Method for producing alkali metal salt of bis(fluorosulfonyl)imide

Abstract

The present invention relates to a process for producing an alkali metal salt of bis(fluorosulfonyl)imide, comprising the steps of: reacting an ammonium salt of bis(fluorosulfonyl)imide with an alkali metal reagent in a reaction medium to produce an alkali metal salt of bis(fluorosulfonyl)imide and ammonia; and simultaneously contacting the reaction medium with an inert gas stream to strip off the ammonia.

Description

Technical Field

[0001] The present invention relates to a method for producing an alkali metal salt of bis(fluorosulfonyl)imide. More specifically, the present invention provides a novel method for producing an alkali metal salt of bis(fluorosulfonyl)imide, which provides a high-purity product. Background Art

[0002] Bis(fluorosulfonyl)imide (often denoted "FSIH") and its salts, particularly the lithium salt of bis(fluorosulfonyl)imide (often denoted "LiFSI"), can be used as intermediate compounds or as final compounds in various technical fields. Bis(fluorosulfonyl)imide and its salts are particularly useful in battery electrolytes. For this type of application, the presence of impurities is a significant issue.

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

[0004] Two similar patent applications, EP 2 674 395 and EP 2 660 196, propose that maximum suppression of contamination with metallic impurities can be achieved 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 first fluorination step can be carried out by reaction with hydrogen fluoride (according to EP 2 674 395) or with NH4F (HF). p (p=0-10) reaction (according to EP 2 660 196). The alkali metal fluorosulfonyl imide salt thus obtained is said to contain no metallic impurities which deteriorate the performance of the electrolyte.

[0005] However, the present inventors have discovered the presence of unexpected new impurities in the alkali metal salts of fluorosulfonylimides obtained according to EP 2 674 395 and EP 2 660 196. Without wishing to be bound by any theory, it is believed that ammonia generated during the cation exchange reaction reacts undesirably with intermediate products and / or with the solvent 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] Prior art document WO 2016 / 093399 further discloses a method for producing and purifying a lithium salt of a sulfonyl imide. The method comprises reacting chlorosulfonic acid and chlorosulfonyl isocyanate to produce a chlorosulfonyl imide, then reacting the chlorosulfonyl imide with ammonium fluoride to produce a fluorosulfonyl imide ammonium salt, then reacting the fluorosulfonyl imide ammonium salt with a lithium compound to obtain a sulfonyl imide lithium salt, and finally purifying the sulfonyl imide lithium salt with the aid of a specific solvent. Here, the problem of impurities is addressed by implementing a final specific purification step.

[0007] We believe that there is still room for improvement to provide a new process for producing alkali metal salts of bis(fluorosulfonyl)imides which provides a high purity product. Summary of the Invention

[0008] The applicants hereunder provide a novel process for producing high-purity alkali metal salts of bis(fluorosulfonyl)imide.

[0009] A subject of the present invention is a process for producing an alkali metal salt of bis(fluorosulfonyl)imide, comprising the steps of reacting an ammonium salt of bis(fluorosulfonyl)imide with an alkali metal reagent in an organic reaction medium to produce an alkali metal salt of bis(fluorosulfonyl)imide and ammonia; and simultaneously contacting the reaction medium with a stream of inert gas to strip off the ammonia.

[0010] Advantageously, the method according to the present invention makes it possible to obtain very high-purity products. Without wishing to be bound by any theory, the inventors believe that, in the method of the prior art, the formation of impurities is due to the unexpected and unknown reaction between the ammonia and the solvent produced during the reaction. In the method of the prior art, the residence time of ammonia in the reaction medium is too long, and the method (such as vacuum) that is used to reduce ammonia content is not suitable for solving this problem. Advantageously, in theory, the amount of the ammonia in the reaction medium can be reduced to zero according to the method of the present invention. The residence time of ammonia in the reaction medium is advantageously very low. In addition, the method according to the present invention can be implemented in continuous mode or discontinuous mode on an industrial scale. DETAILED DESCRIPTION

[0011] In the present disclosure, the expression "included between ... and ..." should be understood to include the limit values.

[0012] The method according to the present invention relates to the production of an alkali metal salt of bis(fluorosulfonyl)imide. The alkali metal salt may be selected from the group consisting of lithium salts, sodium salts and potassium salts. Preferably, the alkali metal salt is a lithium salt, and the alkali metal salt of bis(fluorosulfonyl)imide obtained by the method according to the present invention is a lithium salt of bis(fluorosulfonyl)imide, Li. + (FSO2)2N - (LiFSI).

