Device and method for producing a pyrogenic material

Abstract

The invention relates to a device for producing a pyrogenic material, characterized in that the device comprises: - a sublimation chamber (1) for producing a gas containing metal monoxide by high-temperature heating of a mixture of particles including: - metal particles, and - associated metal oxide particles, - a quench chamber (2), distinct from the sublimation chamber (1), for generating the pyrogenic material.

Description

[0001] DEVICE AND METHOD FOR THE PRODUCTION OF A PYROGENIC MATERIAL SCOPE OF THE INVENTION

[0002] The present invention relates to the general technical field of production – and in particular continuous production or batch production (or “batch”, according to the terminology used in the field of industrial processes) – of a pyrogenic powder such as:

[0003] - a pyrogenated alumina powder (Al2O3), or

[0004] - a pyrogenic titanium dioxide powder (TiO2), or

[0005] - a pyrogenated silica powder SiO2, or

[0006] - a powder of pyrogenated magnesia (MgO), etc.

[0007] More precisely, the invention relates to the field of the production of a powder of pyrogenic material in a device including a heating system such as an arc furnace, an induction furnace or a resistive furnace.

[0008] BACKGROUND OF THE INVENTION

[0009] Pyrogenic materials are inert and non-hazardous substances used in various industrial applications such as paints, food products, cosmetics, or catalysts.

[0010] Among these pyrogenic materials, pyrogenated silica is commonly used as a thickening or dehydrating agent.

[0011] More precisely, fumed silica (or "fumed silica" in English) is a form of silicon dioxide (SiO2) that appears as a powder composed of molten silica droplets cooled by forming three-dimensional chains that organize themselves into amorphous particles of very low apparent density and a very high specific surface area. This particular structure results in behavior that increases the viscosity of the fluids in which fumed silica is used as a thickener.

[0012] To produce fumed silica, a first silicon formation phase is implemented, this first phase comprising the steps of:

[0013] - extract quartz from a mine,

[0014] - grind the extracted quartz to obtain quartz particles,

[0015] - reduce quartz particles with carbon to obtain silicon.

[0016] The silicon thus formed is then transported to another facility to be transformed – in a second phase – into fumed silica. This second phase includes the following steps:

[0017] - react the silicon (obtained from the first phase) with chlorine to form silicon tetrachloride (SiCu),

[0018] - pyrolyze, at high temperature, silicon tetrachloride SiCh with a mixture of gas containing hydrogen H2 and oxygen O2.

[0019] Considering the complete product lifecycle, conventional fumed silica production processes have a very high carbon footprint. Indeed, these conventional processes:

[0020] - consume large amounts of energy,

[0021] - result in a large quantity of CO2 emissions, and of chlorine products harmful to the environment, and

[0022] - generate solid by-products such as silica fumes and slag.

[0023] To overcome these drawbacks, a plasma arc process for the production of fumed silica from quartz has already been proposed in document WO 2022 / 241545. An original feature of the process according to WO 2022 / 241545 lies in the implementation, within a single reactor, of two successive phases: - a first phase of melting, vaporization, and decomposition of the quartz into a vapor phase, and

[0024] - a second quenching phase of the vapor phase obtained to form pyrogenated silica.

[0025] The reactor described in WO 2022 / 241545 comprises:

[0026] - a crucible containing molten quartz,

[0027] - an arc heating system including at least one upper electrode extending to the molten quartz, a conductive plate disposed below the molten quartz, and a lower anode,

[0028] - a quenching system to inject a gas mixture containing argon, hydrogen and oxygen to form amorphous SiO2 particles, - an outlet to allow the gas mixture to exit the reactor.

[0029] In WO 2022 / 241545, the high temperature of the medium (greater than 1700°C, notably greater than 2230°C at the surface (vaporization temperature of quartz)) and the presence of an arc plasma (>4000°C) allow the melting, vaporization, and decomposition of quartz according to the following reaction:

[0030] 2 SiO2 2 SiO (gas) + O2 (gas).

[0031] However, a drawback of the solution according to WO 2022 / 241545 concerns the reactor design, which entails high costs. Indeed, the presence of oxygen (O2) among the products of the quartz decomposition reaction induces strong oxidation of the reaction medium at high temperatures. In order to avoid premature degradation of the reactor, it is therefore necessary to choose a material highly resistant to oxidation – and thus very expensive – for its construction.

