A process for the preparation of fluoroethylene carbonate

Abstract

The application provides a preparation method of fluoroethylene carbonate. The method comprises the following steps: uniformly mixing potassium fluoride, a novel solid base catalyst and an organic solvent, then adding chloroethylene carbonate to perform fluorination reaction; after the reaction is completed, the obtained reaction liquid is filtered and distilled to obtain a crude product, and the obtained crude product is subjected to rectification and crystallization to obtain fluoroethylene carbonate; the novel solid base catalyst is composed of a magnesium-aluminum composite oxide coated magnetic nano Fe3O4 carrier and a double-metal fluoride, and the double metal in the double-metal fluoride is a combination of Rb and Co. Compared with the prior art, the application has the following prominent points: (1) less solvent can be used for reaction, and the reaction condition is mild; (2) high selectivity, high activity, less side reaction and high product yield; (3) simple post-treatment, the solvent can be recycled after being evaporated, the generation of three wastes is less, and the industrial production is green and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte additives, specifically relating to a method for preparing fluoroethylene carbonate. Background Technology

[0002] Lithium-ion battery electrolyte additives have attracted increasing attention due to their advantages of low dosage and high efficacy, becoming a hot topic in lithium-ion battery research in recent years. Using electrolyte additives is one of the most economical and effective methods to improve lithium-ion battery performance. Generally, adding no more than 5% of the electrolyte by mass or volume can significantly improve battery performance.

[0003] Fluorinated ethylene carbonate (FEC) is currently a mainstream additive in the market, used as an important pharmaceutical and pesticide intermediate, electronic chemical, organic solvent, and lithium battery electrolyte additive. Its primary application is in electrolyte additives. FEC can partially inhibit the decomposition of electrolyte solvents, forming a good solid electrolyte interphase (SEI) film on the electrode surface, reducing battery impedance, and improving battery specific capacity and cycle stability. It has a promising development prospect and a market share of approximately 21%.

[0004] Numerous reports have been published both domestically and internationally regarding the synthesis of FEC. Summarizing current patent literature, researchers have optimized and developed FEC production processes by selecting different fluorinating reagents, catalysts, reaction media, and reaction temperatures. Existing methods mainly include: 1. Directly fluorinating ethylene carbonate (EC) using a fluorine / nitrogen mixed gas as the fluorinating reagent, with a yield typically of 40%–60%. However, the fluorine gas used in this process is highly toxic, the operation is hazardous, the post-processing steps are cumbersome, and it is environmentally unfriendly. 2. Reacting hydrogen fluoride with chloroethylene carbonate in the presence of nitrogen-containing compounds such as triethylamine, pyridine, and aromatic amines to produce FEC, with a yield of 70%–85% and a product purity of 99.7%–99.9%. However, this method generates a large amount of crude product after water washing. Fluorine-containing wastewater is difficult to treat; moreover, it requires a large amount of organic base and a high reaction temperature. Thirdly, ethylene carbonate is first chlorinated to produce chloroethylene carbonate, and then reacted with fluorinating agents (such as potassium fluoride, sodium fluoride, barium fluoride, etc.) in a halogen substitution reaction to prepare fluoroethylene carbonate. Although this method has certain drawbacks, it remains the main process for industrial FEC production. Catalyst selection is a key factor, and currently used catalysts are mainly phase transfer catalysts, such as 18-crown-6, ionic liquids, calixarnes, and polymer-supported polyethylene glycol. However, these catalysts are difficult to separate from the product, cannot be recycled, the waste liquid is difficult to treat, causing environmental pollution and severe equipment corrosion.

