High-gas-barrier-property polyphenylene sulfide diaphragm with certain catalytic performance

Abstract

The invention discloses a process for improving hydrophilicity and gas barrier property of a polyphenylene sulfide (PPS) woven fabric or non-woven fabric diaphragm, which comprises the following four steps of: firstly, soaking diaphragm cloth with dilute sulphuric acid, and heating to sulfonate the diaphragm cloth; secondly, nickel-iron mixed salt is exchanged and adsorbed; thirdly, forming nickel-iron hydroxide from nickel-iron ions by using alkali liquor, immobilizing the nickel-iron hydroxide, and filling gaps among the PPS fibers with the nickel-iron hydroxide; and finally, washing off salt generated in the previous reaction with purified water. Compared with an untreated PPS diaphragm, the PPS diaphragm manufactured by the method disclosed by the invention has the advantages that the air tightness and hydrophilicity are greatly improved, and the PPS diaphragm has certain catalytic performance, so that the performance of the alkaline water hydrogen production electrolytic cell is greatly improved.

Description

Technical Field

[0001] This invention relates to a high gas barrier polyphenylene sulfide (PPS) membrane manufacturing technology, and more particularly to a high gas barrier PPS membrane manufacturing technology that combines hydrophilicity, gas repellency and catalytic performance, belonging to the field of membrane production technology for alkaline water electrolysis hydrogen production devices. Background Technology

[0002] The diaphragm is one of the core components of all electrochemical cells, and its functions are generally threefold: (1) to allow substances required for the reactions between the cathode and anode to pass through; (2) to insulate the electrical contact between the cathode and anode; and (3) to prevent the penetration of substances other than those necessary for the transfer between the cathode and anode, if necessary. Generally, the diaphragm should be as thin as possible so that the two electrodes can be brought as close as possible, increasing the electric field strength between the electrodes, thereby reducing the energy consumption of the electrochemical process by accelerating the electromigration of ions. Therefore, the diaphragm is called the third electrode in an electrochemical cell, and its function is comparable to that of the two electrodes.

[0003] Electrolysis of water is a simple and easy-to-implement hydrogen production technology. Alkaline water electrolysis is popular in the market due to its mature technology, use of non-precious metal catalysts, low investment and operating costs, and wide adaptability. However, the asbestos membranes used previously are carcinogenic and therefore banned. In recent years, PPS membranes have been used instead of asbestos membranes. Because PPS is hydrophobic and cannot swell in aqueous solutions, hydrogen and oxygen can easily permeate the membrane. Hydrogen is an extremely flammable and explosive gas with a very wide explosion limit; if the gases in the anode and cathode chambers mix, an explosion is highly likely. Therefore, to prevent hydrogen or oxygen from permeating the membrane, the pressure difference between the anode and cathode chambers must be maintained at a very low level. This is a major problem that has led to its being challenged by other water electrolysis technologies, especially proton exchange membrane electrolysis for hydrogen production. Therefore, there is a strong market demand for surface treatment of PPS membranes to improve their hydrophilicity and gas barrier properties.

[0004] Currently, there are two types of PPS separators on the market: one is a meltblown fabric separator manufactured using nonwoven technology (with...). Figure 1 (Left) One type is a woven fabric diaphragm manufactured using weaving techniques (attached) Figure 1 (Right). Both types of diaphragms exhibit good chemical stability in alkaline water electrolysis environments. However, the fibers, especially the yarns in woven fabrics, have relatively large gaps, allowing gas to pass through when the pressure difference between the anode and cathode chambers is large, resulting in high gas permeability. Woven fabrics typically have larger pores, therefore meltblown fabrics offer better gas barrier properties than woven fabrics.

[0005] There are generally three methods for hydrophilic treatment of PPS: chemical methods, physical methods, and a combination of chemical and physical methods. For example, CN101372752A discloses a method for preparing a nonwoven PPS diaphragm, which includes sulfonation with 90-98% H2SO4 followed by treatment with a 30% potassium hydroxide solution. This method achieves durable performance because it chemically bonds hydrophilic sulfonic acid groups to the benzene ring of PPS. However, it uses high-concentration sulfuric acid, which can easily lead to over-sulfonation and damage to the PPS diaphragm, reducing its mechanical properties and service life. CN118292259A discloses a method for sulfonating PPS diaphragms with chlorosulfonic acid, using chloroalkanes as solvents, as well as amines, aldehydes, and sugars. The resulting diaphragm has good hydrophilicity. However, although the diaphragm obtained by this method meets the requirements of existing technology, its gas barrier properties are still relatively low, with a pressure difference measured by the bubble point method of only about 400 mmH2O column. The above two methods belong to the chemical method of hydrophilic treatment.

