RU2435732C1 - Device and method of obtaining highly-dispersive silicon dioxide - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to technology of obtaining highly-dispersive powder of silicon dioxide by method of burning silicon-containing compounds (precursor) in flame of combustible gases. Device for obtaining silicon dioxide powder with regulated dispersion consists of combustion unit (I) with external displacement of gaseous components, which has internal axial hole of cylindrical shape (1) and two ring cavities (2,3) with side canals (4, 5) for supply of oxygen-containing gas and hydrogen and output canals with circular section, made at angle 20-30° to unit axis, autonomous unit of supply and dispersion of precursor (II) by means of ejecting gas installed into internal axial cylindrical hole of combustion unit with possibility of fixed axial travel with respect to it, and consists of nipple with central canal (8), which has on external surface screw auger for twirling of dispersing gas supplied by canal, formed by external nipple surface and internal surface, nozzle (11) with outlet cone 20-30°. Method of obtaining highly dispersive silicon dioxide from liquid silicon-containing raw material (precursor), in which silicon-containing raw material is introduced into combustion flame at different level on its height at angle 30-90° to flame axis above zone of flowing of combustion components.

EFFECT: invention makes it possible to obtain high-quality silicon dioxide of various dispersion, which changes depending on time, spent by silicon-containing raw material (precursor) in high-temperature zone.

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Description

The invention relates to a technology for producing highly dispersed silicon dioxide powder by the method of burning liquid silicon-containing compounds.

The previously published technical solutions describe various methods for producing silicon dioxide with the highest possible specific surface area. To achieve this, it is proposed to reduce the height of the flame in which hydrolysis occurs, which reduces the residence time of particles in it and the possibility of their fusion. The reaction is performed for the same purpose at an “optimal” temperature of the order of 1000-1200 ° C followed by the introduction of a cooling agent into the flare (GB Patent 726.250, 1953; US Pat. No. 3,086,851, 1963).

The disadvantages of the above methods is the inability to control the dispersion of the final product over a wide range.

The closest in technical essence and adopted as a prototype are a method and device for producing highly dispersed silicon dioxide powder by burning liquid silicon-containing compounds in a combustible gas flame in a burner of a special design, which consists in supplying liquid silicon-containing raw materials to the combustion zone by ejection with compressed gas into the coaxial torch stream (RF Patent 2197334, IPC B05V 7/20, СВВ 33/18, 2003).

The specified method has some disadvantages:

1. The limited ability to control the dispersion of the obtained silicon dioxide by increasing the consumption of atomizing gas. However, the intensification of the process of atomization of the precursor by increasing the flow rate and, consequently, the rate of expiration of the gas stream located in the same plane with the feed zone of the gaseous components of the combustion, can lead to flame failure and termination of the process. In addition, the ejection proportional relationship of gas flow rates and the liquid phase shows that an increase in gas flow rate does not lead to an increase in the degree of dispersion of the precursor, since there is a conservation, not an increase in the specific energy of crushing.

2. The long residence time of the precursor particles in the coaxial flame leads to enlargement of the formed microparticles due to their fusion in the liquid state (coalescence) and subsequent agglomeration (point or planar) due to the difference in particle velocities in the gas stream outside the flame.

The objective of the invention is to obtain high-quality silicon dioxide of various dispersion, which varies depending on the residence time of the silicon-containing raw material (precursor) in the high temperature zone.

To solve this problem, a method and device for producing highly dispersed silicon dioxide is proposed. The method includes supplying the starting components to the high-temperature reaction zone and synthesizing the target product, characterized in that the silicon-containing raw materials are introduced into the combustion torch at different levels along its height at an angle of 30-90º to the axis of the torch above the expiration zone of the combustion components.

The device for producing silicon dioxide powder with controlled dispersion consists of two units: a combustion unit I with an external mixture of gaseous components and an autonomous supply and atomization unit of a precursor with an ejection gas II, characterized in that the autonomous supply and atomization unit of a precursor with an ejection gas and a combustion unit are installed coaxially with the possibility of mutual, fixed axial movement. The combustion unit I consists of a housing 14, a separator 15, a cup 16. It has an internal axial hole of cylindrical shape 1, two annular cavities 2 and 3 with side channels 4 and 5 for supplying oxygen-containing gas and hydrogen and output channels of the circular section, made at an angle 20-30º to the axis of the block, and one of them 2 has a conical outlet.

The feed and spray unit of the precursor II is located inside the combustion unit with the possibility of a fixed axial movement. It consists of a nipple 8 with a central axial hole 10, on the outer surface of which there is a screw screw for twisting the spray gas supplied through the nozzle 6 into the annular cavity 9, and a centering collar with channels for gas passage. The conical outer part of the nipple covers nozzles 11, forming an annular exit gap between them at an angle of 20-30º.

