Method for evaluating interlayer bonding degree of chlor-alkali ion exchange membrane

Abstract

The present application relates to chlor-alkali ion membrane test technical field, specifically to a kind of evaluation method of chlor-alkali ion membrane interlayer bonding degree.The chlor-alkali ion membrane is installed reversely, so that carboxylic acid layer is exposed to anode acidic environment, and it is assisted with abnormal working conditions such as high temperature, high concentration electrolyte, high current density, promotes carboxylic acid layer acidification, increases the voltage between two layers, so that it completes accelerated aging in a short time.After aging, the bonding degree of sulfonic acid layer and carboxylic acid layer is evaluated by visual observation.The present application uses the extreme chemical and physical stress generated by reverse installation, quickly exposes the weak link of interlayer bonding, can complete the key information about membrane interlayer bonding durability in 1 hour, which is obtained in months by traditional long-term test, has the characteristics of fast, sensitive and reliable, and is suitable for rapid quality screening and research and development optimization of chlor-alkali ion membrane.

Description

Technical Field

[0001] This invention relates to the field of chlor-alkali ion exchange membrane testing technology, specifically to a method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes. Background Technology

[0002] Perfluorosulfonic acid / carboxylic acid composite chlor-alkali ion exchange membranes are core components of modern chlor-alkali industries. They are typically composed of chemically resistant reinforcing materials (such as PTFE mesh) and perfluorosulfonic acid and perfluorocarboxylic acid functional layers, facing the anode and cathode respectively. The sulfonic acid layer (usually thicker, facing the anode) is primarily responsible for conducting cations and retaining moisture, while the carboxylic acid layer (usually thinner, facing the cathode) enables extremely high current efficiency. The bonding strength (or adhesion) between these two layers is a key factor determining the membrane's mechanical integrity, long-term operational stability, and lifespan. Poor interlayer bonding can easily lead to blistering, delamination, or peeling under complex operating conditions (such as fluctuations in temperature, pressure, and concentration), resulting in a sharp decline in membrane performance or even failure.

[0003] Currently, the evaluation of interlayer adhesion of new membranes mostly employs conventional physical testing methods, such as peel strength testing. However, this method only reflects the static adhesion of the new membrane in its initial state and cannot simulate the dynamic durability of the membrane under real electrolysis environments (especially abnormal operating conditions, such as reverse voltage and extreme pH values). While conventional long-term aging tests can reflect performance degradation, they are time-consuming (months or even years) and costly, failing to meet the needs of rapid membrane material development, quality control, and lifespan prediction.

[0004] Therefore, there is an urgent need in this field for a method that can rapidly and reliably simulate and evaluate the interlayer binding degree of chlor-alkali ion exchange membranes in a laboratory setting. Summary of the Invention

[0005] To address the problems of long testing cycles, inability to simulate real electrolysis abnormalities, and large discrepancies between static test results and actual operational durability in existing chlor-alkali ion exchange membrane interlayer bonding evaluation technologies, this invention aims to provide a method for evaluating the interlayer bonding of chlor-alkali ion exchange membranes. This method can quickly screen out membrane products with poor interlayer bonding performance, providing key data for membrane material research and development improvement and quality control.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes includes the following steps: (1) The chlor-alkali ion membrane sample to be tested is installed in the experimental electrolytic cell in a reverse installation manner, wherein the membrane has a carboxylic acid layer and a sulfonic acid layer, and during installation, the carboxylic acid layer faces the anode chamber and the sulfonic acid layer faces the cathode chamber; (2) Electrolyte is introduced into the anode chamber and cathode chamber respectively, and the electrolytic cell is operated under abnormal operating conditions to carry out accelerated aging test; The abnormal operating conditions include the following three: ①Increase the operating temperature of the electrolyzer to make it higher than the upper limit of the recommended temperature for the membrane during normal installation; ②Increase the concentration of the anolyte and / or catholyte; ③ Increase the current density; (3) After the accelerated aging time is reached, stop the electrolysis operation and take out the membrane sample that has undergone aging treatment from the electrolytic cell; (4) Visually observe the membrane surface, especially the interface area between the sulfonic acid layer and the carboxylic acid layer, to evaluate whether bubbling, delamination or peeling occurs, and evaluate the interlayer bonding degree between the sulfonic acid layer and the carboxylic acid layer. If it occurs, it is unqualified.

