RU2344081C2 - Method of lithium hexafluorarsenate production - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in production of lithium hexafluorarsenate applied in chemical current sources. Method of lithium hexafluorarsenate production includes interaction of hexafluorarsenic acid derived from aqueous solutions of high-purity arsenic and hydrofluoric acids, and lithium carbonate with water-binding agent acetic anhydride at temperature (55±5)°C in molar ration as follows: H₃AsO₄:HF:(CH₃CO)₂O:Li₂CO₃=1:(6.1÷6.5): (16÷17:(0.5÷1). Derived reaction mass is separated from lithium hexafluorarsenate industrial salt by acetic acid distillation to solid residue. Lithium hexafluorarsenate commercial-grade salt is produced with purification of industrial salt and recrystallisation from ethyl acetate. Produced high-purity lithium hexafluorarsenate contains, wt %: base material 99.98, water 0.02, trace contaminant 10^-4-10^-5.

EFFECT: extra pure lithium hexafluorarsenate salt meeting the requirements to electrolyte components of chemical current sources.

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Description

In modern electrochemical cells - high-capacity compact batteries (HIT) used in cell phones, personal computers, various electronic devices, non-aqueous electrolytes based on lithium-containing salts, in particular lithium hexafluoroarsenate, are widely used.

The invention relates to chemical technology, in particular to the production of a highly pure salt of lithium hexafluoroarsenate in an anhydrous medium, which in quality satisfies the requirements for HIT.

A number of methods are known for producing lithium hexafluoroarsenate using an arsenic-containing component and a fluorinating agent, hydrogen fluoride in various aggregate states (HF gas, HF liquid, HFp-pH ₂ O).

The authors of [1] proposed a method for producing alkali metal hexafluoroarsenates by fluorination with hydrogen fluoride alkali metal compounds using arsenic halides. A mixture of arsenic trichloride with alkali metal fluoride undergoes fluorination, and hydrogen fluoride is fed in a mixture with chlorine and nitric oxide.

In this case, a mixture of chlorine with nitric oxide is an oxidizer of arsenic +3 to arsenic +5.

Known methods for producing lithium hexafluoroarsenate, where the arsenic-containing raw material is hexafluorosenic acid [2, 3].

The authors of [4] obtained hexafluorosenic acid by introducing an excess of gaseous hydrogen fluoride in a mixture of arsenic acid ethyl ester and benzene.

The choice of this or that method of obtaining lithium hexafluoroarsenate will be determined by a number of factors: the availability of arsenic-containing raw materials (or obtaining them locally), the process conditions, environmental safety and ease of process control, process time, economic factors.

Closest to the proposed method for obtaining a particularly pure salt of lithium hexafluoroarsenate (prototype) are works [2, 3]. In [2], a method is described for producing technical hexafluorosenic acid by reacting arsenic acid and hydrogen fluoride in the presence of a sufficient amount of water to form HAsF ₆ · 6H ₂ O. The yield is ~ 50% of theory. In [3], the authors propose a method for producing lithium hexafluoroarsenate by reacting hexafluorosenic acid with an aqueous lithium hydroxide solution, for which HAsF ₆ · 6H ₂ O hexahydrate is gradually added to the aqueous lithium hydroxide solution.

The reaction mixture was kept at a temperature of 80-100 ° C for 5 days, maintaining a pH of 11, periodically adding LiOH to the reaction mixture.

The sludge was filtered off, the pH of the medium was adjusted to 8.5 by the addition of hydrofluoric acid, the mixture was kept for 3 hours, filtered hot, the filtrate was cooled and LiAsF ₆ · 6H ₂ O filtered, which was dried for 4 days. The product was purified by recrystallization from anhydrous formic acid methyl ester while cooling and passing the solution through a molecular sieve column to remove moisture. Then part of the solution was evaporated in vacuo at a temperature of 20-30 ° C. Filtration and evaporation of crystalline lithium hexafluoroarsenate gave highly pure LiAsF ₆ with a moisture content of 0.006%.

The aim of this invention is to develop a method for producing lithium hexafluoroarsenate "osch".

The essence of the proposed method for producing lithium hexafluoroarsenate lies in the fact that two chemical reactions are carried out sequentially in one reactor to obtain it, to obtain an intermediate arsenic-containing compound - hexafluorosenic acid in the first chemical stage, by reacting the osch arsenic acid solution obtained by our method [5], and a solution of hydrofluoric (hydrofluoric) acid in the presence of a water-binding agent, acetic anhydride. Without isolation in the second chemical stage, hexafluorosenic acid reacts with lithium carbonate in an anhydrous medium (acetic acid solution) to form lithium hexafluoroarsenate.

The process is described by the following scheme:

The total equation has the form:

where 4,5 (CH ₃ CO) ₂ O is the number of moles of acetic anhydride necessary for the binding of water formed during reactions 1 and 2,

m (CH ₃ CO) ₂ O is the number of moles of acetic anhydride needed to bind the water contained in the acids.