Figure 1 presents a General view of a device for producing a powder of silicon dioxide. The positions indicated: 1 - axial cylindrical cavity; 2, 3 - annular cavities; 4, 5, 6, 7 - fittings; 8 - nipple; 9 - an annular cavity for supplying atomizing gas; 10 - a cavity for supplying a liquid precursor; 11 - nozzles; 12, 13 - nozzles; 14 - case; 15 - separator; 16 - a glass.

The device operates as follows.

Oxygen-containing gas and hydrogen, respectively, are fed through the fittings 4 and 5 into the cavities 2 and 3, respectively, which are mixed at the outlet to the outer zone, forming an annular flame after ignition. Through the nozzle 6 into the cavity 9 formed by the nozzles 12 and 13, compressed air is supplied. Passing through the channels in the flange of the nipple 8, the gas is twisted by a screw screw and creates a vacuum at the outlet of the nipple, due to which a liquid precursor is sucked through the channel 10 through the nozzle 7. At the outlet, it is dispersed by compressed gas, forming a conical torch, which is embedded in an annular flame.

As you know, the torch in height has a different cross section and temperature. The movement of the input zone of the precursor along the height of the flame, as shown in figure 2, leads to a change in the contact area of the components and their residence time in the high-temperature zone of the flame.

So, in position 1 (figure 2), the degree of coalescence of the formed particles is minimal due to the small contact area "a" and, therefore, their short residence time in the flare, which ensures the production of silicon dioxide powder with an increased specific surface area.

In addition, the proposed input scheme of interacting reaction components

in the torch provides the possibility of intensifying the process by significantly increasing the pressure of the atomizing gas without fear of disruption of the flame.

As can be seen from the vacuum characteristics of the precursor ejection atomizer shown in Fig. 3, increasing the pressure of the atomizing gas in the ascending subsonic section does not provide an improvement in the degree of dispersion, because at the same time there is an increase in the consumption of the liquid precursor.

The transition to a pressure above 8-10 bar on the descending branch of the vacuum characteristic increases the dispersion effect, since in this case the liquid flow rate is inversely reduced due to a decrease in vacuum in the liquid channel, which leads to an increase in the specific energy of crushing. The increase in this case, the gas velocity at a pressure above 8-10 bar allows you to reduce the residence time of the dispersed phase in the flame plume without capturing it in the longitudinal direction, which reduces the level of coalescence. With a relatively small dynamic pressure of the gas-dispersed jet (4-bar), incomplete "piercing" of the section "a" or "c" is possible. In this case, the coaxial movement of the reaction components in the torch sections of various lengths is already affected, which can lead to a decrease in the specific surface of the powder.

Examples of the preparation of silicon dioxide by the proposed method

Example 1

Methyltrichlorosilane (MTXC) with a flow rate of 3.6 kg / h was subjected to burning in an air-hydrogen flame to obtain highly dispersed silicon dioxide. The air-hydrogen mixture has the following composition - 6.0 nm ³ air, 1.2 nm ³ hydrogen, and is fed into the device (figure 1) through channels 2 and 3.

The liquid precursor is ejected from the supply tank due to the vacuum created by air pressure of 4 bar, flowing through channel 9 in an amount of 2.6 nm ³ . In this case, the spray cone of the precursor is in the upper position 1 (figure 2), where the contact area of the components "a" and their residence time in the flame is minimal.

The obtained silica powder has a specific surface area measured by the BET method of 305 m ² / g.

Example 2

MTXC is burned under the same conditions as in example 1, but the spray torch is in position 2 (figure 2). With a maximum area of "c" and a longer contact time, the specific surface of the obtained powder is 260 m ² / g.

Example 3

MTHS in the amount of 1.9 kg / h is burned in an air-oxygen flame of the composition, as in example 1, with an air pressure of 12 bar spray. The specific surface area of the obtained powder is 375 m ² / g.

Claims (3)

1. A method of producing highly dispersed silicon dioxide from a liquid silicon-containing raw material - a precursor, including its supply to the high-temperature reaction zone and synthesis of the target product, characterized in that the silicon-containing raw material is introduced into the combustion torch at different levels along its height at an angle of 30-90 ° to the axis torch above the zone of expiration of the combustion components. 2. The method according to claim 1, characterized in that the precursor is sprayed with a high pressure ejection gas in a mode that provides an inversely proportional relationship between the gas flow rates and the precursor. 3. A device for producing silicon dioxide powder with controlled dispersion, consisting of a combustion unit with an external mixture of gaseous components and an autonomous supply and atomization unit of the precursor with an ejection gas, characterized in that the combustion unit with an external mixture of gaseous components has an internal axial hole of cylindrical shape and two annular cavities with side channels for supplying oxygen-containing gas and hydrogen and output channels of the circular section, made at an angle of 20-30 ° to the axis of the block, and the toner block for feeding and spraying the precursor with ejection gas is installed in the internal axial hole of the cylindrical shape of the combustion unit with the possibility of fixed axial movement relative to it and consists of a nipple with a central channel having a screw auger on the outer surface for twisting the saw gas supplied through the channel formed by the outer surface the nipple and the inner surface of the nozzle with an output cone of 20-30 °.

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