EP2361149A1

EP2361149A1 - Pyrogenic silicic acid manufactured in a small-scale production plant

Info

Publication number: EP2361149A1
Application number: EP09796358A
Authority: EP
Inventors: Herbert Barthel
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2008-12-12
Filing date: 2009-12-10
Publication date: 2011-08-31
Also published as: KR101329381B1; KR20110106364A; DE102008054592A1; CN102245291A; WO2010066828A1; US20110256030A1; US9139444B2; JP2012511416A

Abstract

Disclosed is a flame reactor characterized in that the flame reactor comprises a reactor chamber having a volume of 1 m3 to 10 m3, is 1 m to 10 m high, and includes a reactor nozzle for feeding the reactants.

Description

Pyrogenic silica produced in a small capacity production plant

The invention relates to a method and an apparatus for producing fumed silica.

State of the art

Pyrogenic metal oxides, such as fumed silica, are obtained by high temperature hydrolysis of

Halogensiliziuraverbindungen in a hydrogen-oxygen flame, such as described in Ullmann's Encyclopedia of Industrial Chemistry (Wiley -VCH Verlag GmbH & Co. KGaA, 20Sauerstoff). For many applications, in addition to the intrinsic quality, especially the purity of the silica is of great importance. This applies crosslinking such as in under the influence of moisture at room temperature, especially for the use of the fumed silica in applications in the industry of surface coatings _r in applications for sealants

Silicone sealants and polyurethane sealants, and for use as a consumable in the manufacture of electronic semiconductor devices such as processors, memories, controllers and integrated components.

A known problem is, for example, lack of dispersibility of the fumed silica in silicone compositions, such as silicone sealants and in polyalkylene oxide-containing sealants such as polyurethanes.

Another problem often described is scratch damage that occurs with the use of silica in chemical mechanical polishing applications and planarization of electronic components on semiconductor surfaces and wafers. For the production of silicic acid in a large production plant, there are limitations in the achievement of the desired Produktregalltat.

The object of the invention is to avoid the disadvantages of the prior art and in particular to provide a method and an apparatus for producing a fumed silica and a fumed silica, which has a high quality.

The invention relates to a flame reactor, characterized in that the flame reactor has a reactor chamber with a volume of 1 m ³ to 10 m ³ , a height of 1 m to 10 m and a reactor nozzle for supplying the reactants.

The device according to the invention for the production of fumed silica comprises a reactor, a feed device for the reaction gases, a mixing device for the reaction gases, a reactor nozzle further feed devices for the supply of air.

The device according to the invention for the production of fumed silica preferably has the following units: (a) silane preparation, silane evaporator, optionally

(B) reactor, (c) energy recovery and cooling, (d) optionally pre-separation of silica SiO.sub.2 by preferably one or more cyclones, (e) removal of silica SiO.sub.2 by preferably filters, preferably fabric filters, particularly preferred

Surface filter, (f) purification of the silica of last traces of hydrogen chloride HCl in a dryer, preferably a rotating Tromπieltrockner, preferably with internals, which preferably achieve a combined radial and vertical movement, or preferably in a fluidized bed, or a Fluidized bed, preferably particularly preferably under supply of gases such as air or nitrogen, or inert gas, preferably at temperatures of 100 ⁰ C _f large large 300 ⁰ C, most preferably large SOO ⁰ C, with a Leerrohgasgeschwindigkeit 0.1 to 100 cm / s, more preferably 1-10 cm / s, and <g) preferably homogenization, for example by mixing and fluidization in a silo of a certain defined amount of silicic acid to a homogeneous charge, eg 1 - 20 to, preferably 5 - 15 to, (h) Storage in silos and (i) optionally compaction, for example with roller compactors, screw compressors, reciprocating compressors, preferably roller compactors, {j) filling in containers, for example in 5 - 20 kg bags, in big bags of 50 - 500 kg, or m large containers such as Silo wagon, Silotamer from 500 - 5000 kg content.

Preference is given to a device for the production of fumed silica, wherein this device has a supply device for a fuel gas at least at a location other than the reactor nozzle m of the reactor chamber.

The flame reactor preferably has a height of 1 to 10 m, preferably 3 to 6 m, more preferably 4 to 5 m, and a reaction chamber length of 0.7 to 9 m, preferably 2 to 5 m, particularly preferably 3 , 5 to 4.5 m.

Preferably, the flame reactor has a cross-sectional area of 0.1 m ^? to 1 rα ^, more preferably 0.2 m ^? to 0.9 rα *, more preferably 0.35 m. ^! to 0.75 m ^? ,

The flame reactor preferably has a volume of from 1 m ³ to 10 m ³ , more preferably from 0.5 m ³ to 7 m ³ , particularly preferably from 1.5 m ³ to 4 m ³ . Preferably, the flame reactor has a volume to height ratio of 0.1 m ² to 1 m ^? , more preferably 0.2 m ^? to 0.9 m ² , more preferably from 0.35 m ² to 0.75 m ² .

The orientation of the flame may be horizontal or vertical or at any angle to the vertical. The direction of the flame can be from bottom to top or from top to bottom. The direction from top to bottom is preferred.

In a preferred embodiment, the reactor chamber is open and in open exchange with atmospheric pressure. This may mean that the reactor is outdoors or in a hall open to the atmosphere.

Preferably, the reactor chamber at the head has a diameter of 0.1 to 1.0 m, more preferably 0.2 to 0.5 m. Preferably, the reaction nozzle has a circular cross-section.

Preferably, the reactor chamber has a circular cross-section.

The reactor chamber preferably has a diameter which is larger by 1%, particularly preferably by 10%, in particular preferably by 50%, than the diameter of the reactor chamber at the reactor head.

The reactor nozzle is preferably 0.05 to 0.25 m, particularly preferably 0.05 to 0.15 m, very particularly preferably 0.1 to 0.15 m in diameter.

The exit area of the reactor nozzle is preferably 0.001 m ² to 0.1 m ² , particularly preferably 0.002 m ² to 0.05 m ² , very particularly preferably 0.0075 m ² to 0.015 m ³ . Another object of the invention is a process for the preparation of fumed silica, wherein in a reactor silicon-containing reaction gases are reacted in a flame, characterized in that the content of organic non-silicon compounds in the reaction gas is less than 5 mol%.

In the inventive method for producing pyrogenic silica, wherein in a reactor silicon-containing reaction gases to an amount of preferably 10 to 500 kg / h, preferably 50 to 350 kg / h, particularly preferably 100 to 300 kg / h of silica corresponding to 100 up to 5000 tons per calendar year, preferably 250 to 4000 tons per calendar year, more preferably 500 to 3000 tons per calendar year, very particularly preferably 500 to 1000 tons per calendar year. For this purpose, the reaction gases are fed, comprising the following composition: vapor or gaseous silicon compounds in an amount of preferably 1000 to 10,000 moles per hour, preferably 2000 to 8000 moles per hour, more preferably 3000 to 6000 moles per hour, or 100 to 2000 kg / h, preferably 20 to 1000 kg / h, particularly preferably 100 to 500 kg / h, wherein the nozzle outlet gas velocity or gas velocity of the gases used, at the reactor nozzle, based on standard volumes, between 10 and 100 m / s is preferred between 200 and 80 m / s, more preferably between 40 and 70 m / s, and the gas velocity over the Dusenquerschnitt radially, preferably homogeneously distributed, and is distributed over the reactor cross-section radially, preferably homogeneously, in a flame for reaction to be brought.

Preferably, the capacity of a production plant according to the inventive method is less than 5000 tons, more preferably less than 4000 tons, most preferably smaller 3000 tonnes, in particular preferably less than 1000 tonnes of fumed silica, relative to one calendar year.

One calendar year should be based on 7884 hours production time, with 85% time availability.

365 d * 24 h / d * 0.85 = 7884 h

In a preferred embodiment, the fumed silica is prepared in a single reactor having a capacity of less than 500 kg / h, more preferably less than 400 kg / h, more preferably less than 250 kg / h, most preferably less than 100 kg / h.

The reaction gases are preferably oxygen, ie, for example air, which may be fresh or dried, to a fuel gas, for example hydrogen, a vaporous hydrocarbon (saturated or unsaturated, ie containing double and / or triple bonds), such as methane, ethane, _r iso-propane, n-propane, iso ~ butanes, n-butane, ethene, ethyne, propene, iso-butene and n-butene, and other higher iso- or n- or neo-Älkane, -alkenes and alkynes, lower alcohols such as methanol, ethanol, propanol, with methane being preferred, or mixtures thereof, wherein a fuel gas containing large 90% by volume of hydrogen is preferred, and as a second additional fuel gas containing a large 1% by volume of natural gas containing large 90% by volume of methane, is preferred, and silane containing at least one vaporous silicon-containing compound, such as R _x H _y Si _a X _z Yb where R is alkyl radical having 1 to 8 C atoms, preferably methyl radical, H. Hydrogen,

X is a halogen or an alkoxy group OR, preferably OCH3, Y is oxygen, and a> 0 and an integer. If a = 1, then b = 0, and then x + y + z = 4; preferred examples are: X is chlorine and x = 1 or y = 1 and z = 3, more preferably X is chlorine and z = 4.

