A preparation method of fluoroethylene carbonate

Abstract

The present invention relates to a method for preparing fluoroethylene carbonate, belonging to the technical field of organic fluorine chemicals. The method for preparing fluoroethylene carbonate of the present invention comprises performing a mixed reaction using chloroethylene carbonate and a fluoride salt solution. After the fluoride salt is dissolved in an ionic liquid, its activity increases, and it can undergo a displacement reaction with the chloroethylene carbonate at room temperature to produce fluoroethylene carbonate and a chloride salt. The high-boiling-point solvent and the low-boiling-point product are then separated by distillation to obtain the fluoroethylene carbonate. The fluoroethylene carbonate prepared by the present invention has the advantages of high purity, high yield, and low cost. Furthermore, the ionic liquid can be recycled, further reducing costs.

Description

Technical Field

[0001] The invention relates to a preparation method of fluoroethylene carbonate, belonging to the technical field of organic fluorine chemical industry. Background Art

[0002] Fluoroethylene carbonate (FEC) is the main additive to lithium-ion battery electrolytes. It can form a tightly structured and high-performance SEI film on the electrode surface, preventing further decomposition of the electrolyte, effectively reducing the battery impedance, and improving the low-temperature resistance and cycle performance of lithium batteries.

[0003] At present, the preparation method of FEC mainly contains direct fluorination method and halogen exchange method. Direct fluorination method is generally with ethylene carbonate (EC) as raw material, and fluorinating agent adopts the mixed gas of fluorine gas and inert gas composition. Because fluorine gas activity is very high, the FEC obtained by this method contains difluoro products, causing separation and purification difficulties. Halogen exchange method generally selects chloroethylene carbonate (CEC) as raw material, under the effect of phase transfer catalyst, in organic solvent, with fluorinating agent generation chlorine fluorine exchange reaction and obtain FEC, also can be chloroethylene carbonate directly with hydrogen fluoride liquid reaction to obtain FEC. For example, Chinese patent literature CN105968083B, CN107033119B all adopt chloroethylene carbonate directly with hydrogen fluoride liquid reaction to prepare FEC. But the hydrogen fluoride used in this method has very strong corrosiveness, has high requirements on equipment, and is toxic, has large safety risks, and the purity of products obtained therefrom is not high, needs to be purified by distillation again, causes preparation cost to be higher.

[0004] Room-temperature ionic liquids (RTILs), also known as ionic liquids or ILs in English, refer to salts composed entirely of positive and negative ions that are liquid at or near room temperature. Cations in ionic liquids include imidazolium ions, pyridinium ions, quaternary ammonium ions, and quaternary phosphonium ions, while anions include halogen ions, tetrafluoroborate ions, and hexafluorophosphate ions. Compared to traditional organic solvents, ionic liquids have unique physicochemical properties, such as ultra-low volatility, a wide liquid temperature range, high thermochemical stability, and good solubility. They are considered green solvents and do not produce volatile organic compounds during chemical reactions, making them more environmentally friendly during use. For example, Chinese patent document CN101717391A discloses a method for preparing fluoroethylene carbonate, which comprises reacting a reaction system consisting of chloroethylene carbonate, fluoride and ionic liquid at room temperature to 100°C, then carrying out heat preservation reaction at 80 to 120°C, and finally filtering, distilling under reduced pressure and rectifying to obtain a product with a purity of 99.9%; wherein the fluoride is selected from sodium fluoride and potassium fluoride, and the ionic liquid is selected from imidazole type ionic liquid, pyrrolidine type ionic liquid and quaternary ammonium type ionic liquid. Chinese patent document CN103539772A discloses a method for preparing fluoroethylene carbonate, which comprises the following steps: (1) adding chloroethylene carbonate to a reactor, adding an organic solvent, a fluorination agent and an ether functionalized ionic liquid catalyst to react; (2) filtering, distilling the filtrate to obtain a crude fluoroethylene carbonate product, and further rectifying to obtain a high-purity fluoroethylene carbonate product that meets the application conditions of electronic devices, namely fluoroethylene carbonate.

[0005] However, the above two technical solutions for preparing fluoroethylene carbonate using ionic liquids have the problem of low purity of fluoroethylene carbonate. In order to obtain fluoroethylene carbonate with higher purity, further purification by distillation is required, resulting in high production costs. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing fluoroethylene carbonate, which can solve the problem of high cost when currently using ionic liquid to prepare fluoroethylene carbonate with high purity.

