in the successful preparation of a montmorillonite nanosheet-modified cation exchange membrane. Utilizing the unique layered structure and surface charge characteristics of montmorillonite nanosheets, the montmorillonite nanosheet-modified cation exchange membrane significantly enhances the membrane's selective ion separation capability. Specifically, during electrodialysis, it achieves a high sodium ion permeability of 70%-90%, while effectively retaining macromolecular flavor substances such as amino acids, increasing the relative content of amino acid nitrogen by 6.7%-8%. This highly efficient desalination and precise flavor preservation characteristic fundamentally solves the technical problem of flavor and nutrient loss in traditional salt reduction processes.

[0018] 2. This invention innovatively applies montmorillonite nanosheet-modified cation exchange membranes to an optimized multi-chamber electrodialysis device. The electrodialysis device, through the introduction of a transition chamber, effectively mitigates concentration polarization, improving concentration efficiency and process stability. Simultaneously, by incorporating a barrier liquid, it completely isolates the raw materials from the contamination of the electrode reaction's waste gas, ensuring food safety. This integrated system solution of montmorillonite nanosheet-modified cation exchange membranes and electrodialysis devices not only achieves high efficiency and low energy consumption in the salt reduction process of fermented foods but also ensures that the core flavor and quality of the final product are excellently preserved while the salt content is reduced. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of four membrane modules of the electrodialysis device for reducing salt content in fermented foods prepared according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the electrodialysis device for reducing salt content in fermented foods prepared according to an embodiment of the present invention; Figure 3 Diagram illustrating the principle of reducing salt in fermented foods; In the diagram: 1-First raw material inlet, 2-First concentrated brine inlet, 3-First transition chamber inlet, 4-Second raw material inlet, 5-Second concentrated brine inlet, 6-Second transition chamber inlet, 7-Outer anode plate, 8-Second concentrated brine outlet, 9-Second raw material outlet, 10-Second transition chamber outlet, 11-First concentrated brine outlet, 12-First raw material outlet, 13-First transition chamber outlet, 14-First electrode water outlet, 15-First sodium water outlet, 16-Second sodium water 17 - Second electrode water outlet; 18 - Second electrode water inlet; 19 - Second sodium water inlet; 20 - First sodium water inlet; 21 - First electrode water inlet; 22 - Fixed screw; 23 - First electrode chamber; 24 - Second electrode chamber; 25 - First barrier chamber; 26 - Second barrier chamber; 27 - Soy sauce chamber; 28 - Transition chamber; 29 - Concentrated salt chamber; 30 - Cathode plate; 31 - Reaction module; 32 - Cation exchange membrane; 33 - Anion exchange membrane; 34 - Filter plate. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to embodiments, test examples and accompanying drawings.

