Method for producing highly dispersed silica

Abstract

The present invention relates to an economic process for producing particulate silica in a flame reaction from a mixture comprising silicon compounds which are advantageous in price and / or from the overall economic perspective, which process results in high quality products without any operational interference. The method for producing particulate silica is characterized in that a mixture of at least two silicon compounds, at least one of which contains carbon and at least one of which does not contain carbon, is used as a Si source, to which a fuel gas and an oxygen-containing source are supplied, the mixture containing said source of Si, said fuel gas and said source of oxygen has a C / Si molar ratio of from 10 / BET to 35 / BET and an H / Cl molar ratio of the mixture of from 0.45 + (BET / 600) to 0.95 + (BET / 600), BET being the specific surface area of the pyrolytic silica in production measured by the BET method (corresponding to DIN ISO 9277), introducing the mixture as a main stream into the reaction space and igniting and reacting it, and separating the resulting solids.

Description

[0001] This application is a divisional application, filed on July 13, 2017, with application number 201780058455.0 and entitled "Method for producing highly dispersed silica".

[0002] The subject of this invention is a method for producing finely divided silica, comprising: - Use a mixture of at least two silicon compounds. At least one silicon compound containing carbon And at least one silicon compound does not contain carbon. - Supply fuel gas, - Supply of oxygen-containing sources, - The C / Si molar ratio of the mixture containing the silicon compound, the fuel gas, and the oxygen source is between 10 / BET and 35 / BET, and The H / Cl molar ratio of this mixture is from 0.45+(BET / 600) to 0.95+(BET / 600). BET refers to the specific surface area of ​​pyrolytic silica produced during manufacturing, measured using the BET method (corresponding to DIN ISO 9277). - Introduce the mixture as the main flow into the reaction space, ignite it, and allow it to react. - The solid obtained after separation.

[0003] Particulate (highly dispersed) silica produced by flame reaction (pyrolysis) also refers to silica produced using the term "calcined silica" and has been industrially manufactured for decades. The method is described, for example, in DE 2620737 or EP 0 790 213. Production is carried out in a flame process, in which one or more volatile silicon-containing compounds are hydrolyzed and / or oxidized to obtain silica. In this method, a silicon-containing gasifiable compound or gaseous compound is fed into a flame formed by burning a fuel (typically H2) that forms water and an oxygen-containing gas (typically air). After the reaction, the reaction products are cooled and the silica powder entrained in the residual reaction gases (consisting of gaseous reaction products and unconsumed starting material) is separated. When necessary, the resulting powdered particulate product is subsequently deacidified by removing HCl adsorbed on its surface.

[0004] The resulting silica forms an extremely fine powder with aggregate sizes less than 1 μm. It can have particle sizes ranging from 5 to 600 μm. 2A high specific surface area of ​​ / g is considered one of the most important physical properties. It is usually determined by N2 adsorption and evaluation via adsorption isotherms, according to the method of Brunauer, Emmet, and Teller (known as BET) (according to DIN ISO 9277).

[0005] However, industrially produced small proportions (<0.1%) of pyrolytic silica also contain coarser particles (in most cases, this is also SiO2, albeit in a coarser sintered form), which are destructive in many applications, even at very low levels. For example, a frequently described problem is defects caused by scratches when silica is used in chemical mechanical polishing and planarization applications. When used in coating materials, resins, and silicones, this coarser fraction can significantly impair surface workability (especially filterability), transparency, and appearance. The coarse material present in calcined silica is often referred to as “grit” and is typically determined by the measurement method described in DIN EN ISO 787-18. This method determines the mass fraction of particles retained by a sieve after a specific filtration process. In this invention, a filter with a mesh size of 40 μm is used to determine the grit.

[0006] This document describes a number of silicon-containing compounds that can be used as starting materials in the production of calcined silica. For example, patent applications EP 1 681 265 B1, EP 1 681 266 B1, EP 1 693 343 B1, and EP 1 686 093 B1 include a large number of suitable representatives: silicon tetrachloride, trichlorosilane, dichlorosilane, monochlorosilane, methyltrichlorosilane, dimethyldichlorosilane, methyldichlorosilane, dibutyldichlorosilane, ethyltrichlorosilane, and propyltrichlorosilane. For silicon tetrachloride (STC, SiCl4), trichlorosilane (TCS, SiCl3H), dichlorosilane (DCS, SiCl2H2), methyltrichlorosilane (MTCS, CH3SiCl3), and propyltrichlorosilane (PTCS, C3H7SiCl4), the list of suitable starting materials is also provided. 3) The specification also provides specific examples of the production of particulate silica.

