Method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroether from perfluorocarboxylic acids and their salts

Abstract

The present application belongs to the technical field of fluorinated chemical industry double-carbon emission reduction, and specifically relates to a method for electrocatalytic continuous decarboxylation synthesis of hydrogen-containing hydrofluoroether from perfluorocarboxylic acid and its salt. The method uses a perfluoroproton membrane as a diaphragm to divide an electrolytic cell into an anode and a cathode, uses perfluorocarboxylic acid and its salt as a reaction raw material, and uses a mixture of water and a polar aprotic solvent as a solvent mother liquor. After mixing the solvent mother liquor with the reaction raw material, the mixture is continuously fed into the anode side of the electrolytic cell for electrocatalysis. The effluent flowing out of the anode side is separated by rectification, and the light components containing hydrogen-containing hydrofluoroether and water are distilled off. Hydrogen-containing hydrofluoroether products are obtained by liquid separation, and the separated water is reused and mixed with the remaining liquid after rectification to form a reused mother liquor, realizing the recycling and application of the mother liquor. Subsequently, according to the output of the product, an equal amount of perfluorocarboxylic acid is continuously added to the reused mother liquor to realize continuous production of hydrogen-containing hydrofluoroether. The method reduces the output of waste liquid, and hydrogen is produced on the cathode side, improving the energy utilization efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of carbon emission reduction in fluorochemicals, specifically involving a method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts. Background Technology

[0002] Hydrofluoroethers (HFEEs) are a class of compounds with a predominantly fluorinated ether structure, in which some fluorine atoms are replaced by hydrogen atoms. They mainly fall into two categories: the first category, represented by perfluoroisopropyl methyl ether (HFE-i7100), consists of compounds with entirely non-fluorinated methyl, methylene, or ethyl structures, exhibiting higher hydrogen content and stronger polarity; the second category, represented by 2H-perfluoro (5-methyl-3,6-dioxanonane), consists of fluorinated ether compounds with only one fluorine atom replaced by hydrogen, exhibiting weaker polarity but stronger chemical and thermal stability. HFEEs are primarily used as lubricants, heat transfer media, or reaction solvents in high and low temperature environments.

[0003] The synthesis of the second type of hydrofluoroethers is mostly limited to thermochemical methods. Besides high energy consumption, these methods often generate large amounts of wastewater in post-processing, which contradicts the current global consensus on carbon emission reduction and the needs of human society. For example, Chinese patent document CN105753661A uses a conventional thermochemical method to synthesize the general formula F[CF(CF3)CF2O]. n CHFCF3 is a type of hydrofluoric ether, but its reaction pressure exceeds 0.8 MPa and it cannot be reacted continuously. Alkali washing also generates a large amount of waste liquid.

[0004] Furthermore, existing direct synthesis methods for the second type of hydrofluoroethers also have the following shortcomings: For example, the literature Journal of Fluorine Chemistry, 55 (1991) 93-100 discloses that a certain amount of 2H-perfluoro(5-methyl-3,6-dioxanone) is obtained by fluorination / cyclization of perfluoroolefin precursors at a relatively low temperature of about 70°C, but the yield is low. Patent CN102115428A discloses the direct reaction of alcohols with hexafluoropropylene in a system without the use of organic solvents to obtain hydrofluoroethers. The reaction temperature and pressure are high, and this method cannot be fully and continuously reacted. It is only suitable for the synthesis of hydrofluoroethers with specific structures and generates a large amount of waste liquid.

[0005] Therefore, although some technologies have mentioned using perfluoroolefin precursors as raw materials and using batch equipment such as reaction vessels in a system with alcohols or water as solvents to carry out decarboxylation and addition reactions through conventional thermochemical methods to finally form hydrofluoroether compounds in which one fluorine atom is replaced by hydrogen, subsequent purification operations such as water washing and alkali washing are still required, resulting in a large amount of by-products and wastewater production.

[0006] It is worth noting that, in addition to thermochemical methods, electrocatalysis has also been used in the synthesis of fluorine-containing compounds. For example, patent DE3828848A1 discloses a method for the continuous electrocatalytic decarboxylation synthesis of perfluoroether dimers from perfluorocarboxylic acids and their salts. However, it uses flammable and volatile alcohols as solvents and does not use a diaphragm to separate the anode and cathode of the electrolysis device, which leads to the oxidation of cathode products or the reduction of anode products, further increasing by-products, reducing yield, and resulting in poor product purity. Summary of the Invention

[0007] One objective of this invention is to achieve a safer, more efficient, and less polluting synthesis scheme for hydrofluoroethers than existing thermochemical methods, using perfluorocarboxylic acids and their salts as raw materials and under the combined action of polar aprotic solvents and water. In an electrocatalytic system, this invention enables reactions that require high temperature and pressure in thermochemical processes to occur at room temperature and pressure. Furthermore, it allows for mother liquor reuse in post-processing, reducing waste liquid production and further promoting the carbon emission reduction process in the synthesis of hydrofluoroethers.

