The process for producing metal oxides and / or non-metal oxides.

Abstract

The invention relates to a flame hydrolysis process for the production of metal oxides and / or metalloid oxides using a combustion chamber with a burner having at least two gas inlet and outlet channels, wherein the metal oxide or metalloid oxide is selected from the following groups of oxides: aluminum (Al), titanium (Ti), zirconium (Zr), yttrium (Y), lithium (Li), magnesium (Mg), lanthanum (La), cerium (Ce), iron (Fe), zinc (Zn), and silicon (Si), or mixtures thereof, comprising the following steps: supplying oxygen-containing gas, fuel gas and gaseous metal precursors and / or mixtures containing gaseous metal precursors to the burner; creating a flame by burning the oxygen-containing gas and at least part of the fuel gas at the burner outlet; Release MP and / or MP-containing mixtures into the generated flame, and supply gaseous ammonia (NH3) and / or ammonia-containing gas mixtures in at least one gas channel to the burner outlet and release this gaseous ammonia into the flame, and where the ammonia (NH3) is not pre-mixed with metal precursors before the burner outlet.

Description

[0001] Process for manufacturing metal oxides and / or metalloid oxides

[0002] The invention provides a process for synthesizing a pyrogenic metal oxide powder, a pyrogenic metalloid oxide powder and the use thereof in various applications.

[0003] Background

[0004] Flame hydrolysis processes, such as the Aerosil® process are well-known methods for producing fumed (pyrogenic) metal and metalloid oxides such as SiC>2, AI2O3, TiC>2 etc.

[0005] This process involves strongly exothermic burning of the hydrogen feedstock to produce water (H2 + 0.502 -> H2O) and a simultaneous hydrolysis of a metal precursor, e.g., SiCk or AICI3 using thus obtained water. The overall process (1), on the example with SiCk is exothermic:

[0006] SiCk + 2H2+ O2SiO2+ 4HCI -102 kJ / mol (SiCk) (1)

[0007] Producing metal oxides with a relatively high BET surface area typically requires reducing of the flame temperature. This is usually achieved by the following measures or combinations thereof: (a) using the minimal amount of hydrogen feedstock with respect of the reaction stoichiometry and / or (b) using additional air or water vapor for “diluting” and cooling the flame. A process with a minimal amount of hydrogen feedstock is e.g., described in US 201 / 0030525 A1. This process for producing the silicon dioxide powder having a BET surface area of 400 to 600 m2 / g comprises: igniting in a burner a gas mixture comprising an oxidizable and / or hydrolysable silicon compound, hydrogen and an oxygen-comprising first gas, and burning a resulting flame into a reaction chamber, introducing an oxygen-comprising a second gas into the reaction chamber, and separating the obtained solid material from a gaseous material, wherein in the burner a quotient formed from the supplied amount of hydrogen and a stoichiometrically required amount of hydrogen is from 0.70 to 1.30.

[0008] According to EP 0015315 A1, the use of the additional air in flame hydrolysis processes, and of the minimal additional amount of water vapor is described as beneficial with respect to the higher BET surface area and the particle size.

[0009] However, generally using more diluted streams, such as additional air or additional water vapor (steam), leads to inevitable capacity reduction of the production plant and higher production costs. Reducing the flame temperature without adding of diluting feedstock streams would be therefore beneficial.

[0010] The object of the present invention is to provide a method for producing metal and / or metalloid oxides with a relatively high BET surface area at a high throughput of the production plant and improved mechanical and / or chemical stability of the metal and / or metalloid oxides.

[0011] These requirements could be solved by a process for manufacturing metal oxides and / or metalloid oxides by means of a burner with a burner head having at least two (inner) cannels and an outlet end, wherein the metal oxide or metalloid oxide is selected from the following group of oxides of: aluminum (Al), titanium (Ti), zirconium (Zr), yttrium (Y), lithium (Li), magnesium (Mg), lanthanum (La), cerium (Ce), iron (Fe), zinc (Zn), and silicon (Si), including a mixture thereof, wherein the process comprises the steps:

[0012] Providing an oxygen containing gas and a fuel gas to the burner head

[0013] Providing a gaseous metal precursor and / or a gaseous metalloid precursor (MP) to the burner head;

[0014] Providing a flame by burning the oxygen containing gas and at least a portion of the fuel gas at the outlet end of the burner head;

[0015] Releasing the MP into the provided flame, and

[0016] Providing gaseous ammonia (NHs) through the at least one channel to the outlet end of the burner head and releasing said ammonia (NHs) into the flame, wherein the ammonia (NHs) is not premixed with the MP prior to the outlet end of the burner head.

[0017] An oxygen containing gas, a fuel gas, and a gaseous MP are provided to the outlet end of the burner head is done by means of at least one (inner) gas channel of the burner head. At least two of the four different gases used in the process can be premixed and provided through one common gas channel to the outlet end of the burner head. However, gaseous ammonia (NHs) must be led to the outlet end of the burner head through at least one separate gas channel without contacting or being premixed with MP and directly released into the flame. The term “separate gas channel” means the separation of ammonia from MP prior to combustion and / or flame chamber. Without wishing to be bound by any theory, it is believed that if ammonia is pre-mixed with MP, it may prematurely react with the metal and / or metalloid precursor, leading to clogging gas channels of the burner head.

[0018] The term “MP” means in the context of this invention the respective substance, i.e. metal precursor and / or metalloid precursor, as well as a mixture comprising metal precursor and / or metalloid precursor, present in gaseous form, such as gas, steam or similar, at least at the outlet end of the burner head under reaction conditions.

[0019] “Ammonia” means in the context of this invention the respective gaseous substance, as well as a mixture comprising ammonia (NH3), present in gaseous form, such as gas or steam, at least at the outlet end of the burner head under reaction conditions.

[0020] Overall, surprisingly, it was found that using of ammonia for at least partial substitution of a typical fuel gas in the flame hydrolysis process, e.g. a hydrogen feedstock, leads to substantial reduction of the flame temperature in the process and producing metal oxides and metalloid oxides with higher BET surface areas of at least up to 300 m2 / g.