[0006] Furthermore, the processing technology described in CN118326418A, which uses organic polymer binders and inorganic oxides to cover the surface of PPS fibers, is a physical modification scheme. However, the intermolecular forces between the coating and the PPS film are much weaker than chemical bonds, making them easily washed away by flowing alkaline solutions and bubbles formed on the electrodes, thus affecting the product's lifespan.

[0007] The purpose of this invention is to improve the hydrophilicity of PPS membranes and increase yield through moderate sulfonation. Simultaneously, by using the chemical reaction of sulfonic acid groups and nickel-iron hydroxide (NiFe-LDH), it is firmly filled into the voids of the PPS membrane, thereby achieving high hydrophilicity, high gas barrier properties (pressure difference exceeding 800 mmH2O column in bubble point method), and high OH content. - The invention employs a gas-repellent membrane with low water molecule permeability. Therefore, this invention belongs to a processing technology that combines physical and chemical methods. Furthermore, this invention utilizes the characteristics of NiFe-LDH, which can be reduced at the negative electrode to form a nickel-iron alloy with good catalytic hydrogen evolution reaction, and oxidized at the positive electrode to obtain a hydrated oxide with catalytic oxygen evolution reaction, thus giving the prepared membrane certain catalytic performance. This is the second objective of this invention. Summary of the Invention

[0008] This invention utilizes a controlled sulfonation-salt impregnation-alkali treatment-cleaning technique to treat PPS woven or nonwoven base fabrics, resulting in a high-performance membrane with high hydrophilicity, high ionic conductivity, high gas barrier properties, and certain catalytic performance. The method is as follows: (1) Controlled sulfonation: The PPS woven or nonwoven fabric is impregnated with dilute sulfuric acid, and then heated to dehydrate and partially sulfonate the surface of the polyphenylene sulfide fiber to obtain a partially sulfonated PPS membrane. (2) Salt impregnation: The partially sulfonated PPS membrane is impregnated with a concentrated nickel-iron mixed sulfate solution to fill the gaps between the membrane fibers with the mixed salt solution, and then dehydrated and dried; (3) Alkali treatment: The PPS membrane treated with the concentrated mixed salt solution is treated with concentrated sodium hydroxide solution to solidify the metal ions in the mixed salt in situ in the form of layered hydroxide (LDH), and then heated to age it. n Ni 2+ + Fe 3+ + (2 n +3- x ) OH - + x SO3-PPS - = [Ni n Fe(OH) (2n+2) ]OH 1-x (SO3-PPS) x (4) Cleaning: Use deionized water or distilled water to clean away the salt produced in the above reaction, and then dry to obtain the product.

[0009] In steps (1) and (2), both vacuum and compression methods, or other available methods, need to be used to ensure that the air inside the diaphragm is completely removed so that the dilute sulfuric acid or nickel-iron mixed sulfate solution can completely permeate the diaphragm.

[0010] The sulfonation process in step (1) controls the amount of sulfuric acid adsorbed in the PPS woven or nonwoven fabric by controlling the concentration of sulfuric acid, thereby conveniently controlling the degree of sulfonation and improving the yield. According to production requirements, especially the type, thickness, and weight of the base fabric, preferably, the mass percentage concentration of dilute sulfuric acid is controlled between 30% and 70%; the heating, dehydration, and sulfonation processes are carried out in a tunnel kiln at 120-160°C, and the residence time of the woven or nonwoven fabric is set to within 1 hour.

[0011] The mixed salt solution in step (2) comprises at least nickel sulfate and ferric sulfate, with a nickel-iron molar ratio between 2:3 and 1:5. Its concentration is determined by the amount of water sufficient to dissolve all the salts at the operating temperature and other factors. Preferably, the dehydration and drying process is carried out under reduced pressure in a tunnel kiln with the temperature controlled between 60 and 120 °C.

[0012] Preferably, the mixed salt solution also includes some salts that can promote membrane stability and catalytic performance, such as sulfates of tin, cobalt, and zirconium.

[0013] Chemically, as shown in the reaction equation in section 0008, the anions of the salt and the cations of the base are not important and do not affect the reaction. Therefore, the sulfate can be completely replaced by hydrochloride or nitrate, and the sodium hydroxide can be replaced by potassium hydroxide or other soluble hydroxides. The choice of which compound to use depends solely on the production cost.