[0032] Another drawback of the solution according to WO 2022 / 241545 is that it is not suitable for the formation of other pyrogenic materials such as:

[0033] - of pyrogenic alumina Al2O3, or - of pyrogenic titanium dioxide TiO2, or

[0034] - pyrogenic magnesia (MgO).

[0035] Indeed, the manufacture of such pyrogenic materials requires the use of heating temperatures far exceeding the heating temperature used for the manufacture of pyrogenated silica, and going beyond the temperature limit that the reactor can withstand according to WO 2022 / 241545.

[0036] Thus, due to its structural limitations, the reactor according to WO 2022 / 241545 is not configured for the formation of pyrogenic materials other than pyrogenated silica.

[0037] One aim of the present invention is to propose a device for producing a powder of pyrogenic material which makes it possible to overcome at least one of the aforementioned drawbacks.

[0038] In particular, one aim of the present invention is to provide a device for the industrial production of a pyrogenic material such as:

[0039] - of fumed alumina (Al2O3) or

[0040] - of pyrogenic titanium dioxide TiO2 (or "fumed titania" in English), or - of pyrogenic magnesium oxide MgO (or "fumed magnesia" in English), from a device including a heating system (for example by induction, by resistance, by thermal plasma, etc.) and without using toxic chemical substances.

[0041] Such a device can also be used for the industrial production of fumed silica powder SiO2 (or "fumed silica" in English).

[0042] BRIEF DESCRIPTION OF THE INVENTION

[0043] To this end, the invention proposes a device for the production of a pyrogenic material, remarkable in that the device comprises: - a sublimation chamber for the generation, by high-temperature heating, of a mixture of particles including:

[0044] o metal particles, and

[0045] o associated metallic oxide particles;

[0046] - of a gas containing metal monoxide,

[0047] - a quenching and oxidation chamber, separate from the sublimation chamber, for the generation of:

[0048] o of amorphous nanoparticles by cooling the gas containing metal monoxide, and

[0049] o of pyrogenic material by oxidation of amorphous nanoparticles.

[0050] Preferred but not limiting aspects of the invention are as follows:

[0051] - the quenching and oxidation chamber can also be configured for the generation of a functionalized pyrogenic material by modifying the surface of the pyrogenic material;

[0052] - advantageously:

[0053] or the pyrogenic material can be fumed silica, a mixture of particles including silicon particles (Si) and silicon oxide particles (SiC>2), or

[0054] or the pyrogenic material may be fumed alumina, a mixture of particles comprising aluminum particles (Al) and aluminum oxide particles (Al2O3), or

[0055] or the pyrogenic material may be pyrogenic titanium dioxide, a mixture of particles comprising titanium (Ti) particles and titanium oxide (TiC) particles, or

[0056] o the pyrogenic material can be pyrogenated magnesia, the mixture of particles including magnesium (Mg) particles and magnesium oxide (MgO) particles;

[0057] - advantageously:

[0058] The quantity of metal particles may be between 1 and 50% by mole of the particle mixture, preferably between 10% and 40% by mole, and even more preferably between 20% and 30% by mole, particularly in the order of 25% by mole of the particle mixture; and the quantity of metal oxide may be between 50 and 99% by mole of the particle mixture, preferably between 60% and 90% by mole, and even more preferably between 70% and 80% by mole, particularly in the order of 75% by mole of the particle mixture; the device may include means for:

[0059] to maintain the sublimation chamber at a pressure between 0.1 and 1.1 bar, and

[0060] o maintain the quenching chamber at a pressure lower than the pressure in the sublimation chamber;

[0061] - the device may also include a delivery line connected to the sublimation chamber on one side and to the quenching chamber on the other, the pressure in the sublimation chamber being greater than the pressure in the quenching chamber to facilitate the circulation of the gas containing the metal monoxide between the sublimation chamber and the quenching chamber via the delivery line;

[0062] - advantageously:

[0063] The sublimation chamber may include:

[0064] ■ a chamber containing the particle mixture, and ■ a heating system allowing the particle mixture to be heated to a high temperature to form the gas containing metal monoxide, and

[0065] The tempering chamber may include:

