JPS5934128B2 - Method for producing silicon tetrachloride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an improved process for producing silicon tetrachloride by reacting a mixture of silicon-containing materials and carbon with chlorine at high temperatures.

Silicon tetrachloride is used as a raw material for the synthesis of various organosilicon compounds, as well as fine silica, high-purity synthetic quartz, silicon carbide,
It is useful as a raw material for the synthesis of silicon nitride, etc.

As a method for producing silicon tetrachloride, (1) silicon carbide,
A method of reacting ferrosilicon etc. with chlorine at high temperature, (
2) A method is known in which a mixture of a silicon-containing substance and carbon, such as a mixture of silica stone and activated carbon, or a charcoal of a silicic acid plant, is reacted with chlorine at high temperature.

However, the method (1) above requires a large amount of electricity to produce the raw materials such as silicon carbide and ferrosilicon.
The disadvantage is that the cost of raw materials is very high.

In addition, the method 2) has a major drawback in that the reaction with chlorine must be carried out at a very high temperature exceeding 1200° C. if silicon tetrachloride is to be produced with a certain yield.

In view of these circumstances, the inventors conducted intensive research with the aim of improving the conventional methods, especially the method (2) above, and found that conventionally a mixture of silicon-containing substances and carbon was reacted with chlorine. The inventors discovered that silicon tetrachloride could be produced at a much lower reaction temperature and in a higher yield than conventional methods by containing a boron compound in the mixture and reacting it with chlorine instead, and arrived at this invention. .

The present invention provides a method for producing silicon tetrachloride by reacting a mixture of a silicon-containing substance and carbon with chlorine at high temperature.
The present invention relates to a method for producing silicon tetrachloride, characterized in that the mixture contains a boron compound in an amount of 0.03 to 2 gram atoms of boron per 1 gram atom of silicon in the mixture.

In this invention, carbon includes activated carbon, coke,
Examples include carbon black and graphite.

In addition, silicon-containing substances include (1) silica stone, silica flour (a substance containing a large amount of SiO□, which is a by-product during the production of ferrosilicon), and fly ash (SiO2, which is collected from flues and dust collectors during pulverized coal combustion). (2) carbonized silicic acid plants such as rice and wheat husks and straw, bamboo leaves,
Examples include charred materials made by carbonizing corn leaves, corn leaves, etc. at 300 to 1300°C.

When using silicic acid plant carbide as a silicon-containing substance, the carbide contains amorphous carbon and is itself a mixture with carbon, so there is no need to intentionally mix carbon.

Further, when a silicon-containing substance and carbon are mixed, both the silicon-containing substance and carbon are preferably used in the form of powder as fine as possible, preferably powder with a particle size of 100 μm or less.

Further, it is preferable to use amorphous carbon rather than crystallized carbon because the reaction with chlorine can be carried out at a lower temperature and the yield of silicon tetrachloride can be increased.

In this invention, examples of the boron compound include diboron trioxide, boric acid, sodium tetraborate, potassium tetraborate, and the like.

The boron compound contains 0.03 to 2 gram atoms of boron per gram atom of silicon in the mixture of silicon-containing material and carbon, preferably 0.05 to 1 atom, and more preferably 0.906 to 0.8 atoms. It is necessary to contain it as follows.

If the amount of the boron compound is too small, the effect of its inclusion will not be sufficiently expressed, and if it is too large, the amount of boron trichloride by-product will increase, which is not appropriate.

By containing a boron compound in an amount within the above range per gram atom of silicon in the mixture and reacting it with chlorine, the reaction temperature and reaction time are much lower than conventional methods, and the yield is high. It becomes possible to produce silicon tetrachloride at a high rate.

The method of incorporating the boron compound is not particularly limited.

Typical methods include (1) mixing a silicon-containing substance, carbon, and a boron compound simultaneously or in any order, and (2) forming a molded product by mixing a silicon-containing substance and carbon. Examples include a method in which a carbide of a silicic acid plant is immersed in an aqueous solution of a boron compound to impregnate it with a boron compound.

In the above method (1), the mixing operation may be performed wet or dry.

In this invention, when reacting a mixture containing a boron compound with chlorine, it may be reacted with chlorine in powder form or may be formed into a molded article and reacted with chlorine.

However, it is preferable to mold it into a molded product and react it with chlorine because the reaction can proceed smoothly.

The shape of the molded product may be spherical, columnar, crushed granule, etc., and the shape is not particularly limited.

Further, when molding, for example, water, polyethylene glycol, triethylene glycol, starch, gelatin, cellulose, silica sol, etc. may be used as the binder.

Further, the molding may be carried out using any conventionally known molding machine, such as an extrusion molding machine, a tablet molding machine, and a transfer granulator.

In carrying out this invention, the amount of carbon in the mixture containing the boron compound is not particularly limited, but in order to produce silicon tetrachloride in high yield, generally silicon and boron in the mixture are When forming a chloride, it is appropriate to adjust the amount to 1 to 5 times the stoichiometric amount of the reducing agent.

If the amount of carbon is too small, the yield of silicon tetrachloride will decrease,
Furthermore, since there is no advantage to increasing the amount of carbon excessively, it is appropriate to keep the amount of carbon within the above range.

