RU2349546C1 - Method of producing fine silicon dioxide powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention can be used in chemical industry for producing fine silicon dioxide powder. Oxygen plasma or oxygen-containing gas is generated in plasmatron 1, and fed into reactor 3. Oxidation of silicon tetrachloride by oxygen or oxygen-containing gas takes place at 1000÷2100 °C temperature with 1.0-3.0 molar ratio of consumption of silicon tetrachloride and oxygen. Liquid silicon tetrachloride is atomised using an atomiser 10, in line inside and in the direction of flow of plasma at 0.2÷2.0 MPa pressure, with aperture angle of the atomisation jet of 70÷170°.

EFFECT: the proposed invention allows for producing fine silicon dioxide powder with particle size not less than 30 nm, with uniform particle size distribution.

1 dwg, 2 tbl

Description

The invention relates to the field of chemical technology and can be used to obtain highly dispersed nanopowder of silicon dioxide and improve its quality.

The prior art method for producing dispersed particles of silicon dioxide, in which a volatile silicon-containing component is mixed - silicon tetrachloride (SiCl ₄ ) with a hydrogen-forming gas (for example, Н ₂ , СН ₄ ) and an oxygen-containing gas, this mixture is fed into the reactor, decomposition of a volatile silicon-containing component and oxidation of decomposition products (US 6352679, C01B 33/12, 2002). Moreover, in the flame of the reactor at a temperature of 1000 to 21000 ^° C, supported by the energy of exothermic reactions, the decomposition of SiCl ₄ and the oxidation of the decomposition products with the formation of silicon dioxide - SiO ₂ , as well as hydrochloric acid - HCl and moisture - H ₂ O, the presence of which in the reaction products will reduce the quality of silicon dioxide, complicates the process of its preparation and equipment.

There is also known a method of producing a finely dispersed powder in the form of metal or metalloid oxides by oxidation, including the generation of an oxygen or oxygen-containing gas plasma, atomization of a liquid metal tetrachloride or metalloid in a plasma stream (RU 2119454 C1, C1G 1/02, 1998). In this case, spraying is carried out in the form of several gas-dispersed jets from the periphery into the plasma stream at an angle to the direction of movement of the plasma stream, which does not ensure the production of powder particles with a size of less than 100 nm due to the duration of the oxidation process.

The invention is aimed at improving the quality of silicon dioxide and obtaining nanosized powder with a particle size of less than 30 nm.

The solution to this problem is provided by the fact that the method of producing a finely dispersed powder of silicon dioxide, according to the invention, includes the generation of an oxygen or oxygen-containing gas plasma, the introduction of liquid silicon tetrachloride into the gas plasma stream and the subsequent oxidation of silicon tetrachloride with oxygen or an oxygen-containing gas at a temperature of 1000 ÷ 2100 ^° C and with a molar ratio of silicon tetrachloride and oxygen from 1.0 to 3.0, while spraying liquid silicon tetrachloride produce coaxially inside and in the direction of movement of the plasma stream at a pressure of 0.2-2.0 MPa with an angle of opening of the spray jet 70 ÷ 170 °.

The claimed technical result is achieved due to the fact that silicon dioxide is formed during the oxidation of silicon tetrachloride, sprayed coaxially inside and in the direction of motion of the high-temperature oxygen-containing plasma stream, this reduces the time of mixing of the reagents, heating and evaporation of the droplets and, accordingly, the particle growth time is reduced silicon dioxide (SiO ₂ ). As a result, a nanodispersed powder is obtained with a particle size of less than 30 nm with a uniform particle size distribution.

The drawing shows a process diagram of a device for implementing the inventive method.

The device contains a plasmatron 1 with a nozzle 2 for introducing oxygen or oxygen-containing gas into the plasmatron, a plasma-chemical reactor 3 with a nozzle 4 for introducing silicon tetrachloride, a device for feeding 5 silicon tetrachloride, a quenching chamber 6, a heat exchanger 7, a cyclone 8 and a fabric filter 9. Inside the plasma-chemical reactor 3 (coaxial to the reactor 3 and the plasma flow exit from the plasma torch 1), a nozzle 10 is installed for spraying liquid silicon tetrachloride, out of which the spray of a sprayed liquid with an opening angle of 70-170 ° is directed towards in the plasma flow.