[0013] The method according to the present invention comprises the steps of reacting an ammonium salt of bis(fluorosulfonyl)imide with an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate or alkali metal hydride in an organic reaction medium to produce an alkali metal salt of bis(fluorosulfonyl)imide and ammonia.

[0014] The organic reaction medium comprises at least one organic solvent. Thus, the reaction is carried out in an organic solvent, a mixture of organic solvents, or a mixture of an organic solvent and water. The organic solvent may be selected from aprotic organic solvents, preferably:

[0015] - cyclic and acyclic carbonates, for example ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate,

[0016] - cyclic and acyclic esters, for example γ-butyrolactone, γ-valerolactone, methyl formate, methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, isopropyl acetate, propyl propionate, butyl acetate,

[0017] - cyclic and acyclic ethers, for example 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,

[0018] -amide compounds, such as N,N-dimethylformamide, N-methyloxazolidinone,

[0019] - sulfoxide and sulfone compounds, such as sulfolane, 3-methylsulfolane, dimethyl sulfoxide,

[0020] - cyano-substituted, nitro-substituted, chloro-substituted or alkyl-substituted alkanes or aromatics, for example acetonitrile, valeronitrile, adiponitrile, benzonitrile, nitromethane, nitrobenzene.

[0021] 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.

[0022] The alkali metal reagent is preferably selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates and alkali metal hydrides. The alkali metal hydroxide may be selected from the group consisting of lithium hydroxide, sodium hydroxide and potassium hydroxide. Preferably, the alkali metal hydroxide is lithium hydroxide. The alkali metal carbonate may be selected from the group consisting of lithium carbonate, sodium carbonate and potassium carbonate. Preferably, the alkali metal carbonate is lithium carbonate. The alkali metal bicarbonate may be selected from the group consisting of lithium bicarbonate, sodium bicarbonate and potassium bicarbonate. Preferably, the alkali metal bicarbonate is lithium bicarbonate. The alkali metal hydride may be selected from the group consisting of lithium hydride, sodium hydride and potassium hydride. Preferably, the alkali metal hydride is lithium hydride.

[0023] The expression "alkali metal reagent" here also includes hydrates thereof.

[0024] Preferably, an alkali metal hydroxide or an alkali metal hydroxide hydrate can be used. If the alkali metal reagent is a lithium salt, it can be selected from the group consisting of lithium hydroxide LiOH and lithium hydroxide hydrate LiOH.H2O.

[0025] The alkali metal reagent can be added as a solid, as a pure liquid or as an aqueous solution or organic solution. Preferably, it is necessary to reduce or avoid the presence of water in the reaction medium. Therefore, although not excluded, the use of an aqueous solution of the alkali metal reagent is not preferred.

[0026] The amount of alkali metal from the alkali metal reagent used is preferably between 0.5 and 5 mol, more preferably between 0.9 and 2 mol, and even more preferably between 1 and 1.5 mol per 1 mol of the ammonium salt of bis(fluorosulfonyl)imide. In the case where the alkali metal reagent contains 1 mol of alkali metal based on the number of moles of the alkali metal reagent, the amount of alkali metal reagent used is preferably between 0.5 and 5 mol, more preferably between 0.9 and 2 mol, and even more preferably between 1 and 1.5 mol per 1 mol of the ammonium salt of bis(fluorosulfonyl)imide. If this is not the case, the ratio is calculated accordingly. For example, in the case where the alkali metal reagent contains 2 moles of alkali metal per mole of the alkali metal reagent, the amount of the alkali metal reagent used is preferably comprised between 0.25 mole and 2.5 moles, more preferably between 0.45 mole and 1 mole, and even more preferably between 0.5 mole and 0.75 mole, per 1 mole of the ammonium salt of bis(fluorosulfonyl)imide.

[0027] In addition to the desired product, which is an alkali metal salt of bis(fluorosulfonyl)imide, the reaction between the ammonium salt of the bis(fluorosulfonyl)imide and the alkali metal reagent produces NH4OH, which is in equilibrium with ammonia and water. Simultaneously with the reaction between the ammonium salt of the bis(fluorosulfonyl)imide and the alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate or alkali metal hydride, the process according to the invention further comprises the step of contacting the reaction medium with an inert gas stream to strip off ammonia.

[0028] Stripping the chemical composition dissolved in the liquid phase by gas (commonly referred to as stripping gas) is a method known to personnel performing unit operations in chemical engineering. Stripping ammonia by air has been widely disclosed, especially for sewage treatment. The general principle of this technology can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 2012 "Absorption, 2. Design of Systems and Equipment" (Ullmann's Encyclopedia of Industrial Chemistry, 2012, "Absorption, 2. Design of Systems and Equipment" by Manfred Kriebel. Another application of this technology is disclosed in, for example, US 2009 / 0191113. However, as far as the inventors know, this technology has been applied to the present invention reaction for the first time.

