JPS5934130B2 - Manufacturing method of silicon tetrafluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-purity silicon tetrafluoride, which is useful as a raw material for producing amorphous silicon, which is expected to be used as electronic materials, solar power generation devices, and the like.

Silicon tetrafluoride is generally produced by the reaction of hydrofluoric acid and silicon oxide using the following reaction formula (1), SiO□+4)IP-+siF'4+2H20...(
1), but in the presence of liquid water, the above reaction (2), 3SiF4+2H20→2H2S t Fa + S
t 02 (2) produces hydrosilicic fluoride acid and gel-like silicon oxide, and this gel-like silicon oxide causes clogging of conduits, making it unsuitable for industrial production of silicon tetrafluoride.

Therefore, there is a known method for producing silicon tetrafluoride by reacting hydrogen fluoride gas with silica sand or crushed quartz pieces. A method has been proposed in which a mixture of water and hydrogen fluoride gas is introduced simultaneously and heated to a temperature range of 80°C to 110°C to obtain a reaction product containing a mixture of silicon tetrafluoride, hydrogen fluoride, and water ( (U.S. Pat. No. 3,674,431).

However, this method requires the simultaneous introduction of water and hydrogen fluoride gas in a gas-liquid phase mixture, which makes the operation complicated and
This is not preferable as it requires heating to a temperature in the range of 0 to 110°C.

Furthermore, a method is known in which highly pure silicon tetrafluoride is obtained by suspending crystalline silica powder in glycerol, ethylene glycol, etc. as a medium, introducing hydrogen fluoride gas, and causing a reaction (U.S. Patent No. 2, No. 861,872), the reaction temperature is quite high at 120 to 177°C, and there is also volatilization loss of the medium, making it impractical.

Also, in U.S. Patent No. 2,833,628, 20
A method of obtaining silicon tetrafluoride by adding hydrofluorosilicic acid of Section 28 to sulfuric acid containing silicon oxide is shown, but in this case, the amount of silicon tetrafluoride dissolved in the sulfuric acid is As shown in the figure, when the sulfuric acid concentration is 65 parts or less, the concentration increases rapidly, so in order to increase the recovery efficiency of silicon tetrafluoride, it is desirable to make the sulfuric acid concentration at least 65 parts or more.

When such hydrofluorosilicic acid is used as a raw material, a large amount of water is brought in, the amount of sulfuric acid used becomes large, and the volume of the apparatus becomes large, which is not preferable.

An object of the present invention is to provide a method for producing silicon tetrafluoride that eliminates the drawbacks of the prior art described above.

The purpose of this is to use amorphous silicon oxide as a silicon raw material, suspend and disperse it in sulfuric acid, and introduce hydrogen fluoride gas into the resulting system to cause a reaction, thereby substantially converting silicon tetrafluoride. This can be achieved by efficiently obtaining a reaction product consisting of only

In the present invention, since hydrogen fluoride gas is used, it is easy to introduce it into the reaction system, and the amorphous silicon oxide used as a raw material is better than crystalline silicon oxide, such as natural silica sand or quartz. The reaction rate is extremely fast, and the reaction proceeds completely stoichiometrically to completion.However, in order to uniformly disperse silicon oxide in sulfuric acid, the particle size of silicon oxide must be fine. Generally, it is 300μ or less, preferably 150μ or less.

In the case of crystalline silicon oxide, when it is finely pulverized, silicon oxide is adsorbed to the liquid surface when hydrogen fluoride gas is blown into the liquid, creating a group of fine bubbles with a strengthened bubble film, resulting in cumulative bubbles that are difficult to break down even with stirring, making it difficult to perform the reaction. On the other hand, in the case of amorphous silicon oxide, it is difficult to generate bubbles, and even if bubbles do occur, the silicon oxide adsorbed on the surface of the bubble film is replaced by the fluorine dissolved in the sulfuric acid that makes up the bubble film. This is advantageous because it easily reacts with hydrogen hydride and is removed from the foam surface as silicon tetrafluoride, which causes the foam to break and does not grow as an accumulated foam.

In the case of silica sand, as shown in Figure 1, if the sulfuric acid concentration is 85 parts or higher, the reaction will hardly proceed even if the reaction temperature is maintained at 80 degrees Celsius or higher, and if the sulfuric acid concentration is 80 parts or more, the reaction will hardly proceed at temperatures below 50 degrees Celsius. At sulfuric acid concentrations of 75% or less, the reaction proceeds at room temperature, but there are disadvantages such as the reaction rate gradually decreasing as the reaction progresses compared to the initial stage of the reaction. Similar results were obtained for silicon oxide.

In contrast, according to the present invention, for example, in the case of silicon oxide, which is produced as a by-product in the cryolite production process using sodium silicofluoride as a raw material, the silicon oxide reacts violently at room temperature regardless of the sulfuric acid concentration, and the silicon oxide disappears. The introduced hydrogen fluoride can be almost quantitatively converted into silicon tetrafluoride, and the same advantage exists when using other amorphous silicon oxides. There is.

Note that each curve in FIG. 1 shows the results obtained under the following conditions.

(The horizontal axis is the ratio of added HF equivalent to 5i02, the vertical axis is Si
SiF4 equivalent% generated relative to O□).