[0021] Without wishing to be bound by any theory, it is believed that the beneficial outcome of the inventive process may be explained by overall endothermic process (2) of metal precursor flame hydrolysis as compared to exothermic reaction (1 ) using hydrogen:

[0022] SiCk + 2H2+ O2-> SiO2+ 4HCI -102 kJ / mol (SiCh) (1 )

[0023] Feedstock ammonia (NH3) can preferably be used as a mixture together with the fuel gas, oxygen containing gas, gaseous water (H2O) in form of steam and / or N2. One benefit of adding water steam or N2 gas into the feedstock NH3 may be an enhanced control of the flame temperature, when needed.

[0024] The term “feedstock” means at least one substance, educt and / or a mixture thereof being fed into the burner and / or the burner head, not being formed at least temporary during or by the flame process.

[0025] According to a preferred embodiment of the process, the metal oxide or metalloid oxide is selected from the following group: aluminum oxide (AI2O3), titanium dioxide (TiO2) and / or silicon dioxide (S1O2), and a mixture thereof. Most preferably the metal oxide or metalloid oxide is silicon dioxide (SiO2), or a mixture of metal and / or metalloid oxides comprising silicon dioxide (SiO2).

[0026] According to a further preferred embodiment of the process, the amounts of oxygen and the fuel gases are adjusted to reach the y (ratio gamma) of about 1 to 3, preferably 1.2 to 2.5 and % (ratio lambda) of about 1 to 5, preferably 1.1 to 3.

[0027] Therein, y (ratio gamma) is defined as ratio of hydrogen amount fed into the burner head to the hydrogen amount stoichiometrically required for hydrolysis reaction of the MP; and % (ratio lamda) is defined herein as ratio of oxygen amount fed into the burner head to the hydrogen amount stoichiometrically required for combustion of all fuel (gases).

[0028] It has surprisingly been found that it is essential to release NH3 direct into the flame at the outlet end of the burner head and avoid any pre-mixing of ammonia with the MP, since MP such as SiCh can prematurely react with ammonia and lead to undesired reactor clogging.

[0029] The main benefits of the inventive process are the decreased need of flame-cooling gases such as air or water steam, which in turn leads to increasing plant throughput and / or more economical synthesis of metal and metalloid oxides, especially with a higher BET surface area.

[0030] The burner head as part of a burner can be mounted and located at least partially inside a housing of the burner. The burner may further comprise a combustion chamber, also named a flame chamber, into which the ignited at the outlet end of the burner head flame extends. The housing is typically connected to an outlet (line) or product line. This product line, and / or the burner housing may comprise a flame tube. Preferrable the flame tube forms the outlet part of the flame chamber as part of the housing and / or the first section of the product line. According to an advantageous solution, the flame tube is connected to a (subsequent) cooling pipe, whereby the cooling pipe may be also a section of the product line and / or forms a cooling unit, which can be connected to the product line.

[0031] The term “outlet end” refers in the context of the present invention to the outer part of the burner head i.e., the respective outlet ends of the corresponding gas channels of the burner head, where the gases exit the corresponding channels of the burner head, and the flame is formed.

[0032] The gaseous MP can be obtained by evaporation of MP, e.g. in liquid or solid form, wherein the evaporation takes place prior to the burner and / or burner head in a suitable evaporation unit. Evaporated MP feedstock may be pre-mixed with an oxygen containing gas, nitrogen (N2) and / or a gaseous fuel gas prior to providing it to the reaction in the flame.

[0033] The term “oxygen containing gas” preferably refers to air, oxygen (O2) or 02-enriched air. In the context of this invention "fuel gas” can be hydrogen (H2) or a hydrogen-containing gas mixture, carbon monoxide (CO), and / or an organic compound having at least one hydrogen and at least one carbon atom. Therein, the organic compound can preferably be a hydrocarbon or an alcohol, or mixtures thereof. The hydrocarbon may be an alkane with a general formula CnH2n+2, wherein “n” is preferably an integral number from 1 to 6, and most preferably “n” is an integral number from 1 to 4. The alcohol may be a primary alcohol, secondary alcohol and / or a tertiary alcohol. Most preferably, the fuel gas is hydrogen or a hydrogen-containing gas mixture. These above mentioned “fuel gases” can be understood as examples of a “primary fuel gas” used for the overall exothermic combustion and MP hydrolysis / pyrolysis in the flame process (see equation (1 ) above).

[0034] Additionally, “fuel gas” mixtures comprising other gases may be used, e.g. inert gases such as but not limited to N2, CO2 and / or oxygen containing gases.

[0035] Gaseous ammonia can function as a “secondary fuel gas”, which burns with a total endothermic character of the combustion and MP hydrolysis / pyrolysis (see equation (2) above).

[0036] The term “gaseous” means any non-solid and non-liquid form of the respective substance, such as, but not limited to, gas or steam. Moreover, “gaseous” as a non-liquid form shall exclude droplets, aerosols, or any liquid spray. According to one aspect of the inventive process, gaseous ammonia (NHs) or a gas mixture comprising ammonia (NHs) is led through at least one gas channel to the outlet end of the burner head. For the optimized control of the flame and broadening the range of the possible exit gas velocity of ammonia, gaseous ammonia mixture may include an oxygen containing gas and / or a gaseous fuel gas, such as, but not limited to, gaseous H2 or gaseous alkanes (CnH2n+2).

[0037] According to one preferred embodiment of the process to limit the complexity of the burner head, it may be advantageous for the process to comprise the step of (pre-)mixing at least a portion of the fuel gas with ammonia and optionally with the oxygen containing gas prior to the outlet end of the burner head. Preferably, the process comprises the step of mixing at least a portion of the fuel gas with ammonia and the oxygen containing gas prior to the outlet end of the burner head.

[0038] Analogously, it may be advantageous (pre-)mixing at least a portion of the fuel gas with the MP and optionally with the oxygen containing gas prior to the outlet end of the burner head. Preferably, the process comprises the step of mixing at least a portion of the fuel gas (other than ammonia) with the MP and the oxygen containing gas prior to the outlet end of the burner head. Therefore, the burner head can be in fluid communication to or comprises a (second) mixing chamber having at least a fuel gas inlet, an inlet for the MP and an outlet leading to the burner head and one of the channels. However, this mixing chamber used for mixing MP is then in no fluidic connection with an ammonia (NHs) leading channel.

[0039] According to a further preferred embodiment of the process, it may be advantageous when the fuel gas comprises at least one of hydrogen (H2), carbon monoxide (CO), an alcohol and / or an alkane with the general formula CnH2n+2.

