RU2542274C1 - Method for preparing silicon - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: silicon dioxide melt is flown into a crucible at min. 2,000°C and sealed to generate the environment maintaining an excessive pressure of min. 2.0 MPa in a gas phase above the melted material. A mixture of water vapour and methane ('air blow') is supplied inside the melted silicone dioxide material. By melt temperature, vapour conversion of methane is observed in the mixture of water vapour and methane inside the melted material accompanied by generation of hydrogen, including monoatomic, and carbon oxide. First, silicon dioxide is reduced by hydrogen to elemental silicone, which in turn reacts with silicone dioxide in the melted material to produce silicone monoxide. Silicone monoxide produced by the reaction of silicone monoxide by an excessive pressure above the melted material is not transformed into a gaseous state, and remains liquid in the melted material and does not react to hydrogen, reducing silicone.

EFFECT: invention enables producing silicone with low impurity content, including carbon and oxygen.

Description

The invention relates to the field of chemical technology of inorganic substances and can be used to produce synthetic silicon.

A known method of producing silicon, based on the restoration of the melt of silicon dioxide by carbon at a temperature of at least 1800 ° C, followed by acid treatment. (Chemical Encyclopedia // Ed. By I.L. Knunyants. - M .: Soviet Encyclopedia, 1990, v. 2, p. 508.)

The disadvantage of this method is the low purity of the final product.

A known method of producing silicon, comprising introducing solid silicon dioxide into a silicon-containing melt to form silicon monoxide and then reducing silicon monoxide to elemental silicon with a carbon reducing agent, using silicon dioxide as a silicon-containing melt, into which a mixture of silicon dioxide and elemental silicon powders taken in a stoichiometric ratio, and methane is used as a carbon reducing agent (Patent RU No. 22327639, M. class C.01B 33/027, publ. 06.27.200 8).

The disadvantages of this method are:

- the use of high-purity silicon as a raw material;

- contamination of silicon with carbon contained in methane;

- the need to observe a stoichiometric ratio of the components of the reaction.

A known method of producing silicon, including the preparation of silicon monoxide from silicon dioxide and the subsequent reduction of silicon monoxide to elemental silicon using methane, the silicon monoxide obtained by thermal dissociation of silicon dioxide in an electric arc plasma in a hydrogen atmosphere, and the reduction of silicon monoxide to elemental silicon is carried out in an electric arc plasma using methane in a mixture with hydrogen with a throwing content of 5-10% by volume (patent for invention RU 2367600 C1, M. cl. С01В 33/023 , publ. 09/20/2009 - prototype).

The disadvantages of this method are:

- low productivity of the process, which is limited by a small amount of electric arc plasma;

- the need to maintain proportions in a mixture of methane and hydrogen;

- a low degree of extraction of silicon from silicon dioxide (about 86%).

The technical result of the invention is to simplify the method, increase its productivity and profitability.

The specified technical result is achieved by the fact that in the method for producing silicon, which includes the preparation of silicon monoxide from silicon dioxide and the subsequent reduction of silicon monoxide to elemental silicon using methane, according to the claimed invention, methane is introduced directly into the silicon dioxide melt at a temperature of at least 2000 ° C in a mixture with water vapor and create over the melt overpressure of the vapor-gas mixture.

An example of the method

Silicon dioxide purified from impurities of metals and nonmetals is used as a starting material. A silica melt is poured into a crucible with a capacity of 0.5 to 80 t at a temperature of at least 2000 ° C and the crucible is closed with a lid with a steam and gas drain valve to create conditions for maintaining an overpressure of at least 2.0 MPa in the gas phase above the melt. Then, a mixture of water vapor and methane ("blast") is fed into the silicon dioxide melt through a gas pipeline system. Under the influence of the temperature of the melt in a mixture of water vapor and methane inside the melt, a chemical reaction occurs, known as the "Steam Methane Conversion" (PCM) to produce hydrogen, including atomic, and carbon oxides:

CH ₄ + 2H ₂ O = CO ₂ + 8H (4H ₂ )

Carbon oxides do not interact with the melt and leave the melt under the influence of the "Archimedean" force. The hydrogen obtained inside the melt interacts with the silicon dioxide melt, reducing silicon:

SiO ₂ + 2H ₂ = Si + 2H ₂ O

Due to the fact that the recovery process is stretched in time as hydrogen arrives, first the silicon dioxide is reduced by hydrogen to elemental silicon, which in turn reacts in the melt with silicon dioxide to produce silicon monoxide:

Si + SiO ₂ = 2SiO

The resulting silicon monoxide under the influence of excess pressure above the melt does not sublimate to the gaseous state, but remains in the liquid phase in the melt and interacts with hydrogen, restoring silicon:

SiO + H2 = Si + H2O

Since silicon does not directly interact with hydrogen chemically, substitution of hydrogen in the gas phase over the melt of other products of the silicon reduction reaction serves as an indicator of the end of the silicon reduction reaction.

At the outlet of the gas-vapor mixture from the drainage gas-vapor valve, the burner works for the entire period of the process. A significant increase in the burner flame indicates afterburning of hydrogen, i.e. about the completion of the silicon reduction process.

The inventive method allows to obtain silicon with a low content of impurities, including carbon and oxygen. Reducing the cost of the final product is achieved due to the ability to produce silicon in large quantities and the simplicity of the process, as well as due to the minimum cost of recycling by-products of the silicon reduction reaction, such as water and carbon oxides. Cheaper process is achieved by reducing the consumption of hydrogen per unit mass of silicon produced, as well as the unnecessary precision metrological equipment to ensure a stoichiometric ratio of the mass of silicon dioxide and reducing agent. In addition, the degree of extraction of silicon from silicon dioxide according to the claimed method is significantly higher than that of the prototype method and reaches 93-95% due to the fact that silicon monoxide under the influence of excessive pressure above the melt does not sublimate to the gaseous state, but remains in the liquid phase in the melt and interacts with hydrogen, reducing silicon.

Claims (1)

         A method of producing silicon, including the preparation of silicon monoxide from silicon dioxide and the subsequent reduction of silicon monoxide to elemental silicon using methane, characterized in that methane mixed with water vapor is introduced directly into the silicon dioxide melt at a temperature of at least 2000 ° C and created above the melt overpressure of a gas-vapor mixture of at least 2.0 MPa.