[0008] The second objective of this invention is that, unlike conventional electrocatalytic synthesis processes, the provided aprotic organic solvent can form a homogeneous system with water, raw materials, and products, improving mass and heat transfer efficiency. This allows for more controllable concentration during continuous operation of the device, avoiding changes in reaction rate before and after the electrocatalytic reaction due to concentration gradients and solubility differences. Furthermore, the choice of this solvent alters the reaction mechanism, transforming the reaction product from a perfluoroether to a hydrofluoroether.

[0009] The third objective of this invention is to improve the conventional electrocatalytic process by using a perfluorinated proton exchange membrane as a separator, which avoids the re-contamination of anode and cathode reaction products, significantly reduces the generation of by-products, and enables the co-production of hydrogen on the cathode side, thereby improving energy utilization efficiency.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts involves using a perfluoro proton membrane as a diaphragm, dividing the electrolytic cell into an anode and a cathode, using perfluorocarboxylic acids and their salts as reactants, and using a mixture of water and a polar aprotic solvent as a mother liquor. The mother liquor is mixed with the reactants and continuously introduced into the anode side of the electrolytic cell for electrocatalysis to generate hydrofluoroethers.

[0012] Preferably, in the method, the solvent on the cathode side is water.

[0013] Preferably, the method includes:

[0014] (1) A mixture of water and a polar aprotic solvent is used as the mother solvent, and perfluorocarboxylic acid and its salt are used as the reaction raw materials. The mother solvent and the reaction raw materials are mixed to form an anode feed solution.

[0015] (2) The anode feed liquid is continuously fed into the anode side of an electrolytic cell with a perfluorinated proton exchange membrane as the diaphragm for electrocatalysis, and the resulting effluent flows out from the anode;

[0016] (3) Separate the hydrofluoric ether from the effluent, and use the remaining liquid as a mother liquor for reuse;

[0017] (4) Add perfluorocarboxylic acid of the same molar amount as the separated hydrofluoroether to the recycled mother liquor to form a new anode feed liquid, and repeat steps (2)-(4) to continuously decarboxylate and synthesize hydrofluoroether.

[0018] In a further preferred embodiment, in step (3), the effluent is distilled to obtain a light component, which is a mixture of hydrofluoric ether and water. The mixture is then separated into hydrofluoric ether and water by liquid separation. The separated water is mixed with the remaining liquid after distillation, which consists of unreacted reactants and polar aprotic solvents, to serve as a reuse mother liquor.

[0019] Perfluorinated proton exchange membranes (PTMs) require an acidic environment to ensure their conductivity; therefore, a slightly acidic environment must be maintained on the anode side. Experiments show that if only fluorinated carboxylates are used as reactants, the concentration of hydroxide ions increases during electrolysis, leading to an increase in the pH on the anode side and consequently affecting the conductivity of the PFM. A mixture of perfluorocarboxylic acid and its salt can be used as reactants in the first batch of the reaction, with subsequent batches using perfluorocarboxylic acid as a supplementary reactant. This satisfies the slightly acidic requirement on the anode side, eliminating the need for complex pH adjustments and facilitating a more continuous and stable reaction.

[0020] Electrocatalytic technology enables the recycling of mother liquor. During the distillation of the effluent, water is distilled out, reducing the water content of the remaining liquid and causing the precipitation of carbonates and bicarbonates. These precipitated carbonates and bicarbonates can be converted into a perfluorocarboxylate aqueous solution by adding perfluorocarboxylic acid and water separated from the lighter components, thus forming a homogeneous phase again. This significantly reduces water consumption and hazardous waste generation, and substantially lowers post-treatment costs.

[0021] More preferably, in step (1), the polar aprotic solvent accounts for 25-50% wt% of the mother solvent.

[0022] The amount of polar aprotic solvent used is closely related to whether the electrocatalytic synthesis of hydrofluoroethers can be continuous. The concentration of the mother liquor also needs to be controlled during subsequent reuse; too high or too low a concentration will decrease selectivity. Since unreacted materials have high boiling points and remain in the mother liquor, the light components separated from the mother liquor are only the target product and water, which are immiscible. The water can be easily separated and reused.

[0023] More preferably, the polar aprotic solvent is selected from any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, and the mother solvent can be recycled.

[0024] A further preferred option is to use diethylene glycol dimethyl ether as the polar aprotic solvent.

