A method for removing impurities from a bisfluorosulfimide

Abstract

This invention provides a method for removing impurities from bis(fluorosulfonyl)imide. The crude bis(fluorosulfonyl)imide after fluorination is first purified by one-step distillation. After reaching the impurity removal temperature, an impurity removal agent is added to carry out the impurity removal reaction. Finally, the product is filtered through a filter membrane to remove impurities such as fluorosulfonic acid and sulfur- or oxygen-containing acid groups, thereby obtaining high-purity bis(fluorosulfonyl)imide. This impurity removal method does not introduce foreign ions and has a significant impurity removal effect.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, and specifically relates to a method for removing impurities from bis(fluorosulfonyl)imide. Background Technology

[0002] Electricity is currently the mainstay of renewable resources. The replacement of gasoline-powered vehicles by electric cars is an inevitable trend, and the increasing maturity of lithium battery technology has further fueled the popularity of electric vehicles. Battery demand is surging, especially for lithium batteries, where supply cannot meet demand. The performance of a battery depends not only on its design and electrodes, but also on the performance of the electrolyte. Research on battery electrolytes should not be merely a product of market forces, nor should it simply stop at meeting demand; therefore, electrolyte research has a long and arduous road ahead. Lithium bis(fluorosulfonyl)imide, as a new electrolyte additive, is increasingly recognized by the market and is widely used in ionic liquid preparation and catalysts, with market demand growing daily.

[0003] Patent CN115159479A discloses a method for preparing lithium bis(fluorosulfonyl)imide, which involves a method for purifying bis(fluorosulfonyl)imide. Specifically, it involves adsorbing bis(fluorosulfonyl)imide onto a self-made adsorption resin to achieve purification. This method requires a large amount of adsorption resin, and there is no method for resin regeneration, which greatly increases production costs. Secondly, the resin preparation process introduces foreign ions such as zinc, copper, and amino groups to enhance the adsorption effect. In a strongly acidic environment, residual ions are inevitable. If not properly controlled, this could potentially lead to the final product failing to meet quality standards.

[0004] Therefore, in this field, there is a desire to develop an efficient, environmentally friendly, and low-cost method for removing impurities to address the problem of excessive acid ions in the preparation of lithium bis(fluorosulfonyl)imide by the thionyl chloride method. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the present invention aims to provide a method for removing impurities from bis(fluorosulfonyl)imide. This method involves purifying the crude bis(fluorosulfonyl)imide product after fluorination by distillation, and then adding an impurity removal agent (such as lithium acetylene or lithium carbide) after reaching the impurity removal temperature. This removes fluorosulfonic acid, sulfur-containing and oxygen-containing acidic group impurities. This method does not introduce foreign ions and has a significant impurity removal effect.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for removing impurities from bis(fluorosulfonyl)imide, the method comprising: purifying the crude bis(fluorosulfonyl)imide after fluorination reaction by first performing a one-step distillation, then adjusting to the impurity removal temperature, adding an impurity removal agent to perform the impurity removal reaction, and finally filtering through a filter membrane to obtain high-purity bis(fluorosulfonyl)imide.

[0008] In this invention, the fluorination reaction is a reaction between dichlorosulfonylimide, hydrogen fluoride and an acid catalyst. The reaction temperature is a conventional reaction time, such as 90-110°C. The acid catalyst is a conventional fluorination catalyst, such as concentrated sulfuric acid and / or fuming nitric acid. The crude dichlorosulfonylimide obtained by the fluorination reaction has a purity of 40-95 wt%, preferably 60-95 wt%.

[0009] Furthermore, the distillation temperature is 100-150℃, the pressure is 0.5-50hpa, and the reflux ratio is 2-10:1; preferably, the distillation temperature is 110-130℃, the pressure is 1-10hpa, and the reflux ratio is 3-5:1.

[0010] Furthermore, the purity of the difluorosulfonamide after distillation and purification is ≥95wt%, and the impurities are mainly fluorosulfonic acid and other impurity acids, of which the content of fluorosulfonic acid is 0.01-5wt%, and other impurity acids are a very small amount of sulfur-containing and oxygen-containing acid groups that were not completely removed during distillation.