If a = 2, then x + y + z = 6 and b is 0 or 1.

a is preferably 1 to 5, more preferably 1.

Furthermore, further steams or gases, preferably less than 10% by volume, which do not disturb the reaction, such as N ₂ , Ar, He, CO ₂ , may be present.

The reaction gases are preferably premixed before the reaction.

For this purpose, preference is given to using continuous gas mixers, for example preferably static mixers.

The proportion of gaseous or vaporous or volatile silicon-containing compounds in the reaction gas, the

Reaction is fed, dabeα is preferably 1 mole. % to 20 mol%, preferably 1 mol. % to 10 mol%, more preferably 4 mol% to 6 mol%.

The content of organic Nichtiliziumverbmdungen m the reaction gas is preferably less than 5 mol%, preferably less than 3 mol%, more preferably less than 2 mol%, most preferably less than 1 mol%.

The content of inorganic nichtiliziumverbmdungen m the reaction gas is preferably less than 1% by weight, preferably less than 10 ppm, more preferably less than 500 ppb, most preferably less than 5 ppb. The content of boron compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, particularly preferably less than 10 ppm, based on boron.

The content of Germaniurnverbindungen in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, more preferably less than 10 ppm, based on germanium.

The content of titanium compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, more preferably less than 10 ppm, based on titanium.

The content of iron compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, particularly preferably less than 10 ppm, based on iron.

The content of aluminum compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, particularly preferably less than 10 ppm, based on aluminum.

The content of tin compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, more preferably less than 10 ppm, based on tin.

The content of arsenic compounds in the reaction gases is preferably less than 100 ppm, preferably less than 50 ppm, more preferably less than 10 ppm, based on arsenic.

The content of sulfur compounds in the reaction gases is preferably less than 1 000 ppm, preferably less than 500 ppm, particularly preferably less than 100 ppm, based on sulfur.

The content of phosphorus compounds in the reaction gases is preferably less than 1000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm, based on phosphor. The proportion of oxygen in the reaction gas which is fed to the reaction is preferably 10 mol.% To 50 mol.%, Preferably 15 mol.% To 30 mol.%, Particularly preferably 16 mol. % to 21 mol%.

The proportion of fuel gas in the reaction gas fed to the reaction is preferably 1 mol% to 25 mol%, preferably 5 mol% to 15 mol%, particularly preferably 4 mol. % to 13 mol%, most preferably 5 mol% to 8 mol%.

The reaction gases containing at least one, preferably gaseous or vapor, silicon compound or a mixture of silicon compounds are introduced into the reaction chamber or flame in an amount of preferably 100 to 5000 NmV, preferably 500 to 4000 NmVh, more preferably 1000-3000 NmVh.

The reaction gases preferably contain hydrogen as fuel gas, preferably in amounts of 4 to 15 mol%, preferably 4 to 10 mol%.

Backpressure of the reaction gases below 50% by volume, particularly preferably below 10% by volume, very particularly preferably below 1% by volume, in particular preferably below 0.1% by volume of the total gases, preferably occurs in the reactor chamber. Emphasized preferably no measurable recoil occurs

Preferably, the gas outlet velocity at the nozzle is as low as possible.

Preferably, the gas velocity in the reactor chamber is as low as possible. Preferably, the addition of the reaction gases takes place as steam or as gas.

The reaction gases are preferably premixed before entry into the reactor, preferably homogeneously premixed. The reaction gases are preferably premixed in the gas stream, which is introduced into the nozzle in the reactor, in particular premixed intensive.

In a preferred embodiment, the hot process gases are quenched in the reactor by adding hot, preferably slightly superheated, steam which is preferably diluted with air, preferably hot air, that is, the reaction is moderated or stopped with water.

Examples of the silicon compounds are preferably silicon tetrachloride, hydrogen silicon trichloride, methyl silicon trichloride, and mixtures thereof. Preferably, for reasons of economy and the Qualltat, are mixtures containing Siiiciumtetrachloπd as the main component.

Preferably, the silane is derived from processes which serve to produce amorphous, polycrystalline or monocrystalline silicon metal, such as silicon for the electronics or semiconductor or photovoltaic industries.

In a further preferred embodiment, the silane is preferably derived from processes which are the production of

Methylchlorosilanes, for example, as a raw material for the preparation of silicones such as silicone oils such as polydimethylsiloxanes, or silicone rubbers such as crosslinked polydimethylsiloxanes, or Sxliconharzen serve, for example, the construction industry, the coating industry, or the Automobilmdutrie. The silicon compounds or their mixtures may contain gaseous, vaporous or vaporizable and volatile impurities, such as methane, ethane, isopropane, n-propane, isobutanes, n-butane, due to their manufacturing process.

Ethene, ethyne, propene, isobutene and n-butene _f and other higher iso-, or n- or neo-alkanes, -alkenes and alkines, lower alcohols, such as methanol, ethanol, propanol, or mixtures thereof, or alkyl optionally haloalkyl, such as chloroalkyl-substituted gaseous, vaporous or vaporizable organosilicon compounds, or hydrogen or nitrogen or argon or natural gas or carbon oxides, such as carbon monoxide or carbon dioxide.

In a preferred embodiment, this silicon tetrachloride from the disproportionation and implementation of hydrogen silicon trichloride at temperatures greater than 500 ⁰ C, preferably large 700 ⁰ C, more preferably large 850 ⁰ C, to form silicon tetrachloride, silicon metal and hydrogen, be. The Siliciuintetrachlorid can be separated by distillation and purified.

In a preferred embodiment for technical and economic reasons or for reasons of product quality, the silicon-containing compound, or mixtures thereof, or the silane, has a content of large 10% by volume,% silicon tetrachloride, particularly preferably greater than 90% by volume silicon tetrachloride; more preferably, a large 95% by volume of silicon tetrachloride, most preferably a large 99% by volume of silicon tetrachloride, the remainder m of the mixture being hydrogen silicon trichloride and dihydrogen silicon dichloride.

In another, for economic reasons, preferred embodiment, which may be based on the presence of large amounts of methylsilicon chloride is Methylsilicon trichloride is preferred, particularly preferably in concentrations of greater than 10 mol%.

In another, for economic reasons, preferred embodiment, which may be based on the presence of large amounts of hydrofluoric trichloride, hydrogen silicon trichloride is preferred.

In another preferred embodiment for economic reasons, mixtures of silicon tetrachloride and hydrogen silicon trichloride are preferred.

In another preferred embodiment, for economic reasons, mixtures of silicon tetrachloride, methylsilicon trichloride and hydrofluoric trichloride are preferred.

In a particularly preferred embodiment, mixtures which are preferably less than or equal to 80 mol.% Hydrogen silicon trichloride, most preferably less than or equal to 20 mol. % Hydrogen silicon trichloride, more preferably less than 10 mol. % Hydrogen silicon trichloride contained used.

In another preferred embodiment, mixtures containing 30 mol.% Hydrogen silicon trichloride used.

In another particularly preferred embodiment, mixtures containing more than 10 mol% of methylsilicon trichloride, more preferably more than 20 mol%, are used.

Methylsilicon trichloride _r particularly preferably more than 50 mol. % Methylsilicon trichloride contained used.

In another preferred embodiment, mixtures which are greater than 40 mol% of methylsilicon trichloride are particularly preferred preferably 45 mol. % Methylsilicon trichloride contained used. These mixtures then preferably contain less than 20 mol%, preferably less than 10 mol%, particularly preferably less than 5 mol% of carbon-containing silicon compounds which are not methyl silicate trichloride and less than 20 mol%, preferably less than 10 mol%, particularly preferably less than 5 mol % Hydrogen f-containing silicon compounds and less than 5 mol% of non-silicon-containing, optionally substituted, hydrocarbons.

In another preferred embodiment, mixtures which contain greater than 40 mol% silicon tetrachloride, very particularly preferably 45 mol% silicon tetrachloride are used. These mixtures preferably contain less than 20 mol%, preferably less than 10 mol%, particularly preferably less than 5 mol% Carbon-containing silicon compounds and less than 20 mol%, preferably less than 10 mol%, more preferably less than 5 mol% Wasserstσf f-containing silicon compounds and less than 5 mol% not silicon-containing, optionally substituted, hydrocarbons.

