JPH0248413A - Production of anhydrous potassium fluoride powder - Google Patents

Abstract

PURPOSE:To obtain anhydrous KF powder having high density and adjustable particle size at a low cost by concentrating and crystallizing an aqueous solution of KF and subjecting the obtained crystalline KF to simultaneous drying and crushing. CONSTITUTION:An aqueous solution of KF is concentrated to 40-80wt.%, especially 60-80wt.% and crystallized at 40-80 deg.C, especially 50-70 deg.C spending 1 hr-2 days, especially 1-24hr to obtain crystallized KF. The crystallized KF is filtered and separated at the same temperature as the crystallization temperature. The crystalline KF is pulverized according to drying by the removal of the water of crystallization. A granular anhydrous KF having uniform particle size can be produced at a lower drying temperature by carrying out the crushing of the crystal simultaneous to the above drying process. The bulk density and particle size of the anhydrous KF can be controlled by selecting the concentration of the concentrated KF, the temperature and time of crystallization and the time of drying and crushing steps.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing anhydrous potassium fluoride powder that is suitable as a reducing aid and has a narrow particle size distribution at a low cost. .

[Conventional technology]

Anhydrous potassium fluoride is widely used as a fluorinating agent for organic compounds, as a catalyst as a base, as a dehydrating agent, and as an adjustment for melt reduction treatment of various metals. In many cases, solid-liquid reactions occur, and in order to utilize this effectively, a powder with uniform particle size is desired.

Conventionally, methods for producing anhydrous potassium fluoride powder include (a) the Kalzin method, in which an aqueous potassium fluoride solution is concentrated, further heated and dried, and pulverized to form powdered anhydrous potassium fluoride; (b) fluoride Spray-drying method in which an aqueous potassium fluoride solution is concentrated and dried by heating with a spray dryer to form anhydrous potassium fluoride powder. (C) Freezing in which an aqueous potassium fluoride solution is freeze-dried to form anhydrous potassium fluoride powder. There is a Todry method.

Powdered anhydrous potassium fluoride produced by the above-mentioned spray drying method and freeze drying method has a small bulk density and particle size, whereas the Calzin method produces a powder having a large bulk density and particle size.

[Problem to be solved by the invention]

However, methods (a) and (b) above require a temperature of 300°C or higher, and method (C) requires a cold temperature of -70°C or lower, resulting in high energy costs.
Combined with the complexity of the equipment, there was a drawback that powdered anhydrous potassium could not be obtained at low cost.

In view of the above circumstances, an object of the present invention is to provide a method for producing anhydrous potassium fluoride crystals, which allows powdered anhydrous potassium fluoride to be obtained at low cost and whose bulk density and particle size can be adjusted.

[Means to solve the problem]

In order to achieve the above object, in the method of the present invention, an aqueous potassium fluoride solution is concentrated, crystallized and separated to obtain crystalline potassium fluoride, which is then dried and pulverized at the same time.

[Effect]

Since the present invention has the above configuration, the manufacturing equipment is not complicated and energy consumption is low, and the bulk density and particle size can be adjusted by selecting the conditions of each step.

〔Example〕

The concentration of the potassium fluoride aqueous solution in the present invention is preferably 40 to 80 wt%, particularly 60 to 80 wt%. Potassium fluoride is crystallized from this concentrated solution, and the temperature is preferably 40 to 80°C, particularly 50 to 70°C.
Suitable crystallization time is 1 hour to 2 days, particularly 1 hour to 24 hours. The i-filtration separation of the crystallized potassium fluoride is carried out at the same temperature as the crystallization described above.

(g) If the concentration of concentrated potassium fluoride is less than 40 wt%, sufficient potassium fluoride crystals cannot be obtained;
When the temperature exceeds 2H, the entire liquid becomes potassium fluoride crystals (KF・2H2
0・KF・4H20) and solidifies. If the crystallization temperature is less than 40°C, the entire liquid will solidify, and if it exceeds 80°C, sufficient potassium fluoride crystals will not be obtained. Roughly speaking, if the crystallization time is less than 30 minutes, the crystals become fine and it is difficult to separate them by filtration.If it exceeds 2 days, the crystal grains become coarse or granulated and pulverization becomes difficult.

