Method for producing alkali salt of bis(fluorosulfonyl)imide

Abstract

A method for producing an alkali salt of a bis(fluorosulfonyl)imide is provided. The present invention relates to a method for producing an alkali salt of a bis(fluorosulfonyl)imide, which comprises the steps of reacting an ammonium salt of a bis(fluorosulfonyl)imide with an alkaline agent in an organic reaction medium to produce the alkali salt of the bis(fluorosulfonyl)imide and ammonia, and simultaneously contacting the reaction medium with an inert gas stream to strip the ammonia.

Description

[Technical field]

[0001] The present invention relates to a process for preparing an alkali salt of a bis(fluorosulfonyl)imide. More specifically, the present invention provides a novel process for preparing an alkali salt of a bis(fluorosulfonyl)imide that provides a product of high purity. [Background technology]

[0002] Bis(fluorosulfonyl)imide (commonly referred to as "FSIH") and its salts, particularly the lithium salt of bis(fluorosulfonyl)imide (commonly referred to as "LiFSI"), are useful as intermediate or final compounds in various technical fields. Bis(fluorosulfonyl)imide and its salts are particularly useful in battery electrolytes. For this type of use, the presence of impurities is a significant problem.

[0003] The preparation of bis(fluorosulfonyl)imides and lithium salts of bis(fluorosulfonyl)imides has been widely described in the literature. Among the various techniques described, most use fluorination reactions with HF or metal fluorides such as KF, CsF, AsF3, SbF3, CuF2, ZnF2, SnF2, PbF2, BiF3, etc. Other techniques have also been developed, for example using chlorosulfonyl isocyanate in the presence of oleum and ammonium fluoride, or using urea and fluorosulfonic acid.

[0004] Two similar patent applications, Patent Document 1 and Patent Document 2, suggest that contamination with metal impurities can be suppressed to the maximum extent by first preparing a fluorosulfonylimide ammonium salt from a specific chlorosulfonylimide ammonium salt, and then reacting the fluorosulfonylimide ammonium salt thus obtained with an alkali metal compound to obtain a fluorosulfonylimide alkali metal salt. The initial fluorination step is a reaction with hydrogen fluoride according to Patent Document 1, or with NHF(HF) according to Patent Document 2. p(p=0-10). It is claimed that the fluorosulfonylimide alkali metal salt thus obtained does not contain metal impurities that deteriorate the electrolyte properties.

[0005] However, the inventors of the present invention have discovered the presence of an unexpected new impurity in the fluorosulfonylimide alkali metal salt obtained according to (Patent Document 1) and (Patent Document 2). Without wishing to be bound by any theory, it is believed that the ammonia generated during the cation exchange reaction reacts unfavorably with intermediate products and / or solvents to form undesirable by-products. Even if the cation exchange reaction is carried out under reduced pressure, some ammonia remains in the reaction medium due to the thermodynamic equilibrium between the liquid and gas phases.

[0006] The prior art document (Patent Document 3) further discloses a method for preparing and purifying lithium salts of sulfonylimides. The method consists of reacting chlorosulfonic acid with chlorosulfonyl isocyanate to prepare chlorosulfonylimides, then reacting the chlorosulfonylimides with ammonium fluoride to prepare fluorosulfonylimide ammonium salts, then reacting the fluorosulfonylimide ammonium salts with a lithium compound to obtain lithium sulfonylimide salts, and finally purifying the lithium sulfonylimide salts with the aid of a specific solvent. The problem of the presence of impurities is solved here by implementing a final specific purification step.

[0007] The present inventors believe that there remains room for improvement to provide new processes for the preparation of alkali salts of bis(fluorosulfonyl)imides that provide products of high purity. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent No. 2674395 [Patent Document 2] European Patent No. 2660196 [Patent Document 3] International Publication No. 2016 / 093399 Brochure [Patent Document 4] US Patent Application Publication No. 2009 / 0191113 [Patent Document 5] International Publication No. 2009 / 123328 Brochure [Non-patent literature]

[0009] [Non-Patent Document 1] Ullmann's Encyclopedia of Industrial Chemistry,2012“Absorption,2.Design of Systems and Equipment” Summary of the Invention

[0010] Applicants hereinafter provide a novel method for preparing high purity alkali salts of bis(fluorosulfonyl)imides.

[0011] One subject of the present invention is a process for the preparation of an alkali salt of a bis(fluorosulfonyl)imide which comprises the steps of reacting, in an organic reaction medium, an ammonium salt of the bis(fluorosulfonyl)imide with an alkaline agent to produce the alkali salt of the bis(fluorosulfonyl)imide and ammonia, while simultaneously contacting the reaction medium with a stream of inert gas to strip the ammonia.

