Method for fluorinating hydrogen BIS(chlorosulfonyl)imide in gas phase

Abstract

The present invention relates to a method for producing bis(fluorosulfonyl)imide, which is economically feasible at industrial scale and which provides a high-purity product.

Description

METHOD FOR FLUORINATING HYDROGEN BIS(CHLOROSULFONYL)IMIDE IN GAS PHASECross reference to related patent applications

[0001] This application claims priority filed on 20 December 2023 in Europe with Nr.23307284.2, the whole content of this application being incorporated herein by reference for all purposes.Technical field

[0002] The present invention relates to a method for producing bis(fluorosulfonyl)imide (HFSI), which is economically feasible at industrial scale and which provides a high-purity product.Background

[0003] Fluorosulfonylimide salts, in particular the lithium salt of bis(fluorosulfonyl)imide (LiFSI), are useful compounds for battery electrolytes. Different processes, reactants and intermediates leading to LiFSI have been described in the patent literature, notably patent CA 2 527 802 (Universite de Montreal) which lists several routes to prepare LiFSI, for example the process for preparing LiFSI in one step starting from bis(chlorosulfonyl)imide (HCSI) using anhydrous hydrogen fluoride (HF):

[0004] Known in the art are also two-steps processes to prepare LiFSI, such as a process that involves the fluorination of bis(chlorosulfonyl)imide (HCSI) into bis(fluorosulfonyl)imide (HFSI) using a fluorination agent, for example anhydrous hydrogen fluoride (HF), followed by the lithiation of HFSI into LiFSI using a lithiation agent. An example of such a process is disclosed in US9,725,318, wherein HCSI is reacted with anhydrous HF in the presence of a solvent. The reaction time for obtaining conversion to HFSI is 18 hours.

[0005] Another known two-step process for preparing LiFSI involves a first step of fluorination of bis(chlorosulfonyl)imide (HCSI) into ammonium bis(fluorosulfonyl)imide (NH4FSI) using NH4F(HF)Xas a fluorinating agent, followed by a second step of lithiation of NH4FSI, leading then to the LiFSI product. Such a process is described for example in WO 2017 / 090877 A1 (CLS) and EP 3 170 789 A1 (Nippon Soda).

[0006] Another known two-step process for preparing LiFSI involves the lithiation of HCSI in a first step using a lithiation agent in order to prepare LiCSI as an intermediate product, and then the fluorination of LiCSI into LiFSI using a fluorination agent.

[0007] For example, KR 20200049164 (in the name of CLS) relates to a LIFSI preparation method, comprising a step reacting HCSI with various lithiation reagents in an (S1 ) solvent to produce LiCSI and then reacting it with an anhydrous fluorination reagent directly without purification. A long list of possible solvents is given in the specification, while dimethyl carbonate is used in the examples.

[0008] US 2017 / 0183230 (in the name of SES HOLDINGS PTE LTD) discloses a process for converting HCSI to HFSI that comprises reacting liquid HCSI with anhydrous gaseous HF under conditions of temperature and pressure sufficient to produce gaseous HFSI. The yield of HFSI achieved by this process is about 80%, based on conversion of HCSI.

[0009] As can be read from the patent publications above-cited, the production of HFSI takes place in solvents or with HCSI in liquid phase, in order to disperse the reactive entities to allow them to react or to allow recovery of the unreacted species.

[0010] WO 2024 / 002897 discloses and exemplifies a method for producing HFSI by contacting HCSI with aHF in the absence of a solvent, but wherein nitrogen is provided to the reaction apparatus as a carrier gas.

[0011] The Applicant perceived that there is still the need in the art for improving the manufacturing process of HFSI.

[0012] In particular, the Applicant is well aware that the processes disclosed in the prior art require long reaction time and achieve a low level of selectivity.Summary of the invention

[0013] With the aim of overcoming the above drawbacks, the Applicant faced the problem of providing a continuous production process for preparing bis(fluorosulfonyl)imide (HFSI), with low residence time and with high yield and selectivity.