[0007] Preferably, in step (1), the size of the chlor-alkali ion membrane sample to be tested is 10cm×10cm, which is obtained by cutting it off from the chlor-alkali ion membrane.

[0008] Preferably, in step (1), the experimental electrolytic cell is a small laboratory-grade unipolar electrolytic cell with an effective electrolysis area of ​​50 cm². 2 .

[0009] Preferably, in step (2), the operating temperature is 86-95℃.

[0010] Preferably, in step (2), the anolyte is a sodium chloride solution with a concentration of 180-220 g / L, and the catholyte is a sodium hydroxide solution with a concentration of 33-35 wt%.

[0011] Preferably, in step (2), the current density is 5.6-6.5 kA / m 2 Preferred 6.0 kA / m 2 .

[0012] Preferably, in step (3), the accelerated aging time is 0.5-1 hour.

[0013] Regarding current density and operating temperature: The current standard electrolysis current density in the industry is 4-5.5 kA / m. 2 When the current density is below 5.6 kA / m 2 At that time, it is insufficient to achieve the purpose of accelerating aging, while when the current density is higher than 6.5kA / m 2 At times, there is a risk of excessive current breaking down the membrane, causing safety hazards. The normal electrolysis temperature in the industry is 83-85℃. When the test temperature is below 86℃, it is not enough to achieve the purpose of rapid aging. When the electrolysis temperature is above 95℃, the electrolyte is prone to boiling, which leads to abnormalities in the electrolysis process and makes it impossible to continue.

[0014] A preferred evaluation scheme, wherein the accelerated aging test conditions are as follows: Anodic solution: 180 g / L sodium chloride solution; Catholyte: 33wt% sodium hydroxide solution; Temperature: 95℃; Current density: 5.6 kA / m 2 ; Running time: 1 hour.

[0015] Another preferred evaluation scheme, wherein the accelerated aging test conditions are: Anodic solution: 220 g / L sodium chloride solution; Cathodic solution: 35wt% sodium hydroxide solution; Temperature: 86℃; Current density: 6kA / m 2 ; Running time: 0.5 hours.

[0016] Compared with the prior art, the present invention has the following advantages: (1) This invention utilizes the extreme condition of "reverse installation". In the reverse installation state, the carboxylic acid layer, which should originally face the mild cathode environment, is exposed to the strong oxidizing and highly acidic anode environment, and its chemical stability is severely challenged. At the same time, the balance of osmotic pressure and water content on both sides of the membrane is broken, and the internal stress is redistributed. This abnormal state will greatly aggravate the chemical erosion and physical stress at the interface between the sulfonic acid and carboxylic acid layers, and rapidly amplify and expose potential weak points in the bonding, thereby achieving "accelerated aging".

[0017] (2) Compared with the normal life test that takes several months, the method of the present invention introduces multiple harsh conditions (reverse installation, high temperature, high concentration, high current density) to qualitatively determine the interlayer bonding durability in 0.5-1 hours, which greatly shortens the test cycle and improves the efficiency of R&D and quality inspection.

[0018] (3) By accelerating aging through reverse installation, the membrane with poor interlayer bonding will produce visible defects (such as blistering and delamination). The evaluation criteria are clear and the results are reproducible.

[0019] (4) The present invention can effectively predict the anti-delamination ability of the membrane in long-term operation or under abnormal conditions such as accidental reverse connection through short-term laboratory testing, which has important guiding significance for the reliability design and safety assessment of the membrane.