[0005] Therefore, developing highly selective and high-yield processes for the preparation of fluoroethylene carbonate is of great significance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing fluoroethylene carbonate. The method employs a novel solid base catalyst to catalyze the reaction of potassium fluoride with chloroethylene carbonate to prepare fluoroethylene carbonate. The method yields products with high yield and purity, and has low production costs, making it suitable for industrial applications.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing fluoroethylene carbonate includes the following steps:

[0009] Potassium fluoride, a novel solid base catalyst, and an organic solvent were mixed evenly, and then chloroethylene carbonate was added to carry out a fluorination reaction. After the reaction was completed, the resulting reaction solution was filtered and distilled to obtain a crude product. The crude product was then subjected to distillation and crystallization to obtain chloroethylene carbonate.

[0010] The novel solid base catalyst is composed of a magnetic nano Fe3O4 support coated with magnesium-aluminum composite oxide and a bimetallic fluoride, wherein the bimetal in the bimetallic fluoride is a combination of Rb and Co.

[0011] According to a preferred embodiment of the present invention, the novel solid base catalyst is prepared by the following method:

[0012] (1) Preparation of magnetic nano Fe3O4 support

[0013] Under stirring conditions, NaOH solution was added dropwise to a mixed solution of FeCl3·6H2O and FeCl2·4H2O to adjust the pH of the system to 10.5-11. After standing, the system was heated to 80℃ for aging, followed by sedimentation. The precipitate was then washed and dried to obtain magnetic nano Fe3O4 carrier.

[0014] (2) Preparation of magnesium-aluminum composite oxides

[0015] Prepare a mixed solution I of magnesium nitrate and aluminum nitrate, and a mixed solution II of sodium hydroxide and sodium carbonate. Under stirring, add mixed solution I and mixed solution II dropwise to a three-necked flask at a volume ratio of 1:1, with a dropping rate of 50 mL / h. After the addition is complete, heat to 70 °C for crystallization for 1 h. Then, filter, wash, dry, and calcine to obtain magnesium-aluminum composite oxide.

[0016] (3) Preparation of magnetic nano-Fe3O4 carriers coated with magnesium-aluminum composite oxide

[0017] The magnetic nano Fe3O4 carrier obtained in step (1) and the magnesium-aluminum composite oxide obtained in step (2) were dispersed in deionized water at a mass ratio of 2:1 to obtain a mixed solution; CO2 was introduced into the mixed solution at 85°C to adjust the pH value of the system to 7, and the solution was aged at 85°C for 1 hour. After filtration, washing, separation, drying and calcination, the magnetic nano Fe3O4 carrier coated with magnesium-aluminum composite oxide was obtained.

[0018] (4) Preparation of bimetallic fluorides

[0019] Rubidium nitrate and cobalt nitrate were added to water at a molar ratio of Rb to Co of 2:1 to obtain a mixed solution. The mixed solution was then subjected to a hydrothermal reaction at 120–180 °C for 4–6 h. After the reaction was completed, the mixture was cooled and centrifuged. The resulting solid was then dried at 80–90 °C for 2–3 h to obtain a bimetallic compound. The resulting bimetallic compound was dissolved in an aqueous solution of hydrofluoric acid and stirred at 150–180 °C for 4–5 h. After filtration and washing, the resulting solid was dried at 250–280 °C for 5–6 h to obtain a bimetallic fluoride.

[0020] (5) Preparation of novel solid base catalysts

[0021] Weigh the magnetic nano Fe3O4 support coated with magnesium-aluminum composite oxide obtained in step (3), and then add water droplets to the support until the support absorbs water and reaches saturation. Record the volume of water used. Disperse the bimetallic fluoride obtained in step (4) in water and prepare an impregnation solution of equal volume. Then add the impregnation solution droplets to the support so that the bimetallic fluoride is uniformly loaded onto the support. After standing at room temperature, dry and calcine to obtain a novel solid base catalyst.

[0022] According to a preferred embodiment of the present invention, the molar ratio of FeCl3·6H2O and FeCl2·4H2O in the mixed solution in step (1) is 2:1; and the concentration of FeCl3·6H2O in the mixed solution is 0.012 to 0.015 g / mL.

[0023] According to a preferred embodiment of the present invention, the concentration of the NaOH solution in step (1) is 0.3 to 0.5 mol / L.