[0040] In case of an alkane (CnH2n+2) as a gaseous fuel, “n” is preferably an integer number of 1 to 6, most preferably 1 to 4. The alcohol contained in the fuel and / or forming the fuel gas is preferably selected from the group of primary alcohols, secondary alcohols, and tertiary alcohols.

[0041] According to a further preferred embodiment of the process, it may be advantageous when the MP mixture containing at least one gaseous fuel gas and / or an oxygen containing gas is used. The gaseous fuel gas, other than ammonia, can be selected from the group consisting of hydrogen (H2), an alkane with a general formular CnH2n+2, an alcohol, carbon monoxide (CO), and the mixtures thereof.

[0042] According to a further preferred embodiment of the process, it may be advantageous to feed hydrogen (H2) feedstock and ammonia (NHs) in the molar ratio R1 defined as the ratio of the amount of ammonia (NHs) to the total amount of ammonia and hydrogen (NH3+H2), in the range of 0.05 to 1.0, preferably 0.1 to 0.9, more preferably 0.2 to 0.8. At the molar ratio R1 of lower than 0.05-0.2, the positive effects of introducing ammonia on the process are minimal. No hydrogen may be used in the process (R1 = 1.0). However, it has been found that a relatively low content of hydrogen (R1-0.8) may lead to certain improvement of the flame stability in the process.

[0043] According to a further preferred embodiment of the process, it may be advantageous if the molar ratio R2 of the total amount of all gaseous feedstocks to the amount of MP is less than 8.3. Thus, the term “gaseous feedstock” refers to the total amount or total sum of fed gases to the burner head calculated in Nm3 / h. Preferably R2 is less than 8.0, more preferably less than 7.8, more preferably from 4 to 7.8. Keeping R2 on a relatively low level (R2 < 8.3) means higher throughput of the plant, while the lower range of R2~4 typically represents the minimal technically viable value of R2. Preferably, the gaseous feedstocks are such as, but not limited to, H2, NH3, O2, N2, and MP.

[0044] The gaseous N2 is typically either a part of air as feedstock gas and / or is fed as a separate feedstock gas into the burner head.

[0045] According to a further preferred embodiment of the process, it may be advantageous selecting MP from at least one of the following substances: aluminum chloride (AICI3), aluminum oxychloride (AIOCI), titanium tetrachloride (TiCk), titanium trichloride (TICIs), titanium oxychloride (TiOCh), tetraalkoxytitanate such as tetraethoxytitanate Ti(OC2Hs)4, tetraalkoxysilicate such as tetraethoxysilicate Si(OC2Hs)4, cyclic siloxane ([O-SiR2]n) such as octamethylcyclotetrasiloxane (D4), acyclic siloxane (R3Si-[O-SiR2]n-O-SiR3) such as silicon oils, silicon tetrachloride (SiCk), trichlorosilane (HSiCIs), methyltrichlorosilane (CHsCbSI), dichlorosilane (SiH2CI2) and / or monochlorosilane (SIHsCI).

[0046] The mentioned MP are the most preferred ones, but the process is not limited to these MPs.

[0047] According to a further preferred embodiment of the process, particularly with respect to sustainability, it may be advantageous to produce feedstock ammonia (NH3) at least partly using hydrogen (H2) obtained from electrolysis of water or an aqueous solution, preferably using renewable energy source such as solar energy, wind energy, geothermal energy, hydropower from flowing water, tidal energy, energy obtained from burning of biomass, waste or biofuel, and combinations of these energy sources.

[0048] The feedstock ammonia (NH3) is preferably a gas and / or gasified when fed into the burner and / or burner head.

[0049] According to a further preferred embodiment of the process, the metal oxide and / or metalloid oxide has a BET surface area of 10 to 600 m2 / g, more preferably 15 to 600 m2 / g, more preferably 20 to 600 m2 / g, more preferably 30 to 550 m2 / g, more preferably 50 to 500 m2 / g, most preferably 80 to 400 m2 / g.

[0050] According to a further particularly preferred embodiment of the process, the metal oxide and / or metalloid oxide has a BET surface area of 150 to 500 m2 / g, more preferably 240 to 400 m2 / g, most preferably 240 to 300 m2 / g.

[0051] By the inventive process, metal oxides and / or metalloid oxides with some unique properties may be obtained, such as, but not limited to, an increased nitrogen content of the metal oxides and / or metalloid oxides produced, compared to the products obtained by conventional processes. According to a further preferred embodiment of the process, the burner head comprises in radial direction at least two central channels, and one concentrical (secondary) channel surrounds these central channels, wherein the (first) central channel is concentrically surrounded by the second (central) channel, and wherein the central channels form a pipe-in-pipe system. The secondary channel is radially outside the (central) outer channel and at least one feed line leads into the secondary channel. Secondary air can be led into the secondary channel and subsequently into the flame chamber during the process. Thus, the burner comprises a secondary channel, located between the outer channel and the housing. According to another preferred embodiment, the secondary channel is formed by the flame chamber itself, surrounding at least partially the central channels and secondary air or a (secondary) oxygen containing gas is provided directly into the flame chamber.

[0052] The burner head preferably comprises two (central) channels, wherein preferably ammonia (NH3) and hydrogen (H2) as fuel gas mixture are led through the radial outer (central) channel directly into pyrolysis flame, wherein the fuel gas led through the outer (central) channel can be a fuel gas mixture, comprising hydrogen (H2) and / or an additional gas, such as, but not limited to nitrogen (N2), a ^-containing gas, and / or an oxygen (O2) containing gas. MP or the MP-gas mixture is led by the inner (central) channel into the flame, As an alternative and inverted embodiment, the fuel gas incl. ammonia is led by the first (central) channel into the flame, and MP is led by the outer (central) channel.

[0053] This arrangement, with a direct and closest neighborhood of the inner (central) channels, leads to the direct release of ammonia into the flame and the beneficial high BET-surfaces as well as the high nitrogen content of the metal oxides and / or metalloid oxides, which relates only to metal and / or metalloid nitrides, e.g. silicon nitride (SisN4), aluminum nitride (AIN), titanium nitride (TiN and / or TisN4).