In a preferred embodiment of the invention, a gas mixture with a dosage of 500 to 5000 Nm ³ / hrn, preferably 750 to 3000 Nm ³ / h, more preferably 1000 to 2500 Nm ³ Zh, preferably 0.1 to 100 mol%, particularly preferred 1

50 mol% _{f, more} preferably 1-5 mol% tetrachlorosilane, 0-100 mol%, particularly preferably 1-5 mol% methyltrichlorosilane, 1

20 mol%, preferably 2.5-15 mol% hydrogen, 0.001 to 15 mol%, preferably 1-10 mol% carbon dioxide, 10-30 mol%, preferably 15-25 Mo 1% oxygen, 50-100 mol%, preferably 65

75 mol% of nitrogen, 0-50 mol%, particularly preferably 0.1-10 mol%, very particularly preferably 0.5-5 mol% of hydrogenmethyldichlorosilane, 0.001-100 mol%, particularly preferably 0.1-10 mol% of hydrogentrichlorosilane, 0-50 mole%, more preferably 0.1-10 mole% tetramethylsilane, 0-50 Mol%, particularly preferably 0.1-10 mol% of trimethylchlorosilane and 0-20 mol%, particularly preferably 0.5-10 mol%, of mixtures of alkane, alkene or haloalkyl, ie for example mixtures of propanes, butanols and pentanes, of propenes , Butenes and pentenes as well as from chloropropanes, chlorobutanes and Chlorpentanen and that from a nozzle with a

Gas velocity of 10 to 100 m / s, more preferably 30-70 m / s at the head of a combustion chamber via a nozzle enters a burner chamber, wherein the combustion chamber has a volume of 1 - 10 m ^a , more preferably 2.5 - 5 m ³ has, and a volume to height ratio of 0.1 - 1 m ² , more preferably 0.25 - 0.75 m ^? and a cross-sectional area of 0.1 - 1 m ^? , Particularly preferably 0.25 - 0.75 m ² , in the combustion chamber at 1000 ⁰ C to 2000 ⁰ C reacted.

Preferably, the oxygen for use in the reactor is taken from the air from the surrounding atmosphere. That is, the reactor is preferably supplied with air. The oxygen O2 in the air may be enriched to greater than 20% by volume, for example by the addition of pure oxygen O ₂ or by the addition of air containing a large 20% by volume of oxygen O ₂ .

The air can be used as such, or can be prepared by condensation and / or absorption of the water at less than O ⁰ Cj, preferably at temperatures of less than -10 °, particularly preferably at temperatures of less than -2O ⁰ C, are pre-dried.

In a preferred embodiment of the process for the production of fumed silica, it is possible to feed in additional pure oxygen or air or air / oxygen mixtures or additionally pure nitrogen or air or air / nitrogen mixtures via another reactor nozzle which encloses the reactor nozzle from which the reaction gases exit become. In a preferred embodiment of the process for producing fumed silica, further air can be introduced outside the nozzle at the head of the combustion chamber into the combustion chamber.

Preferably, the reactor chamber is open, and is in open exchange with the atmospheric pressure.

In a preferred embodiment, the hydrogen chloride HCl formed in the reaction is recovered by absorption and desorption, purified and dried and reused.

In a further preferred embodiment, the dry hydrogen chloride HCl thus obtained is used to prepare chlorosilanes such as, preferably, silicon tetrachloride, hydrogen silicon trichloride, dihydrogen silicium dichloride and trihydrogen silicon chloride, more preferably hydrogen silicon trichloride of silicon metal.

Examples of a preferred use are a reaction and production of methylchlorosilanes according to a generally simplified empirical formula

Si + 3 HCl -> HSiCl ₃ + H ₂

whereby side reaction products such as silicon tetrachloride, hydrogen silicon trichloride and others may be formed, or a reaction and production of methylchlorosilanes according to a generally simplified molecular formula

HCl + CH ₃ OH -> CH ₃ Cl + H ₂ O and after separation of Methylchloridel and water, is, if necessary, dried, methyl chloride is reacted with metallic silicon, optionally with the addition of catalysts and promoters such as copper or tin compounds.

Si + 2 CH ₃ Cl -> (CH ₃ J ₂ SiCl ₂

whereby side reaction products such as methylsilicon trichloride, CH ₃ SiCl ₃ , trimethylsilicon chloride, (CH ₃ ) ₃ SiCl and others may be formed.

Examples of inventive chemical reactions for the inventive production of fumed silica according to the invention are the oxidation of the fuel gas with

Atmospheric oxygen at which temperatures of 1000 ° to 200 ° C. in the reaction zone are achieved and high temperature hydrolysis by the water formed for a = 1 and X = Cl and z = 4 or oxidation of the silane and high temperature hydrolysis for other values for a, b , x, y and z of the Si-X bonds by the water formed.

Preferred examples of the reactions are:

Formation of water

O ₂ + 2 H ₂ -> 2H ₂ O

high temperature hydrolysis

SiCl ₄ + 2 H ₂ O -> 4 HCl + SiO ₂ (fumed silica)

Oxidation and high temperature hydrolysis

HSiCl ₃ + O ₂ + H ₂ -> 3 HCl + SiO ₂ (fumed silica) Oxidation, formation of carbon dioxide and high-temperature hydrolysis

CH ₃ SiCl ₃ + ^■ 2 O ₂ -> 3 HCl + CO ₂ + SiO ₂ (fumed silica)

In a preferred embodiment, the size of the reaction zone can be changed by changing the amount of fuel gases.

In a further preferred embodiment of the invention, the reaction mixture from the combustion chamber, preferably in the region of the lower end of the combustion chamber executed, preferably aspirated, then the reaction mixture is preferably cooled, more preferably with energy recovery, preferably temperatures of less than 300 ⁰ C, all more preferably less than 200 ⁰ C, then preferably the gas containing the majority of the resulting hydrogen chloride gas, separated from the resulting fumed silica, more preferably separated by the use of fabric filters, and a further parallel process preferably a recovery of dry hydrogen chloride gas one, more preferably carried out multi-stage absorption and - Desorptionsprozess and environmental reasons in the

Furthermore, a reduction of the resulting excess chlorine gas CI2, and also for environmental reasons, another exhaust gas purification, performed to remove CI2 and HCl.

In a further embodiment of the invention, preference is given to a purification of the pyrogenic compounds produced according to the invention

Silica by blowing through gases, preferably in a fluidized bed, preferably at temperatures of 400 to 800 ⁰ C, more preferably carried out from 500 ⁰ C to 700 ⁰ C.

Preferred is a process in which a fumed silica according to the invention in an amount of 10 ~ 1000 kg / h, according to the invention 100 - 10000 tons per year with an annual output of 7884 hours, ie with a time availability of 85%, with a BET specific surface area of 100 to 300 mVg, a tapped density after Bagging in 10 kg paper bag from 30 to 90 g / l, with a pH of 4 wt .-% aqueous dispersion from 3.6 to 4.6, a Siebrtickstand after Mocker large 40 microns from 0 - 0.01 wt %, a thickening effect η / ηO in a silicone oil of 1-10, a thickening effect η / ηO in an uncrosslinked unsaturated polyester resin of 1-10, a mean spherical equivalent hydrodynamic particle size of 100-500 nm after ultrasound dispersion at 0.3 wt .%, a temperature of 25 ⁰ C and at pH of about 9.5 to 10.5 and measured with a Malvern Zetasizer Nano ZS® at a backscattering angle of 173 ° is obtained.

Preferably, an afterburning of residual oxygen and chlorine gas is additionally carried out by adding a fuel gas into the flame, at least at a location other than the reactor nozzle, in the reactor chamber. Preferably, at various locations in the reaction chamber, further fuel gas, such as hydrogen, may be added to the reaction zone. Preferably, this additional hydrogen is used to reduce chlorine formed in the reactor, Cl ₂ , to HCl. In another preferred embodiment, an afterburning of residual oxygen and chlorine gas is additionally performed by adding, at least at a location other than the reactor chamber, fuel gas below a temperature other than the flame temperature.

Preferably, this additional hydrogen is used to reduce chlorine formed in the reactor, CIa, to HCl. Preference is given to a silicic acid production process in which the chlorine loss is preferably below 10% by weight, preferably below 5% by weight, more preferably below 1% by weight.

Preferably, this may additionally be added hydrogen

Nitrogen, preferably 0.001 to 90 vol.%, Preferably 30-70 vol.%.

In another preferred embodiment, the hydrogen does not contain nitrogen N ₂ .

Preferably, the reactor is fed as fuel gas hydrogen.

Preferably, only hydrogen and no further fuel gas is used. Preferably, this prevents the formation of carbon oxides, such as carbon monoxide CO and the formation of chlorinated aromatic hydrocarbons, such as chlorinated dibenzodioxms.

In one possible embodiment, this is hydrogen from the catalytic thermal conversion of e.g. Methanol to carbon dioxide CO2 and hydrogen.

In a further preferred embodiment, this is hydrogen from the catalytic thermal conversion of hydrocarbons and water to carbon dioxide CO ₂ and hydrogen. Carbon dioxide CO ₂ can be removed absorptively and adsorptively, the hydrogen can be purified in this way.

In another preferred embodiment, this is hydrogen from the Dxsproportionierung and reaction of Wasserstoffsiliciumtπchlorid at temperatures greater than 500 ⁰ C, preferably large 700 ⁰ C, more preferably large 850 ⁰ C, with formation of preferably silicon tetrachloride, silicon metal and hydrogen.

The hydrogen may also preferably be purified by cryogenic condensation of other ingredients.

