JPS5854085B2 - Method for producing silicon dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Particulate silicon is produced by a displacement reaction in a flame with gas and oxygen as gaseous or vaporizable silicon compounds and optionally other silicon compounds which burn producing water. It is known to produce compounds (highly dispersed silicic acid, amorphous silicon) (for example West German Patent No. 9003).
39, West German Patent Publication No. 2,620,737, and US Pat. No. 2,399,687).

Although satisfactory results are obtained using silicon tetrachloride in this case, it is often advantageous to use organosilicon compounds as raw materials.

Until now, only dark-colored products contaminated with carbon were obtained, and in order to prevent this it has been necessary until now to use silicon compounds containing silicon-bonded organic groups, in particular halogen-containing compounds. When used, combustible substances such as hydrogen and hydrocarbons were additionally used together.

A method has now been discovered for producing highly active, particulate silicon dioxide in high purity, which can be produced using gaseous or vaporizable, optionally combustible silicon compounds containing Si-bonded organic groups or The mixture is subjected to a displacement reaction in a flame with a gas containing free oxygen, especially air, without the addition of other combustible gases.

The subject of the present invention is a process for producing highly dispersed silicon dioxide by a displacement reaction in a flame between a gaseous combustible silicon compound and a gas containing free oxygen.

This process involves evaporating the silicon compound in an evaporator with a constant vapor pressure and constant temperature (which is maintained until the next step of mixing the reactants) and a constant liquid silicon compound content, freeing up the free oxygen. This gas mixture is metered into the combustion chamber through a conical inlet, the gas containing free oxygen is introduced through a ring-shaped spray nozzle around this inlet, and the combustion chamber is indirectly cooling by forced cooling, in which after mixing the silicon compound with a free oxygen-containing gas and water vapor, the combustion of the silicon compound is carried out at least in part by the free oxygen-containing gas; mixing the gas with a combustible gaseous silicon compound before entering the combustion chamber, heating it to 100-700° C. before mixing with this silicon compound, and at least a portion of this gas being mixed with water vapor at the latest. This method is characterized by adding it to a silicon compound.

It is advantageous that the method according to the invention makes it possible to save a large amount of combustible material which is burned to produce water.

It is a breakthrough that the addition of water vapor to flammable gaseous silicon compounds and free oxygen-containing gases before feeding them into the reaction chamber has no adverse effect on the products or on the operating life of the equipment. In particular, it is also revolutionary that the conical feed port is not obstructed by silicon dioxide that settles in the burner.

Gaseous and/or vaporizable combustible silicon compounds include other silicon compounds which burn in the hitherto known manner forming gaseous silicon compounds and possibly water, and the combination of this gas with oxygen. Suitable for the production of silicon dioxide by substitution reaction in a flame are those which can be used as gaseous or vaporizable silicon compounds, provided that they are themselves flammable.

The process according to the invention particularly offers the possibility of converting flammable silicon compounds or mixtures thereof, which can generally boil up to about 200°C (at normal pressure) without decomposition, into highly pure, highly dispersed silicon dioxide. This is what we provide.

Such gaseous and/or
or vaporizable combustible silicon compounds, for example the reaction of silicon or alloys of silicon with organic halides, in particular methyl chloride or hydrogen chloride (Miller-Roc
This is something that can be generated using (how synthesis).

In general, organochlorosilanes, hydrogenated chlorosilanes, silanes that have no other substituents other than organic groups and/or hydrogen atoms, and/or silicon valences that are not bonded to substituents include chlorine, Silanols or siloxanes are used which are occupied by hydrogen or organic groups.

Some of these gaseous or vaporizable silicon compounds are undesirable or otherwise unavailable in production quantities.

Until now, these have been removed entirely or in excess as being environmentally unfavorable and economically undesirable.

These silicon compounds are also present as some undesirable by-products, e.g. as initial distillates or distillates, in the case of distillative separation of the products from the reaction of silicon or silicon alloys with organic halides or hydrogen chloride. Occur.

Even if this initial distillate or distillate no longer needs to be separated, it should preferably be free of solid substances such as carbon in order to be used in the process according to the invention.

