JP3204415B2 - Method for producing hexafluorophosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hexafluorophosphate useful as an electrolyte for a lithium secondary battery, a catalyst for an organic synthesis reaction, and the like.

[0002]

2. Description of the Related Art Various methods for producing a hexafluorophosphate, particularly lithium hexafluorophosphate, have been proposed. For example, a method of reacting lithium halide with phosphorus pentachloride in the presence of hydrofluoric anhydride ( JP-A-60-251109). In this method, it is difficult to control the reaction,
Fine crystals are mixed in the obtained lithium hexafluorophosphate. Further, a method (JP 64-72901) which applies a PF ₅ gas in LiF · HF porous are also known. In this method, purification of unreacted components is not easy. Furthermore, a method is known in which phosphorus pentafluoride obtained by reacting hydrofluoric acid with phosphorus pentachloride is introduced into a hydrofluoric acid solution of lithium fluoride (Japanese Patent Laid-Open No. 4-175216). Even in this method, it is difficult to control the reaction in the former stage.

As described above, none of the conventional methods is always satisfactory in terms of the reaction yield, the ease of controlling the reaction, the purity of the product obtained, and the like.

[0004]

[Specific means for solving the problem]
As a result of intensive studies in view of the problems of the related art, the present invention has been achieved.

That is, the present invention is characterized in that phosphorus pentafluoride obtained by reacting phosphorus pentachloride and hydrogen fluoride gas in a temperature range of 60 to 165 ° C. is introduced into a solution of alkali metal fluoride in anhydrous hydrofluoric acid. This is a method for producing hexafluorophosphate.

In the present invention, as the hexafluorophosphate, lithium hexafluorophosphate, potassium hexafluorophosphate and the like are typical, and the production of lithium hexafluorophosphate will be described in detail below. .

In the present invention, phosphorus pentafluoride is first obtained by a gas-solid reaction between phosphorus pentachloride as a solid raw material and hydrogen fluoride gas as a gaseous raw material. In this reaction, the reaction temperature is controlled. Very important, 60-165
C. is preferred. The reaction between phosphorus pentachloride and hydrogen fluoride gas proceeds favorably even below this temperature, but when this reaction gas is introduced into a solution of lithium fluoride in anhydrous hydrofluoric acid to cause reaction crystallization, phosphorus hexafluoride The yield of lithium oxide cannot be increased.

As a result of various studies on the cause, the present inventors have found that the reaction between phosphorus pentafluoride and hydrogen fluoride gas is an exothermic reaction, and is usually 40 to 50 from the viewpoint of controlling the reaction.
The reaction is carried out at about 60 ° C. In this reaction, if the temperature is lower than about 60 ° C., it is considered that the following reaction occurs.

PCl ₅ + 3HF → PF ₃ Cl ₂ + 3HCl (I) This PF ₃ Cl ₂ generates lithium hexafluorophosphate by the following reaction formula. PF ₃ Cl ₂ + LiF + 2HF → LiPF ₆ + 2HCl (II) However, this reaction does not proceed easily, and as a result, LiPF
The yield of ₆ cannot be increased.

When the reaction temperature of the reaction between phosphorus pentachloride and hydrogen fluoride gas is 60 ° C. or higher, the reaction proceeds almost completely.
When the temperature exceeds 0 ° C., the formation of PF ₃ Cl ₂ is hardly recognized,
It was confirmed that phosphorus pentafluoride was selectively obtained. The temperature is preferably up to 165 ° C. in order to prevent the sublimation of the raw material phosphorus pentachloride.

Since the reaction between phosphorus pentachloride and hydrogen fluoride gas has a sufficient reaction rate, a reaction vessel containing solid phosphorus pentachloride is kept at a predetermined temperature range. The reaction proceeds easily only by introducing the hydrogen fluoride gas. The reaction product gas is a mixed gas of phosphorus pentafluoride, some unreacted hydrogen fluoride gas, and hydrogen chloride generated by the reaction. This mixed gas is directly blown into a reaction crystallization tank charged with a solution of lithium fluoride in anhydrous hydrofluoric acid.

In consideration of the efficiency of the apparatus, an excessive amount of phosphorus pentachloride is added to an amount of hydrogen fluoride gas corresponding to a desired amount of phosphorus pentafluoride, and the reaction is stopped when the entire amount of hydrogen fluoride gas is introduced. I do. Phosphorus pentafluoride gas generated with the introduction of hydrogen fluoride gas is continuously blown into a reaction crystallization tank charged with a solution of lithium fluoride in hydrofluoric anhydride to carry out the reaction with stirring.

The composition of the solution of lithium fluoride in anhydrous hydrofluoric acid is such that the molar ratio of hydrofluoric anhydride: lithium fluoride is 12 to
30 is preferable, and when it is 12 or less, lithium fluoride is not completely dissolved and remains as an unreacted substance. If it is 30 or more, the amount of hydrofluoric anhydride is too large, and if the generated LiPF ₆ does not evaporate when it is taken out, no crystals will precipitate.

