FR3081725A1 - PROCESS FOR THE PURIFICATION OF A LITHIUM BIS (FLUOROSULFONYL) IMIDE SALT - Google Patents

Abstract

The present invention relates to a process for purifying a lithium salt of bis (fluorosulfonyl) imide in solution in a composition C1 comprising at least one solvent S1, said process comprising at least one step of continuous liquid-liquid extraction.

Description

FIELD OF THE INVENTION

The present invention relates to a process for the purification of a lithium salt of bis (fluorosulfonyl) imide.

TECHNICAL BACKGROUND

The sulfonylimide anions, by their very low basicity, are increasingly used in the field of energy storage in the form of inorganic salts in batteries, or organic salts in super capacitors or in the field of liquids ionic. The battery market is booming and the reduction of battery manufacturing costs becoming a major issue, a large-scale and low-cost synthesis process of this type of anions is necessary.

In the specific field of Li-ion batteries, the salt currently used most is LiPFe but this salt shows many disadvantages such as limited thermal stability, sensitivity to hydrolysis and therefore lower battery safety. Recently, new salts with the FSO2 group ^- have been studied and have demonstrated many advantages such as better ionic conductivity and resistance to hydrolysis. One of these salts, LiFSI (LiN (FSO2) 2) has shown very interesting properties which make it a good candidate for replacing LiPFe.

The identification and quantification of impurities in salts and / or electrolytes, and the understanding of their impacts on battery performance become essential. For example, impurities with a mobile proton, due to their interference with electrochemical reactions, lead to lower overall performance and stability of Li-ion batteries. The application of Li-ion batteries requires having high purity products (minimum of impurities).

Various methods for purifying LiFSI are known. However, these methods have several drawbacks: use of a large quantity of solvents, bulky equipment, high number of equipment, risk of hydrolysis of LiFSI into sulphates, high investment cost on an industrial scale, ...

There is therefore a need for a process for purifying the lithium salt of bis (fluorosulfonyl) imide which makes it possible to remedy, at least in part, at least one of the above-mentioned drawbacks.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the purification of a lithium salt of bis (fluorosulfonyl) imide in solution in a composition C1 comprising at least one solvent S1, said process comprising at least one step of continuous liquid-liquid extraction.

The process for purifying the lithium salt of bis (fluorosulfonyl) imide according to the invention advantageously comprises a step of continuous liquid-liquid extraction with at least one extraction solvent to extract said lithium salt of bis (fluorosulfonyl) imide of the above-mentioned composition C1.

In the context of the invention, the terms "lithium salt of bis (fluorosulfonyl) imide", "lithium bis (sulfonyl) imide", "LiFSI", "LiN (FSO2) 2", "lithium are used in an equivalent manner. of bis (sulfonyl) imide ", or" bis (fluorosulfonyl) imide of lithium ".

The extraction solvent can be an aqueous solvent or an organic solvent.

The liquid-liquid extraction step can be carried out with a mixture of solvents, such as for example a mixture of an aqueous solvent and one or more organic solvent (s), or a mixture of solvents different organic.

According to one embodiment, the extraction solvent is water, preferably deionized water.

In the context of the invention, the terms "deionized water" and "demineralized water" are used in an equivalent manner.

According to another embodiment, the extraction solvent is an organic solvent, chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and their mixtures. For example, mention may be made of diethylcarbonate, dimethylcarbonate, ethyl methyl carbonate, methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, methyl acetate, acetate butyl, methyl propionate, dichloromethane, tetrahydrofuran, acetonitrile, diethyl ether, and mixtures thereof. Preferably, the extraction solvent is chosen from ethers, esters and their mixtures, and preferably the extraction solvent is chosen from methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate, butyl acetate, and mixtures thereof.

The purification process according to the invention may also comprise one or more additional steps of liquid-liquid extraction which may or may not be carried out continuously.

The continuous liquid-liquid extraction step can be carried out in an extractor chosen from the extraction columns, and the mixer-settlers.

In the context of the invention, the term “extractor” is understood to mean equipment enabling liquid-liquid extraction to be carried out.

Mixer-settlers are well known to those skilled in the art. It is typically a single device comprising a mixing chamber and a settling chamber, the mixing chamber comprising a stirring wheel advantageously allowing the mixing of the two liquid phases. In the settling chamber, the phases are separated by gravity.

The decanter chamber can be supplied from the mixer chamber by overflow, by the bottom of the mixing chamber, or by a perforated wall between the mixer chamber and the decanter chamber.

The extraction column can include:

at least one packing such as for example a loose packing and / or a structured packing. These can be Rashig Rings, Pali Rings, Saddle Rings, Berl Saddles, Intalox Saddles, or Balls;

and / or trays such as, for example, perforated trays, fixed flap trays, movable flap trays, domed trays, or combinations thereof;

and / or devices for atomizing from one phase to another, such as for example nozzles

In the context of the invention, the term "packing" means a solid structure capable of increasing the contact surface between the two liquids brought into contact.

The height and / or diameter of the extraction column typically depends on the nature of the liquids to be separated.

The extraction column can be static or agitated. Preferably, the extraction column is agitated, preferably mechanically. It includes for example stirring mobiles fixed on an axial rotary shaft. Among the stirring mobiles, mention may be made, for example, of turbines (for example straight blade turbines known as Rushton's or curved blade turbines or turbines with curved blades), propellers (for example propellers with profiled blades), discs, and combinations thereof. The agitation advantageously allows the formation of fine droplets to disperse one liquid phase in the other, and thus increase the interfacial exchange area. Preferably, the stirring speed is chosen so as to maximize the interfacial exchange area.

The extraction column may also include baffles integral with the side walls of said column. Baffling advantageously makes it possible to limit the phenomenon of axial mixing.

Preferably, the extraction column is a counter-current liquid-liquid extraction column. In particular, the liquid phase having the lowest density is fed into the lower part of the extraction column while the liquid phase having the highest density is introduced into the upper part of the extraction column.

The extraction column may include a still area, located above the feed point of the phase with the highest density, to collect a "light" phase, and a still area located below the feeding point of the phase with the lowest density, to collect a "heavy" phase.