[0014] Further, the Applicant addressed environmental aspects of routes to HFSI, providing a process that would not need the use of hazardous solvents, which would minimize the amount of solid / salt wastes, and which would provide for opportunities of valorization of side products.

[0015] The method for manufacturing HFSI according to the present invention is characterized by a high conversion and by a high level of selectivity, providing HFSI particularly suited for many applications, notably as an intermediate to prepare bis(fluorosulfonyl)imide salts (FSI salts) suitable for use in battery applications.

[0016] Advantageously, the method of the present invention is a solvent-free method, which means that no liquid solvent, such as liquid organic solvent, is added to the reaction mixture during the method of the present invention. This is advantageous because first, the step for removing the solvent is avoided, thus reducing the complexity of the industrial process, as well as its overall cost; secondly, the preliminary step of treating the solvent to decrease its moisture content is also avoided.

[0017] Advantageously, the fluorination reaction of the present invention is carried out such that HCSI reacts when it is fully in the gas phase.

[0018] In addition, the side-reactions between HCSI and / or HFSI and the organic solvent(s) are avoided, increasing the overall yield and avoiding the occurrence of undesired species.Detailed description

[0019] Thus, in a first aspect, the present application relates to a method for manufacturing bis(fluorosulfonyl)imide (HFSI), said method comprising: step (I) of contacting gaseous bis(chlorosulfonyl)imide (HCSI) with hydrogen fluoride (HF), thus obtaining HFSI; wherein said step (I) is carried out at a pressure below atmospheric pressure, in the absence of liquid solvent(s) and in the absence of gases other than HCSI and HF.

[0020] Advantageously, HFSI is obtained at the end of such step (I) in the gas phase.

[0021] As used in the present description and in the following claims, the expression “in the absence of liquid solvent(s)” is intended to indicate that no liquid organic solvent is added to the reactor or reaction environment.

[0022] As used in the present description and in the following claims, the expression “in the absence of gases other than HCSI and HF” is intended to indicate that no gas is voluntarily introduced into the reactor or reaction environment. Hence, this expression is intended to mean that the reaction is performed in the absence of added gases other than HCSI and HF. For example, no carrier gas is used in admixture with HCSI or with HF, when they are introduced into the reactor. Such expression does not exclude however that gases can be generated during the method of the invention, such as for example HCI.

[0023] Advantageously, it is preferred that HF is anhydrous.

[0024] Anhydrous HF (aHF) means that the HF has a content of moisture below 200 ppm, preferably below 100 ppm, more preferably below 50 ppm, and even more preferably below 20 ppm as determined by Karl-Fisher titration. More preferably and advantageously, aHF has a content of moisture below 10 ppm and more preferably below 5 ppm.

[0025] According to an embodiment, in step (I) gaseous HCSI is reacted with aHF in the gas phase.

[0026] According to another embodiment, in step (I) gaseous HCSI is reacted with aHF that is partially vaporised. Partially vaporised means that aHF is partially liquid and partially in the gas phase.

[0027] According to another embodiment, in step (I) gaseous HCSI is reacted with aHF in the liquid phase.

[0028] HCSI in the gas phase can be obtained from solid HCSI or molten HCSI.

[0029] Solid or molten HCSI is commercially available on the market or may be produced by any known method, for example:- by reacting chlorosulfonyl isocyanate (CISO2NCO) with chlorosulfonic acid (CISO2OH) (CSI route);- by reacting cyanogen chloride (CNCI) with sulfuric anhydride (SO3), and with chlorosulfonic acid (CISO2OH); or- by reacting sulfamic acid (NH2SO2OH) with thionyl chloride (SOCI2) and with chlorosulfonic acid (CISO2OH) (SFA route).

[0030] When solid HCSI is used, before step (I), a step (0-a) of providing solid HCSI and a step (0-b) of melting said solid HCSI to a temperature above its melting temperature (TrriHcsi) to obtain HCSI in a molten state (also called liquid state) are performed.

[0031] Preferably, step (0-b) is performed at a temperature (Ta) suitable for melting HCSI and maintaining HCSI in the molten state, while its thermal degradation is minimised.