Examples of suitable gaseous or vaporizable silicon compounds for use in the process of the invention are: disilane, disilane, trisilane and tetrasilane, trichlorosilane, dichlorosilane, chlorosilane, methylsilane, dimethylsilane, trimethylsilane, Tetramethylsilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, methylchlorosilane,
Methyldichlorosilane, dimethylchlorosilane, hexamethyldisilane, tetramethyldisilane, pentamethylchlorosilane, trimethyltrichlorosilane, dimethyltetrachlorodisilane, as well as compounds with the general formula C1 (Si (
CH3)2)n, a silane represented by n=2 to about 6;
Furthermore, disiloxane, hexamethyldisiloxane, and trimethylsilanol are also used in addition to these.

However, it is desirable to use methyltrichlorosilane, trichlorosilane and tetramethylsilane, either individually or as a mixture.

The vaporizable or gaseous combustible silicon compounds suitable for the process according to the invention are such that their vapor pressure is between 1.2 and 2.2 bar, preferably between 1.4 and 2.0 bar (absolute). At some point, it evaporates.

If a mixture of combustible Si-compounds is used, the temperature of the steam is at most 5 % below the boiling temperature range of the mixture or the boiling point of the combustible Si-compound(s) used.
The temperature is 0°C higher, preferably 20 to 35°C higher.

This boiling point of the combustible Si-compound(s) is maintained until mixing with other oxygen-containing gases takes place.

To achieve this temperature maintenance, the conduit between the evaporator, where the silicon compounds are evaporated, and the burner, where the flame is generated, must be at least partially insulated or in the mantle to prevent the release of heat. It may therefore be expedient to maintain the desired temperature by means of electrical heating inside the conduit.

As the heat transfer medium in this mantle, for example, 95 to 100
Boiling water at a temperature of 0.degree. C. or steam, which can reach temperatures of up to 250.degree. C. when superheated, is used.

The heating of the heat dissipating surfaces in the evaporator, which converts the liquid combustible silicon compound into the gaseous state, is carried out by hot liquid, water vapor or electrically.

Air can be used as the free oxygen-containing gas, especially as a pure elemental oxygen and a gas mixture containing at least 15% by volume of oxygen.

Other gases included in such mixtures must be inert to the reaction, and are preferably inert gases.

The free oxygen-containing gas is heated to a temperature of at least 100°C, generally from 100°C to 7°C, before mixing with the other reaction components.
00C, particularly preferably to a temperature of 150 to 400C.

The temperature in each case must be high enough to prevent liquefaction of the gaseous combustible silicon compounds.

It is expedient for the temperature of the water vapor used in the reaction to be exactly the same as the temperature of the gas containing free oxygen, but it is also possible to deviate somewhat above and below this temperature.

However, the temperature must be such that the temperature of the water vapor or gaseous combustible silicon compound does not drop to liquid form.

The gaseous combustible silicon compound, the free oxygen-containing gas and the water vapor are often mixed in a part of the apparatus such as that already belonging to the burner, but the water vapor is added at the beginning of the reaction to the free oxygen-containing gas or It can be mixed with the silicon compound along with parts.

In particular, it is desirable to simultaneously mix the gaseous combustible silicon compound, the free oxygen-containing gas and the water vapor; however, it is also possible to mix the two listed below in advance as a mixture and then to mix it with the gaseous combustible silicon compound.

Gases containing free oxygen contain all 5i-H and/or
Alternatively, oxidize the Si-organic bond to form a 5i-0 bond, and in some cases, completely burn out the existing organic residue,
It is used in such amounts as to give a colorless gaseous product.

Steam is used in such an amount that it hydrolyzes all other Si-bonds to Si-O-bonds.

Although the ratio of the amounts of each gas component does not have a very important meaning, this amount ratio generally controls the flame temperature to a desirable range of 8.
It is possible to adjust the temperature from 0.00 to about 1,400°C.

In the process according to the invention, oxygen is preferably used in an excess of at least 5% by weight with respect to the stoichiometric amount of oxygen, and generally an excess of 10 to 50% by weight is sufficient.

With respect to the stoichiometric amount of the gas mixture containing oxygen and free oxygen, an excess of 5 to 15% by weight, preferably 10% by weight, is additionally applied from the ring-shaped spray nozzle surrounding the feed opening of the reaction chamber. Specially supplied.

According to one preferred embodiment of the invention, the free oxygen-containing gas which is additionally blown into the reaction chamber by the ring-shaped spray nozzle is
After being heated to , it is mixed with water vapor.