[0007] DE 19605672 also discloses a general formula R n Cl 3-n Si-SiR m Cl 3-m The use of organosilanes, wherein R is a hydrogen or aliphatic or aromatic hydrocarbon group, and n and m are integers from 0 to 3.

[0008] However, commercial production primarily uses silicon tetrachloride (STC) and methyltrichlorosilane (MTCS). This is primarily due to the readily available and low-cost raw materials, and secondly, the high quality of the resulting products.

[0009] Calcined silica is most commonly produced from STC, which is typically obtained through the reaction of Si with HCl (Si + 4 HCl = SiCl4 + 2H2). However, byproducts may also form during this reaction, such as a significant amount of TCS. Other possible byproducts include so-called high-boiling-point substances (polychlorosilanes that boil at high temperatures, such as hexachlorosilane, pentachlorosilane, etc.). Furthermore, numerous impurities present in crude silicon (e.g., boron or aluminum) react with HCl to form chlorides, which are then present in chlorosilanes and thus also in calcined silica. These byproducts and impurities from the reaction of crude silicon with HCl disrupt the operation of calcined silica production and / or adversely affect product quality. For these reasons, STC obtained via this route must be painstakingly purified before the reaction to produce calcined silica in a flame reaction, which significantly increases the cost of this raw material.

[0010] An alternative source for silicon tetrachloride is the production of high-purity polycrystalline silicon, as STC is generated in large quantities as a byproduct in this process. However, this byproduct typically includes perceptible amounts of low-boiling-point chlorosilanes such as TCS, DCS, and MCS (monochlorosilane, SiClH3). First, these chlorosilanes are highly reactive and significantly disrupt flame processes. For example, they can cause backfire, leading to equipment failure and resulting in production losses. Furthermore, these substances promote the formation of coarse silica particles, which are undesirable in most applications.

[0011] The most important second starting material for the production of calcined silica is methyltrichlorosilane. This compound is formed in the synthesis of methylchlorosilanes via the Müller-Rochow process, which is specifically designed for the synthesis of dimethyldichlorosilane (DMDCS, Si(CH3)2Cl2). DMDCS is used as the main raw material for the production of silicones. MTCS is obtained under favorable conditions as an excess byproduct of this reaction, but it exhibits significant drawbacks in the production of pyrolytic silica. The oxidation of the methyl group releases a large amount of energy, thus the stoichiometric reaction of MTCS produces extremely high flame temperatures, resulting in unacceptable product properties. To counteract this, the industrial practice of using MTCS involves adding a large amount of additional air to the reaction to dilute the energy and bring the flame temperature within the desired range. In other words, the flame is drastically diluted by adding a very large amount of air. This dilution significantly reduces the space-time yield of the production equipment, thereby harming the economics of producing calcined silica from MTCS.

[0012] The object of this invention is to provide an economical method for producing particulate silica in a flame reaction from a mixture comprising a favorable silicon compound, the method producing a high-quality product without any operational interruption. In the context of this invention, favorable silicon compounds can be identified as being advantageous in terms of price, i.e., inexpensive, and / or advantageous from a process engineering point of view, for example, as a byproduct of another process (e.g., an unwanted byproduct or "waste"); in other words, they are advantageous from an overall economic point of view.

[0013] This objective is achieved by the method of the present invention for producing particulate silica, the method being characterized by: - Use a mixture of at least two silicon compounds as the Si source. At least one silicon compound containing carbon And at least one silicon compound does not contain carbon. - Supply fuel gas, - Supply of oxygen-containing sources, - The C / Si molar ratio of the mixture containing the silicon compound, the fuel gas, and the oxygen source is between 10 / BET and 35 / BET, and The H / Cl molar ratio of this mixture is from 0.45+(BET / 600) to 0.95+(BET / 600). BET refers to the specific surface area of ​​pyrolytic silica produced during manufacturing, measured using the BET method (corresponding to DIN ISO 9277). - Introduce the mixture as the main stream into the reaction space and ignite it to allow it to react. - The solid obtained after separation.

