JPH0645449B2 - Method for producing silicon tetrachloride - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silicon tetrachloride using rice husks and rice husk combustion ash as a raw material.

[Problems to be Solved by Conventional Techniques and Inventions]

Silicon tetrachloride is used as a synthetic raw material for various organic silicon compounds, and also as a synthetic raw material for fine silica, high-purity synthetic quartz, silicon nitride, silicon carbide, and the like. There are the following three existing methods for producing silicon tetrachloride.

(1) A method of producing silicon tetrachloride as a by-product in the step of chlorinating a metal silicon compound with hydrogen chloride to produce trichlorosilane. (2) A method of reacting chlorine with chlorine, such as ferrosilicon. (3) A method of reacting a mixture of siliceous raw material such as silica stone and carbon with chlorine.

In the method (1), since silicon tetrachloride is obtained as a by-product in the production process of trichlorosilane, silicon tetrachloride depends on the demand amount of trichlorosilane. Furthermore, a large amount of electric power is required to produce metallic silicon, which is a raw material,
The raw material price becomes high. In the method of (2), since a large amount of electric power is required for manufacturing ferrosilicon and silicon carbide,
Raw material price is high. Although the raw material price is low in the method of (3), the reactivity of silica with a mixture of carbon and chlorine is low, and therefore it is necessary to pelletize the raw material or to add an expensive reaction accelerator, which reduces the cost. Becomes higher.

As described above, each of the conventional techniques has drawbacks and is not satisfactory.

As a method for solving these problems, it has been proposed in JP-A-58-55330 to react a carbide of a silicon-accumulated biomass with chlorine at 400 to 1100 ° C. This method can produce silicon tetrachloride at a relatively low temperature, but the reaction rate is not sufficiently satisfactory, and there are problems such as the accumulation of reaction residues during continuous operation for a long time, which is sufficiently satisfactory. Not the way.

Among the conventional techniques for producing silicon tetrachloride, the present inventors have proposed a method for reacting a mixture of a siliceous raw material such as silica stone and carbon with chlorine, which has a low raw material price, with chlorine, more specifically, a siliceous raw material. In order to solve the problems of the conventional method and to develop an industrially advantageous process that has a high reaction rate and can be continuously operated for a long time in the method using silicon-accumulated biomass as .

[Means for Solving the Problems]

That is, the present invention uses 100 parts by weight of rice husks and rice husk burning ash 20 to
It is characterized in that 60 parts by weight is mixed into a solid having a bulk specific gravity of 0.8 to 1.5, which is subjected to a carbonization treatment at a high temperature of 500 to 1200 ° C. and reacted with chlorine at a high temperature of 1100 to 1500 ° C. This is a method for producing silicon tetrachloride.

As in the past, silicon dioxide in siliceous raw material, coke,
Mix carbonaceous materials such as charcoal, chlorinate with chlorine gas,
In the case of producing silicon tetrachloride, it is necessary to grind and mix the siliceous raw material and the carbonaceous material and add an expensive reaction accelerator such as silicon carbide in order to have an industrially sufficient reaction rate. Atsuta

Further, in the method of reacting the carbide of the silicon-accumulated biomass with chlorine, there is a problem that the reaction residue accumulates during continuous operation for a long time, and it is necessary to positively extract the reaction residue from the reactor.

The rice husk burning ash used in the present invention is ash after burning the rice husk in a grate combustion furnace, a floating swirl combustion furnace, a fluidized bed combustion furnace, or the like. The content of silicon dioxide in the rice husk combustion ash varies depending on the combustion conditions and the like, but is generally 85% by weight or more.

The mixture of rice husks and rice husk burning ash is produced by, for example, a screen press. The bulk specific gravity of this solid is preferably 0.8 to 1.5. If it is less than 0.8, the strength of the solid matter is not sufficient, and it is not preferable because it easily collapses during the subsequent carbonization treatment and reaction. A large amount of energy is required to produce a solid material exceeding 1.5, which is an energy disadvantage.

The mixing ratio of rice husks and rice husk combustion ash is preferably 20 to 60 parts by weight of rice husk combustion ash to 100 parts by weight of rice husks. More preferably, it is 30 to 50 parts by weight. If the rice husk combustion ash is less than 20 parts by weight with respect to 100 parts by weight of rice husk, a large amount of carbon is produced as an unreacted residue when reacted with chlorine after the carbonization treatment, which causes a problem in continuously producing silicon tetrachloride. On the other hand, when the rice husk combustion ash exceeds 60 parts by weight, a large amount of silicon dioxide is produced as an unreacted residue, which causes a problem in continuously producing silicon tetrachloride.

The carbonization of the mixture of rice husks and rice husk combustion ash can be carried out in an ordinary charcoal kiln or atmospheric furnace. Carbonization temperature is 500-120
0 ° C is preferred. At a temperature of less than 500 ° C, the rice husks are not sufficiently carbonized, and undesired water and hydrocarbons remain in the next reaction. Carbonization at a temperature exceeding 1200 ° C. not only requires a large amount of energy, but also unfavorably promotes crystallization of silicon oxide.