[0032] Preferably, step (0-b) is conducted at a temperature (Ta) equal to or above the melting point of HCSI (Tmncsi). In this case, Ta > Tmncsi. For example, Ta may be equal to or above the melting point of HCSI (Tmncsi) plus 5°C. In this case, Ta > Tmncsi + 5. As another example, Ta may be equal to or above the melting point of HCSI (Tmncsi) plus 10°C. In this case, Ta > Tmncsi + 10.

[0033] It will be understood that the melting point of HCSI is influenced by the presence and amounts of impurities.

[0034] Preferably, the temperature (Ta) at which step (0-b) is conducted is equal to or higher than 30°C, for example equal to or higher than 37°C, for example equal to or higher than 38°C, equal to or higher than 40°C, equal to or higherthan 45°C or even equal to or higher than 50°C. Temperature Ta is preferably lower than 150°C, more preferably equal or lower than 100°C. In any case, the temperature (Ta) at which step (0-b) is conducted is below the degradation temperature of HCSI.

[0035] Molten HCSI can be provided as such or can be obtained from solid HCSI, for example according to step (0-b) above.

[0036] According to a preferred embodiment, the method according to the present invention comprises before step (I), a step (0-b*) of providing molten HCSI and a step (0-c) of heating the HCSI provided in step (0-b*) to obtain gaseous HCSI.

[0037] Preferably, the heating of molten HCSI is performed at a temperature from about 35°C, more preferably from about 50°C, even more preferably from about 100°C.

[0038] Preferably, the heating of molten HCSI is performed at a temperature up to 200°C, more preferably up to 180°C and even more preferably up to 160°C.

[0039] According to this embodiment, the partial pressure of HCSI is reduced, and the vaporization is more effective.

[0040] Said step (0-b*) can correspond to step (0-b) above mentioned.

[0041] Such step (0-c) can be performed under whichever pressure, including pressure above atmospheric pressure; about atmospheric pressure; or reduced pressure.

[0042] Preferably, HCSI in the gas phase is obtained in step (0-c) under reduced pressure, in conditions to reduce the partial pressure of HCSI, such as by heating into a suitable reactor, optionally thermostated.

[0043] More preferably, such step (0-c) is performed by vaporization of molten HCSI via reactive distillation. Such reactive distillation is performed using a reactive distillation column operating under reduced pressure.

[0044] Preferably, such reduced pressure is from about 1 mbar abs (100 Pa) to about 1013 mbar abs (0.1013 MPa), more preferably from about 2 mbar abs (200 Pa) to about 750 mbar abs (0.0750 MPa) and even more preferably from about 5 mbar abs (500 Pa) to about 500 mbar abs (0.0500 MPa). Goodresults have been obtained with a pressure from about 10 mbar abs (1000 Pa) to 400 mbar abs (0.0400 MPa) or to 200 mbar abs (0.0200 MPa).

[0045] The gaseous HCSI obtained at the end of step (0-c) is then contacted with the aHF in step (I) of the method of the present invention, at a pressure below atmospheric pressure.

[0046] The method of the present invention is performed in a suitable reactor. Such reactor can be selected with appropriate choice of constituent material for being corrosion resistant and compatible with the involved chemicals, which are particularly aggressive because of their acid character.

[0047] Step (I) of the method of the present invention is performed by loading HCSI in the gas phase into a reactor suitable for contacting with aHF.

[0048] Loading molten HCSI into the reactor can be carried out by liquid-transfer methods, such as temperature-controlled pumping via temperature-controlled pipelines (with set-up to maintain HCSI in liquid state), or by cannulation using temperature-controlled conditions, amongst other options.

[0049] The expression “cannulation” is not particularly limited and is intended to encompass means which will operate the inert-gas assisted transfer of HCSI into a reactor.

[0050] Cannulation can be performed in the presence of an inert gas. Such inert gas can be selected from argon or nitrogen.

