A method for preparing high purity perfluoroalkylsulfonimides

Abstract

This invention discloses a method for preparing high-purity perfluoroalkyl sulfonyl imide. The method involves reacting a perfluoroalkyl sulfonamide with perfluoroalkyl sulfonyl fluoride, followed by vacuum distillation to remove the solvent and some impurities, yielding a desolvated reaction solution. This solution is then subjected to preliminary extraction with water, and the organic phase is collected by separation to obtain a crude perfluoroalkyl sulfonyl imide triethylamine salt liquid. An organic solvent, triethylamine, water, and lithium hydroxide are then added to this solution for reaction-extraction. After separation, the organic phase is retained, and a second extraction is performed by adding an organic solvent and triethylamine to the aqueous phase. The two organic phases are combined, and the product obtained after vacuum distillation, acidification, and further vacuum distillation is the perfluoroalkyl sulfonyl imide product. The yield of the obtained perfluoroalkyl sulfonyl imide product can reach over 93%, and the purity can reach over 99.5%. This invention uses a reaction-extraction technique at room temperature to prepare perfluoroalkyl sulfonyl imide, which has simple process conditions, low separation cost, and high product purity.

Description

Technical Field

[0001] This invention relates to the fields of energy chemical industry and green chemical industry, and specifically to a method for preparing high-purity perfluoroalkyl sulfonyl imide. Background Technology

[0002] Perfluoroalkyl sulfonyl imide (HPFSI) is a strong organic acid that can be used as a catalyst in a variety of organic reactions. The structure of HPFSI is shown below, where R1 and R2 are perfluoroalkyl groups. When R1 = R2, HPFSI has a symmetrical structure (hereinafter, perfluoroalkyl groups are referred to as R...). f It means that R f It does not specifically refer to any particular perfluoroalkyl group.

[0003]

[0004] Based on the weak coordination characteristics of HPFSI anions with cations such as metal ions, the salts formed from them exhibit a variety of excellent properties. These salts not only possess high ion mobility and thermal stability, but also demonstrate outstanding antioxidant and anti-reduction capabilities. Benefiting from these comprehensive properties, these substances have clear application potential in multiple fields, primarily including: electrolyte components for high-performance batteries, participation in the synthesis of ionic liquids, and their role in chemical reactions such as Friedel-Crafts alkylation and esterification. Furthermore, they also show certain application value in precision industrial surface treatment and semiconductor chip manufacturing.

[0005] Existing synthetic routes for HPFSI typically employ perfluoroalkyl sulfonyl fluoride (R... f SO2F reacts with ammonia (NH3) to produce perfluoroalkyl sulfonamides (R). f SO2NH2), R f SO2NH2 reacts with another molecule of R in the presence of the acid-binding agent triethylamine (NEt3). f SO2F reacts in a solvent to form perfluoroalkylsulfonylimide triethylamine salt (HPFSI·NEt3). HPFSI·NEt3 is then acidified to yield HPFSI. The reaction mechanism is shown below. R f R1 and R2 represent perfluoroalkyl groups with different structures:

[0006]

[0007] The HPFSI·NEt3 synthesis reaction solution has a complex composition, containing unreacted NEt3 and intermediate product R. f SO2NH2, reaction product HPFSI·NEt3, reaction byproduct perfluoroalkyl sulfonic acid (R fThe product contains several components, including SO3H, triethylamine hydrofluoric acid (NEt3·HF). These components undergo various side reactions under acidic conditions, generating a large number of complex and difficult-to-separate impurities, which seriously affect the purity and quality of HPFSI products. Therefore, it is necessary to separate HPFSI·NEt3 before acidification to obtain high-purity HPFSI·NEt3 before acidification, in order to ensure the acquisition of high-purity HPFSI.