[0025] The electrocatalytic products of perfluorocarboxylic acids and their salts follow three different routes to yield different products, depending on solvent and voltage conditions: dimers produced by the Kolbe reaction, alkenyl ether monomers produced by non-Kolbe reactions, and a 1:1 ratio of hydrofluoroethers and alkenyl ether monomers produced by disproportionation reactions. While common alcohols promote the Kolbe reaction, the electrocatalytic products do not form a 1:1 ratio of hydrofluoroethers and alkenyl ether monomers via the disproportionation route under the action of ethylene glycol dimethyl ether / diethylene glycol dimethyl ether / tetraethylene glycol dimethyl ether and water. Due to the combined action of ethylene glycol dimethyl ether / diethylene glycol dimethyl ether / tetraethylene glycol dimethyl ether and water, the alkenyl ether monomer undergoes further addition at the electrode surface and converts to hydrofluoroethers, resulting in a significantly improved selectivity for hydrofluoroethers, with yields exceeding 99% under suitable conditions.

[0026] More preferably, in step (1), the mass ratio of perfluorocarboxylic acid and its salt is 0.5-2:1.

[0027] More preferably, the perfluorocarboxylic acid has the general structural formula Rf-CF(CF3)COOH, wherein the general structural formula of Rf is CF3O[CF(CF3)CF2O]. m CF3CF2O[CF(CF3)CF2O] m CF3CF2CF2O[CF(CF3)CF2O] m One or more of the following, m is selected from 1 or 2; the perfluorocarboxylate is the potassium or sodium salt corresponding to the perfluorocarboxylic acid.

[0028] The selected perfluorocarboxylic acids and their salts need to have an active end group of -OCF(CF3)COOH or the corresponding potassium or sodium salt structure. This structure will first decarboxylate to form CO2 under both thermochemical and electrocatalytic scenarios, which will reduce the number of carbon atoms in the structure and provide conditions for the -OCF- structure to combine with H elements. However, the electrocatalytic reaction mechanism is an electric field driven reaction, and the reaction takes place on the surface of the electrode plate.

[0029] Preferably, in step (1), the mass ratio of the reactant to the mother solvent in the anode feed liquid is 1:1-2.

[0030] The method of this invention involves the electrocatalytic decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts on the anode side, with hydrogen production occurring simultaneously on the cathode side. The reaction is carried out at ambient temperature and pressure, and both the reaction and post-processing can be performed continuously.

[0031] More preferably, in step (2), the perfluorinated proton exchange membrane is a homogeneous membrane formed by doping one or more of perfluorosulfonic acid, perfluorophosphoric acid or perfluorocarboxylic acid resin.

[0032] More preferably, the perfluorinated proton exchange membrane is any one of a homogeneous membrane made of perfluorophosphate resin doped with perfluorosulfonic acid resin or perfluorocarboxylic acid resin doped with perfluorosulfonic acid resin.

[0033] More preferably, the homogeneous membrane made of perfluorophosphate resin doped with perfluorosulfonic acid resin has a mass ratio of perfluorophosphate resin to perfluorosulfonic acid resin of 1:5~10; the homogeneous membrane made of perfluorocarboxylic acid resin doped with perfluorosulfonic acid resin has a molar ratio of perfluorocarboxylic acid resin to perfluorosulfonic acid resin of 1:5~10.

[0034] Although perfluorinated proton exchange membrane materials do not present compatibility issues with perfluorocarboxylic acids and their salts, as well as water, suitable solvents are required in electrocatalysis to enhance reaction selectivity. Using methanol or other polar solvents can lead to membrane dissolution and perforation after a short period. Therefore, existing electrocatalytic technologies do not use membrane materials for Kolbe, non-Kolbe, or disproportionation reactions. However, when perfluorophosphoric acid or perfluorocarboxylic acid is used as a dopant for perfluorosulfonic acid, the membrane's tolerance to non-alcoholic solvents, such as polar aprotic organic solvents, is significantly enhanced, and perforation and swelling in polar aprotic solvent systems are effectively reduced.

[0035] More preferably, in step (2), the thickness of the perfluorinated proton membrane is 40~120μm.

[0036] More preferably, the thickness of the perfluorinated proton exchange membrane is 80~120μm.

[0037] Preferably, in the method, the anode side is a platinum electrode and the cathode side is a platinum or glassy carbon electrode.

