A woven fabric diaphragm for the electrolytic fluorination of organic substances and its application

Abstract

The present invention provides a woven diaphragm for the electrolytic fluorination of organic substances and its application. The woven diaphragm is a woven diaphragm formed by expanded polytetrafluoroethylene fibers with perfluorosulfonic acid. The maximum pore size of the woven diaphragm is 20 - 80 μm, 70 - 95% of the pores have a size less than 15 μm, and 5 - 30% of the pores have a size not less than 15 μm. The diaphragm for the electrolytic fluorination of organic substances in the present invention has the characteristics of high strength, good ion permeability, and difficulty for bubbles to pass through. During the electrolytic fluorination of organic substances using the woven diaphragm of the present invention, the fluorinated products generated at the anode are directly guided to the anode purification and refining unit, and the hydrogen generated at the cathode is guided to the cathode purification and refining unit, reducing the cold trap that uses liquid nitrogen cooling to separate products and hydrogen in the process. It can not only improve the current efficiency of fluorination electrolysis, but also reduce the risk of mixed explosion of fluorine gas at the anode and hydrogen at the cathode caused by the imbalance of the electrolyte ratio, bringing good economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic electrofluorination, and particularly relates to a woven fabric diaphragm for organic electrofluorination and its application. Background Art

[0002] Organic fluorination can be accomplished through chemical synthesis reactions or electrolysis. Chemical synthesis fluorination has low conversion rate, violent reactions, difficult process control, high safety risks, and many purification steps. Electrochemical fluorination is an effective way to introduce fluorine atoms into organic substances by using electrode reactions, with high conversion rate and mild reactions. Currently, fluorination reactions such as perfluorosulfonyl fluoride and carbonyl fluoride can all be completed through the electrochemical fluorination process.

[0003] The electrochemical fluorination system was invented by the American chemist Simons, and 3M Company began to apply it in industry to produce many organic perfluorides with functional groups. In fluorination electrolysis production, anhydrous hydrogen fluoride is usually used as the fluorinating agent. An organic substance with a functional group and hydrogen fluoride are mixed into an electrolyte in a certain proportion. Currently, the Simons organic electrofluorination process is used industrially. Its fluorination electrolysis system consists of an electrolytic cell and its product treatment system. The electrolytic cell in this system is composed of a cell body and a cell cover. The cathode and anode assemblies are suspended on the cell cover. A cooling system is provided inside or outside the cell body. The cathode and anode assemblies suspended in the cell body are immersed in the electrolyte. The upper part of the cell body is a gas phase space. The organic matter in the electrolyte generates perfluorinated products at the anode and hydrogen at the cathode through electrolysis. The perfluorinated products generated at the anode do not react with the hydrogen generated at the cathode. Therefore, generally, there is no diaphragm between the cathode chamber and the anode chamber. The mixture of perfluorinated products and hydrogen produced by electrolysis is separated from the electrolyte in the gas phase space of the cell body, and the mixture is guided through a pipeline to the product treatment system for separation of perfluorinated products and hydrogen. The perfluorinated products are purified and refined into commercial perfluorinated products.

[0004] The Simons organic electrofluorination process has very high requirements for the ratio of organic matter to hydrogen fluoride. If the proportion of organic matter is high, the yield and recovery rate of perfluorinated products are low. If the proportion of hydrogen fluoride is high, fluorine gas is generated at the anode, and the fluorine gas reacts with the hydrogen generated at the cathode to reduce the current efficiency, and even cause an explosion. The actual mechanism of organic anodic fluorination involves two-step reactions. The first step is the anodic electrolysis reaction to generate fluorine gas, and the second step is the chemical reaction between the organic matter and fluorine gas to generate perfluorinated products. The current efficiency in the fluorination reaction is between 50% and 65%. The reason for the low current efficiency is that the fluorine gas generated at the anode reacts with the hydrogen generated at the cathode to form hydrogen fluoride.

[0005] Expanded polytetrafluoroethylene fiber is a new type of material developed in the 1960s. It is formed by connecting fine randomly arranged fibers into polytetrafluoroethylene nodules. There are voids between the fibers, and it has characteristics such as small pore size, high porosity, uniform pore size distribution, high strength, and low relative density. It is widely used in separation, filtration, and other aspects. However, there is currently no relevant research on applying expanded polytetrafluoroethylene fiber to the electrolytic fluorination of organic compounds.

