Method for purifying bis (fluorosulfonyl) imide

Abstract

The invention provides a bis (fluorosulfonyl) imide purification method which comprises the following steps: 1) mixing a bis (fluorosulfonyl) imide crude product with a solvent, cooling, adding high-purity bis (fluorosulfonyl) imide solid particles as seed crystals, and performing solvent crystallization operation to obtain crystal slurry containing bis (fluorosulfonyl) imide crystals; and 2) carrying out centrifugal separation on the crystal slurry obtained in the step 1) to obtain imidodisulfuryl fluoride crystals and a crystal filtrate, washing the imidodisulfuryl fluoride crystals in the crystal filtrate, adopting liquid high-purity imidodisulfuryl fluoride as a washing agent, and separating and removing a washing solution to obtain a pure imidodisulfuryl fluoride product. According to the recycling process, the production cost for producing the imidodisulfuryl fluoride is reduced, the energy consumption in the production process is also reduced, and meanwhile, a high-quality imidodisulfuryl fluoride product is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of chemical engineering, and in particular to a method for purifying a crude bisfluorosulfonyl imide product. Background Art

[0002] Bis(fluorosulfonyl)imide (HFSI) is a key raw material for an important class of battery electrolytes, mainly used to synthesize lithium bis(fluorosulfonyl)imide (LiFSI), sodium bis(fluorosulfonyl)imide (NaFSI) and a series of onium salts containing bis(fluorosulfonyl)imide anions that help improve battery performance. In the field of lithium batteries, LiFSI is usually used as an additive, added in small amounts to improve battery performance.

[0003] At present, the mainstream production process of bisfluorosulfonyl imide is to use aminosulfonic acid as a raw material, react with chlorosulfonic acid and thionyl chloride to obtain bischlorosulfonyl imide, and then use hydrogen fluoride to react with bischlorosulfonyl imide to obtain bisfluorosulfonyl imide. Due to the limitations of the synthesis process of bisfluorosulfonyl imide itself, the crude bisfluorosulfonyl imide to be purified contains a large amount of inherent impurities such as fluorosulfonic acid, sulfuric acid, hydrogen fluoride, hydrogen chloride, aminosulfonic acid, etc. Among them, aminosulfonic acid and hydrogen fluoride are raw material residues, sulfuric acid is an impurity that is inevitably contained in the raw material chlorosulfonic acid, and hydrogen chloride mainly comes from the by-product hydrogen chloride.

[0004] According to the quality standard of LiFSI "YS / T 1302-2019 Lithium Bis(Fluorosulfonyl)imide for Power Battery Electrolyte", the fluoride content shall not exceed 100ppm, the sulfate content shall not exceed 50ppm, and the chloride content shall not exceed 10ppm. The quality standard of lithium hexafluorophosphate as the main electrolyte "HG / T 4066-2015 Lithium Hexafluorophosphate" stipulates that the HF content shall not exceed 90ppm (corresponding to the fluoride index of LiFSI), the sulfate content shall not exceed 5ppm, and the chloride content shall not exceed 2ppm. It is not difficult to find that the quality requirements of the main electrolyte are significantly more stringent. Therefore, as the dosage ratio of LiFSI continues to rise, its quality has an increasing impact on battery stability, and therefore, its quality requirements are becoming more and more stringent. Due to the physical properties of LiFSI itself, it is difficult to purify LiFSI, the energy consumption is high, and the final product quality is not satisfactory. NaFSI also exists in a similar situation to LiFSI, so reducing impurities to an acceptable concentration in the HFSI stage is a better process choice.

[0005] In the existing process of purifying bis(fluorosulfonyl)imide, due to the active physical and chemical properties of bis(fluorosulfonyl)imide, the purity is generally improved by distillation or rectification without the participation of any solvent. The total impurity content can be reduced to a level below 500 ppm by distillation or rectification. However, it is extremely difficult to further reduce the impurity content, which requires a lot of equipment cost and energy consumption cost, and the resulting reduction in yield is also unacceptable.

[0006] In recent years, a series of other purification processes for bis(fluorosulfonyl)imide have emerged.

[0007] Chinese patent CN111634895A discloses a method for purifying bisfluorosulfonyl imide, wherein bisfluorosulfonyl imide is purified by a solvent crystallization process, and at least one anhydrous organic solvent is used for crystallization. In fact, most of the organic solvents listed in the invention are unstable after forming a solution with bisfluorosulfonyl imide. Among the solvents listed in the invention, only dichloromethane and dichloroethane can form a relatively stable solution with bisfluorosulfonyl imide. However, due to the lack of process design and operation precision, it is difficult to separate HFSI from the solvent well, resulting in trace residues of chlorine-containing compounds in HFSI, which is unacceptable for the quality of HFSI. At the same time, the technical indicators provided in the embodiments (secondary crystallization data: the purified HFSI product of the present disclosure may have the following impurities: F-<20ppm, Cl-<2ppm, SO42-<20ppm, and water <50ppm) are relatively high, which has an adverse effect on battery performance.

[0008] Chinese patent CN112340713A discloses a purification method similar to the method of CN111634895, which adopts a method of mixing a solvent with a crude bis(fluorosulfonyl)imide product and then cooling and crystallizing. The solvent used in this patent is limited to halogenated hydrocarbons such as dichloromethane, but no specific implementation method is provided, nor is the purity of the purified bis(fluorosulfonyl)imide and the data on the process yield. At the same time, this method also cannot solve the problem of excessive chlorine content in bis(fluorosulfonyl)imide.