[0024] According to a preferred embodiment of the present invention, the settling time in step (1) is 10 to 15 minutes; the aging time is 1 to 2 hours; and the settling can be achieved using neodymium iron boron permanent magnets.

[0025] According to a preferred embodiment of the present invention, the washing in step (1) involves repeatedly washing the precipitate with deionized water and anhydrous ethanol alternately until the filtrate is neutral; the drying involves drying at 70-80°C for 5-6 hours.

[0026] According to a preferred embodiment of the present invention, the molar ratio of magnesium nitrate to aluminum nitrate in the mixed solution I in step (2) is 3:1; and the concentration of magnesium nitrate in the mixed solution I is 0.01 to 0.02 g / mL.

[0027] According to a preferred embodiment of the present invention, the molar ratio of sodium hydroxide to sodium carbonate in the mixed solution II in step (2) is 7:3; and the concentration of sodium hydroxide in the mixed solution II is 0.05 to 0.08 g / mL.

[0028] According to a preferred embodiment of the present invention, the washing in step (2) is washing the filter cake with carbon dioxide-free water until the filtrate is neutral; the drying is drying at 90-100°C for 20-30 hours; and the calcination is calcining at 400-800°C for 5-6 hours.

[0029] According to a preferred embodiment of the present invention, the concentration of the magnetic nano Fe3O4 support in the mixed solution in step (3) is 0.01 to 0.015 g / mL.

[0030] According to a preferred embodiment of the present invention, the washing in step (3) is washing the filter cake with water until the filtrate is neutral; the separation is performed using neodymium iron boron permanent magnets; the drying is performed at 80-90°C for 4-6 hours; and the calcination is performed at 500-600°C for 5-7 hours.

[0031] According to a preferred embodiment of the present invention, the concentration of rubidium nitrate in the mixed solution in step (4) is 0.001 to 0.003 g / mL.

[0032] According to a preferred embodiment of the present invention, the volume ratio of hydrofluoric acid to water in the hydrofluoric acid aqueous solution in step (4) is 1:6; the mass ratio of the bimetallic compound to the volume of the hydrofluoric acid aqueous solution is 0.03-0.06 g:1 mL; and the washing is performed by washing with water 3-5 times.

[0033] According to a preferred embodiment of the present invention, the mass ratio of the bimetallic fluoride to the magnetic nano Fe3O4 carrier coated with magnesium-aluminum composite oxide in step (5) is 1:7 to 10.

[0034] According to a preferred embodiment of the present invention, the standing time in step (5) is 8 to 10 hours; the drying is performed at 100 to 120°C for 8 to 10 hours; and the calcination is performed at 500 to 600°C for 3 to 5 hours.

[0035] According to a preferred embodiment of the present invention, the mass of the novel solid base catalyst is 0.2-3% of the mass of chloroethylene carbonate, more preferably 0.5-2.5%, and even more preferably 1-2%.

[0036] According to a preferred embodiment of the present invention, the organic solvent is dimethyl carbonate, and the mass ratio of the organic solvent to chloroethylene carbonate is 1.5 to 5:1.

[0037] According to a preferred embodiment of the present invention, the molar ratio of the chloroethylene carbonate to potassium fluoride is 1:1 to 2; the molar amount of the chloroethylene carbonate is calculated as follows: the added mass of chloroethylene carbonate * purity / 122.51.

[0038] According to a preferred embodiment of the present invention, the chloroethylene carbonate is added to the system over a period of 40 to 70 minutes, and the temperature is controlled at 40 to 100°C during the addition of the chloroethylene carbonate.

[0039] According to a preferred embodiment of the present invention, the temperature of the fluorination reaction is controlled at 70–110°C, and the fluorination reaction time is 1–3 h.

[0040] According to a preferred embodiment of the present invention, the distillation is carried out under conditions of 5–15 mmHg, and the fraction at 65–100°C is collected to obtain crude fluoroethylene carbonate.

