EP2855356A1

EP2855356A1 - High-purity lithium hexafluorophosphate

Info

Publication number: EP2855356A1
Application number: EP13724289.7A
Authority: EP
Inventors: Matthias Boll; Wolfgang Ebenbeck; Eberhard Kuckert
Original assignee: Lanxess Deutschland GmbH
Current assignee: Lanxess Deutschland GmbH
Priority date: 2012-05-25
Filing date: 2013-05-23
Publication date: 2015-04-08
Also published as: US20150155599A1; KR20150016512A; WO2013174941A1; CA2874610A1; JP2015523951A; CN104364197A

Abstract

The invention relates to a method for producing high-purity, in particular low-chloride lithium hexafluorophosphate, in particular in the form of solutions of same in organic solvents, from lithium fluoride and phosphorus pentafluoride.

Description

High purity lithium hexafluorophosphate

The present invention relates to a process for the preparation of high purity, especially low chloride lithium hexafluorophosphate, especially in the form of its solutions in organic solvents, starting from lithium fluoride and phosphorus pentafluoride. The proliferation of portable electronic devices, such as laptops and palmtop computers, cell phones or video cameras, and thus the need for lightweight and powerful batteries and accumulators has dramatically increased in recent years worldwide. In addition, there will be the equipment of electric vehicles with such accumulators and batteries in the future. Lithium hexafluorophosphate (LiPF ₆ ) has attained great industrial importance, especially as conducting salt in the production of powerful batteries. In order to ensure the functionality and lifetime and thus the quality of such batteries, it is of particular importance that the lithium compounds used are highly pure and in particular contain as low as possible amounts of other metal ions, in particular sodium or potassium ions, and the smallest possible amounts of chloride. Foreign metal ions are held responsible for cell shedding due to precipitation (US 7,981,388), chloride for corrosion.

Numerous processes for the production of lithium hexafluorophosphate are known from the prior art. For example, the preparation according to the following reaction scheme offers:

Stage 1 PC1 ₃ + 3 HF -> PF ₃ + 3 HCl

Step 2 PF ₃ + Cl ₂ -> PC1 ₂ F ₃

Step 3 PCI ₂ F ₃ + 2 HF -> PF ₅ + 2 HCl

Stage 4 PF ₅ + LiF → LiPF ₆ With the aim of a low phosphorus trifluoride (PF ₃ ) content in the end product DE 197 12 988 A1 describes a batchwise operated process in an autoclave starting from phosphorus trichloride (PC1 ₃ ). In a dry experimental reactor made of stainless steel while 7.8 g of lithium fluoride were initially charged and heated at 150 ° C under argon. In a laboratory autoclave phosphorus trichloride was initially charged and cooled to -52 ° C, then added hydrogen fluoride. To Cooling down to -58 ° C was the dosage of elemental chlorine. The autoclave was then removed from the cooling bath and the resulting gaseous mixture of hydrogen chloride and phosphorus pentafluoride passed over the lithium fluoride in the experimental reactor. After completion of the transfer of the gas mixture again 7.8 g of LiF were added to the experimental reactor to the resulting lithium hexafluorophosphate. Analogously to the above preparation, a gas mixture of hydrogen chloride and phosphorus pentafluoride was again generated and passed over the mixture of lithium hexafluorophosphate and lithium fluoride. The resulting lithium hexafluorophosphate was crystalline and could be mortared without development of visible vapors. In addition to the abovementioned batchwise process, DE 19722269 A1 also discloses a process with continuous addition of chlorine in an autoclave also starting from phosphorus trichloride. The starting materials used were phosphorus trichloride (mass: 61.8 g = 0.45 mol), highly pure hydrogen fluoride (mass: 96.9 g = 3.84 mol) and elemental (mass: 40.0 g = 0.56 mol). The excess of hydrogen fluoride based on phosphorus was thus 70.6%. The vessels used were dried in a drying oven. In the laboratory autoclave, the phosphorus trichloride was introduced and metered more than the equivalent amount of hydrogen fluoride required together with nitrogen slowly, with the excess of hydrogen fluoride served as a solvent. The temperatures in the laboratory autoclave during the subsequent continuous chlorine dosing in the open system were between -65.7 ° C and -21.7 ° C. During the metering of the chlorine, a gas mixture of hydrogen chloride and phosphorus pentafluoride was formed, which was removed from the autoclave. The mixture was separated by customary separation methods, for example pressure distillation.

In another example of the same prior art, phosphorus trichloride was metered into the autoclave, which was then sealed. After cooling the autoclave to -57.6 ° C, the hydrogen fluoride was metered in and cooled again to -59.3 ° C. Then elemental chlorine was added. The cooling was then removed, it came to a pressure build-up to 43 bar at 25, 1 ° C. The resulting gas mixture of hydrogen chloride and phosphorus pentafluoride was drained from the autoclave and could be passed without further treatment in a reactor with lithium fluoride, in which then formed lithium hexafluorophosphate. In the gas mixture no phosphorus trifluoride could be detected.

Also starting from phosphorus trichloride and elemental chlorine CN 101723348 A describes a process for the preparation of lithium hexafluorophosphate in the liquid phase, wherein acts as a solvent hydrogen fluoride and the reaction of the gas mixture containing Phosphorus trichloride, fluorine and hydrogen chloride with elemental chlorine at 35 to 70 ° C and the implementation of phosphorus pentafluoride with lithium fluoride at -30 to -10 ° C is performed.

JP 11171518 A2 likewise describes a process for the preparation of lithium hexafluorophosphate, which proceeds from phosphorus trichloride and hydrogen fluoride via phosphorus trifluoride, the latter being reacted with elemental chlorine first to phosphorodichloride trifluoride, this in turn with hydrogen fluoride to phosphorus pentafluoride and the latter finally with lithium fluoride to lithium hexafluorophosphate in an organic solvent , The solvents used are diethyl ether and dimethyl carbonate. Although JP 11171518 A2 indicates the formation of toxic HCl gas, there are no indications in the prior art of the chloride content in the resulting lithium hexafluorophosphate. The procedure, however, suggests a significant chloride content.

The prior art shows that it is technically very complicated to achieve high purities for lithium hexafluorophosphate and in particular to keep the content of foreign metal ions and the content of chloride low. Consequently, not all purity requirements can be met with the hitherto known processes for the preparation of lithium hexafluorophosphate.

Accordingly, it was an object of the present invention to provide an efficient process for the preparation of high purity lithium hexafluorophosphate or high purity solutions containing lithium hexafluorophosphate in organic solvents, which does not require extensive purification operations and consistently yields high yields. The solution of the object and subject of the present invention is now a process for the preparation of solutions containing lithium hexafluorophosphate comprising at least the steps: a) contacting solid lithium fluoride with a gas containing phosphorus pentafluoride wherein a reaction mixture containing lithium hexafluorophosphate and unreacted lithium fluoride is obtained

b) bringing the reaction mixture formed according to a) into contact with an organic solvent, the lithium hexafluorophosphate formed at least partially dissolving

c) separation of solid components from the solution containing lithium hexafluorophosphate. It should be noted at this point that the scope of the invention includes all possible and possible combinations of the above-listed and listed below, general or preferred ranges mentioned components, value ranges or process parameters. In step a), solid lithium fluoride is contacted with a gas containing phosphorus pentafluoride to obtain a reaction mixture containing lithium hexafluorophosphate and unreacted lithium fluoride.

The lithium fluoride used in step a) has, for example, a purity of 98.0000 to 99.9999% by weight, preferably 99.0000 to 99.9999% by weight, more preferably 99.9000 to 99.9995% by weight. , particularly preferably 99.9500 to 99.9995% by weight and very particularly preferably 99.9700 to 99.9995% by weight, based on anhydrous product.

