MXPA98004547A - Procedure for the manufacture of li hexafluorofosfato - Google Patents

Abstract

The process of the present invention consists in contacting, on the one hand, gaseous phosphorus pentafluoride or a gaseous mixture comprising phosphorus pentafluoride and hydrochloric acid, and on the other hand, a solution of hydrofluoric acid lithium fluoride, on a column having a sufficient number of transfer units to carry out the reaction of PF5 with LiF under the chosen conditions of temperature, pressure and molar ratio of the two contrasting reagents and with complete or substantially complete absorption of the PF5 in the column; this procedure makes it possible to solve the blocking problems by avoiding the recrystallizations of salts, to discharge the heat released by the reaction by evaporating a portion of the HF, and to separate the HC1 that may be contained in the starting PF5, without loss of PF5, thus allowing recovery and increment of the subsequent value of this HC1, in addition, this procedure This is very simple, with a small number of stages, which makes it possible to avoid any entry of air or moisture capable of contaminating the LiPF6

Description

PROCEDURE FOR THE MANUFACTURE OF LITHIUM HEXAFLUOROFOSFATO DESCRIPTIVE MEMORY The present invention relates to a process that makes it possible to efficiently manufacture lithium hexafluorophosphate < LiPFß), a product that can be used as an electrolyte in lithium batteries. In the past, lithium perchlorate was widely used for this application "but this product has been found to be dangerous. Lithium hexafluorophosphate, which exhibits excellent application properties and for the environment, emerges as an essential substitute in the manufacture of lithium batteries. A large number of patents and publications found in the literature, which refer in general to the manufacture of LiPFß, refer only to the synthesis of phosphorus pentafluoride (PFM), without extending in any way to the method used to react this product with lithium fluoride (LiF). In this way, patent JP-41 75 216 essentially provides a method for the preparation of PFW without metals, without SO 2 * ions and without heavy products; Patent JP-52 79003 is directed to the production of PFW, which is free of impurity POF3; Patent JP-65 S 413 is directed to the production of PF., without PF Cla; German Patent Application DE-A-196 14 503 also provides a method for accessing a purer PFß. The other patents and publications, which cover in greater detail a procedure for the synthesis of the same "¥", generally provide methods that are complex, of little industrial use and prone to the introduction of impurities. Thus, for example, US Pat. No. 3,994,402 provides a method for the preparation and / or purification of LiPFβ which includes the intermediate step of a complex between acetonitrol and LiPF, ¥; United States Patent US-A-3 607 200 provides for the realization of the reaction between solid LiF and gaseous PFB in an organic solvent in which the LiF is insoluble, the PFβ is soluble and the LiPFß is "reasonably" soluble » Japanese Patent JP-60 251 109, provides the direct reaction of solid PClβ with a lithium salt in solution with HF; Japanese Patent JP-64 72 901 provides a method that makes it possible to make solid porous LiF and then react with gaseous PF ^. All these methods are very complex for their industrialization, since they use processes with multiple stages and / or include solid / gas or solids / 11"reactions and / or require the use of intermediate organic solvents. The quality requirements demanded by the market for LiPFß, means that the procedure that is implemented must be as simple as possible, that is to say »the number of unit operations must be minimized and operations that directly handle solids must be avoided and the production line is open correspondingly: the particular purpose of this is to prevent the entry of air and moisture into the process that can generate impurities containing hydrolysable oxygen »incompatible with the purity specifications desired for the LiPFß. In this investigation »directed to a method that would make it possible to obtain L PFß in a simple way, the company of the applicant considered for this synthesis to put gaseous PFß in contact with, and make it react with» LiF previously dissolved in HF. However, this contacting operation has several practical problems: - firstly, the simple spray of PF ^ in a LiF + HF solution »inevitably results in blockages» a phenomenon not mentioned in the literature: This is explained by the rate of the formation reaction of LiPFw »on the one hand» and by the limited solubilities of LiF and LiPFβ in HF. on the other hand »- subsequently. the reaction is rapid and exothermic: in this way it is advisable to take measures to control the temperature rise of the mixture »to avoid excessive evaporation of the HF. which could immediately cause recrystallization of the lithium salts and consequent blockages "or overheating detrimental to the safety of the plant and to the stability of the LiPFß formed. The most economical methods to produce PFM naturally include those that start with the cheapest starting materials, which are PC13 or PClß. Therefore »the PFB formed in this way is accompanied by HCl. Having studied the balance HF / PF ^ / HCl. the company of the applicant has shown that it is impossible to separate HCl in a simple way from pfrm; It is necessary, in the synthesis stage of LiPFβ, to use a method that is compatible with the presence of this HCl "in other words" that can start from a crude PFß that originates from a reaction using PC13 or PCI. "The applicant's company has now shown that it is possible to continuously and reliably generate LiPFw by contacting" in a column that has a sufficient number of transfer units, on the one hand, PFß gas "alone or accompanied by HCl (Crude PFß originating from a reaction using PClβ or PClβ) and »on the other hand» a solution of LiF in HF This procedure introduces a simple solution to the combination of the problems mentioned above. contacting PF ^ with LiF because the reaction configurations that can be provided based on the process of the invention, make it possible in particular to absorb the heat evolved