[0007] In order to achieve the above purpose, the technical solution adopted in the preparation method of fluoroethylene carbonate of the present invention is:

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

[0009] (1) adding ethylene chlorocarbonate to a fluoride salt solution, and mixing and reacting the mixture after the addition is complete; the solvent in the fluoride salt solution is mainly an ionic liquid; the boiling point of the solvent is higher than the boiling point of ethylene fluorocarbonate;

[0010] (2) After the mixed reaction is completed, the system after the mixed reaction is distilled to obtain fluoroethylene carbonate.

[0011] The method for preparing fluoroethylene carbonate of the present invention comprises performing a mixed reaction between chloroethylene carbonate and a fluoride salt solution. After the fluoride salt is dissolved in an ionic liquid, its activity increases, and it can undergo a displacement reaction with the chloroethylene carbonate at room temperature to produce fluoroethylene carbonate and a chloride salt. The high-boiling-point solvent and the low-boiling-point product are then separated by distillation to obtain the fluoroethylene carbonate. The fluoroethylene carbonate prepared by the present invention has the advantages of high purity, high yield, and low cost. In addition, the ionic liquid can be recycled, further reducing costs.

[0012] It can be understood that, in the present invention, the boiling point of the solvent is higher than the boiling point of fluoroethylene carbonate means that under the same conditions, the boiling point of the solvent is higher than the boiling point of fluoroethylene carbonate.

[0013] In order to ensure that ethylene chlorocarbonate can be quickly and evenly dispersed in the fluoride salt solution when added to the fluoride salt solution, thereby improving the selectivity and conversion rate of the reaction, ethylene chlorocarbonate is preferably added to the fluoride salt solution in a mixed state. For example, ethylene chlorocarbonate is added to the fluoride salt solution in a stirring state.

[0014] In order to prevent low-volatile substances in the solvent from entering the product fluoroethylene carbonate during distillation, resulting in reduced product purity, the boiling point of the solvent in the fluoride salt solution needs to be higher than the boiling point of fluoroethylene carbonate.

[0015] Preferably, the solvent in the fluoride salt solution is an ionic liquid. Compared to conventional methods, the present invention uses ionic liquids as reaction solvents, requiring less equipment, lowering investment costs and minimizing safety risks. Because ionic liquids are non-volatile, the distilled fluoroethylene carbonate product is free of impurities, allowing for direct production of a high-purity fluoroethylene carbonate product without the need for further distillation and purification, effectively reducing production costs.

[0016] In order to ensure that the fluoride salt can be completely dissolved and has an appropriate concentration, thereby ensuring a sufficient reaction rate, preferably, in the fluoride salt solution, the mass ratio of the fluoride salt to the ionic liquid is (2-20):100.

[0017] All fluoride salt-based fluorinating agents used in the prior art for preparing fluoroethylene carbonate are suitable for use in the present invention. To improve the reaction rate and selectivity, the fluoride salt is preferably an alkali metal fluoride salt. For example, the fluoride salt is selected from one or any combination of sodium fluoride, potassium fluoride, lithium fluoride, and rubidium fluoride.

[0018] In order to avoid side reactions and improve product yield and purity, preferably, the addition rate of the ethylene chlorocarbonate is 0.5 to 5 g / min. In order to further reduce the occurrence of side reactions and improve product yield and purity, preferably, the ethylene chlorocarbonate is added to the fluoride salt solution in a dropwise manner.

[0019] Preferably, the ratio of the amount of substance of the ethylene chlorocarbonate to the amount of substance of the fluorine element in the fluoride salt is less than 1:1. Preferably, the ratio of the amount of substance of the ethylene chlorocarbonate to the amount of substance of the fluorine element in the fluoride salt is (0.6-0.8):1. For example, the ratio of the amount of substance of the ethylene chlorocarbonate to the amount of substance of the fluorine element in the fluoride salt is (0.65-0.8):1. The amount of substance of the ethylene chlorocarbonate is less than the amount of substance of the fluorine element in the fluoride salt. The excess fluoride salt can ensure that the ethylene chlorocarbonate is fully fluorinated, thereby avoiding the presence of ethylene chlorocarbonate that is difficult to remove in the system after the mixed reaction, thereby reducing the subsequent purification cost and improving the purity and yield of the product.

[0020] In order to ensure that the reaction proceeds fully and to avoid the occurrence of side reactions, preferably, the mixing reaction time is 1 to 3 hours.

[0021] To ensure that the fluoride salt solution can be used at room temperature, the product fluoroethylene carbonate and the ionic liquid can be separated by distillation. Preferably, the boiling point of the ionic liquid is not less than 250° C. To ensure that the ionic liquid can adapt to low temperature environments, the melting point of the ionic liquid is preferably not greater than 0° C.