On the other hand, the reaction between silicon oxide and hydrogen fluoride produces water as shown in equation (1), but since the method of the present invention uses sulfuric acid as a medium, the water produced in the reaction is absorbed by the medium and substantially Specifically, only silicon tetrafluoride is extracted as a reaction product, and the water is equivalent to the vapor pressure that is in equilibrium with the sulfuric acid concentration at that time.
Very small amounts do not reach the dew point at normal temperatures.

Therefore, problems such as scaling due to the formation of silicon oxide according to equation (2) can be completely ignored.

In addition, H2O generated in the reaction is absorbed into sulfuric acid, and H2S
As the O2 concentration is diluted, a part of the produced silicon tetrafluoride dissolves in sulfuric acid, but as shown in Figure 2, the solubility of SiF4 in sulfuric acid increases rapidly at a H2SO4 concentration of 65% or less. was known.

Figure 2 shows the amount of SiF4 dissolved in the reaction residual liquid (40-60℃)
The horizontal axis is the H2SO4 concentration (related) in the reaction residual liquid.
, the vertical axis is 5IF4 (as F).

Therefore, in order to increase the recovery efficiency of silicon tetrafluoride, it is necessary to maintain the H2SO4 concentration at 65 parts or more, preferably 70 parts or more during the entire reaction process.

Therefore, it is desirable that the amount of water brought into the reaction system be as small as possible, and in this sense, it is also preferable to use hydrogen fluoride gas.

Furthermore, hydrogen fluoride gas dissolves well in sulfuric acid, and since amorphous silicon oxide with excellent reactivity is used, the amount of unreacted hydrogen fluoride mixed into the reaction product is extremely small. The conversion rate of hydrogen gas to silicon tetrafluoride is x1o
0% and the product purification load is extremely small.

The reaction conditions in the present invention are that the reaction can proceed satisfactorily at normal temperature and normal pressure, but at the same time as hydrogen fluoride gas is added, the temperature of the liquid increases due to the heat of reaction.

Examples of the natural or artificial amorphous silicon oxide used in the present invention include natural products such as activated clay, opal, and diatomaceous earth, silicic acid gel powder, finely powdered silicon oxide produced as a by-product in the process of chemical reactions, and artificial products such as glass powder. can be mentioned.

Addition ratio of sulfuric acid medium to silicon oxide (weight ratio 9 is preferably 3 to 10 from the viewpoint of dispersion state and reaction efficiency.

In addition, the sulfuric acid after the completion of the reaction contains 1 to 2 fractions of F, but if it is necessary to reuse the sulfuric acid, it can be recovered by volatilization during the process of concentrating it to the required concentration, or it can be recovered by evaporation in the process of concentrating it to the required concentration, or it can be collected by wet method. It can also be used as is for acid production.

The present invention will be specifically explained below using examples.

Example 1 Finely powdered silicon oxide (SiO2 90%, dry basis) produced as a by-product in the cryolite production process using Na25iFa as a raw material was thoroughly dried, 50 g of it was added and mixed into 280 g of 99% H2S02, and then placed in a Teflon reaction vessel. at room temperature (18°C) while supplying hydrogen fluoride gas at a rate of 16g/hour.
).

The pressure during the reaction was 2 to 4 m H.g, and at the same time as hydrogen fluoride gas was added, the liquid temperature rose due to the reaction heat and reached a maximum of 55°C.

The generated gas is dehumidified by passing it through 99% concentrated sulfuric acid.
It was cooled to .degree. C. and powdered SiF4 was recovered.

The amount of hydrogen gas added was 60g, and the recovered Si
F4 was 77.5.9.

Furthermore, SiF4 was confirmed from the infrared absorption pattern of this gas.

The medium sulfuric acid concentration at the end of the reaction was 88.5%, and the residual F
The concentration was 0.1%.

The analytical values for impurities in the produced gas were as follows.

802 20ppm 804 401l PO40,3// B O,31/ As O,Ill Fe O,5ppm Ni O,1// Example 2 Activated clay dried and crushed to a particle size of 60 mesh (soluble 5iO280); Total SiO□89%) 8 for 50g
4,280 g of 0% H2S0 were mixed to form a slurry, and hydrogen fluoride gas was introduced into the slurry at a rate of 16 g/hour.

When the liquid temperature was 20°C and the pressure was O~2mH, 9, the liquid temperature started to rise simultaneously with the addition of hydrogen fluoride gas and reached a maximum of 53°C.

The generated gas was washed with 99% sulfuric acid and SiF4 was recovered.

71g of SiF4 was generated for 56g of hydrogen fluoride added.
The medium sulfuric acid concentration at the end of the reaction was 73.2%, and the F concentration was 0.4%.

[Brief explanation of drawings]

Of the attached drawings, Figure 1 is a graph showing the amount of silicon tetrafluoride generated using sulfuric acid concentration as a parameter when amorphous silicon oxide and crystalline silicon oxide are used as raw materials, and Figure 2 is a graph showing the reaction residual liquid. The concentration of sulfuric acid in the solution and the amount of dissolved SiF4 (40~
60°C).

Claims (1)

[Claims] 1. A method for producing silicon tetrafluoride, which comprises introducing hydrogen fluoride gas into a system in which natural or artificial amorphous silicon oxide is suspended and dispersed in sulfuric acid.