[0012] Advantageously, the process according to the invention makes it possible to obtain a product of very high purity. Without wishing to be bound by any theory, the inventors believe that the formation of impurities in the prior art processes is due to an unexpected and unknown reaction between the ammonia generated during the reaction and the solvent. In the prior art processes, the ammonia remains in the reaction medium for too long, and methods such as vacuum used to reduce the ammonia content were not adequate to solve this problem. Advantageously, the process according to the invention makes it possible to reduce the amount of ammonia in the reaction medium, theoretically to zero. The residence time of the ammonia in the reaction medium is advantageously very short. In addition, the process according to the invention can be carried out on an industrial scale, either according to a continuous or discontinuous mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In this disclosure, the phrase "from, inclusive" should be understood as including both ends.

[0014] The process according to the invention relates to the preparation of an alkali salt of a bis(fluorosulfonyl)imide. The alkali salt can be selected from the group consisting of lithium salts, sodium salts, and potassium salts. Preferably, the alkali salt is a lithium salt, and the alkali salt of a bis(fluorosulfonyl)imide obtained by the process according to the invention is the lithium salt of a bis(fluorosulfonyl)imide, Li + (FSO2)2N - (LiFSI).

[0015] The process according to the invention comprises reacting an ammonium salt of a bis(fluorosulfonyl)imide with an alkali hydroxide, alkali carbonate, alkali bicarbonate, or alkali hydride in an organic reaction medium to produce the alkali salt of the bis(fluorosulfonyl)imide and ammonia.

[0016] The organic reaction medium comprises at least one organic solvent. The reaction is therefore carried out in an organic solvent, a mixture of organic solvents or a mixture of an organic solvent and water. The organic solvent can be chosen from aprotic organic solvents, preferably: cyclic and acyclic carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, cyclic and acyclic esters, such as gamma-butyrolactone, gamma-valerolactone, methyl formate, methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, isopropyl acetate, propyl propionate, butyl acetate, cyclic and acyclic ethers, such as diethyl ether, diisopropyl ether, methyl tert-butyl ether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, amide compounds, such as N,N-dimethylformamide, N-methyloxazolidinone, sulfoxide and sulfone compounds, such as sulfolane, 3-methylsulfolane, dimethylsulfoxide, cyano-, nitro-, chloro- or alkyl-substituted alkanes or aromatic hydrocarbons, such as acetonitrile, valeronitrile, adiponitrile, benzonitrile, nitromethane, nitrobenzene, You can choose from.

[0017] According to a preferred embodiment, the solvent is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile, and acetonitrile.

[0018] The alkaline agent is preferably selected from the group consisting of an alkali hydroxide, an alkali carbonate, an alkali hydrogen carbonate and an alkali hydride. The alkali hydroxide may be selected from the group consisting of lithium hydroxide, sodium hydroxide and potassium hydroxide. Preferably, the alkali hydroxide is lithium hydroxide. The alkali carbonate may be selected from the group consisting of lithium carbonate, sodium carbonate and potassium carbonate. Preferably, the alkali carbonate is lithium carbonate. The alkali hydrogen carbonate may be selected from the group consisting of lithium hydrogen carbonate, sodium bicarbonate and potassium bicarbonate. Preferably, the alkali hydrogen carbonate is lithium hydrogen carbonate. The alkali hydride may be selected from the group consisting of lithium hydride, sodium hydride and potassium hydride. Preferably, the alkali hydride is lithium hydride.

[0019] The expression "alkaline agent" as used herein also includes hydrates thereof.

[0020] Preferably, an alkali hydroxide or an alkali hydroxide hydrate can be used. When the alkaline agent is a lithium salt, it can be selected from the group consisting of lithium hydroxide LiOH and lithium hydroxide hydrate LiOH.H2O.

[0021] The alkaline agent can be added as a solid, as a pure liquid, or as an aqueous or organic solution. Preferably, the presence of water in the reaction medium must be reduced or avoided. Thus, although not excluded, the use of aqueous solutions of alkaline agents is not preferred.

[0022] The amount of alkali metal from the alkali agent used is preferably 0.5 to 5 moles, more preferably 0.9 to 2 moles, and even more preferably 1 to 1.5 moles per mole of the ammonium salt of bis(fluorosulfonyl)imide. When the alkali agent contains 1 mole of alkali metal per mole of the alkali agent, the amount of the alkali agent used is preferably 0.5 to 5 moles, more preferably 0.9 to 2 moles, and even more preferably 1 to 1.5 moles per mole of the ammonium salt of bis(fluorosulfonyl)imide. If this is not the case, the proportion is calculated accordingly. For example, in the case of an alkali agent containing 2 moles of alkali metal per mole of the alkali agent, the amount of the alkali agent used is preferably 0.25 to 2.5 moles, more preferably 0.45 to 1 mole, and even more preferably 0.5 to 0.75 moles per mole of the ammonium salt of bis(fluorosulfonyl)imide.