The lithium fluoride used furthermore preferably has foreign ions:

1) a content of 0, 1 to 250 ppm, preferably 0, 1 to 75 ppm, more preferably 0, 1 to 50 and particularly preferably 0.5 to 10 ppm and most preferably 0.5 to 5 ppm

Sodium in ionic form and

2) a content of 0.01 to 200 ppm, preferably 0.01 to 10 ppm, more preferably 0.5 to 5 ppm and more preferably 0.1 to 1 ppm of potassium in ionic form.

The lithium fluoride used furthermore preferably has foreign ions

3) a content of 0.05 to 500 ppm, preferably 0.05 to 300 ppm, more preferably 0.1 to

250 ppm and particularly preferably 0.5 to 100 ppm of calcium in ionic form and / or 4) a content of 0.05 to 300 ppm, preferably 0.1 to 250 ppm and more preferably

0.5 to 50 ppm magnesium in ionic form.

The lithium fluoride used furthermore has, for example, foreign ions

i) a content of 0, 1 to 1000 ppm, preferably from 0, 1 to 100 ppm and more preferably 0.5 to 10 ppm of sulfate and / or

ii) a content of 0.1 to 1000 ppm, preferably 0.5 to 500 ppm chloride,

also based on the anhydrous product and it is true that the sum of lithium fluoride and the aforementioned foreign ions does not exceed 1,000,000 ppm based on the total weight of the technical lithium carbonate based on the anhydrous product.

In one embodiment, the lithium fluoride contains a total of foreign metal ion content of 1000 ppm or less, preferably 300 ppm or less, more preferably 20 ppm or less, and most preferably 10 ppm or less.

Contacting solid lithium fluoride with a gas containing phosphorus pentafluoride to give a reaction mixture containing lithium hexafluorophosphate and unreacted lithium fluoride can be accomplished by any method known to those skilled in the art of gaseous solid reacting. For example, the contacting can take place in a fixed bed or a fluidized bed, the contacting in a fluidized bed is preferred. In one embodiment, the fluidized bed may be configured as a stirred fluidized bed.

The solid lithium fluoride used can, in particular when used as a fixed bed, for example in the form of moldings or in the form of fine particles, e.g. that is to say in the form of a powder, the use of fine particles or powders being preferred, in particular for use as a fluidized bed.

The water content of powders is preferably 0 to 1500 ppm, preferably 0 to 1000 ppm and more preferably 0 to 800 ppm. In a further embodiment, the water content is preferably 300 to 800 ppm. When using moldings, preference is given to those which have a solids content in the range from 20 to 95% by weight, preferably in the range from 60 to 90% by weight, particularly preferably at 67 to 73% by weight and very particularly preferably approx. 70 wt .-% is.

Shaped bodies can in principle be in any desired form, with spherical, cylindrical or annular shaped bodies being preferred. Preferably, the shaped bodies are not larger than 3 cm in any dimension, preferably not larger than 1.5 cm.

Moldings are prepared, for example, by extrusion from a mixture of lithium fluoride and water, wherein the moldings after extrusion at temperatures of 50 to 200 ° C, preferably at temperatures of 80 to 150 ° C, more preferably dried at about 120 ° C, and they only have a water content of 0 to 5 wt .-%, preferably 0.05 to 5 wt .-%, alternatively from 0.0 to 0.5 wt .-%, preferably from 0, 1 to 0.5 wt. % exhibit. Such shaped bodies are typically cylindrical.

Water contents are, unless stated otherwise, determined by the method according to Karl Fischer, which is known to the person skilled in the art and described, for example, in P.Bruttel, R. Schlink, "Water Determination by Karl Fischer Titration", Metrohm Monograph 8.026.5001, 2003 -06.

The reaction kinetics in step a) depends on the reaction temperature, the effective surface area of the lithium fluoride, the flow resistance caused by the fixed bed or fluidized bed and the flow velocity, the pressure and the increase in volume of the reaction mixture, without the applicant's intention to be scientifically defined during the reaction. While temperature, pressure and flow velocity can be controlled by process technology, the effective surface area of lithium fluoride depends on the flow resistance and the volume increase of the reaction mixture from the morphology of the lithium fluoride used.

It has been found that it is advantageous both for use for the production of moldings and for use in the form of fine particles, lithium fluoride having a D50 value of 4 to 1000 μιη, preferably 15 to 1000 μιη, more preferably 15 to 300 ppm , Particularly preferably 15 to 200 μιη and even more preferably 20 to 200 μιη use.

The lithium fluoride used furthermore preferably has a D10 value of 0.5 μιη or more, preferably 5 μιη or more, more preferably 7 μιη or more. In another embodiment, the lithium fluoride has a DlO value of 15 μιη or more. By the D50 value or the D10 value is meant the particle size in and below which a total of 10% by volume or 50% by volume of the lithium fluoride is present.

The lithium fluoride further preferably has a bulk density of 0.6 g / cm ³ or more, preferably 0.8 g / cm ³ or more, more preferably 0.9 g / cm ³ or more, and particularly preferably 0.9 g / cm ³ to 1.2 g / cm ³ . The lithium fluoride having the aforementioned specifications can be obtained, for example, by a process comprising at least the following steps: i) providing an aqueous medium containing dissolved lithium carbonate

ii) reacting the aqueous medium provided according to a) with gaseous hydrogen fluoride to form an aqueous suspension of solid lithium fluoride

iii) separating the solid lithium fluoride from the aqueous suspension

iv) drying the separated lithium fluoride.

According to step i), an aqueous solution containing lithium carbonate is provided.

The term "aqueous medium containing dissolved lithium carbonate" is to be understood here as meaning a liquid medium which

i) contains dissolved lithium carbonate, preferably in an amount of at least 2.0 g / 1, more preferably 5.0 g / 1 to the maximum solubility in the aqueous medium at the selected temperature, most preferably 7.0 g / 1 to maximum solubility in the aqueous medium at the selected temperature. In particular, the content of lithium carbonate is 7.2 to 15.4 g / l. The skilled person is known that the solubility of lithium carbonate in pure water at 0 ° C 15.4 g / 1 at 20 ° C 13.3 g / 1, at 60 ° C 10.1 and at

100 ° C 7.2 g / 1 and consequently certain concentrations can be achieved only at certain temperatures ii) contains at least 50% by weight of water, preferably 80% by weight, more preferably at least 90% by weight, based on the total weight of the liquid medium, and

iii) preferably also solids-free or has a solids content of more than 0.0 to 0.5 wt .-%, preferably solids-free or a solids content of more than 0.0 to 0, 1

% By weight, more preferably solids-free or has a solids content of more than 0.0 to 0.005 wt., And particularly preferably solids-free,

wherein the sum of components i), ii) and preferably iii) is at most 100% by weight, preferably 98 to 100% by weight and particularly preferably 99 to 100% by weight, based on the total weight of the aqueous medium containing dissolved lithium carbonate ,

The aqueous medium containing dissolved lithium carbonate may in another embodiment of the invention as a further component

iv) contain at least one water-miscible organic solvent. Suitable water-miscible organic solvents are, for example, monohydric or polyhydric alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol,

Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol, 1,3-propanediol or glycerol, ketones such as acetone or ethyl methyl ketone.

If the aqueous medium containing dissolved lithium carbonate contains at least one water-miscible organic solvent, their proportion may be, for example, more than 0.0% by weight to 20% by weight, preferably 2 to 10% by weight, in which case in each case in that the sum of components i), ii), iii) and iv) contains at most 100% by weight, preferably 95 to 100% by weight and particularly preferably 98 to 100% by weight, based on the total weight of the aqueous medium dissolved lithium carbonate is.

Preferably, however, the aqueous medium containing dissolved lithium carbonate is free of water-miscible organic solvents.

The aqueous medium containing dissolved lithium carbonate may contain as further component v) a complexing agent, preferably in an amount of 0.001 to 1 wt .-%, preferably 0.005 to 0.2% by weight based on the total weight of the aqueous medium containing dissolved lithium carbonate.