[0014] Particulate silicon dioxide is produced from silicon-containing compounds, thus the silicon-containing compounds represent a source of Si atoms and are referred to as Si sources. According to the invention, a mixture of at least two silicon compounds is used, comprising at least one carbon-containing silicon compound and at least one carbon-free silicon compound (Si compound).

[0015] The carbon-containing Si compound used is preferably methyltrichlorosilane (MTCS), methyldichlorosilane (MDCS), or a mixture of MTCS and MDCS.

[0016] The carbon-free Si compound used is preferably silicon tetrachloride (STC), trichlorosilane (TCS), dichlorosilane (DCS), or a mixture of at least two of the compounds. A mixture of at least two of the compounds means that the mixture contains at least two compounds selected from the group consisting of STC, TCS, and DCS.

[0017] It is particularly preferred to use a mixture of at least three silicon compounds as the Si source.

[0018] A mixture of silicon tetrachloride (STC), trichlorosilane (TCS), dichlorosilane (DCS) and methyltrichlorosilane (MTCS) is particularly preferred as the Si source.

[0019] According to the invention, the method is carried out in the presence of a fuel gas or mixture of fuel gases, which also serves as a source of H atoms and optionally a source of C atoms. Preferred fuel gases used are hydrogen, methane, natural gas, ethane, propane, and / or other gaseous hydrocarbons, or mixtures thereof. Hydrogen is particularly preferred as the fuel gas.

[0020] According to the present invention, an oxygen-containing source is supplied to the method, which is used on the one hand, together with the fuel gas, to achieve the desired temperature, and on the other hand, is an O atom source. Oxygen, air, or a mixture thereof are preferably used as the oxygen-containing source. Air is particularly preferred. For the purposes of the present invention, this air is also referred to as primary air (PL).

[0021] According to the present invention, a mixture comprising silicon compounds, fuel gas and an oxygen source is referred to as the mainflow.

[0022] According to the present invention, the mainstream molar ratio of carbon atoms relative to each silicon atom (C / Si ratio) is 10 / BET to 35 / BET, where BET is the specific surface area of ​​particulate silica produced by means of the BET method (corresponding to DIN ISO 9277).

[0023] According to the present invention, the mainstream molar ratio of hydrogen atoms to chlorine atoms (H / Cl ratio) is 0.45+(BET / 600) to 0.95+(BET / 600), wherein BET is the specific surface area of ​​particulate silica produced by means of the BET method (corresponding to DIN ISO 9277).

[0024] The molar ratio of carbon atoms relative to each silicon atom and the molar ratio of hydrogen atoms relative to each chlorine atom are determined by dividing the amount of carbon atoms or hydrogen atoms present in all compounds used in the mainstream by the amount of silicon atoms or chlorine atoms present in all compounds used in the mainstream, respectively.

[0025] A particular advantage of the present invention is that, based on the desired specific surface area (BET) of the product, it is possible to determine the preferred mixing ratio of available starting compounds, or whether additional or different starting compounds are required.

[0026] The main stream is introduced into the reaction space via a nozzle. There it is ignited and reacted, i.e., the reaction occurs in a flame. In the context of this invention, the terms "reaction chamber," "combustion chamber of a reactor," and "reaction space" are used synonymously. Similarly, the terms "nozzle," "burner," and "burner nozzle" are used synonymously.

[0027] The resulting solid was then separated. This solid contained particulate silica. In the context of this invention, particulate silica is often also referred to as calcined silica because it is obtained by flame processing and can be considered an oxyacid of silicon due to the silanol groups on the particle surface.

[0028] In an advantageous and preferred embodiment of the invention, the flame is surrounded by a secondary gas. Air is the preferred secondary gas used. For the purposes of this invention, this air is also referred to by the term "secondary air" (SL).

