CN1224405A - LipF6 production process - Google Patents

Abstract

The invention relates to a LiPF6 production process, wherein LiF is reacted with PCl5 or PCl3 at a temperature of -20 to 300 DEG C for a reaction time of 0.1 to 10 hours to give LiPF6, and LiPF6 is isolated as a solution from the reaction mixture, using ether, nitrile, ester, sulphone, carbonate ester, halogenated hydrocarbon and/or tertiary amines as the solubilizing agent.

Description

Preparation of LiPF6Method (2)

The invention relates to a method for preparing LiPF₆The method of (1). This compound is used in particular as electrolyte in batteries and as catalyst.

LiPF₆Can be produced from LiF and PF at elevated temperatures and elevated pressures₅Production, as is known. However, this reaction is uneconomical because of its low yield. The yield can be increased by using reactive LiF, but the production of reactive LiF is technically complex and requires considerable costs. PF as a raw material₅Cannot be purchased in the market, and must be in LiPF₆Produced before synthesis. Further, PF₅Has toxicity and easy reactivity and is difficult to handle.

LiPF₆It can also be produced from red phosphorus and LiF in a closed reactor at 200 ℃ and pressure in the presence of HF. This method is technically difficult to achieve due to the corrosive nature of HF, and pure LiPF is obtained₆The cost of (2) is high. Further, LiPF₆It is also possible to use PF in anhydrous HF in a closed reactor at 25 ℃ and pressure₅Reaction with LiF. In this process, the yield of the product is also low and great efforts are made to purify the product, in particular to quantitatively separate HF and other by-products, which is difficult.

US-PS3,607,020 proposes a method for producing LiPF₆The method of (1), wherein LiF and PF₅In an inert organic solvent, suitable solvents include, inter alia, lower saturated alkyl ethers, and lower alkyl esters of aliphatic saturated monocarboxylic acids. PF (particle Filter)₅Readily soluble in these solvents and the process can be carried out at temperatures of from 0 to 50 ℃. However, there is the disadvantage that PF has to be synthesized directly before the process is carried out₅Since a raw material cannot be purchased from the market.

US-PS3,907,977 discloses a method for producing LiPF₆The method of (1). In this process, LiF and PF₅In acetonitrile solvent at-40 to 80 ℃. PF (particle Filter)₅Is introduced into the LiF-acetonitrile suspension at low temperature, and then the reaction mixture is heated to 60 to 80 ℃ and filtered. The filtrate was cooled to 0 ℃ to precipitate the complex Li (CH)₃CN)₄PF₆. The complex was converted to LiPF by heating it to 80 ℃ in vacuo, releasing acetonitrile from the complex₆. As a sourceThe process also uses PF₅There are also difficulties in its handling.

JP-OS 60-251,109 discloses a method for producing LiPF₆In which PCl₅With LiF in liquid HF at-78 to 0 ℃. Problems arise due to the use of liquid HF as a solvent, which requires purification of the final product from HF. However, the toxicity of anhydrous HF is notIt is usually large. This process uses inexpensive raw materials but requires high cost cryogenic techniques.

Because of the compound LiPF₆Is the only industrial raw material of interest which can be produced in the purest possible manner from inexpensive raw materials by simple, technically controllable processes, and it is therefore the underlying object of the present invention to propose a process for producing the aforementioned compounds which uses readily available, inexpensive raw materials, provides products of high purity and can be carried out under the simplest process conditions, avoiding as far as possible the use and formation of corrosive and toxic substances.

The invention is based on the object of producing LiPF₆In which LiF is reacted with PCl₅Or POCl₃Reacting at a reaction temperature of-20 to 300 ℃ for 0.1 to 10 hours, wherein the reaction formula is as follows:

a)

b)

and wherein, LiPF₆Separated from the reaction mixture in the form of a solution, ethers, nitriles, esters, sulfones, carbonates, halogenatedhydrocarbons and/or quaternary amines may be used as solvents.