Complexing agents are preferably those whose complexes with calcium ions and magnesium ions form complexes which have a solubility of more than 0.02 mol / l at a pH of 8 and 20 ° C. Examples of suitable complexing agents are ethylenediaminetetraacetic acid (EDTA) and its alkali metal or ammonium salts, with ethylenediaminetetraacetic acid being preferred. In one embodiment, however, the aqueous medium containing dissolved lithium carbonate is free of complexing agents.

To provide the aqueous solution containing lithium carbonate, the procedure is preferably such that solid lithium carbonate is brought into contact with a lithium carbonate-free or lithium-carbonate-poor aqueous medium so that the solid lithium carbonate at least partially dissolves. By low-lithium carbonate, aqueous medium is meant an aqueous medium which has a lithium carbonate content of up to 1.0 g / l, preferably up to 0.5 g / l of lithium carbonate, but is not free of lithium carbonate.

The aqueous medium used for the preparation fulfills the conditions mentioned above under ii) and iii) and optionally comprises the components iv) and v).

In the simplest case, the aqueous medium is water, preferably water with a specific electrical resistance of 5 Ω · cm at 25 ° C or more.

In a preferred embodiment, the steps i) to iv) are repeated one or more times. In this case, in the repetition for providing the aqueous medium containing dissolved lithium carbonate used as lithium carbonate-free or lithium carbonate poor aqueous medium, the aqueous medium obtained in a previous step iii) in the separation of solid lithium fluoride from the aqueous suspension of lithium fluoride. In this case, the lithium carbonate-free or lithium carbonate-poor aqueous medium contains dissolved lithium fluoride, typically up to the saturation limit at the respective temperature.

In one embodiment, the contacting of the lithium carbonate-free or aqueous medium with the solid lithium carbonate may be accomplished in a stirred reactor, flow-through reactor, or any other apparatus known to those skilled in the art for contacting liquid with solids. Preferably, in the sense of a short residence time and achieving a concentration of lithium carbonate in the aqueous medium used as close as possible to the saturation point, an excess of lithium carbonate is used, ie, so much that complete dissolution of the solid lithium carbonate can not take place. In order to limit the solids content according to (ii) in this case, filtration, sedimentation, centrifugation or any other method known to the person skilled in the art for the separation of solids from or from liquid is then carried out, filtration being preferred. If the process steps i) to iii) are repeated and / or carried out continuously, filtration through a cross-flow filter is preferred. The temperature when contacting can be carried out, for example, from the freezing point to the boiling point of the aqueous medium used, preferably 0 to 100 ° C, more preferably 10 ° to 60 ° C and particularly preferably 10 ° to 35 ° C, in particular 16 to 24 ° C.

The pressure when contacting can be, for example, 100 hPa to 2 MPa, 900 hPa to 1200 hPa, in particular ambient pressure is particularly preferred.

In the context of the invention, technical lithium carbonate is understood as meaning lithium carbonate which has a purity of 95.0 to 99.9% by weight, preferably 98.0 to 99.8% by weight and particularly preferably 98.5 to 99.8% by weight. -% based on anhydrous product possesses.

Preferably, the technical lithium carbonate further contains foreign ions, i. ions that are not lithium or carbonate ions

1) a content of 200 to 5000 ppm, preferably 300 to 2000 and more preferably 500 to 1200 ppm of sodium in ionic form and / or

2) a content of 5 to 1000 ppm, preferably 10 to 600 ppm of potassium in ionic form and / or

3) a content of 50 to 1000 ppm, preferably 100 to 500 and particularly preferably 100 to 400 ppm of calcium in ionic form and / or

4) a content of 20 to 500 ppm, preferably 20 to 200 and particularly preferably 50 to 100 ppm of magnesium in ionic form. Furthermore, the technical lithium carbonate further contains foreign ions, i. ions which are not lithium or carbonate ions: i) a content of 50 to 1000 ppm, preferably 100 to 800 ppm of sulfate and / or ii) a content of 10 to 1000 ppm, preferably 100 to 500 ppm of chloride,

also based on the anhydrous product.

In general, the sum of lithium carbonate and the abovementioned foreign ions 1) to 4) and optionally i) and ii) does not exceed 1,000,000 ppm, based on the total weight of the technical lithium carbonate, relative to the anhydrous product.

In a further embodiment, the technical lithium carbonate has a purity of 98.5 to 99.5% by weight and a content of 500 to 2000 ppm of foreign metal ions, i. Sodium, potassium, magnesium and calcium.

In a further embodiment, the technical lithium carbonate preferably additionally has a content of 100 to 800 ppm of foreign anions, ie sulfate or chloride, based on the anhydrous product. Unless otherwise stated, the ppm data given herein are based on parts by weight in general, the contents of said cations and anions are determined by ion chromatography, unless stated otherwise in the experimental section.

In one embodiment of the method according to the invention, the provision of the aqueous medium containing lithium carbonate or the contacting of a lithium carbonate-free or poor, aqueous medium with solid lithium carbonate batchwise or continuously, wherein the continuous implementation is preferred.

The aqueous medium containing dissolved lithium carbonate provided according to step i) typically has a pH of 8.5 to 12.0, preferably of 9.0 to 11.5, measured or calculated at 20 ° C and 1013 hPa.

Before the aqueous medium containing dissolved lithium carbonate provided in step i) is used in step (ii), it can be passed over an ion exchanger in order, in particular, to at least partially remove calcium and magnesium ions. For example, weakly or strongly acidic cation exchangers can be used for this purpose. For use in the process according to the invention, the ion exchangers can be used in devices, such as, for example, flow columns which are filled with the cation exchangers described above, for example in the form of powders, beads or granules.

Particularly suitable are ion exchangers containing copolymers of at least styrene and divinylbenzene, which also contain, for example, aminoalkylenephosphonic acid groups or iminodiacetic acid groups.

Such ion exchangers are, for example, those of the Lewatit ™ type such as Lewatit ™ OC 1060 (AMP type), Lewatit ™ TP 208 (IDA type), Lewatit ™ E 304/88, Lewatit ™ S 108, Lewatit TP 207, Lewatit ™ S 100; Amberlite ™ type such as Amberlite ™ IR 120, Amberlite ™ IRA 743; those of the Dowex ™ type, such as Dowex ™ HCR; those of the Duolite type, such as Duolite ™ C 20, Duolite ™ C 467, Duolite ™ FS 346; and Imac ™ type such as Imac ™ TMR, with Lewatit ™ types being preferred.

Preferably, such ion exchangers are used, which are as low-sodium as possible. For this purpose, it is advantageous to rinse the ion exchanger before use with the solution of a lithium salt, preferably an aqueous solution of lithium carbonate.

In one embodiment of the method according to the invention, no treatment with ion exchangers takes place. According to step ii), the reaction of the aqueous medium provided according to step i) comprising dissolved lithium carbonate with gaseous hydrogen fluoride is carried out to give an aqueous suspension of solid lithium fluoride.

The reaction can be carried out, for example, by introducing or passing a gaseous hydrogen fluoride-containing gas stream into or over the aqueous medium containing dissolved lithium carbonate, or by spraying, atomizing or flowing through the aqueous medium containing dissolved lithium carbonate in or through a gas containing gaseous hydrogen fluoride.

Due to the very high solubility of gaseous hydrogen fluoride in aqueous media, it is preferred to pass, spray, mist or flow through it, with pass-over being even more preferred.

Gaseous hydrogen fluoride contained as a gaseous hydrogen fluoride gas or gas containing gaseous hydrogen fluoride can be used as such or a gas containing gaseous hydrogen fluoride and an inert gas, an inert gas is to be understood as a gas that does not react with lithium fluoride under the usual reaction conditions. Examples are air, nitrogen, argon and other noble gases or carbon dioxide, with air and more nitrogen being preferred.