[0041] According to a preferred embodiment of the present invention, the distillation is performed by vacuum distillation of the crude product under conditions of 4–10 mmHg, and the fraction at 60–95°C is collected.

[0042] According to a preferred embodiment of the present invention, the crystallization step is as follows: the liquid obtained by distillation is crystallized at 0-5°C. After no crystals precipitate, it is filtered to obtain the fluoroethylene carbonate product. The obtained product has high purity and can meet the requirements of electronic grade products.

[0043] The technical features and beneficial effects of this invention are as follows:

[0044] This invention uses a novel solid base catalyst to catalyze the halogen substitution reaction of chloroethylene carbonate with potassium fluoride as a fluorinating agent to prepare fluoroethylene carbonate. Compared with the prior art, it has the following advantages: (1) It uses less solvent for the reaction and the reaction conditions are mild; (2) The catalyst used in this invention is a magnetic nano Fe3O4 support coated with magnesium aluminum composite oxide to support bimetallic fluoride. The resulting catalyst is nano-sized, has a large specific surface area, and has many active centers. At the same time, it uses Rb-Co bimetallic fluoride, which has better activity and selectivity. The catalyst of this invention has the advantages of high selectivity, high activity, few side reactions, and high product yield. Its catalytic activity and selectivity are much higher than those of traditional catalysts; (3) The post-processing of the method of this invention is simple. The product can be obtained by evaporating the solvent and cooling and crystallizing. The obtained solvent can be recycled, and the amount of waste generated is small. The industrial production is green and environmentally friendly. At the same time, the catalyst of this invention can be recycled. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments, making the advantages of the present invention more apparent. It should be understood that the content therein is for illustrative purposes only and is not intended to limit the scope of protection of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0046] Preparation Example 1

[0047] A novel method for preparing a solid base catalyst includes the following steps:

[0048] (1) Preparation of magnetic nano Fe3O4 support

[0049] Under stirring conditions, 0.5 mol / L NaOH solution was added dropwise to a mixed solution of FeCl3·6H2O and FeCl2·4H2O to adjust the pH of the system to 11. After standing for 10 min, the system was aged at 80℃ for 1 h. Then, a neodymium iron boron permanent magnet (model N35) was used for adsorption and precipitation. The precipitate was washed repeatedly with deionized water and anhydrous ethanol alternately until the filtrate was neutral. Then, it was dried at 75℃ for 5 h to obtain magnetic nano Fe3O4 carrier. The molar ratio of FeCl3·6H2O to FeCl2·4H2O in the mixed solution was 2:1, and the concentration of FeCl3·6H2O in the mixed solution was 0.012 g / mL.

[0050] (2) Preparation of magnesium-aluminum composite oxides

[0051] A mixed solution I of magnesium nitrate and aluminum nitrate was prepared, and a mixed solution II of sodium hydroxide and sodium carbonate was prepared. Under stirring, mixed solutions I and II were simultaneously added dropwise to a three-necked flask at a volume ratio of 1:1 at a dropping rate of 50 mL / h. After the addition was completed, the temperature was raised to 70 °C for crystallization for 1 h. After filtration, the filter cake was washed with carbon dioxide-free water until the filtrate was neutral. The filter cake was dried at 95 °C for 24 h and then placed in a muffle furnace and calcined at 600 °C for 6 h to obtain magnesium-aluminum composite oxide. The molar ratio of magnesium nitrate to aluminum nitrate in mixed solution I was 3:1, and the concentration of magnesium nitrate in mixed solution I was 0.015 g / mL. The molar ratio of sodium hydroxide to sodium carbonate in mixed solution II was 7:3, and the concentration of sodium hydroxide in mixed solution II was 0.07 g / mL.