by the reaction, Evaporation of a portion of the HF serves to remove the heat evolved by the reaction, and prevents blockages created by undesirable recrystallization of salts. The process according to the present invention is also simple, thus very significantly differing from all the other complex methods provided hitherto which employ solid / gas or solid / liquid reactions, or use intermediate organic solids. At the same time, the process according to the present invention makes it possible, in a completely unexpected way, to advantageously use crude PFβ "accompanied by HCl" because it has been shown to be possible "which was not obvious a priori. completely absorb the PFm without any loss in the flow of HCl that escapes the reaction system »achieving this without any blockage and with a perfectly controlled temperature profile. This separation of HCl »contained in this case in the starting PF ^ without loss of PFW» allows an easy subsequent treatment to increase the recovery / value of this HCl because »according to the present invention» this is found virtually pure and completely free of PFM. Finally, by minimizing the number of process steps, no air or moisture capable of contaminating the final LiPFw is allowed and thus the product is obtained with a high purity. In this way, the subject of the present invention is a process for the manufacture of lithium hexafluorophosphate by reaction of phosphorus pentachloride with lithium floride, characterized in that they are contacted, on the one hand. (A) gaseous phosphorus pentachloride or a gaseous mixture comprising phosphorus pentachloride and hydrochloric acid and. on the other hand »(B) a solution of lithium fluoride in hydrofluoric acid» in a column having a sufficient number of transfer units to carry out the reaction of phosphorus pentafluoride with lithium fluoride under the chosen temperature conditions » of pressure and molar ratio of the two contrast reagents and with complete or substantially complete absorption of the phosphorus pentafloride in the column. As will be apparent to the person skilled in the art »the number of transfer units required to carry out the reaction of PFm with LiF. it is highly dependent on the temperature »also depends on the working pressure. This number also depends on the molar ratio PFß / LiF. By way of example, when the temperature is less than 20 °, the number of transfer units is generally between 2 and 20 and preferably between 4 and 10. The molar ratio supplied of phosphorus pentafluoride and lithium fluoride is generally between 0.6 and 1.2 »preferably between 1.05 and 1.15. It is preferable to employ a slight excess of PFM with respect to the stoichiometry of the reaction to minimize the presence of LiF in LiPFw. The content of lithium fluoride in its solution in the charged hydrofluoric acid (B) is generally chosen in such a way that the concentration of the hydrofluoric acid at any point in the column is above the solubility threshold of lithium fluoride and the salts of lithium hexafluorophosphate »taking into account also the evaporation of a fraction of hydrofluoric acid by the energy released from the reaction. The weight content of LiF is conveniently between 2 and 6%. and preferably between 3 and 5%. Furthermore, the reaction according to the invention is generally carried out at a general pressure of between atmospheric pressure and 3 MPa »and preferably between atmospheric pressure and 2 MPa» and at a temperature generally between -20 and 70 ° C »preferably between -10 and 40 ° C. However, it would not depart from the invention to carry out the reaction according to the invention at pressures below atmospheric pressure. The reaction according to the invention can be carried out under adiabatic conditions; the column is then crowned with a condenser intended to recondense and return the hydrofluoric acid portion evaporated from said column as a result of the exothermic nature of the reaction between phosphorus pentafluoride and lithium fluoride. The reaction according to the invention can also be carried out under isothermal conditions, the column being cooled to absorb the heat released by the reaction. According to a first modality »the column is charged upstream» the gas stream (A), composed of »or containing, phosphorus pentafluoride» is introduced into? the lower end of the column and the solution of lithium fluoride in hydrofluoric acid (B) is introduced at the upper end »leaving the column the lithium hexafluorophosphate at the lower end in hydrofluoric acid solution. In accordance with a second modality »the column is loaded concurrently; the gas stream < TO). composed of »or containing» penta fluoride phosphorus »and the solution of lithium fluoride in hydrofluoric acid (B)» are introduced at the base of the column, which then functions as a sealed flow reactor »separating the resulting liquid solution of lithium hexafluorophosphate in hydrofluoric acid at the upper end of the column. In accordance with a third mode, the column is charged concurrently with the gaseous stream (A) »composed of» or containing »phosphorus pentafluoride» and the solution of lithium fluoride with hydrofluoric acid (B). they are introduced at the upper end of the column, the resulting liquid solution of lithium hexafluorophosphate being separated into hydrofluoric acid in a separation vessel mounted on the extraction line at the base of said column. According to a very advantageous possibility of the invention, the starting material is a gaseous mixture obtained as a crude product in the manufacture of phosphorus pentafluoride from phosphorus tri-chloride or phosphorus pentachloride and which. consequently, it contains hydrochloric acid »chlorine and hydrofluoric acid; then escaping the hydrochloric acid in the material ventilated »completely or substantially completely free of phosphorus pentafluoride. According to the present invention "to obtain the desired product in a pure state" the resulting solution of lithium hexafluorophosphate in hydrofluoric acid can be easily evaporated to crystallize the lithium hexafluorophosphate "and the crystal suspension thus obtained can be treated afterwards. to completely purify the finished product. The column