[0029] The expression "simultaneously" is intended here to mean that stripping of ammonia from the reaction medium is carried out during the majority of the reaction time, i.e., during more than 50% of the reaction time, preferably during more than 75% of the reaction time, even more preferably during more than 90% of the reaction time. According to a preferred embodiment, stripping is carried out at least during the beginning of the reaction, when the production of ammonia is more pronounced.

[0030] The inert gas can be any suitable gas that does not chemically react with any compound present in the reaction medium. Preferably, for safety reasons, the inert gas can be selected based on the solvent of the reaction medium to remain outside the flammability limit of the reaction medium. It can be selected from the group consisting of nitrogen, argon and depleted air. In this article, "depleted air" means oxygen-depleted air, for example, air containing less than 10% oxygen. According to a preferred embodiment, the inert gas is nitrogen.

[0031] The reaction and the stripping can be carried out in a continuous stirred tank reactor, a series of continuously stirred tank reactors or in a tower reactor in batch mode, semi-batch mode or continuous mode, preferably in continuous mode.

[0032] According to a first embodiment, the reaction according to the present invention is carried out in a stirred tank reactor equipped with a gas injector at the bottom and a gas collector at the top. Inert gas is fed into the bottom of the stirred tank reactor via the gas injector, comes into contact with the reaction medium, and is released at the top of the stirred tank reactor via the gas collector. This first embodiment is suitable for low production volumes.

[0033] According to a second embodiment, the reaction according to the present invention is carried out in a multi-stage gas-liquid stripping tower (also referred to as a stripping tower). The stripping tower has a gas injector at the bottom of the tower and a gas collector at the top of the tower. The inert gas is fed to the bottom of the tower through the gas injector, contacts the reaction medium by flowing upward countercurrently with the downwardly flowing reaction medium, and is released at the top of the tower through the gas collector. Typically, the stripping tower can have 3 to 15 theoretical plates. External heat load can be provided to the tower, particularly in the second and last stages. This second embodiment is applicable to high throughput. Those skilled in the art will be able to select a suitable device among commercially available devices.

[0034] During contact with the reaction medium, the inert gas absorbs ammonia; thus, the released inert gas is enriched in ammonia, while the concentration of ammonia in the reaction medium decreases. The contact between the liquid and the gas can be improved by using suitable internals. Typically, the internals of the tower can be selected from mass transfer trays, random packings, and structured packings. For stirred tanks, the contact between the liquid and the gas can be improved by using gas diffusers or porous plates.

[0035] The temperature of the reaction medium may be comprised between 0°C and 100°C, more preferably between 10°C and 60°C, and 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 + / - 20°C compared to the reaction medium. Instead of an external heating system, provision of hot inert gas may be employed. 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; preferably, the temperature follows an ascending slope. For safety reasons, depending on the inert gas selected, the temperature may be kept below the flammability limit of the reaction medium.

[0036] Preferably, the reaction is carried out at atmospheric pressure, but operation below or above atmospheric pressure is not excluded, 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.

[0037] The concentration of the ammonium salt of bis(fluorosulfonyl)imide in the reaction medium may be comprised between 5% and 50%, preferably between 10% and 40% and even more preferably between 15% and 35% by weight.

[0038] The flow rate of the inert gas is adjusted according to the design of the reactor and other parameters of the reaction to obtain effective removal of ammonia. Generally, the flow rate of the inert gas may be between 0.2 and 30 tons based on the tonnage of the ammonium salt of bis(fluorosulfonyl)imide+solvent. More specifically, when the reaction is carried out in a stirred tank reactor, the flow rate of the inert gas may be between 1 and 30 tons, preferably between 2 and 20 tons, or even more preferably between 3 and 10 tons, based on the tonnage of the ammonium salt of bis(fluorosulfonyl)imide+solvent. In addition, when the reaction is carried out in a multi-stage gas-liquid extraction tower, the flow rate of the inert gas may be between 0.2 and 20 tons, preferably between 0.2 and 2 tons, or even more preferably between 0.4 and 1 ton, based on the tonnage of the ammonium salt of bis(fluorosulfonyl)imide+solvent. When the reaction is carried out in a multi-stage gas-liquid extraction tower, the amount of inert gas can be one-fifth to one-fifteenth compared to the same reaction carried out in a stirred tank reactor.