[0009] Chinese patent CN 116924357 A provides a method for crystallizing bis(fluorosulfonyl)imide, which realizes stable control of the crystallization process by adding solid bis(fluorosulfonyl)imide as a seed. However, due to the high concentration of melt crystallization itself, it is difficult to control the crystallization process, which can easily cause explosive crystallization of bis(fluorosulfonyl)imide, affecting product quality. In addition, the crystallization operation steps are lengthy, which is a well-known relatively inefficient process in the industry, and also requires high equipment investment costs in the industrialization work. Summary of the invention

[0010] In order to solve the shortcomings of the prior art, the present invention provides a method for purifying bis(fluorosulfonyl)imide, which adopts a solvent crystallization method and controls operations such as seed crystallization during the crystallization process to prepare high-purity bis(fluorosulfonyl)imide with a purity of more than 99%. Under certain operating conditions, the impurities in the final product, except for hydrogen chloride and fluorosulfonic acid, can be reduced to below the detection limit (<1ppm), far exceeding the technical indicators that can be achieved by the prior art.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for purifying bis(fluorosulfonyl)imide, under the condition of isolating water and oxygen in the whole process, comprises the following steps:

[0013] 1) mixing a crude bisfluorosulfonyl imide product with a solvent, cooling the mixture, adding high-purity solid bisfluorosulfonyl imide particles as seed crystals, and performing a solvent crystallization operation to obtain a crystal slurry containing bisfluorosulfonyl imide crystals;

[0014] 2) The crystal slurry of step 1) is centrifuged to obtain bisfluorosulfonyl imide crystals and a crystal filtrate, and the bisfluorosulfonyl imide crystals are washed with liquid high-purity bisfluorosulfonyl imide as a washing agent. After separating and removing the washing liquid, a pure bisfluorosulfonyl imide product is obtained.

[0015] In one embodiment, the method for purifying bis(fluorosulfonyl)imide further comprises the following steps 3) and 4):

[0016] 3) combining the crystallization filtrate and the washing liquid in step 2), removing the solvent by a falling film evaporator, and obtaining a bisfluorosulfonyl imide solution enriched with impurities;

[0017] 4) The impurity-enriched bisfluorosulfonyl imide solution is distilled to remove light components and heavy components to obtain a purified bisfluorosulfonyl imide solution, and the purified bisfluorosulfonyl imide solution is returned to step 1) as a crude bisfluorosulfonyl imide raw material for cyclic treatment.

[0018] In one embodiment, the crude bisfluorosulfonyl imide product of step 1) has no special requirements for its purity and the types of impurities it may contain. Any bisfluorosulfonyl imide product containing any impurities and any concentration can be used as a crude raw material, and further purified by the method of the present invention. The experimental results show that the type and concentration of impurities have no significant effect on the product purity and yield of the purification method. In a preferred embodiment, the crude bisfluorosulfonyl imide product can also be the bisfluorosulfonyl imide solution purified in step 4), which is returned to step 1) as a crude bisfluorosulfonyl imide raw material for cyclic treatment. It can be directly returned to the equipment for cyclic use by setting a bypass, or it can be applied to the next batch operation after recovery, or it can be collected and stored for other purposes. The present invention has no special requirements for this.

[0019] The crude bisfluorosulfonyl imide of the present invention has no special requirements for its preparation source. For example, it can be a bisfluorosulfonyl imide product obtained by mainstream production process using aminosulfonic acid as raw material, or a bisfluorosulfonyl imide product obtained by other processes, a primary product directly separated from the reaction solution, or a refined product treated by separation methods such as distillation, rectification, and crystallization. However, due to the limitations of the existing bisfluorosulfonyl imide synthesis route and refining process, the purity of these products is usually lower than 92wt%, mostly in the range of 90-92wt%, and the rest is impurities; wherein the impurities may be one or more of hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, macromolecular polymers, chlorine-containing alkanes, fluorine-containing alkanes, etc.;

[0020] The pure bisfluorosulfonyl imide obtained by the purification method of the present invention is a high-purity bisfluorosulfonyl imide with a content of more than 99 wt%, wherein the impurities are mainly hydrogen chloride and fluorosulfonic acid; wherein, by further controlling the detailed parameters of the crystallization operation or repeating crystallization, recycling, etc., the total impurity content can be reduced to below 100 ppm, including but not limited to 100 ppm, 90 ppm, 80 ppm, 70 ppm, 60 ppm, 50 ppm, 40 ppm, 30 ppm, 20 ppm, 10 ppm, 5 ppm or less, etc., preferably reduced to below 1 ppm, the purity of the final product can be close to 100%, and except for hydrogen chloride and fluorosulfonic acid, other impurities can be reduced to below the detection limit (<1 ppm).

[0021] In one embodiment, the solvent in step 1) is selected from an inert solvent that can stably coexist with bis(fluorosulfonyl)imide at a temperature of ≥50° C., preferably one or more of dichloromethane, dichloroethane, toluene, chlorobenzene, etc., more preferably dichloroethane;

[0022] Preferably, the purity of the solvent is required to be ≥ 99.5%.

[0023] In one embodiment, in step 1), the mass ratio of the crude bisfluorosulfonyl imide to the solvent is 100:10-100, preferably 100:15-25; the amount of solvent added is related to the purity of the bisfluorosulfonyl imide, so that the crude bisfluorosulfonyl imide is dissolved in the solvent and exists in a solution state. Generally, the solution temperature is 20-50°C, preferably 20-25°C, at which temperature the crude bisfluorosulfonyl imide solution can be in a liquid state; specifically, the mass ratio of the crude bisfluorosulfonyl imide to the solvent includes but is not limited to 100:10, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100 or a range composed of any two thereof.