According to a preferred embodiment, the above-mentioned method comprises:

(i) a step comprising at least one liquid-liquid extraction of LiFSI from composition C1 with at least one extraction solvent SE1 making it possible to recover a raffinate Ri. _o comprising the solvent S1, and an extract E1.0 comprising LiFSI and the extraction solvent SE1;

(ii) a step comprising at least one liquid-liquid extraction of the extract E1.0, with at least one extraction solvent SE2, making it possible to recover a raffinate R2.0 comprising the extraction solvent SE1, and an extract E2.0 comprising LiFSI and the extraction solvent SE2;

at least one of steps (i) or (ii) comprising a liquid-liquid extraction carried out continuously.

According to one embodiment, the method according to the invention comprises:

(i) a step comprising:

at least one liquid-liquid extraction of LiFSI from composition C1 with at least one extraction solvent SE1 making it possible to recover a raffinate R1.0 comprising the solvent S1, and an extract E1.0 comprising LiFSI and the solvent for SE1 extraction, the liquid-liquid extraction being able to be repeated n times, with n ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a raffinate Ri.n and to an extract Ei. _n , each liquid-liquid extraction being carried out from the raffinate obtained in the previous extraction Ri, _n -i „in the event of repetition, step (i) comprises gathering E1.0 with each of the extracts formed to form an extract E, (ii) a step comprising:

at least one liquid-liquid extraction of the extract obtained in step (i), with at least one extraction solvent SE2, making it possible to recover a raffinai R2.0 comprising the extraction solvent SE1, and an extract E2 .0 comprising LiFSI and the extraction solvent SE2;

the liquid-liquid extraction being able to be repeated m times, with m ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a refinement R2.m and to an extract E2.n1, each liquid-liquid extraction being made from the raffinai obtained at the previous extraction R2. _m -i, in the event of repetition, step (ii) comprises gathering E2.0 with each of the extracts formed to obtain an extract E ';

at least one of steps (i) or (ii) comprising a liquid-liquid extraction carried out continuously.

According to one embodiment, the method is such that:

step (i) comprises one or more liquid-liquid extractions carried out continuously; or step (ii) comprises one or more liquid-liquid extractions carried out continuously; or each of steps (i) and (ii) comprises one or more liquid-liquid extractions carried out continuously.

Preferably, the method is such that:

all the liquid-liquid extractions of step (i) are carried out continuously; or all the liquid-liquid extractions of step (ii) are carried out continuously; or all the liquid-liquid extractions of step (i) and of step (ii) are carried out continuously.

According to one embodiment, the method according to the invention is such that:

(1) the liquid-liquid extraction of step (i) is carried out in a continuous extraction column, preferably against the current, and the extraction (extractions) of step (ii) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous);

(2) the liquid-liquid extraction of stage (i) is carried out in a continuous extraction column, preferably against the current, and the liquid-liquid extraction of stage (ii) is carried out in a continuous extraction column;

(3) the extraction (extractions) of step (i) is (are) performed (s) by means of several mixer-settlers in series (continuous or discontinuous); and the liquid-liquid extraction of step (ii) is carried out in a continuous extraction column, preferably against the current;

(4) the extraction (extractions) of step (i) is (are) performed (s) using several mixer-settlers in series (continuous or discontinuous); and the extraction (extractions) of step (ii) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous), at least one extraction being carried out continuous.

Step (i)

The liquid-liquid extraction of step (i) advantageously allows the transfer of the LiFSI from the composition C1 comprising the solvent S1 to the extraction solvent SE1. The R1.0 raffinate is advantageously depleted in LiFSI (compared to the initial composition C1), while the Ei .o extract is advantageously enriched in LiFSI (compared to the initial extraction solvent SE1). Ri. _o corresponds in particular to the initial composition C1 but depleted in LiFSI.

The liquid-liquid extraction in step (i) can be repeated n times, with n ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a raffinate Ri. _n and to an extract Ei. _n , each liquid-liquid extraction being carried out from the raffinate obtained in the preceding extraction Ri. _n -i For example, if n = 1, a liquid-liquid extraction of the LiFSI is carried out from the raffinate Ri. _o , with the extraction solvent SE1 to lead to a raffinate Ru comprising the solvent S1, and an extract Ei.1 comprising LiFSI and the extraction solvent SE1. The Ru raffinate is advantageously depleted in LiFSI (compared to the initial Ri. _O raffinate), while the extract E1.0 is advantageously enriched in LiFSI (compared to the extraction solvent SE1 used in this extraction). For example, if n = 2, a first liquid-liquid extraction of the LiFSI is carried out from the raffinate Ri. _o , with the extraction solvent SE1 to lead to a raffinate Ru comprising the solvent S1, and an extract Ei.1 comprising LiFSI and the extraction solvent SE1. Then, a second liquid-liquid extraction of the LiFSI is carried out from the raffinate Ru, with the extraction solvent SE1 to yield a raffinate R1.2 comprising the solvent S1, and an extract E1.2 comprising the LiFSI and the solvent d SE1 extraction. The raffinate R1.2 is advantageously depleted in LiFSI (compared to the initial Ru raffinate), while the extract E1.2 is advantageously enriched in LiFSI (compared to the extraction solvent SE1 used in this extraction).

When the liquid-liquid extraction of step (i) is repeated n times, step (i) comprises, at the end of the liquid-liquid extractions, the collection of E1.0 with each of the extracts formed (for example Eu if n = 1, Eu and E1.2 if n = 2 ...) to obtain a single extract E.

The liquid-liquid extraction of step (ii) can be carried out on the extract obtained in step (i), namely:

E1.0 if the extraction of step (i) is not repeated, or E if the liquid-liquid extraction of step (ii) is repeated.

The Ri refinery can comprise a LiFSI mass content of less than or equal to 40% by mass, preferably between 10% and 40%, advantageously between 10% and 35% relative to the total mass of said Ri refinery. _o .