In another preferred embodiment, hydrogen is used, which is formed in the reaction of silicon metal with hydrogen chloride, HCl, to Wasserstoffsiliciumtrichloπd.

Preferably, the process for preparing fumed silica includes the following, preferably sequential, steps: (1) silane supply, silane evaporator, optionally

Air treatment, (2) reactor (3) Energy jerk and cooling, (4) optionally, pre-separation of the silica S1O2 by preferably one or more cyclones, separation of the silica SiO ₂ by preferably filters, preferably fabric filter, particularly preferably upper flat filter (5) Purification of the silica of, preferably last, traces of hydrogen chloride HCl m a dryer, preferably in a rotating Troinmeltrockner, preferably with internals, which preferably achieve a combined radial and vertical movement, or preferably xn a fluidized bed, or a

Fluidized bed, preferably below Zufuhrung of gases such as air or nitrogen or an inert gas, preferably at temperatures high 100 ⁰ C, particularly preferably larger 300 ⁰ C, most preferably large 400 ⁰ C, with a Leerrohgasgeschwindigkeit of 0.1 - 100 cm / s more preferably 1-10 cm / s, preferably the traces of hydrogen chloride HCl, analytically measured by a measurement of the pH, recordably by suspending 4 g of silica in 100 ml of water and (6) preferably homogenization, for example by mixing and fluidization m a silo of a certain defined amount from silicic acid to a homogeneous charge, eg 1-20 tons, preferably 5-15 tons, (7) storage in silos and (8) optionally compression, for example with roller compressors, screw compressors, - piston compressors, preferably roller compressors, (9) filling in Container, for example in 5 - 20 kg bags, consisting of multi-ply paper, optionally coated one or more layers, preferably polyethylene coated, preferably perforated with small holes, or in big bags of 50-500 kg, preferably polyethylene or polypropylene , preferably 2 or more layers, for example as described in EP773159B1, or in bulk containers such as silo wagons, silo containers, preferably silo containers containing an inner container or inner bag or liner for protecting the silica from impurities, for example from polyethylene or polypropylene, of 500 - 5000 kg content.

The generation of the gas temperature in a fluidized bed, or a Flieδbett, for purifying the fumed silica, for example of hydrogen chloride, HCl, preferably with the supply of gases such as air or nitrogen or inert gas, for purifying the silica of HCl can be done by electrical heating of the gas or, for reasons of economy and conservation of energy resources, by burning a fuel gas such as hydrogen, methane, ethane, propane, butane) with air or oxygen-containing gas; Preferably, this hydrogen is used.

In a preferred embodiment, no additional water is added throughout the process, except for the water produced by the reaction of the reaction gases.

In another preferred embodiment, before, preferably during, or after the purification of the fumed silica, preferably to improve the desorption of HCl from the silica, additionally added to water vapor. In another preferred embodiment, steam is added to standardize and abreact the silicic acid surface and to stabilize the silicic acid; This can at the same time a conditioning of the silica surface, preferably over the reaction with humidity, - be achieved.

Method for compacting

In a further preferred embodiment, the silica can be compacted by moistening with a liquid and subsequent drying.

Moistening can be carried out by Exnruhren or Emdispergieren in a liquid.

In a further particularly preferred embodiment, the moistening can be carried out by spraying, that is to say the silica is compacted by spraying with liquid and subsequent drying.

Preference is given to using fumed silica. The pyrogenic silica can be used both as hydrophilic and with organosilicon compounds silylated ß silicic acid. Preference is given to using hydrophilic silica.

Preferably, the silica has a tap density according to DIN of 20 to 120 g / l, more preferably 25 to 45 g / l prior to compacting.

Preferably, the silica has a after compression

Tap density according to DIN of 60 to 300 g / l, more preferably 70 to 150 g / l. Spraying with liquids takes place according to the aerosol technique described in DE 4419234.

Drying of the silica is preferably carried out by drying techniques as described in DE 4419234, US 5,686,054 or DE 10145162, σS 6,800,413.

Preferred liquids for densifying silica are preferably low-viscosity and low-volatile siloxanes, such as hexamethyldisiloxane, low-viscosity and low-volatile hydrocarbons, such as n-hexane or toluene, are low-viscosity and low-volatility alkyl alcohols such as methanal, ethanol or isopropanol, even those denatured by additives are ketones, such as acetone, or ethers, such as tetrahydrofuran, or protic solvents, such as water, and mixtures thereof.

Preferred liquids are those with a high dielectric constant, particularly preferably with a dielectric constant of greater than 20.

Preferred liquids are those of high density, more preferably having a density of greater than 0.9 g / cm ³ .

Preferred liquids are those with high surface tension, more preferably with a surface tension greater than 40 mN / m.

Fumed silica inventively produced, preferably 30 to 500 m ² / q, preferably 70-330 MVG, particularly preferably 80 to 230 MVG, particularly preferably 130 to 170 m ^Ä / g specific surface area, preferably measured by the BET method, and an average Äggregatspartikelgroße, preferably measured as sphere-equivalent hydrodynamic diameter, of preferably 50 to 500 nr, preferably 120 to 350 nrn, particularly preferably 130 to 200 nm and a relative Thickening effect in liquids η / ηθ of preferably greater than 2.0, preferably greater than 4.0, particularly preferably greater than 6.0, very particularly preferably greater than 7.5 and a fraction of less than 0.03% by weight, preferably less than 0.015% by weight .%, Particularly preferably less than 0.008 wt.% Coarse particles, preferably

Coarse particles larger than 10 microns in diameter, more preferably greater than 40 microns, based on the pyrogenic silica and less than 100,000 coarse particles, preferably less than 20,000 coarse particles, more preferably less than 10,000 coarse particles, most preferably less than 5,000 coarse particles, in particular preferably smaller as 1,000 coarse particles greater than 10 microns, more preferably greater than 2 microns, per 1 milliliter {ml or cm ³ ) in an aqueous suspension containing 1 gram of silica.

Another object of the invention is a fumed silica, wherein this a Verdickungswrrkung, described as relative thickening η / ηO in a silicone oil with optimum dispersion, preferably greater than 2.0, a mean spherical equivalent hydrodynamic diameter in water at pH greater than 9 of 150 to 300 nanometers, a content of boron of less than 1 ppm, a content of titanium of less than 1 ppm, an iron content of less than 1 ppm, an aluminum content of less than 10 ppm, a content of nickel smaller 1 ppm, a content of copper of less than 1 ppm, a germanium content of less than 1 ppm.

The silicic acid which is produced by the process according to the invention is a fumed silica, preferably the 30 to 500 mVg, preferably 70 to 330 m ^z / g, particularly preferably 80 to 230 m ^? / g, more preferably 80 to 170 m ^? / g specific surface area, preferably measured according to BET, and is a fumed silica which has an average aggregate particle size, preferably measured as spherical equivalent hydrodynamic diameter, of 100 to 500 nm, preferably 150 to 350 nm, more preferably from 150 to 250 nm, preferably measured measured as described above and is a fumed silica having a relative thickening effect in liquids η / ηö of preferably large 2.0, preferably large 4.0, especially preferably large 6.0 very particularly preferably large 7.5, preferably measured as described above, and is a fumed silica which has a fraction of less than 0.03 wt.%, preferably less than 0.015 wt.%, particularly preferably less than 0.005 wt.% Coarse particles, preferably coarse particles larger than 10 microns

Diameter, particularly preferably greater than 40 μm, based on the fumed silica, and is a pyrogenic silica which is less than 100% of coarse particles, preferably less than 20,000 coarse particles, more preferably less than 10,000 coarse particles, very particularly preferably less than 5,000 coarse particles, in particular, less than 1,000 coarse particles of greater than 10 μm, particularly preferably greater than 1.5 μm, very particularly preferably greater than 1.0 μm, in particular preferably greater than 0.56 μm per 1 milliliter (ml or cm ³ ), preferably based on a 1 to 50% by weight, particularly preferably on a 10% strength by weight aqueous dispersion of the silica.

Furthermore, the fumed silica prepared according to the invention preferably exhibits a proportion of coarse

Sintered particles of preferably less than 0.05% by weight, preferably less than 0.03% by weight, more preferably less than 0.015% by weight, very particularly preferably less than 0.008% by weight. An example of a suitable measuring method is a gravimetric determination of the screen pressure level, for example according to Mocker {oversize> 40 μm}.

Preferably, the fumed silica produced according to the invention contains less than 0.05% by weight, preferably less than 0.03 Gew%, more preferably less than 0.015 wt.%, Most preferably less than 0.008 wt.% Coarse sintered particles having a density of 200 to 2500 g / l and having a diameter of 0.5 to 500 microns. An example of suitable measuring methods is the use of the optical centrifuge, for example the LÜMifuge® device.