[0023] In addition to the desired product, which is the alkali salt of the bis(fluorosulfonyl)imide, the reaction between the ammonium salt of the bis(fluorosulfonyl)imide and the alkaline agent produces NH4OH in equilibrium with ammonia and water. Simultaneously with the reaction between the ammonium salt of the bis(fluorosulfonyl)imide and the alkali hydroxide, carbonate, bicarbonate, or hydride, the process according to the invention further comprises a step consisting of contacting the reaction medium with an inert gas stream to strip the ammonia.

[0024] Stripping of chemical components dissolved in a liquid phase by gases, usually called stripping gases, is a method known to those who carry out unit operations in chemical engineering. Stripping of ammonia by air has been widely described, in particular for wastewater treatment. The general principle of this technique can be found, for example, in Manfred Kriebel's (Non-Patent Document 1). Further applications of this technique are disclosed, for example, in (Patent Document 4). However, to the inventors' knowledge, this is the first time that this technique has been applied to the present reaction.

[0025] The expression "simultaneously" is intended here to mean that the stripping of ammonia from the reaction medium is carried out during a significant part of the reaction time, i.e. more than 50% of the reaction time, preferably more than 75% of the reaction time, and even more preferably more than 90% of the reaction time. According to a preferred embodiment, the stripping is carried out at least during the start of the reaction, when the production of ammonia is greater.

[0026] The inert gas can be any suitable gas that does not chemically react with any of the compounds present in the reaction medium. Preferably, for safety reasons, the inert gas can be selected according to the solvent of the reaction medium so as to remain outside the explosion limits of the reaction medium. It can be selected from the group consisting of nitrogen, argon and hypoxic air. In this document, "hypoxic air" means air that is deficient in oxygen, for example air that contains less than 10% oxygen. According to a preferred embodiment, the inert gas is nitrogen.

[0027] The reaction and stripping can be carried out in a batch, semi-batch or continuous mode, preferably continuous mode, in a continuous stirred tank reactor, in a series of continuous stirred tank reactors, or in a column reactor.

[0028] According to a first embodiment, the reaction according to the invention is carried out in a stirred tank reactor equipped with a gas inlet at the bottom and a gas recovery port at the top. An inert gas is fed through the gas inlet to the bottom of the stirred tank reactor, contacts the reaction medium and is released at the top of the stirred tank reactor through the gas recovery port. This first embodiment can be adapted for small production runs.

[0029] According to a second embodiment, the reaction according to the invention is carried out in a multi-stage gas-liquid extraction column, also known as a stripper. The stripper is equipped with a gas inlet at the bottom of the column and a gas recovery port at the top of the column. An inert gas is fed to the bottom of the column through the gas inlet, contacts the reaction medium by flowing countercurrently upwards towards the reaction medium flowing below, and is discharged at the top of the column through the gas recovery port. Typically, the stripper may exhibit a number of theoretical stages between 3 and 15. An external heat load may be provided to the column, especially in the second and last stages. This second embodiment can be adapted for large scale production. The skilled person will be able to select the appropriate equipment from among the commercially available equipment.

[0030] During contact with the reaction medium, the inert gas adsorbs ammonia. Thus, the released inert gas is enriched in ammonia, while the concentration of ammonia in the reaction medium is reduced. The contact between the liquid and the gas can be improved by using a suitable intercalant. Typically, the intercalant of the column can be selected from mass transfer plates, random packing, structured packing. For stirred tanks, the contact between the liquid and the gas can be improved by using gas diffusers or perforated plates.

[0031] The temperature of the reaction medium may be comprised between 0°C and 100°C, more preferably between 10°C and 60°C, even more preferably between 20°C and 50°C. The temperature of the inert gas before contacting the reaction medium may be the same as the temperature of the reaction medium or may be + / - 20°C compared to the reaction medium. Instead of an external heating system, a supply of hot inert gas may be used. According to a first embodiment, the temperature is constant during the reaction. According to a second embodiment, the temperature is not kept constant during the reaction, but rather follows a preferably increasing ramp. For safety reasons, depending on the selected inert gas, the temperature may be kept below the explosion limit of the reaction medium.

[0032] Preferably, the reaction is carried out at atmospheric pressure, without excluding carrying it out below or above atmospheric pressure, for example between 5 mbar and 1.5 bar, preferably between 5 mbar and 100 mbar. According to another embodiment, the process according to the invention is carried out under reduced pressure.

[0033] The concentration of the ammonium salt of bis(fluorosulfonyl)imide in the reaction medium may be comprised between 5% and 50% by weight, preferably between 10% and 40% by weight, and more preferably between 15% and 35% by weight.