[0024] In one embodiment, the mixed solution of crude bis(fluorosulfonyl)imide and solvent in step 1) is cooled, and then high-purity solid particles of bis(fluorosulfonyl)imide are added as seed crystals;

[0025] The cooling is to cool the mixed solution in the crystallization kettle to the seed adding temperature at a certain cooling rate, and then keep the temperature for a certain period of time;

[0026] In a specific example, the cooling rate is required to be ≤0.1°C / min, preferably 0.05-0.1°C / min; in a specific example, the seed addition temperature is controlled to be 10-20°C, preferably 14-18°C; in a specific example, the insulation time is ≥1h, preferably 1-2h; specifically, the cooling rate includes but is not limited to 0.1°C / min, 0.09°C / min, 0.08°C / min, 0.07°C / min, 0.06°C / min, 0.05°C / min, 0.04°C / min, 0.03°C / min, 0.02°C / min, 0 .01℃ / min or any range therebetween, the seed addition temperature includes but is not limited to 10℃, 11℃, 12℃, 13℃, 14℃, 15℃, 16℃, 17℃, 18℃, 19℃, 20℃ or any range therebetween, the insulation time includes but is not limited to 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.3h, 2.5h, 2.8h, 3h or any range therebetween; in specific implementation, the cooling rate, seed addition temperature and insulation time are affected by the purity of bis(fluorosulfonyl)imide and can be determined in combination with actual conditions.

[0027] In one embodiment, the high-purity bis(fluorosulfonyl)imide solid particles used as seed crystals in step 1) are required to have a chemical purity of ≥99.99%; and / or

[0028] The high-purity bis(fluorosulfonyl)imide solid particles have a particle size in the range of 0.1-10 mm, preferably in the range of 0.1-5 mm. Specifically, the particles include but are not limited to 0.1 mm, 0.5 mm, 1 mm, 3 mm, 5 mm, 7 mm, 9 mm, 10 mm or a range between any two of them.

[0029] In one embodiment, the high-purity solid particles of bisfluorosulfonyl imide used as seeds in step 1) are added in an amount of 0.01-0.03wt% of the crude bisfluorosulfonyl imide, including but not limited to 0.01wt%, 0.012wt%, 0.015wt%, 0.018wt%, 0.02wt%, 0.022wt%, 0.025wt%, 0.028wt%, 0.03wt% or any range therebetween.

[0030] In one embodiment, the solvent crystallization operation in step 1) is to add high-purity bis(fluorosulfonyl)imide solid particles and then keep the temperature for a certain period of time to grow the crystals;

[0031] After the crystal growing is completed, the temperature is lowered to the terminal crystallization temperature at a certain cooling rate, and after being kept at the terminal crystallization temperature for a certain period of time, the crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals;

[0032] In a specific example, the crystal growing time is ≥1h, preferably 1-2h; in a specific example, the cooling rate is ≤0.01℃ / min, preferably 0.005-0.01℃ / min; in a specific example, the terminal crystallization temperature is -10-12℃, preferably 3-7℃; in a specific example, the holding time at the terminal crystallization temperature is ≥2h, preferably 2-4h; specifically, the crystal growing time includes but is not limited to 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.3h, 2.5h, 2.8h, 3h or a range between any two of them, and the cooling rate is but is not limited to 0.01℃ / min, 0.009℃ / min, 0.008℃ / min, 0.0 The terminal crystallization temperature includes but is not limited to -10°C, -8°C, -5°C, -3°C, -1°C, 0°C, 2°C, 5°C, 8°C, 10°C, 12°C or any range therebetween; the holding time of the terminal crystallization temperature includes but is not limited to 2h, 2.2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h, 4h, 4.5h or any range therebetween; in specific implementation, these parameters can be adjusted according to the purity of bisfluorosulfonimide.

[0033] In the present invention, the solvent crystallization operation in step 1) can be performed in an intermittent or continuous manner. In one embodiment, based on the above content, an example is given of performing the solvent crystallization operation in an intermittent manner, wherein a specific process is as follows:

[0034] (a) cooling the mixed solution of crude bis(fluorosulfonyl)imide and solvent in a crystallization kettle to a seed adding temperature at a certain cooling rate under an appropriate stirring speed, and keeping the temperature for a certain period of time;

[0035] (b) adding high-purity bis(fluorosulfonyl)imide solid particles to the mixed solution of step (a), and keeping the mixture warm for a certain period of time to perform a crystal growing operation;

[0036] (c) After the crystal growing in step (b) is completed, the temperature is lowered to the terminal crystallization temperature at a certain cooling rate, and after being kept at the terminal crystallization temperature for a certain period of time, the crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals.

[0037] In the foregoing, the relevant conditions for the above-mentioned solvent crystallization operation are defined, and the definitions of the various parameters in the intermittent mode related conditions are consistent therewith. For other operating and process conditions in the crystallization operation of the present invention, and the devices used therein, corresponding conventional selections in the art can be adopted, and there are no special restrictions on this. Technicians can optimize them according to actual needs based on the known processes in the prior art.

[0038] In one embodiment, based on the above content, an example is given of performing the solvent crystallization operation in a continuous manner, wherein a specific process is as follows: on the basis of completing the above intermittent crystallization operation, the crude bisfluorosulfonyl imide and the solvent are continuously fed into the crystallization kettle at a certain mass rate in a certain ratio, and at the same time, the crystal slurry containing the bisfluorosulfonyl imide crystals is continuously taken out at the same mass rate, and the material ratio and content in the crystallization kettle are kept stable during the operation. In specific implementation, the mass ratio of the crude bisfluorosulfonyl imide to the solvent during the solvent crystallization operation in a continuous manner under the same batch is the same as the mass ratio of the crude bisfluorosulfonyl imide to the solvent during the solvent crystallization operation in an intermittent manner.

