JPS6344686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing potassium fluoride, and more particularly to a novel method for producing potassium fluoride by direct fluorination of potassium carbonate or potassium bicarbonate.

Potassium fluoride is used in high-grade glass fluxes, various metal smelting agents, aluminum welding agents, catalysts, and also as a fluorinating agent for organic compounds by utilizing the dissociative properties of potassium fluoride, especially as a reagent in the halogen exchange method. In such reaction systems, potassium fluoride is difficult to dissolve in organic chlorides, and most of them are solid-liquid reactions, so potassium fluoride is effectively utilized and separated, and potassium chloride, which is a by-product of the reaction, is fluoridated. Since it precipitates and coats the surface of potassium, the effective use of potassium fluoride is hindered. Therefore, the actual situation is that the amount of potassium fluoride used in the reaction is generally about twice or more than the amount of chlorine atoms to be replaced.

The purpose of the present invention is to provide highly reactive potassium fluoride suitable as these fluorinating agents.
This objective is achieved by a gas-solid reaction of potassium carbonate or potassium hydrogen carbonate with hydrogen fluoride gas.

Conventional methods for producing potassium fluoride include adding ethanol to a solution of potassium hydroxide or potassium carbonate neutralized with an equivalent amount of hydrofluoric acid to precipitate potassium fluoride dihydrate, which is then heated to produce anhydrous How to make salt. Alternatively, the neutralized solution produced by reacting potassium carbonate and hydrofluoric acid with an aqueous solution is concentrated and cooled to 50 to 55°C, which is a temperature higher than the melting point of KF dihydrate, and the precipitated crystals are centrifuged and dried. Alternatively, a method of turning a concentrated solution of hot potassium fluoride into flakes using a heated rotary drum dryer. [Kirk-Othmer., Encyclopedia of
Chemical techmology Vol. 9, 649 (1966)] Furthermore, there is also a method of drying a reaction solution of potassium hydroxide and hydrofluoric acid with a spray dryer [ibid.
Vol. 10, 789 (1980)] are mainly liquid-one-liquid reactions.

The present invention provides a method for producing potassium fluoride that is completely different from these conventional methods, and involves producing granular or powdered potassium fluoride through a gas-solid reaction between potassium carbonate or potassium hydrogen carbonate and hydrogen fluoride gas. The present invention was achieved by discovering that it can be easily manufactured.

That is, the present invention is based on the following formula: K ₂ CO ₃ (solid) + 2HF (gas) △ → 2KF (solid) + CO ₂ (gas) + H ₂ O (gas) K ₂ CO ₃ (solid) + 2HF (gas) △ →2KF (solid) + CO ₂ (gas) + H ₂ O (gas) KHCO ₃ (solid) + HF (gas) △ → KF (solid) + CO ₂ (gas) + H ₂ O (gas) Solid potassium carbonate or potassium hydrogen carbonate The reaction is carried out by reacting hydrogen fluoride gas with hydrogen fluoride gas and removing by-product carbon dioxide and water from the reaction system as quickly as possible.

In the present invention, the amount of reaction between potassium carbonate or potassium hydrogen carbonate and hydrogen fluoride is expressed as a chemical equivalent ratio.
It is in the range of 0.1 to 5.0, and if the fluorination time is appropriately combined within this range, fluorination by gas-solid reaction can be carried out efficiently. If the reaction is carried out in the presence of excess hydrogen fluoride gas, the reaction will proceed further and double salts such as KF・HF, KF・2HF, K・3HF will be easily generated, and these will melt in the reaction system. It is difficult to obtain potassium fluoride in granular or powder form.

The potassium carbonate or potassium hydrogen carbonate used should preferably be in the form of powder or granules with a particle size as small as possible, usually 10 μm to 5 mm, preferably
Those with a diameter of 20μ to 500μ are adopted. In addition, when the particle size is 5 mm or more, the diffusion of fluorine between the particles is easier than when the particle size is fine, but the productivity is inferior. The fluorination apparatus may be any simple one, and may be of any type or type, such as a reactor equipped with a stirrer or a fluidized reactor, without any particular restrictions.

Fluorination temperature is 150~800℃, preferably 200~
600℃, and if the reaction temperature is below 150℃, the fluorination reaction itself will proceed, but it will be difficult to remove the by-product water, and a part of the product in the reaction system will melt, resulting in particulate products. Hard to obtain. Further, the upper limit of the reaction temperature is not particularly limited, but considering the material of the reactor, thermal energy, etc., it is 800°C or less, preferably 600°C or less.

The supply rate of hydrogen fluoride may be determined by a method of detecting hydrogen fluoride in the exhaust gas discharged outside the reactor system and controlling the amount of excess hydrogen fluoride gas. A more suitable method for removing by-product water is to carry out fluorination while introducing air, carbon dioxide, nitrogen, or oxygen into the reactor, as this makes it easier to produce particulate potassium fluoride. potassium can be produced. The dry method potassium fluoride obtained in this way is much more active than the potassium fluoride obtained by the conventional wet method, so it can be used as a fluorinating agent for organic compounds to achieve better effects. can. The present invention will be described in detail below with reference to Examples.

Example 1 2g of potassium carbonate with an average particle size of 200μ was collected on a platinum board and placed in a reaction tube (sus 304) installed in an electric furnace.
This was inserted into the reactor, and hydrogen fluoride gas (0.017 g/min) and nitrogen (0.03 g/min) were passed through the reactor at 400°C for 67 minutes to carry out a fluorination reaction. (Equivalent ratio: 1.96) After the reaction was completed, the mixture was cooled to room temperature while flowing nitrogen gas.