When the crystals separated by filtration (above) are dried, the water of crystallization is removed and the crystals are pulverized. If pulverization is performed at the same time, powdered anhydrous potassium fluoride with a uniform particle size can be obtained, and the drying temperature can be low.

The above-mentioned dryer may be of any type as long as it has the functions of drying and pulverizing. For example, a rotary hot-air dryer containing corrosion-resistant and heat-resistant balls such as ceramics and having the function of a ball mill is suitable. The hot air temperature used is 150 to 200°C.

The bulk density and particle size of the powdered anhydrous potassium fluoride are determined by the concentration of concentrated potassium fluoride, crystallization temperature, time, drying,
It is adjustable by choosing the grinding time.

Example 1 2000 g of a potassium fluoride aqueous solution having a concentration of 3 Qwt% was concentrated to 7Qwt% by a vacuum concentration method while stirring and maintaining the bath temperature at 70°C. At the end of the concentration, the entire aqueous solution had become pasty. The bath was maintained at 170° C., the vacuum was stopped, and crystallization and crystal growth were performed for an additional 3 hours.

Next, this concentrated crystallized solution was maintained at 40° C. or higher and centrifuged to separate solid and liquid. As a result, the particle size was 200I1
m, fine fluorine (hypotassium crystals with a moisture content of about 8%)
09 was obtained.

The crystals were placed in a rotary heat R1 dryer and dried by blowing hot air at 170°C. Alumina balls of No. H were added and the mixture was dried and ground for 1 hour.

As a result, 360 g of uniformly fine anhydrous potassium fluoride crystals with a particle size of 150 μm were obtained. The water content of this crystal is 1
wt% or less, the bulk density was 1.3 bi/d.

Example 2 Same as Example 1 except that concentration of potassium fluoride was carried out to 60 wt%, the filtration valve was separated, and the particle size was 200 μm.
, 250 g of fine crystals with a water content of 3 wt% were obtained.

These crystals were dried and pulverized under the same conditions as in Example 1, resulting in uniform fine anhydrous potassium fluoride crystals with a particle size of 150 μm.
I got g. The water content of this crystal was 1 wt% or less, and the bulk density was 1.3 g/c-+++'.

Comparative Example 1 Anhydrous potassium fluoride powder was prepared in the same manner as in Example 1 except that alumina balls were not added during drying. The particle size of this powdered anhydrous potassium fluoride varied from 200 to 800 μm, and the bulk density was 1.0 g/cTl'.

Comparative Example 2 11 [2000 g of a 30 wt% potassium fluoride aqueous solution was concentrated under reduced pressure at a bath temperature of 90°C to a concentration of 95 wt%.
It was reduced to %. The entire solution solidified into crystals, and was dried and ground in a rotary hot air dryer with alumina balls placed therein, but the grinding was not sufficient and only blocked crystals were obtained.

Comparative Example 3 The procedure was the same as in Example 1 except that the temperature of crystallization and τ filtration separation was 30°C. As a result, blocked crystals were obtained during i-filtration, and during dry pulverization, pulverization with alumina balls was not performed sufficiently, and only coarse blocked crystals were obtained.

Examples 3 to 8 Concentration of 11 degrees 3Qwt% potassium fluoride aqueous solution,
Anhydrous potassium fluoride powder was prepared by varying the temperature and time of crystallization, and the time of drying and pulverization, and its bulk density and particle size were measured. The results are shown in Table 1. [Effects of the Invention] As described above, the method for producing anhydrous potassium fluoride powder according to the present invention has a simple device, uses a small amount of energy, and can be improved by changing the conditions. The bulk density,
Particle size can be adjusted and bulk density is 0.9, suitable as a reduction aid.
~1. , l/cI! This is an excellent method for obtaining powder with a narrow particle size distribution in the 1' range at low cost.

Claims (1)

[Claims] A method for producing anhydrous potassium fluoride powder, which comprises concentrating and crystallizing an aqueous potassium fluoride solution to obtain crystalline potassium fluoride, which is then dried and simultaneously pulverized.