The starting materials used in the process are all commercially available, inexpensive products and are extremely readily available in very pure form. The use of pure LiF is very advantageous, but LiF contaminated with small amounts of other alkali and alkaline earth metal fluorides can also be used. The chemical reaction of the method of the invention provides the final product LiPF₆While the other reaction products are easily separated and recovered. The solvents required for carrying out the process according to the invention must be acid-free, aprotic, be obtained in very pure form and be recovered and purified in a simple manner. The reaction times and reaction temperatures required on an industrial scale are easy to control, even in the presence of the starting materials required for carrying out the process, since the corresponding reactors are provided by the prior art. PBr may also be used₅And POBr₃In place of PCl₅And POCl₃The process of the present invention is carried out, but bromine compounds are very expensive and difficult to purchase from the market. Thus, PBr₅And POBr₃Is not suitable for working inThe process of the invention is carried out on an industrial scale.

In the process of the present invention, it is preferred to use diethyl ether as the solvent, since LiPF₆Particularly readily dissolved in diethyl ether.

In the process of the invention, 1mol of PCl is added₅And POCl₃On the basis, when an excess of 0.1 to 2mol of LiF is present, the reaction time is shortened and/or the yield is increased.

In one aspect, the process of the invention may be carried out in the following manner: the reaction is first carried out at a temperature of 150 to 300 ℃ for 0.1 to 5 hours, followed by a temperature of 60 to 120 ℃ for 0.1 to 5 hours, and then LiPF is extracted from the solid reaction mixture at 0 to 80 ℃ using a solvent₆. This process is carried out in a closed reactor under pressure, which is caused by the starting materials and the reaction temperature. The PF can be formed in situ at 150 to 300 DEG C₅And then reacted with LiF at 60 to 120 ℃ to form the final product. During the solvent extraction of the cold solid reaction mixture, the final product goes into solution and can be separated from the solid reaction residue by filtration. The residue consists of LiCl, LiF and possibly lithium phosphate and can be treated in a known manner. The solvent used for extraction can be purified by distillation or reused for extraction.

In order to use the inexpensive starting material PCl in the process of the invention₃In the present invention, PCl₅And POCl₃Is made of PCl₃Provided in situ during the reaction at 150 to 300 ℃, the corresponding reaction formula is as follows:

c)

d)

it will be apparent to those skilled in the art that the process of the present invention, which is carried out in accordance with the gas-solid reaction, is not impaired by the presence of chlorine and oxygen.

In another aspect, the method of the invention may be carried out by: the reaction is carried out in the presence of a solvent at-20 to 100 ℃ for 0.1 to 5 hours, and the filtrate contains LiPF₆Is separated from the insoluble reaction product.

A particular advantage in this alternative process is that relatively low reaction temperatures can be used, reaction temperatures of from 0 to 80 ℃being preferred in the process according to the invention. In addition, the reaction is carried out in a solvent with good yield, LiPF₆Easily soluble in solvent, and other reaction products can pass throughThe filtration was isolated as a solid. PCl₅Can advantageously be reacted with LiF in diethyl ether, and dimethyl carbonate, ethylene carbonate or propylene carbonate as solvents in POCl₃In the reaction with LiF, the solvents acetonitrile, tetrahydrofuran and methyltetrahydrofuran are particularly useful.

In the present invention, before or during the reaction in the solvent, PCl₅By chlorinating PCl in the presence of a solvent at a temperature of-20 to 100 ℃ as follows₃And the production of:

e)

thus, the inexpensive raw material PCl can be used₃A variant of the process of the invention is carried out at from-20 to 100 ℃ in the presence of a solvent. PCl₃The chlorination of (a) is highly exothermic (Δ H =125 kJ/mol).

The economics of the process of the present invention are improved when the solvent contains from 5 to 50 weight percent liquid aliphatic or aromatic hydrocarbon. This approach will not be to LiPF₆The solubility of the product is negatively affected, and the cost of the process is reduced by the use of inexpensive liquid hydrocarbons.

Finally, in the process of the invention, the solvent is evaporated from the solution containing LiPF₆In solution to obtain LiPF in crystalline form₆. It is advantageous to separate the solvent and the process products by distillation facilitated by a flow of inert gas and/or distillation under reduced pressure. It should be noted that the organic solvent used is easier to remove than HF, with less residue.

In the practice of the inventionIn the case of the process, it is of course ensured that no water is present in the individual reactions. The solvent used should be substantially anhydrous. In any case, the feedstock for carrying out the reaction of the invention is lower than the gaseous PF₅It is easier to handle. LiF is used in the form of fine crystals. In the gas-solid reaction belonging to the process of the invention, as well as in the reaction taking place in the liquid phase, only very little PF is detected in the reaction mixture as a result of the reaction being complete₅Or not detectable; however, it can be assumed that PF₅Formed in situ in each reaction and then immediately decomposed. The reaction time of the reaction of the present invention can be shortened by stirring or milling stirring. To avoid POF formation during the process₃Escape from the uncontrolled reactor of LiF and POCl₃The reaction in the solvent should be carried out in a closed, pressure-tight reactor. Here, the relatively low pressure is easily controllable.