[0029] The volume ratio of secondary gas to mainstream is preferably 0.01 to 0.4, and very preferably 0.01 to 0.045. The ratio of the flow rate of secondary gas to mainstream is preferably maintained at 0.1 to 0.8.

[0030] The envelopment of the flame by secondary gas prevents backfire and reduces destructive product deposition on the nozzle. However, the secondary gas reduces the space-time yield of the method because it does not directly participate in the reaction. Maintaining a consistent volume ratio of secondary gas to the mains gas has proven advantageous. Furthermore, it has been surprisingly observed that the outflow rate of the secondary gas affects the flame reaction. By maintaining this rate within a certain ratio to the mains outflow rate, the amount of secondary gas can be minimized without sacrificing its positive effects on backfire and deposition. Moreover, the introduction of secondary gas leads to a decrease in flame temperature, which must be compensated for by a larger amount of fuel gas. Therefore, minimizing the amount of secondary gas also contributes to fuel gas conservation.

[0031] For the purposes of this invention, flow rate refers to the rate at which a gas or gas mixture flows into or through a space; for example, the rate at which a gas or gas mixture flows into or through a burner nozzle into a reaction space or into the combustion chamber of a reactor. It can be calculated from the volume of the flowing gas or gas mixture and the supply area of ​​the device (i.e., for example, the cross-sectional area of ​​the burner nozzle for the main flow and the cross-sectional area of ​​the ring surrounding the burner nozzle for the secondary gas). More simply, for the purposes of this invention, for the purpose of calculating flow rate, the gas volume per unit time in standard cubic meters is examined. Changes in cross-sectional area due to thermal expansion of components are ignored. Since flow rate is the rate at which a gas or gas mixture flows into or through a space, it is also referred to as "outflow velocity".

[0032] When introduced into the reaction space, the secondary gas should preferably have a temperature approximately the same as the mainstream gas introduced through the burner nozzle. Therefore, it is preferable that the secondary gas introduced into the reaction space has been heated to the temperature of the mainstream gas. Particularly preferred is this temperature of 70 to 120°C.

[0033] After the flame reaction, the resulting solids are separated. During the separation of the solids, it is preferable to remove gaseous substances. After separation, it is preferable to treat the resulting solids with hot gas. Particularly preferably, the hot gas is formed by the combustion of methane, hydrogen, or natural gas. Particularly preferably, steam is not mixed into the hot gas. The treatment is preferably carried out at 400-600°C. In a particularly preferred embodiment, the desired temperature is set by adding air to the combustion exhaust gas.

[0034] A notable advantage of the method of the present invention is that, when a specific composition of silicon compounds characterized by the desired C / Si and H / Cl ratios is used in the method, the method not only operates without interruption and backfire, but also produces high-quality particulate silica with a low grit or coarse material fraction. Simultaneously, the method exhibits good space-time yield, meaning it is economically viable. Surprisingly, any desired silicon source, especially advantageous (from a price and / or overall economic point of view) silicon sources, such as, for example, chlorosilanes from polysilicon production or mixtures from MTCS synthesized in Müller-Rochow, can be used to produce high-quality particulate silica, provided that the mixture contains at least one carbon-containing silicon compound and one carbon-free silicon compound, and the mainstream exhibits the desired C / Si and H / Cl ratios.

[0035] Another advantage of the present invention is the low level of fuel gas consumption (e.g., evident from the low H / Cl ratio), which contributes to the economic efficiency of the method.

[0036] The particle size fraction or coarse particle size fraction can be determined as described in the analytical methods. The coarse particle size fraction in metal oxides is a key determinant of quality: a low coarse particle size fraction is advantageous in many applications. Particularly in the context of use as a reinforcing filler in elastomers, in rheological control of paints, varnishes, adhesives, and sealants, and in the field of chemical mechanical planarization of surfaces in the semiconductor industry, a low coarse particle size fraction is beneficial. These types of particle dispersions are also used, for example, in the polishing of semiconductor devices, where large particles can cause scratches.

[0037] From each 1 Nm 3 The space-time yield (ST yield) is calculated based on the product amount (SiO2, g) of the starting material (silicon compound + fuel gas + primary gas + secondary gas). The ST yield is preferably higher than 200 - (BET / 3) g / Nm. 3 More preferably, it is higher than 250-(BET / 3) g / Nm 3 And it is highly preferred to be higher than 300-(BET / 3) g / Nm 3 BET is the specific surface area of ​​calcined silica produced by means of the BET method (corresponding to DIN ISO 9277).