The proportion of inert gas can vary as desired and, for example, 0.01 to 99 vol .-%, preferably 1 to 20 vol .-%. In a preferred embodiment, the gaseous hydrogen fluoride used contains 50 ppm of arsenic in the form of arsenic compounds or less, preferably 10 ppm or less. The indicated arsenic contents are determined photometrically after conversion to arsenic hydrogen and its reaction with silver diethyldithiocarbaminate to give a red color complex (spectrophotometer, for example LKB Biochrom, Ultrospec) at 530 nm. In a likewise preferred embodiment, the gaseous hydrogen fluoride used contains 100 ppm of hexafluorosilicic acid or less, preferably 50 ppm or less. The indicated hexafluorosilicic acid content is determined photometrically as silicomolybdic acid and its reduction with ascorbic acid to a blue color complex (spectrophotometer, e.g., LKB Biochrom, Ultrospec). Disturbing effects of fluorides are suppressed by boric acid, interfering reactions of phosphate and arsenic by the addition of tartaric acid.

In the reaction according to step ii), lithium fluoride is formed, which precipitates due to the fact that it is less soluble in the aqueous medium than lithium carbonate, and consequently an aqueous Forms suspension of solid lithium fluoride. It is known to those skilled in the art that lithium fluoride has a solubility of about 2.7 g / l at 20 ° C.

The reaction is preferably carried out in such a way that the resulting aqueous suspension of solid lithium fluoride reaches a pH of 3.5 to 8.0, preferably 4.0 to 7.5, and more preferably 5.0 to 7.2. Carbon dioxide is liberated at the stated pH values. In order to enable its release from the suspension, it is advantageous to pass the suspension to, for example, stirring or via static mixing elements.

The temperature in the reaction according to step ii) can be, for example, from the freezing point to the boiling point of the aqueous medium containing dissolved lithium carbonate, preferably 0 to 65 ° C., more preferably 15 ° to 45 ° C. and particularly preferably 15 ° to 35 ° C., especially 16 to 24 ° C.

The pressure in the reaction according to step ii) can be, for example, 100 hPa to 2 MPa, 900 hPa to 1200 hPa, in particular ambient pressure is particularly preferred.

In step iii), the separation of the solid lithium fluoride from the aqueous suspension. Separation is accomplished, for example, by filtration, sedimentation, centrifugation, or any other method known to those skilled in the art for separating solids from or from liquids, with filtration being preferred.

If the filtrate for step i) is used again and the process steps a) to c) are carried out repeatedly, filtration through a cross-flow filter is preferred. The solid lithium fluoride thus obtained typically still has a residual moisture of from 1 to 40% by weight, preferably from 5 to 30% by weight.

Before the lithium fluoride separated in step iii) is dried according to step iv), it can be washed once or several times with water or a medium containing water and water-miscible organic solvents. Water is preferred. Water having an electrical resistance of 5 ΩΩ-crri at 25 ° C or more, alternatively 15 ΩΩ-crri at 25 ° C or more is particularly preferable. From step iii) adhering to the solid lithium fluoride water with foreign ions is thereby removed as far as possible.

In step iv), the lithium fluoride is dried. The drying can be carried out in any apparatus known to the person skilled in the art for drying. Preferably, the drying is carried out by heating the lithium fluoride, preferably at 100 to 800 ° C, more preferably 200 to 500 ° C.

The production of lithium fluoride will be explained in more detail with reference to FIG. In a device for producing lithium fluoride 1 is solid lithium carbonate (Li ₂ C0 ₃ (s)) with water (H ₂ 0) and, if it is not the Erstbefüllung the device 1, the filtrate from the filtration unit 19 in the template 3, wherein the lithium carbonate at least partially dissolves. The suspension thus obtained is conveyed via the line 4 through the pump 5 via a filtration unit 6, which is designed here as a cross-flow filter, wherein undissolved lithium carbonate is recycled to the template 3 via line 7 and the filtrate, the aqueous medium containing dissolved Lithium carbonate is introduced via the line 8 in the reactor 9. In the reactor 9, a gas stream containing gaseous hydrogen fluoride, which in this case contains gaseous hydrogen fluoride and nitrogen, is introduced via line 10 into the gas space 11 of the reactor, which is located above the liquid space 12 of the reactor. By the pump 13, the contents of the liquid space 12, which initially consists essentially of the aqueous medium containing dissolved lithium carbonate and is converted by the reaction into a suspension containing solid lithium fluoride, passed via line 14 to a packed column 15, in the release of the promoted carbon dioxide formed during the reaction from the suspension. About the outlet 16, the carbon dioxide and the nitrogen used as a diluent is discharged. After passing through the packed column, the contents of the liquid space 12 guided out of the reactor 9 flow back into the liquid space 12 through the gas space 11. The return through the gas space 11 has the advantage that the liquid surface, in part also by passive atomization, is increased, which promotes the reaction with gaseous hydrogen fluoride. After reaching the target pH or sufficient formation of solid lithium fluoride, the resulting suspension of solid lithium fluoride is pumped by the pump 17 via line 18 to the filtration unit 19, which is designed here as a cross-flow filter. The solid lithium fluoride (LiF (s)) is recovered, the filtrate, the lithium carbonate-free or lithium carbonate poor aqueous medium is recycled via line 20 in the template 3. Since the recovered lithium fluoride has a residual content of water and water is discharged via the outlet 16 with the carbon dioxide, the supply of water (H ₂ 0) in the template 3 is essentially after the initial filling of the device 1 to compensate for the loss of water described above in further cycles.

It is clear to the person skilled in the art that foreign metal ions, in particular sodium and potassium, which form readily water-soluble carbonates and fluorides, accumulate in the circulation stream of the aqueous media. However, it was found that even with a high number of cycles of 10 to 500 cycles even without discharge of filtrate of the filtration unit 19 a consistently high quality of lithium fluoride could be obtained. Optionally, a portion of the filtrate of the filtration unit 19 via the outlet 22 on the valve 21, which is designed here as an example as a three-way valve, be discharged. By returning the filtrate of the filtration unit 19 in the template 3, it is possible in the Lithiumfluoridherstellung a degree of conversion of 95% or more, especially at high repetition numbers of steps a) to d), also called cycle numbers, for example, 30 or more even of 97% or more to be achieved, wherein the degree of conversion is the yield of high-purity lithium fluoride based on the lithium carbonate used.

In step a), solid lithium fluoride is contacted with a gas stream containing phosphorus pentafluoride. The phosphorus pentafluoride can be prepared in a manner known per se by a process which comprises at least the following steps.

1) Reaction of phosphorus trichloride with hydrogen fluoride to phosphorus trifluoride and

Hydrochloric

2) reaction of phosphorus trifluoride with elemental chlorine to trifluoride phosphorodichloride

3) Reaction of phosphorodichloride trifluoride with hydrogen fluoride

Phosphorus pentafluoride and hydrogen chloride The gas mixture obtained according to step 3) can be used directly with or without removal of the hydrogen chloride in step a) as gas containing phosphorus pentafluoride without there being any appreciable accumulation of chloride in the resulting lithium hexafluorophosphate.

As the gas containing phosphorus pentafluoride, therefore, typically, a gas mixture containing 5 to 41% by weight of phosphorus pentafluoride and 6 to 59% by weight of hydrogen chloride, preferably 20 to 41% by weight of phosphorus pentafluoride and 40 to 59% by weight of hydrogen chloride is particularly preferred 33 to 41 wt .-% phosphorus pentafluoride and 49 to 59 wt .-% hydrogen chloride are used, wherein the proportion of phosphorus pentafluoride and hydrogen chloride, for example 11 to 100 wt .-%, preferably 90 to 100 wt .-% and particularly preferably 95 to 100 Wt .-% is. The difference to 100 wt .-%, if present at all, may be inert gases, wherein an inert gas is to be understood here as a gas that does not react with phosphorus pentafluoride, fluorine or hydrogen chloride or lithium fluoride under the usual reaction conditions. Examples are nitrogen, argon and other noble gases or carbon dioxide, with nitrogen being preferred.