In addition, if water is contained in the mixture containing the boron compound or if water is generated during the reaction with chlorine, the yield of silicon tetrachloride will decrease. It is preferable to subject it to heat dehydration treatment and to react with chlorine.

The heat dehydration treatment is generally carried out under an inert gas atmosphere such as argon, helium, or nitrogen, or under reduced pressure at 150 to 1
It is suitable to carry out at 000°C.

The reaction between the mixture containing a boron compound and chlorine may be carried out by any method as long as the chlorine and the mixture can be brought into sufficient contact. Let's do it.

The chlorine gas may be of high purity or may be diluted with an inert gas such as argon, helium, nitrogen, etc.

The reaction temperature when reacting with chlorine is generally 400 to 1200°C, because if it is too low, the reaction will not proceed sufficiently, and if it is too high, there is no particular advantage and it is not economical. , preferably 450-100
0°C is suitable.

When the reaction with chlorine is carried out at the above temperature, the reaction proceeds smoothly and silicon tetrachloride is produced in gaseous form.

The reaction time varies depending on the reaction temperature, the amount of chlorine supplied, etc., but is generally 0.5 to 5 hours.

The produced silicon tetrachloride can be recovered by a method known per se.
For example, this can be easily carried out by condensation, distillation, etc.

This invention can be carried out using any reaction method such as fixed bed, moving bed, or fluidized bed.

Next, Examples and Comparative Examples will be shown.

Examples 1 to 6 Activated carbon powder (specific surface area 950 rrl/jj), silica flour (average particle size 2μ, containing 91.5 weight coefficient as 5IO2) and boric acid [H3BO] were weighed in the amounts listed in Table 1. After mixing in a mortar, it is made into a tablet with a diameter of 10 m using a tablet forming machine.
The pellets were molded into columnar pellets with a height of 10 mvt and a height of 10 mvt, and the pellets were dried at 160° C. for one day and night.

Next, the pellets were filled into an alumina reaction tube with an inner diameter of 25 mm, and heated and dehydrated at 700°C for 1 hour while circulating helium, and then chlorine gas was added at 110 ml/min at the reaction temperature listed in Table 1. The pellets are reacted by flowing the pellets through the reaction tube for 1.5 hours at a flow rate of Obtained.

The yield and yield of silicon tetrachloride were as shown in Table 1.

Comparative Example 1 Silicon tetrachloride was produced in the same manner as in Example 1, except that boric acid was not mixed.

The results are shown in Table 1.

Example 7 Instead of the silica flour of Example 1, silica stone (containing 95.7% by weight as SiO□) 5.6,9 was used, and 3 g of silica stone (containing 30% by weight as SiO2) was used as a binder. Silicon tetrachloride was produced in the same manner as in Example 1, except that .

The results are shown in Table 1.

Example 8 Sodium tetraborate (Na
Silicon tetrachloride was produced in the same manner as in Example 1, except that 2B407・10H20) 1.19 was used and the reaction temperature was changed to 500°C.

The results are shown in Table 1.

Comparative Example 2 Silicon tetrachloride was produced in the same manner as in Example 7, except that boric acid was not used and the amount of silica stone used was 6.4 g.

The results are shown in Table 1. Note that in Comparative Example 2, S i
Since the amount of CIJ 4 produced was small, water was added to the collected material without distilling it, S t C14 in the collected material was hydrolyzed and evaporated to dryness, and the mixture was incubated at 700°C for 2 hours in an air atmosphere. The mixture was heated at a lower temperature and weighed as SiO□, and converted into S r C14 to determine the yield and yield of S t C14.

Example 9 20 g of rice husk was carbonized by heating at 500° C. for 2 hours in a helium atmosphere to obtain a carbide of rice husk.

8 g of rice husk charcoal was added to 500 ml of water at 80°C with boric acid [
After impregnating the carbide with boric acid by immersing it in a boric acid aqueous solution in which H3BO3]409 was dissolved, it was heated to 160°C.
8. Dry for one day and night to obtain a carbide supporting boric acid.
57g was obtained.

In addition, Si in this carbide has a weight ratio of 21.9, and B has a weight coefficient of 1.
．． The weight of the bag was 0.

Next, a carbide carrying boric acid (B/5i=0.
25, atomic ratio) 7.59, and put this into an inner diameter of 251r.
After filling an r71L alumina reaction tube and heating and dehydrating it at 450°C for 1 hour while flowing helium, chlorine gas was flowed in place of helium at a flow rate of 110m4/min, and the reaction was carried out at 450°C for 1 hour. The gas from the reaction outlet is cooled, liquefied and collected in a dry ice/methanol trap, and the collected material is distilled to obtain silicon tetrachloride 10.1
I got it.

Note that the yield of silicon tetrachloride was 61 mol/%.

Comparative Example 3 Silicon tetrachloride was produced in the same manner as in Example 9, except that boric acid was not supported.

As a result, the yield of silicon tetrachloride was 6.2 g, and the yield was 3.
It was in charge of 5 moles.

Claims (1)

[Claims] 1. A method for producing silicon tetrachloride by reacting a mixture of a silicon-containing substance and carbon with chlorine at high temperature, wherein the mixture contains 0.00% boron per gram atom of silicon in the mixture.
1. A method for producing silicon tetrachloride, which comprises containing a boron compound in an amount of 0.3 to 2 gram atoms.