[0038] According to the invention, the method is a stable method, meaning that the reactor used to produce particulate silica operates without interruption and without backfire. The mainstream is ignited only in the reactor's combustion chamber. No interruption means no ignition occurs before entering the reaction chamber. There is also no backfire from the burner nozzle to the mixing element, filter, and / or compartment located upstream of the burner nozzle.

[0039] To aid understanding, the present invention is illustrated by the embodiments and comparative embodiments described below, but is not limited thereto.

[0040] Analysis methods and general information: 1. Determination of pH The pH was determined according to DIN EN 787-9, but using a 4% dispersion of the sample in water.

[0041] 2. Determination of specific surface area Specific surface area is usually determined by N2 adsorption and evaluation via adsorption isotherms, according to the method of Brunauer, Emmet, and Teller (referred to as BET) (according to DIN ISO 9277).

[0042] 3. Determination of coarse particle content The coarse particle content (also known as sand fraction or coarse particle fraction) is determined by the DIN EN ISO 787-18 method, using a sieve with a mesh size of 40 μm to separate and determine the coarse particle fraction.

[0043] Unless otherwise stated, all percentage figures are based on mass / weight.

[0044] Standard cubic meter (abbreviation Nm) 3 A standard cubic meter (SCM) is a unit used in process engineering to measure the standard volume of gas. The definition of a standard cubic meter is specified in DIN 1343 and ISO 2533. A standard cubic meter is the amount of gas corresponding to one cubic meter at a pressure of 1.01325 bar, 0% atmospheric humidity (dry gas), and a temperature of 0°C (DIN 1343) or 15°C (ISO 2533). In other words, under specified conditions, one standard cubic meter of gas has 1 m³ of gas. 3 The volume is fixed, but generally, it varies under different conditions and can be determined by specific transformations.

[0045] Nm 3 / h is the volume of gas or vapor supplied per unit hour.

[0046] Example: In all cases, as described in the prior art (see, for example, EP 1 693 343 B1, EP 1 686 093 B1, EP 1 681 266 B1, EP 1 381 265 B1 or DE 26 20 737 C2), particulate silica is produced using the following parameters and composition: The mixture of silicon compounds is vaporized individually or together, and the gas phase containing the silicon compounds is mixed with hydrogen and air. The fraction of silicon compounds in the mixture is listed as a mass percentage in the various embodiments.

[0047] In the case of individual compositions, all key components are listed. In industrial practice, it is not impossible for the mixture to also contain trace amounts of other silicon compounds. However, these additional unspecified impurities are consistently below 0.5 wt% and therefore have no impact on the production process.

[0048] A mixture A, comprising a vaporized silicon compound, fuel gas (hydrogen in all embodiments), and air (referred to as primary air, PL), is transferred as the main stream through a burner into the reaction chamber and reacts in a flame reaction after ignition. A secondary gas (air in all embodiments) is introduced into the reaction chamber surrounding this mixture A, which surrounds the flame. The secondary air is introduced in a controlled manner, with the outflow rate and velocity adjusted. Calculations of the outflow velocities of the main stream and secondary air through the burner are performed under standard conditions (20°C, 1 atm), regardless of the fact that the components are introduced at a slightly elevated temperature (95°C in all embodiments). After the reaction, solids are separated from the gaseous substance and then deacidified to a pH of 4.0 to 5.0 using hot gas. Hot gas is formed by the combustion of natural gas with air.

[0049] Comparative Example V1: In this comparative example, the Si source used was a silane mixture consisting of 90% STC, 5% TCS, and 5% DCS. This silane mixture was vaporized at a rate of 1000 kg / h and then reacted with 265 Nm³ / h Si. 3 / h hydrogen and 850 Nm 3 A primary air (PL) mixture is introduced into the reaction after initial ignition in the flame. The exit velocity (v(HS)) of the main stream from the burner nozzle, consisting of the silane mixture, hydrogen, and primary air components, is 44 m / s. Additionally, 600 Nm 3 Secondary air (SL) is introduced into the combustion chamber of the reactor at a speed of 40 m / s (v(SL)) and surrounds the flame.