used in the process of the invention can be »for example» an empty column »packed or plate. In addition, the process of the invention is advantageously carried out continuously. Next, a description will be given in greater detail of six possible reaction configurations for the implementation of the method according to the invention "without considering this list as exhaustive" with reference to the respective figures 1 to 6 which are the corresponding assembly plans. A first reaction configuration, illustrated in FIG. 1, comprises a column 10 charged countercurrently: the gas (A), which is formed by PFβ and which may or may not be accompanied by HCl, is supplied at the lower end while that the solution LiF + HF (B) is supplied at the upper end. The product »LiPFß» leaves the column at the lower end, in HF solution (solution C). In this adiabatic configuration »the column 10 is topped by a condenser 11 through which runs a refrigerant (R): this device is used to recondense and to return the portion of the HF evaporated from the column 10 as a result of the exothermic nature of the the reaction between LiF and PFß (flow D). In the case of using a pure PFß, a small amount of HF escapes at the upper end of the condenser 13 (ventilated material E). In case of using a PF ", crude accompanied by HCl", ventilated material (E) is formed at the upper end of the condenser 13 by HCl which entrains a small amount of HF "but in general, it is virtually free of PFß. This HCl can then be transported to a treatment unit known to a person skilled in the art, to be defluorinated and thus increase its value. The reaction column 10 is an absorption column which can be of any type: empty, packed or in plate. Its dimensions are chosen to allow the preparation of a sufficient number of transfer units for the absorption and reaction of the PFB to take place under good conditions: this number can vary signifi- cantly, depending on the temperature and the concentration conditions. The amount of HF introduced at the upper end of the column "and therefore the concentration of LiF at the top end load" should be such that the concentration of HF at any point in the column is above the solubility threshold of the salts of LiF and LiPF ^ »taking into account the evaporation of a fraction of the HF by the energy released from the reaction. This places the LiF content in the HF supplied at the upper end of the column "in less than 6% by weight" and preferably between 3% and 5% by weight "depending on the ratio of PFB to LiF delivered. In general, it is preferred to operate with an excess of PF ,,, »in such a way to consume all the LiF and thus obtain an HF + LiPF ,, solution. that does not contain LiF; under these conditions »some traces of PFW will be found in the gas flow coming out of the upper end of the column. The temperature profile depends essentially on the pressure at which the column operates. However, it is advisable to limit the temperature to less than 70 ° C. without the maximum constituting a limit for the invention: the only interest here is to promote the reaction and not redirect the LiPFß that has been formed. The solution of LiPF ^. in HF obtained at the lower end of the column »is then subjected to a treatment consisting of removing the HF by evaporation, to crystallize the LiPFß »and then treat the suspension of crystals thus obtained to completely purify the finished product. - A second reaction configuration, illustrated in figure 2, corresponds to the alternative isothermal form of the previous case: it is cooled to column 10 by any means (a jacket in which circulates a refrigerant (R), exchanger or exchangers integral, and similar), to absorb the heat released by the reaction. Apart from the fact that it is no longer necessary to have a capacitor at the top end, all the recommendations made with respect to the first reaction configuration are valid. The third reaction configuration applies particularly well to the proposed problem: it uses a concurrent column 10 '"as illustrated in Figure 3. The two reaction charges, namely (A) PF ,,,. which may or may not be accompanied by HCl. on the one hand, and (B) the solution of LiF in HF "on the other hand, are introduced at the base of column 10 '. Under these conditions. the column 10 '»which may be empty, but preferably is packed» is used as a sealed flow reactor »along which the reaction proceeds. At the upper end of the column 10 '»the liquid solution (C). composed of LiPFß + HF »is separated from the gas phase composed of the evaporated HF portion by the exothermic nature of the reaction» which may or may not be accompanied by HCl: a condenser 11 makes it possible to recondense the HF and recirculate it (flow D) to the base the column 10 ', while any HCl that may be present escapes at the upper end, carrying a small amount of HF (flow E) »but usually virtually completely free of PFM. Then, this HCl can be transported to a treatment unit known to a person skilled in the art »to be defluorinated and thus increase its value. The advantage of this concurrent configuration is, as mentioned above, the production of a sealed-flow type reactor: it is known that this type of reactor is generally more efficient than the stirred reactor, since, on the one hand, it requires a shorter residence time to achieve a given degree of reaction conversion, and on the other hand, it is generally more selective. In the case where the reaction in question is exothermic and when only a small increase in temperature is acceptable, which is the case here, the tubular-type sealed-flow reactor is generally impractical because it offers a surface area. Excessively low exchange rate for the required heat discharge. The ability of the configuration provided here is that it permits the discharge of heat by evaporation of a fraction of the HF. while at the same time maintaining the character of plugged flow: the combination of flows traveling from the bottom up (including the evaporated HF and the non-reactive HCl), on the one hand, and the presence of appropriate packaging »on the other hand »Makes it possible to maintain sealed flow conditions despite the turbulence caused by the boiling of a portion of the HF and the presence of a gas phase.