[0006] Based on this, the present invention proposes a woven fabric diaphragm for the electrolytic fluorination of organic compounds and its application. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a woven fabric diaphragm for the electrolytic fluorination of organic compounds and its application in view of the deficiencies of the above-mentioned prior art, so as to solve the problems raised in the above background art.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: a woven fabric diaphragm for the electrolytic fluorination of organic compounds, the woven fabric diaphragm is a woven fabric diaphragm formed by perfluorosulfonic acid expanded polytetrafluoroethylene fibers, the maximum pore size of the woven fabric diaphragm is 20 - 80 μm, the pores with a pore size less than 15 μm account for 70 - 95%, and the pores with a pore size not less than 15 μm account for 5 - 30%.

[0009] Further, in the woven fabric diaphragm, the warp yarns form bends around the weft yarns, and the curvature rate of the warp yarns is 8 - 20%; the weft yarns form bends around the warp yarns, and the curvature rate of the weft yarns is 5 - 10%.

[0010] Further, in the woven fabric diaphragm, the buckling wave height of the warp yarns is 850 - 1300 μm, and the buckling wave height of the weft yarns is 600 - 900 μm.

[0011] Further, there are 500 - 1600 pores per square centimeter in the woven fabric diaphragm.

[0012] Further, the airtightness of the woven fabric diaphragm is 3 - 10 Kpa.

[0013] Further, the number of warp yarns per 10 cm of the woven fabric diaphragm is not less than 140, and the number of weft yarns is not less than 76; the thickness of the woven fabric diaphragm is 1 - 3 mm.

[0014] Further, the woven fabric diaphragm is a plain weave, twill weave or satin weave fabric.

[0015] Further, the preparation method of the perfluorosulfonic acid expanded polytetrafluoroethylene fiber is specifically: using expanded polytetrafluoroethylene fiber as the base, immersing the expanded polytetrafluoroethylene fiber in perfluorosulfonic acid resin, and making it through impregnation and drying.

[0016] Further, the preparation method of the expanded polytetrafluoroethylene fiber is specifically as follows: a preform obtained by extruding paste polytetrafluoroethylene into a longitudinally arranged fibrous shape is dried to remove additives, and then subjected to high-speed stretching at a temperature lower than the melting point of polytetrafluoroethylene, with an elongation rate reaching 150-1500%. Subsequently, the semi-finished polytetrafluoroethylene fiber in a stretched state is pretreated at a temperature higher than the melting point to obtain an expanded polytetrafluoroethylene fiber with a porosity of 40-97%.

[0017] An electrochemical electrolytic cell, the electrolytic cell is an external circulation series electrolytic cell composed of a negative terminal plate, a bipolar plate, a diaphragm and a positive terminal plate, and the diaphragm is the above-mentioned woven fabric diaphragm.

[0018] The present invention has the following advantages compared with the prior art:

[0019] The diaphragm for the electrolytic fluorination of organic substances in the present invention has the characteristics of high strength, good ion permeability and difficult bubble penetration, and can be applied to the electrolysis process of producing perfluorinated products from organic substances by electrochemical fluorination. During the electrolytic fluorination of organic substances using the woven fabric diaphragm of the present invention, the fluorinated products generated at the anode are directly guided to the anode purification and refining unit, and the hydrogen generated at the cathode is guided to the cathode purification and refining unit, reducing the cold trap that uses liquid nitrogen cooling to separate products and hydrogen in the process. The present invention can not only improve the current efficiency of electrolytic fluorination, but also reduce the risk of mixed explosion of fluorine gas at the anode and hydrogen at the cathode caused by the imbalance of the electrolyte ratio, bringing good economic and social benefits. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the electrolysis device in Embodiment 2 of the present invention;

[0021] Figure 2 It is a schematic diagram of the electrolysis device in Embodiment 3 of the present invention. Detailed Embodiments

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] Embodiment 1, the present invention provides a technical solution: a woven fabric diaphragm for the electrolytic fluorination of organic substances, the woven fabric diaphragm is a woven fabric diaphragm formed by expanded polytetrafluoroethylene fibers with perfluorosulfonic acid, the maximum pore size of the woven fabric diaphragm is 20-80 μm, the pores with a diameter less than 15 μm account for 70-95%, and the pores with a diameter not less than 15 μm account for 5-30%.