Fumed silica produced according to the invention, and aqueous dispersion prepared therefrom, or chemical formulation based on such a dispersion, in which, after optimal dispersion, for example with an ultrasound tip or ultrasound generator or ultrasound homogenizer of preferably greater than 1 minute, preferably 2 to 5 minutes, and optimum stabilization , Preferably alkaline stabilization at pH 9-11, preferably pH 9.9 to 10.2, and in the after separation of the finely divided fumed silica non-silica particles and silica coarse particles, such as coarse and dense sintered particles having a density of 200 to 2500 g / l and with a diameter of 0.5 to 500 microns, with commercially available counting method for the determination of large particles, for example based on light-extinction method, for example, white light or laser light, preferably less than 10,000 particles, preferably less than 2000 particles, especially preferred It preferably contains less than 1000 particles, more preferably less than 500 particles, preferably less than 100 particles larger than 10 microns, more preferably larger than 1.5 microns, most preferably larger than 1.0 microns, especially preferably larger than 0.56 μm per ml, after deduction of the blank value of particles of the water used to prepare the dispersion.

Preferably, the fumed silica contains agglomerates and flakes with a density of 10 to 200 g / l and with a diameter of 1 to 500 μrα, The size of the silica agglomerates can preferably be measured with the Fraunhofer light diffraction on the silica in aqueous dispersion or as a dry aerosol or powder or with sieve methods. Suitable devices are offered, for example, by Malvern®, Sympatec®, Coulter®, Zilas® or Horiba®.

Preferably, the fumed silica preferably exhibits low contamination with non-silica portions.

The fumed silica preferably has a content of a non-silicon element of less than 1% by weight, preferably less than 0.1% by weight, more preferably less than 0.01% by weight, very particularly preferably less than 10 ppm by weight, in particular preferably less than 1 ppm by weight, based on the total silica.

In addition, the silica prepared according to the invention has an aluminum content of less than 10 ppm by weight, preferably less than 1 ppm of aluminum, less than 10 ppm by weight of boron, preferably less than 1 ppm of boron, less than 1 ppm by weight of titanium, preferably less than 200 ppb by titanium. and to iron, cobalt, nickel and copper less than 1 ppm by weight, preferably iron, cobalt, nickel and copper smaller than 200 ppb, based on the total silica.

Preferably, the silica produced has one of the specific surface SO, measured by BET, and the material density p. of 2200 g / l, according to d = 6 / (p * SO) calculated primary particle diameter d or Sauter

Diameter d of 5-100 nm, a specific surface area measured by BET of 30-500 m ² / g and a hydrodynamic diameter, which formed from primary particles, preferably stable sintered aggregates, from 100-500 nm, measured as described above or with the dynamic light scattering or Photocorrelation spectroscopy or inelastic light scattering measured in suspension in a liquid in pure form <5 mPas viscosity, such as aqueous suspension in water or alcoholic suspension, or from 100 to 1000 ran aerodymic diameter, measured in air or gas, or a via

Rheology measured diameter of large 100 nm, a geometric diameter of agglomerates formed from aggregates, measured by the Fraunhofer light diffraction, in fluids such as water or alcohol or oils of 500 nra to 100 microns, and measured in air or gases of 1 .mu.m to 1 mm ,

Preferably, the silicic acid produced has a fractal surface dimension of less than 3, preferably from 1.9 to 2.7, more preferably from 2.0 to 2.1.

Preferably, the silicic acid produced has a fractal dimension of the mass of less than 3, preferably 1.5 to 2.8, more preferably from 1.8 to 2.3, most preferably from 1.9 to 2.1.

Preferably, the silicic acid produced has a content of surface silanol groups SiOH of 1.5 ~ 2.0, preferably 1.7-1.9 SiOH per nm ^? specific surface area measured according to BET, or measured as acidic SiOH by means of a titration method based on the method of Sears.

Preferably, the silica does not contain any chlorinated polyaromatic hydrocarbons, especially those containing oxygen atoms. In particular, the content of chlorinated aromatic dioxins and furans is less than 1 ppb wt.

Analytics of the properties Preferably, the relative thickening effect η / ηO of the fumed silica is measured as the quotient of the viscosity η _{t of} a liquid medium containing fumed silica, measured at a temperature of 25 ° C and from the viscosity ηO of a liquid medium containing no fumed silica, measured at a temperature of 25 ° C. Examples of liquid medium are mixtures of a polyester resin, for example about 65 wt.%, For example, a condensation product of ortho-phthalic anhydride and maleic anhydride on the one hand and a diol, for example 1,2-propanediol, on the other hand, with a solvent, for example about 35% by weight, for example of a reactive monomer, for example monostyrene, or for example silicone, for example preferably polydimethylsiloxane, preferably end-capped with trirethylethylsiloxy groups, preferably those having a viscosity at 25 ° C. of from 0.5 to 5.0 Pa s, preferably 0.9 - 2.1 Pa s, more preferably about 1.0 Pa s. The amount of pyrogenic silica in the liquid medium is preferably 1 to 5% by weight, more preferably 1.8 to 3.4% by weight, most preferably 2% by weight.

Preferably, the measurements of the viscosity at a temperature of 25 ⁰ C and at the same constant shear rate, preferably at a constant shear rate of 0.5 to 200 l / s, more preferably 0.9 to 20 l / s, more preferably at 10 l / s.

The dispersion of the fumed silica in the liquid medium is preferably carried out with optimal dispersion, for example with a Zahnscheibendissolver at a

Peripheral velocity of 4 to 20 m / s, preferably at 11 m / s, preferably over an optimal period, more preferably over 3 to 10 minutes, most preferably over 5 minutes. The average aggregate particle size is preferably measured as the mean sphere-equivalent hydrodynamic diameter, preferably measured by photocorrelation spectroscopy or dynamic light scattering or quasi-elastic light scattering, at an angle of 1 to 179 °, preferably about 90 °, or in another preferred embodiment in backscatter at an angle of 170 ° to 179 °, preferably at an angle of about 173 °, for example with the device Malvern Zetasizer® or Malvern Nanosizer® and, for example, reading the Z-average value according to a cumulative analysis or the standard algorithm, as mean aggregate diameter and preferably after dispersion at 0.001 to 5 wt.%, Preferably about 0.3 wt.% In preferably alkaline water, preferably pH 9, more preferably from about pH 10, preferably adjusted with ammonia, and preferably in dispersion with a Magnetetruhrer, preferably at 100 to 500 revolutions per minute, in particular rs preferably at 300 revolutions per minute, and with ultrasound, preferably an ultrasound tip at 75-95% power, more preferably at 90% power, for example a Bandelin UM6Ö ultrasound tip, for 1 to 15 minutes, preferably 5 to 10 minutes, more preferably 5 min., At a temperature of 25 ° C.

The proportion of coarse particles, for example sintered particles, is preferably determined gravimetrically. Examples of a suitable method of measurement here is a gravimetric determination of the screen residue level after screening of the silica scrubbed with water, with screens of less than or equal to 100 μm mesh sizes, preferably less than or equal to 40 μm, particularly preferably less than or equal to 10 μm. A particularly preferred example of this is the method of Mocker, for example by means of water jet and weighing the coarse particles on a 40 micron sieve {after weighing so gravimetrically obtained the Uberkorn> 40 microns). The proportion of coarse particles is preferably determined to be coarse sintered particles having a density of 100 to 2500 g / l, preferably 200 to 2500 g / l and a diameter of 0.5 to 500 μm, preferably 2 μra to 100 μm.

An example of suitable measuring methods is the use of the optical centrifuge, for example the LUMifuge® device.

Preferably, the proportion of coarse particles in the fumed silica prepared by the process according to the invention on an aqueous dispersion _f or chemical formulation, based on such a dispersion which has been prepared from the silica by means of optimal dispersion, for example with an ultrasonic tip and a dispersion time of greater 1 minute, preferably 2.5 minutes, and more optimal

Stabilization, for example alkaline stabilization at pH 9 - H _r preferably pH 9.2 to 10.2, with commercially available counting methods for the determination of large particles, for example based on light extinction methods or light scattering methods, for example on white light or from laser light, for example with an Accusizer® 680 or 780 device, or a Liquilaz® device from PSM, Oregon, USA, or a device FAS® 815 from Topas, Germany.

Preferably, the quality of the product silica is checked at regular intervals by sampling and analysis of these samples with typical silica methods such as the specific surface area, for example measured by BET, or, for example, measured by acid-base titration, as described, for example, by Sears et al. _f such as the particle size, for example, the average aggregate diameter, for example, as a hydrodynamic diameter, for example as measured by dynamic light scattering, or in the other methods specified, such as the pH, for example, measured as the pH of a Dispersion of 4% by weight of silicic acid in water, such as the screen residue on coarse components, for example measured by the Mocker method using a water jet and a 40 μm sieve, or as payment methods for the analysis of coarse particles, for example with white light or laser light extinction - and

Numbering method as described above, such as the thickening effect in liquid media, for example as described above, preferably according to defined protocols.

Preferably, the sample is drawn with a specific sampling device.