This water vapor, which generally has the same temperature as the oxygen-containing gas, is mixed with the gaseous combustible silicon compound and the free oxygen-containing gas and is fed through the conical feed port of the reaction chamber.

In this case, amounts of water vapor of about 5 to 20% by weight relative to the stoichiometrically required amount are sufficient.

Burners suitable for the method according to the invention are, for example, those described in DE 26 20 737 A1.

The burner has a conical inlet for a mixture of combustible silicon compounds, free oxygen-containing gas, and water vapor, the inner diameter of which is generally between 20 and 100 mm, preferably between about 50 and 70 mm. It is.

Surrounding this inlet is a ring-shaped spray nozzle for supplying free oxygen-containing gas and in particular a mixture of this gas and water vapor; It is useful to have voids.

The large amount of heat generated during the reaction of the combustible silicon compound with the highly dispersed silicic acid is released by indirect forced cooling.

This can be done by cooling the combustion chamber externally, for example by means of a cooling mantle with water or the like.

The combustion chamber is preferably cooled by a free oxygen-containing gas, in particular air, which can be used for the reaction wholly or partially as a free oxygen-containing gas, further heated or cooled if necessary. Can be done.

The silicon dioxide produced according to the invention generally has a particle size of less than 1 micrometer and typically 50 to 450 m"/g.
, preferably with a BET area of 100 to 400 ml g.

It is generally suitable for all applications for which pyrogenically obtained finely divided silicon dioxide was suitable, for example in the thickening of polar and non-polar liquids and as a reinforcing filler, especially in organopolysiloxane elastomers. used.

This organopolysiloxane elastomer is made of a peroxide compound and is crosslinked by heat.

Problems arise from so-called one-component or two-component materials that are crosslinked at room temperature and that are crosslinked by the deposition of Si-bonded H on aliphatic multiple bonds.

In the following examples, quantities are determined under normal conditions: Example 1 Methyltrichlorschiff 25 kg/h at 2.5 bar (
(absolute) pressure into the evaporator by a membrane pump.

The evaporator has a 0.5 m wide heat dissipation surface, also called power heat surface, which is heated with 1.5 bar (absolute) steam.

The water vapor flow is controlled by a regulator (Samson-regulator) controlled by the vapor pressure in the evaporator of methyltrichlorosilane with a constant level height of the liquid organosilane and 1.5 bar of the methyltrichlorosilane ( absolute)
The pressure is adjusted so that a constant pressure is maintained.

The temperature is approximately 78°C.

The conduit between the evaporator and the burner is heated by a mantle through which water vapor flows at a pressure of 1.5 bar (absolute), but inside the burner is further equipped with a regulator to keep the temperature constant. , 25 kg/hour of methyl trichlorschiff, 100 m3/hour of air at about 200°C, and about 10 kg of water vapor.
/h and feed this mixture to the combustion chamber through a conical feed port with a 50 ii air gap.

The barnaro has sharp edges and thin walls.

For this burnaro, H2O-vapor rich air flow 8
Injecting N771"/hour, it exits from a ring-shaped spray nozzle with a 0.5 mvt air gap surrounding the burner.

A reaction chamber with a diameter of 60 CTL and a length of 350 cfrL is surrounded by a mantle fixed at intervals of 5C'rfL.

800 m/h of air at approximately 20° C. is absorbed through this gap.

Air discharged from the mantle (120℃, 100m3/h
) is used as reaction air after further heating.

The homogeneous gas mixture flowing through the burnaro is combusted and converted in the flame below the burnaro.

Particle size less than 1 μm and measured by BET method, 188
A highly transparent, highly dispersed silicon dioxide with an area of m''/j! is obtained.

Example 2 The working procedure described in Example 1 was repeated, except that 22 kg/h of trichlorosilane was used instead of 25 kg/h of methyltrichloroschiff and 90 rr'/h of air was used instead of 100 m'/h.

A highly transparent, highly dispersed silicon dioxide with a BET area of 395 m''/g was obtained.

Example 3 The working method described in Example 1 except that 25 kg/h of methyldichloroschiff was used instead of 25 kg/h of methyltrichlorschiff and 130,771"/h of air was used instead of 100 l/h of air. repeated.

A highly dispersed silicon dioxide with a BET area of 1877 ri'/g was obtained.

Example 4 25 kg/h of methyltrichlorosilane 50% by volume of methyltrichlorosilane instead of 7 hours 25 kg/h of a mixture consisting of 50% by volume of 10-trichlorosilane and 100 m of air
The procedure described in Example 1 was repeated, except that 64 m37 hours of air was used instead of '/hour.