The use of a water-binding reagent - acetic anhydride - at the first chemical stage (equation 1) allows the process to be carried out in an anhydrous environment, which shifts the process towards the formation of hexafluorosenic acid and minimizes the formation of impurities associated with the hydrolysis of reaction products. and the formation of incomplete acid fluorination products (HAsF ₅ OH, HAsF ₄ (OH) ₂ , etc.). Thereby increasing the yield and quality of hexafluorosenic acid at the first chemical stage.

The molar ratio of reagents is

H ₃ AsO ₄ : HF: (CH ₃ CO) ₂ O: Li ₂ CO ₃ = 1: (6.1 ÷ 6.5) :( 16 ÷ 17) :( 0.5 ÷ 1).

When the ratio of reagents H ₃ AsO ₄ : HF is less than 1: 6.1, the complete conversion of H ₃ AsO _{4 is} not guaranteed, and at a ratio above 1: 6.5 there is an inappropriate overconsumption of hydrofluoric acid. A preferred molar ratio of H ₃ AsO ₄ : HF = 1: 6.2.

The process at temperatures above 70 ° C increases the likelihood of side processes with the formation of incomplete fluorination products. Keeping the process below 40 ° C does not guarantee complete conversion of the starting reagents.

The optimum temperature of the process mode (55 ± 5) ° С.

The above ratio of reagents and the temperature in the reaction zone (55 ± 5) ° С ensure the completeness of the process at both chemical stages and minimize the formation of by-products formed in the first chemical stage and, as a result, produce lithium hexafluoroarsenate in an anhydrous medium with practically quantitative output in the second stage. The temperature (55 ± 5) ° C is supported by the rate of mixing of the reagents, in particular, the feed rate of acetic anhydride.

The use of reagents of technical quality (arsenic acid, hydrofluoric acid, lithium carbonate) leads to the appearance of undesirable microimpurities in the target product, worsening its quality. Purification from these impurities at the stage of the final product is very difficult. The most appropriate use of reagents of the osch category. For example, a solution of arsenic acid of the required quality can be obtained by the method [5].

The process is fast (the process time is regulated only by the time of mixing the reagents) with the formation of the target product in an anhydrous environment.

The technological process is easily controlled, the use of an aqueous solution of hydrofluoric (hydrofluoric) acid reduces the environmental burden on the environment and the danger to maintenance personnel.

Upon completion of the process, a solution of lithium hexafluoroarsenate in acetic acid is obtained. The yield of lithium hexafluoroarsenate at the chemical stage is almost 100% (the content of LiAsF ₆ in the solution of acetic acid is the same as calculated and determined analytically).

Lithium hexafluoroarsenate is isolated from the solution by distillation of acetic acid to a dry salt. The resulting salt is subjected to two-stage purification, it is:

1. Treatment with a 10% lithium hydroxide solution to neutralize acidic impurities, followed by clarification of the solution with activated carbon, separation of coal and water-insoluble impurities by filtration, stripping of water to dry salt, followed by drying.

2. Recrystallization of LiAsF ₆ from anhydrous ethyl acetate, which includes the following operations: dissolving it in ethyl acetate, separating insoluble impurities in ethyl acetate by filtration, distilling off ethyl acetate to dry salt, followed by drying.

The result is lithium hexafluoroarsenate with a basic substance content of 99.98% by _weight and 0.02% by _{weight of} water and a 80% yield from the last step; taking into account the regenerated LiAsF ₆ from the waste, the yield increases to 93% of the _mass .

Example 1

An aqueous solution of arsenic acid (concentration 86.63% _wt. ), Obtained by the method [5], in the amount of 50.51 g and with constant stirring from a polyethylene dropping funnel, hydrofluoric acid (concentration 41% _wt. ) Is loaded into the reactor from fluoroplastic _. in the amount of 94.0 g. The temperature in the reaction zone at the level of (55 ± 5) ° C is supported by the feed rate of hydrofluoric acid. Then, 503 g of acetic anhydride (concentration of 99% by _weight ) are supplied to bind water, both formed during the reaction and contained in the acids. The temperature in the reaction zone (55 ± 5) ° C is maintained by cooling the reactor with cold water and the feed rate of acetic anhydride.

After a dosage of ~ 2/3 of the total amount of acetic anhydride, the temperature in the reaction zone begins to drop, and to maintain the temperature in the reaction zone (55 ± 5) ° С, the reaction mixture is heated in a hot water bath. Upon completion of the dosage of the total calculated amount of acetic anhydride, the reaction mixture was kept under constant stirring and at a temperature of (55 ± 5) ° C for 40-60 minutes and then 16.24 g of lithium carbonate were added in small portions. During this reaction, carbon dioxide was released . At the end of the process, 657 g of a 9.2% solution of LiAsF ₆ in acetic acid are obtained (the theoretically calculated and determined analytically amount is 9.2%).