[0051] As cannulation is completed, such inert gas is completely evacuated via a suitable system and does not remain into the reactor during step (I).

[0052] According to a preferred embodiment, step (I) is performed in a reactor selected from a reactive distillation column.

[0053] This embodiment is particularly preferred because it allows to perform step (I) of the method of the invention in a continuous manner. Hence, this embodiment is particularly advantageous from an industrial perspective as it allows to simplify the process scheme, while the reaction between HCSI and aHF is fully performed in the gas phase.

[0054] Preferably, the gaseous HCSI has a purity of at least 95% by moles, preferably of at least 98% by moles, more preferably of at least 99.5% by moles.

[0055] Preferably, the aHF can be introduced into the reactor by injection.

[0056] Under step (I) of the method of the invention, aHF can be introduced into the reactor: before HCSI is loaded, or as the loading of HCSI proceeds, or after the loading of HCSI is finished.

[0057] Gaseous aHF is preferably provided to the reactor at atmospheric pressure. Gaseous aHF is preferably provided to the reactor at a temperature ranging from 19.5°C to 200°C, preferably at a temperature from 19.5°C to 150°C.

[0058] Liquid aHF is preferably provided to the reactor at a pressure above atm pressure. The pressure as well as the temperature for performing this step of providing liquid aHF are not limited.

[0059] The step of introducing aHF is preferably performed continuously.

[0060] Typically, aHF is continuously added or added in a controlled manner throughout the reaction time at a substantially constant rate.

[0061] The molar ratio between gaseous HCSI and aHF is preferably between 1 :1 to 1 :100, more preferably between 1 :1 to 1 :50 and even more preferably between 1 :1 and 1 :10. The preferred molar ratio can be selected considering for example the need for recycling excess of HF, and the kinetics / yield dependence upon the said HCSkHFSI ratios.

[0062] The reaction between HCSI and aHF in the gas phase under step (I) generally takes place at temperature and at a pressure that are suitable for keeping all the reactants into the gas phase.

[0063] Step (I) is carried out at a pressure below atmospheric pressure.

[0064] Preferably, step (I) is carried out at a pressure of from about 1 mbar abs (100 Pa) to about 1013 mbar abs (0.1013 MPa), more preferably from about 2 mbar abs (200 Pa) to about 750 mbar abs (0.0750 MPa) and even more preferably from about 5 mbar abs (500 Pa) to about 500 mbar abs (0.0500 MPa). Good results have been obtained with a pressure from about 10 mbarabs (1000 Pa) to 400 mbar abs (0.0400 MPa) or to 200 mbar abs (0.0200 MPa).

[0065] Typically, the reaction is carried out at a temperature of from 100 to 300 °C, more preferably from 160 to 220 °C, still more preferably from 160 to 180 °C.

[0066] Preferably, the residence time of the reactants in the reactor is between 1 millisecond to 3 hours.

[0067] The reaction conditions are maintained such that the HFSI produced is removed from the reaction mixture as a gas.

[0068] HFSI can be obtained at the end of step (I) in admixture with unreacted aHF or with unreacted HCSI, etc. Such a mixture can be referred to as mixture (M1 ).

[0069] At the end of the reaction under step (I) or as step (I) proceeds, HFSI is separated from the other components of such a mixture (M1 ) by suitable methods. For example, HFSI can be separated by condensation. According to this embodiment, HFSI is obtained as a liquid.

[0070] Preferably, such a separation step is performed such that the other gaseous products, such as HCI and HF, remain in the gas phase.

[0071] According to certain embodiments, the excess gaseous products, such as unreacted HF and HCI can be separated by any method known in the art, such as distillation or stripping.

[0072] More preferably, HF is advantageously recovered for reuse in the method of the present invention.

[0073] The embodiments described allow direct conversion of HCSI to HFSI with anhydrous HF in a high-atom efficiency approach that enables continuous fluorination with good to excellent yield and reduced environmental impact (mostly valorizable gaseous effluents).