Preferably, the traces of HCl, measured analytically by measuring the pH, are obtained by suspending 4 g of silica in 100 ml of water

This can be assessed visually by an evaluation of the screen print area by Mocker (> 40 μm), preferably with a magnifying glass, particularly preferably with a light microscope which makes dark, white and colored to> 10 μm, preferably to> 1 μm visible, or for example by scanning electron microscopy or

Transmission electron microscopy, or by suspending silica in carbon tetrachloride, in the fumed silica or fumed silica dispersions, because of the same refractive index, appear transparent, and so non-Siliziumdioxxd proportions are more visible, for example, to the human eye, but preferably with a magnifying glass or be visible with the Lichtro.ikrosk.op. Non-silicon elements are preferably qualitatively or semi-quantitatively detected after fuming of the silica with hydrofluoric acid by means of spectral analysis or quantitatively measured by means of inductive-coupled plasma and optical emission analysis or mass spectrometry.

The fumed silica according to the invention is preferably used as thickener, rheology additive, thixotropic agent, reinforcing agent for elastomers, elastomers and duromers, for example in surface coatings, paints and inks, adhesives, sealants, glass fiber reinforced plastics, composites, rubbers and others Plastics, as abrasive particles in the chemical-mechanical planarization in the Halbleitindustπe, as a polishing agent, as a thermal insulation material and as a raw material for thermal insulation materials, for the production of print media, as a flow aid, for creating layers and moldings that may be dense or porous, as an additive and Filler for paints, varnishes, inks, adhesives and sealants and rubbers, of silicones or synthetic or natural rubber, eg for tires and soles.

The pyrogenic silica prepared according to the method according to the invention is referred to as fumed silica

Matting agents used in paints and coatings as well as for adhesive and sealant systems.

Surprisingly, it was also found that finer and more easily dispersible spatial structures of the fumed silica particles can be achieved with these inventive systems, ie, finer aggregates of the silica are formed, thus an improvement in the property of a rheological additive, as a reinforcing filler for elastomers, plastomers and resins, is achieved as a thermal insulating base material, as a coating material for printing media.

Preferably, the silica is used as rheological.es additive and as a filler in sealants in amounts of 5 to 15%, preferably as a sealant for joints in the sanitary and cake sector, in window and facade construction, in building construction and civil engineering and in machinery and in toolmaking.

Preferably, the silica is used in the process of chemical mechanical polishing in optics, in the semiconductor industry, in the electrical and in the electronics industry and in the surface treatment of metals, ceramics and glasses as abrasives or polishing agents.

Another object is a Formkorper, coating or impregnation containing the novel silica.

Preferably, the silica is used in coating materials, surface layers, textiles, polymers adhesives, sealants, rubbers and composite materials, as well as in coating materials, adhesives, sealants, rubbers and composite materials for controlling the rheology or mechanical properties, or for controlling rheology and reinforcement.

Another object is a powder or toner containing the silicic acid according to the invention.

Preferably, the silica is used in powder, in

Toners, in electrophotography, in fire-extinguishing powder, as well as in powders, in toners in electrophotography, in fire-extinguishing powder for controlling the dry flowability or the electrical charge, or in controlling the dry flowability and the electric charge. FIG. 1

FIG. 1 shows a flame reactor according to the invention with flame orientation from top to bottom, in longitudinal section, where 1 denotes the reactor chambers and 1.1 the diameter at the reactor head and 1.2 the diameter at half the reactor length. 1.3 means the height equal to the length of the reactor chamber, 1.4 being the diameter of the reactor chamber. 2 designates the nozzle and 2.1 the diameter of the nozzle.

Examples

example 1

A gas mixture, which enters from a nozzle with a gas velocity of 58 m / s at the head of a combustion chamber via a nozzle in a burner chamber, the combustion chamber a length of

4650 mm and a cross-sectional area of 0.71 m ^? has, and none compared to the current external pressure, and the gas mixture has a temperature between 100 ⁰ C and 200 ⁰ C, and the reaction zone has a length of 3875 mm, and the gas mixture with 2085 Nm ³ / hm the combustion chamber is introduced, and the gas mixture has 0.049 mol% of methyltrichlorosilane, 0.019 mol% of hydrogen, - 0.17 mol% of oxygen and 0.70 mol% of nitrogen, at the inlet m, the combustion chamber at 1000 ⁰ C to 2000 ⁰ C reacted. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption process, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silica of residual hydrogen chloride and other volatile compounds, in a fluidized bed by hot gases at 400 to 800 ⁰ C, is a pyrogenic silica with a BET specific surface area of 150 ra ^? / g, with a tap density after bagging in 10 kg paper bag of 43 g / l, with a pH of 4 wt% aqueous dispersion of 4.2, a Siebruckstand after Mocker large 40 microns of 0.003 wt.%, a thickening effect η / ηO in a 3.5% siliconeol, a mean bead equivalent hydrodynamic particle size of 220 nm after ultrasonic dispersion at 0.3 wt%, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® a throwing angle of 173 °, obtained.

Example 2

A premixed gas mixture which enters from a nozzle with a gas velocity of 73 m / s at the head of a combustion chamber via a nozzle in a burner chamber, wherein the combustion chamber has an overpressure of less than 50 mbar compared to the current external pressure, and the gas mixture has a temperature between 100 ⁰ C and 200 ⁰ C is reacted in the combustion chamber at 1000 ⁰ C to 2000 ⁰ C, wherein in the combustion chamber 6 vol.% Silane, with a content of methyltrichlorosilane of large 90 vol.%, 88 vol.% Air from the environment, the air being supplied to 94% by volume from the nozzle and 6% by volume from other feeders outside the nozzle at the top of the combustion chamber, and 5% by volume of fuel gas, the fuel gas being greater than 90% by volume. Contains hydrogen gas, react. After suction from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filter, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption process, reduction of excess chlorine gas, and exhaust gas purification, as well as purification of the fumed silica in a fluidized bed by hexagonal gases at 400 to 800 ⁰ C, a fumed silica with exner specific surface BET of 150 mVg, with a tap density after AbsacJcung in 10 kg paper bag of 40 g / l, with a pH of a 4% by weight dispersion of 4.1, a screen size of 40 μm by Mocker of 0.005 wt.%, a thickening effect η / ηO in a silicone oil of 4.0, a mean spherical equivalent hydrodynamic particle size of 220 nm after ultrasonic dispersion at 0.3% by weight, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173.

Example 3

A gas mixture with a dosage of 1630 NmVh containing 4.9 mol% of methyltrichlorosilane, 5 _r 8 mol% hydrogen, 1.9 mol% carbon dioxide, 17 mol% oxygen and 70 mol% of nitrogen as gases, and that from a nozzle with one

Gas velocity of 34 m / s at the head of a combustion chamber via a nozzle in a Brennerkarnmer enters, the combustion chamber has a volume of 1.7 m ³ , and a volume to height ratio of 0.38 m ^? and a cross-sectional area of 0.38 m ^? which is brought into the combustion chamber at 1000 ⁰ C to 2000 ⁰ C to the reaction .. After aspiration of the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the fumed silica by fabric filters, recovery was dry hydrogen chloride gas in a multistage Absorption and desorption process, reduction of the excess chlorine gas, and exhaust gas purification, and purification of fumed silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, a pyrogenic silica in an amount of 217 kg / h, corresponding to 1920 tons per Year at an annual rate of 8864 hours, having a specific surface according to BET of 150 m ^p / g, a tap density after bagging in 10 kg paper sack of 40 g / l, having a pH of 4 ~ wt% aqueous dispersion of 4.1, a Siebruckstand by Mocker large 40 microns of 0.005 wt.%, A Verdickungswirkυng η / ηθin a silicone oil of 6, 5, a Verdickungswirkuπg η / ηθin an uncrosslinked unsaturated polyester resin of 4.5, a mean spherical equivalent hydrodynamic particle size of 220 nm after ultrasonic dispersion at 0 , 3 wt.%, A temperature of 25 ⁰ C and at pH 10 and measured with a

Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °.

Example 4

A gas mixture with a dosage of 1630 NmVh containing 4.9 mol% of methyltrichlorosilane, 5.8 mol% of hydrogen, 17 mol% of oxygen and 71.9 mol% of nitrogen as gases, and from a nozzle with a gas velocity of 34 m / s at the head of a combustion chamber via a nozzle in a burner chamber, wherein the combustion chamber has a volume of 1.7 m ³ , and a volume to height ratio of 0.38 m ^> and has a cross-sectional area of 0.38 m ² , is reacted in the combustion chamber at 1000 ⁰ C to 2000 ⁰ C for reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption, reduction of excess chlorine gas, and exhaust gas purification, and

Purification of the fumed silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, is a pyrogenic silica in an amount of 217 kg / h, corresponding to 1920 tons per year with a yearly bars of 8864 hours, with a BET specific surface area of 150 m ⁷ / g, with a Tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of 4 wt .-% aqueous dispersion of 4.1, a Siebruckstand Mocker large 40 μin of 0.005 wt.% ₇ a thickening η / ηθin a silicone oil of 6.5, a thickening effect η / ηθ in an uncrosslinked unsaturated polyester resin of 4.5, a mean ball-equivalent hydrodynamic particle size of 220 nm after ultrasonic dispersion at 0.3 wt%, a temperature of 25 ° C and at pH 10 and measured obtained with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °.