[0039] In one embodiment, the operations in step 1) are all carried out under stirring, and the crystallization effect is ensured by controlling the appropriate rotation speed in the crystallization kettle, and the stirring speed is 150-200 rpm, including but not limited to 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm or a range between any two of them.

[0040] In one embodiment, the liquid high-purity bis(fluorosulfonyl)imide used for washing the bis(fluorosulfonyl)imide crystals in step 2) is required to have a chemical purity of ≥99.99%; and / or

[0041] The amount of the liquid high-purity bisfluorosulfonyl imide used in a single washing is not less than 1% of the mass of the bisfluorosulfonyl imide crystals, preferably 2-3%, including but not limited to 1%, 1.5%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 4% or any range between two thereof;

[0042] In a specific example, the number of times of washing the bis(fluorosulfonyl)imide crystals is ≥ 3 times, and the filtered washing liquid is applied to the crystallization filtrate, and the two are combined for subsequent treatment.

[0043] In step 2) of the present invention, the pure bis(fluorosulfonyl)imide obtained by washing with liquid high-purity bis(fluorosulfonyl)imide has a purity of 99 wt% or more; preferably, the purity is 99.99 wt% or more, the total impurity content is less than 100 ppm, mainly comprising hydrogen chloride and fluorosulfonic acid, and other impurities are all below the detection limit (<1 ppm).

[0044] In one embodiment, the centrifugal separation in step 2) is required to be carried out under the condition of isolating water and oxygen, and the centrifuge can be a closed centrifuge that can be operated in a closed manner and isolate air;

[0045] The whole process of the present invention is carried out under the above-mentioned water-oxygen isolation conditions, that is, it is required to be operated under air-isolated conditions, such as in an environment of inert protective gas such as nitrogen. In general, the conventional operation is to fully replace the entire equipment system with nitrogen before starting operation to ensure that the gas atmosphere in the system maintains a low water and oxygen content, for example, controlling the water content to be less than 50ppm and the oxygen content to be less than 50ppm.

[0046] In one embodiment, in step 3), during the process of removing the solvent by a falling film evaporator, the falling film evaporation has a temperature of 57-60°C, a pressure of 15-20 kPaA, and a time of 5-10 s; specifically, the temperature includes but is not limited to 57°C, 57.5°C, 58°C, 58.5°C, 59°C, 59.5°C, 60°C or a range composed of any two thereof, the pressure includes but is not limited to 15 kPaA, 15.5 kPaA, 16 kPaA, 16.5 kPaA, 17 kPaA, 17.5 kPaA, 18 kPaA, 18.5 kPaA, 19 kPaA, 19.5 kPaA, 20 kPaA or a range composed of any two thereof, and the time includes but is not limited to 5-10 s or a range composed of any two thereof.

[0047] In step 3) of the present invention, the solvent separated and removed by the falling film evaporator has a purity of ≥99.5wt%;

[0048] In the impurity-enriched bisfluorosulfonyl imide solution obtained by separation, the bisfluorosulfonyl imide content is 60-95wt%, the solvent content is less than 1wt%, and the rest is impurities.

[0049] In one embodiment, the impurity-enriched bis(fluorosulfonyl)imide solution in step 4) is distilled to remove light components and heavy components, wherein the distillation device and related operations are conventionally selected in the field, and preferably the impurities in the bis(fluorosulfonyl)imide are separated by continuous distillation, wherein the light component impurities are fluorosulfonic acid, hydrogen fluoride, hydrogen chloride, fluorine-containing alkanes, chlorine-containing alkanes, etc.; the heavy component impurities are sulfuric acid, aminosulfonic acid and macromolecular polymers, etc.;

[0050] In step 4) of the present invention, the purified bisfluorosulfonyl imide solution obtained by distillation separation has a purity of 90-99.9wt%, and the rest is impurities. The impurity-containing bisfluorosulfonyl imide solution is separated by continuous distillation to separate the light component impurities in the bisfluorosulfonyl imide into fluorosulfonic acid, hydrogen fluoride, hydrogen chloride, fluorine-containing alkanes, and chlorine-containing alkanes; the heavy component impurities are sulfuric acid, aminosulfonic acid and macromolecular polymers.

[0051] According to the different initial concentrations of the crude bisfluorosulfonyl imide raw material, the purification operation of the present invention can be repeated 1-2 times as needed, so that the chemical purity of the pure bisfluorosulfonyl imide can be ≥99.99%.

[0052] The above technical solution has the following technical effects:

[0053] The bisfluorosulfonyl imide purification process provided by the present invention realizes the preparation of bisfluorosulfonyl imide with a chemical purity of more than 99%, preferably ≥99.99%, from low-purity bisfluorosulfonyl imide rich in impurities based on solvent crystallization.