[0008] Existing separation processes for HPFSI·NEt3 and similar systems mainly employ conventional techniques such as distillation, crystallization, and adsorption. Patent CN117534042A discloses a method for removing impurities from difluorosulfonylimide, which involves purifying the crude difluorosulfonylimide after fluorination by distillation, followed by separation and purification with lithium acetylene. This method is energy-intensive, costly, and unsuitable for the separation and purification of complex systems. Patent CN119569001A discloses a solvent crystallization method, preparing difluorosulfonylimide by controlling seed crystal operations during crystallization. This process requires complete isolation from water and oxygen, resulting in harsh process conditions, low purification yield, and high energy consumption. Patent CN119683579A purifies difluorosulfonylimide by chemically adsorbing the impurity fluorosulfonic acid onto a resin containing nitrogen-containing aromatic ring groups, thus facilitating the separation of fluorosulfonic acid and difluorosulfonylimide. However, this method only targets one substance and is unsuitable for the separation and purification of complex systems, exhibiting low separation efficiency.

[0009] Therefore, given the difficulty in removing impurities after HPFSI・NEt3 acidification, there is an urgent need to develop a method that can efficiently remove impurities and prepare high-purity HPFSI. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing high-purity perfluoroalkyl sulfonyl imide. This method employs a reaction-extraction technique, utilizing the change in solubility of impurity components in the HPFSI·NEt3 synthesis reaction solution after salt formation. Lithium hydroxide (LiOH) and triethylamine (NEt3) are used to react the impurities into lithium salts, followed by extraction and separation to purify the target substance. This process is simple to operate, has low energy consumption, is suitable for complex systems, and yields high-purity HPFSI·NEt3 after separation. Finally, high-purity HPBFSI product can be obtained by acidifying and distilling the obtained HPFSI·NEt3.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A method for preparing high-purity perfluoroalkyl sulfonyl imide specifically includes the following steps:

[0013] (1) Add acetonitrile, perfluoroalkyl sulfonyl fluoride and ammonia to the reaction vessel and react for 1-6 h. After filtration, obtain an acetonitrile solution of perfluoroalkyl sulfonamide. Add the acetonitrile solution of perfluoroalkyl sulfonamide and triethylamine to the reaction vessel containing perfluoroalkyl sulfonyl fluoride using a horizontal flow pump and react for 2-8 h. Then remove the acetonitrile and triethylamine from the reaction solution by vacuum distillation to obtain a desolvated reaction solution.

[0014] (2) Extract the desolvation reaction solution obtained in step (1) with deionized water, remove the aqueous phase after separation and retain the organic phase to obtain crude liquid of perfluoroalkyl sulfonylimide triethylamine salt.

[0015] (3) Add organic solvent, triethylamine, deionized water and lithium hydroxide to the crude product solution obtained in step (2) to carry out reaction-extraction, and after separation, organic phase 1 and aqueous phase 1 are obtained;

[0016] (4) Add organic solvent and triethylamine to the aqueous phase 1 obtained in step (3) for a second extraction, and separate the liquid to obtain organic phase 2 and aqueous phase 2;

[0017] (5) After mixing the organic phase 1 obtained in step (3) and the organic phase 2 obtained in step (4), the mixture is subjected to vacuum distillation to remove the organic solvent, triethylamine and water, and a liquid of perfluoroalkyl sulfonylimide triethylamine salt is obtained.

[0018] (6) Add the perfluoroalkyl sulfonamide triethylamine salt liquid obtained in step (5) to a mixed acid composed of concentrated sulfuric acid and polyphosphoric acid for acidification treatment, and then distill under reduced pressure to obtain perfluoroalkyl sulfonamide.

[0019] Furthermore, in step (1), the number of carbon atoms of the perfluoroalkyl group in the perfluoroalkyl sulfonyl fluoride and the perfluoroalkyl sulfonamide is less than or equal to 8, and the number of carbon atoms in the two can be the same or different.

[0020] Furthermore, in step (2), the mass ratio of deionized water to the desolvation reaction solution is (1~5):1, and the extraction temperature is 10~40℃. o C, extraction time is 10~30 min.

[0021] Further, the organic solvent mentioned in steps (3) and (4) is one or more combinations of dichloromethane, dichloroethane, dichloropropane or trichloroethane.

[0022] Further, in step (3), the volume ratio of the organic solvent, deionized water, and crude product solution is (1~8):(0.8~6):1, and the reaction-extraction temperature is 5~50°C. o C, the reaction-extraction time is 10~30 min.