[0034] The inert gas flow is adjusted according to the design of the reactor and other parameters of the reaction to effectively remove ammonia. Typically, the inert gas flow can be comprised between 0.2 and 30 tons per ton of the ammonium salt of bis(fluorosulfonyl)imide and the solvent. More specifically, when the reaction is carried out in a stirred tank reactor, the inert gas flow can be comprised between 1 and 30 tons, preferably between 2 and 20 tons, more preferably between 3 and 10 tons per ton of the ammonium salt of bis(fluorosulfonyl)imide and the solvent. Also, when the reaction is carried out in a multi-stage gas-liquid extraction column, the inert gas flow can be comprised between 0.2 and 20 tons, preferably between 0.2 and 2 tons, more preferably between 0.4 and 1 tons per ton of the ammonium salt of bis(fluorosulfonyl)imide and the solvent. The amount of inert gas can be 5 to 15 times lower when the reaction is carried out in a multi-stage gas-liquid extraction column compared to the same reaction carried out in a stirred tank reactor.

[0035] According to a preferred embodiment, after ammonia stripping, the ammonia-rich inert gas is recovered, scrubbed and recycled. An additional scrubbing and recycling step can consist of capturing the ammonia in a scrubber filled with an acidic aqueous solution and recovering pure inert gas from the scrubber.

[0036] According to a preferred embodiment, after ammonia stripping, the reaction medium contains less than 10000 ppm of ammonia, more preferably less than 5000 ppm of ammonia, more preferably less than 1000 ppm of ammonia, more preferably less than 500 ppm of ammonia, more preferably less than 300 ppm of ammonia, more preferably 0-100 ppm of ammonia, more preferably 1 ppm-50 ppm of ammonia, even more preferably 5 ppm-20 ppm of ammonia. In this document, the content of ammonia refers to the NH3 and NH4 content in the medium under consideration. + For ammonium salts, it refers to the weight concentration of NH4 + Only the weight of the salt is taken into account, not the total weight of the salt.

[0037] Additional treatment of the reaction medium may be performed to recover a highly pure alkali salt of the bis(fluorosulfonyl)imide. The reaction medium may be a biphasic (aqueous / organic) solution, particularly if the alkali salt is an aqueous solution. In this case, the method may include a phase separation step in which the aqueous phase is removed and the alkali salt of the bis(fluorosulfonyl)imide is recovered in the organic phase. Additional steps may include filtration, concentration, extraction, recrystallization, purification by chromatography, drying, and / or formulation.

[0038] Advantageously, the alkali salts of bis(fluorosulfonyl)imides obtained by the process according to the invention have a very high purity, which may represent a purity of the salt of more than 90%, preferably more than 95%, more preferably between 99% and 100%.

[0039] Preferably, it may exhibit the following anion content: - less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 1000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm chloride ions (Cl - ) content; and / or - less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 1000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm fluoride ions (F - ) content; and / or - less than 30,000 ppm, preferably less than 10,000 ppm, more preferably less than 5,000 ppm sulfate ions (SO 2- ) content.

[0040] Preferably, it may exhibit the following metal element contents: an iron (Fe) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or - a chromium (Cr) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or a nickel (Ni) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or a zinc (Zn) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or a copper (Cu) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or - a bismuth (Bi) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm.

[0041] In addition, when the alkali salt of the bis(fluorosulfonyl)imide is not sodium bis(fluorosulfonyl)imide, it may exhibit the following: - a sodium (Na) content of less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 500 ppm.

[0042] In addition, when the alkali salt of the bis(fluorosulfonyl)imide is not potassium bis(fluorosulfonyl)imide, it may show the following: A potassium (K) content of less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 500 ppm.

[0043] Due to their very high purity, the alkali salts of bis(fluorosulfonyl)imides, preferably lithium bis(fluorosulfonyl)imide, obtained by the process according to the invention can be advantageously used in electrolyte compositions for batteries.

[0044] Advantageously, the alkali salts of bis(fluorosulfonyl)imides obtained by the process according to the invention are free of by-products due to undesired reactions of ammonia with intermediates and / or solvents.One object of the invention relates to the alkali salts of bis(fluorosulfonyl)imides obtained, obtainable or obtainable by the process according to the invention.

[0045] Another object of the present invention is to use inert gas stripping during the reaction of the ammonium salt of the bis(fluorosulfonyl)imide with the alkaline agent to produce the alkali salt of the bis(fluorosulfonyl)imide and reduce or avoid the formation of by-products.