[0054] The purification method of the present invention provides a complete set of process flows including bis(fluorosulfonyl)imide solvent crystallization, solvent recovery, and impurity separation, which fills the technical gap in this field in the industry; the present invention provides a complete post-processing process flow, which not only improves the product yield, but also reduces the amount of high-risk fluorine-containing wastes, reduces product costs, improves the competitiveness of the technology, and also reduces the loss of bis(fluorosulfonyl)imide during the production process, so that except for hydrogen chloride and fluorosulfonic acid, no other impurities are detected in the final product, which far exceeds the technical indicators that can be achieved by the existing technology. DETAILED DESCRIPTION

[0055] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0056] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0057] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0058] In each embodiment and comparative example of the present invention, the sources of the main raw materials used are as follows:

[0059] Ethylene dichloride: purity ≥99.5%, purchased from Aladdin, product number D431341;

[0060] High-purity bis(fluorosulfonyl)imide solid particles: According to the crystallization method provided in the present application, without adding seed crystals and without washing with liquid high-purity bis(fluorosulfonyl)imide, purification is performed multiple times in a manner without taking the yield into account to obtain liquid high-purity bis(fluorosulfonyl)imide, which is then frozen to obtain solid particles;

[0061] Liquid high-purity bisfluorosulfonyl imide: According to the crystallization method provided in the present application, without washing with liquid high-purity bisfluorosulfonyl imide, purification is performed multiple times in a manner without taking into account the yield to obtain liquid high-purity bisfluorosulfonyl imide;

[0062] Crude bisfluorosulfonyl imide: Crude bisfluorosulfonyl imide was prepared according to the process for preparing bisfluorosulfonyl imide according to patent CN114873571B.

[0063] The main analytical methods used in the examples and comparative examples of the present invention are as follows:

[0064] Substance content test: Thermo Fisher ion chromatography HPIC was used to quantify the components by external standard method, and the chromatographic column was an anion analysis column.

[0065] Example 1 - Batch Crystallization Process Operation

[0066] Before starting the experimental operation, the entire equipment system was fully replaced with nitrogen to ensure that the gas atmosphere in the system maintained a low water and oxygen content (water content less than 50 ppm, oxygen content less than 50 ppm).

[0067] 1) Add 8.7 kg of crude bis(fluorosulfonyl)imide (purity of 90.06 wt%, the rest of which is impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and dichloroethane) and 1.3 kg of dichloroethane (adjust the temperature to 20° C. in advance) to a 20 L crystallization kettle, start stirring, and stir at a speed of 200 rpm to mix the materials evenly. Continue stirring during the subsequent crystallization process, and keep the stirring speed at 200 rpm.

[0068] Start intermittent solvent crystallization operation, the process flow is as follows:

[0069] (a) cooling the mixed solution in the crystallization kettle to a seeding temperature of 14°C at a cooling rate of 0.1°C / min and keeping the temperature for 1 hour;

[0070] (b) adding high-purity bis(fluorosulfonyl)imide solid particles (0.8 g, particle size range 0.1-5 mm, purity ≥ 99.995%) to the mixed solution of step (a) through a closed feeder, and keeping the mixture warm for 1 hour to perform a crystal growing operation;

[0071] (c) After the crystal growing in step (b) is completed, the temperature is lowered to the final crystallization temperature of 3°C at a cooling rate of 0.01°C / min, and the temperature is kept at the final crystallization temperature for 2 hours. The intermittent solvent crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals.

[0072] 2) The crystal slurry containing bisfluorosulfonyl imide crystals obtained in step 1) is intermittently centrifuged in a closed centrifuge to obtain bisfluorosulfonyl imide crystals and a crystal filtrate, and about 0.51 kg of liquid high-purity bisfluorosulfonyl imide (chemical purity ≥ 99.995%) at a temperature of 20° C. is used to wash the bisfluorosulfonyl imide crystals in the centrifuge three times to obtain 5.66 kg of pure bisfluorosulfonyl imide (primary crystal).

[0073] 3) combining the crystallization filtrate and the washing liquid in step 2) to a total of 4.85 kg, removing the solvent by a falling film evaporator, the falling film evaporation process temperature is 60° C., the pressure is 20 kPaA, and the residence time is 5 s, to obtain 2.53 kg of impurity-enriched bisfluorosulfonyl imide solution;

[0074] 4) The impurity-enriched bisfluorosulfonyl imide solution is distilled (distillation tower parameters: bottom operating temperature 120° C., operating pressure 1.5 kPaA, theoretical plate number 10, feed plate number 4) to remove light components and heavy components to obtain 1.78 kg of purified bisfluorosulfonyl imide solution (one distillation). The purified bisfluorosulfonyl imide solution can be returned to step 1) as a crude bisfluorosulfonyl imide raw material for further purification.

[0075] During the experiment, each component was sampled and analyzed, and the results are shown in Table 1 below.

[0076] Table 1

[0077]

[0078]

[0079] Example 2 - Batch Crystallization Process Operation

[0080] Before starting the experimental operation, the entire equipment system was fully replaced with nitrogen to ensure that the gas atmosphere in the system maintained a low water and oxygen content (water content less than 50 ppm, oxygen content less than 50 ppm).

[0081] 1) Add 8 kg of crude bis(fluorosulfonyl)imide (taken from the pure bis(fluorosulfonyl)imide crystallized once in Example 1, with a purity of 99.69 wt%, and the rest are impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and dichloroethane) and 2 kg of dichloroethane (adjust the temperature to 20° C. in advance) into a 20 L crystallization kettle, start stirring, and the stirring speed is 150 rpm to mix the materials evenly. Stirring is continuously turned on during the subsequent crystallization process, and the stirring speed is maintained at 150 rpm.

[0082] Start intermittent solvent crystallization operation, the process flow is as follows:

[0083] (a) cooling the mixed solution in the crystallization kettle to a seeding temperature of 18°C ​​at a cooling rate of 0.05°C / min and keeping the temperature for 2 hours;

[0084] (b) adding high-purity bis(fluorosulfonyl)imide solid particles (2.4 g, particle size range 0.1-5 mm, purity ≥ 99.995%) to the mixed solution of step (a) through a closed feeder, and keeping the mixture warm for 1 hour to perform a crystal growing operation;

[0085] (c) After the crystal growing in step (b) is completed, the temperature is lowered to the final crystallization temperature of 7°C at a cooling rate of 0.005°C / min, and the temperature is kept at the final crystallization temperature for 2 hours. The intermittent solvent crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals.