[0052] (3) Preparation of magnetic nano-Fe3O4 carriers coated with magnesium-aluminum composite oxide

[0053] The magnetic nano Fe3O4 carrier obtained in step (1) and the magnesium-aluminum composite oxide obtained in step (2) were dispersed in deionized water at a mass ratio of 2:1 to obtain a mixed solution (the concentration of magnetic nano Fe3O4 carrier in the mixed solution was 0.012 g / mL). CO2 was introduced into the mixed solution at 85°C to adjust the pH value of the system to 7. The solution was aged at 85°C for 1 h, filtered, and the solid was washed with water until the filtrate was neutral. Magnetic separation was performed using a neodymium iron boron permanent magnet (model N35). The solution was dried at 85°C for 4 h and then placed in a muffle furnace and calcined at 500°C for 6 h to obtain the magnetic nano Fe3O4 carrier coated with magnesium-aluminum composite oxide.

[0054] (4) Preparation of metal fluorides

[0055] Rubidium nitrate and cobalt nitrate were added to water at a molar ratio of Rb to Co of 2:1 to obtain a mixed solution (the concentration of rubidium nitrate in the mixed solution was 0.002 g / mL). The mixed solution was subjected to hydrothermal reaction at 150 °C for 5 h. After the reaction was completed, it was naturally cooled to room temperature, and the reaction product was removed and centrifuged. The obtained solid was dried at 80 °C for 2 h to obtain a bimetallic compound. The dried bimetallic compound was then dissolved in an aqueous hydrofluoric acid solution (the volume ratio of hydrofluoric acid to water in the aqueous hydrofluoric acid solution was 1:6, and the mass ratio of the bimetallic compound to the volume of the aqueous hydrofluoric acid solution was 0.05 g: 1 mL). The mixture was stirred at 160 °C for 4 h. After filtration, the obtained solid was washed three times with deionized water and dried at 250 °C for 6 h to obtain a bimetallic fluoride.

[0056] (5) Preparation of novel solid base catalysts

[0057] Weigh 10g of the magnetic nano Fe3O4 support coated with magnesium-aluminum composite oxide obtained in step (3), and then slowly add distilled water dropwise to the support until the support absorbs water and reaches saturation. Record the volume of distilled water used as 30mL. Disperse 1.11g of the bimetallic fluoride obtained in step (4) in 30mL of water to prepare an impregnation solution of equal volume. Then add the impregnation solution dropwise to the magnetic nano Fe3O4 support coated with 10g of magnesium-aluminum composite oxide to uniformly load the bimetallic fluoride onto the support. After standing at room temperature for 8h, place it in an oven and dry at 120℃ for 8h. After drying, place the obtained solid in a muffle furnace and calcine at 500℃ for 4h to obtain a novel solid base catalyst.

[0058] Preparation Example 2

[0059] A novel solid base catalyst is prepared as described in Preparation Example 1, except that the mass of the bimetallic fluoride in step (5) is 1.25 g.

[0060] Preparation Example 3

[0061] A novel solid base catalyst is prepared as described in Preparation Example 1, except that the mass of the bimetallic fluoride in step (5) is 1.00 g.

[0062] Example 1

[0063] A method for preparing fluoroethylene carbonate includes the following steps:

[0064] 90.1 g of potassium fluoride and 316.6 g of dimethyl carbonate were added to a three-necked flask, followed by 0.79 g of the novel solid base catalyst obtained in Preparation Example 1. The mixture was then thoroughly mixed, and 158.3 g of ethylene chloride carbonate (80% purity) was added dropwise. The temperature was controlled at 70–80 °C during the dropwise addition, and the addition time was 60 min. As ethylene chloride carbonate was added, the color of the system changed from colorless to brown. After the addition was complete, the reaction was carried out at 90 °C for 3 h. The reaction solution was then allowed to cool naturally to... The filtrate was filtered at room temperature and then distilled at 10–15 mmHg. The fraction at 65–100 °C was collected to obtain crude fluoroethylene carbonate. The crude product was then subjected to vacuum distillation at 5–10 mmHg, and the fraction at 60–95 °C was collected. The liquid obtained from the distillation was cooled to 0–5 °C to allow crystallization. After no crystals precipitated, the product was filtered to obtain 98.5 g (yield 89.8%) of fluoroethylene carbonate with a purity of 98.74%.