The difference to 100 wt .-%, if any, may alternatively or additionally continue to be hydrogen fluoride. Based on the overall process via stages 1) to 3), hydrogen fluoride is used, for example, in an amount of 4.5 to 8, preferably 4.8 to 7.5 and particularly preferably 4.8 to 6.0 mol of hydrogen fluoride per mole of phosphorus trichloride.

Typically, the gas containing phosphorus pentafluoride is therefore a gas mixture containing 5 to 41% by weight of phosphoφentafluoride, 6 to 59% by weight of hydrogen chloride and 0 to 50% by weight of hydrogen fluoride, preferably 20 to 41% by weight of phosphorus pentafluoride, 40 to 59 % By weight of hydrogen chloride and 0 to 40% by weight of hydrogen fluoride, particularly preferably 33 to 41% by weight of phosphorus pentafluoride, 49 to 59% by weight of hydrogen chloride and 0 to 18% by weight of hydrogen fluoride, the proportion of phosphorus pentafluoride, Hydrogen chloride and hydrogen fluoride, for example 11 to 100 wt .-%, preferably 90 to 100 wt .-% and particularly preferably 95 to 100 wt .-% is.

The reaction pressure in step a) is, for example, 500 hPa to 5 MPa, preferably 900 hPa to 1 MPa, and more preferably 0, 1 MPa to 0.5 MPa.

The reaction temperature in step a) is for example -60 ° C to 150 ° C, preferably between 20 ° C to 150 ° C and most preferably between -10 ° C and 20 ° C or between 50 and 120 ° C. At temperatures above 120 ° C., it is preferable to work under a pressure of at least 1500 hPa.

The reaction time in step a) is, for example, from 1 to 24 hours, preferably from 5 seconds to 10 hours, alternatively from 10 seconds to 24 hours, preferably from 5 to 10 hours. When using a gas containing phosphorus pentafluoride and hydrogen chloride gas leaving the fixed bed reactor or the fluidized bed in an aqueous solution of alkali hydroxide, preferably an aqueous solution of potassium hydroxide, more preferably in a 5 to 30 wt%, most preferably in a 10 to 20 wt .-%, in particular preferably collected in a 15 wt .-% potassium hydroxide in water. Surprisingly, under the conditions typical of the invention, hydrogen chloride does not react measurably with lithium fluoride, so that hydrogen chloride exits from the fixed-bed or fluidized-bed reactor and is then preferably neutralized.

Preferably, the preparation of the gas or gas mixture used in step a) takes place in the gas phase. The reactors to be used for this purpose, preferably tube reactors, in particular stainless steel tubes, and the fixed bed or fluidized bed reactors to be used for the synthesis of the lithium hexafluorophosphate are known to the person skilled in the art and are described, for example, in US Pat Textbook of Technical Chemistry - Volume 1, Chemical Reaction Engineering, M. Baerns, H. Hofmann, A. Renken, Georg Thieme Verlag Stuttgart (1987), pp. 249-256.

In step b), the contacting of the reaction mixture formed according to a) is carried out with an organic solvent. The reaction mixture typically contains the valuable product lithium hexafluorophosphate and unreacted lithium fluoride.

Preferably, the reaction is conducted so that 1 to 98 wt .-%, preferably 90 to 98 wt .-% of the solid lithium fluoride used are converted into lithium hexafluorophosphate.

Alternatively, the reaction is conducted so that 2 to 80 wt .-% and preferably 4 to 80 wt .-% of the solid lithium fluoride used are converted into lithium hexafluorophosphate.

The contacting of the reaction mixture formed according to a) with an organic solvent takes place in a preferred embodiment, after the fixed bed or the fluidized bed is purged with inert gas and thus traces of fluorine or hydrogen chloride or phosphorus pentafluoride were removed. Inert gases are to be understood as meaning gases which do not react with phosphorus pentafluoride, fluorine or hydrogen chloride or lithium fluoride under the usual reaction conditions. Examples are nitrogen, argon and other noble gases or carbon dioxide, with nitrogen being preferred.

Organic solvents which are preferably used are organic solvents which are liquid at room temperature and have a boiling point of 300 ° C. or less at 1013 hPa and which furthermore contain at least one oxygen atom and / or one nitrogen atom.

Preferred solvents are furthermore those which have no protons which have a pKa value at 25 ° C., based on water or an aqueous comparison system of less than 20. Such solvents are also referred to in the literature as "aprotic" solvents.

Examples of such solvents are liquid at room temperature nitriles, esters, ketones, ethers, acid amides or sulfones.

Examples of nitriles are acetonitrile, propanitrile and benzonitrile.

Examples of ethers are diethyl ether, diisopropyl ether, methyl tert-butyl ether,

Ethylene glycol dimethyl and diethyl ether, 1,3-propanedioldimethyl and diethyl ether, dioxane and tetrahydrofuran. Examples of esters are methyl and ethyl acetate and butyl acetate or organic carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) or propylene carbonate (PC) or ethylene carbonate (EC).

An example of sulfones is sulfolane.

Examples of ketones are acetone, methyl ethyl ketone and acetophenone

Examples of acid amides are N, N-dimethylformamide, Ν, Ν-dimethylacetamide, N-methylformanilide, N-methylpyrrolidone or hexamethylphosphoric triamide.

Particular preference is given to using acetonitrile, dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) or ethylene carbonate (EC) or a mixture of two or more of these solvents. Particular preference is given to using dimethyl carbonate.

Preferably, contacting the reaction mixture formed with an organic solvent to dissolve the resulting lithium hexafluorophosphate for a period of 5 minutes to 24 hours, more preferably from 1 hour to 5 hours, using a bed or fluidized bed reactor such that the reactor contents of the fixed bed reactor or the fluidized bed reactor is brought into contact with organic solvent as long as possible, preferably with stirring or with pumping, until the content of lithium hexafluorophosphate in the solvent remains constant.

For example, the weight ratio of organic solvent used to originally used lithium fluoride is 1: 5 to 100: 1.

In a further embodiment, so much organic solvent is used that the concentration of lithium hexafluorophosphate in the organic solvent resulting from step b) or c) is from 1 to 35% by weight, preferably from 5 to 35% by weight and more preferably from 8 to 30 Wt .-% is.

The organic solvent to be used is preferably subjected to a drying process prior to its use, more preferably a drying process over a molecular sieve.

The water content of the organic solvent should be as low as possible. In one embodiment, it is 0 to 500 ppm, preferably 0 to 200 ppm, and more preferably 0 to 100 ppm.

Molecular sieves preferably to be used according to the invention for drying are zeolites. Zeolites are crystalline aluminosilicates that can be found in many modifications in nature, but can also be produced synthetically. More than 150 different zeolites have been synthesized, 48 naturally occurring zeolites are known. The natural zeolites are summarized mineralogically under the term zeolite group. The composition of the substance group zeolites is:

Mn ⁺ _{x / n} [A10 ₂ ] _x (Si0 ₂ ) _y ] z H ₂ 0

The factor n is the charge of the cation M and is preferably 1 or 2.

M is preferably a cation of an alkali or alkaline earth metal. These cations are required for electrical charge balance of the negatively charged aluminum Tertraeder and are not incorporated into the main Gitte of the crystal, but remain in cavities of the lattice and are therefore also easily within the grid movable and also in the

Retrospectively interchangeable.

The factor z indicates how many water molecules were absorbed by the crystal.

Zeolites can absorb water and other low-molecular substances and release them again on heating without destroying their crystal structure.

• The molar ratio of Si0 ₂ to A10 ₂ or x / y in the empirical formula is called modulus. It can not be less than 1 due to the Löwenstein rule.