The Ei extract can contain a mass content of LiFSI greater than or equal to 10% by mass, preferably between 10% and 50%, advantageously between 10% and 40% relative to the total mass of said extract E1.0.

The Ru refinery may comprise a mass content of LiFSI less than or equal to 35% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said Ru refinery.

The Eu extract may comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 5% and 30% relative to the total mass of said Eu extract.

The Rup refinery may comprise a mass content of LiFSI less than or equal to 30% by mass, preferably between 1% and 30%, advantageously between 1% and 25% relative to the total mass of said refinery R1.2.

The extract Ei. ₂ may comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said extract E1.2.

The R1.3 raffinai may comprise a mass content of LiFSI less than or equal to 25% by mass, preferably between 1% and 25%, advantageously between 1% and 20% relative to the total mass of said R1.3 raffinai.

The extract can contain a mass content of LiFSI greater than or equal to 2% by mass, preferably between 2% and 30%, advantageously between 2% and 25% relative to the total mass of said extract E1.3.

The refinery Ri. _n with n strictly greater than 3 may comprise a mass content of LiFSI less than or equal to 15% by mass, preferably between 0.5% and 15%, advantageously between 0.5% and 10% relative to the total mass of said refinery Ri. _n .

Extract E may comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 10% and 30% relative to the total mass of said extract E.

Each of the liquid-liquid extraction (s) of step (i) can (wind) be carried out: at a temperature ranging from 5 to 50, preferably from 10 to 30, and in particular the temperature is room temperature (23 ° C);

and / or at a pressure ranging from 0.5 to 3 bar abs, preferably from 0.5 to 2 bar abs, and in particular the pressure is atmospheric pressure.

The composition C1 mentioned above can comprise LiFSI in a mass content ranging from 5% to 55%, preferably from 5% to 50%, preferably from 10% to 55%, advantageously from 10% to 50%, for example from 10% to 40%, in particular from 15% to 40%, and preferably from 25% to 35% by mass, relative to the total mass of the composition C1.

The above-mentioned composition C1 can comprise the solvent S1 in a mass content greater than or equal to 45%, preferably ranging from 45% to 95%, preferably from 50% to 95%, preferably from 45% to 90%, advantageously from 50 % to 90%, for example from 60% to 90%, in particular from 60% to 85%, and preferably from 65% to 75% by mass, relative to the total mass of the composition C1.

Composition C1 comprising the lithium salt of bis (fluorosulfonyl) imide can come from any synthesis of the lithium salt of bis (fluorosulfonyl) imide, comprising in particular the following steps:

i) synthesis of bis (chlorosulfonyl) imide;

ii) fluorination of bis (chlorosulfonyl) imide to bis (fluorosulfonyl) imide;

iii) preparation of an alkaline or alkaline earth salt of bis (fluorosulfonyl) imide by neutralization of bis (fluorosulfonyl) imide;

iv) cation exchange to obtain the lithium salt of the bis (fluorosulfonyl) imide.

At the end of these steps, the lithium salt of the bis (fluorosulfonyl) imide is preferably obtained in solution in a solvent (corresponding in particular to solvent S1), at a mass concentration of between 5% and 55% by mass per relative to the total mass of the solution.

Such a method is for example described in document WO 2015/158979.

Composition C1 can also comprise ionic impurities resulting from the preparation process used, such as for example alkali or alkaline earth ions and chloride ions.

The liquid-liquid extraction of step (i) advantageously allows the transfer of the LiFSI and any ionic impurities from the composition C1 comprising the solvent S1 to the extraction solvent SE1. The raffinate Ri. _o is advantageously depleted in LiFSI (compared to the initial composition C1), while the extract Ei.o is advantageously enriched in LiFSI and any ionic impurities (compared to the initial extraction solvent SE1). The same applies advantageously in the case of repetition of the liquid-liquid extraction n times, namely that the Ri. _n is advantageously depleted in LiFSI (relative to the composition Ri _n -i), while the extract Ei. _n is advantageously enriched in LiFSI and any ionic impurities (relative to the extraction solvent SE1 used in the extraction).

According to one embodiment, the solvent S1 mentioned above is chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and their mixtures. Preferably, the solvent S1 is chosen from dichloromethane, ethyl acetate, butyl acetate, tetrahydrofuran, acetronitrile, diethyl ether, and their mixtures. Preferably, the organic solvent S1 is butyl acetate.

The liquid-liquid extraction (s) of step (i) above can be carried out with an extraction solvent SE1 or a mixture of extraction solvents SE1.

The extraction solvent SE1 is advantageously chosen so that:

to be immiscible with the solvent S1 of the initial composition C1 in which LiFSI is in solution; and / or that LiFSI and any ionic impurities are soluble therein; and / or to have a density different from the solvent S1.

By "immiscible" is meant solvents which do not mix and which form a heterogeneous mixture characterized by the formation of 2 distinct liquid phases, the liquid phase with the lowest density being located above the other.

The extraction solvent SE1 can be chosen from an aqueous solvent, and an organic solvent chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. For example, mention may be made of diethylcarbonate, dimethylcarbonate, ethyl methyl carbonate, methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, methyl acetate, acetate butyl, methyl propionate, dichloromethane, tetrahydrofuran, acetonitrile, diethyl ether, and mixtures thereof.

Preferably, the extraction solvent SE1 is an aqueous solvent, preferably deionized water.

The liquid-liquid extraction of step (i) can be carried out in an extractor as defined above, namely an extraction column or a mixer-decanter in particular as defined above.

According to one embodiment, at least one liquid-liquid extraction of step (i) is carried out in an extraction column.

According to one embodiment, at least one liquid-liquid extraction of step (i) is carried out in a mixer-settler. Preferably, in this case, the liquid-liquid extraction is repeated n times, advantageously in several mixer-settlers in series. The transfer between each mixer-settler can be done by pump or by the effect of gravity.

The mass ratio of extraction solvent SE1 / composition C1 can range from 0.5 to 5.0, preferably from 0.5 to 4.0, and advantageously from 0.5 to 3.0 It is the mass ratio at the start of the extraction, namely at the input d 'extractor.