[0046] The ammonium salt of bis(fluorosulfonyl)imide used in the process according to the invention can be obtained by any method known to those skilled in the art. It can be purchased or prepared in an upstream process. According to one embodiment, the invention relates to a method for producing an alkali salt of bis(fluorosulfonyl)imide, comprising preparing an ammonium salt of bis(fluorosulfonyl)imide, then reacting the ammonium salt of bis(fluorosulfonyl)imide with an alkaline agent in a reaction medium to produce an alkali salt of bis(fluorosulfonyl)imide and ammonia; and simultaneously contacting the reaction medium with an inert gas stream to strip the ammonia.

[0047] Examples of methods for preparing ammonium salts of bis(fluorosulfonyl)imides can be found, for example, in U.S. Patent No. 5,399,623, U.S. Patent No. 5,399,623, and U.S. Patent No. 5,499,633. One specific method for preparing ammonium salts of bis(fluorosulfonyl)s is disclosed below.

[0048] The preliminary step of preparing the ammonium salt of the bis(fluorosulfonyl)imide may involve reacting the bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride to produce the ammonium salt of the bis(fluorosulfonyl)imide.

[0049] Bis(chlorosulfonyl)imide or a salt thereof is used as the raw material, which can be represented by the following formula: (Cl-SO2-N - -SO2-Cl) X + (wherein X represents one selected from the group consisting of H, Li, Na, K, Cs, and NH4).

[0050] According to a preferred embodiment, the starting material is a bis(chlorosulfonyl)imide of formula (Cl-SO2)2-NH, commonly designated CSIH, which is commercially available or can be prepared by known methods, for example: - reacting chlorosulfonyl isocyanate ClSO2NCO with chlorosulfonic acid ClSO2OH; - reacting cyanogen chloride CNCl with sulfuric anhydride SO3 and chlorosulfonic acid ClSO2OH; - reacting sulfamic acid NH2SO2OH with thionyl chloride SOCl2 and chlorosulfonic acid ClSO2OH.

[0051] According to a preferred embodiment, the fluorinating agent is ammonium fluoride NH4F. Within the present invention, the expression "ammonium fluoride" refers to the HF adduct of ammonium fluoride, e.g. NH4F(HF) nIn the formula, n is 1 to 10, preferably 1 to 4, more preferably NH4F.HF or NH4F(HF)2. The fluorinating agents are commercially available or can be prepared by known methods.

[0052] According to a preferred embodiment, the ammonium fluoride is anhydrous. The water content may be preferably less than 5000 ppm, more preferably less than 1000 ppm, and even more preferably less than 500 ppm.

[0053] The amount of ammonium fluoride used is comprised between 1 and 10 equivalents, more preferably between 1 and 7 equivalents, and further preferably between 2 and 5 equivalents, per mole of bis(chlorosulfonyl)imide or a salt thereof.

[0054] The reaction can be preferably carried out in an organic solvent. The organic solvent can be selected from aprotic organic solvents, preferably: cyclic and acyclic carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, cyclic and acyclic esters, such as gamma-butyrolactone, gamma-valerolactone, methyl formate, methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, isopropyl acetate, propyl propionate, butyl acetate, cyclic and acyclic ethers, such as diethyl ether, diisopropyl ether, methyl tert-butyl ether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, amide compounds, such as N,N-dimethylformamide, N-methyloxazolidinone, sulfoxide and sulfone compounds, such as sulfolane, 3-methylsulfolane, dimethylsulfoxide, cyano-, nitro-, chloro- or alkyl-substituted alkanes or aromatic hydrocarbons, such as acetonitrile, valeronitrile, adiponitrile, benzonitrile, nitromethane, nitrobenzene, It is.

[0055] According to a preferred embodiment, the organic solvent is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile, and acetonitrile.

[0056] According to a preferred embodiment, the organic solvent is anhydrous. The water content may be preferably less than 5000 ppm, more preferably less than 1000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, and even more preferably less than 50 ppm.

[0057] The reaction can be carried out at temperatures between 0° C. and 200° C., preferably between 30° C. and 100° C. Preferably, the reaction is carried out at atmospheric pressure, but it is not excluded that it can be carried out below or above atmospheric pressure, for example between 800 mbar and 1.2 bar.

[0058] The reaction can be carried out in a batch, semi-batch or continuous manner. According to a preferred embodiment, ammonium fluoride is first added to an organic solvent. Then, bis(chlorosulfonyl)imide or a salt thereof can be added to the reaction medium.

[0059] According to the present invention, the ammonium salt of bis(fluorosulfonyl)imide can be obtained by reacting bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride.