[0054] The invention further comprises pyrogenic metal oxide and / or metalloid oxide selected from the oxides of: aluminum (Al), titanium (Ti), zirconium (Zr), yttrium (Y), lithium (Li), magnesium (Mg), lanthanum (La), cerium (Ce), iron (Fe), zinc (Zn), and silicon (Si), or a mixture thereof, with a BET surface area of the metal oxide and / or the metalloid oxide of from 10 to 600 m2 / g and having a ratio R3 of nitrogen content in % by weight (wt%) to BET surface area in m2 / g of at least 1.0*1 O’4wt%*g / m2. Preferably R3 is at least 1.1*1 O’4wt%*g / m2, more preferably at least 1.2*1 O’4wt%*g / m2, more preferably at least 1.3*10'4wt%*g / m2, more preferably at least 1.5*10'4wt%*g / m2’ more preferably at least 1.7*10'4wt%*g / m2, more preferably at least 1.9*1 O’4wt%*g / m2, more preferably at least 2.0*1 O’4wt%*g / m2, more preferably at least 2.5*104wt%*g / m2, more preferably at least 3.0*104wt%*g / m2, most preferably at least 4,0*104wt%*g / m2, wherein the nitrogen content relates only to metal and / or metalloid nitrides.

[0055] The term “nitrogen content related to metal and / or metalloid nitrides” (Nnitride) is defined in the context of the present invention as:

[0056] Wherein: means the total content of nitrogen (N) in the metal and / or metalloid oxide in % by weight (wt%), preferably determined by elemental analysis according to EN IS03262-20:2000 (Chapter 8),

[0057] - “Nnon-nitride", means the nitrogen content in wt% of all non-nitride nitrogen compounds including, but not limited to, ammonia, amines, ammonium salts, nitro- and / or nitroso compounds. The can be preferably calculated by using chemical formulas of the corresponding nonnitride nitrogen compounds and using carbon, hydrogen and / or oxygen content of the metal and / or metalloid oxide determined by elemental analysis.

[0058] Thus, if no above-described non-nitride components like ammonia or amines are used or formed in the process, then is equal to If a non-nitride nitrogen compound like ammonia is present in the metal and / or metalloid oxide, the non-nitride nitrogen (“Nnon-nitride") content related to ammonia (NNHS) may be calculated from hydrogen content of the oxide determined by elemental analysis. The process according to the present invention typically involves complete burning of all nitrogen components which can be oxidized (like ammonia and amines), therefore no ammonia, amines or ammonium salts can typically be determined in the resulting metal and / or metalloid oxide. Also, no nitroso compounds and / or nitro compounds are typically added or formed by the process. Hence, in the inventive process typically

[0059] Without wishing to be bound by any theory, it is believed that the nitrogen contained in the inventive metal oxide and / or metalloid oxide and / or in the metal oxide and / or metalloid oxide produced by the inventive process, is firmly bounded to metal / metalloid and is at least partially, preferably exclusively, present in the form of the corresponding nitrides (e.g. SisN4) or similar compounds. These nitrogencontaining compounds seem to be well-spread in the metal / metalloid oxide particles and may have, even in small quantities, significant impact on some metal / metalloid oxide properties such as for example mechanical strength, resistance to attrition (and fines formation), increased electrical conductivity and / or improved electrostatic behavior thereof, which may have benefits for various applications. Additionally, a higher chemical stability may be possible due to at least local passivation of the metal oxide and / or metalloid oxide by the corresponding metal nitride coating.

[0060] In a preferred embodiment of the invention, the pyrogenic metal oxide and / or metalloid oxide has a nitrogen content relating only to metal and / or metalloid nitrides of the following group: silicon nitride (SisN4), aluminum nitride (AIN), titanium nitride (TiN and / or TisN4).

[0061] Improved pyrogenic metal oxide and / or metalloid oxide may have a ratio R3 of nitrogen content in % by weight to BET surface area in m2 / g of at most 20*1 O'4wt%*g / m2, preferably at most 10*1 O'4wt%*g / m2, more preferably at most 8.0*104wt%*g / m2, more preferably at most 6*104wt%*g / m2, more preferably at most 5.0*1 O'4wt%*g / m2. Moreover, the ratio R3 of nitrogen content in % by weight to BET surface area in m2 / g may be in a range, defined by the lower limit and the upper limit as stated above. Thickening effect (also known as thixotropic index) can be measured according to the method described in example 2 of WO2013 / 156337: 3.85 wt % of fumed oxide is incorporated and dispersed in a Renlam® M1 epoxy resin (manufacturer: Huntsman Corporation) using the vacuum dissolver VMA-Getzmann Dispermat® CA 20-M1 during 5 minutes at rotation speed of 3000 rpm. Resulting viscosities of the epoxy resin filled with fumed oxide can be calculated using the Anton-Paar Physica® Rheometer MCR 301 , measuring system CP25-2 at 23 °C, at share rates of 5 s1and 50 s1. Thixotropic-Indices of the fumed oxides can be calculated as the quotient of the corresponding viscosities at 5 s1divided by the viscosity at 50 s1.

[0062] Thixotropic index of the pyrogenic metal and / or metalloid oxide according to the present invention is preferably at least 1750, more preferably at least 1800, more preferably at least 2000.

[0063] Preferably the pyrogenic metal oxide and / or metalloid oxide is silicon dioxide (silica, SiCh) or a mixture comprising silicon dioxide.

[0064] The described pyrogenic metal oxide and / or metalloid oxide preferably has a BET surface area of from 10 m2 / g to 600 m2 / g, more preferably 15 to 600 m2 / g, more preferably 20 to 600 m2 / g, more preferably 30 to 550 m2 / g, more preferably 50 to 500 m2 / g, most preferably 80 to 400 m2 / g The BET surface can be determined according to DIN ISO 9277:2003-05.

[0065] Tamped density of the inventive metal oxides and / or metalloid oxides is typically below 200 g / L, preferably at most 100 g / L, more preferably at most 50 g / L.

[0066] Tamped density (also referred to as “tapped density”) can be determined according to DIN ISO 787- 11 :1995 “General methods of test for pigments and extenders - Part 11 : Determination of tamped volume and apparent density after tamping”.

[0067] In a preferred embodiment of the invention, the pyrogenic metal oxide and / or metalloid oxide has a nitrogen content of at least 0.03 wt%, preferably at least 0.04 wt%, more preferably 0.05-0.20 wt%. Moreover, in a further preferred embodiment, the pyrogenic metal oxide and / or metalloid oxide has a nitrogen content of at least 0.03 wt%, preferably at least 0.04 wt%, more preferably 0.05-0.20 wt%.