[0039] According to a preferred embodiment, after ammonia stripping, the ammonia-rich inert gas is collected, scrubbed and recycled. Additional scrubbing and recycling steps may include collecting the ammonia in a scrubber filled with an acidic aqueous solution and recovering pure inert gas from the scrubber.

[0040] According to a preferred embodiment, after ammonia stripping, the reaction medium contains less than 10,000 ppm of ammonia, more preferably less than 5,000 ppm of ammonia, more preferably less than 1,000 ppm of ammonia, more preferably less than 500 ppm of ammonia, more preferably less than 300 ppm of ammonia, more preferably from 0 to 100 ppm of ammonia, more preferably from 1 ppm to 50 ppm of ammonia, and even more preferably from 5 ppm to 20 ppm of ammonia. In this context, the ammonia content refers to NH3 and NH4 + Concentration by weight in the medium under consideration. For ammonium salts, only NH4 + weight, regardless of the total weight of the salt.

[0041] The reaction medium may be further processed to recover a very pure alkali metal salt of the bis(fluorosulfonyl)imide. The reaction medium may be a biphasic (aqueous / organic) solution, particularly when the alkali metal salt is an aqueous solution. In this case, the method may include a phase separation step during which the aqueous phase is removed and the alkali metal salt of the bis(fluorosulfonyl)imide is recovered in the organic phase. Additional steps may include filtration, concentration, extraction, recrystallization, chromatography, drying, and / or formulation.

[0042] Advantageously, the alkali metal salt of bis(fluorosulfonyl)imide obtained by the process according to the invention has a very high purity. It may exhibit a salt purity higher than 90%, preferably higher than 95%, more preferably between 99% and 100%.

[0043] Preferably, it may exhibit the following anion content:

[0044] -chloride ion (Cl - ) content is less than 10 000 ppm, preferably less than 5 000 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; and / or

[0045] -Fluoride ion (F - ) content is less than 10 000 ppm, preferably less than 5 000 ppm, more preferably less than 1 000 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; and / or

[0046] -Sulfate (SO4 2- ) content is lower than 30 000 ppm, preferably lower than 10 000 ppm, more preferably lower than 5 000 ppm.

[0047] Preferably, it may exhibit the following metal element contents:

[0048] - an iron (Fe) content of less than 1 000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or

[0049] - a chromium (Cr) content of less than 1 000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or

[0050] - nickel (Ni) content below 1 000 ppm, preferably below 800 ppm, more preferably below 500 ppm; and / or

[0051] - a zinc (Zn) content of less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or

[0052] - a copper (Cu) content of less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or

[0053] The bismuth (Bi) content is less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm.

[0054] In addition, when the alkali metal salt of bis(fluorosulfonyl)imide is not sodium bis(fluorosulfonyl)imide, it may exhibit:

[0055] - The sodium (Na) content is less than 10 000 ppm, preferably less than 5 000 ppm, more preferably less than 500 ppm.

[0056] In addition, when the alkali metal salt of bis(fluorosulfonyl)imide is not potassium bis(fluorosulfonyl)imide, it may exhibit:

[0057] The potassium (K) content is less than 10 000 ppm, preferably less than 5000 ppm, more preferably less than 500 ppm.

[0058] Due to its very high purity, the alkali metal salt of bis(fluorosulfonyl)imide, preferably lithium bis(fluorosulfonyl)imide, obtainable by the process according to the invention can advantageously be used in electrolyte compositions for batteries.

[0059] Advantageously, the alkali metal salt of bis(fluorosulfonyl)imide obtained by the process according to the invention does not contain by-products due to undesired reactions of ammonia with intermediate products and / or with solvents. An object of the present invention relates to an alkali metal salt of bis(fluorosulfonyl)imide obtained, obtainable or obtainable by the process according to the invention.

[0060] Another object of the present invention is the use of inert gas stripping to reduce or avoid the formation of by-products during the reaction of the ammonium salt of bis(fluorosulfonyl)imide with an alkali metal reagent to produce the alkali metal salt of bis(fluorosulfonyl)imide.

[0061] The ammonium salt of the bis(fluorosulfonyl)imide used in the method according to the present invention can be obtained by any method known to those skilled in the art. It can be purchased or prepared by an upstream process. According to one embodiment, the present invention relates to a method for producing an alkali metal salt of a bis(fluorosulfonyl)imide, the method comprising preparing an ammonium salt of a bis(fluorosulfonyl)imide, and then reacting the ammonium salt of the bis(fluorosulfonyl)imide with an alkali metal reagent in a reaction medium to produce an alkali metal salt of the bis(fluorosulfonyl)imide and ammonia; and simultaneously contacting the reaction medium with an inert gas stream to strip out the ammonia.