[0066] ■ a precipitation chamber through which the gas containing metal monoxide circulates,

[0067] ■ a set of injection nozzles including quenching and oxidation nozzles configured to inject into the precipitation chamber, a quenching and oxidation gas, such as air or dioxygen, for the generation of amorphous nanoparticles; - the sublimation chamber can be configured so that the atmosphere in the enclosure has a reducing behavior, and the quenching chamber is configured so that the atmosphere in the precipitation chamber has an oxidizing behavior;

[0068] - advantageously:

[0069] The enclosure may include at least one through-hole connected to an injection channel for an inert gas, such as Argon, the enclosure being devoid of a through-hole for the injection of gases containing reactive species such as hydrogen (H2), oxygen (O2), or water vapor (H2O),

[0070] o The precipitation chamber may include:

[0071] ■ the first nozzles configured to inject a quenching and oxidation gas chosen from air, oxygen O2, water vapor H2O, or a mixture thereof in order to:

[0072] • to cool the gas containing the metal monoxide from the sublimation chamber to obtain the amorphous nanoparticles, and

[0073] • to oxidize the amorphous nanoparticles to obtain the pyrogenic material.

[0074] BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Other advantages and features of the invention will become clearer from the following description of several embodiment variants, given by way of non-limiting examples, from the drawing illustrated in Figure 1, which is a schematic representation of a device for producing a pyrogenic material.

[0076] DETAILED DESCRIPTION OF THE INVENTION

[0077] We will now describe different examples of the implementation of the invention with reference to Figure 1.1. Presentation

[0078] 1.1. Case of fumed silica

[0079] Unlike the process according to WO 2022 / 241545, which proposes to produce fumed silica by decomposition of quartz in a reactor including a heating system (resistive furnace, induction furnace, arc furnace, etc.), the present invention proposes to produce fumed silica (fumigation SiO2) by decomposition of a mixture composed of:

[0080] - of silicon (Si), and

[0081] - of quartz (SiO2).

[0082] More precisely, and as will be described in more detail later:

[0083] - Heating the mixture of silicon (Si) and quartz (SiO2) at a pressure between 0.1 bar and 1.1 bar allows the formation of a gas containing silicon monoxide (SiO) according to the following reaction:

[0084] Si + SiO2 → 2 SiO (gas)

[0085] - Cooling (or quenching) the gas containing silicon monoxide (SiO) under an oxidizing atmosphere (i.e., in the presence of O2) allows the formation of fumed silica according to the following reaction:

[0086] 2 SiO + O2 → 2 SiO2 (solid).

[0087] Producing fumed silica from a mixture of silicon and silicon oxide reduces the temperature required to form the gas containing silicon monoxide.

[0088] Indeed, the energy required - and therefore the heating temperature required - to form a gas containing silicon monoxide (SiO) from a mixture of metal (silicon Si) and metal oxide (quartz SiO2) is less than the energy required - and therefore the heating temperature required - to form a gas containing silicon monoxide (SiO) from quartz (SiC) alone.

[0089] Furthermore, using a mixture of silicon and quartz particles to form the gas containing silicon monoxide reduces the oxidizing character of the reaction medium, since a smaller amount of oxygen is produced during the formation of the gas containing silicon monoxide.

[0090] Thanks to these different advantages of the solution according to the invention, it then becomes possible to form other types of pyrogenic materials, unlike the solution described in WO 2022 / 241545.

[0091] 1.2. Case of other oxygen-producing materials

[0092] In addition to the production of fumed silica, the present invention is adapted for the production of other pyrogenic materials such as:

[0093] - of pyrogenated alumina, or

[0094] - pyrogenic titanium dioxide, or

[0095] - of pyrogenated magnesia, etc.

[0096] Therefore, more generally than the description given in point 1.1, the present invention proposes to produce a pyrogenic material from a mixture comprising:

[0097] - metal particles, and

[0098] - particles of its associated metallic oxide, possibly in crystalline form.

[0099] More specifically, in the case of training:

[0100] - of pyrogenic alumina (pyrogenic Al2O3), the invention proposes the use of a mixture of aluminum particles (Al) and aluminum oxide particles (Al2O3), - of pyrogenic titanium dioxide (pyrogenic TiO2), the invention proposes the use of a mixture of titanium particles (Ti) and titanium oxide particles (TiO2),

[0101] - of pyrogenic magnesia (pyrogenic MgO), the invention proposes the use of a mixture of magnesium particles (Mg) and magnesium oxide (MgO).