Synthetic zeolites preferably to be used as molecular sieve according to the invention are:

The organic solvent containing lithium hexafluorophosphate usually also contains amounts of unreacted, not or not appreciably soluble lithium fluoride, which is separated from the organic solvent according to step c). The separation in step c) preferably takes place by means of filtration, sedimentation, centrifugation or flotation, particularly preferably by means of filtration, particularly preferably by filtration through a filter having an average pore size of 200 nm or less. Further possibilities for solids separation are known to the person skilled in the art. The separated lithium fluoride is preferably recycled for use in step a). In this way, a total of 95 wt .-% or more, preferably 98 wt .-% or more of the lithium fluoride used can ultimately be converted into lithium hexafluorophosphate.

The inventively available solutions of lithium hexafluorophosphate typically have a chloride content <100 ppm, preferably <50 ppm, more preferably <5 ppm, whereby they can be processed in particular to suitable for electrochemical storage devices electrolyte.

The apparatus used in the present work is described in FIG. In Fig. 2 mean

I template tempered, anhydrous hydrogen fluoride with Massflow controller

2 original phosphorus trichloride

3 template elemental chlorine

4 pump

5 phosphorus trichloride evaporator

6 stainless steel pipe

7 stainless steel pipe

8 heat exchangers

9 fluidized bed reactor

10 stirrers

I I scrubber

12 disposal containers

Preferably, a combination of at least two series-connected tube reactors, preferably stainless steel tube 6 and stainless steel tube 7, is used for the production of phosphorus pentafluoride in combination via at least one heat exchanger with at least one fixed bed reactor or fluidized bed reactor, in which then the reaction of the phosphorus pentafluoride and finally solid lithium fluoride to lithium hexafluorophosphate. The reaction flow of the reactants is described by way of example with reference to FIG. 2, here with two tubular reactors, a heat exchanger and a fluidized-bed reactor, as follows. By a heated stainless steel tube 6, preferably at temperatures of 20 ° C to 600 ° C, more preferably at 300 ° C to 500 ° C or alternatively 100 ° C to 400 ° C, pre-tempered hydrogen fluoride, preferably preheated to 30 ° C to 100 ° C, gaseously dosed from a template 1 and reacted with gaseous phosphorus trichloride. The gaseous phosphorus trichloride is previously liquid from template 2 by means of pump 4 in the evaporator 5, preferably tempered between 100 ° C and 400 ° C, more preferably between 200 ° C and 300 ° C, transferred and mixed from this with the hydrogen fluoride in stainless steel pipe 6 and this heated, preferably at the above temperatures. The resulting reaction mixture is transferred to stainless steel tube 7 and mixed there with elemental chlorine from template 3, preferably at 0 ° C to 400 ° C, alternatively tempered at 40 ° C to 400 ° C, more preferably at 0 ° C to 40 ° C, and reacted. The resulting gas mixture containing phosphorus pentafluoride is cooled by means of heat exchangers, preferably at -60 ° C to 80 ° C, more preferably at -10 ° C to 20 ° C, and with solid lithium fluoride in the fluidized bed reactor 9, preferably at temperatures of -60 ° C. up to 150 ° C, preferably between 20 ° C to 150 ° C and most preferably between -10 ° C and 20 ° C or between 50 and 120 ° C, brought into contact, preferably by stirring by means of stirrer 10, or by turbulence or a combination of both. The gas mixture leaving the fluidized-bed reactor 9 is freed of acidic gases in the scrubber 11 and the resulting halide-containing solution is transferred to the disposal container 12. The solid reaction mixture remains in the fixed bed reactor / fluidized bed reactor 9 and is there partially dissolved by contacting with the organic solvent and the resulting suspension separated from the solid.

If the solution containing lithium hexafluorophosphate is not used directly as an electrolyte or for the preparation of an electrolyte, the removal of organic solvent can be carried out as step d) at least in part.

If the removal is partial, the setting of a specific content of lithium hexafluorophosphate is possible. If it is largely complete, highly pure lithium hexafluorophosphate can be obtained as a solid. Almost complete here means that the remaining content of organic solvent is 5000 ppm or less, preferably 2000 ppm or less.

The invention therefore furthermore relates to the use of the solutions obtained according to the invention as or for the preparation of electrolytes for lithium batteries or for the production of solid lithium hexafluorophosphate. The invention further relates to a process for the preparation of electrolytes for

Lithium accumulators characterized in that it comprises at least steps a) to c) and optionally d).

The advantage of the invention lies in particular in the efficient procedure and the high purity of the lithium hexafluorophosphate obtained.

Examples

In the following, the term "%" always means wt .-%.

The particle size distributions given in the following examples were determined by laser diffractometry using a Coulter LS230 particle size analyzer in ethanol. Three measurements were taken per sample and these were averaged - if no trend could be seen. Each measurement took 90s. As a result, the "D10" and "D50" values are given below, as explained above.

With regard to the ion chromatography used in the present work, reference is made to the publication of the TU Bergakademie Freiberg, Faculty of Chemistry and Physics, Institute of Analytical Chemistry from March 2002 and the literature cited therein.

The analysis for the present anions (in particular chloride and hexafluorophosphate) and cations are carried out by ion chromatography. The following devices and settings are used for this:

Cations (Dionex ICS 2100):

Column: IonPac CS16 3 * 250-mm Analytical column with protective device

Sample volume: 1 μΐ

Eluent: 36 mM constant concentration methanesulfonic acid

Eluen flow rate: 0.5 ml / min

Temperature: 60 ° C

SRS: CSRS 300 (2mm)

Anions (Dionex ICS 2100):

Column: IonPac AS20 2 * 250-mm Analytical column with protection device

Sample volume: 1 μΐ

Eluent: KOH gradient: 0 min / 15 mM, 10 min / 15 mM, 13 min / 80 mM,

27 min / 100 mM, 27.1 min / 15 mM, 34 min / 15 mM

Eluen flow rate: 0.25 ml / min

Temperature: 30 ° C

SRS: ASRS 300 (2mm) Example 1: Preparation of high purity Lithiumfluoi id

In a device according to FIG. 1, in the original 3, 500 g of solid lithium carbonate of industrial grade (purity:> 98% by weight, Na: 231 ppm, K: 98 ppm, Mg: 66 ppm, Ca: 239 ppm) and 20 liters of water submitted and prepared at 20 ° C, a suspension. After about five minutes, the suspension was passed through the filtration unit 6, which was designed as a cross-flow filter, and the resulting medium containing dissolved lithium carbonate, here an aqueous solution of lithium carbonate with a content of 1.32 wt .-%, via line 8th transferred to the reactor 9.

After a total of 4 kg of the medium were pumped into the reactor 9, the feed from the filtration unit 6 and was stopped in the reactor 9 gaseous hydrogen fluoride in the gas space 1 1 with continuous pumping of the medium through the pump 13, the line 14 and the packed column 15th began. This dosage was terminated when the pH of the pumped solution was 7.0.

The resulting suspension from the reactor 9 was conveyed via the pump 17 and the line 18 to the filtration unit 19, which was designed here as Drucknutsche, filtered there, and the filtrate, here fed back a lithium carbonate-free aqueous medium via the line 20 to the template 3. The lithium carbonate-free aqueous medium had a lithium fluoride content of about 0.05% by weight.

The above procedure was repeated five times. The still wasserfeuchte Lithiumfluoiid (total 148g) separated on the filtration unit 19 was removed and washed on a further pressure filter three times with water having a conductivity of 5 ΩΩ-cm at 25 ° C (30 ml each).

The Lithiumfluoiid thus obtained was dried in a vacuum oven at 90 ° C and lOOmbar. Yield: 120g of a white, fine powder.