[0038] More preferably, in step (2), the electrocatalytic reaction temperature is 20~60℃. The reaction can proceed at room temperature, but it is exothermic, and the temperature increases as the reaction progresses. Furthermore, the lower the voltage, the more pronounced the advantage of the water electrolysis oxygen reaction. Appropriate high voltage helps promote the conversion of perfluorocarboxylic acids and their salts, but excessively high voltage leads to energy waste. According to the formula Q=UIt, with a fixed resistance, the higher the voltage, the greater the heat release. Considering overall energy consumption, this reaction can use circulating water for heat removal; therefore, controlling the temperature at 20~60℃ can reduce energy consumption without affecting the reaction's progress.

[0039] More preferably, in step (3), the general structural formula of the hydrofluoroether is Rf-CHFCF3, wherein the general structural formula of Rf is: CF3O[CF(CF3)CF2O] m CF3CF2O[CF(CF3)CF2O] m CF3CF2CF2O[CF(CF3)CF2O] m One or more of them, where m is selected from 1 or 2.

[0040] More preferably, step (4) further includes: periodically detecting the water content on the anode side and the cathode side and replenishing the water, so that the mass ratio of polar aprotic solvent to water on the anode side is 0.33~1:1.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) This invention provides the optimal electrocatalytic reaction method for perfluorocarboxylic acid and its salt raw materials, and uses mother liquor reuse technology, which significantly reduces the generation of hazardous waste and is more in line with the environmental protection requirements of "circular economy".

[0043] (2) The process solution provided by this invention is more energy-efficient and environmentally friendly. It adopts electrocatalytic synthesis technology, which reduces the reaction temperature and reaction pressure, reduces the energy consumption of the equipment, and is more in line with the requirements of "dual carbon emission reduction".

[0044] (3) The present invention uses a variety of resin-doped perfluorinated proton exchange membrane materials, which have good tolerance to polar aprotic organic solvents such as diethylene glycol dimethyl ether in the electrocatalytic synthesis system of perfluorinated carboxylic acids and their salts. This effectively expands the application of perfluorinated proton exchange membranes in the field of organic synthesis and simultaneously expands the potential application scenarios of electrocatalytic synthesis systems. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the electrolytic cell used in an embodiment of the present invention. Detailed Implementation

[0046] In all the examples and comparative examples below, the perfluorinated proton exchange membranes used had a molecular weight of 200,000 for the perfluorosulfonic acid resin and an ion exchange capacity of 1.1 mmol / g; a molecular weight of 30,000 for the perfluorophosphate resin and an ion exchange capacity of 1.5 mmol / g; and a molecular weight of 20,000 for the perfluorocarboxylic acid resin and an ion exchange capacity of 0.95 mmol / g.

[0047] The preparation method of perfluorinated proton exchange membranes formed by doping perfluorophosphate resin or perfluorocarboxylic acid resin with perfluorosulfonic acid resin is as follows:

[0048] (1) Transform perfluorophosphate resin, perfluorocarboxylic acid resin, and perfluorosulfonic acid resin from sodium form or potassium form to hydrogen form, respectively;

[0049] (2) After mixing the hydrogen-form resin obtained in step (1) in a predetermined ratio, a perfluorinated proton membrane is obtained by high-temperature melt extrusion at 200°C.

[0050] The electrolysis apparatus used in the embodiments and comparative examples includes, for example, the electrolysis apparatus used in the embodiments and comparative examples. Figure 1 The electrolytic cell with a cooling system, as well as the distillation and mother liquor recycling system shown, are examples of this. The electrolytic cell uses a perfluorinated proton exchange membrane as the separating material, dividing the cell into an anode side and a cathode side. The anode side contains an anode plate. The solvent mother liquor, mixed with the reactants, is continuously pumped into the anode of the electrolytic cell via a peristaltic pump to carry out a continuous electrocatalytic decarboxylation reaction of perfluorocarboxylic acids and their salts to synthesize hydrofluoroethers. The resulting effluent flows out through the anode side. Simultaneously, CO2 and O2 are also generated on the anode side. The effluent is separated by distillation, and the distilled light component is a mixture of hydrofluoroether and water, which are immiscible. Hydrofluoroether products are obtained through simple separation, while water is also separated. The separated water is reused and mixed with the remaining liquid after distillation to form a recycled mother liquor, achieving mother liquor recycling. As the reaction proceeds, equimolar amounts of perfluorocarboxylic acids are continuously added to the recycled mother liquor according to the product yield, achieving continuous production of hydrofluoroethers. The cathode side contains a cathode plate, using water as a solvent to co-produce hydrogen gas. The water content on both the anode and cathode sides is periodically monitored and replenished.

[0051] Example 1

[0052] The synthesis method of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 and the mixture of CF3OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 are as follows:

[0053] (1) A mixture of 50%wt diethylene glycol dimethyl ether and 50%wt water was used as the solvent mother liquor. Then, CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH and CF3OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOK were mixed at a mass ratio of 2:1 to form the reaction raw material. Then, an equal mass of solvent mother liquor was added. After the solvent mother liquor and the reaction raw material were mixed evenly, a peristaltic pump was used to pump it into the anode of the electrolytic cell at a flow rate of 10mL / min.