[0011] In this invention, the impurity removal temperature is -20 to 120°C, preferably 20 to 50°C;

[0012] In this invention, the impurity remover is one or more of lithium acetylene, lithium tetracarbide, lithium tricarbide, and other carbide metal compounds; preferably lithium acetylene or lithium tetracarbide; lithium acetylene and lithium tetracarbide and other lithium carbon compounds undergo a dynamic change process in the solvent. For example, lithium tetracarbide will continuously convert lithium ions to higher valence states due to changes in external temperature and other conditions.

[0013] Furthermore, the amount of impurity remover added is 50%-200% of the mass of the impurity acid, preferably 70%-110%; the impurity removal reaction time is 5-120 min, preferably 20-60 min; and the impurity removal pressure is 0.1-2 MPaG, preferably 0.5-1 MPaG.

[0014] Furthermore, during the impurity removal reaction, a purification solvent can be added, and the impurities can be removed subsequently by evaporation.

[0015] Furthermore, the impurity removal solvent is a carbonate such as DEC, EMC, or DMC, or a chloroalkanes such as dichloromethane or dichloroethane; the amount of the impurity removal solvent added is 10%-100% of the mass of the difluorosulfonylimide after distillation and purification, preferably 40%-60%. The evaporation is carried out according to the boiling point of the solvent, and the product is considered qualified when the residual solvent is less than 100 ppm.

[0016] In this invention, the filter membrane is made of tetrafluoroethylene (PTFE), and the pore size of the membrane is 100-200 nm, preferably 120-180 nm.

[0017] In this invention, an impurity remover can remove acidic group impurities such as fluorosulfonic acid by precipitating methane and metal salts, thereby achieving the purpose of removing impurity acids.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] In the preparation of lithium bisfluorosulfonylimide using the thionyl chloride method, although the reaction yield and selectivity of the intermediate bisfluorosulfonylimide with the fluorinating reagent are relatively ideal, the impurity content is high, mainly consisting of fluorosulfonic acid, aminosulfonic acid, hydrogen chloride, and sulfuric acid. While most impurities can be removed by subsequent distillation, some impurities with boiling points close to the product are difficult to remove. For example, fluorosulfonic acid and other impurity acids are extremely difficult to separate from the product and will remain in the product, significantly impacting the final product quality and electrolyte performance. This invention, by adding a purification agent, effectively removes impurity acids, separating them from the bisfluorosulfonylimide in the form of gas and precipitate, without introducing impurity ions, thus fundamentally improving product quality. Detailed Implementation

[0020] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0021] Unless otherwise specified, the main raw materials used in the embodiments of this invention are all commercially available raw materials.

[0022] Unless otherwise specified, the experimental procedures involved in the following embodiments or comparative examples are conventional experimental methods in the art.

[0023] Analytical methods: NMR instrument: Bruker AVANCE III 400M configuration: ULTRASHIELD 400 magnet / B-ACS 60-position autosampler / Topstin 3.0 software / 5mm Dual (13C, 1H) dual-core probe / 5mm BBO probe.

[0024] Example 1

[0025] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 90wt%) was purified by distillation at 120℃, 5hpa, and a reflux ratio of 3:1. After purification, the purity of difluorosulfonylimide was 98wt%, fluorosulfonic acid was 1.3wt%, and other impurity acids were 0.7wt%. 100g of the purified difluorosulfonylimide was taken, 50g of dichloroethane was added, the temperature was raised to 30℃, and then 1.6g of lithium carbide was added. The pressure was increased to 0.8MpaG with nitrogen, and the reaction was carried out for 30min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a tetrafluoroethylene membrane (pore size: 150nm) to remove impurities. The solvent was then evaporated to meet the standard (less than 100ppm). Sampling and testing showed that fluorosulfonic acid was undetectable, and other impurity acids were 10ppm.

[0026] Example 2

[0027] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 40wt%) was purified by distillation at 150℃, 50hpa, and a reflux ratio of 10:1. The purity of the purified difluorosulfonylimide was 95.4wt%, fluorosulfonic acid was 1.8wt%, and other impurity acids were 2.8wt%. 100g of the purified difluorosulfonylimide was taken, 40g of dichloroethane was added, the temperature was raised to 120℃, and then 2.3g of lithium acetylene was added. The pressure was increased to 2.0MPa with nitrogen, and the reaction was carried out for 120min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a tetrafluoroethylene membrane (pore size: 200nm) to remove impurities. The solvent was then evaporated to remove less than 100ppm, and a sample was taken. Fluorosulfonic acid was undetectable, and other impurity acids were 15ppm.