[0074] The method according to the present invention advantageously provides a high conversion of HSCI to HFSI. More preferably, the residence time, temperature, pressure and other parameters are selected such that under step (I) of the method of the invention proceeds HCSI is converted into HFSI and the formation of undesired intermediate compounds, such as for exampleheavier intermediate compounds like (CI-SO2)NH(SO2-F), is avoided or limited as much as possible.

[0075] Advantageously, the residence time of the reactants HCSI and aHF can be properly selected so that yields above 90%, preferably above 95%, and more preferably above 99% are obtained.

[0076] The HFSI isolated after the end of the reaction may include some impurities, such as fluorosulfuric acid. Such fluorosulfuric acid can be in an amount up to 5% by moles. In preferred embodiments of the present invention, the amount of impurities in HFSI is lower than 2% by moles and even more preferably lower than 0.5% by moles.

[0077] Furthermore, the method according to the present invention advantageously provides HFSI with a high level of conversion and selectivity, in a molar yield which may be as high as > 90%, and even higher than 99%, which makes it particularly suited for many applications, notably as an intermediate to prepare LiFSI used in battery applications.

[0078] A further advantage of the present invention is that the above mentioned high level of conversion and high level of selectivity are obtained without the need to add catalyst(s), thus reducing the operating costs and expenses of the process.

[0079] Advantageously, the method of the present invention is carried out in the absence of added catalyst, such as cobalt oxides, nickel oxides, molybdenum oxides and mixtures thereof, which can be supported or not supported for example on silica, alumina or active charcoal. This leads to a more sustainable and economically viable process.

[0080] Thus, more advantageously, the method of the present invention is carried out in the absence of any liquid organic solvent, in the absence of any added gas and in the absence of any catalyst.

[0081] If required, the HFSI obtained at the end of step (I) can be purified to produce a high-purity HFSI.

[0082] Such purification step is not limited and can be performed via techniques such as distillation or crystallisation.

[0083] All raw materials used in the method according to the invention, including reactants, may preferably show very high purity criteria. Preferably, their content of metal components such as Na, K, Ca, Mg, Fe, Cu, Cr, Ni, Zn, is below 10 ppm, more preferably below 5 ppm, or below 2 ppm.

[0084] The HFSI as obtained at the end of the process of the present invention can be advantageously used as such for other reactions.

[0085] HFSI obtained by the process of the present invention may also be salified by subjecting it to a cation exchange step in order to obtain alkali metal salts, alkaline-earth metal salts or a quaternary ammonium cation salt.

[0086] Consistently, the present invention further pertains to a method of making an alkali metal salt, an alkaline-earth metal salt or a quaternary ammonium cation salt of HFSI, said method comprising: step (I) of contacting vaporized or gaseous bis(chlorosulfonyl)imide (HCSI) with hydrogen fluoride (HF), thus obtaining HFSI; optionally, step (II) of separating the HFSI obtained in step (I); optionally, step (III) of purifying the HFSI obtained in step (I) or (II); and step (IV) of salifying the HFSI obtained at the end of step (I), (II) or (III), wherein said method is carried out in the absence of liquid solvent and in the absence of gases different from HF; and said step (IV) is performed with a salt selected from lithium, sodium, potassium or ammonium.

[0087] According to a preferred embodiment, HFSI is salified with a lithium salt, a sodium salt or a potassium salt. Preferably, HFSI is salified with a lithium salt to provide direct lithiation of HFSI to lithium bis(fluorosulfonyl)imide (LiFSI), suitable for use in secondary batteries the person skilled in the art.

[0088] Advantageously, the lithium bis(fluorosulfonyl)imide (LiFSI) prepared according to the method of the present invention can be used in an electrolyte composition for an electrochemical cell.

[0089] In a further aspect, the present invention pertains to an electrolyte composition comprising the LiFSI as obtained with the method of the presentinvention. Advantageously, said electrolyte composition is a non-aqueous electrolyte composition.

[0090] Some of the steps or all steps of the method according to the invention are advantageously carried out in equipment capable of withstanding the corrosion of the reactants, reaction medium and products.