A highly disperse silicon dioxide with a BET area of 278 rri'/9 was obtained.

Example 5 Miller-Rochow starting from methyl chloride instead of 50 volumes of methyltrichlorosilane
25 kg/h of a mixture of various silicon compounds obtained as the first distillate during distillation of the crude product of the synthesis were used, the temperature of the evaporator and the conduit following it was above 60'C, and 1
．． The vapor pressure was adjusted to 8 bar (absolute), the heating of the evaporator and the conduits was carried out electrically, 110 m'/h of air with a temperature of 200 °C was used instead of 100 m'/h of air, and 150 °C Example 1, except that 10 kg/h of steam with a temperature of The working method described in 1 was repeated.

The mixture of combustible silicon compounds consists of (as determined by gas chromatography) nitrichlorosilane, methyldichlorosilane, dimethylchlorosilane, tetramethylsilane, other silanes as well as hydrocarbons.

BET - Particle size 1μ with area 154 tri”/g
m of silicon dioxide was obtained.

Example 6 25 kg distillate mixture/hour instead of 25 kg initial distillate mixture
/h, the temperature of the evaporator and the conduit connected to it was above 140°C, the vapor pressure was adjusted to 2.0 bar (absolute), and the temperature of 200°C was used instead of 110 m'/h of air. with air 110 m'/h and 150°C
Example 5, except that about 20 kg/hour of H20 steam at a temperature of I repeated the method described above.

A mixture of combustible silicon compounds consists of (determined by gas chromatography) Nidimethyldichlorosilane, ethylmethyldichlorosilane, tetramethyldichlorosiloxane, dimethyltetrachlorodisilane, other volatile silicon compounds as well as hydrocarbons.

Silicon dioxide was obtained with a particle size of less than 1 μm and a BET area of 196 m/g.

Comparative Example 1 The procedure of Example 6 was repeated without adding water vapor to the air mixed with the silicon compound prior to combustion and the air blown into the ring-shaped spray nozzle.

Off-white to gray gypsum-like silica with a BET area of 80-110 m2/g was obtained in a yield of about 5-10% of theory, but most of the silica had passed through the cyclone.

Comparative Example 2 The operation of Comparative Example 1 was repeated by blowing water vapor into the ring-shaped spray nozzle of Example 6.

A gray-white gypsum-like silica was obtained, whose BFT surface compared to Comparative Example 1 was slightly increased to 150 rn'7 g and the yield to about 20% of the theoretical amount.

Comparative Example 3 The operation of Example 6 was repeated without adding water vapor to the air blown into the ring-shaped spray nozzle of Example 6.

Colorless silica having an area of about 180 rri:/g was obtained in a yield of about 85% of theory.

This product was not completely satisfactory due to the presence of agglomerates of flour-like particles.

The above Examples and Comparative Examples demonstrate the excellent effect when water vapor is added to the free acid-containing gas delivered from the ring-shaped spray nozzle according to the present invention.

Claims (1)

[Claims] 1. Evaporation of a silicon compound in an evaporator with a constant vapor pressure and a constant temperature (which is maintained until the mixing of the reaction components in the next step) and a constant liquid silicon compound content. is mixed with a free oxygen-containing gas, this gas mixture is metered into the combustion chamber through a conical inlet, the free oxygen-containing gas is introduced through a ring-shaped spray nozzle around this inlet, and the free oxygen-containing gas is introduced into the combustion chamber through a conical inlet. A process for producing highly dispersed silicon dioxide by reaction of a gaseous combustible silicon compound with a free oxygen-containing gas in a flame, comprising cooling the silicon compound by indirect forced cooling of the silicon compound with the free oxygen-containing gas and water vapor. combusting the silicon compound after mixing with the silicon compound; 1 before mixing
A process characterized in that it is heated to 00-700[deg.] C. and that at least part of it is mixed into the silicon compound at the latest simultaneously with water vapor. 2 The free oxygen-containing gas is first heated to 150-400°C, part of it is mixed with gaseous combustible silicon compounds and water vapor, and the other part is mixed with water vapor and sprayed through a ring-shaped spray nozzle. Claim 1, characterized in that the air is additionally blown, is also claimed in claim 1.3. The method according to item 1 or 2.