[0050] The resulting silica and reactant gases are passed into a cooling system, where they are first cooled to below 200°C. The solids are then separated from the process gases using a cyclone separator or filter. The silica is subsequently treated with hot gases at approximately 500°C, thereby deacidifying it.

[0051] The method is characterized by low stability. Combustion is disrupted by sporadic flashbacks, leading to equipment failure. The resulting products have a specific surface area of ​​150 m². 2 / g. In addition, the obtained powdered product has a relatively high coarse particle content of 0.02 wt%.

[0052] The experimental and analytical data are listed in Table 1.

[0053] Comparative Example V2: In this comparative example, calcined silicon dioxide was produced in the same manner as in Comparative Example V1. The difference was that MTCS was used as the Si source, which was produced at a rate of 500 kg / h with 50 Nm 3 / h hydrogen and 1000 Nm 3 / h air mixing.

[0054] The combustion of this mixture proceeds steadily and produces a solution at a depth of 150 m. 2 The product has a lower sand particle fraction of 0.01% for the same specific surface area per g. A major drawback of this process according to the prior art is the low space-time yield. Therefore, in this embodiment, processing approximately the same total gas volume (silane + hydrogen + primary air + secondary air) as in Comparative Example 1 results in a ST yield of only about 60%.

[0055] The experimental and analytical data are listed in Table 1.

[0056] Comparative Example V3: In this comparative example, calcined silicon dioxide was produced in the same manner as in Comparative Example V1. The difference was that a mixture of STC (68%) and MTCS (32%) was used as the Si source, which was produced at a rate of 700 kg / h with 150 Nm 3 / h hydrogen and 1000 Nm 3 / h air mixing.

[0057] Stable combustion of mixtures is possible. However, this process has a relatively low space-time yield. Furthermore, the specific surface area is 300 m². 2 The silica produced has a relatively high sand content of 0.015% per g.

[0058] The experimental and analytical data are listed in Table 1.

[0059] Comparative Example V4: In this comparative example, calcined silicon dioxide was produced in the same manner as in Comparative Example V1. The difference was that a mixture of STC (76%), TCS (19%), and MTCS (5%) was used as the Si source, which was produced at a rate of 700 kg / h with 250 Nm³. 3 / h hydrogen and 900 Nm 3 / h air mixing.

[0060] The mixture reacts in a flame reaction to produce a specific surface area of ​​150 m². 2 / g of calcined silica. However, this process is characterized by an unstable flame, leading to continuous reaction failures due to backfire. Furthermore, the resulting product exhibits a relatively high sand content of 0.015%.

[0061] The experimental and analytical data are listed in Table 1.

[0062] Example 1 (Invention) In this embodiment, a silane mixture from the preparation of polycrystalline silicon (comprising STC, TCS, and DCS, as in Comparative Example V1) was combined with a fourth component, MTCS, to produce a new mixture having the following composition: STC 81%, TCS 4.5%, DCS 4.5%, and MTCS 10%. For the production of pyrolytic silica, this new four-component silane mixture was prepared at 1000 kg / h with 220 Nm³ of silane in the same manner as for Comparative Example V1. 3 / h hydrogen and 850 Nm 3 / h air is mixed together and reacted by ignition. The outlet velocity of the reaction mixture from the nozzle is 43 m / s. In addition, 600 Nm 3 Secondary air is introduced into the combustion chamber of the reactor at a rate of 40 m / s and surrounds the flame. After separation and deacidification, a BET surface area of ​​150 m² is obtained. 2 / g of product. Compared to Comparative Example V1, combustion was not interrupted and produced fine powder with a low coarse particle fraction (sand content of 0.008%). Compared to Comparative Example V2, the reaction proceeded with a significantly higher space-time yield.

[0063] The experimental and analytical data are listed in Table 2.