The product obtained had a potassium content of 0.5 ppm and a sodium content of 2.5 ppm, the magnesium content of the product was 99 ppm, the calcium content of 256 ppm. The chloride content was less than 10 ppm. The measurement of the particle size distribution gave a D50 value of 45 μηι and a DlO value of 22 μηι. The bulk density was 1.00 g / cm ³ .

When performing 50 cycles (repetitions), a total of 97% of the lithium used was obtained in the form of high-purity lithium fluoride.

Example 2

In a device according to Figure 1, but in addition in line 8 a flow column with a bed of the ion exchanger Lewatit TP 207, a iminodiacetic acid-containing copolymers of styrene and divinylbenzene had, were in the template 3 500 g of solid lithium carbonate technical grade (purity: > 98 wt .-%, Na: 231 ppm, K: 98 ppm, Mg: 66 ppm, Ca: 239 ppm) and 20 liters of water and prepared at 20 ° C, a suspension. After about five minutes, the suspension was passed through the filtration unit 6, which was designed as a cross-flow filter, and the resulting medium containing dissolved lithium carbonate, here an aqueous solution of lithium carbonate with a content of 1.32 wt .-%, via line 8th and the flow column described above, transferred to the reactor 9. The further reaction was carried out according to Example 1.

The ion exchanger used was previously washed by rinsing with an approximately 1% strength lithium carbonate solution until the leaving water had a sodium content <1 ppm.

Yield: 149.8 g of a white, fine powder. The product obtained had a potassium content of 0.5 ppm and a sodium content of 1 ppm, the magnesium content of the product was 13 ppm, the calcium content was 30 ppm. The chloride content was less than 10 ppm.

The measurement of the particle size distribution gave a D50 value of 36 μπι and a DlO value of 14 μπι. The bulk density was 0.91 g / cm ³ . Examples 3 to 6:

Preparation of Electrolyte Solutions Containing Lithium Hexafluorophosphate EXAMPLE 3 A metal tube about 6 m long and heated to 450 ° C. with an internal diameter of 8 mm gave a mixture of about 1.03 mol / h of gaseous hydrogen fluoride and 0.21 mol / h of gaseous phosphorus trichloride directed. In this reaction mixture, 8 1 / h of chlorine were introduced and the reaction mixture passed through another, about 4 m long metal tube which was heated to 250 ° C. The gaseous reaction product was cooled to room temperature and then passed through a Teflon frit through a stainless steel tube with a 45 mm inner diameter Teflon inner tube to 190 mm with lithium fluoride powder (300.0 g) prepared according to Example 1 , was stocked. During the reaction, the lithium fluoride powder was stirred with a stirrer. The flow rate was about 40 1 / h.

The gas mixture exiting the reactor was collected in an aqueous potassium hydroxide solution (15% by weight).

After a total reaction time of 7 hours, the metered addition of the educts was replaced by the metered addition of an inert gas and the reactive gas was displaced from the system.

By washing the solid reaction residue with anhydrous acetonitrile, a total of 76.9 g of lithium hexafluorophosphate could be isolated and detected. The remaining unreacted lithium fluoride was reused for further experiments.

The acetonitrile was evaporated with the exclusion of water and oxygen, and the resulting residue was taken up in a mixture of dimethyl carbonate and ethylene carbonate (1: 1 w / w) to obtain a 11.8% by weight solution of lithium hexafluorophosphate. This solution was characterized among other things as follows:

Na <3 ppm

K <1 ppm

Ca <1 ppm

Mg <1 ppm

Sulfate <1 ppm Chloride <1 ppm

Example 4:

A mixture of about 1.03 mol / h of gaseous hydrogen fluoride and 0.21 mol / h of gaseous phosphorus trichloride was passed through a metal tube with an inner diameter of 8 mm, which was heated to 450.degree. C. and about 6 m long. In this reaction mixture, 8 1 / h of chlorine were introduced and the reaction mixture passed through another, about 4 m long metal tube which was heated to 250 ° C.

The gaseous reaction product was cooled to -10 to 0 ° C and then passed through a stainless steel tube with an inner diameter of about 18 mm, which was equipped with shaped bodies of lithium fluoride (52.2 g). These moldings were previously prepared by extrusion from a mixture of lithium fluoride with water, wherein the solids content was about 70% and the moldings were dried for several days after the extrusion at 120 ° C.

The lithium fluoride used was obtained commercially and had a purity of> 98% by weight. The D10 value was 0.43 μτη, the D50 value 4.9 μτη. The bulk density was 0.65 g / cm ³ . The gas mixture exiting the reactor was collected in an aqueous potassium hydroxide solution (15% by weight). After a total reaction time of 4 hours, the metered addition of the educts was replaced by the metered addition of an inert gas and the reactive gas was displaced from the system. Subsequently, 446.3 g of a mixture of dimethyl carbonate and ethylene carbonate (1: 1 based on the weights used) were pumped over the reactor containing unreacted lithium fluoride and the reaction product lithium hexafluorophosphate in circulation for about 20 hours. There were obtained 358.8 g of a reaction mixture from which a sample was filtered through a syringe filter with a 0.2 μιη filter and examined by means of ion chromatography. The filtered reaction mixture contained 9, 15 wt .-% lithium hexafluorophosphate, the chloride content was <5 ppm.

Example 5:

A mixture of about 1.03 mol / h of gaseous hydrogen fluoride and 0.21 mol / h of gaseous phosphorus trichloride was passed through a metal tube with an inner diameter of 8 mm, which was heated to 450.degree. C. and about 6 m long. In this reaction mixture, 8 1 / h of chlorine were introduced and the reaction mixture passed through another, about 4 m long metal tube which was heated to 250 ° C. The reaction product was cooled to -10 to 0 ° C and then passed through a fixed bed reactor with a diameter of about 18 mm, which was equipped with shaped bodies of lithium fluoride (359 g). These moldings were previously prepared by extrusion from a mixture of lithium fluoride with water, wherein the solids content was about 70% and the moldings were dried for several days after the extrusion at 120 ° C.

The lithium fluoride used was obtained commercially and had a purity of> 98% by weight. The D10 value was 0.43 μτη, the D50 value 4.9 μτη. The bulk density was 0.65 g / cm ³ .

The gas mixture exiting the reactor was collected in an aqueous potassium hydroxide solution (15% by weight). After a total of about 16 hours of reaction time, the dosage of the educts was replaced by the metering of an inert gas and displaced the reaction gas from the system. Thereafter, 1401 g of acetonitrile dried over molecular sieve 4A were pumped through the reactor containing unreacted lithium fluoride and the reaction product lithium hexafluorophosphate in the circulation for about 2 hours. There were obtained 1436 g of a reaction mixture from which a sample was filtered through a syringe filter with a 0.2 μιη filter and analyzed by ion chromatography. The filtered reaction mixture contained 16, 17 wt -.% Lithium hexafluorophosphate, the chloride content was 67 ppm.

Example 6: A mixture of 23 l / h HF and 0.48 g / min PC1 ₃ (both in gaseous form) was passed through a stainless steel tube (ID 8 mm) heated to 450 ° C., about 6 m long. 5.3 l / h of chlorine were introduced into this reaction mixture and passed through another, approximately 4 m long, stainless steel tube (ID 8 mm), which was heated to 250 ° C.

The reaction product was cooled to -10 to 0 ° C and then passed through a fixed bed reactor with a diameter of about 18 mm, which was equipped with moldings of LiF (384 g). These moldings were previously prepared by extrusion from a mixture of LiF with water, wherein the solids content was about 70% and the moldings were dried for several days after the extrusion at 120 ° C.