If lithium fluoride is dissolved in the filtrate after the precipitation of the crystals and the reaction is carried out, a yield of about 95% based on the phosphorus used can be obtained. After the completion of the reaction, crystals of LiPF ₆ are precipitated, but the temperature of the solution is raised to about room temperature to completely dissolve the product, and then, while slowly stirring at about 1 rpm, -20 Recrystallization is performed by cooling to about ° C, and LiPF having a uniform particle size of 1 to 3 mm.
_Six crystals are obtained. The resulting crystals can be separated by filtration to remove the attached hydrofluoric acid under reduced pressure to a purity of 99% or more.

The same applies to the production of potassium hexafluorophosphate.

[0016]

The present invention will be described in detail with reference to the following examples. Example 1 32 g (1.23 mol) of lithium fluoride was charged into a 1000 ml polytetrafluoroethylene reaction crystallization tank,
500 g of hydrofluoric anhydride was added, and the mixture was cooled to −20 ° C., stirred sufficiently, and completely dissolved. Next, 500ml, SUS3
257 g of phosphorus pentachloride (1.23 mol)
l) and heated to 100 ° C. 150 g (7.50 mol) of hydrogen fluoride gas was gradually introduced therein,
It was reacted with phosphorus pentachloride at 00-140 ° C. The mixed gas of phosphorus pentafluoride and hydrogen chloride generated at that time was continuously blown into a reaction crystallization tank charged with the previously prepared anhydrous solution of lithium fluoride and hydrofluoric acid, and the reaction was carried out with stirring.

After completion of the reaction, crystals of LiPF ₆ are precipitated, but the temperature of the solution is raised to about room temperature to completely dissolve the product, and then the solution is slowly stirred at about 1 rpm for one day. Then, recrystallization was performed by cooling to −20 ° C. Thereby, L having a uniform particle size of 1 to 3 mm is obtained.
iPF ₆ crystals were obtained.

This was separated by filtration to remove attached hydrofluoric acid under reduced pressure. The obtained LiPF ₆ was 65 g (yield 35%), and the purity was 99% or more. In addition, 113 g of L was contained in the filtrate.
iPF ₆ is present and the filtrate is recycled.

Example 2 Using the same apparatus as in Example 1, lithium fluoride 11.1 was used.
g (0.4 mol) was dissolved in the filtrate obtained in Example 1. Next, 90 g (0.4 mol) of phosphorus pentachloride was charged into the packed tower, and a reaction was performed under the same conditions as in Example 1.

After the completion of the reaction, recrystallization was performed, and the filtrate was separated by filtration to remove attached hydrofluoric acid under reduced pressure. The LiPF ₆ thus obtained was 62 g (95% yield), and the purity was 99%.
% Or more.

Example 3 Using the same apparatus as in Example 1, potassium fluoride 40.6
g (0.7 mol) was dissolved in 500 g of hydrofluoric anhydride.
Next, 146 g (0.7 mol) of phosphorus pentachloride was charged into the packed column, and the reaction was carried out under the same conditions as in Example 1 to obtain KPF _6.
Was synthesized.

After completion of the reaction, the temperature of the hydrofluoric acid solution of KPF ₆ was raised to around room temperature, and hydrofluoric anhydride as a solvent was removed under reduced pressure. The KPF ₆ thus obtained was 122 g (yield 95%) and the purity was 99% or more.

Comparative Example 1 Using the same apparatus as in Example 1, lithium fluoride 11.1 was used.
g (0.4 mol) was dissolved in the filtrate obtained in Example 1. Next, 90 g (0.4 mol) of phosphorus pentachloride was charged into the packed tower, and a reaction was carried out at 40 to 50 ° C. by introducing hydrogen fluoride gas.

After the completion of the reaction, recrystallization was performed, and the filtrate was separated by filtration to remove attached hydrofluoric acid under reduced pressure. LiPF ₆ thus obtained was 40 g (yield 62%), and the purity was 99%.
That was all.

[0025]

According to the present invention, a hexafluorophosphate useful as an electrolyte for a lithium secondary battery, a catalyst for an organic synthesis reaction, or the like can be produced with high purity and high yield.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Kobayashi 5253 Oki Ube, Oji, Ube City, Yamaguchi Prefecture Inside Central Glass Co., Ltd. Ube Research Laboratories (56) References JP-A-5-279008 (JP, A) JP-A Heihei 4-175216 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 25/455 C01B 25/10

Claims (1)

(57) [Claims] 1. A phosphorous pentachloride and hydrogen fluoride gas of 60 to 1
A method for producing a hexafluorophosphate, comprising reacting at 65 ° C. and introducing the obtained phosphorus pentafluoride into a solution of alkali metal fluoride in hydrofluoric anhydride.