[0054] (2) The electrolytic cell is set to a voltage of 32V. Both the anode and cathode plates are platinum plates, each 10cm x 10cm in size. The perfluorinated proton exchange membrane is a homogeneous membrane made of 120μm thick perfluorosulfonic acid resin and perfluorophosphate resin (mass ratio of perfluorosulfonic acid to perfluorophosphate resin is 5:1). The reaction temperature is controlled at 60℃ by water cooling. After feeding, the reaction current is maintained at 6A. The reaction products are distilled after leaving the anode of the electrolytic cell. This electrocatalytic reaction is carried out at atmospheric pressure, with hydrogen co-produced on the cathode side.

[0055] (3) After distillation, the light component distilled out is a mixture of product and water. After separation, a mixture of hydrofluoric ether products, namely CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 and CF3OCF(CF3)CF2OCF(CF3)CF2OCHFCF3, with a mass ratio of 2:1, is obtained. The separated water is combined with the remaining liquid after distillation to form a recycled mother liquor.

[0056] (4) As the reaction proceeds, according to the product yield, equimolar mixtures of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH and CF3OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor to achieve continuous production of hydrofluoric ether. The ratio of the two in the mixture still follows the mass ratio of 2:1. The water content on the anode side and the cathode side is detected every 8 hours and water is added to keep the mass ratio of polar aprotic solvent to water on the anode side in the range of 0.33~1:1.

[0057] After the reaction stabilized for 24 hours, the overall yield of the continuous reaction was 93%, and the purity of the distilled product was 98.5%, of which 1% of the impurities were olefin ether monomers.

[0058] Example 2

[0059] The synthesis method of CF3CF2CF2OCF(CF3)CF2OCHFCF3 is as follows:

[0060] (1) A mixture of 25%wt tetraethylene glycol dimethyl ether and 75%wt water was used as the mother liquor of the solvent. Then, CF3CF2OCF(CF3)CF2OCF(CF3)COOH and CF3CF2OCF(CF3)CF2OCF(CF3)COOK were mixed at a mass ratio of 1:1 to form the reaction raw material. The mother liquor of the solvent and the reaction raw material were then mixed at a mass ratio of 2:1. After the mixture was homogeneous, it was pumped into the anode of the electrolytic cell using a peristaltic pump at a flow rate of 1 mL / min.

[0061] (2) The electrolytic cell is set to 3V. The anode electrode is a platinum plate, and the cathode electrode is glassy carbon, with a size of 20cm×20cm. The perfluorinated proton exchange membrane is a homogeneous membrane made of perfluorosulfonic acid-carboxylic acid doped with a thickness of 40μm, wherein the ratio of perfluorosulfonic acid resin to perfluorocarboxylic acid resin is 7:1. The reaction temperature is controlled at 20℃ by low-temperature water cooling. After feeding, the reaction current is maintained at 1A. After the reaction product leaves the anode of the electrolytic cell, it is subjected to distillation. This electrocatalytic reaction is carried out at atmospheric pressure, and hydrogen is co-produced on the cathode side.

[0062] (3) After distillation, the light component distilled out is a mixture of product and water. After separation, the hydrofluoric ether product CF3CF2OCF(CF3)CF2OCHFCF3 is obtained. The separated water is combined with the remaining liquid after distillation to form a recycled mother liquor.

[0063] (4) As the reaction proceeds, equimolar amounts of CF3CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor according to the product yield to achieve continuous production of hydrofluoric ether. In addition, the water content on the anode and cathode sides is detected every 8 hours and water is added to keep the mass ratio of polar aprotic solvent to water on the anode side in the range of 0.33~1:1.

[0064] After the reaction stabilized for 24 hours, the overall yield of the continuous reaction was 93%, the product purity was 99.2%, and the content of alkenyl ether monomer impurities was only 0.5%.

[0065] Example 3

[0066] The synthesis method of CF3CF2CF2OCF(CF3)CF2OCHFCF3 is as follows:

[0067] (1) A mixture of 50%wt ethylene glycol dimethyl ether and 50%wt water was used as the mother liquor of the solvent. Then, CF3CF2CF2OCF(CF3)CF2OCF(CF3)COOH and CF3CF2CF2OCF(CF3)CF2OCF(CF3)COONa were mixed at a mass ratio of 1:1 to form the reaction raw material. The mother liquor of the solvent and the reaction raw material were mixed at a mass ratio of 1:1. After the mixture was evenly mixed, it was pumped into the anode of the electrolytic cell by a peristaltic pump at a flow rate of 5mL / min.