[0062] Examples of processes for preparing ammonium salts of bis(fluorosulfonyl)imides can be found, for example, in patent applications WO 2009 / 123328, EP 2 674 395 and EP 2 660 196. A specific process for preparing ammonium salts of bis(fluorosulfonyl)imides is disclosed below.

[0063] The preparatory step of preparing the ammonium salt of bis(fluorosulfonyl)imide may include reacting bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride to produce the ammonium salt of bis(fluorosulfonyl)imide.

[0064] Bis(chlorosulfonyl)imide or its salt is used as a raw material. It can be represented by the following formula:

[0065] (Cl-SO2-N - -SO2-Cl)X +

[0066] wherein X represents one selected from the group consisting of H, Li, Na, K, Cs, and NH 4 .

[0067] According to a preferred embodiment, the raw material is a bis(chlorosulfonyl)imide (usually represented by CSIH) having the formula (Cl-SO2)2-NH. CSIH is commercially available or produced by known methods, for example:

[0068] - by reacting chlorosulfonyl isocyanate ClSO2NCO with chlorosulfonic acid ClSO2OH;

[0069] - by reacting cyanogen chloride CNCl with sulfuric anhydride SO3 and with chlorosulfonic acid ClSO2OH;

[0070] - by reacting aminosulfonic acid NH2SO2OH with thionyl chloride SOCl2 and with chlorosulfonic acid ClSO2OH.

[0071] According to a preferred embodiment, the fluorinating agent is ammonium fluoride NH4F. In the present invention, the expression "ammonium fluoride" also includes HF adducts of ammonium fluoride, such as NH4F(HF) n , wherein n is 1 to 10, preferably 1 to 4, more preferably NH 4 F.HF or NH 4 F(HF) 2. The fluorination agent may be commercially available or produced by a known method.

[0072] According to a preferred embodiment, the fluorination agent is anhydrous. The moisture content may be preferably less than 5000 ppm, more preferably less than 1000 ppm, even more preferably less than 500 ppm.

[0073] The amount of ammonium fluoride used is preferably comprised between 1 and 10 equivalents, more preferably between 1 and 7 equivalents, and even more preferably between 2 and 5 equivalents, per 1 mole of bis(chlorosulfonyl)imide or its salt.

[0074] The reaction can be preferably carried out in an organic solvent. The organic solvent can be selected from aprotic organic solvents, preferably:

[0075] - cyclic and acyclic carbonates, for example ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate,

[0076] - cyclic and acyclic esters, for example γ-butyrolactone, γ-valerolactone, methyl formate, methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, isopropyl acetate, propyl propionate, butyl acetate,

[0077] - cyclic and acyclic ethers, for example 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,

[0078] -amide compounds, such as N,N-dimethylformamide, N-methyloxazolidinone,

[0079] - sulfoxide and sulfone compounds, such as sulfolane, 3-methylsulfolane, dimethyl sulfoxide,

[0080] - cyano-substituted, nitro-substituted, chloro-substituted or alkyl-substituted alkanes or aromatics, for example acetonitrile, valeronitrile, adiponitrile, benzonitrile, nitromethane, nitrobenzene.

[0081] 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.

[0082] According to a preferred embodiment, the organic solvent is anhydrous. The moisture 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, even more preferably less than 50 ppm.

[0083] The reaction can be carried out at a temperature between 0° C. and 200° C., preferably between 30° C. and 100° C. Preferably, the reaction is carried out at atmospheric pressure, but operation below or above atmospheric pressure is not excluded, for example between 800 mbar and 1.2 bar.

[0084] The reaction can be carried out in batch mode, semi-batch mode or continuous mode. According to a preferred embodiment, ammonium fluoride is first added to an organic solvent. Then, bis(chlorosulfonyl)imide or its salt can be added to the reaction medium.

[0085] By reacting bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride according to the present invention, an ammonium salt of bis(fluorosulfonyl)imide can be obtained.

[0086] According to a preferred embodiment, the step of preparing the ammonium salt of bis(fluorosulfonyl)imide can further include the optional step of adding a basic compound to the reaction medium. The basic compound can be a solid, a pure liquid, an aqueous solution or an organic solution or a gas. The basic compound can be selected from the group consisting of: gaseous ammonia, ammoniacal liquor, an amine, a hydroxide, carbonate, phosphate, silicate, borate, formates, acetates, stearates, palmitates, propionates or oxalates of an alkali metal or alkaline earth metal. In amine, any type of amine can be suitable, including: aliphatic amine (such as ethylamine, propylamine, butylamine, amylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, 2-ethylhexylamine, trimethylamine, triethylamine, tripropylamine and tributylamine), alkylenediamine (such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine), alkanolamine (such as monoethanolamine, The basic compound according to the present invention is preferably gaseous ammonia or aqueous ammonia.