[0068] It can be advantageous to produce pyrogenic metal oxide and / or metalloid oxides of the invention according to one of the versions and / or embodiments of a pyrogenic process as described herein.

[0069] The invention further provides the use of the metal oxide and / or metalloid oxide as described herein and optionally produced according to a version and / or an embodiment of the inventive process, wherein the use is as a constituent of paints or coatings, silicones, pharmaceutical or cosmetic preparations, adhesives or sealants, toner compositions, for modifying rheology properties of liquid systems, as antisettling agent, for improving flowability of powders, for improving mechanical or optical properties of silicone compositions, as constituents of lithium-ion batteries. The process of the present invention and suitable burners and burner heads shall be illustrated in more detail by means of the following figures. These figures only represent some exemplary suitable embodiments of the used equipment (e.g., burner and burner head), and should not be understood as in any way limiting the scope of the invention itself. Thus, it is shown as follows:

[0070] Fig. 1 : A first burner and burner head as two sectional views (I, II), one parallel to and including the longitudinal axis and another perpendicular to the longitudinal axis;

[0071] Fig. 2: A second burner and burner head as two sectional views (I, II), one parallel to and including the longitudinal axis and another perpendicular to the longitudinal axis;

[0072] Fig. 3: A third burner head as sectional view; and

[0073] Fig. 4: A sectional view perpendicular to the longitudinal axis as a partial view of further burner head types.

[0074] The burner 200 is shown schematically in figure 1 in partial view I, having a burner head 100 with a longitudinal axis A, several feed lines 150, 152 a housing 160 and one product line 170 (outlet). The reference number 190 indicates the flame, shown in a very schematical way as dotted line, having a flame axis parallel or identical with the longitudinal axis A. The general flow direction of the burner head 100 as shown in figure 1 (I) is indicated by the arrow B. The burner head 100 comprises an inlet end 102, an outlet end 104 and two channels 112, 114 each having outlet opening 140, 142 at the outlet end 104. As one version, the outlet openings are approximately arranged in one common plane. Any additional equipment needed to run the burner and the process in question, such as, but not limited to, further processing units, pumps, compressors, tanks, sensors, actors, igniting equipment, electrical supply etc. is not shown in the figures. In flow direction B and connected with the product line 170, there can be further process units, such as, but not limited to, a cooling unit, a deacidification unit, and a separation unit for the metal oxide and / or metalloid oxide produced by the inventive process (not shown).

[0075] Furthermore, a flame tube may be part of the product line 170 e.g., as a first section and / or as a connecting part to the flame chamber 162 of housing 160 (not shown). Alternatively, a flame tube may be an integrated part ofthe flame chamber 162 and / or the housing 160 (not shown). Such a flame tube may have in axial direction a conical shape.

[0076] The “flame axis” is defined by the main or central axis ofthe gases and or the pyrolysis flame released form the burner head, the terms “flame axis” and “central axis” are herein used synonymously. Even though one single flame axis is mentioned, it is understood that a dynamic gas release or flame does define a corridor in which multiple axis are located rather than one single axis in a mathematical meaning. Thus, the central axis means the place and orientation of the axis with a highest statistical likeliness. Moreover, the axis is alternatively or additionally defined by the symmetry ofthe burner head and / or the outlet openings of the flame forming gases. Analogously, “central” shall mean radially close or overlapping to the central axis and / or close or overlapping to the flame axis. The term “plane” means a surface area, projection plane, and / or direct surface in a technical not in a mathematical meaning. It is used for explanation and illustration reasons. Thus, a “plane” may have not only two dimensions, but can have a limited third dimension, such a height or depth, and can be a narrow corridor. The terms “combustion chamber" and “flame chamber” are used synonymously.

[0077] According to the example of figure 1 shown in partial view I, the burner head 100 comprises in radial direction two channels 112, 114, and one concentrical (secondary) channel 118 surrounds these central channels 112, 114. Channel 112 is concentrically surrounded by the second channel 114, the channels form a pipe-in-pipe system. The plane 148 aligned perpendicular to the longitudinal axis A defines in flow direction B the beginning or entrance of the flame chamber 162. In the shown embodiment of figure 1, the outlet openings 140, 142 of the channels 112, 114 of the burner head 100 are (approximately) located in this plane 148. The burner 200 comprises a combustion chamber 162, alternatively named as “flame chamber” wherein the pyrolysis takes place. Each of the incoming feed lines 150, 152 are connected to one of the inner channels 112, 114 of the burner head 100.

[0078] The burner 200 comprises a secondary channel 118, being located between the outer channel 114 and the housing 160. The secondary channel 118 is radially outside the outer channel 114. At least one feed line 157, e.g., connected to at least one flange element 158, leads into the secondary channel 118. Secondary air can be led into the secondary channel 118 and subsequently into the flame chamber 162 during the process. According to an embodiment not shown in the figures, the burner 100 comprises no such secondary channel and secondary air or an (secondary) oxygen containing gas is provided directly into the flame chamber 162 by at least one feed line.

[0079] The partial view II of figure 1 shows the concentrical orientation of the channels 112, 114, 118, and the housing 160 of the burner 200. The D-D line indication shows the orientation of the cross-section, being identical, analogously, and / or parallel oriented to the plane 148.

[0080] Channel 118 is open to the atmosphere via the flange 158 and secondary oxygen containing gas e.g., air, is sucked in by means of an orifice and the flange 158. The secondary channel 118 can be defined as a channel of the burner 200 or as the transition spacing between burner head 100 and the housing 160 of the burner 200. According to an alternative embodiment (not shown), the secondary channel 118 is part of the burner head 100 and concentrically surrounding the outer channel 114.

[0081] The outlet openings 140, 142, 148 of the channels 112, 114, 118 are located (approximately) within plane 148. Plane 148 represents in flow direction B the inlet end of the inner combustion chamber 162 in which the flame 190 expands.

[0082] During the process feedstocks ammonia (NH3) and hydrogen (H2) are provided as mixture by feed line 152 to the (second) channel 114 aligned equal to the longitudinal axis A. Additionally, feedstock MP and (primary) air is provided through the central channel 112 directly into the flame 190, provided by the feed line 156. No premixing of NH3 with MP prior to the pyrolysis flame and / or combustion chamber 162 takes place.

[0083] The fuel gas led through the channel 114 can be a fuel gas mixture, comprising hydrogen (H2) and / or an additional gas. The additional gas may be nitrogen (N2), a ^-containing gas, and / or an oxygen (O2) containing gas. The additional gas has a diluting effect and can be also provided by the third feed line (not shown).