[0091] For this purpose, materials are selected for the part in contact with the reaction medium that are corrosion-resistant, such as the alloys based on molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminium, carbon and tungsten, sold under the Hastelloy® brands or the alloys of nickel, chromium, iron and manganese to which copper and / or molybdenum are added, sold under the name Inconel® or Monel™, and more particularly the Hastelloy C276 or Inconel 600, 625 or 718 alloys. Use may also be made of equipment consisting of or coated with a polymeric compound resistant to the corrosion of the reaction medium. Mention may in particular be made of fluorinated polymers, such as PTFE (polytetrafluoroethylene or Teflon(R)), PFA (perfluoroalkyl resins), FEP (fluorinated ethylene propylene), PCTFE (polychlorotrifluoroethylene). Glass and glass-lined as well as enamel equipment may also be used. Furthermore, corrosion-resistant silicon carbide (or SiC) materials can be advantageously used. It will not be outside the scope of the invention to use an equivalent material (tungsten carbide, etc).

[0092] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Claims

Claims1 . A method for manufacturing bis(fluorosulfonyl)imide (HFSI), said method comprising: step (I) of contacting gaseous bis(chlorosulfonyl)imide (HCSI) with hydrogen fluoride (HF), thus obtaining HFSI; wherein said step (I) is carried out at a pressure below atmospheric pressure, in the absence of liquid solvent(s) and in the absence of gases other than HCSI and HF.

2. The method according to Claim 1 , wherein the HFSI obtained at the end of step (I) is in the gas phase.

3. The method according to any one of the preceding Claims, wherein said HF is anhydrous (aHF).

4. The method according to any one of the preceding Claims, wherein said HF is in the gas phase, partially vaporized or in the liquid phase.

5. The method according to any one of the preceding Claims, wherein HCSI in the gas phase is obtained from solid HCSI or molten HCSI.

6. The method according to Claim 5, wherein HCSI in the gas phase is obtained from solid HCSI and the method comprises before step (I), a step (0-a) of providing solid HCSI and a step (0-b) of melting said solid HCSI to a temperature above its melting temperature (TrriHcsi) to obtain HCSI in a molten state.

7. The method according to Claim 5, wherein HCSI in the gas phase is obtained from molten HCSI and the method comprises before step (I), a step (0-b*) of providing molten HCSI and a step (0-c) of heating the HCSI provided in step(0-b*) to obtain gaseous HCSI.

8. The method according to Claim 7, wherein said step (0-c) of heating is performed at a temperature from 35°C and / or up to 200°C.

9. The method according to any one of the preceding Claims, wherein step (I) is performed at a pressure from 1 mbar abs (100 Pa) to 1013 mbar abs (0.1013 MPa), more preferably from 2 mbar abs (200 Pa) to 750 mbar abs (0.0750 MPa) and even more preferably from 5 mbar abs (500 Pa) to 500 mbar abs (0.0500 MPa).

10. The method according to any one of the preceding Claims, wherein step (I) is performed in a reactor selected from reactive distillation column.11 .The method according to any one of the preceding Claims, said method comprising at the end of step (I) or as step (I) proceeds, a step (II) of separating HFSI.

12. The method according to Claim 11 , wherein said separation of HFSI is performed by condensation and HFSI is obtained in the liquid phase.

13. The method according to any one of the preceding Claims, said method comprising after step (I) and / or after step (II), a step (III) of purification, preferably performed by distillation or crystallisation.

14. A method for manufacturing a salt of bis (fluorosulfonyl) imide, said method comprising: step (I) of contacting vaporized or gaseous bis(chlorosulfonyl)imide (HCSI) with hydrogen fluoride (HF), thus obtaining HFSI; optionally, step (II) of separating the HFSI obtained in step (I); optionally, step (III) of purifying the HFSI obtained in step (I) or (II); andstep (IV) of salifying the HFSI obtained at the end of step (I), (II) or (III), wherein said method is carried out in the absence of liquid solvent and in the absence of gases different from HF; and said step (IV) is performed with a salt selected from lithium, sodium, potassium or ammonium.

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