[0021] Example

[0022] Example 1 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic disperser to exfoliate the montmorillonite nanosheets (MMTNS) at an ultrasonic frequency of 300 W. S2. Weigh 0.3 g MMTNS, 2 g sulfonated polyethersulfone, and 1.7 g polyethersulfone, add 15 g DMAc, heat in an oil bath at 65°C, stir magnetically for 3.5 h until completely dissolved, let stand for 2 h to remove bubbles, and obtain the casting solution. S3. Pour the casting solution onto a glass plate and use a 400 μm doctor blade to coat the membrane; vacuum dry at 70℃ for 10 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0023] Example 2 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic disperser to exfoliate the montmorillonite nanosheets (MMTNS) at an ultrasonic frequency of 350 W. S2. Weigh 0.3 g MMTNS, 2 g sulfonated polysulfone, and 1.7 g polysulfone, add 15 g DMAc, heat in an oil bath at 70°C, stir magnetically for 4 h until completely dissolved, let stand for 2 h to remove bubbles, and obtain the casting solution. S3. Pour the casting solution onto a glass plate and use a 350 μm doctor blade to coat the membrane; dry under vacuum at 75℃ for 9 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0024] Example 3 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic dispersant to exfoliate it with an ultrasonic frequency of 250 W to obtain montmorillonite nanosheets (MMTNS). S2. Weigh 0.3g MMTNS, 2g sulfonated polysulfone, and 1.7g polyethersulfone, add 15g DMAc, heat in an oil bath at 60℃, stir magnetically for 3 hours until completely dissolved, let stand for 2 hours to remove bubbles, and obtain the casting solution. S3. Pour the casting solution onto a glass plate and use a 375 μm doctor blade to coat the membrane; vacuum dry at 65℃ for 11 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0025] Example 4 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic dispersant to exfoliate it with an ultrasonic frequency of 400 W to obtain montmorillonite nanosheets (MMTNS). S2. Weigh 0.3 g MMTNS, 2 g sulfonated polyethersulfone, and 1.7 g polysulfone, add 15 g DMAc, heat in an oil bath at 62°C, stir magnetically for 3.2 h until completely dissolved, let stand for 2 h to remove bubbles, and obtain the casting solution. S3. Pour the casting solution onto a glass plate, use a 350 μm doctor blade to coat the membrane, and vacuum dry at 68℃ for 9.5 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0026] Example 5 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Freeze it again at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic dispersant to ultrasonically exfoliate it at an ultrasonic frequency of 350 W to obtain montmorillonite nanosheets (MMTNS). S2. Weigh 0.3 g MMTNS and 3.7 g polyethersulfone, add 15 g NMP, heat in an oil bath at 70°C, stir magnetically for 3.5 h until completely dissolved, let stand for 2 h to remove bubbles, and obtain casting solution. S3. Pour the casting solution onto a glass plate and use a 450 μm doctor blade to coat the membrane; vacuum dry at 72℃ for 9 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0027] Example 6 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Freeze it again at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic dispersant to ultrasonically exfoliate it at an ultrasonic frequency of 400 W to obtain montmorillonite nanosheets (MMTNS). S2. Weigh 0.3 g MMTNS and 3.7 g polysulfone, add 15 g NMP; heat in an oil bath at 75°C and stir magnetically for 4 h until completely dissolved; let stand for 2 h to remove bubbles and obtain the casting solution. S3. Pour the casting solution onto a glass plate and use a 320 μm doctor blade to coat the membrane; vacuum dry at 78℃ for 8.5 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0028] Example 7 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Freeze it again at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic disperser to ultrasonically exfoliate the montmorillonite nanosheets (MMTNS) at an ultrasonic frequency of 250 W. S2. Weigh 0.3 g MMTNS and 3.7 g sulfonated polysulfone, add 15 g NMP; heat in an oil bath at 68°C, and stir magnetically for 3 h until completely dissolved; let stand for 2 h to remove bubbles, and obtain the casting solution; S3. Pour the casting solution onto a glass plate and use a 370 μm doctor blade to coat the membrane; vacuum dry at 68℃ for 10 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0029] Example 8 The preparation method of montmorillonite nanosheet modified cation exchange membrane includes the following preparation steps: S1. Weigh 1 g of montmorillonite, add 100 mL of deionized water, and stir magnetically for 1 h to obtain a montmorillonite suspension. Freeze the montmorillonite suspension at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Freeze it again at -20℃ for 12 h, then thaw it at 20℃ for 12 h. Use an ultrasonic dispersant to ultrasonically exfoliate it at an ultrasonic frequency of 300 W to obtain montmorillonite nanosheets (MMTNS). S2. Weigh 0.3 g MMTNS and 3.7 g sulfonated polyethersulfone, add 15 g NMP; heat in an oil bath at 65°C and stir magnetically for 3.2 h until completely dissolved; let stand for 2 h to remove bubbles and obtain the casting solution. S3. Pour the casting solution onto a glass plate, use a 460 μm doctor blade to coat the membrane, and vacuum dry at 70℃ for 8 h to obtain a montmorillonite nanosheet modified cation exchange membrane.