[0020] (5) This method is not only applicable to the quality control of commercially available chlor-alkali ion membranes, but also to the formulation optimization and process improvement of new chlor-alkali ion membrane materials in the research and development stage, providing a key testing method for improving the overall performance of membrane products. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the normal installation of a chlor-alkali ion exchange membrane in an electrolytic cell. Figure 3 This is a schematic diagram of a chlor-alkali ion exchange membrane installed in reverse in an electrolyzer. Figure 4 This is a photograph of the membrane surface of membrane sample A, which had substandard interlayer bonding after accelerated aging in Example 1. Figure 5 This is a photograph of the membrane surface of membrane sample B, which has qualified interlayer bonding after accelerated aging in Example 1. Figure 6 This is a photograph of the membrane surface of membrane sample A, which had substandard interlayer bonding after accelerated aging in Example 2. Figure 7 This is a photograph of the membrane surface of membrane sample B, which has qualified interlayer bonding after accelerated aging in Example 2. Figure 8 This is a photograph of the membrane surface of membrane sample A after 1 hour of normal installation and operation in Comparative Example 1. Figure 9 This is a photograph of the membrane surface of membrane sample B after 1 hour of normal installation and operation in Comparative Example 1. Figure 10 This is a photograph of the membrane surface of membrane sample A after 0.5 hours of normal installation and operation in Comparative Example 2. Figure 11 This is a photograph of the membrane surface of membrane sample B after 0.5 hours of normal installation and operation in Comparative Example 2. Figure 12 This is a photograph of the membrane surface of membrane sample A after 3 months of normal installation and operation in Comparative Example 3; Figure 13 This is a photograph of the membrane surface of membrane sample B after 3 months of normal installation and operation in Comparative Example 3. In the diagram: 1. Anode; 2. Cathode; 3. Chlor-alkali ion exchange membrane; 31. Sulfonic acid layer; 32. Carboxylic acid layer; 4. Anode chamber; 5. Cathode chamber. Detailed Implementation

[0022] The present invention can be further described through the following embodiments; however, the scope of the present invention is not limited to the following embodiments. Those skilled in the art will understand that various changes and modifications can be made to the present invention without departing from its spirit and scope.

[0023] Many of the materials and methods used in the experiments of this invention are well known in the art, but the invention is still described in as much detail as possible herein.

[0024] Example 1 Test subject: DF2808 perfluorosulfonic acid / carboxylic acid composite chlor-alkali ion exchange membrane (hereinafter referred to as "ion exchange membrane") commercially available from Shandong Dongyue Polymer Materials Co., Ltd.

[0025] The evaluation is conducted according to the following steps, as shown in the flowchart. Figure 1 As shown: (1) Sample preparation: Take a sample of the new membrane of this model with a size of 10cm×10cm from two batches of ion exchange membranes that have been verified in the market, and denote them as sample A and sample B.

[0026] Sample Batch A: Electrolyzed in an electrolytic cell of a large domestic chlor-alkali customer (NCZ electrolytic cell of Bluestar (Beijing) Chemical Machinery Co., Ltd., electrolysis temperature 85℃, current density 5.5kA / m³). 2 Within one year of operation, the entire membrane exhibited bubbling and delamination (with an average outlet alkali concentration of 32.04%).

[0027] Sample Batch: Electrolyzed in an electrolytic cell of a large domestic chlor-alkali customer (NCZ electrolytic cell of Bluestar (Beijing) Chemical Machinery Co., Ltd., electrolysis temperature 85℃, current density 5.5kA / m³). 2 (With an average outlet alkali concentration of 32.04%), no membrane bubbling or delamination has occurred in the four years of operation.

[0028] (2) Electrolytic cell assembly: Samples A and B are installed in reverse orientation in a laboratory monopolar electrolytic cell (for the material and structure of the electrolytic cell, please refer to patent CN217378045U and the paper "Preferred Scheme for Laboratory-Grade Chlor-Alkali Ion Exchange Membrane Anode Electrolytic Cell" (published in "China Chlor-Alkali" 2025, No. 9), specifically the e-type cell). This ensures that the carboxylic acid layer of the membrane faces the anode chamber and the sulfonic acid layer faces the cathode chamber. A schematic diagram of the reverse installation is shown below. Figure 3 As shown.

[0029] (3) Accelerated aging operation: Anodic solution: 180 g / L sodium chloride solution; Catholyte: 33wt% sodium hydroxide solution; Temperature: 95℃; Current density: 5.6 kA / m 2 ; Running time: 1 hour.