[0028] Example 3

[0029] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 60wt%) was purified by distillation at 110℃, 20hpa, and a reflux ratio of 5:1. The purity of the purified difluorosulfonylimide was 96.8wt%, fluorosulfonic acid was 2.3wt%, and other impurity acids were 0.9wt%. 100g of the purified difluorosulfonylimide was taken, 60g of DEC was added, the temperature was lowered to -20℃, and then 6.4g of trilithium carbide was added. The mixture was pressurized with nitrogen to 1.0MpaG and reacted for 15min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a PTFE membrane (pore size: 100nm) to remove impurities. The solvent was then evaporated to meet the standard (less than 100ppm). Sampling and testing showed that fluorosulfonic acid was undetectable, and other impurity acids were 12ppm.

[0030] Example 4

[0031] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 95wt%) was purified by distillation at 100℃, 40hpa, and a reflux ratio of 4:1. The purity of the purified difluorosulfonylimide was 99wt%, fluorosulfonic acid was 0.5wt%, and other impurity acids were 0.5wt%. 100g of the purified difluorosulfonylimide was taken and 100g of DMC was added. The temperature was raised to 50℃, and then 1.80g of lithium acetylene was added. The pressure was increased to 0.1MPaG with nitrogen and the reaction was carried out for 60min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a PTFE membrane (pore size: 120nm) to remove impurities. The solvent was then evaporated to meet the standard (less than 100ppm). The sample was tested and no fluorosulfonic acid was detected. The other impurity acid content was 20ppm.

[0032] Example 5

[0033] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 80wt%) was purified by distillation at 100℃, 0.5hpa, and a reflux ratio of 3:1. The purity of the purified difluorosulfonylimide was 95.6wt%, fluorosulfonic acid was 3.1wt%, and other impurity acids were 1.3wt%. 100g of the purified difluorosulfonylimide was taken, 10g of EMC was added, the temperature was raised to 20℃, and then 2.2g of lithium carbide was added. The nitrogen pressure was increased to 0.5MpaG, and the reaction was carried out for 20min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a PTFE membrane (pore size: 180nm) to remove impurities. The solvent was then evaporated to meet the standard (less than 100ppm). Sampling and testing showed that fluorosulfonic acid was undetectable, and other impurity acids were 19ppm.

[0034] Example 6

[0035] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 91wt%) was purified by distillation at 130℃, 10hpa, and a reflux ratio of 7:1. The purified difluorosulfonylimide had a purity of 98.5wt%, fluorosulfonic acid of 1.0wt%, and other impurity acids of 0.5wt%. 100g of the purified difluorosulfonylimide was taken, 30g of dichloromethane was added, the temperature was raised to 100℃, and then 1.65g of lithium acetylene was added. The mixture was pressurized with nitrogen to 1.5MPaG and reacted for 90min with thorough stirring. After the reaction was completed, the reaction solution was filtered through a PTFE membrane (pore size: 110nm) to remove impurities. The solvent was then evaporated to meet the standard (less than 100ppm). Samples were taken for testing: fluorosulfonic acid was undetectable, and other impurity acids were 14ppm.

[0036] Example 7

[0037] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 90wt%) was purified by distillation at 120℃, 5hpa, and a reflux ratio of 3:1. The purified difluorosulfonylimide had a purity of 98wt%, fluorosulfonic acid of 1.3wt%, and other impurity acids of 0.7wt%. 100g of the purified difluorosulfonylimide was heated to 30℃, and 1.60g of lithium carbide was added. The mixture was pressurized with nitrogen to 0.8MPaG and reacted for 30min with thorough stirring. After the reaction, the reaction solution was filtered through a tetrafluoroethylene membrane (pore size: 150nm). Samples were taken for testing: fluorosulfonic acid was undetectable, and other impurity acids were present at 23ppm.

[0038] Comparative Example 1

[0039] Take 100g of the purified difluorosulfonamide from Example 7, add 50g of DMC, heat to 30°C, then add 6.0g of lithium carbide, pressurize with nitrogen to 0.8 MPaG, and react for 30 minutes with thorough stirring. After the reaction is complete, filter the reaction solution after impurity removal using a tetrafluoroethylene membrane (pore size: 150nm), and then evaporate the solvent to meet the standard (less than 100ppm). Take a sample for testing: no fluorosulfonic acid was detected, and other impurity acids were 12ppm.