[0086] 2) The crystal slurry containing bisfluorosulfonyl imide crystals obtained in step 1) is intermittently centrifuged in a closed centrifuge to obtain bisfluorosulfonyl imide crystals and a crystal filtrate, and about 0.41 kg of liquid high-purity bisfluorosulfonyl imide (chemical purity ≥ 99.995%) at a temperature of 20° C. is used to wash the bisfluorosulfonyl imide crystals in the centrifuge three times to obtain 6.86 kg of pure bisfluorosulfonyl imide (secondary crystals).

[0087] 3) combining the crystallization filtrate and the washing liquid in step 2), removing the solvent by a falling film evaporator, wherein the falling film evaporation process has a temperature of 57° C., a pressure of 17.5 kPaA, and a residence time of 10 s, to obtain 0.73 kg of an impurity-enriched bis(fluorosulfonyl)imide solution;

[0088] 4) The impurity-enriched bisfluorosulfonyl imide solution is distilled (distillation tower parameters: bottom operating temperature 120° C., operating pressure 1.5 kPaA, theoretical plate number 10, feed plate number 4) to remove light components and heavy components to obtain 0.693 kg of purified bisfluorosulfonyl imide solution (secondary distillation). The purified bisfluorosulfonyl imide solution can be returned to step 1) as a crude bisfluorosulfonyl imide raw material for further purification.

[0089] During the experiment, each component was sampled and analyzed, and the results are shown in Table 2 below.

[0090] Table 2

[0091]

[0092] Example 3 - Continuous Crystallization Process Operation

[0093] Before starting the experimental operation, the entire equipment system was fully replaced with nitrogen to ensure that the gas atmosphere in the system maintained a low water and oxygen content (water content less than 50 ppm, oxygen content less than 50 ppm).

[0094] 1) Add 8.7 kg of crude bis(fluorosulfonyl)imide (purity of 90.06 wt%, the rest of which is impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and dichloroethane) and 1.3 kg of dichloroethane (adjust the temperature to 20° C. in advance) to a 20 L crystallization kettle, start stirring, and stir at a speed of 175 rpm to mix the materials evenly. Continue stirring during the subsequent crystallization process, and keep the stirring speed at 175 rpm.

[0095] Start the continuous solvent crystallization operation, the process flow is as follows:

[0096] (a) cooling the mixed solution in the crystallization kettle to a seeding temperature of 16°C at a cooling rate of 0.1°C / min and keeping the temperature for 1.5 hours;

[0097] (b) adding high-purity bis(fluorosulfonyl)imide solid particles (0.8 g, particle size range 0.1-5 mm, purity ≥ 99.995%) to the mixed solution of step (a) through a closed feeder, and keeping the mixture warm for 1 hour to perform a crystal growing operation;

[0098] (c) After the crystal growing in step (b) is completed, the temperature is lowered to the final crystallization temperature of 3°C at a cooling rate of 0.01°C / min, and the temperature is kept at the final crystallization temperature for 1.5 hours;

[0099] (d) continuously feeding the crude bis(fluorosulfonyl)imide product and ethylene dichloride into the crystallization kettle at a mass ratio of 6.67 / 1 and at a rate such that the crude bis(fluorosulfonyl)imide product stays in the crystallization kettle for 4 hours, and continuously extracting a slurry containing bis(fluorosulfonyl)imide crystals from the crystallization kettle at the same rate;

[0100] 2) The crystal slurry containing bisfluorosulfonyl imide crystals obtained in step 1) is subjected to intermittent centrifugal separation in a closed centrifuge to obtain bisfluorosulfonyl imide crystals and a crystal filtrate. A total of 10 kg of material is added as one batch. About 0.46 kg of liquid high-purity bisfluorosulfonyl imide (chemical purity ≥ 99.995%) at a temperature of 20° C. is used to wash the bisfluorosulfonyl imide crystals in the centrifuge three times to obtain 5.67 kg of pure bisfluorosulfonyl imide (primary crystal).

[0101] 3) combining the crystallization filtrate and the washing liquid obtained in step 2), and continuously separating dichloroethane and the impurity-enriched bis(fluorosulfonyl)imide solution by a falling film evaporator (operating temperature 60° C., operating pressure 20 kPaA, residence time 7.5 s), condensing and recovering the solvent dichloroethane at the gas phase outlet, and obtaining the impurity-enriched bis(fluorosulfonyl)imide solution at the liquid phase outlet;

[0102] 4) The impurity-enriched bisfluorosulfonyl imide solution is separated from the light components and heavy components of the bisfluorosulfonyl imide by continuous distillation (bottom operating temperature 120° C., operating pressure 1.5 kPaA, theoretical plate number 10, feed plate number 4) to obtain a purified bisfluorosulfonyl imide solution (primary distillation), and the purified bisfluorosulfonyl imide solution is returned to the aforementioned step (d) as a crude bisfluorosulfonyl imide for the crystallization step. It is calculated that the distillation yield of bisfluorosulfonyl imide is about 95% after stable operation for 24 hours.

[0103] The one-way loss rate of bis(fluorosulfonyl)imide was calculated to be 1.5% in the whole process.

[0104] The test results of sampling and analysis of materials in each step are shown in Table 3:

[0105] Table 3

[0106]

[0107]

[0108] Example 4 - Continuous Crystallization Process Operation

[0109] Before starting the experimental operation, the entire equipment system was fully replaced with nitrogen to ensure that the gas atmosphere in the system maintained a low water and oxygen content (water content less than 50 ppm, oxygen content less than 50 ppm).