The residue in each reaction contained LiCl or LiCl and Li₃PO₄And excess LiF, treated with water. LiF and Li₃PO₄Obtained in insoluble form. If PCl is used₅As starting material, the insoluble residue consists only of LiF, which can be reused as starting material after filtration and drying. When treated with water, LiCl goes into solution, can be recovered from the aqueous solution, and can be reused in other ways.

As is known, the product LiPF₆Form other products with water, so that the applicability of such substances, in particular as electrolytes for batteries, is limited. In order to remove residual traces of water, it is possible in particular for this water to enter the reaction system with the starting materialsused and, before further processing, to produce LiPF according to the process of the invention₆The solution is reacted with an organolithium compound, in particular methyllithium or butyllithium, or with lithium hydride. These compounds form lithium hydroxide with water as well as hydrocarbons, such as methane or butane and hydrogen. Lithium hydroxide can be filtered off, while hydrocarbons and hydrogen escape from the solution in the form of gases. In any case, however, the water content of the product solution is very low, since the LiCl formed in the process of the invention is hygroscopic and has been dissolved in waterThe water contained in the liquid is largely bound together. The drying effect of LiCl makes the solvent unnecessary to be quantitatively anhydrous, advantageously reducing the dehydration cost of the solvent.

LiPF can be purified by recrystallization from a solvent₆Because the product is readily soluble in the solvent at elevated temperatures and not at lower temperatures. Diethyl ether is particularly useful as a solvent, and is suitable for use in LiPF₆By recrystallization of (1), LiPF₆Dissolving at 30-40 deg.C, and recrystallizing at 0-10 deg.C. In any case, the purity of the product produced by the process of the invention is>99.0%, usually>99.8%. The product is substantially anhydrous; the water content of the product-containing solution obtained after extraction or filtration was still<10ppm (determined by k. The product obtained by the method can be sold in the form of solution or solid.

In the case of gas-solid reactions, the yields after extraction are generally from 80 to 95%, while in the case of reactions carried out in solvents, the yields after filtration are generally from 90 to 96%.

The subject matter of the invention will be explained in detail below by means of specificembodiments. Example 1

500g (2.4mol) of PCl₅(purity 99%) and 448g (17.3mol) of driedLiF was added to a stainless steel reaction kettle and heated to 300 ℃ over one hour while stirring. The temperature was maintained for about 1 hour. The pressure was automatically increased to 55 bar. The temperature was then lowered to about 80 ℃ and stirred at this temperature for 3 hours. Cool to room temperature and finally reach a pressure of about 5 bar.

The gaseous reaction product was absorbed into an aqueous sodium hydroxide solution. They contain about 1% of a volatile halide containing phosphorus. The remaining fine white powder was put into a glass apparatus under an inert atmosphere, mixed with 1500ml of diethyl ether, and stirred for about 30 minutes. The insoluble constituents (573.4G, consisting of a mixture of LiCl and LiF) are filtered off with a fritted glass filter (G3) and rinsed three times with about 200ml of diethyl ether. The combined filtrates had a water content of<10ppm (Karl Fischer titration).³¹The P-NMR spectrum showed only a signal at-143.5 ppm (heptad), indicating the formation of PF₆ ^-. 335g of fine LiPF are left after the ether has been separated off₆Powder (yield 91.9%). The product contained 0.2% chlorine and was about 99.8% pure. Example 2

To 8.04g (0.31mol) of dry LiF dispersed in 80ml of propylene carbonate (commercially available, 99% purity) was added 8.97g (0.043mol) of PCl over about 15 minutes₅The temperature of the reaction mixture increased from 20 ℃ to about 32 ℃. After stirring at room temperature for one hour, the reaction was completed (³¹The P-NMR spectrum showed a signal at-143.5 ppm only). The filtered solution (90.8g) had a water content of<10ppm and contained 6.2g LiPF₆(yield 86.1%). The precipitate was rinsed with propylene carbonate in 90% yield. Example 3