The mass solvent extraction ratio SEI / R1.0 can range from 0.1 to 3.0, preferably from 0.2 to 2.5, and advantageously from 0.2 to 2.0; and / or the extraction solvent mass ratio SEI / R1.1 may preferably range from 0.2 to 2.5, and advantageously from 0.2 to 2.0; and / or the SEI / R1.2 extraction solvent mass ratio may preferably range from 0.2 to 2.5, and advantageously from 0.2 to 2.0; and / or the extraction solvent mass ratio SEI / R1.3 may preferably range from 0.2 to 2.5, and advantageously from 0.2 to 2.0.

The liquid-liquid extraction of step (i) can be carried out in

0.1

0.1

0.1 a

3,0,

3,0,

3.0, from counter-current extraction column.

According to one embodiment, when the liquid-liquid extraction of step (i) is carried out in a counter-current extraction column, the composition C1 comprising LiFSI and the solvent S1, is notably supplied in the lower part of the column, while the extraction solvent SE1 is in particular supplied in the upper part of said column. The extract E1.0 obtained is in particular collected in the lower part of said column, in particular in a tranquilization zone located below the feed point of composition C1; while the raffinate Ri.o is in particular collected in the upper part of said column, in particular in a tranquilization zone situated above the feed point of the extraction solvent SE1.

Each liquid-liquid extraction of step (i) can lead to an extract comprising at least 25%, preferably at least 30%, preferably at least 35%, more preferably at least 40%, and advantageously at least 45%, and in particular at least 50% of the mass of LiFSI initially present in the initial composition (before said extraction).

For example :

the liquid-liquid extraction of step (i) from composition C1 leads to an extract E1.0 comprising at least 25%, preferably at least 30%, preferably at least 35%, more preferably at least 40%, and advantageously at least 45%, and in particular at least 50% of the mass of LiFSI initially present in composition C1;

- the liquid-liquid extraction of step (i) from the raffinate Ri. _o leads to an Eu extract comprising at least 25%, preferably at least 30%, preferably at least 35%, more preferably at least 40%, and advantageously at least 45%, and in particular at least 50% of the mass of LiFSI initially present in Ri. _o .

The method according to the invention may include an additional step of concentrating the extract obtained in step (i) (Ei.oor E), between step (i) and step (ii). In this particular case, step (ii) is carried out on the concentrated extract. The concentration step can be carried out by any means of evaporation known to a person skilled in the art, for example with an evaporator under reduced pressure, at a pressure of less than 50 mbar abs (preferably less than 30 mbar abs), and / or at a temperature between 25 ° C and 60 ° C, preferably between 25 ° C and 50 ° C, preferably between 30 ° C and 45 ° C, for example at 40 ° C.

Step (ii)

The liquid-liquid extraction of step (ii) advantageously allows the transfer of the LiFSI from the extract E1.0 comprising the extraction solvent SE1 to the extraction solvent SE2. The R2.0 raffinate is advantageously depleted in LiFSI (compared to the initial E1.0 or initial E composition), while the extract E2.0 is advantageously enriched in LiFSI (compared to the initial SE2 extraction solvent).

The liquid-liquid extraction in step (ii) can be repeated m times, with m ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a R2 raffinate. _m and to an extract E2.n1, each liquid-liquid extraction being carried out from the raffinate obtained in the previous extraction R2. _m -i. For example, if m = 1, a liquid-liquid extraction of the LiFSI is carried out from the raffinate R2.0 comprising the solvent SE1, with the extraction solvent SE2 to yield a raffinate R2.1 comprising the solvent SE1, and an extract E2.1 comprising LiFSI and the extraction solvent SE2. The raffinate R2.1 is advantageously depleted in LiFSI (compared to the initial raffinate R2.0), while the extract E2.1 is advantageously enriched in LiFSI (compared to the extraction solvent SE2 used in this extraction). For example, if m = 2, a first liquid-liquid extraction of the LiFSI is carried out from the raffinate R2.0, with the extraction solvent SE2 to lead to a raffinate R2.1 comprising the solvent S1, and an extract E2 .1 including LiFSI and extraction solvent SE2. Then, a second liquid-liquid extraction of LiFSI is carried out from the raffinai R ₂ .i, with the extraction solvent SE2 to yield a raffinai R2.2 comprising the solvent S1, and an extract E2.2 comprising the LiFSI and the solvent SE2 extraction. The raffinai R2.2 is advantageously depleted in LiFSI (compared to the initial raffinai R2.1), while the extract E2.2 is advantageously enriched in LiFSI (compared to the extraction solvent SE2 used in this extraction).

When the liquid-liquid extraction of step (ii) is repeated m times, step (ii) comprises, at the end of the liquid-liquid extractions, the gathering of E2.0 with each of the extracts formed (for example E2 .1 if m = 1, E2.1 and E2.2 if m = 2 ...) to obtain a single extract E '.

The raffinate R2.0 may comprise a mass content of LiFSI less than or equal to 50% by mass, preferably between 10% and 50%, advantageously between 10% and 45% relative to the total mass of said raffinate R2.0.

The extract E2.0 may comprise a mass content of LiFSI greater than or equal to 10% by mass, preferably between 10% and 50%, advantageously between 10% and 40% relative to the total mass of said extract E ₂ . o.

The raffinate R2.1 may comprise a mass content of LiFSI less than or equal to 45% by mass, preferably between 10% and 45%, advantageously between 10% and 40% relative to the total mass of said raffinate R2.1.

The extract E2.1 can comprise a mass content of LiFSI greater than or equal to 10% by mass, preferably between 10% and 40%, advantageously between 10% and 30% relative to the total mass of said extract E2.1 .

The raffinate R2.2 can comprise a mass content of LiFSI less than or equal to 40% by mass, preferably between 5% and 40%, advantageously between 5% and 35% relative to the total mass of said raffinate R2.2.

The extract E ₂ .2 can comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 30%, advantageously between 5% and 25% relative to the total mass of said extract E2.2 .

The raffinate R2.3 can comprise a mass content of LiFSI less than or equal to 35% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said raffinate R2.3.