[0110] 1) Add 10 kg of crude bis(fluorosulfonyl)imide (purity of 90.06 wt%, the rest of which is impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and dichloroethane) and 2 kg of dichloroethane (adjust the temperature to 20° C. in advance) into a 20 L crystallization kettle, start stirring, and stir at a speed of 175 rpm to mix the materials evenly. Continue stirring during the subsequent crystallization process, and keep the stirring speed at 175 rpm.

[0111] Start the solvent crystallization operation, the process flow is as follows:

[0112] (a) cooling the mixed solution in the crystallization kettle to a seeding temperature of 18°C ​​at a cooling rate of 0.75°C / min and keeping the temperature for 1.5 hours;

[0113] (b) adding high-purity bis(fluorosulfonyl)imide solid particles (1.6 g, particle size range 0.1-5 mm, purity ≥ 99.995%) to the mixed solution of step (a) through a closed feeder, and keeping the mixture warm for 1 hour to perform a crystal growing operation;

[0114] (c) After the crystal growing in step (b) is completed, the temperature is lowered to an end point crystallization temperature of 2.5°C at a cooling rate of 0.0075°C / min, and the temperature is maintained at the end point crystallization temperature for 1.5 h.

[0115] (d) continuously feeding the crude bis(fluorosulfonyl)imide product and ethylene dichloride into the crystallization kettle at a mass ratio of 5 / 1 and at a rate such that the crude bis(fluorosulfonyl)imide product stays in the crystallization kettle for 4 hours, and continuously extracting a slurry containing bis(fluorosulfonyl)imide crystals from the crystallization kettle at the same rate;

[0116] 2) The crystal slurry containing bisfluorosulfonyl imide crystals obtained in step 1) is subjected to intermittent centrifugal separation in a closed centrifuge to obtain bisfluorosulfonyl imide crystals and a crystal filtrate. A total of 12 kg of material is added as one batch, and about 0.64 kg of liquid high-purity bisfluorosulfonyl imide (chemical purity ≥ 99.995%) at a temperature of 20° C. is used to wash the bisfluorosulfonyl imide crystals in the centrifuge three times to obtain 8.56 kg of pure bisfluorosulfonyl imide (primary crystal).

[0117] 3) combining the crystallization filtrate and the washing liquid obtained in step 2), and continuously separating dichloroethane and the impurity-enriched bis(fluorosulfonyl)imide solution by a falling film evaporator (operating temperature 60° C., operating pressure 20 kPaA, residence time 7 s), condensing and recovering the solvent dichloroethane at the gas phase outlet, and obtaining the impurity-enriched bis(fluorosulfonyl)imide solution at the liquid phase outlet;

[0118] 4) The impurity-enriched bisfluorosulfonyl imide solution is separated from the light components and heavy components of the bisfluorosulfonyl imide by continuous distillation (bottom operating temperature 120° C., operating pressure 1.5 kPaA, theoretical plate number 10, feed plate number 4) to obtain a purified bisfluorosulfonyl imide solution (primary distillation), and the purified bisfluorosulfonyl imide solution is returned to the aforementioned step (d) as a crude bisfluorosulfonyl imide for the crystallization step. It is calculated that the distillation yield of bisfluorosulfonyl imide is about 98% after stable operation for 24 hours.

[0119] The one-way loss rate of bis(fluorosulfonyl)imide was calculated to be 0.5% in the whole process.

[0120] The test results of sampling and analysis of materials in each step are shown in Table 4:

[0121] Table 4

[0122]

[0123] Comparative Example 1

[0124] The crude bis(fluorosulfonyl)imide raw material of Example 1 was used for purification according to the method provided in Example 4 of patent CN111634895A, and the steps were as follows:

[0125] In a 500 mL dry filter funnel, 200 g of crude bisfluorosulfonyl imide raw material (purity of 90.06 wt%, the rest being impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and dichloroethane) is dissolved in 150 g of solvent under a dry nitrogen atmosphere, and the bisfluorosulfonyl imide concentration is 51.46% by weight. The filter funnel is closed with a stopper and stored at 0° C. for 4 hours. Crystals of HFSI product are formed. The HFSI product is filtered under a dry nitrogen atmosphere and washed with 25 mL of cold dichloromethane. The product yield based on bisfluorosulfonyl imide is 75% to obtain pure bisfluorosulfonyl imide, wherein bisfluorosulfonyl imide 99.601 wt%, hydrogen chloride 0.072 wt%, fluorosulfonic acid 0.115 wt%, and other impurities 0.212 wt%.

[0126] Comparative Example 2

[0127] The crude bis(fluorosulfonyl)imide raw material of Example 1 was used for purification according to the method provided in Example 1 of patent CN106365132 A, and the steps were as follows:

[0128] 100 g of crude bisfluorosulfonyl imide (purity of 90.06 wt%, the rest being impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and ethylene dichloride) was dissolved in 200 g of diethyl carbonate solvent, and the mixture was recrystallized and filtered at -100°C to obtain purified bisfluorosulfonyl imide, wherein the content of bisfluorosulfonyl imide was 99.69 wt%, hydrogen chloride was 0.02 wt%, fluorosulfonic acid was 0.12 wt%, and other impurities were 0.17 wt%.

[0129] Comparative Example 3

[0130] The crude bis(fluorosulfonyl)imide raw material of Example 1 was used for purification according to the method provided in Example 2 of patent CN106365132 A, and the steps were as follows:

[0131] The crude raw material of bisfluorosulfonyl imide (purity of 90.06wt%, the rest being impurities such as hydrogen fluoride, hydrogen chloride, aminosulfonic acid, sulfuric acid, fluorosulfonic acid, and ethylene dichloride) was distilled under reduced pressure at 169°C to obtain purified bisfluorosulfonyl imide, wherein the content of bisfluorosulfonyl imide was 91.89wt%, hydrogen chloride was 0.23wt%, fluorosulfonic acid was 3.56wt%, and other impurities were 4.38wt%.