[0030] (4) Termination and sampling: Stop the operation and take out samples A and B.

[0031] (5) Evaluation of binding degree: Visual observation: Multiple visible bubbling and delamination phenomena (e.g., on the surface of sample A, especially at the edges and center) were observed. Figure 4 As shown), no bubbling or delamination was observed on the membrane surface of sample B (including the edge and center areas). Figure 5 (As shown).

[0032] Judgment: According to the preset standard, the interlayer bonding degree of batch A membrane is deemed unqualified, while the interlayer bonding degree of batch B membrane is qualified.

[0033] Example 2 Test subject: DF2808 perfluorosulfonic acid / carboxylic acid composite chlor-alkali ion exchange membrane (hereinafter referred to as "ion exchange membrane") commercially available from Shandong Dongyue Polymer Materials Co., Ltd.

[0034] The evaluation is conducted according to the following steps, as shown in the flowchart. Figure 1 As shown: (1) Sample preparation: Take a sample of the new membrane of this model with a size of 10cm×10cm from two batches of ion exchange membranes that have been verified in the market, and denote them as sample A and sample B.

[0035] Sample Batch A: Electrolyzed in an electrolytic cell of a large domestic chlor-alkali customer (NCZ electrolytic cell of Bluestar (Beijing) Chemical Machinery Co., Ltd., electrolysis temperature 85℃, current density 5.5kA / m³). 2 Within one year of operation, the entire membrane exhibited bubbling and delamination (with an average outlet alkali concentration of 32.04%).

[0036] Sample Batch: Electrolyzed in an electrolytic cell of a large domestic chlor-alkali customer (NCZ electrolytic cell of Bluestar (Beijing) Chemical Machinery Co., Ltd., electrolysis temperature 85℃, current density 5.5kA / m³). 2 (With an average outlet alkali concentration of 32.04%), no membrane bubbling or delamination has occurred in the four years of operation.

[0037] (2) Electrolytic cell assembly: Samples A and B are installed in reverse orientation in a laboratory monopolar electrolytic cell (for the material and structure of the electrolytic cell, please refer to patent CN217378045U and the paper "Preferred Scheme for Laboratory-Grade Chlor-Alkali Ion Exchange Membrane Anode Electrolytic Cell" (published in "China Chlor-Alkali" 2025, No. 9), specifically the e-type cell). This ensures that the carboxylic acid layer of the membrane faces the anode chamber and the sulfonic acid layer faces the cathode chamber. A schematic diagram of the reverse installation is shown below. Figure 3 As shown.

[0038] (3) Accelerated aging operation: Anodic solution: 220 g / L sodium chloride solution; Cathodic solution: 35wt% sodium hydroxide solution; Temperature: 86℃; Current density: 6kA / m 2 ; Running time: 0.5 hours.

[0039] (4) Termination and sampling: Stop the operation and take out samples A and B.

[0040] (5) Evaluation of binding degree: Visual observation: Multiple visible bubbling and delamination phenomena (e.g., on the surface of sample A, especially at the edges and center) were observed. Figure 6 As shown), no bubbling or delamination was observed on the membrane surface of sample B (including the edge and center areas). Figure 7 (As shown).

[0041] Judgment: According to the preset standard, the interlayer bonding degree of batch A membrane is deemed unqualified, while the interlayer bonding degree of batch B membrane is qualified.

[0042] Comparative Example 1 The membrane sample used was from the same batch as in Example 1, but installed in the forward orientation (sulfonic acid layer facing the anode, carboxylic acid layer facing the cathode, as shown in the schematic diagram of normal installation). Figure 2 (As shown) it was run for 1 hour under the same electrolyte concentration, temperature and current density.

[0043] After removing samples A and B, the membrane surfaces were observed to be intact, with no bubbling or delamination (e.g., Figure 8 , 9 (As shown).

[0044] This comparative example demonstrates that, under normal installation conditions, even under relatively harsh conditions, the membrane did not exhibit significant interlayer separation problems, highlighting the effectiveness and sensitivity of the "reverse installation" method of this invention for specifically assessing interlayer bonding.