[0030] Example 9 Reference Figure 1 and Figure 2 An electrodialysis device for reducing salt content in fermented foods includes an anode plate 7, a first electrode chamber 23, a first barrier chamber 25, a reaction module 31, a second barrier chamber 26, a second electrode chamber 24, and a cathode plate 30, all distributed horizontally. The reaction module 31 is provided in multiple sets. In this embodiment, the reaction module 31 is provided in four sets. Each set of reaction modules 31 is provided with a soy sauce chamber 27, a transition chamber 28 and a concentrated salt chamber 29 in sequence along the direction from the anode plate 7 to the cathode plate 30. Montmorillonite nanosheet modified cation exchange membranes 32 are respectively provided between the soy sauce chamber 27, the transition chamber 28 and the concentrated salt chamber 29. A montmorillonite nanosheet modified cation exchange membrane 32 is provided between the first electrode chamber 23 and the first barrier chamber 25. A montmorillonite nanosheet modified cation exchange membrane 32 is provided between the second electrode chamber 24 and the second barrier chamber 26. An anion exchange membrane 33 is provided between each pair of adjacent reaction modules.

[0031] Reference Figure 1 and Figure 2 The anode plate 7 is located on one side of the electrodialysis device. The lower part of the anode plate 7 is provided with a first raw material inlet 1, a first concentrated brine inlet 2, a first transition chamber inlet 3, a second raw material inlet 4, a second concentrated brine inlet 5, and a second transition chamber inlet 6. The upper part of the anode plate 7 is provided with a first transition chamber outlet 13, a first raw material outlet 12, a first concentrated brine outlet 11, a second transition chamber outlet 10, a second raw material outlet 9, and a second concentrated brine outlet 8. The cathode plate 30 is located on the side of the electrodialysis device opposite to the anode plate 7.

[0032] Reference Figure 1 and Figure 2The first electrode chamber 23 is located near the anode plate 7. A first electrode water outlet 14 is located at the top of the first electrode chamber 23, and a first electrode water inlet 21 is located at the bottom of the first electrode chamber 23. The second electrode chamber 24 is located near the cathode plate 30. A second electrode water outlet 17 is located at the top of the second electrode chamber 24, and a second electrode water inlet 18 is located at the bottom of the second electrode chamber 24. A first barrier chamber 25 is located inside the first electrode chamber 23. A first sodium water outlet 15 is located at the top of the first barrier chamber 25, and a first sodium water inlet 20 is located at the bottom of the first barrier chamber 25. A second barrier chamber 26 is located inside the second electrode chamber 24. A second sodium water outlet 16 is located at the top of the second barrier chamber 26, and a second sodium water inlet 19 is located at the bottom of the second barrier chamber 26.

[0033] Reference Figure 1 and Figure 2 A filter plate 34 is provided between the first electrode chamber 23, the first barrier chamber 25, the soy sauce chamber 27, the transition chamber 28, the concentrated salt chamber 29, the second barrier chamber 26, and the second electrode chamber 24; and the anode plate 7, the first electrode chamber 23, the first barrier chamber 25, the reaction module 31, the second barrier chamber 26, the second electrode chamber 24, and the cathode plate 30 are tightly connected by a fixing screw 22.

[0034] Example 10 Combination Figure 1-3 As shown, the electrodialysis reactor consists of 50 working units and 153 membranes. The specific arrangement and connection of each component are as follows: the leftmost anode plate is connected to the positive terminal of a DC power supply, and the rightmost cathode plate is connected to the negative terminal of a DC power supply. Cation exchange membranes are assembled on the inner sides of these two plates, and the 50 working units are positioned between these two cation exchange membranes. Each working unit consists of two cation exchange membranes and two anion exchange membranes. Through the combination of the membranes and working units, the area between the two plates is divided into multiple independent chambers. From the anode chamber to the cathode chamber, the chambers are arranged in the following order: anode chamber, sodium solution barrier chamber, feed chamber, transition chamber, concentrated salt chamber, sodium solution barrier chamber, and cathode chamber.