[0014] Preferably, the mass percentage concentration of the sodium hydroxide solution in step (3) is close to that of its saturated solution; the heating and aging temperature is around 90 °C and the time is about 1 h.

[0015] Preferably, the sodium hydroxide solution also contains dissolved salts that can promote membrane stability and catalytic performance, such as tungstates, molybdates, and silicates.

[0016] When nickel, iron, tin, cobalt, and zirconium are treated with sulfates and sodium hydroxide is used as the alkali, and tungsten, molybdenum, and silicates are treated with sodium salts, the solution obtained in step (4) of the cleaning process mainly contains sodium sulfate. Preferably, sodium sulfate solid and purified water are obtained by mechanical compression steam technology or multi-effect evaporation technology, and the obtained purified water is further used for diaphragm cleaning. The salts obtained using other substances are determined by their anions and cations.

[0017] The advantages of this invention are as follows: First, by controlling the sulfonation degree of the polyphenylene sulfide membrane with the concentration and adsorption amount of dilute sulfuric acid, its hydrophilicity can be improved without degrading the membrane's performance, thus increasing the yield. Second, NiFe-LDH is generated in situ within the voids formed by the membrane fibers and is fixed by the sulfonic acid groups of polyphenylene sulfide, preventing it from being stripped from the membrane by flowing alkaline solution and bubbles, thereby increasing its service life. Third, the generated NiFe-LDH is a hydrophilic alkaline compound solid particle that easily allows water molecules and hydroxide ions to penetrate the membrane. Simultaneously, it swells slightly in water, further blocking the voids and preventing gas penetration. Furthermore, its nano-micron-sized particles are gas-repellent. Fourth, the hydroxides of metals such as nickel-iron dissolve in small amounts at the reduction potential on the cathode side and are reduced to form a nickel-iron alloy. This nickel-iron alloy is an excellent hydrogen evolution catalyst, and the substance formed by its oxidation on the anode side is also an excellent oxygen evolution catalyst. Therefore, the resulting membrane possesses certain catalytic properties. Therefore, the PPS diaphragm modified and manufactured using the method disclosed in this invention not only has excellent airtightness and can support a much larger pressure difference between the anode and cathode chambers than the untreated diaphragm, but also has better hydrophilicity, gas-repellency and certain catalytic performance, thereby significantly improving the performance of the alkaline water hydrogen production electrolyzer. Attached Figure Description

[0018] Appendix Figure 1 The left image shows PPS meltblown fabric, and the right image shows an optical photograph of the woven fabric base.

[0019] Appendix Figure 2These are optical photographs of the PPS meltblown fabric diaphragm obtained in Example 2. The left image is a front view, and the right image is a side cross-sectional photograph.

[0020] Appendix Figure 3 The images are electron microscope (EM) images of the PPS meltblown fabric diaphragm before (a, b) and after (c, d) treatment in Example 2.

[0021] Appendix Figure 4 The electrochemical performance of the PPS meltblown fabric diaphragm obtained in Example 2 is shown. Among them, (a) is the linear voltammetry obtained by assembling the diaphragm before and after treatment and after cleaning off the nickel-iron hydroxide with dilute hydrochloric acid in the same electrolytic cell with bare nickel mesh as positive and negative electrodes; (b) is the relationship between current density and time in the electrolytic cell when the cell voltage is 2 V. Detailed Implementation

[0022] The invention discloses a manufacturing technology for a polyphenylene sulfide (PPS) membrane with high hydrophilicity, high gas repellency, high gas barrier properties, and catalytic activity in an alkaline water electrolysis hydrogen production device. The technology comprises four steps: controlled sulfonation, impregnation with concentrated mixed brine, pore blockage with layered hydroxides, and removal of soluble salts. The membrane base fabric used is either a woven or non-woven PPS fabric. The processing methods are chemically identical.

[0023] Secondly, the technology can be implemented as a production line. The method involves forming the diaphragm into long rolls and then automatically processing them sequentially through appropriate processing devices.

[0024] Third, the metal salts used can be soluble salts such as hydrochlorides, nitrates, and sulfates, and sodium hydroxide can be potassium hydroxide or other soluble hydroxides. The examples only use relatively inexpensive sulfates and sodium hydroxide; if changes are needed, simply follow the chemical reaction requirements.

[0025] Fourth, regarding the metal salts used, apart from nickel and iron salts which are essential, others such as tin, cobalt, and zirconium salts are added solely to further improve the membrane performance, and their dosage can be optimized according to standard optimization methods. Similarly, sodium hydroxide is essential, and substances such as sodium silicate, sodium tungstate, and sodium molybdate are also added to improve performance, and their dosage can also be optimized in standard optimization schemes.