[0084] In an inverted embodiment analogous to figure 1 , the ammonia leading channel is the central channel 112, and the MP leading channel is the outer channel 114.

[0085] According to an alternative embodiment shown in figure 2 (in both partial views I, II), the burner 200 having a burner head 100 with a longitudinal axis A, several feed lines 152, 154, 156 a housing 160 and one product line 170. The burner head 100 comprises an inlet end 102, an outlet end 104 and several channels 112, 114, 116 each having outlet opening 140, 142, 144 at the outlet end 104. The outlet openings can be approximately arranged in one common plane 146. The burner 200 is usually connected to and controllable by a control unit 120, wherein the data connection is indicated by dotted data line 122. Any additional equipment or unit needed to run the burner and the process in question are generally known, and thus not shown in the figures.

[0086] According to the example of figure 2, the burner 200 comprises in radial direction three channels 112, 114 and 116. These channels form a pipe-in-pipe system. The first, central channel 112 is concentrically surrounded by the second channel 114, the third (outer) channel 116. The third channel 116 is in radial direction the ultimate channel of burner head 100. In longitudinal direction the burner 200 comprises three main sections 130, 132, 134 The main sections in axial direction are the following: the infeed section 130, the lead section 132, and the release section 134. The plane 148 aligned perpendicular to the longitudinal axis A defines in flow direction B the end of the lead section 132 and the beginning of the release section 134 and / or the flame chamber 162. In the shown embodiment of figure 2, the outlet openings 140, 142, 144 of the channels 112, 114, 116 of the burner head 100 are located (approximately) in this plane 148. The release section 134 comprises the combustion chamber 162, also named as flame chamber, wherein the pyrolysis takes place. The infeed section 130 is defined as the section comprising at least partially incoming feed lines 152, 154, 156 each connected to at least one of the inner channels 112, 114, 116 of the burner head 100.

[0087] According to the embodiment of figure 2, the burner 200 comprises a secondary channel 118, being located between the third (outer) channel 116 and the housing 160. The secondary channel 118 is at least partially radially outside the outer channel 116. At least one feed line 157, connected e.g., with at least one flange element 158, leads into the secondary channel 118 and secondary air can be led into the secondary channel 118 and subsequently into the flame chamber 162. According to an embodiment not shown in the figures, the burner comprises no such secondary channel and secondary air or an (secondary) oxygen containing gas is provided directly into the flame chamber 162 by at least one orifice and / or at least one feed line.

[0088] The partial view II of figure 2 shows the concentrical orientation of the channels 110 - 118, and the housing 160 of the burner 200. The D-D line indication shows the orientation of the cross-section, being identical or analogously oriented to the plane 148.

[0089] The lead section 132 is in flow direction downstream to the infeed section 130, whereby the lead section 132 is defined by the completed infeed of any feedstock (educt) in at least one of the inner channels 112, 114, 116 of the burner head 100, and if applicable, air into the secondary channel 118 of the burner 200. In other words, in the lead section 132 no more (main) feed lines are connected and the final gas flow in flow direction B is formed. Channel 118 is open to the atmosphere via the flange 158 and secondary oxygen containing gas, e.g. air, is sucked in by means of at least one suitable element.

[0090] At the opposite (with respect to section 130) end of the lead section 132 the release section 134 is located. Terminal end of the lead section 132 is basically defined and limited in flow direction B by the outlet openings 140, 142, 144 of the channels 112, 114, 116 (approximately) within the plane 148. The plane 148 represents in flow direction B the inlet end of the inner combustion chamber 162 and the release section 134 in which the flame 190 extends.

[0091] During the process feedstock MP and primary air can be provided analogously to figure 1 by feed line 156 to the central channel 112 aligned concentrically to the longitudinal axis A. Additionally, ammonia (NHs) and a fuel gas, such as hydrogen (H2), are provided by the feed line 152 to the second (next) channel 114 and released directly into the flame 190, no premixing of ammonia (NH3) with MP prior to the pyrolysis flame and / or combustion chamber 162. Thus, by the feed line 152 a first portion of fuel gas is provided to form the pyrolysis flame 190. A second portion of fuel gas and an additional gas, such as nitrogen and / or optionally oxygen containing gas is provided by the feed line 154 to the third (outer) channel 116. The gas led through the outer (jacket) channel 116 is meant to form a jacket flame (not shown). Finally, secondary oxygen containing gas, such as atmospheric air, is sucked into the secondary channel 118 and released into the flame chamber 162 as soon as the flame is ignited.

[0092] In the embodiment shown in figure 3, the burner 200 is basically analogously build to the one of figure 2, so the missing components can be taken from one of the other figures. However, the burner head 100 comprises four inner channels 110, 112, 114 and 116 and provides the formation of the flame 190 by means of a conus section 136. The conus section 136 is part of the lead section 132. Additionally, the conus section 136 comprises an optional (short) ring section 138 at the outlet end (plane 148). the conus section 136 has an advantageous influence forming a stable and homogenous pyrolysis flame.

[0093] The burner head 100 according to figure 3 comprises and / or is connected to a mixing chamber 180, which is connected to the feed line 154 leading to the outer channel 116, wherein one gas is premixed, e.g., a fuel gas mixture. The channels according to embodiment of figure 3 are meant for piping gas in the following way into the combustion chamber 162:

[0094] - first channel 112 a first portion of a fuel gas,

[0095] - second channel 114 the MP and a first portion of primary air,

[0096] - third channel 110 the ammonia and a second portion of primary air, and forth (outer) channel 116 a second portion of fuel gas and nitrogen containing gas.

[0097] A secondary channel 118 analogous to figure 1 or figure 2 may be part of the burner 200.

[0098] Finally, in figure 4 the concept of forming a concentrical channel by a group of smaller pipes 115, 117 is shown in one embodiment. This embodiment is an alternative solution to the burner 200 shown in figure 3. However, the concept of a group of (smaller) pipes can be used for at least one concentrical (gas) channel of any of the described embodiments. The term “smaller” refers to the diameter of these “pipes” 115, 117 compared to the related channel formed by the respective group of pipes. The smaller pipes 115, 117 having a round sectional area. In figure 4only some of the group of smaller pipes building one channel are drawn. Nevertheless, the entirely channel is built and / or filled with the group of small pipes, as indicated by the respective dotted lines. However, the small pipes of one group of pipes may be in direct contact to each other or having a distance in circumferential direction to each other (not shown). Alternatively, small(er) pipes of one group may have non-round shapes (not shown).