[0087] The amount of the basic compound added is preferably between 0.1 and 10 equivalents, preferably between 0.5 and 5 equivalents, more preferably between 0.5 and 3 equivalents, based on the initial amount of bis(chlorosulfonyl)imide or its salt.

[0088] The temperature is preferably maintained between 0 and 100° C., more preferably between 15 and 90° C. Advantageously, this optional step may be carried out at the same temperature as the previous step of reacting the bis(chlorosulfonyl)imide or its salt with ammonium fluoride.

[0089] Optionally, the method according to the present invention may include an intermediate separation step. This intermediate separation step can be carried out by any typical separation means known to those skilled in the art, for example by filtering (for example under pressure or under vacuum) or decantation. Alternatively or additionally, this intermediate separation step can be carried out after adding the basic compound.

[0090] The ammonium salt of bis(fluorosulfonyl)imide obtained can be further purified, preferably by crystallization.

[0091] Prior to starting the crystallization, the concentration of the ammonium salt of bis(fluorosulfonyl)imide in the reaction medium may comprise between 10% and 95% by weight, preferably between 30% and 80% by weight, and more preferably between 40% and 70% by weight. The method may comprise a further step comprising 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 via heating, reduced pressure, or both. According to one embodiment, the concentration step may comprise distilling the solvent at a temperature comprised between 0°C and 120°C, preferably between 5°C and 80°C, and more preferably between 10°C and 70°C. The pressure may be adjusted according to the nature of the solvent, typically between atmospheric pressure and 10°C. -2 The distillation pressure is between 100 and 200 mbar, preferably between 1 mbar and 500 mbar, and more preferably between 5 mbar and 100 mbar. The distillation can be carried out in a continuous process mode or in a discontinuous / batch mode by any typical means known to those skilled in the art, such as continuous batch mode solvent evaporation, batch distillation, short path continuous flow distillation, or a thin film evaporator.

[0092] Crystallization of the salt can be obtained by lowering the temperature of the reaction mixture containing the salt (which may have optionally been concentrated beforehand) and / or by adding a precipitation solvent.

[0093] The temperature of the reaction mixture containing the salt can be lowered to a value below the solubility temperature of the salt. Preferably, the temperature is lowered 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. During the temperature reduction, the pressure can preferably be kept constant. However, a simultaneous reduction in pressure is not excluded. This may cause a portion of the organic solvent of the reaction mixture to evaporate. The pressure can be lowered to a value comprised between atmospheric pressure and 10°C. -2 mbar, preferably between 1 mbar and 500 mbar, and more preferably between 5 mbar and 100 mbar.

[0094] Alternatively or additionally, at least one precipitation solvent may be added to the reaction mixture containing the salt. The precipitation solvent may preferably be selected from organic solvents that are highly soluble in the organic solvent of the reaction mixture but are poor solvents for the ammonium salt of bis(fluorosulfonyl)imide. The precipitation solvent may be selected from the group consisting of: halogenated solvents such as dichloromethane, dichloroethane, chloroform, and carbon tetrachloride; substituted aromatic solvents such as chlorobenzene and toluene; and alkane solvents such as hexane and heptane. The precipitation solvent may preferably be selected from dichloromethane and dichloroethane. The volume ratio between the precipitation 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.

[0095] According to one embodiment of the present invention, the purification of the ammonium salt of bis(fluorosulfonyl)imide includes reducing the temperature of the reaction mixture containing salt when not adding a precipitation solvent. According to another embodiment of the present invention, the purification of the ammonium salt of bis(fluorosulfonyl)imide includes adding a precipitation solvent and not reducing the temperature of the reaction mixture containing salt. According to the 3rd embodiment (it is preferred), the purification of the ammonium salt of bis(fluorosulfonyl)imide includes adding a precipitation solvent and reducing the temperature of the reaction mixture containing salt. Preferably, first add a precipitation solvent, and reduce the temperature afterwards. However, do not exclude carrying out in an opposite manner, or carry out these two operations simultaneously.