[0040] Comparative Example 2

[0041] 500g of crude difluorosulfonylimide reaction solution (difluorosulfonylimide: 90wt%) was purified by distillation at 130℃, 10hpa, and a reflux ratio of 7:1. The purity of the purified difluorosulfonylimide was 98wt%, fluorosulfonic acid was 1.3wt%, and other impurity acids were 0.7wt%. 100g of the purified difluorosulfonylimide was taken, heated to 30℃, and 1.6g of sodium chloride was added. The mixture was stirred thoroughly for 30min, and then pressurized with nitrogen to 1.8MPaG. After the reaction was completed, the reaction solution was filtered through a tetrafluoroethylene membrane (pore size: 150nm). The sample was tested and found to contain fluorosulfonic acid of 172ppm, other impurity acids of 55ppm, and chloride ions of 380ppm.

[0042] Comparative Example 1 shows that when the impurity removal agent is used in excess, the impurity removal effect remains basically unchanged, but the corresponding impurity removal cost increases, which is economically unreasonable. Therefore, it is only necessary to keep the amount of impurity removal agent used within a certain range. Comparative Example 2 shows that the existing technology removes fluorosulfonic acid using sodium chloride, but the effect is not good, and chloride ions remain in the product, affecting product quality.

Claims

1. A method for removing impurities from difluorosulfonyl imide, characterized in that, The crude difluorosulfonyl imide after fluorination is first purified by one-step distillation. The impurities in the purified difluorosulfonyl imide are mainly impurity acids, including fluorosulfonic acid. The temperature is then adjusted to remove impurities, and an impurity removal agent is added to carry out the impurity removal reaction. Finally, the product is filtered through a filter membrane to obtain high-purity difluorosulfonyl imide. The impurity removal agent is one or more of lithium acetylene, lithium tetracarbide, and lithium tricarbide. An impurity removal solvent is added during the above impurity removal reaction. The impurity removal solvent is selected from DEC, EMC, DMC, dichloromethane, or dichloroethane.

2. The impurity removal method according to claim 1, characterized in that, The crude concentration of bis(fluorosulfonyl)imide is 40-95 wt%.

3. The impurity removal method according to claim 2, characterized in that, The crude difluorosulfonamide concentration is 60-95 wt%.

4. The method for removing impurities according to any one of claims 1-3, characterized in that, The distillation temperature is 100-150℃, the pressure is 0.5-50hPa, and the reflux ratio is 2-10:

1.

5. The impurity removal method according to claim 4, characterized in that, The distillation temperature is 110-130℃, the pressure is 1-10hPa, and the reflux ratio is 3-5:

1.

6. The impurity removal method according to claim 5, characterized in that, The purity of difluorosulfonamide after distillation is ≥95wt%.

7. The impurity removal method according to claim 1, characterized in that, The content of fluorosulfonic acid in the impurities is 0.01-5 wt%.

8. The impurity removal method according to claim 1, characterized in that, The impurity remover is lithium acetylene or lithium carbide.

9. The method for removing impurities according to claim 1 or 8, characterized in that, The amount of impurity remover added is 50%-200% of the mass of the impurity acid.

10. The impurity removal method according to claim 9, characterized in that, The amount of impurity remover added is 70%-110% of the mass of the impurity acid.

11. The impurity removal method according to claim 1, characterized in that, The amount of impurity removal solvent added is 10%-100% of the mass of the difluorosulfonyl imide after distillation purification.

12. The impurity removal method according to claim 11, characterized in that, The amount of impurity removal solvent added is 40%-60% of the mass of the difluorosulfonyl imide after distillation and purification.

13. The method for removing impurities according to any one of claims 1-3, characterized in that, The impurity removal temperature is -20~120℃, the impurity removal time is 5-120min, and the impurity removal pressure is 0.1-2MPaG.

14. The impurity removal method according to claim 13, characterized in that, The impurity removal temperature is 20-50℃, the impurity removal time is 20-60min, and the impurity removal pressure is 0.5-1MPaG.

15. The impurity removal method according to claim 1, characterized in that, The filter membrane is made of PTFE and has a pore size of 100-200 nm.

16. The impurity removal method according to claim 15, characterized in that, The membrane has a pore size of 120-180 nm.