Example 5

A gas mixture with a dosage of 1405 NmVh containing 4 _r 3 mol% tetrachlorosilane, 12 mol% hydrogen, 4 mol% carbon dioxide, 16 mol% oxygen and 64 mol% nitrogen as gases, and that from a nozzle with a gas velocity of 34 at the head of a combustion chamber via a nozzle enters into a burner chamber, the combustion chamber has a volume of 1.7 m ³ , and a volume to height ratio of 0.38 nα ^? and a cross-sectional area of 0.38 m ^? has, in the combustion chamber at 1000 ⁰ C to 2000 ⁰ C reacted. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filter, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, a fumed silica in an amount of 161 kg / h, corresponding to 1420 tons per year with a yearly bars of 8864 hours, with a specific surface area of BET of 150 mVg, with a tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of a 4 wt% aqueous dispersion of 4.1, a Siebruckstand after Mocker large 40 microns of 0.005 wt.%, A thickening η / ηθin a silicone oil of 6.5, a thickening η / ηθin a uncrosslinked unsaturated polyester resin of 4.5, a mean spherical equivalent hydrodynamic particle size of 220 nm after

Ultrasonic dispersion at 0.3 wt.%, A temperature of 25 ⁰ C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a scattering angle of 173 °, obtained.

Example 6

A gas mixture with a dosage of 1405 Nm ³ / h, which contains 4.3 mol% tetrachlorosilane, 12 mol% hydrogen, 16 mol% oxygen and 68 mol% nitrogen as gases, and from a nozzle with a gas velocity of 34 m / s enters the combustion chamber at the head of a combustion chamber via a nozzle, the combustion chamber has a volume of 1.7 m ³ , and a volume to height ratio of 0.38 m ^? and a cross-sectional area of 0.38 m ^? has, is brought to 1000 ° C in the combustion chamber at 1000 ⁰ C to the reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and - Desorptionsprozess, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silica in a fluidized bed by means of hot gases at 400 to 800 ⁰ C, becomes a fumed silica in an amount of 161 kg / h, corresponding to 1420 tons per year with a yearly intervals of 8864 hours, with a specific BET surface area of 150 m '/ g, with a tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of 4 ~% by weight aqueous dispersion of 4.1, a screen count of 40 m mocker of 0.005 wt.%, a thickening effect η / ηO in a siliconeol of 6.5, a thickening effect η / ηO in one uncrosslinked unsaturated polyester resin of 4.5, a mean sphere-equivalent hydrodynamic particle size of 220 nm after ultrasonic dispersion at 0.3 wt.%, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °, received.

Example 7

A gas mixture with a dosage of 2600 NmVh containing 4.6 mol% methyltrichlorosilane, 7.6 mol% hydrogen, 2.5 mol% carbon dioxide, 17 mol% oxygen and 68 mol% of nitrogen as gases, and from a nozzle with a gas velocity of 54 m / s at the head of a combustion chamber via a nozzle enters a combustion chamber, the combustion chamber has a volume of 3, 3 m ³ , and a volume to height ratio of 0.71 m ² and a cross-sectional area of 0, 71 m ^2, is brought into the combustion chamber at 1000 ⁰ C to 2000 ⁰ C to the reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting

Hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and - Desorptionsprozess, reduction of excess chlorine gas, and exhaust gas purification, and purification of the fumed silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, a fumed silica in an amount of 321 kg / h, corresponding to 2850 tonnes per annum for an annual population of 8864 hours, with a BET specific surface area of 200 m ² / g, with a tap density after bagging in 10 kg

Paper sack of 40 g / l, having a pH of 4% by weight aqueous dispersion of 4.0, a sieve residue of Mocker greater than 40 μm of 0.005% by weight, a thickening effect η / ηO in a silicone oil of 7.5, a thickening effect η / ηO in an uncrosslinked unsaturated polyester resin of 6.7, a average spherical equivalent hydrodynamic particle size of 200 nm after ultrasonic dispersion at 0.3 wt.%, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °.

Example 8

A gas mixture with a dosage of 2600 NmVh containing 4.6 mol% of methyltrichlorosilane, 7.6 mol% of hydrogen, 17 Mo1% oxygen and 70.5 mol% of nitrogen as gases, and that from a nozzle with a gas velocity of 54 m / s at the head of a combustion chamber via a nozzle enters a combustion chamber, the combustion chamber has a volume of 3.3 m ³ , and a volume to height ratio of 0.71 m ^? and a

Cross-sectional area of 0.71 m ² , is brought to 1000 ° C in the combustion chamber at 1000 ⁰ C to the reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silicic acid in a fluidized bed by hot gases at 400 to 800 ⁰ C, is a fumed silica in an amount of 321 kg / h, corresponding to 2850 tons per year with a yearly intervals of 8864 hours, with a specific surface area BET of 200 ra ^z / g, with a tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of 4% by weight aqueous dispersion of 4.0, a Siebruckstand after Mocker large 40 microns of 0.005 wt.%, a thickening effect η / ηO in a silicone oil of 7.5, a thickening effect η / ηO in an uncrosslinked unsaturated polyester resin of 6.7, an average a ball-equivalent hydrodynamic particle size of 200 nm Ultrasound dispersion at 0.3 wt.%, A temperature of 25 ⁰ C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °, was obtained.

Example 9

A gas mixture with a dosage of 3300 Nm ³ / h, the 14 mol% ϊrachrachlorosilane, 0.1 mol% methyltrichlorosilane, 6.4 mol% hydrogen, 2.1 mol% carbon dioxide, 17 mol% oxygen, 69 mol% nitrogen, 7 , 2 mol% Hydrogenπtethyldichlorsilan, 1.3 mol% Hydrogentrichlorsilan, 2 mol% tetramethylsilane, 1.4 mol% trimethylchlorosilane and 1.1 mol% alkane {mixture of propanes, butanes and pentanes, propenes, butenes and pentenes and chloropropanes, chlorobutanes and Chlorpentanen) as gases, and which enters from a nozzle with a gas velocity of 63 m / s at the head of a combustion chamber via a nozzle in a burner chamber, wherein the combustion chamber has a volume of 3.3 m ³ , and a ratio of volume to height of 0.71 m ^? and has a cross-sectional area of 0.71 m ² , is reacted in the combustion chamber at 1000 ⁰ C to 20Ö0 ° C for reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filters, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, is a fumed silica in an amount of 323 kg / h, corresponding to 2860 tons per year with an annual output of 8864 hours, with a BET specific surface area of 200 m ² / g, with a tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of 4 wt% aqueous dispersion of 4.0, a sieve residue after mocker large 40 microns of 0.005 wt.%, a thickening effect η / ηO in a siliconeol of 7.5, one Thickening effect η / ηθ in an uncrosslinked α-unsaturated polyester resin of 6.7, a mean spherical equivalent hydrodynamic particle size of 200 nm after ultrasound dispersion at 0.3 wt%, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °, obtained.

Example 10

Em gas mixture with a dosage of 2450 Nm ³ / h, the 0 mol% tetrachlorosilane, 5.2 mol% Methyltπchlorsilan, 6.2 Mo1% hydrogen, 2.1 Mo1% carbon dioxide, 17 mol% oxygen, 69 mol% nitrogen, 0 Mol% Hydrogenmethyldichlorosilane, 0 mol% Hydrogentπchlorsilan, 0 mol% tetramethylsilane, 0 mol% Tπmethylchlorsilan and 0 mol% alkane (mixture of propanes, butanes and pentanes, propenes, butenes and pentenes and chloropropanes, chlorobutanes and Chlorpentanen) as gases, and from a nozzle with a gas velocity of 51 m / s at the head of a combustion chamber via a nozzle in a burner chamber, wherein the combustion chamber has a volume of 3.3 m ³ , and a volume to height ratio of 0.71 m ² and a Cross-sectional area of 0.71 rn ² , is brought in the combustion chamber at 1000 ⁰ C to 2000 ⁰ C to the reaction. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filter, recovery of dry hydrogen chloride gas in a multi-stage absorption and desorption, reduction of excess chlorine gas, and exhaust gas purification, and purification of the pyrogenic Silicic acid in a fluid bed by hot gases at 400 to 800 ⁰ C, is a fumed silica in an amount of 341 kg / h, corresponding to 3020 tons per year with an annual output of 8864 hours, with a specific BET surface area of 150 m ^? / g, with a tap density after bagging in 10 kg paper bag of 40 g / l, with a pH of a 4% by weight aqueous dispersion of 4.1, a Mocker screen size of 40 μm of 0.005% by weight, a thickening effect η / ηθ in a siliconeol of 5.5, a thickening effect η / ηO in an uncrosslinked unsaturated polyester resin of 4.5, an average sphere-equivalent hydrodynamic particle size of 220 nm after ultrasound dispersion at 0.3 wt.%, a temperature of 25 ⁰ C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscattering angle of 173 °, receive.