The extract E2.3 may comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 25%, advantageously between 5% and 20% relative to the total mass of said extract E2.3 .

The R2 raffinate. _m with m strictly greater than 3 may comprise a mass content of LiFSI less than or equal to 20% by mass, preferably between 1% and 20%, advantageously between 1% and 15% relative to the total mass of said raffinate R2. _m .

Extract E ’can comprise a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 5% and 30% relative to the total mass of said extract E’.

Each of the liquid-liquid extraction (s) of step (ii) can (wind) be carried out: at a temperature ranging from 5 to 50, preferably from 10 to 30, and in particular the temperature is room temperature (23 ° C);

and / or at a pressure ranging from 0.5 to 3 bar abs, preferably from 0.5 to 2 bar abs, and in particular the pressure is atmospheric pressure.

The liquid-liquid extraction (s) of step (ii) above can be carried out with an extraction solvent SE2 or a mixture of extraction solvents SE2.

The extraction solvent SE2 is advantageously chosen so as to be immiscible with the solvent SE1 of the extract Ei.o (or E) in which LiFSI is in solution, and / or have a density different from that of SE1.

The extraction solvent SE2 can be an organic solvent, preferably chosen from the group consisting of esters, nitriles, ethers, cycloalkanes, chlorinated solvents, aromatic solvents, and mixtures thereof. For example, mention may be made of diethylcarbonate, dimethylcarbonate, ethyl methyl carbonate, methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, methyl acetate, acetate butyl, methyl propionate, dichloromethane, tetrahydrofuran, acetonitrile, diethyl ether, cyclohexane, and mixtures thereof.

Preferably, the extraction solvent SE2 is an organic solvent chosen from diethylcarbonate, dimethylcarbonate, ethylmethyl carbonate, methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate , methyl acetate butyl acetate, methyl propionate, dichloromethane, tetrahydrofuran, acetronitrile, diethyl ether, cyclohexane, and mixtures thereof. In particular, the extraction solvent SE2 is butyl acetate or a mixture of butyl acetate and cyclohexane, preferably the extraction solvent SE2 is butyl acetate.

The liquid-liquid extraction of step (ii) can be carried out in an extractor as defined above, namely an extraction column or a mixer-decanter in particular as defined above.

According to one embodiment, at least one liquid-liquid extraction of step (ii) is carried out in an extraction column, preferably against the current.

According to one embodiment, at least one liquid-liquid extraction of step (ii) is carried out in a mixer-settler. Preferably, in this case, the liquid-liquid extraction is repeated m times, advantageously in several mixer-settlers in series. The transfer between each mixer-settler can be done by pump or by the effect of gravity.

The extraction solvent SE2 / E1.0 (or SE2 / E) mass ratio can range from 0.1 to 2, preferably from 0.1 to 1.5 and advantageously from 0.1 to 1. mass ratio at the start of the extraction, namely at the extractor inlet.

According to one embodiment, when the liquid-liquid extraction of step (ii) is carried out in a counter-current extraction column, the extract E1.0 (or E) comprising LiFSI and the solvent SE1, is notably supplied in the upper part of the column, while the extraction solvent SE2 is in particular supplied in the lower part of said column. The extract E2.0 obtained is in particular collected in the upper part of said column, in particular in a tranquilization zone situated above the feed point of the extract Ei.o (or E); while the Fù.o raffinate is collected in particular in the lower part of said column, in particular in a tranquilization zone located below the feed point of the extraction solvent SE2.

Each liquid-liquid extraction of step (ii) can lead to an extract comprising at least 30%, preferably at least 35%, preferably at least 40%, more preferably at least 45%, and advantageously at least 50% of the mass of LiFSI initially present in the initial composition (before said extraction).

For example :

the liquid-liquid extraction of step (ii) from the extract Ei.o (or E) leads to an extract E2.0 comprising at least 20%, preferably at least 25%, preferably at least 30%, more preferably at least 35%, and advantageously at least 40% of the mass of LiFSI initially present in the extract Ei.o (or E);

the liquid-liquid extraction of step (ii) from the raffinate R2.0 leads to an extract E2.1 comprising at least 20%, preferably at least 25%, preferably at least 30%, more preferably at at least 35%, and advantageously at least 40% of the mass of LiFSI initially present in R2.0.

Step (Hi)

According to one embodiment, the method according to the invention comprises:

(i) a step comprising:

at least one liquid-liquid extraction of LiFSI from composition C1 with at least one extraction solvent SE1 making it possible to recover a refinery Ri. _o comprising the solvent S1, and an extract E1.0 comprising LiFSI and the extraction solvent SE1, the liquid-liquid extraction being able to be repeated n times, with n ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a refinement Ri.n and to an extract Ei. _n , each liquid-liquid extraction being carried out from the raffinai obtained in the previous extraction Ri. _n -i „in the event of repetition, step (i) comprises gathering E1.0 with each of the extracts formed to obtain an extract E, (ii) a step comprising:

at least one liquid-liquid extraction of the extract obtained in step (i), with at least one extraction solvent SE2, making it possible to recover a raffinai R2.0 comprising the extraction solvent SE1, and an extract E2 .0 comprising LiFSI and the extraction solvent SE2;

the liquid-liquid extraction being able to be repeated m times, with m ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a refinement R2.m and to an extract E2.n1, each liquid-liquid extraction being made from the raffinai obtained at the previous extraction R2. _m -i, in the event of repetition, step (ii) comprises gathering E2.0 with each of the extracts formed to obtain an extract E ';

(iii) a step comprising:

at least one liquid-liquid extraction of the extract obtained in step (ii), with at least one extraction solvent SE3, making it possible to recover a raffinai R3.0 comprising LiFSI and the extraction solvent SE2, and a extract E3.0 comprising the extraction solvent SE1 and the extraction solvent SE3;

the liquid-liquid extraction being able to be repeated p times, with p ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a refinement Rs.p and to an extract Es. _P , each liquid-liquid extraction being carried out from the raffinai obtained in the preceding extraction R3.P-1, in the event of repetition, step (iii) comprises gathering E3.0 with each of the extracts formed to obtain an extract E ”;

at least one of steps (i) or (ii) comprising a liquid-liquid extraction carried out continuously.