117.5g (0.56mol) of PCl were added to the dispersion at a reaction temperature of 20 ℃ in a jacketed reactor over about 30 minutes₅The dispersion was 96.7g (3.73mol) LiF dispersed in 480ml of diethyl ether. The temperature was maintained at 22 ℃ by cooling. Then, the reaction solution was stirred at 20 ℃ for about 1 hour, the insoluble components (127.1g, a mixture of LiCl and LiF) were separated by filtration, and the filtration residue was washed with diethyl ether three times each with 50 ml. The solvent was evaporated from the combined filtrates and the residue was dried under vacuum until constant weight. 82.0g (95.7% yield) of pure LiPF remain₆. Example 4

27.7g (0.2mol) of Pcl are added₃Dissolved in 99g of dichloromethane. Dry chlorine gas is introduced into the solution by cooling it to 20-30 ℃. PCl₃The chlorination of (a) is an exothermic reaction, which ends when no heat evolution is observed. Formed PCl₅Contained in methylene chloride, a part exists in a dissolved form, and a part exists in a dispersion form. Excess chlorine is washed out of the dispersion with a stream of dry nitrogen. Subsequently, the dispersion was diluted with 105.5g of diethyl ether, and then 37.4g (1.44mol) of LiF was added over 50 minutes. PCl₅The exothermic reaction with LiF started immediately and the temperature was maintained at 20-28 ℃ by cooling. When all the LiF was introduced into the dispersion, stirring was continued for two hours. Then, the solid was filtered off, the solvent in the filtrate was distilled off, and the filtrate was purified by recrystallization from etherRemaining LiPF₆. With PCl₃The yield was 83% on a basis. Example 5

In a reaction kettle, 8.65g of POCl₃(65.4mmol) and 9.8g (370mmol) of finely divided dry LiF are mixed with 50ml of tetrahydrofuran. The mixture was stirred for 9 hours at 25 ℃ with a grinding mill, generating an overpressure of about 0.1 bar. After cooling, the autoclave was depressurized and the reaction mixture was filtered. No POCl was detected in the filtrate₃. The tetrahydrofuran was evaporated from the filtrate in vacuo leaving LiPF₆And (5) recrystallizing and purifying the product by using diethyl ether.

Claims (11)

1. Preparation of LiPF₆The method of (2), characterized by: LiF and PCl₅Or POCl₃Reacting at a reaction temperature of-20 to 300 ℃ for a reaction time of 0.1 to 10 hours to form LiPF₆The reaction formula is as follows: a) b) wherein, LiPF₆Separated from the reaction mixture in the form of a solution, and ether, nitrile, ester, sulfone, carbonate, halogenated hydrocarbon and/or quaternary amine is used as a solvent.

2. The method of claim 1, wherein: the solvent is diethyl ether.

3. A method according to claims 1-2, characterized in that: the excess of LiF is 0.1-2 mol.

4. A method according to claims 1-3, characterized by: the reaction is first carried out at a temperature of 150 to 300 ℃ for 0.1 to 5 hours, followed by a temperature of 60 to 120 ℃ for 0.1 to 5 hours, and then LiPF is extracted from the solid reaction mixture at 0 to 80 ℃ using a solvent₆。

5. The method of claim 4, wherein: PCl₅And POCl₃Is made of PCl₃In situ at 150 to 300 ℃ during the reactionThe corresponding reaction formula is as follows: c) d) 。

6. a method according to claims 1-3, characterized by: the reaction is carried out in the presence of a solvent at-20 to 100 ℃ for 0.1 to 5 hours, and the filtrate contains LiPF₆Is separated from the insoluble reaction product.

7. The method of claim 6, wherein: the reaction is carried out at 0 to 80 ℃ in the presence of a solvent.

8. A method as claimed in claims 6 and 7, characterized by: before or during the reaction, PCl in a solvent₅From-20 to 100 ℃ in the presence of a solventBy chlorination of PCl as follows₃And the production of: e) 。

9. the method of claims 1-8, wherein: the solvent contains 5 to 50 wt% of a liquid aliphatic or aromatic hydrocarbon.

10. A method according to claims 1-9, characterized by: LiPF₆Is prepared by evaporating solvent from the mixture containing LiPF₆Is obtained in crystalline form in solution.

11. The method of claims 1-10, wherein: in treating LiPF₆By reaction with organolithium compounds, especially methyllithium or butyllithium, or lithium hydride, before solution in LiPF₆The solution is dried.