The gaskets used in this configuration will preferably be chosen from those promoting gas-liquid contact and radial mixing, while reducing axial agitation: mention may be made of static cross-shaped mixer components without this limiting the invention. or in helical form »for example. As in the previous configurations, the height of the column must be sufficient to provide correct absorption and correct reaction of the PF ,,,. Likewise »the LiF content in the introduced solution must be such that» at any point in column 10 '»there is always sufficient HF to dissolve the lithium salts' taking into account the evaporation of a fraction of the HF by the energy released by the reaction. In general, it will be preferable to operate with a slight excess of PFB and thus obtain "at the upper end" a solution of LiPF "in HF that does not contain LiF: under these conditions" some traces of PFW will be found in the gas flow which comes out at the upper end of the column 10 '. As stated above. The temperature profile depends essentially on the pressure at which the column operates. However, it is advisable to limit the temperature to less than 70 ° C, without this maximum constituting a limit for the invention, in order to promote the reaction and not to redissolve the LiPFß that has formed. The solution (C) of LiPFw in HF obtained at the upper end of the column 10 '»is then subjected to a treatment consisting in the removal of HF by evaporation, to crystallize the LiPF ^, and then to treat the suspension of crystals obtained from this way to completely purify the finished product. A fourth reaction configuration, illustrated in FIG. 4, corresponds to the alternative isothermal form of the preceding case: the column 10 'is cooled by any means to absorb the heat evolved by the reaction, thus avoiding the installation of a upper capacitor. This configuration can depart from the sealed flow reactor if internal exchangers are used, but it is still a concurrent configuration that falls within the scope of the invention as it makes it possible to perfectly solve all the proposed problems. - A fifth reaction configuration »illustrated in figure 5» corresponds to a column 10"which is also a concurrent column" but this time the charges of (A) and (B) are made at the upper end. particularly effective if the system is arranged in such a way that the descending liquid flow (B) brings the gas (A) down, since in this way the reactor still retains its obturated flow character while acquiring a very high degree of radial agitation, which is favorable for the gas / liquid transfers and therefore for the production reaction of LiPF- At the base of the column 10"» a separation vessel l ~. it makes it possible to separate the gaseous phase of HCl + HF (+ excess of PFB) from the desired liquid phase (C): LiPFB in HF. A condenser 11 »through which a refrigerant (R) passes. receives this gaseous phase to return the HF (flow D) to the upper end of the column 10"» forming the ventilated material (E) as above With respect to the operating conditions »the same recommendations as those mentioned for the preceding reaction configurations • The alternative isothermal form of the preceding case also applies to the invention and is shown in figure 6 »the same operation recommendations also apply The following examples illustrate the present invention but nevertheless do not limit the In these examples, the following formulas are used: L PFw = lithium hexafluorophosphate LiF = lithium fluoride PFB = phosphorus pentafluoride HF = hydrofluoric acid HCl = hydrochloric acid PCIa as phosphorus trichloride PClf, = pentachloride of phosphor EXAMPLE 1 The operation is carried out according to the modality shown in diagram in figure 1. in an assembly as shown in figure 7. A packed column 10 is loaded for 1 hour, in which it has been estimated at 4. approximately , the number of theoretical stages, with the following flows: At the lower end, a gaseous mixture (A) originating from the production reaction of PFW from PCla is introduced. of chlorine and HF. This reaction mixture is stored in an autoclave 13 under autogenous pressure at room temperature; has the following composition: PFB - 11.1 X molar HCl = 55.7% molar HF not converted = 25.35. molar Unconverted Cla = 7.9% molar The total flow rate per hour is 10,770 mol / h, ie 484.44 g / h. including 151.2 g / h of PFM (ie 1.2 mol / h). • A solution (B) of LiF in HF is charged at the upper end. which has the following composition: LiF = 1.9% by weight HF = 9B.1 5 by weight The total flow rate is 123.570 mol / h. that is, 2482.16 g / h. including 46.6 g / h of LiF (i.e. 1,794 mol / h). A) Yes. The LiF / PFB molar ratio is in the region of 1.5. Column 10 is maintained at 0 ° C using a jacket through which runs a refrigerant (R). and it is additionally equipped with an upper condenser 11 »through which the refrigerant (R) also runs.