[0096] The separation of the ammonium salt of the crystalline bis(fluorosulfonyl)imide can be carried out by any typical separation means known to those skilled in the art, for example by filtration. Filtering can be carried out at atmospheric pressure, under pressure or under vacuum by any means known to those skilled in the art. The mesh size of the filter medium can preferably be 2 microns or less, more preferably 0.45 microns or less and even more preferably 0.22 microns or less. The isolated product can be washed once or several times with a suitable solvent. The crystallization and separation steps can be carried out once, or can be repeated twice or more if necessary to improve the purity of the isolated crystalline salt.

[0097] Finally, the isolated crystalline salt is preferably dried to obtain a pure dry product.The drying step can be performed by any means known to those skilled in the art, typically under reduced pressure and / or by heating and / or using an inert gas flow, typically nitrogen flow.

[0098] Advantageously, the crystalline ammonium salt of bis(fluorosulfonyl)imide is of very high purity. It may exhibit:

[0099] - a salt purity higher than 90%, preferably higher than 95%, more preferably between 99% and 100% (mass percentage); and / or

[0100] The solvent content is lower than 20%, preferably lower than 10%, more preferably between 0% and 1% (mass percentage).

[0101] Preferably, it may exhibit the following anion content:

[0102] -chloride ion (Cl - ) content is less than 10 000 ppm, preferably less than 5 000 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; and / or

[0103] -Fluoride ion (F -) content is less than 10 000 ppm, preferably less than 5 000 ppm, more preferably less than 1 000 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; and / or

[0104] -Sulfate (SO4 2- ) content is lower than 30 000 ppm, preferably lower than 10 000 ppm, more preferably lower than 5 000 ppm.

[0105] Preferably, it may exhibit the following metal element contents:

[0106] - an iron (Fe) content of less than 1 000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or

[0107] - a chromium (Cr) content of less than 1 000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm; and / or

[0108] - nickel (Ni) content below 1 000 ppm, preferably below 800 ppm, more preferably below 500 ppm; and / or

[0109] - a zinc (Zn) content of less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or

[0110] - a copper (Cu) content of less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; and / or

[0111] The bismuth (Bi) content is less than 1 000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm.

[0112] Additionally, it can present:

[0113] - a sodium (Na) content of less than 10 000 ppm, preferably less than 5 000 ppm, more preferably less than 500 ppm, and / or

[0114] The potassium (K) content is less than 10 000 ppm, preferably less than 5000 ppm, more preferably less than 500 ppm.

[0115] In general, all raw materials used in the process 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 is less than 10 ppm, more preferably less than 2 ppm.

[0116] In addition, some or all of the steps of the process according to the invention are advantageously carried out in equipment that can withstand the corrosion of the reaction medium. For this purpose, corrosion-resistant materials are selected for the parts that come into contact with the reaction medium, such as alloys based on molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon and tungsten (in the form of or alloys of nickel, chromium, iron, and manganese to which copper and / or molybdenum are added (sold under the name or Monel TM (available on the market), and more particularly Hastelloy C276 or Inconel 600, 625, or 718 alloys. Stainless steels, such as austenitic steels and more particularly 304, 304L, 316, or 316L stainless steels, may also be selected. Steels having a nickel content of up to 22% by weight, preferably between 6% and 20%, and more preferably between 8% and 14%, are used. The nickel content of 304 and 304L steels varies between 8% and 12%, and the nickel content of 316 and 316L steels varies between 10% and 14%. More particularly, 316L steel is selected. Equipment composed of or coated with polymer compounds resistant to corrosion by the reaction medium may also be used. Materials such as PTFE (polytetrafluoroethylene or Teflon) or PFA (perfluoroalkyl resin) may be mentioned in particular. Glass equipment may also be used. The use of equivalent materials does not exceed the scope of the present invention. Graphite derivatives may also be mentioned as other materials suitable for contact with the reaction medium. The material used for filtration must be compatible with the medium used. Fluorinated polymers (PTFE, PFA), supported fluorinated polymers (Viton TM ), as well as polyester (PET), polyurethane, polypropylene, polyethylene, cotton and other compatible materials.

[0117] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that a term is unclear, the present description shall take precedence.

[0118] Examples

[0119] Example 1

[0120] In a 250 mL stirred tank reactor, 40 g of crystalline NH4FSI was dissolved in 93 mL of ethyl methyl carbonate. The reactor temperature was maintained 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 allowed to proceed for 8 hours while continuing to sparge the reactor.

[0121] The ammonium content was titrated by IPC. After 8 hours of reaction, NH4 + / NH3 content is less than 100ppm.

[0122] Example 2

[0123] The same reaction as in Example 1 was carried out without N2 bubbling.

[0124] After 20h of reaction, NH4 + / NH3 content is still above 10,000ppm.