[0065] Example 2

[0066] A method for preparing fluoroethylene carbonate includes the following steps:

[0067] 97.0 g of potassium fluoride and 339.0 g of dimethyl carbonate were added to a three-necked flask, followed by 1.70 g of the novel solid base catalyst obtained in Preparation Example 1, which was mixed thoroughly. Then, 169.5 g of ethylene chloride carbonate (80% purity) was added dropwise at a controlled temperature of 70–80 °C for 60 min. As ethylene chloride carbonate was added, the system changed from colorless to brown. After the addition was complete, the reaction was carried out at 90 °C for 3 h. The reaction solution was then allowed to cool naturally to room temperature. The solution was filtered at room temperature, and the filtrate was distilled at 10–15 mmHg. The fraction at 65–100 °C was collected to obtain crude fluoroethylene carbonate. The crude product was then subjected to vacuum distillation at 5–10 mmHg, and the fraction at 60–95 °C was collected. The liquid obtained from the distillation was cooled to 0–5 °C to allow crystallization. After no crystals precipitated, the solution was filtered to obtain 108.6 g (yield 92.5%) of fluoroethylene carbonate with a purity of 99.95%.

[0068] Example 3

[0069] A method for preparing fluoroethylene carbonate includes the following steps:

[0070] 71.5 g of potassium fluoride and 252.4 g of dimethyl carbonate were added to a three-necked flask, followed by 3.16 g of the novel solid base catalyst obtained in Preparation Example 1. The mixture was then thoroughly mixed, and 126.2 g of ethylene chloride carbonate (80% purity) was added dropwise. The temperature was controlled at 70–80 °C during the dropwise addition, and the addition time was 60 min. As ethylene chloride carbonate was added, the system color changed from colorless to brown. After the addition was complete, the reaction was carried out at 90 °C for 3 h. The reaction solution was then allowed to cool naturally to... The filtrate was filtered at room temperature and then distilled at 10–15 mmHg. The fraction at 65–100 °C was collected to obtain crude fluoroethylene carbonate. The crude product was then subjected to vacuum distillation at 5–10 mmHg, and the fraction at 60–95 °C was collected. The liquid obtained from the distillation was cooled to 0–5 °C to allow crystallization. After no crystals precipitated, the product was filtered to obtain 79.2 g (yield 90.7%) of fluoroethylene carbonate with a purity of 99.36%.

[0071] Example 4

[0072] A method for preparing fluoroethylene carbonate is described in Example 2, except that the reaction temperature is 85°C, yielding 106.4 g (yield 90.6%) of fluoroethylene carbonate with a purity of 99.87%.

[0073] Example 5

[0074] A method for preparing fluoroethylene carbonate is described in Example 2, except that the reaction temperature is 100°C, yielding 107.1g (yield 91.2%) of fluoroethylene carbonate with a purity of 99.90%.

[0075] Example 6

[0076] A method for preparing fluoroethylene carbonate is described in Example 2, except that the novel solid base catalyst prepared in Example 2 is used to obtain fluoroethylene carbonate with a purity of 96.81% and a yield of 89.4%.

[0077] Example 7

[0078] A method for preparing fluoroethylene carbonate is described in Example 2, except that the novel solid base catalyst prepared in Example 3 is used, resulting in fluoroethylene carbonate with a purity of 97.45% and a yield of 89.6%.

[0079] Comparative Example 1

[0080] A method for preparing fluoroethylene carbonate is described in Example 2, the difference being that no catalyst is used, and the purity of the fluoroethylene carbonate obtained is 82.87%, with a yield of 70.5%.

[0081] Comparative Example 2

[0082] A method for preparing fluoroethylene carbonate is described in Example 2, the difference being that: instead of using a novel solid base catalyst, 18-crown ether-6 is used, resulting in fluoroethylene carbonate with a purity of 89.21% and a yield of 77.6%.