[0024] In the woven fabric diaphragm, the warp threads form bends around the weft threads, and the curvature rate of the warp threads is 8-20%; the weft threads form bends around the warp threads, and the curvature rate of the weft threads is 5-10%.

[0025] In the woven fabric diaphragm, the wave height of the warp thread buckling is 850-1300 μm, and the wave height of the weft thread buckling is 600-900 μm.

[0026] In the woven fabric diaphragm, there are 500-1600 holes per square centimeter, and the air tightness of the woven fabric diaphragm is 3-10 Kpa.

[0027] The thickness of the woven fabric diaphragm is 1-3 mm, and the woven fabric diaphragm is a plain weave, twill weave or satin weave fabric.

[0028] The preparation method of the perfluorosulfonic acid expanded polytetrafluoroethylene fiber is specifically as follows: taking the expanded polytetrafluoroethylene fiber as the substrate, immersing the expanded polytetrafluoroethylene fiber in the perfluorosulfonic acid resin, and drying after impregnation.

[0029] The preparation method of the expanded polytetrafluoroethylene fiber is specifically as follows: extruding the paste polytetrafluoroethylene into a longitudinally arranged fibrous preform, drying to remove the additives, performing high-speed stretching at a temperature below the melting point of polytetrafluoroethylene, with an elongation rate reaching 150-1500%, and then performing pretreatment on the semi-finished polytetrafluoroethylene fiber in the stretched state at a temperature higher than the melting point to obtain an expanded polytetrafluoroethylene fiber with a porosity of 40-97%.

[0030] An electrochemical electrolytic cell, the electrolytic cell is an external circulation series electrolytic cell composed of a negative terminal plate, a bipolar plate, a diaphragm and a positive terminal plate, and the diaphragm is the above-mentioned woven fabric diaphragm.

[0031] The polytetrafluoroethylene cloth used as the diaphragm in the present invention is processed by machine spinning of long tetrafluoro fibers, has high strength, and its technology must meet the requirements that the diaphragm part must be a whole piece without splicing; the cloth pattern is made into twill; the number of threads per 10 cm of cloth: the number of warp threads is not less than 140, and the number of weft threads is not less than 76; the thickness of the diaphragm is 1-3 mm; there should be no exposed thread ends, missing warps, broken wefts, mechanical marks, etc. on the diaphragm, and the surface should be uniform and flat; for the water pressure air tightness measurement of the diaphragm cloth, no bubbles are allowed to generate under a pressure of 5 KPa.

[0032] Quality requirements for the diaphragm: In the electrolytic cell, hydrogen is generated at the cathode and fluorinated products are generated at the anode. If they are not separated, hydrogen and fluorine will mix, which will not only fail to meet the yield requirements but also pose serious risks. Therefore, a diaphragm is needed to strictly separate the cathode chamber and the anode chamber. The quality of the diaphragm directly affects the purity of hydrogen and fluorinated products and the power consumption. The requirements for the diaphragm are as follows: Gas bubbles cannot pass through; it can be wetted by the electrolyte; it has sufficient mechanical strength; the resistance to the passage of conductive ions is small, so the thickness cannot be too large; it is not corroded by the electrolyte in the electrolyte and has strong chemical stability; it is cheap and suitable for industrial use.

[0033] Example 2, as Figure 1 shown, trifluoromethanesulfonyl fluoride is an important chemical raw material. Trifluoromethanesulfonic acid, trifluoromethanesulfonic anhydride, and lithium bis(trifluoromethanesulfonyl)imide prepared from trifluoromethanesulfonyl fluoride are high-value-added products. Trifluoromethanesulfonic acid and trifluoromethanesulfonic anhydride are important raw materials for many drugs. Lithium bis(trifluoromethanesulfonyl)imide is a new type of electrolyte lithium salt. Compared with lithium hexafluorophosphate, it is easier to dissociate lithium ions, has higher conductivity, a decomposition stability higher than 200 °C, higher thermal stability and safety, good compatibility with the electrode, and unique advantages in improving low-temperature discharge and high-temperature storage.