According to one embodiment, the method according to the invention is such that:

(1) the liquid-liquid extraction of step (i) is carried out in a continuous extraction column, preferably against the current, and the extractions of step (ii) and of step ( iii) are carried out by means of several mixer-settlers in series (continuous or discontinuous); or (2) the liquid-liquid extraction of step (i) is carried out in a continuous extraction column, preferably against the current, the liquid-liquid extraction of step (ii) is carried out in a continuous extraction column, preferably against the current, and the liquid-liquid extraction of step (iii) is carried out in a continuous extraction column, preferably against the current; or (3) the extraction (extractions) of step (i) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous), the liquid-liquid extraction of stage (ii) is carried out in a continuous extraction column, preferably against the current, and the liquid-liquid extraction of stage (iii) is carried out in a continuous extraction column, preference to countercurrent; or (4) the liquid-liquid extraction of step (i) is carried out in a continuous extraction column, preferably against the current, the liquid-liquid extraction of step (ii) is carried out in a continuous extraction column, preferably against the current, and the extractions of step (iii) are carried out by means of several mixer-settlers in series (continuous or discontinuous); or (5) the liquid-liquid extraction of step (i) is carried out in a continuous extraction column, preferably against the current, the extractions of step (ii) are carried out by means of several mixer-settlers in series (continuous or discontinuous), and the liquid-liquid extraction of step (iii) is carried out in a continuous extraction column, preferably against the current; or (6) the extraction (extractions) of step (i) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous), the liquid-liquid extraction of stage (ii) is carried out in a continuous extraction column, preferably against the current, and the extractions of stage (iii) are carried out by means of several mixer-settlers in series (continuous or in discontinuous);

(7) the extraction (extractions) of step (i) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous), the extractions of step (ii ) are carried out by means of several mixer-settlers in series (continuous or discontinuous), and the liquid-liquid extraction of step (iii) is carried out in a continuous extraction column, preferably against the current;

(8) the extraction (extractions) of step (i) is (are) carried out by means of several mixer-settlers in series (continuous or discontinuous), the extractions of step (ii ) are carried out by means of several mixer-settlers in series (continuous or discontinuous), and the extractions of step (iii) are carried out by means of several mixer-settlers in series (continuous or discontinuous, at least one extraction being performed continuously.

The liquid-liquid extraction (s) of step (iii) above can be carried out with an extraction solvent SE3 or a mixture of extraction solvents SE3.

The extraction solvent SE3 can be chosen from the group consisting of esters, nitriles, ethers, cycloalkanes, alkanes, chlorinated solvents, aromatic solvents, and mixtures thereof. For example, mention may be made of diethylcarbonate, dimethylcarbonate, ethylmethyl carbonate, methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate, methyl acetate acetate. butyl, methyl propionate, dichloromethane, tetrahydrofuran, acetronitrile, diethyl ether, cyclohexane, pentane, heptane, hexane, and mixtures thereof.

Preferably, the extraction solvent SE3 is an organic solvent, preferably chosen from diethylcarbonate, dimethylcarbonate, ethylmethyl carbonate, methyl-tbutyl ether, cyclopentylmethyl ether, ethyl acetate, acetate of propyl, methyl acetate butyl acetate, methyl propionate, dichloromethane, tetrahydrofuran, acetronitrile, diethyl ether, cyclohexane, pentane, heptane, hexane, and mixtures thereof. In particular, the extraction solvent SE3 is cyclohexane.

Process

The method according to the invention can also comprise an additional step of concentrating the extract obtained in step (ii) (E2.0 OR E ') and / or the raffinate obtained in step (iii) (R3.0 or Rs.p). In this particular case, any possible step subsequent to step (ii) is carried out on the concentrated extract.

The concentration step can be carried out by any means of evaporation known to a person skilled in the art, for example with an evaporator under reduced pressure.

The concentration step can be carried out at a pressure of less than 50 mbar abs (preferably less than 30 mbar abs), and / or at a temperature of between 25 ° C and

60 ° C, preferably between 25 ° C and 50 ° C, preferably between 30 ° C and 45 ° C, for example at 40 ° C.

The concentration step can be carried out in two stages, namely understanding:

a first concentration step carried out in an evaporator under reduced pressure; and a second concentration step carried out in a thin film evaporator with short path, under the following conditions:

- temperature between 30 ° C and 95 ° C, preferably between 30 ° C and 90 ° C, preferably between 40 ° C and 85 ° C;

- pressure between 10 ' ³ mbar abs and 5 mbar abs;

- residence time less than or equal to 15 min, preferably less than or equal to 10 min, and advantageously less than or equal to 5 min.

In the context of the invention, and unless otherwise stated, the term "residence time" means the time which elapses between the entry of the solution into the evaporator and the exit of the first drop of the solution.

The aforementioned short path thin film evaporators are also known by the name "Wiped film short path" (WFSP). They are typically called so because the vapors generated during evaporation make a "short trip" (short distance) before being condensed in the condenser. Among the short path thin film evaporators, we can notably mention the evaporators marketed by the companies Buss SMS Ganzler ex Luwa AG, LUC Gmbh or VTA Process.

The method according to the invention can also further comprise an additional step of purifying the extract obtained at the end of the above-mentioned step (ii) (E2.0 or E ', said E2.0 or E' possibly having has been subjected to a concentration step) or at the end of the above-mentioned step (iii) (R3.0 or Rs.p, said R3.0 or Rs. _P having possibly been subjected to a concentration step). The additional purification step can be carried out by any known conventional method. It may for example be a recrystallization step. Preferably, the recrystallization step is:

performed at a temperature less than or equal to 25 ° C; and / or produced in an organic solvent chosen from chlorinated solvents, such as for example dichloromethane, from alkanes such as pentane, hexane, cyclohexane, heptane, and aromatic solvents, such as for example toluene.

Preferably, the LiFSI crystallized at the end of the recrystallization step is recovered by filtration.