[0023] Furthermore, the molar ratio of the triethylamine in step (3) to the perfluoroalkyl sulfonyl imide triethylamine salt in the crude liquid obtained in step (2) is (1~8): 1.

[0024] Furthermore, the molar ratio of the total amount of perfluoroalkyl sulfonamide and perfluoroalkyl sulfonic acid in the lithium hydroxide in step (3) to the total amount of the crude liquid obtained in step (2) is (1~2):1.

[0025] Further, the volume ratio of the organic solvent to the aqueous phase 1 in step (4) is (1~4):1, and the molar ratio of triethylamine to the perfluoroalkyl sulfonyl imide triethylamine salt in the crude liquid obtained in step (2) is (1~8):1.

[0026] Furthermore, the temperature for the secondary extraction in step (4) is 5~50°C. o C, the second extraction time is 10~30 min.

[0027] Furthermore, the mass ratio of concentrated sulfuric acid to polyphosphoric acid in step (6) is (1~6): 1.

[0028] The reaction-separation mechanism proposed in this invention is as follows:

[0029] Utilizing NH3 and R in a reaction vessel f SO2F reacts in the solvent acetonitrile (MeCN) to prepare R f SO2NH2, after filtration, yields R. f A MeCN solution of SO2NH2; R f SO2NH2 in MeCN solution and NET3 were added using a horizontal flow pump to a solution containing R. f HPFSI·NEt3 was generated in the SO2F reactor. After the reaction, the solution was separated by vacuum distillation to obtain MeCN and unreacted NEt3. After vacuum distillation, the solution was extracted with water and separated to obtain a crude HPFSI·NEt3 solution. The obtained crude HPFSI·NEt3 was subjected to reaction-extraction, and LiOH solution was added to adjust the pH of the system. [R] in the system was removed. f SO2NH][HNEt3]、[R f Impurities such as SO3][HNEt3] and NET3·HF are converted into R, which has higher solubility in the aqueous phase. f SO2NHLi, R f Lithium salts such as SO3Li and LiF are extracted into the aqueous phase, while HPFSI·NEt3, which does not react with LiOH, remains in the organic phase (as shown in the appendix). Figure 2 As shown); an organic phase solution containing high-purity HPFSI·NEt3 was obtained through phase separation, and high-purity HPBFSI·NEt3 was obtained after rotary evaporation and solvent removal, and then high-purity HPFSI was obtained after acidification and distillation.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] This invention utilizes reaction-extraction technology to maximize the separation of impurities in the HPFSI production process. This reaction-extraction method is applicable to the synthesis and purification of various HPFSIs, achieving HPFSI yields of over 93%. The process is characterized by mild conditions, simple operation, and high economic efficiency, showing promising application prospects in HPFSI synthesis and separation. Attached Figure Description

[0032] Figure 1 This is a process flow diagram for the reaction-extraction purification of crude HPFSI·NEt3.

[0033] Figure 2 This is a schematic diagram of the reaction-extraction purification mechanism of crude HPFSI·NEt3. Detailed Implementation

[0034] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0035] Unless otherwise specified, the experimental methods used in this invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0036] The analysis methods in the following embodiments are as follows:

[0037] Quantitative analysis was performed using an ion chromatograph (IC-D150) from Qingdao Shenghan and a gas chromatograph (GC-2014) from Shimadzu. The yield and purity of HPFSI·NEt3 and HPFSI were calculated using the following formula:

[0038]

[0039]

[0040]

[0041]

[0042] Example 1

[0043] (1) Add 20 g MeCN to the reactor. After checking for leaks with nitrogen, add 25 g of perfluoroethyl sulfonyl fluoride (CF3CF2SO2F, CAS: 354-87-0) and 4.81 g (6.2 L) of ammonia (NH3) to the reactor using a gas cylinder. oThe reaction was carried out at C for 2 h to obtain a MeCN solution containing perfluoroethane sulfonamide (CF3CF2SO2NH2, CAS: 78491-70-0). The resulting ammonium fluoride (NH4F) was filtered to obtain 43.6 g of MeCN solution containing CF3CF2SO2NH2.