Results * Column 10 works in a very stable way "without any blockage or accumulation of solids during the whole experiment. The analysis of the upper gas (E) shows a virtual absence of phosphorus: only 0.012 mol / h »that is to say a phosphorus yield of 995í. The upper gas (E) only contains HF carrying HCl. Solution (C) containing LiPFß and LiF not converted to HF. It is collected at the lower end. After removing the HF by evaporation, a solid is collected which is analyzed and found to have the following composition by weight: HF at 3.2X LiPFw = 89.3% LiF = 7.5X After this solid can be subjected to a specific treatment for Remove excess HF.

* EJEMPWQ Z The assembly of figure 7 was used. Column 10 is loaded, also for one hour, with the following flows: • At the lower end, the same crude PFβ (A) as in example 1 and with the same speed flow. In practice »484 g / h containing 151 g / h of PFM are in fact supplied. * At the upper end, a solution (B) of LiF in HF is supplied. which has the following composition: LiF ss 3.9% by weight. HF = 96.1% by weight The total flow rate is divided by two compared to Example 1. Which actually means 1220 g / h containing 47.1 g / h of LiF (1811 mol / h). So »the molar ratio Li / PF? It is also in the region of 1.5. Column 10 is also kept at 0 ° C »both by its jacket and by its condenser 11.

Results: Despite the highest concentration of LiF in the fluid loaded, there was no blockage or accumulation of solid in column 10; This column works without interruption during the whole experiment. The analysis of the upper gas (E) also reveals the presence of only 0.012 mol / h of phosphorus, which results in a phosphorus yield of 99%. A solution (C) containing LiPF ^ and LiF not converted to HF. It is collected at the lower end. After removing the HF by evaporation, a solid which is analized is collected and found to have the following composition by weight: HF = 1.6% LiPFß ss 90.9% LiF s = 7.4% Afterwards, this solid can be subjected to a treatment specific to remove excess HF.