[0034] Industrially, trifluoromethanesulfonyl fluoride is prepared by the electrochemical fluorination of methylsulfonyl fluoride. The electrolytic cell is an external circulation series electrolytic cell composed of a negative terminal plate, bipolar plates, several bipolar plates, several diaphragms, and a positive terminal plate. The electrolytic cell contains an electrolyte composed of methylsulfonyl fluoride, anhydrous hydrogen fluoride, and a small amount of potassium fluoride. The positive pole of the high-frequency switch DC power supply is connected to the negative terminal plate of the electrolytic cell, and the negative pole of the high-frequency switch DC power supply is connected to the positive terminal plate of the electrolytic cell;

[0035] Under the action of the DC power supply in each small cell unit of the electrolytic cell, the methylsulfonyl fluoride on the anode side of the electrolytic cell undergoes an oxidation reaction to generate trifluoromethanesulfonyl fluoride, and the hydrogen ions at the cathode undergo a reduction reaction to generate hydrogen. The anode gas trifluoromethanesulfonyl fluoride and the electrolyte enter the anode gas-liquid separator through the anode gas collecting pipe, and further enter the anode gas condenser. After condensation, the trifluoromethanesulfonyl fluoride product is further output through a pipeline. The cathode hydrogen and the electrolyte enter the cathode gas-liquid separator through the cathode gas collecting pipe, and further enter the anode gas condenser. After condensation, the hydrogen product is further output through a pipeline. The electrolytes separated by gravity in the anode gas-liquid separator and the cathode gas-liquid separator converge at the lower connecting pipe at the bottom and then enter the lower inlet of the negative terminal plate in the electrolytic cell.

[0036] During the electrolysis process, methylsulfonyl fluoride and anhydrous hydrogen fluoride are added to the electrolytic cell in a certain proportion. The working voltage is 4 - 8V, and the current density is 30 - 100 mA / cm 2, the bipolar plate is made of graphite or nickel. The electrolysis temperature of the electrolytic cell chamber unit is -15 to 20 °C, and trifluoromethanesulfonyl fluoride with a boiling point of -21.7 °C is obtained by electrolysis under normal pressure.

[0037]

[0038] It can be seen from the comparison between the examples and comparative examples in the above table that after using the diaphragm of the present invention between the cathode and anode of the electrolytic cell for the electrolytic fluorination of methylsulfonyl fluoride to produce trifluoromethanesulfonyl fluoride, the electrolysis efficiency increases by 38%, and the effect is remarkable.

[0039] Example 3, hydrofluoroether HFE-7100, methyl nonafluorobutyl ether, chemical formula C5H3F9O. Due to its excellent properties such as excellent inertness, high density, low viscosity, low surface tension, low dielectric constant, etc., and its characteristics of non-flammability, colorlessness, odorlessness, non-toxicity, non-corrosiveness, and no volatile residue, it is widely used in electronic precision cleaning, leak detection liquid or airtightness test liquid for electronic components, insulating liquid, heat-conducting cooling liquid, solvent diluent, etc. Perfluoroisobutyryl fluoride is an intermediate product for producing hydrofluoroether HFE-7100.

[0040] Perfluoroisobutyryl fluoride can be produced by electrochemically fluorinating isobutyryl fluoride. The boiling point of isobutyryl fluoride is 81 °C, and that of perfluoroisobutyryl fluoride is -9 °C. The electrolytic cell is an external circulation series electrolytic cell composed of a negative terminal plate, several bipolar plates, several diaphragms, and a positive terminal plate. The electrolytic cell contains an electrolyte composed of isobutyryl fluoride, anhydrous hydrogen fluoride, and a small amount of potassium fluoride. The positive electrode of the high-frequency switch DC power supply is connected to the negative terminal plate of the electrolytic cell, and the negative electrode of the high-frequency switch DC power supply is connected to the positive terminal plate of the electrolytic cell. Under the action of the DC power supply in each small chamber unit of the electrolytic cell, isobutyryl fluoride on the anode side of the electrolytic chamber undergoes an oxidation reaction to generate perfluoroisobutyryl fluoride, and hydrogen ions at the cathode undergo a reduction reaction to generate hydrogen. The anode gas perfluoroisobutyryl fluoride and the electrolyte enter the anode gas-liquid separator through the anode gas collecting pipe, and further enter the anode gas condenser. After condensation, perfluoroisobutyryl fluoride products are output through the pipeline;