[0083] Comparative Example 3

[0084] A method for preparing fluoroethylene carbonate is described in Example 2, the difference being that: instead of using a novel solid base catalyst, tetramethylammonium bromide is used, resulting in fluoroethylene carbonate with a purity of 91.83% and a yield of 87.4%.

[0085] The present invention has been described in detail above to explain some of its features. Its purpose is to enable those skilled in the art to understand and implement the content of the present invention. However, it should not be construed as limiting the scope of protection of the present invention. Moreover, the present invention is not limited to the above-described embodiments. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing fluoroethylene carbonate, comprising the following steps: Potassium fluoride, a novel solid base catalyst, and an organic solvent were mixed evenly, and then chloroethylene carbonate was added to carry out a fluorination reaction. After the reaction was completed, the resulting reaction solution was filtered and distilled to obtain a crude product. The crude product was then subjected to distillation and crystallization to obtain chloroethylene carbonate. The novel solid base catalyst is composed of a magnetic nano Fe3O4 support coated with magnesium-aluminum composite oxide and a bimetallic fluoride, wherein the bimetal in the bimetallic fluoride is a combination of Rb and Co.

2. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The novel solid base catalyst was prepared according to the following method: (1) Preparation of magnetic nano Fe3O4 support Under stirring conditions, NaOH solution was added dropwise to a mixed solution of FeCl3·6H2O and FeCl2·4H2O to adjust the pH of the system to 10.5~11. After standing, the system was heated to 80℃ for aging, followed by sedimentation. The precipitate was then washed and dried to obtain magnetic nano Fe3O4 carrier. (2) Preparation of magnesium-aluminum composite oxides Prepare a mixed solution I of magnesium nitrate and aluminum nitrate, and a mixed solution II of sodium hydroxide and sodium carbonate. Under stirring, add mixed solution I and mixed solution II dropwise to a three-necked flask at a volume ratio of 1:1, with a dropping rate of 50 mL / h. After the addition is complete, heat to 70 °C for crystallization for 1 h. Then, filter, wash, dry, and calcine to obtain magnesium-aluminum composite oxide. (3) Preparation of magnetic nano Fe3O4 carriers coated with magnesium-aluminum composite oxide The magnetic nano Fe3O4 carrier obtained in step (1) and the magnesium-aluminum composite oxide obtained in step (2) were dispersed in deionized water at a mass ratio of 2:1 to obtain a mixed solution; CO2 was introduced into the mixed solution at 85°C to adjust the pH value of the system to 7, and the solution was aged at 85°C for 1 hour. After filtration, washing, separation, drying and calcination, the magnetic nano Fe3O4 carrier coated with magnesium-aluminum composite oxide was obtained. (4) Preparation of bimetallic fluorides Rubidium nitrate and cobalt nitrate were added to water at a molar ratio of Rb to Co of 2:1 to obtain a mixed solution. The mixed solution was then subjected to a hydrothermal reaction at 120–180 °C for 4–6 h. After the reaction was completed, the mixture was cooled and centrifuged. The resulting solid was then dried at 80–90 °C for 2–3 h to obtain a bimetallic compound. The resulting bimetallic compound was dissolved in an aqueous solution of hydrofluoric acid and stirred at 150–180 °C for 4–5 h. After filtration and washing, the resulting solid was dried at 250–280 °C for 5–6 h to obtain a bimetallic fluoride. (5) Preparation of novel solid base catalysts Weigh the magnetic nano Fe3O4 support coated with magnesium-aluminum composite oxide obtained in step (3), and then add water droplets to the support until the support absorbs water just to saturate, and record the volume of water used; disperse the bimetallic fluoride obtained in step (4) in water, prepare an impregnation solution of equal volume, and then add the impregnation solution droplets to the support so that the bimetallic fluoride is uniformly loaded onto the support; after standing at room temperature, dry and calcinate to obtain a novel solid base catalyst.