[0068] (2) The electrolytic cell is set to a voltage of 20V. The anode electrode plate is a platinum plate, and the cathode electrode plate is glassy carbon, with a size of 15cm×15cm. The perfluorinated proton exchange membrane is an 80μm thick homogeneous membrane made of perfluorosulfonic acid and perfluorocarboxylic acid resin doped together (the mass ratio of perfluorosulfonic acid to perfluorocarboxylic acid resin is 10:1). The reaction temperature is controlled at 40℃ by water cooling. After feeding, the reaction current is maintained at 5A. After the reaction product leaves the anode of the electrolytic cell, it is subjected to distillation. This electrocatalytic reaction is carried out at atmospheric pressure, and hydrogen is co-produced on the cathode side.

[0069] (3) The light component distilled out after rectification is a mixture of product and water. After separation, the hydrofluoric ether product CF3CF2CF2OCF(CF3)CF2OCHFCF3 is obtained. The separated water is combined with the remaining liquid after rectification to form a recycled mother liquor.

[0070] (4) As the reaction proceeds, equimolar amounts of CF3CF2CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor according to the product yield to achieve continuous production of hydrofluoric ether. In addition, the water content on the anode and cathode sides is detected every 8 hours and water is added to keep the mass ratio of polar aprotic solvent to water on the anode side in the range of 0.33~1:1.

[0071] After the reaction stabilized for 24 hours, the overall yield of the continuous reaction was 95%, the product purity was 99%, and the content of alkenyl ether monomer impurities was only 0.5%.

[0072] Comparative Example 1

[0073] Using a 100L reactor as the reaction equipment, 50L of water was added as a solution. Since the thermochemical method can only convert carboxylates, KOH was used to fully react the mixture of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH and CF3OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH until it became neutral before adding it to the 100L reactor. After adding 30kg of raw material, the reactor was heated to 140℃ and the maximum pressure reached 0.5MPa. The reaction was carried out for 20h. After distillation, a mixture of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 and CF3OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 was obtained. The reaction selectivity was 99%. Therefore, the total conversion rate, i.e. the yield, was 81%. Extending the reaction time did not change the yield to 81%. Unreacted material entered the wastewater, forming 78 kg of carboxylate residue, with hazardous waste generation nearly twice that of the product output. This reaction was a batch reactor and could not be operated continuously.

[0074] Comparative Example 2

[0075] The synthesis method of CF3CF2OCF(CF3)CF2OCHFCF3 is as follows:

[0076] (1) A mixture of 25%wt tetraethylene glycol dimethyl ether and 75%wt water was used as the solvent mother liquor. Then, CF3CF2OCF(CF3)CF2OCF(CF3)COOH and CF3CF2OCF(CF3)CF2OCF(CF3)COOK were mixed at a mass ratio of 1:1 to form the reaction raw material. The solvent mother liquor and the reaction raw material were then mixed at a mass ratio of 2:1. After the solvent mother liquor and the reaction raw material were mixed evenly, they were pumped into the electrolytic cell by a peristaltic pump at a flow rate of 1mL / min.

[0077] (2) The electrolytic cell was set to 3V. Platinum plates were used as the anode electrode and glassy carbon plates were used as the cathode electrode, with dimensions of 10cm × 10cm. No diaphragm material was used for isolation. The reaction temperature was controlled at 20℃ by low-temperature water cooling. After feeding, the reaction current was maintained at 1A. The reaction products were distilled after leaving the anode of the electrolytic cell. This electrocatalytic reaction was carried out at atmospheric pressure, but the hydrogen produced at the cathode was difficult to separate from the oxygen and carbon dioxide produced at the anode, and occasional flashover occurred during the experiment.

[0078] (3) After distillation, the light component distilled out is a mixture of product and water. After separation, the hydrofluoric ether product CF3CF2OCF(CF3)CF2OCHFCF3 is obtained. The separated water is combined with the remaining liquid after rectification to form a recycled mother liquor.

[0079] (4) As the reaction proceeds, equimolar amounts of CF3CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor according to the product yield to achieve continuous production of hydrofluoric ether. In addition, the water content on the anode and cathode sides is detected every 8 hours and water is added to keep the mass ratio of polar aprotic solvent to water on the anode side in the range of 0.33~1:1.