EXAMPLE 3 The assembly of figure 7 is used. Column 10 is loaded, also for 1 hour, with the following flows: At the lower end, a crude PFtH having a composition similar to that of the preceding examples, namely: PFra = ??? 7% molar HCl == 58.4% molar HF not converted == 27.7% molar Unconverted Cla = * 2.2% molar The total flow rate per hour is 16,923 mol / h, that is 730.4 g / h, including 249.48 g / h of PF ^ (ie 1.9B0 mol / h).

At the upper end »a solution (B) of LiF in HF is provided having the following composition: LiF == 2% by weight HF = 98% by weight The total flow rate is 116.46 mol / h, ie 2340 g / h »including 46.8 g / h of LiF (ie 1.8 mol / h). The molar ratio LiF / PFß is in this case in the region of 0.909 »that is to say that there is an excess of 10 mol% of PFβ. Column 10 is also maintained at 0 ° C »both by its jacket and by its condenser 11.

Results: Column 10 worked properly »without any blockage or accumulation of solids during the whole experiment. Despite operating at a higher gas flow velocity and with excess PFB, the upper gas (E). composed essentially of HCl and HF, it only carries 0.200 mol / h of phosphorus, which results in a phosphorus yield of 89% (10% excess + 1% losses). A solution (C) containing LpFm in HF is collected at the lower end. After removing the HF by evaporation, a solid which is analyzed is collected and found to have the following composition by weight: HF = l.B% LiPF. = 9B.2% LiF s = traces Afterwards, this can only be subjected to a specific treatment to remove excess HF.

E EMPUP * < CP «for ÍYQ > The assembly illustrated in Figure 8 was used. A solution (B *), composed of 550 mmoles of LiF and 19. 400 mmoles of HF, that is to say with a 3.55% by weight analysis of LiF, at approximately 0 ° C, in a receptacle 14 equipped with a jacket through which runs a refrigerant (R). An attempt was made to spray a crude PFß (A) in this solution. which originates from the reaction of PC13 with chlorine and HF; this gaseous mixture, maintained in an autoclave 13 at autogenous pressure at 20 ° C, has the following composition: PFIS - 4.6% molar HCl = 23.2% molar HF not converted = 70.9% molar Cl ,. unconverted = 1.3% molar A total flow of 12 956 mmoles of this gas was supplied successively over a very long period (due to the observed blockages): this amounts to the supply of 600 mmoles of PFB. which corresponds to a PFB / LiF ratio = 1.08.

Results: Many duct blockages are observed immersed in the LiF + HF solution: approximately 30 during the period of the test. At the end of the test, an unconverted product is observed which corresponds to a yield of phosphorus in the region of 93%. The solid obtained after evaporation of the HF from the solution contained in the receptacle 14. has the following composition by weight: HF ß 2% LiPFβ == 98% LiF SB traces The ventilated material (E) is composed of the following compounds : Non-converted PFW = 0.7% molar HCl = 46.7 molar% HF not converted = 2.6 molar% Cl ^ not converted = 50.0 molar% This test shows that to contact PFm with LiF. it is necessary to take precautions to always maintain »even locally. a sufficient HF content to prevent blockages. On one side. and a sufficient number of transfer units to achieve a good performance in the conversion of the reagents "on the other hand.

Claims (7)

NQVEP? P PE L? INVENTION REIVTNPICACIPNES

1. - Process for the manufacture of lithium hexafluorophosphate by reaction of phosphorus pentafluoride with lithium fluoride »characterized in that» on the one hand »phosphorus lutein or gaseous phosphorus or phosphorus pentafluoride is contacted with (A) pentafluoride acid hydrochloric and. on the other hand »(B) a solution of lithium chloride in hydrofluoric acid» in a column (10; 10 '; 10") that has a sufficient number of transfer units to carry out the reaction of phosphorus pentafluoride with lithium fluoride under the chosen conditions of pressure temperature and molar ratio of the two contrasting reagents and with complete or substantially complete absorption of the phosphorus pentafluoride in the column.

2. Procedure according to claim 1. characterized in that the molar ratio of phosphorus pentafluoride / lithium fluoride supplied is between 0.6 and 1.2"and preferably between 1.05 and 1.15.

3. Method according to any of claims 1 and 2. characterized in that the content of lithium fluoride in its solution in the hydrofluoric acid feed (B) is chosen in such a way that the concentration of hydrofluoric acid at any point in the the column (10; 10 '; 10") is above the solubility threshold of lithium fluoride and the salts of lithium hexafluorophosphate" also taking into account the evaporation of a fraction of hydrofluoric acid by the energy released by the reaction .