The lithium fluoride used was obtained commercially and had a purity of> 98% by weight. The D10 value was 0.43 μτη, the D50 value 4.9 μτη. The bulk density was 0.65 g / cm ³ . The gas mixture exiting the reactor was collected in an aqueous potassium hydroxide solution (15% by weight). After a total reaction time of about 7 hours, the metered addition of the educts was replaced by the metered addition of an inert gas and the reactive gas was displaced from the system. Anschießend 400 g of dimethyl carbonate were pumped through the reactor containing unreacted lithium fluoride and the reaction product lithium hexafluorophosphate in circulation for about 3 hours. There were obtained 306.5 g of a reaction mixture from which a sample was filtered through a syringe filter with a 0.2 μιη filter and analyzed by ion chromatography. The filtered reaction mixture contained 32.6 wt .-% lithium hexafluorophosphate, the chloride content was 11 ppm.

Example 7:

A mixture of Hastelloy (C4) with a length of 12 m and an inner diameter of about 9 mm heated by a reactor tube heated to 280 ° C, a mixture of 2.25 mol / h HF and 0.3 mol / h PC1 ₃ (both gaseous ). The reaction mixture was cooled to room temperature and metered 0.35 mol / h of chlorine. Subsequently, the gas mixture thus obtained was passed at 20 ° C through a 12 m long pipe with an inner diameter of 4 mm. The resulting gas mixture was passed through a cooled to 20 ° C stainless steel reactor with an inner diameter of 50 mm and with a built-stainless steel stirrer, in which 150 g of LiF powder (5.8 mol) were filled with a d50 value of 42 μπι. The introduction was carried out until it was detectable at the reactor outlet PF ₅ . Then the dosage of PC1 ₃ was reduced so that as little as possible or no PF _{5 was} detectable. In the course of 33 hours, a total of 799 g of PC1 ₃ (5.8 mol) were reacted.

The reaction product was taken out of the reactor and analyzed. It consisted of 96 wt .-% of LiPF ₆ . 100 g of the LiPF ₆ thus obtained were dissolved in 400 g of acetonitrile having a water content of less than 30 ppm and filtered through a 50 nm filter. The filtrate contained 18.6% by weight of LiPF _{6 at} a chloride level of less than 1 ppm.

Claims

A process for producing solutions containing lithium hexafluorophosphate comprising at least the steps: a) bringing solid lithium fluoride into contact with a gas containing phosphorus pentafluoride, whereby a reaction mixture containing lithium hexafluorophosphate and unreacted lithium fluoride is obtained

b) bringing the reaction mixture formed according to a) into contact with an organic solvent, the lithium hexafluorophosphate formed at least partially going into solution

c) Separation of solid components from the solution containing lithium hexafluorophosphate.

Method according to claim 1, characterized in that the lithium fluoride used in step a) has a degree of purity of 98.0000 to 99.9999% by weight, preferably 99.0000 to 99.9999% by weight, more preferably 99.9000 to 99.9995% by weight, particularly preferably 99.9500 to 99.9995% by weight and most preferably 99.9700 to 99.9995% by weight, based on anhydrous product.

Method according to claim 1 or 2, characterized in that the lithium fluoride used contains foreign ions:

1) a content of 0.1 to 250 ppm, preferably 0.1 to 75 ppm, more preferably 0.1 to 50 and particularly preferably 0.5 to 10 ppm and most preferably 0.5 to 5 ppm sodium in ionic form and

2) has a content of 0.01 to 200 ppm, preferably 0.01 to 10 ppm, more preferably 0.5 to 5 ppm and particularly preferably 0.1 to 1 ppm of potassium in ionic form.

Method according to one of claims 1 to 3, characterized in that the lithium fluoride used contains foreign ions

i) a content of 0.1 to 1000 ppm, preferably 0.1 to 100 ppm and particularly preferably 0.5 to 10 ppm sulfate and/or

ii) has a content of 0.1 to 1000 ppm, preferably 0.5 to 500 ppm chloride.

5. The method according to any one of claims 1 to 4, characterized in that bringing solid lithium fluoride into contact with a gas containing phosphorus pentafluoride in a fixed bed or in a fixed bed reactor or a fluidized bed or a fluidized bed reactor.

6. The method according to any one of claims 1 to 5, characterized in that the solid lithium fluoride used is used in the form of shaped bodies or in the form of fine particles or in the form of a powder.

7. The method according to claim 6, characterized in that the solid lithium fluoride used is used in the form of shaped bodies which have a solids content in the range from 20 to 95% by weight, preferably in the range from 60 to 90% by weight, particularly preferably at 67 to 73% by weight and most preferably about 70% by weight.

8. The method according to any one of claims 1 to 7, characterized in that the solid lithium fluoride used has a D50 value of 4 to 1000 μm, preferably 15 to 1000 μm, more preferably 15 to 300 ppm, particularly preferably 15 to 200 μm and more more preferably 20 to 200 μιη.

9. The method according to any one of claims 1 to 8, characterized in that the solid lithium fluoride used has a D10 value of 0.5 μm or more, preferably 5 μm or more, more preferably 7 μm or more or a D10 value of 15 μιη or more.

10. The method according to any one of claims 1 to 9, characterized in that the solid lithium fluoride used has a bulk density of 0.6 g/cm ³ or more, preferably 0.8 g/cm ³ or more, more preferably 0.9 g/ cm ³ or more and particularly preferably from 0.9 g/cm ³ to 1.2 g/cm ³ .

11. The method according to any one of claims 1 to 10, characterized in that the phosphorus pentafluoride is produced by a method comprising at least the following steps.

1) Reaction of phosphorus trichloride with hydrogen fluoride to form phosphorus trifluoride and hydrogen chloride

2) Reaction of phosphorus trifluoride with elemental chlorine to produce phosphorus dichloride trifluoride

3) Reaction of phosphorus dichloride trifluoride with hydrogen fluoride to form phosphorus pentafluoride and hydrogen chloride.

12. The method according to any one of claims 1 to 11, characterized in that the gas containing phosphorus pentafluoride is a gas mixture containing 5 to 41% by weight of phosphorus pentafluoride and 6 to 59% by weight of hydrogen chloride, preferably 20 to 41% by weight of phosphorus pentafluoride and 40 to 59% by weight of hydrogen chloride, particularly preferably 33 to 41% by weight of phosphorus pentafluoride and 49 to 59% by weight of hydrogen chloride is used, the proportion of phosphorus pentafluoride and hydrogen chloride being, for example, 11 to 100% by weight, preferably 90 to 100% by weight and particularly preferably 95 to 100% by weight .- % amounts.

13. The method according to any one of claims 1 to 12, characterized in that the reaction pressure in step a) is 500 hPa to 5 MPa, preferably 900 hPa to 1 MPa and particularly preferably 1500 hPa to 0.5 MPa.

14. The method according to any one of claims 1 to 13, characterized in that the reaction according to step a) is carried out in such a way that 1 to 98% by weight, preferably 2 to 80% by weight and particularly preferably 4 to 80% by weight. -% of the solid lithium fluoride used in

Lithium hexafluorophosphate can be transferred.

15. The method according to any one of claims 5 to 14, characterized in that the reaction according to step a) is carried out in such a way that 50 to 100%, preferably 80 to 100%, particularly preferably 90 to 99.5% of the in the fixed bed or fluidized bed reactor are absorbed by the lithium fluoride.

16. The method according to any one of claims 2 to 15, characterized in that unreacted lithium fluoride is separated off in step c) and returned to step a).

17. The method according to any one of claims 2 to 16, characterized in that in step b) organic solvents which are liquid at room temperature and have a boiling point of 300 ° C or less at 1013 hPa are used as the organic solvent, which contain at least one oxygen atom and / or contain a nitrogen atom.

18. The method according to any one of claims 2 to 17, characterized in that in step b) acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate or ethylene carbonate or a mixture of two or more of these solvents is used.

19. The method according to any one of claims 2 to 18, characterized in that it comprises, as a further step d), the at least partial removal of organic solvent.

20. A process for producing electrolytes for lithium accumulators, characterized in that it comprises at least steps a) to c) and optionally d).