[0041] The cathode hydrogen and the electrolyte enter the cathode gas-liquid separator through the cathode gas collecting pipe, and further enter the anode gas condenser. After condensation, hydrogen products are output through the pipeline. The electrolytes separated by gravity in the anode gas-liquid separator and the cathode gas-liquid separator converge at the lower connecting pipe at the lower part and then enter the electrolytic cell through the lower inlet of the negative terminal plate. During the electrolysis process, isobutyryl fluoride and anhydrous hydrogen fluoride are added to the electrolytic cell in a certain proportion, the working voltage is 4 - 8V, and the current density is 10 - 50 mA / cm 2 , the bipolar plate is made of graphite or nickel. The electrolysis temperature of the electrolytic cell chamber unit is -15 to 20 °C, and perfluoroisobutyryl fluoride with a boiling point of -9 °C is obtained by electrolysis under normal pressure.

[0042]

[0043] As can be seen from the comparison between the examples and comparative examples in the above table, after using the diaphragm of the present invention between the cathode and anode of the electrolytic cell for electrolytic production of perfluoroisobutyryl fluoride from isobutyryl fluoride, the electrolysis efficiency increases by 35%, and the effect is remarkable.

[0044] It should be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0045] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A woven fabric diaphragm for the electrolytic fluorination of organic substances, characterized in that: The woven fabric diaphragm described above is a woven fabric diaphragm formed by expanded polytetrafluoroethylene fibers with perfluorosulfonic acid groups. The maximum pore size of the woven fabric diaphragm is 20 - 80 μm, 70 - 95% of the pores have a pore size less than 15 μm, and 5 - 30% of the pores have a pore size not less than 15 μm.

2. The woven fabric diaphragm for organic electrofluorination according to claim 1, characterized in that, In the woven fabric diaphragm, the warp threads form bends around the weft threads, and the curvature rate of the warp threads is 8 - 20%; the weft threads form bends around the warp threads, and the curvature rate of the weft threads is 5 - 10%.

3. The woven fabric diaphragm for organic electrolytic fluorination according to claim 1, characterized in that, In the woven fabric diaphragm, the wave height of the warp thread buckles is 850 - 1300 μm, and the wave height of the weft thread buckles is 600 - 900 μm.

4. A woven fabric diaphragm for organic electrolytic fluorination according to claim 1, characterized in that, There are 500 - 1600 pores per square centimeter in the woven fabric diaphragm.

5. The woven fabric diaphragm for organic electrolytic fluorination according to claim 1, characterized in that, The air tightness of the woven fabric diaphragm is 3 - 10 Kpa.

6. The woven fabric diaphragm for organic electrofluorination according to claim 1, characterized in that, In the woven fabric diaphragm, the number of warp threads per 10 cm of cloth is not less than 140, and the number of weft threads is not less than 76; the thickness of the woven fabric diaphragm is 1 - 3 mm.

7. A woven fabric diaphragm for the electrolytic fluorination of organic substances according to claim 1, characterized in that, The woven fabric diaphragm is a plain weave, twill weave or satin weave fabric.

8. The woven fabric diaphragm for electrolytic fluorination of organic substances according to claim 1, characterized in that, The preparation method of the expanded polytetrafluoroethylene fiber with perfluorosulfonic acid groups is specifically as follows: using the expanded polytetrafluoroethylene fiber as a substrate, immersing the expanded polytetrafluoroethylene fiber in perfluorosulfonic acid resin, and drying it after impregnation.

9. A woven fabric diaphragm for organic electrofluorination according to claim 8, characterized in that, The preparation method of the expanded polytetrafluoroethylene fiber is specifically as follows: extruding the paste polytetrafluoroethylene into a longitudinally arranged fibrous preform, drying to remove the auxiliary agent, then performing high-speed stretching at a temperature lower than the melting point of polytetrafluoroethylene, with an elongation rate reaching 150 - 1500%, and then pre-treating the semi-finished polytetrafluoroethylene fiber in a stretched state at a temperature higher than the melting point to obtain an expanded polytetrafluoroethylene fiber with a porosity of 40 - 97%.

10. An electrochemical electrolytic cell, characterized in that, The electrolytic cell is an external circulation series electrolytic cell composed of a negative terminal plate, bipolar plates, a diaphragm and a positive terminal plate, and the diaphragm is the woven fabric diaphragm described in any one of claims 1 - 9.

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