A method of obtaining a fine powder of silicon dioxide is implemented as follows.

Oxygen or oxygen-containing gas is fed into the plasma torch 1 through the nozzle 2. The plasma stream leaving the plasma torch 1 at a temperature of 1200 ÷ 3400 ° C enters the plasma chemical reactor 3. Liquid silicon tetrachloride through the pipe 4 through the feeding device 5 enters the nozzle 10 installed inside the plasma chemical reactor 3 with a pressure in the range from 0.2 to 2.0 MPa and is sprayed onto small droplets, moreover, spraying is carried out inside the plasma stream in the direction of its movement, and the angle of the spray nozzle is 70 ÷ 170 °, while trajectories of liquid droplets intersect the plasma streamlines at an angle of 35 ÷ 85 °. Drops enter the plasma medium directly in the spray zone, and all drops of silicon tetrachloride (SiCl ₄ ) mix with the plasma, heat up and evaporate almost at the same time, which leads to a reduction in the mixing time of the reagents and to rapid heating and evaporation of the liquid droplets. The processes of heating and evaporation of droplets of SiCl ₄ and the oxidation of silicon tetrachloride vapors with the formation of silicon dioxide and chlorine occur with a decrease in the temperature of the gas phase from the plasma temperature of 1200 ÷ 3400 ° C to the equilibrium temperature of the reaction products 1000 ÷ 2100 ° C. The reaction products are cooled in the quenching chamber 6 and in the heat exchanger 7 and in the form of a dust and gas stream enter the deposition apparatus: cyclone 8 and fabric filter 9. From the fabric filter, silicon dioxide is returned to cyclone 8, and the gas phase of the reaction products through the pipe 11 is sent to chlorine-containing silicon-containing raw materials. Finished product - silicon dioxide powder is discharged from cyclone 8 through pipe 12.

The tables show the operational parameters of the processes of implementing the inventive method and the main quality indicators of the target product — the specific surface area of silicon dioxide particles, determined by the BET method, and the average particle size, calculated by the specific surface according to known formulas. The plasma temperature and the equilibrium temperature of the reaction products were determined by the calorimetric method.

Process performance parameters and quality indicators of the target product Plasma torch SiCl ₄ feed Example No. Gas type Kg / h consumption power, kWt Plasma temperature ° C Consumption of SiCl ₄ , kg / h The ratio of the molar flow rate of O ₂ and SiCl ₄ Feed pressure, MPa one Oxygen 117 320 3400 220 one 2.0 2 Oxygen 190 222 2720 180 2 1,6 3 Oxygen 215 170 2250 160 2.5 1,2 four Oxygen 220 88 1200 140 3 0.7 5 Air 275 127 1440 one hundred 1,2 0.2

Example No. Reactor process SiO ₂ powder Torch opening angle, ° Process temperature ° C Yield kg / h Specific Surface m ² / g Particle size, nanometer one 170 2100 76 122 22 2 160 1700 62 117 23 3 150 1500 55 105 26 four 110 1000 48 112 24 5 70 1200 34 138 twenty

Claims (1)

A method of producing a highly dispersed silicon dioxide powder, including the generation of an oxygen or oxygen-containing gas plasma, the introduction of liquid silicon tetrachloride into a gas plasma stream and the subsequent oxidation of silicon tetrachloride with oxygen or an oxygen-containing gas at a temperature of 1000 ÷ 2100 ° C and with a molar ratio of silicon tetrachloride and oxygen from 1.0 to 3.0, while the sawing of liquid silicon tetrachloride is carried out coaxially inside and in the direction of plasma flow at a pressure of 0.2 ÷ 2.0 MP angle of atomization plume opening 70 ÷ 170 °.