[0044] (2) Add 27.21 g of CF3CF2SO2F to the reactor and check for leaks. Then, pump 43.6 g of CF3CF2SO2NH2 in MeCN solution and 35.63 g of triethylamine (NEt3) into the reactor using a horizontal flow pump and heat to 80°C. o After reacting at C for 6 h, 104.32 g of a MeCN solution of bis(perfluoroethyl sulfonyl)imide triethylamine salt (HBPFSI·NEt3, where the CAS of bis(perfluoroethyl sulfonyl)imide is 152894-10-5) was obtained. Preliminary vacuum distillation was performed to remove acetonitrile and triethylamine from the reaction solution, yielding 64.24 g of the desolvated reaction solution. 80 g of deionized water was added to this solution for extraction at 25°C. oC, extraction time was 25 min, and the organic phase was separated to obtain 57.31 g of crude HBPFSI·NEt3 liquid. 340 g of CH2Cl2, 22 g of NEt3, 130 g of deionized water, and 1.41 g of LiOH were added to this liquid. The reaction-extraction was carried out at room temperature for 20 min. The volume ratio of CH2Cl2, deionized water, and organic phase (crude HBPFSI·NEt3 liquid) was 4:2:1. The molar amount of NEt3 added was 2.5 times the molar amount of HBPFSI·NEt3 in the crude product. The crude HBPFSI·NEt3 contained 12 g of [CF3CF2SO2NH][HNEt3] and 2.76 g of [CF3CF2SO2NH][HNEt3]. The amount of LiOH added was 1.2 times the total molar amount of [CF3CF2SO3][HNEt3] and [CF3CF2SO3][HNEt3] (the content of [CF3CF2SO2NH][HNEt3] and [CF3CF2SO3][HNEt3] should be calculated using ion chromatography with external standard method before adding LiOH). After separation, organic phase 1 (406.32 g) and aqueous phase 1 (144.41 g) were obtained. 220 g of CH2Cl2 and 15 g of NEt3 were added to the aqueous phase 1 obtained from the reaction-extraction, and extraction was continued for 20 min at room temperature. After separation, organic phase 2 and CH2Cl2 were obtained, with a volume ratio of 1.5:1 to the aqueous phase 2 obtained from the reaction-extraction. The molar amount of NEt3 added was 1.7 times the molar amount of HBPFSI·NEt3 in the crude product. The organic phases obtained from the two processes were combined, and the combined organic phase was subjected to vacuum distillation to remove CH2Cl2 and NEt3, yielding 44.74 g of HBPFSI·NEt3. An acidifying agent was prepared by mixing 9.2 g of polyphosphoric acid and 45 g of 98% concentrated sulfuric acid. The obtained HBPFSI·NEt3 was slowly added to the acidifying agent and stirred for 30 min. Afterward, vacuum distillation was performed to obtain 35.01 g of high-purity HBPFSI.

[0045] In this embodiment, the yield of HBPFSI obtained after acidification and distillation reaches 93.32%, and the purity of the obtained HBPFSI reaches 99.61%.

[0046] Example 2

[0047] The purification process in this embodiment differs from that in Example 1 in that the organic solvent used is dichloroethane. Specifically, 322.5 g of dichloroethane is added during the first reaction-extraction, and 241.9 g of dichloroethane is added to the aqueous phase obtained from the reaction-extraction for further extraction. The rest of the process is the same as in Example 1. Using dichloroethane as the solvent in this embodiment for reaction-extraction, the final yield of HBPFSI after acid distillation reaches 90.32%, and the purity of the obtained HBPFSI reaches 99.50%.

[0048] Example 3

[0049] The purification process in this embodiment differs from that in Example 1 in that the organic solvent used is trichloroethane; otherwise, it is the same as in Example 1. Specifically, 368.2 g of trichloroethane is added during the first reaction-extraction, and 276.1 g of trichloroethane is added to the aqueous phase obtained from the reaction-extraction for further extraction. Using trichloroethane as the solvent in this embodiment, the final HBPFSI yield reaches 89.30%, and the purity of the obtained HBPFSI reaches 99.37%.