Example 11

A gas mixture with a dosage of 2690 NmVh containing 1.6 mol% tetrachlorosilane, 0.1 mol% methyltrichlorosilane, 5.7 mol% hydrogen, 1.9 mol% carbon dioxide, 17 mol% oxygen, 69 mol% nitrogen, 0, 8 mol% of hydrogenmethyldichlorosilane, 0.15 mol% of hydrogentrichlorosilane, 0.24 mol% of tetramethylsilane, 1.6 mol% of trimethylchlorosilane and 1.3 mol% of alkane (mixture of propanes, butanes and pentanes, propenes, butenes and pentenes and chloropropanes, chlorobutanes and chlorine pentanes) as gases, and which enters the combustion chamber from a nozzle having a gas velocity of 56 m / s at the head of a combustion chamber via a nozzle, the combustion chamber having a volume of 3.3 m ³ , and a volume to volume ratio Height of 0.71 m ² and a cross-sectional area of 0.71 m ^? is in the

Combustion chamber at 1000 ⁰ C to 2000 ⁰ C reacted. After aspirating from the combustion chamber, cooling to less than 200 ⁰ C, separating the resulting hydrogen chloride gas from the resulting fumed silica by fabric filter, recovery of dry hydrogen chloride gas in one

Multi-stage absorption and desorption process, reduction of excess chlorine gas, and exhaust gas purification, and purification of the fumed silica in a fluidized bed by hot gases at 400 to 800 ⁰ C, a pyrogenic silica in an amount of 343 kg / h, corresponding to 3040 tons per year at an annual output of 8864 hours, with a BET specific surface area of 150 mVg, with a tap density after bagging in the 10 kg paper bag of 40 g / l, with a pH of a 4% by weight aqueous dispersion of 4.1, a screen residue after mocker greater than 40 microns of 0.005 wt.%, a thickening effect η / ηθin a silicone oil of 5 _r 5, a thickening η / ηθin a uncrosslinked unsaturated polyester resin of 4.5, a mean spherical equivalent hydrodynamic particle size of 220 ran after ultrasonic dispersion at 0.3% by weight, a temperature of 25 ° C and at pH 10 and measured with a Malvern Zetasizer Nano ZS® at a backscatter angle of 173 °.

Example 12

100 g of a silica according to Example 6 with a BET of 150 are coated with a finely divided Aerosl a liquid in a Glasapperatur and inert nitrogen atmosphere under Flzudisierung with paddle stirrers, so that a total of 100 g of the liquid are applied to the silica and the silica further the appearance of a has dry colloidal powder. Subsequently, the so loaded silica is placed in a porcelain dish in a drying oven of 300 liters volume with a gas circulation of 900 liters per minute and cleaned under inert nitrogen atmosphere of liquid and dried to at least> 99% by weight silica content. Subsequently, the tap density is determined according to DIN. The tapped densities thus obtained with various liquids are summarized in Table 1. Table 1

Example 13

Silica according to Example 1 - 11 is incorporated in a built-up on a Acetatvernetzersystem at room temperature crosslinking silicone sealant system with black color.

Subsequently, a small amount is applied to a polyethylene film with a spatula and pulled smooth.

Then the appearance of the surface is evaluated:

Very good - no particles, good - few particles, satisfactory - some particles, sufficient - several particles, poor - many particles, insufficient - very many particles on the surface. The result is summarized in Tabel le 2,

Measuring methods:

Specific surface area according to BET: according to DIN 9277/66132 pH value: according to EN ISO 787/9

Sieve residue according to Mocker (greater than 40 μm): according to EN ISO 787/18

Tap density: according to EN ISO 787/11

Humidity (weight loss at 2 hours and 105 ^° C): according to EN ISO

787/2

Definition of Nm ³ / h:

Nm ³ / h is the volume of gas or steam delivered per 1 hour.

Definition of Nm ³ The standard cubic meter (abbreviation: m ³ (iN), obsolete abbreviation: Nm ³ or often simplified also Nm3 written) is a unit used in process engineering for the standard volume of a gas. The definition of the standard cubic rower is defined in DIN 1343 and ISO 2533.

A standard cubic meter is that amount which bar one cubic meter of gas at a pressure of 1.01325, a humidity of 0% (dry gas) and a temperature of 0 ⁰ C {DIN 1343) or 15 ° C (ISO 2533) corresponds.

That is, a standard cubic meter of gas has been established under the

Conditions a volume of 1 m3, but in the case of divergent conditions, generally another volume which can be determined by special conversions.

In the compressed air industry deviating values according to DIN 1945 apply. Here the standard volume is given for a pressure of one bar, a temperature of 20 ^° C. at 0% atmospheric humidity.

Claims

claims

1. Flammenmen reactor, characterized in that the flame reactor has a reactor chamber with a volume of 1 m ³ to 10 m ³ , a height of 1 m to 10 m and a reactor nozzle for supplying the reactants.

2. Flame reactor according to claim 1, characterized in that the reactor chamber has a Qυerschnittsflache of 0.1 m ^? to 1 τa '.

3. Flame reactor according to claim 1 or 2, characterized in that the flame reactor has a ratio of volume to height of 0.1 m ² to 1 m ² .

4. Flame reactor according to one or more of claims 1 to

3, characterized in that the reactor chamber at the head has a diameter of 0.1 m to 1.0 m.

5. Flame reactor according to one or more of claims 1 to

4, characterized in that the reactor chambers half a length by at least 10% more diameter than the diameter of the reactor chamber at the reactor head.

6. Flame reactor according to one or more of claims 1 to

5, characterized in that the reactor chamber has a circular cross-section.

7. Flame reactor according to one or more of claims 1 to 6, characterized in that the reactor chamber is open and thus is in open exchange with the atmospheric pressure.

8. Flame reactor according to one or more of claims 1 to 7, characterized in that the reactor nozzle is 0.05 m to 0.25 m in diameter.

9. Flame reactor according to one or more of claims 1 to

8, characterized in that the outlet surface of the reactor nozzle is 0.001 m ² to 0.1 m ^{2 in} size.

10. Flame reactor according to one or more of claims 1 to

9, characterized in that the cross section of the reactor nozzle is circular.

11. Flame reactor according to one or more of claims 1 to

10, characterized in that the reactor nozzle is disposed in the vertical reactor chamber at the top and the reactor nozzle is oriented downwards.

12. A process for the production of fumed silica, wherein in a reactor silicon-containing reaction gases are reacted in a flame, characterized in that the content of organic non-silicon compounds in the reaction gas is less than 5 mol%.

13. A process for the production of fumed silica according to claim 12, characterized in that the content of inorganic non-silicon compounds in the reaction gas is less than 1 wt.%.

14. A process for producing fumed silica according to claim 12 or 13, characterized in that the content of boron compounds, germanium compounds, titanium compounds, iron compounds, aluminum compounds, tin compounds, arsenic compounds, sulfur compounds, phosphorus compounds in the reaction gases is in each case less than 100 ppm, based in each case to the respective element.

15. A process for the preparation of pyrogenic silica according to one or more of claims 12 to 14, characterized characterized in that mixtures more than 10 mol. % Methylsiliciurntrichlorid contained used.

16. A process for the preparation of fumed silica according to claim 15, characterized in that these mixtures, less than 20 mol% of carbon-containing silicon compounds, which are not Methylsiliciurntrichlorid, and less than 20 mol% of hydrogen-containing silicon compounds and less than 5 mol% not containing silicon, optionally substituted, hydrocarbons.

17. A process for the preparation of pyrogenic silica according to one or more of claims 12 to 14, characterized in that mixtures containing more than 10 mol.% Silicon tetrachloride, can be used.

18. A process for the preparation of fumed silica according to claim 17, characterized in that the mixtures less than 20 Mo 1% carbon-containing silicon compounds and less than 20 mol% hydrogen-containing

Silicon compounds and less than 5 mol% of non-silicon-containing, optionally substituted, hydrocarbons.

19. A process for the preparation of pyrogenic silica according to one or more of claims 12 to 18, characterized in that a gas mixture with a dosage of 100 to 5000 NmVh, the 0.1 ~ 100 Mo 1% tetrachlorosilane, 0 - 100 mol% methyltrichlorosilane , 1 - 20 Mo1% hydrogen, 0.001 to 15 mol% carbon dioxide, 10 - 30 mol% oxygen, 50 - 100 mol%

Nitrogen, 0-50 mol% of hydrogenmethyldichlorosilane, 0.001-100 mol% of hydrogentrichlorosilane, 0-50 mol% of tetramethylsilane, 0-50 mol% of trimethylchlorosilane and 0-20 mol% of mixtures of alkane, alkene or haloalkyl, from a nozzle having a gas velocity from 10 to 100 m / s at the head of a combustion chamber via a nozzle enters a burner chamber and in the Combustion chamber at 100Ö ° C to 2000 ⁰ C is brought to Reaktxon.

20. A process for the preparation of fumed silica according to one or more of claims 12 to 18, characterized in that the density of the silica by

Moistening and subsequent drying of the silica is increased.