[0060] According to a preferred embodiment, the process for preparing the ammonium salt of bis(fluorosulfonyl)imide may further comprise an optional step consisting of adding a basic compound to the reaction medium. The basic compound may be a solid, a pure liquid, an aqueous or organic solution, or a gas. The basic compound may be selected from the group consisting of gaseous ammonia, aqueous ammonia, amines, or hydroxides, carbonates, phosphates, silicates, borates, formates, acetates, stearates, palmitates, propionates, or oxalates of alkali or alkaline earth metals. Among the amines, aliphatic amines (such as ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, 2-ethylhexylamine, trimethylamine, triethylamine, tripropylamine, and tributylamine), alkylenediamines (such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine), alkanolamines (monoethanolamine, diethanolamine, triethanolamine, mono ... Any type of amine may be advantageous, including isopropanolamine, diisopropanolamine, and triisopropanolamine, alicyclic amines (such as cyclohexylamine and dicyclohexylamine), aromatic amines (such as benzylamine and metaxylenediamine), ethylene oxide adducts of these amines, formamidines, guanidines, amidines, and heterocyclic amines (such as diazabicycloundecene, diazabicyclononene, piperidine, morpholine, piperazine, pyrimidine, pyrrole, imidazole, imidazoline, triazole, thiazole, pyridine, and indole). The basic compound according to the present invention is preferably gaseous ammonia or aqueous ammonia.

[0061] The amount of the basic compound added is preferably 0.1 to 10 equivalents, preferably 0.5 to 5 equivalents, and more preferably 0.5 to 3 equivalents, based on the initial amount of bis(chlorosulfonyl)imide or a salt thereof.

[0062] The temperature is preferably maintained between 0° C. and 100° C., more preferably between 15° C. and 90° C. Advantageously, this optional step can be carried out at the same temperature as the previous step in which the bis(chlorosulfonyl)imide or a salt thereof is reacted with ammonium fluoride.

[0063] Optionally, the process according to the invention may comprise an intermediate separation step, which may be carried out by any typical separation means known to the person skilled in the art, for example by filtration (for example under pressure or under vacuum) or decantation. Alternatively or in addition, such an intermediate separation step may be carried out after the addition of the basic compound.

[0064] The resulting ammonium salt of the bis(fluorosulfonyl)imide can be further purified, preferably by crystallization.

[0065] Before the start of the crystallization, the concentration of the ammonium salt of bis(fluorosulfonyl)imide in the reaction medium may be comprised between 10% and 95% by weight, preferably between 30% and 80% by weight, more preferably between 40% and 70% by weight. The method may comprise an additional step consisting of concentrating the ammonium salt of bis(fluorosulfonyl)imide in the reaction medium, typically by evaporating a portion of the organic solvent of the reaction medium, by heating, by reducing the pressure, or both. According to one embodiment, the concentration step may consist of distillation of the solvent at a temperature comprised between 0° C. and 120° C., preferably between 5° C. and 80° C., more preferably between 10° C. and 70° C. The pressure may vary, depending on the nature of the solvent, typically between atmospheric pressure and 10° C. -2 The pressure can be adjusted between 1 mbar and 500 mbar, preferably between 5 mbar and 100 mbar. The distillation can be carried out by any typical means known to the skilled person in a continuous process or discontinuous / batch mode, such as continuous batch solvent evaporation, batch distillation, short path continuous flow distillation, or thin film evaporator.

[0066] Crystallization of the salt can be obtained by lowering the temperature of the reaction mixture containing the optionally previously concentrated salt and / or by adding a precipitation solvent.

[0067] The temperature of the reaction mixture containing the salt can be reduced to a value below the dissolution temperature of the salt. Preferably, the temperature is reduced to a value comprised between the boiling point of the solvent and -20°C, more preferably between 70°C and -10°C, and even more preferably between 30°C and 0°C. While the temperature is reduced, the pressure can preferably be kept constant. However, it is not excluded to reduce the pressure at the same time. This may lead to the evaporation of part of the organic solvent of the reaction mixture. The pressure can be reduced to a value comprised between atmospheric pressure and 10°C. -2 The pressure can be reduced to a value comprised between 1 mbar and 500 mbar, preferably between 5 mbar and 100 mbar.

[0068] Alternatively or in addition, at least one precipitating solvent may be added to the reaction mixture containing the salt. The precipitating solvent may preferably be selected from among organic solvents that are highly soluble in the organic solvent of the reaction mixture and are poor solvents for the ammonium salt of bis(fluorosulfonyl)imide. The precipitating solvent may be selected from the group consisting of halogenated solvents such as dichloromethane, dichloroethane, chloroform, and carbon tetrachloride; substituted aromatic hydrocarbon solvents such as chlorobenzene and toluene; and alkane solvents such as hexane and heptane. The precipitating solvent may preferably be selected from dichloromethane and dichloroethane. The volume ratio between the precipitating solvent and the organic solvent of the reaction mixture may be comprised between 0.1 and 50, preferably between 0.2 and 20, more preferably between 0.5 and 15, and even more preferably between 1 and 10.