[0050] Example 4

[0051] The purification process in this embodiment differs from that in Example 1 in that the volume ratio of CH2Cl2, deionized water, and organic phase added during the reaction-extraction is 3:2:1, and the mass of CH2Cl2 added during the reaction-extraction is 255 g. The rest of the process is the same as in Example 1. Using CH2Cl2 as a solvent in this embodiment for reaction-extraction, the yield of HBPFSI after acidification and distillation reaches 94.60%, and the purity of the obtained HBPFSI reaches 99.01%.

[0052] Example 5

[0053] The difference between the purification operation in this embodiment and that in Example 1 is that the molar ratio of the added LiOH to the total molar ratio of [CF3CF2SO2NH][HNEt3] plus [CF3CF2SO3][HNEt3] is 1.4:1, i.e., the mass of added LiOH is 1.65g. The rest is the same as in Example 1. In this embodiment, the HBPFSI yield after acidification and distillation using the reaction-extraction method reaches 93.22%, and the purity of the obtained HBPFSI reaches 99.31%.

[0054] Example 6

[0055] The purification operation in this embodiment differs from that in Example 1 in that the molar ratio of the added LiOH to the total molar ratio of [CF3CF2SO2NH][HNEt3] plus [CF3CF2SO3][HNEt3] is 0.9:1, i.e., 1.06 g of LiOH is added. The rest is the same as in Example 1. The yield of HBPFSI·NEt3 obtained by the reaction-extraction method in this embodiment is 99.24%, and the yield of HBPFSI obtained by acidification distillation after reaction-extraction reaches 91.22%, with a purity of 97.21%.

[0056] Example 7

[0057] The purification process in this embodiment differs from that in Example 1 in that the purchased trifluoromethanesulfonamide (CF3SO2NH2) is reacted with CF3CF2SO2F to generate trifluoromethanesulfonyl (perfluoroethylsulfonyl)imine triethylamine salt. The remaining conditions are the same as in Example 1. In this embodiment, the yield of trifluoromethanesulfonyl (perfluoroethylsulfonyl)imine obtained after acidification and distillation using the reaction-extraction method reaches 94.51%, and the purity of the obtained trifluoromethanesulfonyl (perfluoroethylsulfonyl)imine reaches 99.81%.

[0058] Example 8

[0059] The purification process in this embodiment differs from that in Example 1 in that trifluoromethanesulfonamide (CF3SO2NH2) reacts with perfluorobutylsulfonyl fluoride (CF3CF2CF2CF2SO2F) to generate perfluorobutylsulfonyl (trifluoromethanesulfonyl)imine triethylamine salt; the rest is the same as in Example 1. The perfluorobutylsulfonyl (trifluoromethanesulfonyl)imine obtained after acidification and distillation using the reaction-extraction method in this embodiment achieves a yield of 88.51% and a purity of 99.24%.

[0060] Comparative Example 1: Extraction Experiment

[0061] 58.83 g of crude HBPFSI·NEt3 (organic phase) was prepared using the same method as in Example 1. 340 g of CH2Cl2 and 130 g of deionized water were added to the organic phase for extraction, with a volume ratio of CH2Cl2:deionized water:organic phase of 4:2:1. After extraction for 30 min, the organic phase was separated. 220 g of CH2Cl2 was added to the aqueous phase obtained from the extraction, and extraction was continued for 20 min. The organic phase was then separated, and the two organic phases were combined. After removing CH2Cl2 by vacuum distillation, the organic phase was slowly added to an acidifying reagent consisting of 45 g of 98% concentrated sulfuric acid and 9.2 g of polyphosphoric acid. The acidification was carried out for 30 min, yielding the target substance HBPFSI. 24.88 g of HBPFSI was obtained.

[0062] The yield of HBPFSI obtained in this comparative example was 66.32%, and the purity of the product was 86.62%. The results indicate that extraction method cannot effectively purify and separate HBPFSI.