3. The method for preparing fluoroethylene carbonate according to claim 2, characterized in that, The molar ratio of FeCl3·6H2O and FeCl2·4H2O in the mixed solution in step (1) is 2:1; the concentration of FeCl3·6H2O in the mixed solution is 0.012~0.015 g / mL; The concentration of the NaOH solution mentioned in step (1) is 0.3~0.5 mol / L; The settling time in step (1) is 10-15 min; the aging time is 1-2 h; the sedimentation is carried out using neodymium iron boron permanent magnets; the washing is carried out by repeatedly washing the precipitate with deionized water and anhydrous ethanol until the filtrate is neutral; the drying is carried out at 70-80℃ for 5-6 h.

4. The method for preparing fluoroethylene carbonate according to claim 2, characterized in that, In step (2), the molar ratio of magnesium nitrate to aluminum nitrate in mixed solution I is 3:1; the concentration of magnesium nitrate in mixed solution I is 0.01~0.02 g / mL; the molar ratio of sodium hydroxide to sodium carbonate in mixed solution II is 7:3; the concentration of sodium hydroxide in mixed solution II is 0.05~0.08 g / mL. The washing in step (2) involves washing the filter cake with carbon dioxide-free water until the filtrate is neutral; the drying involves drying at 90~100℃ for 20~30h; and the calcination involves calcining at 400~800℃ for 5~6h.

5. The method for preparing fluoroethylene carbonate according to claim 2, characterized in that, The concentration of the magnetic nano Fe3O4 support in the mixed solution in step (3) is 0.01~0.015 g / mL; the washing involves washing the filter cake with water until the filtrate is neutral; the separation involves magnetic separation using a neodymium iron boron permanent magnet; the drying involves drying at 80~90℃ for 4~6 h; and the calcination involves calcining at 500~600℃ for 5~7 h. The concentration of rubidium nitrate in the mixed solution described in step (4) is 0.001~0.003 g / mL; In step (4), the volume ratio of hydrofluoric acid to water in the hydrofluoric acid aqueous solution is 1:6; the mass ratio of the bimetallic compound to the volume of the hydrofluoric acid aqueous solution is 0.03~0.06g:1mL; and the washing is performed by washing with water 3~5 times.

6. The method for preparing fluoroethylene carbonate according to claim 2, characterized in that, In step (5), the mass ratio of the bimetallic fluoride to the magnesium-aluminum composite oxide-coated magnetic nano Fe3O4 carrier is 1:7~10; the standing time is 8~10h; the drying is at 100~120℃ for 8~10h; and the calcination is at 500~600℃ for 3~5h.

7. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The mass of the novel solid base catalyst is 0.2-3% of the mass of chloroethylene carbonate.

8. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The mass of the novel solid base catalyst is 0.5 to 2.5% of the mass of chloroethylene carbonate.

9. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The mass of the novel solid base catalyst is 1 to 2% of the mass of chloroethylene carbonate.

10. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The organic solvent is dimethyl carbonate, and the mass ratio of the organic solvent to ethylene chlorinated carbonate is 1.5~5:1; the molar ratio of ethylene chlorinated carbonate to potassium fluoride is 1:1~2; the ethylene chlorinated carbonate is added dropwise to the system over a time of 40~70 min, and the temperature is controlled at 40~100℃ during the dropwise addition process.

11. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The fluorination reaction temperature is controlled at 70~110℃, and the fluorination reaction time is 1~3h.

12. The method for preparing fluoroethylene carbonate according to claim 1, characterized in that, The distillation was carried out under conditions of 5-15 mmHg, and the fraction at 65-100℃ was collected to obtain crude fluoroethylene carbonate. The distillation is carried out by vacuum distillation of the crude product under conditions of 4~10 mmHg, and the fraction at 60~95℃ is collected. The crystallization step is as follows: the liquid obtained by distillation is crystallized at 0~5℃. After no crystals precipitate, it is filtered to obtain the fluoroethylene carbonate product.