[0064] Example 2 (Invention) In this embodiment of the invention, the Si source used is a silane mixture of STC (68%), TCS (17%), and MTCS (15%). It is reacted with hydrogen (210 Nm³) at a rate of 1000 kg / h. 3 / h) and primary air (900 Nm 3 The mixture is stirred and ignited to allow it to react. The amount of secondary air around the flame is 600 Nm³. 3 / h. Combustion proceeds stably and forms a specific surface area of ​​150 m². 2 / g of particulate silica. The fine powder product has a low concentration of coarse particles of 0.007%.

[0065] The experimental and analytical data are listed in Table 2.

[0066] Example 3 (Invention) In this embodiment, as in comparative embodiment V3, a specific surface area of ​​300 m² is generated. 2 / g of particulate SiO2. The Si source used was the same silane, although the mixing ratios were different: STC (90.6%) and MTCS (9.4%). The silane mixture at a rate of 800 kg / h was ignited with hydrogen gas (210 Nm³). 3 / h) and primary air (900 Nm 3 / h) react together.

[0067] Similarly, in Comparative Example V3, the method of the present invention exhibited stable combustion. However, the method produced a significantly higher and therefore more economically advantageous space-time yield (relative to 140 g / Nm³). 3 157 g / Nm 3 In addition, with 300 Nm 3 The silica produced with a specific surface area of ​​ / h is noteworthy for its low grain size of 0.007%.

[0068] The experimental and analytical data are listed in Table 2.

[0069] Example 4 (Invention) In this embodiment of the invention, a silane mixture of STC (72%), TCS (18%), and methyldichlorosilane (10%) is used, and it is reacted with hydrogen (190 Nm³) at a rate of 1000 kg / h. 3 / h) and primary air (950 Nm 3 The mixture ( / h) is brought together and reacted by ignition.

[0070] The flame reaction of the mixture produces a specific surface area of ​​150 m². 2 / g of calcined silica. The process did not exhibit any flame instability. A relatively low grit content of 0.006% was determined for the produced product.

[0071] The experimental and analytical data are listed in Table 2.

[0072] Example 5 (Invention) In this embodiment, the same silane mixture as in Example 1 was used, i.e., the same components in matched amounts. The secondary air quantity was halved to 300 Nm compared to Example 1. 3 / h. The amounts of hydrogen and primary air used are 210 and 825 Nm³, respectively. 3 / h.

[0073] Combustion proceeds stably and produces a specific surface area of ​​150 Nm².3 / h of calcined silica. Due to the optimized process scheme regarding secondary air, the sand particle fraction in the product can be reduced to 0.005%. Also noteworthy is the even slightly better space-time yield.

[0074] The experimental and analytical data are listed in Table 2.

[0075] Example 6 (Invention) This embodiment was carried out in the same manner as Example 5; the starting materials were the same and used in almost the same amounts (see Table 2 below). As a difference, the introduction of secondary air surrounding the flame was redesigned to reduce its outflow velocity to 10 m / s. It has been found that, with the aid of this improved process, flame stability remains consistently good, it is possible to produce flames with a diameter of 150 m... 2 The same product surface area per g, but with a very low sand content of 0.003%.

[0076] The experimental and analytical data are listed in Table 2.

[0077] Example 7 (Invention) This embodiment was carried out in the same manner as in Embodiment 6. The amount of secondary air was drastically reduced to 30 Nm³. 3 The flow rate was adjusted to maintain a constant outflow rate. The amounts of hydrogen and primary air used were 190 and 775 Nm³, respectively. 3 / h.

[0078] The production of calcined silica was carried out stably again using this method, resulting in a matched specific surface area of ​​150 m². 2 / g of product. In this case, the coarse particle fraction is very low, at 0.002%.

[0079] The experimental and analytical data are listed in Table 2.