[0063] Comparative Example 2: Distillation Experiment

[0064] 57.16 g of crude HBPFSI·NEt3 (organic phase) was prepared using the same method as in Example 1. It was then added to an acidifying reagent consisting of 45 g of 98% concentrated sulfuric acid and 9.2 g of polyphosphoric acid and acidified for 30 min. The target substance obtained after acidification was HBPFSI. The acidified HBPFSI solution was purified by distillation at 0.3 kPa, and 70 g of the solution was collected. o C~110 o The fraction of C was subjected to qualitative and quantitative analysis of the distillate obtained at different distillation times. The final yield was 24.11 g of HBPFSI.

[0065] The yield of HBPFSI obtained in this comparative example was 64.25%, and the purity of the product was 92.32%. The results indicate that distillation is not an effective method for purifying and separating HBPFSI.

[0066] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity perfluoroalkyl sulfonyl imide, characterized in that: Specifically, the following steps are included: (1) Add acetonitrile, perfluoroalkyl sulfonyl fluoride and ammonia to the reaction vessel and react for 1-6 h. After filtration, obtain an acetonitrile solution of perfluoroalkyl sulfonamide. Add the acetonitrile solution of perfluoroalkyl sulfonamide and triethylamine to the reaction vessel containing perfluoroalkyl sulfonyl fluoride using a horizontal flow pump and react for 2-8 h. Then remove the acetonitrile and triethylamine from the reaction solution by vacuum distillation to obtain a desolvated reaction solution. (2) Extract the desolvation reaction solution obtained in step (1) with deionized water, remove the aqueous phase after separation and retain the organic phase to obtain crude liquid of perfluoroalkyl sulfonylimide triethylamine salt. (3) Add organic solvent, triethylamine, deionized water and lithium hydroxide to the crude product solution obtained in step (2) to carry out reaction-extraction, and after separation, organic phase 1 and aqueous phase 1 are obtained; (4) Add organic solvent and triethylamine to the aqueous phase 1 obtained in step (3) for a second extraction, and separate the liquid to obtain organic phase 2 and aqueous phase 2; (5) After mixing the organic phase 1 obtained in step (3) and the organic phase 2 obtained in step (4), the mixture is subjected to vacuum distillation to remove the organic solvent, triethylamine and water, and a liquid of perfluoroalkyl sulfonylimide triethylamine salt is obtained. (6) Add the perfluoroalkyl sulfonamide triethylamine salt liquid obtained in step (5) to a mixed acid composed of concentrated sulfuric acid and polyphosphoric acid for acidification treatment, and then distill under reduced pressure to obtain perfluoroalkyl sulfonamide.

2. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: In step (1), the number of carbon atoms of the perfluoroalkyl group in the perfluoroalkyl sulfonyl fluoride and the perfluoroalkyl sulfonamide is less than or equal to 8, and the number of carbon atoms in the two can be the same or different.

3. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: In step (2), the mass ratio of deionized water to desolvation reaction solution is (1~5):1, the extraction temperature is 10~40℃, and the extraction time is 10~30min.

4. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The organic solvent mentioned in steps (3) and (4) is one or more combinations of dichloromethane, dichloroethane, dichloropropane or trichloroethane.

5. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The volume ratio of organic solvent, deionized water and crude product solution in step (3) is (1~8): (0.8~6): 1, the reaction-extraction temperature is 5~50℃, and the reaction-extraction time is 10~30 min.

6. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The molar ratio of the triethylamine in step (3) to the perfluoroalkyl sulfonyl imide triethylamine salt in the crude liquid obtained in step (2) is (1~8):

1.

7. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The molar ratio of the total amount of perfluoroalkyl sulfonamide and perfluoroalkyl sulfonic acid in the lithium hydroxide in step (3) to the crude liquid obtained in step (2) is (1~2):

1.

8. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The volume ratio of the organic solvent to the aqueous phase 1 in step (4) is (1~4):1, and the molar ratio of triethylamine to the perfluoroalkyl sulfonyl imide triethylamine salt in the crude liquid obtained in step (2) is (1~8):

1.

9. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: In step (4), the temperature for the second extraction is 5~50℃ and the extraction time is 10~30 min.

10. The method for preparing high-purity perfluoroalkyl sulfonyl imide according to claim 1, characterized in that: The mass ratio of concentrated sulfuric acid to polyphosphoric acid in step (6) is (1~6): 1.

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