[0035] In terms of membrane placement, cation exchange membranes are installed between the anode chamber and the sodium solution barrier chamber, between the feed chamber and the concentration chamber, and between the sodium solution barrier chamber and the cathode chamber; anion exchange membranes are only installed between the feed chamber and the concentration chamber. All membranes are uniformly 80 cm × 40 cm in size.

[0036] This electrodialysis device operates in continuous mode. The material supply and parameter settings during operation are as follows: the original fermented food to be processed is introduced into the raw material chamber; a 4 g / L NaCl solution is injected into the concentration chamber; a 44 g / L NaCl solution is introduced into the sodium barrier chamber; and a 35 g / L NaCl solution is introduced into the electrode chamber. The material flow rate in each chamber is controlled within the range of 3–7 m³ / h. The DC power supply operates in constant current mode, with a set current value of 150 A. Driven by the electric field, sodium ions in the fermented food in the raw material chamber penetrate the cation exchange membrane and migrate towards the concentration chamber. As the device operates for an extended period, the sodium ion content continuously decreases, while amino acids are gradually enriched. In actual operation, the sodium and amino acid content in the final fermented food can be precisely controlled by adjusting parameters such as the number of working units, material flow rate, and current magnitude.

[0037] Comparative Example

[0038] Comparative Example 1 The cation exchange membrane (SYMC-1) was purchased from Zhongke Xinyang Membrane Technology Co., Ltd.

[0039] Test case

[0040] Test Example 1 The cation exchange membranes prepared in Examples 1-8 and Comparative Example 1 were subjected to desalination treatment in the manner described in Example 10, with a current of 150-255 A and a temperature of 27-29°C.

[0041] The results are shown in Table 1. The sodium ion permeability of Examples 1-8 of this invention is between 70% and 86%, indicating that the montmorillonite nanosheet modified cation exchange membranes prepared by this invention can achieve efficient and stable desalination. In contrast, the sodium ion permeability of the commercial membrane SYMC-1 used in Comparative Example 1 is 70%, which is at the lower limit of the effective range of the examples of this invention. This shows that the modified membrane of this invention is at least comparable to the commercial membrane in desalination efficiency, and under most preparation conditions (such as Examples 1, 3, 6, and 7), its desalination efficiency is significantly better than that of the comparative commercial membrane.

[0042] The relative content of amino acid nitrogen after treatment in Examples 1-8 of this invention is all >106.7%, indicating effective enrichment of amino acids, with their content increasing by 6.7% to 8.0%. In contrast, the relative content of amino acid nitrogen after treatment in Comparative Example 1 is only 104.8%. This fully demonstrates that the cation exchange membrane prepared by modification with montmorillonite nanosheets in this invention, while efficiently removing sodium ions, has a significantly better retention capacity for flavor substances such as amino acids than traditional commercial membranes, perfectly achieving the core objective of reducing salt and preserving flavor.

[0043] Compared with existing commercial membranes, the montmorillonite nanosheet modified cation exchange membrane provided by this invention is not only competitive in desalination efficiency, but also significantly improves the retention capacity of key flavor substances, solving the industry problem of easy loss of flavor substances in traditional electrodialysis desalination technology.

[0044] Table 1 Test conditions and parameter indicators of the products obtained in Examples 1-8 and Comparative Example 1

Claims

1. A method for preparing a montmorillonite nanosheet-modified cation exchange membrane, characterized in that, Includes the following steps: S1. Add montmorillonite to deionized water, stir and disperse to obtain montmorillonite suspension; S2. The montmorillonite suspension obtained in step S1 is placed in a sealed bottle, frozen and then thawed, and ultrasonically treated to prepare montmorillonite nanosheets. S3. Take the polymer matrix and the montmorillonite nanosheets obtained in step S2 and mix them with an organic solvent. Heat and stir in an oil bath until the polymer is completely dissolved. Let stand to obtain a uniformly dispersed casting solution. S4. Pour the casting solution obtained in step S3 onto the surface of a glass plate, spread it evenly with a scraper, place the glass plate in a vacuum drying oven to dry, and after evaporating the solvent, obtain the montmorillonite nanosheet modified cation exchange membrane.

2. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, The freezing and thawing conditions in step S2 are as follows: first freeze at -20℃ for 12 hours, then thaw at 20℃ for 12 hours, and repeat 1-2 times.

3. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, The frequency of ultrasonic treatment in step S2 is 200-450 W.

4. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, In step S3, the montmorillonite nanosheets and polymer matrix are solid components, and the mass of the solid components accounts for 21% of the total mass of the casting solution; the mass of the montmorillonite nanosheets accounts for 7.5% of the total mass of the solid components. The polymer matrix is ​​at least one of polyethersulfone, polysulfone, sulfonated polysulfone, and sulfonated polyethersulfone.

5. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, The organic solvent in step S3 is at least one of N,N-dimethylacetamide and N-methylpyrrolidone.

6. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, In step S3, the heating and stirring temperature is 60-80℃, and the time is 3-4 hours. The settling time in step S3 is 2 hours.

7. The method for preparing the montmorillonite nanosheet modified cation exchange membrane according to claim 1, characterized in that, In step S4, the coating thickness is 300-600 μm; In step S4, the drying temperature is 60-80℃ and the drying time is 8-12 h.

8. The montmorillonite nanosheet modified cation exchange membrane prepared by the preparation method according to any one of claims 1-7.

9. An electrodialysis device for reducing salt content in fermented foods, comprising a montmorillonite nanosheet-modified cation exchange membrane prepared by any one of claims 1-7, characterized in that, It includes an anode plate (7), a first electrode chamber (23), a first barrier chamber (25), a reaction module (31), a second barrier chamber (26), a second electrode chamber (24), and a cathode plate (30) distributed in a horizontal direction; The reaction module (31) is provided in multiple groups. Each group of reaction modules (31) is provided with a soy sauce chamber (27), a transition chamber (28) and a concentrated salt chamber (29) in sequence along the direction from the anode plate (7) to the cathode plate (30). Montmorillonite nanosheet modified cation exchange membranes (32) are respectively provided between the soy sauce chamber (27), the transition chamber (28) and the concentrated salt chamber (29). Montmorillonite nanosheet modified cation exchange membranes (32) are provided between the first electrode chamber (23) and the first barrier chamber (25). Montmorillonite nanosheet modified cation exchange membranes (32) are provided between the second electrode chamber (24) and the second barrier chamber (26). Anion exchange membranes (33) are provided between each pair of adjacent reaction modules.

10. The electrodialysis device for reducing salt content in fermented foods according to claim 9, characterized in that, The anode plate (7) has a first raw material inlet (1), a first concentrated brine inlet (2), a first transition chamber inlet (3), a second raw material inlet (4), a second concentrated brine inlet (5), and a second transition chamber inlet (6) at its lower part. The anode plate (7) has a first transition chamber outlet (13), a first raw material outlet (12), a first concentrated brine outlet (11), a second transition chamber outlet (10), a second raw material outlet (9), and a second concentrated brine outlet (8) at its upper part. The first polar chamber (23) has a first polar water outlet (14) at the top and a first polar water inlet (21) at the bottom. The upper part of the second polar chamber (24) is provided with a second polar water outlet (17), and the lower part of the second polar chamber (24) is provided with a second polar water inlet (18). The upper part of the first barrier chamber (25) is provided with a first sodium water outlet (15), and the lower part of the first barrier chamber (25) is provided with a first sodium water inlet (20). The second barrier chamber (26) is provided with a second sodium water outlet (16) at the top and a second sodium water inlet (19) at the bottom. A filter plate (34) is provided between the first electrode chamber (23), the first barrier chamber (25), the soy sauce chamber (27), the transition chamber (28), the concentrated salt chamber (29), the second barrier chamber (26), and the second electrode chamber (24); The anode plate (7), the first electrode chamber (23), the first barrier chamber (25), the reaction module (31), the second barrier chamber (26), the second electrode chamber (24), and the cathode plate (30) are tightly connected by a fixing screw (22).

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