[0080] After 24 hours of stabilization, the overall yield of the continuous reaction was 88%, the product purity was 95%, the alkenyl ether monomer impurity content was 1%, the alkenyl ether monomer hydrogenation byproduct (CF3CF2OCF(CF3)CF2OCHFCHF2) accounted for 1%, and other hydrogenolysis multi-hydrogen products accounted for 3%. Even with the selection of tetraethylene glycol dimethyl ether solvent for effective selective catalysis, which suppressed the production of alkenyl ether monomer, many multi-hydrogenation byproducts were still produced, mainly due to the hydrogenolysis of the product by hydrogen gas on the cathode side.

[0081] Comparative Example 3

[0082] The synthesis method of CF3CF2CF2OCF(CF3)CF2OCHFCF3 is as follows:

[0083] (1) A mixture of 50%wt ethylene glycol dimethyl ether and 50%wt water was used as the mother solvent. The mother solvent and the reaction raw materials composed of CF3CF2CF2OCF(CF3)CF2OCF(CF3)COOH and CF3CF2CF2OCF(CF3)CF2OCF(CF3)COONa (the mass ratio of carboxylic acid to sodium salt is 2:1) were mixed at a mass ratio of 1:1. After the mother solvent and the reaction raw materials were mixed evenly, a peristaltic pump was used to pump them into the anode of the electrolytic cell at a flow rate of 5 mL / min.

[0084] (2) The electrolytic cell is set to a voltage of 40V. The anode electrode plate is made of platinum, and the cathode electrode plate is made of glassy carbon, both measuring 20cm × 20cm. The perfluorinated proton exchange membrane is an 80μm thick perfluorosulfonic acid membrane with a reinforcing layer. The reaction temperature is controlled at 40℃ by water cooling. The initial reaction current after feeding is 10A. After the reaction product leaves the anode of the electrolytic cell, it undergoes distillation. This electrocatalytic reaction is carried out at atmospheric pressure, and hydrogen is co-produced on the cathode side.

[0085] (3) After distillation, the light component distilled out is a mixture of product and water. After separation, the hydrofluoric ether product CF3CF2CF2OCF(CF3)CF2OCHFCF3 is obtained. The separated water is combined with the remaining liquid after distillation to form a recycled mother liquor.

[0086] (4) As the reaction proceeds, equimolar amounts of CF3CF2CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor according to the product yield to achieve continuous production of hydrofluoric ether. In addition, the water content on the anode and cathode sides is detected every 8 hours and water is added to keep the mass ratio of polar aprotic solvent to water on the anode side in the range of 0.33~1:1.

[0087] After 24 hours of stabilization, the overall yield of the continuous reaction decreased to 90% and showed a downward trend. The product purity was 98%, and the impurity content of the alkenyl ether monomer was only 1%. However, the current showed an irreversible decrease during the reaction, gradually decreasing from 10A to 6A, and the perfluorosulfonic acid film material with the reinforcing layer exhibited significant delamination and perforation. As the reaction proceeded, these adverse phenomena became increasingly pronounced, clearly indicating that unsuitable membrane materials and reaction conditions would negatively impact the stable operation of this reaction.

[0088] The perfluorosulfonic acid membrane with reinforcement layer used is manufactured by Shandong Dongyue Future Hydrogen Energy Materials Co., Ltd., and its model is DM6525.

[0089] Comparative Example 4

[0090] The synthesis methods of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 and CF3OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 are as follows:

[0091] (1) A mixture of 10%wt diethylene glycol dimethyl ether and 90%wt water was used as the solvent mother liquor. Then, CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH and CF3OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOK were mixed at a mass ratio of 2:1 to form the reaction raw material. Then, the solvent mother liquor and the reaction raw material were mixed at a mass ratio of 2:1. After the solvent mother liquor and the reaction raw material were mixed evenly, a peristaltic pump was used to pump it into the anode of the electrolytic cell at a flow rate of 10mL / min.

[0092] (2) The electrolytic cell is set to a voltage of 32V. Both the anode and cathode plates are platinum plates, each 10cm x 10cm in size. The perfluorinated proton exchange membrane is a homogeneous membrane made of 120μm thick perfluorosulfonic acid resin and perfluorophosphate resin (mass ratio of perfluorosulfonic acid to perfluorophosphate resin is 5:1). The reaction temperature is controlled at 60℃ by water cooling. After feeding, the reaction current is maintained at 6A. The reaction products are distilled after leaving the anode of the electrolytic cell. This electrocatalytic reaction is carried out at atmospheric pressure, with hydrogen co-produced on the cathode side.

[0093] (3) After distillation, the light component distilled out is a mixture of product and water. After separation, a mixture of hydrofluoric ether products, namely CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCHFCF3 and CF3OCF(CF3)CF2OCF(CF3)CF2OCHFCF3, with a mass ratio of 2:1, is obtained. The separated water is combined with the remaining liquid after distillation to form a recycled mother liquor.