4. Process according to the rei indication 3 »characterized in that the content by weight of lithium fluoride in solution in the hydrofluoric acid (B) charge is between 2 and 6%, preferably between 3 and 5%.

5. Method according to one of the rei indications 1 to 4, characterized in that the reaction is carried out at a pressure between atmospheric pressure and 3 MPa »and preferably between atmospheric pressure and 2 MPa.

6. Method according to one of claims 1 to 5, characterized in that the reaction is carried out at a temperature of between -20 and 70 ° C and preferably between -10 and 40 ° C.

7. Method according to one of the claims 6 »characterized in that the reaction is carried out under adiabatic conditions» in which case the column (10; 10 '; 10") is topped by a condenser (11) intended to recondense and return (flow D) the hydrofluoric acid portion evaporated from said column »as a result of the exothermic nature of the reaction between phosphorus pentafluoride and lithium fluoride. B. Method according to one of claims 1 to 6 »characterized in that the reaction is carried out under isothermal conditions» in which case the column (10; 10 '; 10") is cooled to absorb the heat evolved by the reaction. 9. Method according to one of claims 1 to 8, characterized in that the column (10) is charged in countercurrent mode "in which case the gas stream (A)» which is composed of »or contains» phosphorus pentafluoride »is enter at the bottom end of the column and the solution of lithium fluoride in hydrofluoric acid (B) is introduced at the upper end »leaving the column at the lower end the lithium hexafluorophosphate» in hydrofluoric acid solution (flow C). 10. Method according to one of claims 1 to 8 »characterized in that the column (10 ') is loaded concurrently, in which case the gas stream (A), composed of. or containing »phosphorus pentafluoride» and the solution of lithium fluoride in hydrofluoric acid (B). they are introduced at the base of the column »which then functions as a sealed flow reactor; the resulting liquid solution (C) of lithium hexafluorophosphate in hydrofluoric acid is separated at the upper end of the column. 11. Method according to one of claims 1 to 8, characterized in that the column (10") is loaded concurrently" in which case "the gas stream (A), composed of» or containing »phosphorus pentafluoride »And the solution of lithium fluoride in hydrofluoric acid (B) are introduced at the upper end of the column; The resulting liquid solution (O) of lithium hexafluorophosphate in hydrofluoric acid is separated in a separation vessel (12) mounted on the extraction line at the base of said column 12. Process according to one of claims 1 to 11. characterized in that the starting material is a gaseous mixture obtained as a crude product in the manufacture of phosphorus pentafluoride from phosphorus trichloride or from phosphorus pentachloride »and which consequently contains hydrochloric acid, chlorine and hydrofluoric acid» hydrochloric acid then escapes in the ventilated material (E), completely or substantially free of phosphorus pentafluoride 13.- Procedure according to one of the rei indications 1 to 12 »characterized in that the resulting solution (C) of lithium hexafluorophosphate in hydrofluoric acid evaporates to crystallize the lithium hexafluorophosphate, and because the crystal suspension obtained from this This is then treated to completely purify the finished product. 14. Method according to one of claims 13 characterized in that the column (10; 10 '; 10") is an empty, packed or plate-absorbing column 15.- Procedure in accordance with one of the rei indications 1 to 14 »characterized in that it is carried out continuously. RESU? IN PE .A I VENCIPN The process of the present invention consists in contacting »on the one hand» gaseous phosphorus pentafluoride or a gaseous mixture comprising phosphorus pentafluoride and hydrochloric acid »and on the other hand» a solution of l thyl fluoride in hydrofluoric acid »In a column having a sufficient number of transfer units to carry out the reaction of PFW with LiF under the chosen conditions of pressure temperature and molar ratio of the two contrasting reagents and with complete or substantially complete absorption of the PFW in the column; this procedure makes it possible to solve the blocking problems by avoiding the recrystallizations of salts; discharge the heat evolved by the reaction by evaporating a portion of the HF; and separating the HCl that may be contained in the starting PFB "without loss of PFB, thus allowing recovery and increasing the subsequent value of this HCl; In addition »this procedure is very simple» with a small number of stages »which makes it possible to avoid any air or humidity entry capable of contaminating the final LiPFß. P98 / 565 EA / ram * the t * amm