[0099] In figure 4 the third channel 110 and the outer channel 116 are built by a group of small pipes 115, 117. In an alternative embodiment, only one of the channels 110, 112, 114 or 116 is built by a group of smaller pipes, or more than two channels are built by a group of smaller pipes.

[0100] It is obvious for a person skilled in the art, that the burner 200 and / or the burner head 100 may have any orientation different to the orientation shown in the figures and any details provided herein in this regard needs to be understood analogously in connection with a different orientation of the burner or burner head. Moreover, the burner 200 and / orthe burner head 100 needn’t have the simplified elongate form as shown in the figures but any useful inner and outer curved and / or angulated geometry.

[0101] In general, any hint, advantage and detail provide regarding the burner and burner head, especially together with the discussion of figures 1 to 4, shall apply for the process identically or if necessary, analogously, and vice versa: the process embodiments and details can be applied in combination with the details described with the discussion of figures 1 to 4. Experiments

[0102] General process description:

[0103] In a burner 200 comprising a burner head 100 schematically shown in figure 1 , 0.395 Nm3 / h* of SiCl4 vapor pre-mixed with (primary) air were introduced into a burner 100 through the central channel 112. The burner head 100 comprises two channels 112, 114, wherein the central channel 112 is also named as first (inner) channel 112 and the radial outer channel 114 is also named as second (outer) channel 114. Ammonia (NHs) and hydrogen (H2) as fuel gas mixture were led through the radial outer channel 114 into pyrolysis flame 190 and the combustion chamber 162.

[0104] Secondary air was separately introduced into the burner 200 via the secondary channel 118, located between the second channel 114 and the housing 160. “Primary” oxygen containing gas, also primary air” is defined as oxygen containing gas or air directly channeled through at least one channel of the burner head. “Secondary” oxygen containing gas, also “secondary” air, means usually air surrounding the flame outside of the burner head and / or being sucked or pumped into the flame during the pyrolysis synthesis. In all examples except for comparative example 6, ammonia, if used, was separately introduced into the burner head through the second outer channel 114.

[0105] The amounts of oxygen and fuel gases (H2 + NH3) were adjusted in all experiments so that gamma ratio (for H2+NH3) = 1.5; and lambda ratio (for H2 +NH3) = 1.

[0106] The introduced gases were mixed and ignited at the outlet of the burner head resulting in a flame spreading along the flame axis A into the combustion chamber 162. The particle gas mixture was further cooled down and the fumed silica powder formed was separated from the gases and deacidified using water steam at 600 °C in a conventional deacidification unit. The specific flow rates of ammonia, H2, (primary) air, O2, and N2 used in the comparative and inventive examples 1-6 are given in table 1. The properties of the obtained fumed silica samples are given in table 2 below.

[0107] In all experiments and as used herein, Nm3 / h is meant and defined as gas throughput (volume / time) at standard temperature (0°C; 273.15 K) and pressure (1 atm; 1013.25 mbar).

[0108] “Gamma” is defined as the ratio of hydrogen amount fed into the burner head to the hydrogen amount stoichiometrically required for SiCl4 hydrolysis reaction; and “lambda” is defined as the ratio of oxygen amount fed into the burner head to the hydrogen amount stoichiometrically required for combustion of the fuel gases H2 and NH3. The volume flow of SiCl4 was 0.395 Nm3 / h.

[0109] The volume of secondary air, sucked into the combustion chamber and the pyrolysis flame via secondary channel 118 surrounding the burner head 100, was not calculated with regard to lambda, gamma or any other ratio as provided herein. T able 1 : Process parameters

[0110] Therein: R1 = NH3 / (H2+NH3); R2 = (H2+NH3+air+O2+N2+SiCl4) / SiCl4

[0111] Regarding comparative example 6, SiCk as MP and ammonia feedstock were pre-mixed priorto outlet end of the burner head and prior to feeding into the flame. This premixing led to a fast clogging of the reactor, observed at the outlet end of the burner. Thus, a continuous process over the intended production time was not possible. Thus, no product has been isolated in the comparative example 6.

[0112] With reference to table 1 and figure 1 , the channels of burner head 100 were used for the respective gas flows as given in table 1 A:

[0113] Table 1A: Process parameters

[0114] Table 2: Product properties Adding ammonia and separating it from the metal precursor during feeding into the flame allows producing fumed silica continuously without any clogging.

[0115] Thus, using gaseous ammonia allows increasing plant productivity as shown in the last column of table 1, where decreasing the R2 ratio, i.e. the ratio of the total gas amount per given SiCk amount from 8.32 mol / mol (comparative example 1) down to 6.22 mol / mol (example 5) is shown. It also allows increasing of the thickening effect of the resulting silica as show in table 2, form 1740 (comparative example 1 ) up to 2455 (example 3), and significant increasing of BET surface area in the experiments 2 and 3 (with adding ammonia, without adding additional oxygen) vs. comparative example 1 (without adding ammonia).

[0116] The BET surface was determined according to DIN ISO 9277:2003-05.

[0117] Thickening effect (also known as thixotropic index) was measured according to the method described in example 2 of WO2013 / 156337:

[0118] 3.85 wt% of fumed silica was incorporated and dispersed in a Renlam® M1 epoxy resin (manufacturer: Huntsman Corporation) using the vacuum dissolver VMA-Getzmann Dispermat® CA 20-M1 during 5 minutes at rotation speed of 3000 rpm. Resulting viscosities of the epoxy resin filled with silica were calculated using the Anton-Paar Physica® Rheometer MCR 301 , measuring system CP25-2 at 23 °C, at share rates 5 s1and 50 s1. Thixotropic-Indices of the silica samples were calculated as the quotient of the corresponding viscosities at 5 s1divided by the viscosity at 50 s-1.

[0119] Silicas obtained with using ammonia are characterized by a significantly higher nitrogen content (determined by elemental analysis) than those prepared underthe same reaction conditions but without using ammonia (table 2).