The reaction temperature of the carbonized product of the mixture of rice husks and rice husk combustion ash and chlorine is 1100 to 1500 ° C. If the reaction temperature is less than 1100 ° C., the reaction rate is not fast enough, the combustion ash does not react sufficiently, and unreacted residues are produced, which causes troubles in the continuous production of silicon tetrachloride. At a temperature above 1500 ° C., the effect of increasing the chlorination reaction rate accompanying it is not so great, and it is thermally uneconomical.

The reaction type may be either a fixed bed (moving bed) or a fluidized bed, but a fixed bed (moving bed) is preferable. When the reaction is carried out in a fixed bed (moving bed), the shape of the carbide is preferably lump or granular with an average particle size of 1 to 50 mm. The lump or granular carbide having an average particle diameter of 1 to 50 mm is produced by crushing a solid material of a mixture of rice husks and rice husk combustion ash, or crushing a solid material of the mixture as it is. Can be manufactured. The cutting can be carried out by a general coarse crusher such as a Joke crusher, a roll crusher or a cutter mill, and an intermediate crusher.

〔Example〕

 Next, the present invention will be described in more detail with reference to Examples.

Example 1 100 parts by weight of rice husks and 40 parts by weight of rice husk burning ash (silicon dioxide content: 95% by weight) per hour were added to a single-screw extruder (product name: Sumilite Machine released by Sumikin Bussan Co., Ltd.) with a paddle mixer. Supply while mixing,
A solid having a bulk specific gravity of 1.3 was used. Subsequently, the solid matter obtained was carbonized in an atmosphere furnace at 800 ° C. for 30 minutes. The obtained carbide was crushed with a Diyoke crusher to obtain a 3 mm square sieve and a 10 mm square sieve. The composition analysis of the agglomerated carbide revealed that it was 68.6% silicon dioxide and 30.1% carbon. 75 g of the massive carbide was charged into a graphite reactor having a volume of 300 ml and reacted at 1300 ° C. while supplying chlorine of 160 ml per minute from the lower part. The reaction product gas was analyzed by a gas chromatograph every 15 minutes, and when unreacted chlorine was detected in an amount of 1% by volume or more, the introduction of chlorine was stopped and the reaction was terminated. The reaction product gas was introduced into a condenser at -30 ° C to collect the produced silicon tetrachloride.

The chlorine introduction time was 195 minutes, and the amount of silicon tetrachloride collected by the condenser was 109.7 g. The residue remaining in the reactor after the reaction was 16.4 g.

Examples 2 and 3 The chlorination reaction was carried out in the same manner as in Example 1 except that the reaction temperature was changed to 1150 ° C and 1450 ° C. The results are shown in the table below.

Comparative Example 1 Rice husks were carbonized in a nitrogen atmosphere at 800 ° C. for 2 hours. The obtained rice husk carbide has a carbon content of 56% by weight,
The bulk specific gravity was 0.06. A graphite reactor having a volume of 300 ml was charged with 16 g of the obtained chaff charcoal, and the reaction temperature was 105.
The chlorination reaction was carried out at 0 ° C in the same manner as in Example 1.

When the reaction gas was analyzed 20 minutes after the start of chlorine introduction, unreacted chlorine exceeded 1 volume percent, and the reaction was completed.

Comparative Example 2 The rice husk carbide obtained in Comparative Example 1 was ground to a bulk specific gravity of 0.2.
A rice husk carbide powder of 5 was obtained. The obtained rice husk carbide powder is 75
The reaction was conducted at a reaction temperature of 10 by filling a graphite reactor having a volume of 300 ml.
The chlorination reaction was carried out at 50 ° C. in the same manner as in Example 1.

The chlorine introduction time was 105 minutes, and the amount of silicon tetrachloride collected by the condenser was 57.5 g. The residue remaining in the reactor after the reaction was 45.2 g.

Comparative Example 3 100 parts by weight of Sabah silica stone having an average particle size of 30 μm and an average particle size of 5
75 g of a mixture of 40 parts by weight of 0 μm coke, volume 3
It was filled in a reactor made of graphite (00 ml) and the chlorination reaction was carried out at the reaction temperature of 1300 ° C. in the same manner as in Example 1.

When the reaction gas was analyzed 20 minutes after the start of chlorine introduction, unreacted chlorine exceeded 1 volume percent, and the reaction was completed.

〔The invention's effect〕

The conventional method of mixing a carbonaceous substance with a siliceous raw material and chlorinating it requires the addition of an expensive reaction accelerator.
In addition, the carbide of the silicon-accumulated biomass is 400 to 1100.
In the method of chlorination at ℃, there is a problem that the reaction residue accumulates in the continuous operation for a long time, but according to the method of the present invention, there is no need to add an expensive reaction accelerator, and the reaction residue Silicon tetrachloride can be easily produced with almost no accumulation.

Claims (1)

[Claims] 1. 100 parts by weight of rice husk and rice husk burning ash 20 to 6
0 parts by weight was mixed to form a solid having a bulk specific gravity of 0.8 to 1.5, which was carbonized at a high temperature of 500 to 1200 ° C to give 1
A method for producing silicon tetrachloride, characterized by reacting with chlorine at a high temperature of 100 to 1500 ° C.