[0125] Purity analysis

[0126] The reaction mixtures obtained in Examples 1 and 2 were subjected to potentiometry (NH4 + content), capillary electrophoresis and ion chromatography, and 19 F NMR analysis was performed.

[0127] The results are reported in Table 1.

[0128] time <![CDATA[NH4 + / NH3]]> Impurity 1* Impurity 2* Impurity 3* Example 1 8h <100ppm does not exist Very low does not exist Example 2 20h 14,000ppm exist exist exist

[0129] *Impurities 1, 2 and 3 were confirmed on the analytical spectrum. Without wishing to be bound by any theory, it is believed that these impurities correspond to by-products of the reaction of ammonia with EMC.

[0130] In the absence of any ammonia removal (Example 2), the reaction time is long and the final product contains impurities whose presence is undesirable for electronic device applications.

[0131] When the reaction is carried out according to the present invention (Example 1), the reaction time is reduced and the purity is improved. It is believed that the remaining trace amount of impurity 2 is low enough not to damage the performance of the electronic device.

Claims

1. A method for producing an alkali metal salt of bis(fluorosulfonyl)imide, the method comprising the steps of: An ammonium salt of a bis(fluorosulfonyl)imide is reacted with an alkali metal reagent in an organic reaction medium to produce an alkali metal salt of a bis(fluorosulfonyl)imide and ammonia; and the reaction medium is simultaneously contacted with a stream of an inert gas to strip off the ammonia.

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

4. The process according to claim 1 or claim 2, wherein the organic reaction medium comprises at least one organic solvent selected from aprotic organic solvents.

5. The process according to claim 1 or claim 2, 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 claim 1 or claim 2, wherein the alkali metal reagent is selected from alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates and alkali metal hydrides.

7. The method according to claim 1 or claim 2, wherein the alkali metal reagent is lithium hydroxide LiOH or lithium hydroxide hydrate LiOH.H2O.

8. The method according to claim 1 or claim 2, wherein the inert gas is selected from the group consisting of nitrogen, argon and depleted air.

9. The method according to claim 1 or claim 2, wherein the inert gas is nitrogen.

10. The process according to claim 1 or claim 2, wherein the reaction is carried out in a stirred tank reactor having a gas injector at the bottom and a gas collector at the top, and the inert gas is fed to the bottom of the stirred tank reactor through the gas injector, contacts the reaction medium, and is released at the top of the stirred tank reactor through the gas collector.

11. The method according to claim 1 or claim 2, wherein the reaction is carried out in a multi-stage gas-liquid extraction tower having a gas injector at a lower portion of the tower and a gas collector at an upper portion of the tower, and the inert gas is fed into the lower portion of the tower through the gas injector, contacts the reaction medium by flowing upward countercurrent to the downwardly flowing reaction medium, and is released at the upper portion of the tower through the gas collector.

12. The process according to claim 1 or claim 2, wherein the temperature of the reaction medium is comprised between 0°C and 100°C.

13. Process according to claim 1 or claim 2, wherein the temperature of the reaction medium is comprised between 10°C and 60°C.

14. Process according to claim 1 or claim 2, wherein the temperature of the reaction medium is comprised between 20°C and 50°C.

15. The process according to claim 1 or claim 2, wherein the flow rate of inert gas is comprised between 0.2 and 30 tons, based on the tons of ammonium salt of bis(fluorosulfonyl)imide and solvent in the organic reaction medium.

16. The method of claim 1 or claim 2, wherein the reaction is carried out under reduced pressure or at atmospheric pressure.

17. The process according to claim 1 or claim 2, wherein the process further comprises a step consisting of collecting, washing and recycling the inert gas enriched in ammonia after ammonia stripping.

18. The process according to claim 1 or claim 2, wherein the process further comprises post-treatment of the reaction medium, and if the reaction medium is a biphasic (aqueous / organic) solution, the post-treatment comprises a phase separation step during which the aqueous phase is removed and the alkali metal salt of the bis(fluorosulfonyl)imide is recovered in the organic phase.

19. The method according to claim 1 or claim 2, wherein the method further comprises a preparative step comprising preparing the ammonium salt of the bis(fluorosulfonyl)imide by reacting bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride to produce the ammonium salt of the bis(fluorosulfonyl)imide.

20. Use of an inert gas stripping for reducing the formation of by-products during the reaction of an ammonium salt of a bis(fluorosulfonyl)imide with an alkali metal reagent, wherein the reaction is carried out in an organic reaction medium to produce an alkali metal salt of a bis(fluorosulfonyl)imide and ammonia; and the reaction medium is simultaneously contacted with an inert gas stream to strip off the ammonia.