The results are shown below.

Reaction product 1.64g KF yield 96.1% KF purity 98.0% Specific surface area 0.4 m ² /g Example 2 2.0g of potassium carbonate with an average particle size of 150μ was collected in the same device as Example 1, and the reaction temperature was 450℃. Hydrogen fluoride gas (0.1g/min) and nitrogen (0.1g/min)
The fluid was circulated for 29 minutes to carry out the fluorination reaction. (equivalent ratio
5.0) The results are shown below.

Reaction product 1.67g KF yield 98.8% KF purity 99.0% Specific surface area 0.3 m ² /g Example 3 2.0g of potassium hydrogen carbonate with an average particle size of 300μ was collected in the same device as Example 1, and the reaction temperature was 190℃. Hydrogen fluoride gas (0.01g/min) and nitrogen (0.01g/min)
) was passed for 60 minutes to carry out the fluorination reaction. (Equivalence ratio 1.5) The results are shown below.

Reaction product 1.10g KF yield 92.9% KF purity 98.0% Specific surface area 0.3 m ² /g Example 4 150g of potassium carbonate with an average particle size of 200μ was collected in a 500ml round-bottom reactor equipped with a stirrer (sus 304) and stirred. (300r.pm) while maintaining the temperature at 500℃ while supplying hydrogen fluoride gas (0.26g/min) and nitrogen (0.43g/min)
The fluorination reaction was carried out by supplying for 10 minutes. (equivalent ratio
1.14) Thereafter, the reactor was cooled to room temperature while introducing nitrogen into the reactor.

The results are shown below.

Reaction product 116 g KF yield 91.5% KF purity 99.0% Specific surface area 0.4 m ² /g Example 5 150 g of potassium carbonate with an average particle size of 200 μ was collected in the same device as in Example 4, and stirred (300 rpm). The fluorination reaction was carried out by maintaining the temperature at 400°C and supplying hydrogen fluoride gas (0.15 g/min) and nitrogen (0.3 g/min) for 5 hours. (Equivalent ratio: 1.03) Thereafter, the reactor was cooled to room temperature while introducing nitrogen into the reactor.

The results are shown below.

Reaction product 120 g KF yield 93.7% KF purity 98.0% Specific surface area 0.4 m ² /g Example 6 Average particle size in 10 stirred reactors (sus 304)
5.0 kg of 200μ potassium carbonate was collected, and while stirring (30 rpm) and maintaining the temperature at 350°C, hydrogen fluoride gas (8.2 g/min) was supplied for 3 hours and 30 minutes to perform a fluorination reaction. (Equivalent ratio: 1.19) After that, nitrogen was introduced into the reactor and the reactor was cooled to room temperature.

The results are shown below.

Reaction product 4.0Kg KF 98.0% Specific surface area 0.4m ² /g Comparative example 1 Fluorination reaction was carried out in the same manner as in Example 1 except that the reaction temperature was 140°C. As a result, the reaction product was melted by water. It remained molten and could not maintain its powder form.

The results are shown below.

Reaction product 1.7g KF yield 91.5% KF purity 90% Specific surface area 0.4m ² /g Comparative example 2 2.0g of potassium carbonate with an average particle size of 200μ was collected in the same device as in Example 1, and the reaction temperature was 200℃. Hydrogen fluoride gas (0.1g/min) and nitrogen (0.1g/min)
The fluid was circulated for 35 minutes to carry out the fluorination reaction. (equivalent ratio
6.0) As a result, 2.1g of the reaction product was obtained, which was equivalent to KF/0.7HF containing an excess of fluorine equivalent to 0.7HF compared to KF based on the fluorine analysis value.

Comparative Example 3 2.0g of potassium chloride with an average particle size of 300μ was collected in the same device as in Example 1, and hydrogen fluoride gas (0.017g/min) and nitrogen (0.038g/min) were added at a reaction temperature of 400°C.
) was passed for 90 minutes to carry out the fluorination reaction. (Equivalence ratio 5.0) As a result, 1.95 g of the reaction product remained potassium chloride and was hardly fluorinated.

Reference Example A fluorination reaction of an organic halide was carried out using the potassium fluoride of the present invention.

2 autoclave (sus 316) Example 6
232 g (4 mol) of the potassium fluoride obtained in step 1, 315 g (2 mol) of 4-chloronitrobenzene, 750 g of dimethylacetamide as a solvent, and 60 g of benzene were added, and the mixture was heated and stirred. To remove water in the reaction system,
After about 160 g of the solvent was recovered by distillation at a temperature of 150 to 170°C, the reaction was carried out at a reaction temperature of 215°C for 6 hours.

The reaction product was filtered and the filtrate was distilled to obtain 183 g (1.3 mol) of 4-fluoronitrobenzene.

On the other hand, potassium fluoride, a first-class reagent (specific surface area 0.05
m ² /g) under the same reaction conditions,
151 g (1.07 mol) of 4-fluoronitrobenzene was obtained. From the above results, it was confirmed that the potassium fluoride of the present invention had good reactivity.

Claims (1)

[Claims] 1 Potassium carbonate or potassium hydrogen carbonate and hydrogen fluoride gas in a chemical equivalence ratio of 1.0 to 5.0, and
A method for producing potassium fluoride, characterized by carrying out a fluorination reaction at a temperature of 150 to 800°C.