[0022] Preferably, the ionic liquid is an imidazolium ionic liquid. Further preferably, the cation in the ionic liquid is a 1-alkyl-3-alkylimidazolium cation; the anion in the ionic liquid is a halide ion, a tetrafluoroborate ion, or a perfluoroalkylsulfonate ion. For example, the 1-alkyl-3-alkylimidazolium cation is a 1-ethyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, or a 1-hexyl-3-methylimidazolium cation; and the perfluoroalkylsulfonate ion is a trifluoromethylsulfonate ion. When the anion in the ionic liquid is a halide ion, the ionic liquid is a 1-alkyl-3-alkylimidazolium halide salt; when the anion in the ionic liquid is a tetrafluoroborate ion, the ionic liquid is a 1-alkyl-3-alkylimidazolium tetrafluoroborate; and when the anion in the ionic liquid is a perfluoroalkylsulfonate ion, the ionic liquid is a 1-alkyl-3-alkylimidazolium perfluoroalkylsulfonate. Compared with other types of ionic liquids, the melting point and boiling point of imidazole ionic liquids can meet the above requirements, and at the same time have the advantage of good stability, which can improve the purity and yield of the product.

[0023] In order to prevent the impurities in the ionic liquid from adversely affecting the selectivity of the reaction, increasing the cost of impurity removal and affecting the purity of the product, the ionic liquid can be impurity-removed before use. For example, the ionic liquid can be subjected to reduced pressure distillation to remove volatile impurities and moisture in the ionic liquid to avoid the introduction of impurities into subsequent products.

[0024] In order to avoid excessively high temperatures during distillation, which may cause product decomposition or decomposition of the solvent in the system, thereby affecting product purity and yield, the distillation is preferably performed under reduced pressure, and the temperature used for the distillation is no higher than 150°C. Preferably, the vacuum degree of the distillation is -92 to -100 kPa, and the temperature is 100 to 150°C. For example, the vacuum degree of the distillation is -92 to -96 kPa, and the temperature is 120 to 150°C.

[0025] In the present invention, after the system after the mixed reaction is distilled, the remaining high-boiling-point substances are mainly ionic liquids and chloride salts generated by the reaction. In order to further reduce costs, the high-boiling-point substances can be removed and separated to obtain two products, chloride salts and ionic liquids. The obtained ionic liquid can be recycled. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0027] The ionic liquids used in the following examples and comparative examples were purified before use. The purification process involved distilling the ionic liquids under vacuum conditions of -95 kPa and 140° C. for more than 4 hours until no fraction was produced.

[0028] Example 1

[0029] The preparation method of fluoroethylene carbonate of the present embodiment specifically comprises the following steps:

[0030] (1) At room temperature, 40 g of sodium fluoride and 400 g of ionic liquid were added to a dry container and stirred until the sodium fluoride was completely dissolved to obtain a sodium fluoride solution; the ionic liquid used in this example was 1-hexyl-3-methylimidazolium chloride;

[0031] (2) At room temperature, 80 g of chloroethylene carbonate was added dropwise to a sodium fluoride solution at a rate of 0.5 g / min under stirring. After the addition was completed, the mixture was stirred and reacted for 2 h. After the reaction was completed, the system was transferred to a rotary evaporator for vacuum distillation to obtain 67 g of fluoroethylene carbonate. The remaining ionic liquid in the rotary evaporator can be recycled. In this embodiment, the vacuum degree used for the vacuum distillation was -92 kPa, the temperature was 150° C., and the vacuum distillation time was 3 h.

[0032] Example 2

[0033] The preparation method of fluoroethylene carbonate of the present embodiment specifically comprises the following steps:

[0034] (1) At room temperature, 80 g of potassium fluoride and 400 g of ionic liquid were added to a dry container and stirred until the potassium fluoride was completely dissolved to obtain a potassium fluoride solution; the ionic liquid used in this example was 1-butyl-3-methylimidazolium tetrafluoroborate;

[0035] (2) At room temperature, 120 g of chloroethylene carbonate was added dropwise to a potassium fluoride solution at a rate of 5 g / min under stirring. After the addition was completed, the mixture was stirred and reacted for 3 h. After the reaction was completed, the system was transferred to a rotary evaporator for vacuum distillation to obtain 101 g of fluoroethylene carbonate. The remaining ionic liquid in the rotary evaporator was recycled after impurity removal. In this embodiment, the vacuum degree used for the vacuum distillation was -96 kPa, the temperature was 120° C., and the vacuum distillation time was 3 h.