[0069] According to one embodiment of the present invention, the purification of the ammonium salt of the bis(fluorosulfonyl)imide consists of lowering the temperature of the reaction mixture containing the salt without adding a precipitation solvent. According to another embodiment of the present invention, the purification of the ammonium salt of the bis(fluorosulfonyl)imide consists of adding a precipitation solvent without lowering the temperature of the reaction mixture containing the salt. According to a third preferred embodiment, the purification of the ammonium salt of the bis(fluorosulfonyl)imide consists of adding a precipitation solvent and lowering the temperature of the reaction mixture containing the salt. The precipitation solvent is preferably added first and the temperature is then lowered. However, it is not excluded to proceed in the other way or to carry out the two actions simultaneously.

[0070] The crystallized ammonium salt of bis(fluorosulfonyl)imide can be separated by any typical separation means known to those skilled in the art, such as filtration. Filtration can be carried out under atmospheric pressure, under pressure, or under vacuum by any means known to those skilled in the art. The mesh size of the filtration medium can be preferably 2 micrometers or less, more preferably 0.45 micrometers or less, and even more preferably 0.22 micrometers or less. The separated product can be washed with a suitable solvent one or more times. The crystallization and separation steps can be carried out once, or can be repeated two or more times as necessary to improve the purity of the separated crystallized salt.

[0071] Finally, the separated crystallized salt is preferably dried to obtain a pure dry product. The drying step can be carried out by any means known to the skilled artisan, typically under reduced pressure and / or by heating and / or using a stream of inert gas, typically a stream of nitrogen.

[0072] Advantageously, the crystallized ammonium salt of the bis(fluorosulfonyl)imide has a very high purity. This is because - a purity of the salt of more than 90%, preferably more than 95%, more preferably between 99% and 100% (percent by mass); and / or - a solvent content of less than 20%, preferably less than 10%, more preferably between 0% and 1% (percent by mass); It can be shown that

[0073] Preferably, it may exhibit the following anion content: - less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 1000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm chloride ions (Cl - ) content; and / or - less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 1000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm fluoride ions (F - ) content; and / or - less than 30,000 ppm, preferably less than 10,000 ppm, more preferably less than 5,000 ppm sulfate ions (SO 2- ) content.

[0074] Preferably, it may exhibit the following metal element contents: an iron (Fe) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or - a chromium (Cr) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or a nickel (Ni) content of less than 1000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or a zinc (Zn) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or a copper (Cu) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or - a bismuth (Bi) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm.

[0075] In addition, this - a sodium (Na) content of less than 10000 ppm, preferably less than 5000 ppm, more preferably less than 500 ppm; and / or - a potassium (K) content of less than 10 000 ppm, preferably less than 5 000 ppm, more preferably less than 500 ppm; It can be shown that

[0076] Generally speaking, all raw materials used in the method according to the invention, including solvents, reagents etc., may preferably exhibit very high purity standards. Preferably, their content of metal components such as Na, K, Ca, Mg, Fe, Cu, Cr, Ni, Zn etc. is less than 10 ppm, more preferably less than 2 ppm.

[0077] In addition, some or all of the steps of the method according to the invention are advantageously carried out in equipment capable of withstanding the corrosion of the reaction medium. For this purpose, the parts in contact with the reaction medium may be made of alloys based on molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon and tungsten, such as those sold under the Hastelloy® brand, or Inconel® or Monel®. TMA material is selected that is resistant to corrosion, such as an alloy of nickel, chromium, iron and manganese with the addition of copper and / or molybdenum, sold under the name Hastelloy C276 or more preferably the Inconel 600, 625 or 718 alloys. Austenitic steels may also be selected, more particularly stainless steels such as 304, 304L, 316 or 316L stainless steels. Steels are used that have a nickel content of up to 22% by weight, preferably between 6% and 20%, more preferably between 8% and 14%. 304 and 304L steels have a nickel content that varies between 8% and 12%, and 316 and 316L steels have a nickel content that varies between 10% and 14%. More particularly, 316L steel is selected. It is also possible to use equipment made of or coated with polymeric compounds that are resistant to the corrosion of the reaction medium. In particular, materials such as PTFE (polytetrafluoroethylene or Teflon) or PFA (perfluoroalkyl resins) may be mentioned. Glassware may also be used. It is not beyond the scope of the invention to use equivalent materials. Other materials that may be suitable for contact with the reaction medium may also include graphite derivatives. The material for filtration must be compatible with the medium used. Fluorinated polymers (PTFE, PFA), loaded fluorinated polymers (Viton TM ), polyester (PET), polyurethane, polypropylene, polyethylene, cotton, and other compatible materials can be used.