Claims

1. A method for purifying bis(fluorosulfonyl)imide, characterized in that: Under the condition of isolating water and oxygen in the whole process, the following operation steps are included: 1) mixing a crude bisfluorosulfonyl imide product with a solvent, cooling the mixture, adding high-purity solid bisfluorosulfonyl imide particles as seed crystals, and performing a solvent crystallization operation to obtain a crystal slurry containing bisfluorosulfonyl imide crystals; 2) The crystal slurry of step 1) is centrifuged to obtain bisfluorosulfonyl imide crystals and a crystal filtrate, and the bisfluorosulfonyl imide crystals are washed with liquid high-purity bisfluorosulfonyl imide as a washing agent. After separating and removing the washing liquid, a pure bisfluorosulfonyl imide product is obtained.

2. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: The method includes the following steps 3) and 4): 3) combining the crystallization filtrate and the washing liquid in step 2), removing the solvent by a falling film evaporator, and obtaining a bisfluorosulfonyl imide solution enriched with impurities; 4) The impurity-enriched bisfluorosulfonyl imide solution is distilled to remove light components and heavy components to obtain a purified bisfluorosulfonyl imide solution, and the purified bisfluorosulfonyl imide solution is returned to step 1) as a crude bisfluorosulfonyl imide raw material for cyclic treatment.

3. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: Step 1) The solvent is selected from an inert solvent that can stably coexist with bis(fluorosulfonyl)imide at a temperature of ≥50° C., preferably one or more of dichloromethane, dichloroethane, toluene, and chlorobenzene, more preferably dichloroethane; Preferably, the purity of the solvent is required to be ≥ 99.5%; and / or In step 1), the mass ratio of the crude bisfluorosulfonyl imide to the solvent is 100:10-100, preferably 100:15-25.

4. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: The cooling in step 1) is to cool the temperature of the mixed solution in the crystallization kettle to the seed adding temperature at a certain cooling rate, and then keep it warm for a certain time; preferably, The cooling rate is ≤0.1°C / min, preferably 0.05-0.1°C / min; and / or The seed crystal addition temperature is 10-20°C, preferably 14-18°C; and / or The insulation time is ≥ 1h, preferably 1-2h.

5. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: The high-purity bis(fluorosulfonyl)imide solid particles in step 1) are required to have a chemical purity of ≥ 99.99%; and / or Step 1) the high-purity bis(fluorosulfonyl)imide solid particles have a particle size of 0.1-10 mm, preferably 0.1-5 mm; and / or In step 1), the high-purity bis(fluorosulfonyl)imide solid particles are added in an amount of 0.01-0.03 wt % of the crude bis(fluorosulfonyl)imide.

6. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: The solvent crystallization operation in step 1) is to add high-purity bis(fluorosulfonyl)imide solid particles and then keep the temperature for a certain period of time to grow the crystals; After the crystal growing is completed, the temperature is lowered to the terminal crystallization temperature at a certain cooling rate, and after being kept at the terminal crystallization temperature for a certain period of time, the crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals; Preferably, the crystal growing time is ≥ 1 h, preferably 1-2 h; Preferably, the cooling rate is ≤0.01°C / min, preferably 0.005-0.01°C / min; Preferably, the terminal crystallization temperature is -10-12°C, preferably 3-7°C; Preferably, the holding time at the terminal crystallization temperature is ≥ 2 h, preferably 2-4 h.

7. The method for purifying bisfluorosulfonyl imide according to claim 1, characterized in that: The solvent crystallization operation in step 1) can be performed in an intermittent or continuous manner; Wherein, the solvent crystallization operation is carried out in an intermittent manner, and the steps include: (a) cooling the mixed solution of crude bis(fluorosulfonyl)imide and solvent in a crystallization kettle to a seed adding temperature at a certain cooling rate under an appropriate stirring speed, and keeping the temperature for a certain period of time; (b) adding high-purity bis(fluorosulfonyl)imide solid particles to the mixed solution of step (a), and keeping the mixture warm for a certain period of time to perform a crystal growing operation; (c) After the crystal growing in step (b) is completed, the temperature is lowered to the terminal crystallization temperature at a certain cooling rate, and after being kept at the terminal crystallization temperature for a certain period of time, the crystallization operation is completed to obtain a crystal slurry containing bis(fluorosulfonyl)imide crystals.

8. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: The operations in step 1) are all carried out under stirring, and the stirring speed is 150-200 rpm.

9. The method for purifying bis(fluorosulfonyl)imide according to claim 1, characterized in that: Step 2) the liquid high-purity bis(fluorosulfonyl)imide used for washing the bis(fluorosulfonyl)imide crystals is required to have a chemical purity of ≥99.99%; and / or Step 2) the liquid high-purity bis(fluorosulfonyl)imide is used in a single washing in an amount not less than 1% of the mass of the bis(fluorosulfonyl)imide crystals, preferably 2-3%; and / or Step 2) The number of times of washing the bis(fluorosulfonyl)imide crystals is ≥ 3 times, and the filtered washing liquid is applied to the crystallization filtrate, and the two are combined for subsequent treatment.

10. The method for purifying bis(fluorosulfonyl)imide according to claim 2, characterized in that: Step 3) the falling film evaporation has a temperature of 57-60°C, a pressure of 15-20 kPaA and a time of 5-10 s.

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