[0036] Example 3

[0037] The preparation method of fluoroethylene carbonate of the present embodiment specifically comprises the following steps:

[0038] (1) At room temperature, 8 g of lithium fluoride and 400 g of an ionic liquid were added to a dry container and stirred until the lithium fluoride was completely dissolved to obtain a lithium fluoride solution; the ionic liquid used in this example was 1-ethyl-3-methylimidazolium trifluoromethylsulfonate;

[0039] (2) At room temperature, 30 g of chloroethylene carbonate was added dropwise to the lithium fluoride solution at a rate of 2 g / min under stirring. After the addition was completed, the mixture was stirred and reacted for 1 h. After the reaction was completed, the system was transferred to a rotary evaporator for vacuum distillation to obtain 24 g of fluoroethylene carbonate. The remaining ionic liquid in the rotary evaporator was recycled after impurity removal. The vacuum degree used in the vacuum distillation in this embodiment was -96 kPa, the temperature was 130°C, and the vacuum distillation time was 2 h.

[0040] Comparative Example 1

[0041] The only difference between the preparation method of fluoroethylene carbonate in this comparative example and the preparation method of fluoroethylene carbonate in Example 1 is that in the preparation method of fluoroethylene carbonate in this comparative example, chloroethylene carbonate is not added dropwise, but is directly added to the sodium fluoride solution at one time. At the same time, the time for continuing the mixing reaction under stirring is adjusted in this comparative example. The time for continuing the mixing reaction under stirring in this comparative example is equal to the sum of the time for dropping chloroethylene carbonate and the time for continuing the mixing reaction under stirring in Example 1.

[0042] Comparative Example 2

[0043] The only difference between the preparation method of fluoroethylene carbonate in this comparative example and the preparation method of fluoroethylene carbonate in Example 2 is that in the preparation method of fluoroethylene carbonate in this comparative example, the mass of chloroethylene carbonate is adjusted and the molar ratio of chloroethylene carbonate to potassium fluoride is 1:1.

[0044] Comparative Example 3

[0045] The only difference between the preparation method of fluoroethylene carbonate in this comparative example and the preparation method of fluoroethylene carbonate in Example 1 is that the ionic liquid used in the preparation method of fluoroethylene carbonate in this comparative example is 1-butyl-3-methylimidazolium hexafluorophosphate.

[0046] Experimental example

[0047] In order to evaluate the quality difference between the fluoroethylene carbonates prepared in Examples 1-3 and Comparative Examples 1-3, the purity and yield of the fluoroethylene carbonates prepared in Examples 1-3 and Comparative Examples 1-3 are listed in Table 1. The yields in Table 1 are the yields of fluoroethylene carbonate calculated relative to chloroethylene carbonate, i.e., the product of the ratio of the amount of fluoroethylene carbonate prepared to the amount of chloroethylene carbonate added during the reaction and 100.

[0048] Table 1 Purity and yield of fluoroethylene carbonate prepared in Examples 1-3 and Comparative Examples 1-3

[0049]

[0050]

Claims

1. A method for preparing fluoroethylene carbonate, characterized in that: The following steps are involved: (1) Adding ethylene chlorocarbonate to a fluoride salt solution, and after the addition is completed, mixing and reacting; the solvent in the fluoride salt solution is an ionic liquid; the boiling point of the solvent is higher than the boiling point of ethylene fluorocarbonate; the addition rate of the ethylene chlorocarbonate is 0.5-5 g / min; in the fluoride salt solution, the mass ratio of the fluoride salt to the ionic liquid is (2-20):100; the ratio of the amount of the ethylene chlorocarbonate to the amount of the fluorine element in the fluoride salt is less than 1:1; the fluoride salt is an alkali metal fluoride salt; the ionic liquid is 1-hexyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium trifluoromethylsulfonate; (2) After the mixing reaction is completed, the system after the mixing reaction is distilled to obtain fluoroethylene carbonate.

2. The method for preparing fluoroethylene carbonate as claimed in claim 1, wherein The fluoride salt is selected from one or any combination of sodium fluoride, potassium fluoride, lithium fluoride and rubidium fluoride.

3. The method for preparing fluoroethylene carbonate as claimed in claim 1, wherein The boiling point of the ionic liquid is not less than 250°C.

4. The method for preparing fluoroethylene carbonate as claimed in claim 1, wherein The mixing reaction time is 1 to 3 hours.

5. The method for preparing fluoroethylene carbonate as claimed in claim 1, wherein The distillation is vacuum distillation, and the temperature used in the vacuum distillation is not higher than 150°C.

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