[0078] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference conflicts with the statements of this application to the extent that it may render a term unclear, this statement shall control. EXAMPLES

[0079] Example 1 In a 250 mL stirred tank reactor, 40 g of crystallized NH4FSI was dissolved in 93 mL of ethyl methyl carbonate. The temperature of the reactor was fixed at 30°C. 8.7 g of LiOH.H2O was added. N2 gas was injected into the bottom of the reactor at a rate of 170 g / h, and the reaction was carried out for 8 hours with continuous N2 bubbling. The ammonium content was titrated by IPC. After 8 hours of reaction, NH4 + The / NH3 content was less than 100 ppm.

[0080] Example 2 The same reaction as in Example 1 was carried out without N2 bubbling. After 20 hours of reaction, NH4 + / NH3 content was still above 10,000ppm.

[0081] purity analysis The reaction mixtures obtained in Examples 1 and 2 were subjected to potentiometric (NH + content), capillary electrophoresis and ion chromatography, and 19 The compounds were analyzed by F NMR, and the results are reported in Table 1.

[0082] [Table 1]

[0083] When ammonia removal is not performed (Ex.2), the reaction time is long and the final product contains impurities whose presence is undesirable for electronics applications. When the reaction is performed according to the present invention (Ex.1), the reaction time is short and the purity is improved. The remaining trace amounts of impurity 2 are believed to be sufficiently low so as not to impair the performance of electronic devices.

Claims

1. 1. A process for producing an alkali salt of a bis(fluorosulfonyl)imide, comprising the steps of reacting an ammonium salt of a bis(fluorosulfonyl)imide with an alkaline agent in an organic reaction medium to produce an alkali salt of the bis(fluorosulfonyl)imide and ammonia, and simultaneously contacting the reaction medium with a stream of inert gas to strip the ammonia.

2. 2. The method of claim 1, wherein the alkali salt is selected from the group consisting of lithium salts, sodium salts, and potassium salts.

3. The method of claim 1, wherein the alkaline salt is a lithium salt.

4. The process according to any one of claims 1 to 3, wherein the organic reaction medium comprises at least one organic solvent, the organic solvent being selected from aprotic organic solvents.

5. The method of claim 1, wherein the organic reaction medium comprises at least one organic solvent selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile, and acetonitrile.

6. The method according to any one of claims 1 to 5, wherein the alkaline agent is selected from alkali hydroxides, alkali carbonates, alkali hydrogen carbonates, and alkali hydrides.

7. The method according to any one of claims 1 to 5, wherein the alkaline agent is lithium hydroxide LiOH or lithium hydroxide hydrate LiOH.H2O.

8. The method according to any one of claims 1 to 7, wherein the inert gas is selected from the group consisting of nitrogen, argon and low-oxygen air.

9. 9. The method according to claim 1, wherein the reaction is carried out in a stirred tank reactor equipped with a gas inlet at the bottom and a gas recovery port at the top, and an inert gas is supplied to the bottom of the stirred tank reactor through the gas inlet, contacts the reaction medium, and is released at the top of the stirred tank reactor through the gas recovery port.

10. 9. The process according to any one of claims 1 to 8, wherein the reaction is carried out in a multi-stage gas-liquid extraction column equipped with a gas inlet at the bottom of the column and a gas recovery port at the top of the column, and an inert gas is fed to the bottom of the column through the gas inlet, contacts the reaction medium by flowing countercurrently upwards towards the reaction medium flowing below, and is discharged at the top of the column through the gas recovery port.

11. The process according to any one of claims 1 to 10, wherein the temperature of the reaction medium is comprised between 0°C and 100°C.

12. 12. The process according to any one of claims 1 to 11, wherein the inert gas flow is comprised between 0.2 and 30 tons per ton of ammonium salt of bis(fluorosulfonyl)imide plus solvent from the organic reaction medium.

13. The process according to any one of claims 1 to 12, wherein the reaction is carried out under reduced pressure or at atmospheric pressure.

14. 14. The process according to any one of claims 1 to 13, wherein the process further comprises the step of recovering, scrubbing and recycling the ammonia-rich inert gas after ammonia stripping.

15. 15. The process according to any one of claims 1 to 14, further comprising a work-up of the reaction medium, which, when the reaction medium is a biphasic (aqueous / organic) solution, comprises a phase separation step in which the aqueous phase is removed and the alkali salt of the bis(fluorosulfonyl)imide is recovered in the organic phase.

16. 16. The method of any one of claims 1 to 15, further comprising a preliminary step consisting of preparing the ammonium salt of a bis(fluorosulfonyl)imide by reacting a bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride to produce the ammonium salt of a bis(fluorosulfonyl)imide.

17. Use of inert gas stripping during the reaction of an ammonium salt of a bis(fluorosulfonyl)imide with an alkaline agent to produce an alkali salt of a bis(fluorosulfonyl)imide and reduce or avoid the formation of by-products.

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