The method according to the invention advantageously allows better mass transfer of LiFSI from one liquid phase to another, which has the effect of minimizing the amount of solvents used. In addition, the method advantageously makes it possible to reduce the overall duration of the purification process, and to reduce the contact times between the solvents and the LiFSI. In particular, when one of the extraction solvents is water, the reduction in the amount of water and in the contact times with LiFSI, advantageously makes it possible to avoid the hydrolysis of said LiFSI and thus its contamination by sulfates. generated by hydrolysis. In addition, the method according to the invention advantageously makes it possible to minimize the size of the equipment used, as well as their number, which results in a simplification of the method and a lower investment cost. These advantages are all the more observed with the implementation of a liquid-liquid extraction in a continuous extraction column.

The method according to the invention advantageously leads to a LiFSI of high purity, and in particular comprising a reduced content of both water and sulphates. In particular, the method leads to a LiFSI having a purity at least equal to 99.5% by weight, advantageously at least equal to 99.95% by weight, and preferably at least equal to 99.99% and optionally comprising the impurities following in the contents indicated: 0 <H ₂ O <100 ppm (preferably 0 <H ₂ O <50 ppm), 0 <CI '<100ppm (preferably 0 <CI'<50 ppm), 0 <SO ₄ ² '<100 ppm (preferably 0 <SCU ² ^ 50 ppm), 0 <F'<20 ppm, 0 <FSO3L1 <20 ppm, 0 <FSO ₂ NH ₂ <5 ppm, 0 <K ⁺ <50 ppm, and 0 <Na ⁺ <80 ppm.

In the context of the invention, the term "ppm" means ppm by weight.

In the context of the invention, by "lying between x and y", or "ranging from x to y", is meant an interval in which the limits x and y are included. For example, the temperature "between 30 and 100 ° C." includes in particular the values 30 ° C. and 100 ° C.

All of the embodiments described above can be combined with each other. In particular, each embodiment of any stage of the process of the invention can be combined with another particular embodiment.

Claims (16)