Lithium hexafluoroarsenate is isolated from the solution by distilling off acetic acid on a film rotary evaporator to a dry residue. The dry residue in the cube of the evaporator is dried at a temperature of (85 ± 5) ° С and P≈1 mm Hg. within 2-3 hours for a more complete removal of volatile acidic impurities. The result is 65.35 g of a yellowish loose technical salt LiAsF ₆ with a basic substance content of 92.41% of the _mass , and impurities of 7.59% of the _mass . Salt has an acidic character (pH≈4).

Technical salt 65.35 g is dissolved in 60 g of distilled water and neutralized with a 10% solution of lithium hydroxide in an amount of 43.29 g to a pH of 8-9. With stirring, the solution is heated to a temperature of (65 ± 5) ° C, 1 g of activated carbon (OAA grade) is added, the solution with carbon is kept under stirring for 5-10 minutes and cooled in a mixture of water and ice, after which impurities insoluble in water are filtered off. and coal. The filter cake was washed with 10 g of distilled cold water, combining the filtrate with washings.

After drying, 20.16 g of waste is obtained containing 44.73% by _{weight of} lithium hexafluoroarsenate.

The filtrate is evaporated on a film-rotary evaporator to a dry residue, followed by deep drying of the salt in a cube of the evaporator at a temperature of (85 ± 5) ° С and a pressure of ~ 1 mm Hg. within 4-5 hours.

Get salt in the amount of 56.27 g, containing 91.11% of the mass of LiAsF ₆ , pH 11.

After neutralizing acidic impurities, lithium hexafluoroarsenate is recrystallized from anhydrous ethyl acetate, for which 56.27 g of LiAsF _{6 are} dissolved in 80 g of ethyl acetate, the solution is cooled in ice-water and the impurities insoluble in ethyl acetate are filtered off, after drying, 8.26 g of dry residue are obtained with a content of 48.0% by mass of LiAsF ₆ . The filtrate — a solution of LiAsF ₆ in ethyl acetate — is evaporated on a rotary evaporator to a dry residue, followed by drying of the salt in a cube of the evaporator at a temperature of (65 ± 5) ° С and P = 1 mm Hg. within 3-4 hours. To protect the contact of LiAsF ₆ with air humidity, recrystallization is carried out in dry nitrogen.

After drying, 47.26 g of lithium hexafluoroarsenate of the qualification “OPC” with a basic substance content of 99.98% by _weight are obtained _. moisture 0.02% of the _mass. and pH 6.9 (very dry solvents are used in the preparation of electrolyte solutions, the residual moisture content in them is at the level of 0.0001%, therefore, the moisture content in the salt of 0.02% will not exceed the requirements for the moisture content in electrolyte solutions of 0.002% of the _mass. )

The salt yield in the last stage is 78.24% of theoretically possible. After the regeneration of LiAsF ₆ from the waste, the yield of the last stage increases to 93%. The resulting lithium hexafluoroarsenate meets all the requirements for electrolyte components for Chit. The content of trace elements (Na, K, Fe, Pb, Cl) at the level of 10 ^-3 -10 ^-4 %.

Literature

1. The method of obtaining lithium hexafluoroarsenate. // USSR Copyright Certificate, No. 1367369 (C 01 G 28/02) decl. 04/18/76.

2. Laweless E.W., Wiegand C.J.W., Mizumoto Y., Wies C. // Inorg. Chem. 1971, 10, No.5, 1084-1086.

3. Raybon C.R., Wiesboeck R.A./ Method for the production of high purity lithium hexafluoroarsenate // US Patent No. 3848063 (C 01 B 27/00, C 01 B 27/02), decl. 08.16.73, publ. 12.11.74.

4. Kolditz L., Hass D. // Z. anorg. allgem. Chem., 1961, 307, 209-303.

5. Knyazev B.A., Vaher V.F. / Method for producing highly pure arsenic acid. // Patent Application No. 2005 114300-15.

Claims (1)

A method of obtaining a pure salt of lithium hexafluoroarsenate LiAsF ₆ qualification “OPC” by reacting an arsenic-containing acid and a lithium-containing compound, characterized in that the arsenic acid is fluorinated with 41% hydrofluoric acid to obtain hexafluorosenic acid, then lithium carbonate is added, the process being carried out in one the reactor in the presence of a water-binding agent - acetic anhydride at a temperature of (55 ± 5) ° С and the following molar ratio of reactants:
H ₃ AsO ₄ : HF: (CH ₃ CO) ₂ O: Li ₂ CO ₃ = 1: (6.1 ÷ 6.5) :( 16 ÷ 17) :( 0.5 ÷ 1),
followed by recrystallization of lithium hexafluoroarsenate LiAsF ₆ from anhydrous ethyl acetate.