[0026] Specifically, the embodiments listed herein are merely illustrative of detailed operational schemes for obtaining the product of the present invention, and are not necessarily the optimal solutions. Any operation based on similar principles should be considered within the scope of protection of the present invention. The numerical ranges mentioned in this invention should be understood as the control ranges that best obtain the product of the present invention, including every intermediate value between the upper and lower limits. Control values ​​outside this range may still yield the product, but the performance may not be better. Example 1

[0027] Controlled sulfonation: First, immerse the clean PPS membrane base fabric in 30 wt% dilute sulfuric acid. Remove the gas from the base fabric by squeezing and pumping to allow the sulfuric acid to fully permeate the membrane. Then, gently scrape off the sulfuric acid on the surface and heat-treat at 160 ℃ for 60 min to obtain the controlled sulfonation membrane. Metal salt solution soaking: Weigh nickel sulfate and ferric sulfate at a molar ratio of 5:1, add water to just dissolve them; then immerse the sulfonated diaphragm in it, similarly, remove the air so that the mixed salt enters the gaps of the diaphragm, then gently scrape off the excess solution on the surface, and then dry under reduced pressure at about 100 °C. Layered hydroxide blockage of pores: A 40 wt% NaOH solution is evenly sprayed onto both sides of a dry diaphragm that has been impregnated with nickel sulfate and ferric sulfate. The amount of NaOH sprayed is controlled so that all the sulfates in the diaphragm are converted into hydroxides. Then, the diaphragm is aged at 90 °C. Sodium sulfate cleaning: Soak the aged diaphragm in clean water to dissolve the sodium sulfate. The cleaning process should be repeated at least three times to ensure that the sodium sulfate is completely removed. The resulting sodium sulfate solution is dehydrated using energy-saving technologies such as mechanical steam recompression or multi-effect evaporation, causing the sodium sulfate to crystallize out and be sold as a byproduct. The clean water obtained is then reused in the diaphragm cleaning process. Example 2

[0028] In this embodiment, only the sulfuric acid in step (1) of Example 1 is replaced with 50 wt% sulfuric acid, the treatment temperature is 140℃, and the treatment time is 30 min; the molar ratio of nickel sulfate and iron sulfate in step (2) is 3:1; the sodium hydroxide in step (3) is a saturated solution, and other conditions and treatment methods remain unchanged.

[0029] Optical photographs of the PPS meltblown fabric base used in this embodiment are attached. Figure 1 As shown. An optical photograph of the processed PPS meltblown fabric separator is attached. Figure 2 The left image is a front view, and the right image is a side cross-section photo. Figure 3 The images shown are electron microscope (EM) images, where (a, b) are untreated meltblown fabric membranes, and (c, d) are treated meltblown fabric membranes. It can be seen that the nickel-iron hydroxide crystals are present between the meltblown fabric fibers, blocking the voids. The electrochemical properties of the treated PPS meltblown fabric membranes are shown in the attached figure. Figure 4(a) shows the linear voltammetry plots obtained by assembling the diaphragm before and after treatment, and after cleaning away the nickel-iron hydroxide with dilute hydrochloric acid, in an electrolytic cell with the same bare nickel mesh as the positive and negative electrodes; (b) shows the relationship between current density and time in the electrolytic cell at a cell voltage of 2 V. It can be seen that the performance of the diaphragm is significantly improved after treatment, and the electrode current density stabilizes at 0.11 A / cm² at a cell voltage of 2 V. 2 The performance of the membrane was improved by more than 20% compared to the untreated PPS membrane. After washing away the nickel-iron hydroxide, the membrane performance was basically the same as the untreated membrane. This indicates that the filled nickel-iron hydroxide does indeed have certain catalytic properties.

[0030] The bubble point pressure of the obtained PPS diaphragm was tested using the bubble point method. The bubble point pressure of the meltblown fabric diaphragm reached 840 mmH2O column, which is much higher than the current industry requirement of 120 mmH2O column. The untreated meltblown fabric diaphragm can only reach about 300 mmH2O column. This means that the pressure difference control of the anode and cathode chambers of the alkaline water electrolyzer can be greatly relaxed. Example 3

[0031] In this embodiment, the sulfuric acid in step (1) is replaced with 70 wt% sulfuric acid, the treatment temperature is 120 ℃, and the treatment time is 20 min; the molar ratio of nickel sulfate and iron sulfate in step (2) is 3:2; the sodium hydroxide in step (3) is a saturated solution, and other conditions and treatment methods remain unchanged. Example 4