1. Method for purifying a lithium salt of bis (fluorosulfonyl) imide in solution in a composition C1 comprising at least one solvent S1, said method comprising at least one step of continuous liquid-liquid extraction. 2. Method according to claim 1, in which the liquid-liquid extraction step is carried out in an extractor chosen from the extraction columns, and the mixer-settlers. 3. Method according to any one of claims 1 or 2, comprising: - (i) a step comprising at least one liquid-liquid extraction of the lithium salt of bis (fluorosulfonyl) imide from composition C1 with at least one extraction solvent SE1 making it possible to recover a raffinate Ri o comprising the solvent S1 , and an extract E ₁₀ comprising a lithium salt of bis (fluorosulfonyl) imide and the extraction solvent SE1; (i) a step comprising at least one liquid-liquid extraction of the extract Ei. _o , with at least one extraction solvent SE2, making it possible to recover a raffinate R2.0 comprising the extraction solvent SE1, and an extract E _{2 0} comprising the lithium salt of bis (fluorosulfonyl) imide and the solvent for SE2 extraction; at least one of steps (i) or (ii) comprising a liquid-liquid extraction carried out continuously. 4. Method according to any one of claims 1 to 3, comprising: (i) a step comprising: at least one liquid-liquid extraction of the lithium salt of bis (fluorosulfonyl) imide from composition C1 with at least one extraction solvent SE1 making it possible to recover a raffinate R1.0 comprising the solvent S1, and an extract E1 .0 comprising a lithium salt of bis (fluorosulfonyl) imide and the extraction solvent SE1, the liquid-liquid extraction can be repeated n times, with n ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a refinement Ri. _n and to an extract Ei. _n , each liquid-liquid extraction being carried out from the raffinai obtained in the preceding extraction Ri.ni., - in case of repetition, step (i) includes the gathering of Ei. _o with each of the extracts formed to form an extract E, (ii) a step comprising: at least one liquid-liquid extraction of the extract obtained in step (i), with at least one extraction solvent SE2, making it possible to recover a raffinate R ₂₀ comprising the extraction solvent SE1, and an extract E ₂₀ comprising the lithium salt of bis (fluorosulfonyl) imide and the solvent extraction SE2; the liquid-liquid extraction being able to be repeated m times, with m ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a raffinate R _{2 m} and to an extract E _{2 m} , each liquid-liquid extraction being carried out from the raffinate obtained in the preceding extraction R _{2 m} -i, - In the event of repetition, step (ii) comprises gathering E ₂ .o with each of the extracts formed to obtain an extract E '; at least one of steps (i) or (ii) comprising a liquid-liquid extraction carried out continuously. 5. Method according to claim 4, in which: - step (i) comprises one or more liquid-liquid extractions carried out continuously; or - step (ii) includes one or more liquid-liquid extractions carried out continuously; or each of steps (i) and (ii) comprises one or more liquid-liquid extractions carried out continuously, said process preferably being characterized in that: - all the liquid-liquid extractions of step (i) are carried out continuously; or - all the liquid-liquid extractions of step (ii) are carried out continuously; or - all the liquid-liquid extractions of step (i) and of step (ii) are carried out continuously. 6. Method according to any one of claims 3 to 6, in which: composition C1 comprises the lithium salt of bis (fluorosulfonyl) imide in a mass content ranging from 5% to 55%, preferably from 5% to 50%, preferably from 10% to 55%, advantageously from 10% to 50 %, for example from 10% to 40%, in particular from 15% to 40%, and preferably from 25% to 35% by mass, relative to the total mass of the composition C1; or the raffinate R ₁₀ comprises a mass content of lithium salt of bis (fluorosulfonyl) imide less than or equal to 40% by mass, preferably between 10% and 40%, advantageously between 10% and 35% relative to the mass total of said Ri o raffinate; or the extract E1.0 comprises a mass content of lithium salt of bis (fluorosulfonyl) imide greater than or equal to 10% by mass, preferably between 10% and 50%, advantageously between 10% and 40% relative to the total mass of said extract E1.0; or the raffinate Ru (when n = 1) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide less than or equal to 35% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said Ru raffinate; or the extract Eu (when n = 1) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 5% and 30 % relative to the total mass of said extract Eu; or the raffinate Ri. ₂ (when n = 2) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide less than or equal to 30% by mass, preferably between 1% and 30%, advantageously between 1% and 25% relative to the total mass of said raffinate R1.2; or - the extract E1.2 (when n = 2) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide greater than or equal to 5% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said extract E1.2; or the raffinate R1.3 (when n = 3) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide less than or equal to 25% by mass, preferably between 1% and 25%, advantageously between 1% and 20% relative to the total mass of said raffinate R1.3; or the extract E1.3 (when n = 3) comprises a mass content of lithium salt of bis (fluorosulfonyl) imide greater than or equal to 2% by mass, preferably between 2% and 30%, advantageously between 2% and 25% relative to the total mass of said extract E1.3; or the extract E comprises a mass content of lithium salt of bis (fluorosulfonyl) imide greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 10% and 30% relative to the mass total of said extract E. 7. Method according to any one of claims 1 to 6, in which the extraction solvent SE1 is chosen from an aqueous solvent, and an organic solvent chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents , aromatic solvents, and mixtures thereof, the extraction solvent SE1 preferably being an aqueous solvent, preferably deionized water. 8. Method according to any one of claims 3 to 7, in which the mass ratio of extraction solvent SE1 / composition C1 can range from 0.5 to 5, preferably from 0.5 to 4, and advantageously from 0, 5 to 3 9. Method according to any one of claims 3 to 8, in which: - the liquid-liquid extraction of step (i) is carried out in an extractor chosen from an extraction column (preferably against the current) or a mixer-settler; and / or the extraction of step (ii) is carried out in an extractor chosen from an extraction column (preferably against the current) or a mixer-settler. 10. Method according to any one of claims 3 to 9, comprising an additional step of concentrating the extract obtained in step (i), between step (i) and (ii). 11. Method according to any one of claims 3 to 10, in which: the raffinate R ₂ .o comprises a mass content of LiFSI less than or equal to 50% by mass, preferably between 10% and 50%, advantageously between 10% and 45% relative to the total mass of said raffinate R2.0; or the extract Ε2.0 comprises a mass content of LiFSI greater than or equal to 10% by mass, preferably between 10% and 50%, advantageously between 10% and 40% relative to the total mass of said extract E2.0 ; or the raffinate R2.1 comprises a mass content of LiFSI less than or equal to 45% by mass, preferably between 10% and 45%, advantageously between 10% and 40% relative to the total mass of said raffinate R2.1; or the extract E ₂₁ comprises a mass content of LiFSI greater than or equal to 10% by mass, preferably between 10% and 40%, advantageously between 10% and 30% relative to the total mass of said extract E ₂ .i ; or the raffinai R2.2 comprises a mass content of LiFSI less than or equal to 40% by mass, preferably between 5% and 40%, advantageously between 5% and 35% relative to the total mass of said raffinate R2.2; or the extract E2.2 comprises a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 30%, advantageously between 5% and 25% relative to the total mass of said extract E2.2 ; or the raffinate R2.3 comprises a mass content of LiFSI less than or equal to 35% by mass, preferably between 5% and 35%, advantageously between 5% and 30% relative to the total mass of said raffinate R2.3; or the extract E2.3 comprises a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 25%, advantageously between 5% and 20% relative to the total mass of said extract E2.3 ; or the extract E 'comprises a mass content of LiFSI greater than or equal to 5% by mass, preferably between 5% and 40%, advantageously between 5% and 30% relative to the total mass of said extract E'. 12. Method according to any one of claims 3 to 11, in which the extraction solvent SE2 is an organic solvent, preferably chosen from the group consisting of esters, nitriles, ethers, cycloalkanes, chlorinated solvents, aromatic solvents, and mixtures thereof, the extraction solvent SE2 preferably being an organic solvent chosen from the group consisting of diethylcarbonate, dimethylcarbonate, ethylmethyl carbonate, methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate, methyl acetate, butyl acetate, methyl propionate, dichloromethane, tetrahydrofuran, acetronitrile, diethyl ether, cyclohexane , and mixtures thereof, the solvent SE2 being in particular butyl acetate or a mixture of butyl acetate and cyclohexane, the solvent SE2 preferably being butyl acetate. 13. Method according to any one of claims 3 to 12, in which the mass solvent extraction ratio SE2 / E1.0 (or SE2 / E) can range from 0.1 to 2, preferably from 0.1 to 1.5, and advantageously from 0.1 to 1. 14. Method according to any one of claims 3 to 13, further comprising: (iii) a step comprising: at least one liquid-liquid extraction of the extract obtained in step (ii), with at least one extraction solvent SE3, making it possible to recover a raffinate R3.0 comprising LiFSI and the extraction solvent SE2, and a extract E ₃ .o comprising the extraction solvent SE1 and the extraction solvent SE3; the liquid-liquid extraction being able to be repeated p times, with p ranging from 1 to 10, preferably from 1 to 4, each extraction leading to a Rs.p raffinate and to an extract E ₃ . _p , each liquid-liquid extraction being carried out from the raffinate obtained in the preceding extraction R _{3 p} -i, - In the event of repetition, step (iii) comprises gathering E _{3 0} with each of the extracts formed to obtain an extract E ”. 15. Method according to any one of claims 3 to 13, comprising an additional step of concentrating the extract obtained in step (ii) (E ₂ .o or E ') and / or the extract obtained in step (iii) (R _{3 0} or R _{3. p} ). 16. The method of claim 15, wherein the concentration step comprises: a first concentration step carried out in an evaporator under reduced pressure; and a second concentration step carried out in a thin film evaporator with short path, under the following conditions: - temperature between 30 ° C and 95 ° C, preferably between 30 ° C and 90 ° C, preferably between 40 ° C and 85 ° C; - pressure between 10 ' ³ mbar abs and 5 mbar abs; - residence time less than or equal to 15 min, preferably less than or equal to 10 min, and advantageously less than or equal to 5 min.