Claims

Claims1. Process for manufacturing metal oxide and / or metalloid oxide by means of a burner (200) comprising a burner head (100) having at least two channels (112, 114) and an outlet end (104), wherein the metal oxide or metalloid oxide is selected from the following group of oxides of: aluminum (Al), titanium (Ti), zirconium (Zr), yttrium (Y), lithium (Li), magnesium (Mg), lanthanum (La), cerium (Ce), iron (Fe), zinc (Zn), and silicon (Si), or a mixture thereof, wherein the process comprises the steps:- Providing an oxygen containing gas and a fuel gas to the burner head (100);- Providing a gaseous metal precursor and / or a gaseous metalloid precursor (MP) to the burner head (100);- Providing a flame (190) by burning the oxygen containing gas and at least a portion of the fuel gas at the outlet end (104) of the burner head (100);Releasing the MP and / or the MP containing mixture into the provided flame (190), characterized by providing gaseous ammonia (NHs) and / or a gaseous ammonia mixture through at least one gas channel (112, 114) to the outlet end (104) of the burner head (100) and releasing said ammonia (NHs) into the flame (190), wherein the ammonia (NHs) is not premixed with the MP or MP- containing mixture prior to the outlet end (104) of the burner head (100).

2. The process according to claim 1 , comprising the step of mixing at least a portion of the fuel gas with ammonia and / or with the oxygen containing gas prior to the outlet end (104) of the burner head (100).

3. The process according to claim 1 or 2, comprising the step of mixing at least a portion of the fuel gas with the MP and / or with the oxygen containing gas prior to the outlet end (104) of the burner head (100).

4. The process according to any preceding claim, wherein the fuel gas comprises hydrogen (H2), carbon monoxide (CO), an alcohol and / or an alkane with the general formular CnH2n+2.

5. The process according to claim 4, wherein the molar ratio R1 of the amount of ammonia (NHs) to the sum of the amounts of ammonia and hydrogen (NH3+H2) is in the range of 0.05 to 1.0, preferably 0.1 to 0.9, more preferably 0.2 to 0.8.

6. The process according to any preceding claim, wherein the molar ratio R2 of the total amount of gaseous feedstocks to the amount of MP is less than 8.3, preferably less than 8.0, more preferably less than 7.8, more preferably from 4.0 to 7.8.

7. The process according to any preceding claim, wherein the MP is selected from at least one of the following substances: aluminum chloride (AlCb), aluminum oxychloride (AIOCI), titanium tetrachloride (TiCk), titanium trichloride (TiCIs), titanium oxychloride (TiOCb), tetraalkoxytitanate such as tetraethoxytitanate Ti(OC2Hs)4, tetraalkoxysilicate such as tetraethoxysilicate Si(OC2Hs)4, cyclic siloxane ([O-SiR2]n) such as octamethylcyclotetrasiloxane (D4), acyclic siloxane (RsSi-[O- SiR2]n-O-SiR3) such as silicon oils, silicon tetrachloride (SiCk), trichlorosilane (HSiCb), methyltrichlorosilane (CHsSiCb), dichlorosilane (H2SiCl2) and / or monochlorosilane (FbSiCI).

8. The process according to any preceding claim, wherein the feedstock ammonia (NH3) is at least partly produced using hydrogen (H2) obtained from electrolysis of water or an aqueous solution, preferably using renewable energy source such as solar energy, wind energy, geothermal energy, hydropower from flowing water, tidal energy, energy obtained from burning of biomass, waste or biofuel, and combinations of these energy sources.

9. The process according to any preceding claim, wherein the metal oxide and / or metalloid oxide has a BET surface area of 10 to 600 m2 / g, preferably 20 to 600 m2 / g.

10. The process according to any preceding claim, wherein the burner head (100) comprises in radial direction at least two central channels (112, 114), and one concentrical (secondary) channel (118) surrounds these central channels (112, 114), wherein channel (112) is concentrically surrounded by the second channel (114), and wherein the channels (112, 114) form a pipe-in- pipe system.

11. Pyrogenic metal oxide and / or metalloid oxide selected from the oxides of: aluminum (Al), titanium (Ti), zirconium (Zr), yttrium (Y), lithium (Li), magnesium (Mg), lanthanum (La), cerium (Ce), iron (Fe), zinc (Zn), and silicon (Si), or a mixture thereof, with a BET surface area of the metal oxide and / or the metalloid oxide of from 10 to 600 m2 / g and having a ratio R3 of nitrogen content in % by weight to BET surface area in m2 / g of at least 1.0*1 O’4wt%*g / m2, preferably at least 1.1*1 O’4wt%*g / m2, more preferably at least 1.2*1 O’4wt%*g / m2, more preferably at least 1.3*1 O’4wt%*g / m2, more preferably at least 1.5*1 O'4wt%*g / m2, more preferably at least 1.9*1 O'4wt%*g / m2, more preferably at least 2.5*1 O’4wt%*g / m2, more preferably at least 3.0*1 O’4wt%*g / m2, wherein the nitrogen content relates only to metal and / or metalloid nitrides.

12. Pyrogenic metal oxide and / or metalloid oxide according to claim 11 , wherein the nitrogen content of the metal oxides and / or metalloid oxides relates only to metal and / or metalloid nitrides of the following group: silicon nitride (SbN4), aluminum nitride (AIN), titanium nitride (TiN and / or TbN4).

13. Pyrogenic metal oxide and / or metalloid oxide according to claim 11 or 12, having a ratio R3 of nitrogen content in % by weight to BET surface area in m2 / g of at most 20*104wt%*g / m2, preferably at most 10*10’4wt%*g / m2, more preferably at most 8.0*10’4wt%*g / m2, more preferably at most 6*10'4wt%*g / m2, more preferably at most 5.0*10'4wt%*g / m2.

14. Pyrogenic metal oxide and / or metalloid oxide according to one of claims 11 to 13, wherein nitrogen content of the metal oxide and / or metalloid oxide is at least 0.03 wt%, preferably at least 0.04 wt%, more preferably 0.05-0.20 wt%.

15. Pyrogenic metal oxide and / or metalloid oxide according to one of the claims 11 to 14, obtained by a pyrogenic process according to one of the claims 1 to 10.

16. Use of the metal oxide and / or metalloid oxide according to one of claims 11 to 15 as a constituent of paints or coatings, silicones, pharmaceutical or cosmetic preparations, adhesives or sealants, toner compositions, for modifying rheology properties of liquid systems, as anti-settling agent, for improving flowability of powders, for improving mechanical or optical properties of silicone compositions, as constituents of lithium-ion batteries.