[0045] Comparative Example 2 The membrane sample used was from the same batch as in Example 2, but installed in the forward orientation (sulfonic acid layer facing the anode, carboxylic acid layer facing the cathode, as shown in the schematic diagram). Figure 2 (As shown) it was run for 0.5 hours under the same electrolyte concentration, temperature and current density.

[0046] After removing samples A and B, the membrane surfaces were observed to be intact, with no bubbling or delamination (e.g., Figure 10 , 11 (As shown).

[0047] This comparative example demonstrates that, under normal installation conditions, even under relatively harsh conditions, the membrane did not exhibit significant interlayer separation problems, highlighting the effectiveness and sensitivity of the "reverse installation" method of this invention for specifically assessing interlayer bonding.

[0048] Comparative Example 3 The membrane samples were from the same batch as in Example 2, but were operated for 3 months in the same electrolyte concentration, temperature and current density, with the sulfonic acid layer facing the anode and the carboxylic acid layer facing the cathode.

[0049] Visual observation: Multiple visible bubbling and delamination phenomena (e.g., on the surface of sample A, especially at the edges and center) were observed. Figure 12 As shown), no bubbling or delamination was observed on the membrane surface of sample B (including the edge and center areas). Figure 13 (As shown).

[0050] In summary, this invention, by reverse-mounting the chlor-alkali ion exchange membrane and combining it with an accelerated aging method that improves operating conditions, successfully identified potential defects in the interlayer bonding of this commercial membrane within one hour. Conventional testing and aging tests under normal installation conditions failed to effectively expose this problem. This method provides a powerful tool for rapidly assessing and improving the reliability of chlor-alkali ion exchange membranes.

Claims

1. A method for evaluating the interlayer binding degree of a chlor-alkali ion exchange membrane, characterized in that, Includes the following steps: (1) The chlor-alkali ion membrane sample to be tested is installed in the experimental electrolytic cell in a reverse installation manner, wherein the membrane has a carboxylic acid layer and a sulfonic acid layer, and during installation, the carboxylic acid layer faces the anode chamber and the sulfonic acid layer faces the cathode chamber; (2) Electrolyte is introduced into the anode chamber and cathode chamber respectively, and the electrolytic cell is operated under abnormal operating conditions to carry out accelerated aging test; The abnormal operating conditions include the following three: ①Increase the operating temperature of the electrolyzer to make it higher than the upper limit of the recommended temperature for the membrane during normal installation; ②Increase the concentration of the anolyte and / or catholyte; ③ Increase the current density; (3) After the accelerated aging time is reached, stop the electrolysis operation and take out the membrane sample that has undergone aging treatment from the electrolytic cell; (4) Visually observe whether blistering, delamination or peeling occurs on the membrane surface to evaluate the interlayer bonding between the sulfonic acid layer and the carboxylic acid layer. If these phenomena occur, the membrane is unqualified.

2. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (1), the size of the chlor-alkali ion exchange membrane sample to be tested is 10cm×10cm.

3. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (1), the experimental electrolytic cell is a small laboratory-grade unipolar electrolytic cell with an effective electrolysis area of ​​50 cm². 2 .

4. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (2), the operating temperature is 86-95℃.

5. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (2), the anolyte is a sodium chloride solution with a concentration of 180-220 g / L, and the catholyte is a sodium hydroxide solution with a concentration of 33-35 wt%.

6. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (2), the current density is 5.6-6.5 kA / m. 2 .

7. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, In step (3), the accelerated aging time is 0.5-1 hour.

8. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, The accelerated aging test conditions are as follows: Anodic solution: 180 g / L sodium chloride solution; Catholyte: 33wt% sodium hydroxide solution; Temperature: 95℃; Current density: 5.6 kA / m 2 ; Running time: 1 hour.

9. The method for evaluating the interlayer binding degree of chlor-alkali ion exchange membranes according to claim 1, characterized in that, The accelerated aging test conditions are as follows: Anodic solution: 220 g / L sodium chloride solution; Catholyte: 35wt% sodium hydroxide solution; Temperature: 86℃; Current density: 6kA / m 2 ; Running time: 0.5 hours.

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