[0094] (4) As the reaction proceeds, according to the product yield, equimolar mixtures of CF3CF2OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH and CF3OCF(CF3)CF2OCF(CF3)CF2OCF(CF3)COOH are continuously added to the recycled mother liquor to achieve continuous production of hydrofluoric ether. The ratio of the two in the mixture still follows the mass ratio of 2:1. Furthermore, the water content on the anode side and the cathode side is detected every 8 hours and water is added to maintain the mass ratio of polar aprotic solvent to water on the anode side within the range of 0.1~0.3:1.

[0095] After 24 hours of stabilization, the overall yield of the continuous reaction was only 51%, and the purity of the product after distillation was 95%, with 3% of the impurities being alkenyl ether monomers. The product yield decreased significantly with decreasing polar aprotic solvent content, and the electrolysis process was dominated by hydrogen and oxygen evolution reactions, resulting in extremely low energy utilization. Similarly, the alkenyl ether monomer content increased.

[0096] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts, characterized in that, The method uses a perfluorinated proton exchange membrane as a diaphragm, divides the electrolytic cell into an anode and a cathode, uses perfluorocarboxylic acid and its salts as reactants, and uses a mixture of water and a polar aprotic solvent as a mother liquor, with the polar aprotic solvent accounting for 25-50% wt of the mother liquor. The mother liquor is mixed with the reactants and continuously introduced into the anode side of the electrolytic cell for electrocatalysis to generate hydrofluoric ethers. The perfluorinated proton exchange membrane is any one of a homogeneous membrane made of perfluorophosphate resin doped with perfluorosulfonic acid resin or perfluorocarboxylic acid resin doped with perfluorosulfonic acid resin. The polar aprotic solvent is selected from any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; The perfluorocarboxylic acid has the general structural formula Rf-CF(CF3)COOH, wherein the general structural formula of Rf is CF3O[CF(CF3)CF2O]. m CF3CF2O[CF(CF3)CF2O] m CF3CF2CF2O[CF(CF3)CF2O] m One or more of the following, m is selected from 1 or 2; the perfluorocarboxylate is the potassium or sodium salt corresponding to the perfluorocarboxylic acid; The general structural formula of hydrofluoroethers is Rf-CHFCF3, where the general structural formula of Rf is CF3O[CF(CF3)CF2O]. m CF3CF2O[CF(CF3)CF2O] m CF3CF2CF2O[CF(CF3)CF2O] m One or more of them, where m is selected from 1 or 2.

2. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 1, characterized in that, The method includes: (1) A mixture of water and a polar aprotic solvent is used as the mother solvent, and perfluorocarboxylic acid and its salt are used as the reaction raw materials. The mother solvent and the reaction raw materials are mixed to form an anode feed solution. (2) The anode feed liquid is continuously fed into the anode side of an electrolytic cell with a perfluorinated proton exchange membrane as the diaphragm for electrocatalysis, and the resulting effluent flows out from the anode; (3) Separate the hydrofluoric ether from the effluent, and use the remaining liquid as a mother liquor for reuse; (4) Add perfluorocarboxylic acid of the same molar amount as the separated hydrofluoro ether to the recycled mother liquor to form a new anode feed liquid, and repeat steps (2)-(4) to continuously decarboxylate and synthesize hydrofluoro ether.

3. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 2, characterized in that, In step (3), the effluent is distilled to obtain a light component, which is a mixture of hydrofluoric ether and water. The mixture is separated into hydrofluoric ether and water by liquid separation. The separated water is mixed with the remaining liquid after distillation as a mother liquor for reuse.

4. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 2, characterized in that, In step (1), the mass ratio of perfluorocarboxylic acid and its salt is 0.5-2:1; in the anode feed liquid, the mass ratio of the reaction raw material to the solvent mother liquor is 1:1-2.

5. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 2, characterized in that, In step (2), the thickness of the perfluorinated proton membrane is 40~120μm.

6. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 5, characterized in that, The thickness of the perfluorinated proton exchange membrane is 80~120μm.

7. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 1, characterized in that, The homogeneous membrane made of perfluorophosphate resin doped with perfluorosulfonic acid resin has a mass ratio of perfluorophosphate resin to perfluorosulfonic acid resin of 1:5~10; the homogeneous membrane made of perfluorocarboxylic acid resin doped with perfluorosulfonic acid resin has a mass ratio of perfluorocarboxylic acid resin to perfluorosulfonic acid resin of 1:5~10.

8. The method for the electrocatalytic continuous decarboxylation synthesis of hydrofluoroethers from perfluorocarboxylic acids and their salts according to claim 2, characterized in that, The electrocatalytic reaction temperature in step (2) is 20~60℃.

Images