[0080] Table 1: Overview of data from comparative examples

[0081] Table 2: Overview of data in embodiments of the present invention

[0082] Abbreviations used in Tables 1 and 2: - STC, silicon tetrachloride, SiCl4 - TCS, trichlorosilane, SiCl3H - DCS, dichlorosilane, SiCl2H2 - MTCS, methyltrichlorosilane, CH3SiCl3 - MDCS, methyldichlorosilane, Si(CH3)Cl2H - PL, primary air - HS, mainstream - v(HS), the mainstream flow velocity entering the reaction space or reactor combustion chamber through the burner nozzle. (Note: When calculating the flow velocities of HS and SL, use standard cubic meters or Nm³ respectively.) 3 (Gas volume and gas flux per hour) - SL, secondary air - v(SL), the flow rate of secondary air surrounding the flame as it enters the reaction space through the burner or into the combustion chamber of the reactor. - V'(SL) / V'(HS), the volume ratio of secondary air to mainstream air. (Note: For volume, the symbol V' is used in the context of this invention to avoid confusion with the symbol v used for rate / velocity.) - C / Si, the molar ratio of carbon (C) to silicon (Si) atoms in mainstream applications. Because according to the claim: C / Si = 10 / BET to 35 / BET, for BET = 150 m 2 / g, this value must be between 0.067 and 0.233, and for BET = 300 m 2 / g, this value must be between 0.033 and 0.117.

[0083] - H / Cl, the molar ratio of hydrogen (H) to chlorine (Cl) in the mainstream. Since, according to the claim, the H / Cl ratio in the mainstream is from 0.45 + (BET / 600) to 0.95 + (BET / 600), therefore for BET = 150 m 2 / g, this value must be between 0.70 and 1.20, and for BET = 300 m 2 / g, this value must be between 0.95 and 1.45.

[0084] - BET specific surface area of ​​the obtained solid determined by the BET method - Sand content, fraction of coarse material - Combustion characteristics a) unst., unstable, characterized by flashback, or b) st., stable, undisturbed during combustion, and without backfire. - ST yield, from per 1 Nm 3 Space-time yield calculated from the product amount (SiO2, g / h) of the starting materials (silane + fuel gas + primary air + secondary gas). - Percentages are expressed in wt%.

Claims

1. A method for producing particulate silica, comprising: - Use a mixture of at least two silicon compounds as the Si source. At least one silicon compound contains carbon. And at least one silicon compound does not contain carbon. - Supply fuel gas, - Supply of oxygen-containing sources, - The C / Si molar ratio of the mixture containing the silicon compound, the fuel gas, and the oxygen source is between 10 / BET and 35 / BET, and The H / Cl molar ratio of this mixture is from 0.45+(BET / 600) to 0.95+(BET / 600). BET refers to the specific surface area of ​​pyrolytic silica produced during manufacturing, measured using the BET method (corresponding to DIN ISO 9277). - Introduce the mixture as the main stream into the reaction space, ignite it, and allow it to react. - The separated solids have a coarse particle content of less than 0.01% by weight, which is determined according to DIN EN ISO787-18 using a sieve with a mesh size of 40 μm.

2. The method of claim 1, wherein the carbon-containing silicon compound used comprises methyltrichlorosilane (MTCS), methyldichlorosilane (MDCS), or a mixture of MTCS and MDCS.

3. The method according to one or more of claims 1 or 2, wherein the carbon-free silicon compound used comprises silicon tetrachloride (STC), trichlorosilane (TCS), dichlorosilane (DCS), or a mixture of at least two of the compounds.

4. The method according to one or more of claims 1 to 3, wherein the Si source used comprises a mixture of at least three silicon compounds.

5. The method according to one or more of claims 1 to 4, wherein the Si source used comprises a mixture of silicon tetrachloride, trichlorosilane, dichlorosilane and methyltrichlorosilane.

6. The method according to one or more of claims 1 to 5, wherein the fuel gas used comprises hydrogen.

7. The method according to one or more of claims 1 to 6, wherein the oxygen source used comprises air.

8. The method according to one or more of claims 1 to 7, wherein the flame is surrounded by secondary gas.

9. The method of claim 8, wherein the secondary gas used comprises air.

10. The method according to one or more of claims 8 or 9, wherein the volume ratio of the secondary gas to the mainstream is 0.01 to 0.

4.

11. The method according to one or more of claims 8 to 10, wherein the flow rate ratio of the secondary gas to the mainstream is 0.1 to 0.

8.

12. The method according to one or more of claims 8 to 11, wherein the secondary gas introduced into the reaction space has been heated to the temperature of the mainstream.

13. The method according to one or more of claims 1 to 12, wherein the separated solids are treated with hot gas.

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