[0032] In this embodiment, only the sulfuric acid in step (2) of Example 1 is replaced with 40 wt% sulfuric acid, the treatment temperature is 150℃, and the treatment time is 45 min; the molar ratio of nickel sulfate and ferric sulfate in step (2) is 4:1, and zirconium sulfate is added so that its molar ratio with ferric sulfate is 0.2:1; the sodium hydroxide in step (3) is a 50 wt% solution, and other conditions and treatment methods remain unchanged. Example 5

[0033] In this embodiment, the sulfuric acid in step (2) of Example 1 is replaced with 50 wt% sulfuric acid, the treatment temperature is 150℃, and the treatment time is 25 min; the molar ratio of nickel sulfate and ferric sulfate in step (2) is 4:1, and zirconium sulfate is added so that its molar ratio with ferric sulfate is 0.3:1; the sodium hydroxide in step (3) is a 50 wt% solution, and 5% of sodium silicate by mass of sodium hydroxide is dissolved; other conditions and treatment methods remain unchanged. Example 6

[0034] In this embodiment, zirconium sulfate in Example 4 is replaced with stannous sulfate or cobalt sulfate, so that the molar ratio of zirconium sulfate to nickel sulfate is 0.2:1; in step (3), sodium hydroxide is a saturated solution, and sodium tungstate and sodium molybdate, each with a mass of 1% sodium hydroxide, are dissolved; other conditions and processing methods remain unchanged.

[0035] The embodiments described above are merely exemplary descriptions of the implementation schemes of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high gas barrier polyphenylene sulfide membrane with certain catalytic properties, characterized in that, The diaphragm is manufactured using industrially produced polyphenylene sulfide woven or non-woven fabric as the base material, through a controlled process of sulfonation, salt impregnation, alkali treatment, and cleaning. (1) The polyphenylene sulfide woven or nonwoven base fabric is impregnated with dilute sulfuric acid, and then heated to dehydrate it so that the surface of the polyphenylene sulfide fibers is partially sulfonated to obtain a partially sulfonated polyphenylene sulfide membrane. (2) The partially sulfonated polyphenylene sulfide membrane is impregnated with a concentrated nickel-iron mixed sulfate solution to fill the gaps between the membrane fibers with the mixed salt solution, and then dehydrated and dried. (3) Treat the polyphenylene sulfide membrane treated with the concentrated mixed salt solution with concentrated sodium hydroxide solution to solidify the metal ions in the mixed salt in situ in the form of hydroxides, and then heat it at about 90 °C to age it. (4) Use deionized water to wash away the salt produced in step (3) and then dry to obtain the product.

2. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, The manufacturing method involves continuous steps, forming an assembly line.

3. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In steps (1) and (2) of the manufacturing method, the dilute sulfuric acid and concentrated mixed salt solution are used for impregnation, and air in the diaphragm is removed using vacuum and extrusion techniques.

4. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (1) of the manufacturing method, the mass percentage concentration of dilute sulfuric acid is between 30% and 70%; the partial sulfonation process is carried out in a tunnel kiln at 120 to 160 ℃, and the residence time of the diaphragm cloth is set to within 1 hour.

5. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (2) of the manufacturing method, the nickel-iron mixed sulfate has a nickel-iron molar ratio between 2:3 and 1:

5. Its concentration is determined by the amount of water that can just dissolve all the salts at the operating temperature. The dehydration and drying process is carried out in a tunnel kiln under reduced pressure, with the temperature controlled at around 100 ℃.

6. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (2) of the manufacturing method, the mixed salt solution may contain nickel sulfate and ferric sulfate, as well as other salts such as sulfates of tin, cobalt, and zirconium; the sulfates may also be replaced by nitrates, hydrochlorides, or other soluble salts.

7. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (3) of the manufacturing method, the concentrated sodium hydroxide solution can be replaced by concentrated potassium hydroxide or concentrated solutions of other soluble hydroxides, the concentration of which is close to the saturation concentration.

8. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (3) of the manufacturing method, one or more of tungstate, molybdate and silicate are dissolved in the concentrated sodium hydroxide solution.

9. The high gas barrier polyphenylene sulfide membrane with certain catalytic performance according to claim 1, characterized in that, In step (4) of the manufacturing method, the salt solution generated by rinsing the diaphragm with deionized water mainly contains sodium sulfate (or other salts, depending on the use of salts in claims 6 to 8). The sodium sulfate solid and pure water are concentrated by mechanically compressed steam or multi-effect evaporation technology, and the pure water is used for diaphragm cleaning.

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