[0102] Advantageously, the quantity of metal particles in the mixture is between 1 and 50% by weight of the mixture, preferably between 10% and 40% by weight, and even more preferably between 20% and 30% by weight, particularly around 25% by weight of the mixture. The quantity of metal oxide in the mixture is, for its part, between 50 and 99% by weight of the mixture, preferably between 60% and 90% by weight, and even more preferably between 70% and 80%, particularly around 75% by weight of the mixture.

[0103] From a thermodynamic point of view, it is preferable for the mixture to have a molar ratio of 50% between metal particles and metal oxide particles. This ensures that all the reactants (metal + metal oxide) are consumed to produce the gas containing metal monoxide.

[0104] However, since the cost of metal particles is higher than the cost of metal oxide particles, it is preferable to limit the quantity of metal particles used in order to reduce the production costs of the pyrogenic material. A person skilled in the art will be able to adjust the quantities of metal particles and metal oxide particles used according to these two criteria (heating temperature for the formation of the gas containing metal monoxide and the price of the metal particles).

[0105] As previously indicated in the case of fumed silica, it is more advantageous - from a thermodynamic point of view - to form a metal monoxide gas (such as SiO(gas), AlO(gas), TiO(gas), MgO(gas)) from a metal-metal oxide mixture (such as Si-SiO2, Al-Al2O3, Ti-TiO2, Mg-MgO), rather than to form said metal monoxide gas from only the metal oxide (SiO2, Al2O3, TiO2, MgO).

[0106] Furthermore, using a mixture of metal oxide particles and metal particles for the formation of the pyrogenic material reduces the oxidizing character of the reaction medium, since a lower quantity of oxygen is produced during the formation of metal monoxide gas.

[0107] We will now describe in more detail a device for producing pyrogenic material.

[0108] The device according to the invention will be presented with reference to the production of pyrogenated silica, it being understood that the device can also be used for the production of other pyrogenic materials.

[0109] More precisely, in the following, we will consider (for the presentation of the device according to the invention) that:

[0110] - The mixture of metal particles and associated metal oxide is composed of:

[0111] of silicon particles (metal particles), and

[0112] o of quartz particles (associated metallic oxide particles), and that - the resulting pyrogenic material is pyrogenated silica.

[0113] 2. Device for producing a pyrogenic material

[0114] 2.1. General Information

[0115] With reference to Figure 1, the device comprises:

[0116] - a sublimation chamber 1,

[0117] - a quenching and oxidation chamber 2, and

[0118] - a conveying conduit 3 between the sublimation chamber 1 and the quenching and oxidation chamber 2. The sublimation chamber 1 allows the high-temperature decomposition reaction of the mixture 4 of silicon particles and silicon dioxide to take place. This decomposition reaction allows the formation of silicon monoxide gas.

[0119] The quenching and oxidation chamber 2 allows the gas containing silicon monoxide from the sublimation chamber 1 to be cooled and oxidized to form pyrogenated silica particles.

[0120] Advantageously, the sublimation chamber 1 and the quenching and oxidation chamber 2 are distinct and separate, said chambers being connected via the supply line 3. This allows, in particular, for faster cooling of the silicon monoxide gas than with the apparatus according to WO 2022 / 241545 in which the steps:

[0121] - vaporization of quartz to form silicon monoxide, and

[0122] - quenching and oxidation of silicon monoxide formed to produce fumed silica,

[0123] are carried out in a single reactor.

[0124] Indeed, the vaporization stage requires heating the quartz to a very high temperature, while the quenching stage requires rapidly cooling the silicon monoxide. Implementing these two stages within a single reactor, as proposed in WO 2022 / 241545, is therefore very complicated.

[0125] The fact that the device according to the invention comprises a sublimation chamber 1 separate from the quenching and oxidation chamber 2 further allows said chambers to be independent in terms of shape and dimensions. It is thus possible to define different shapes and dimensions for the sublimation chamber 1 and for the quenching and oxidation chamber 2, the shape and dimensions of each chamber 1, 2 being particularly suited to the function it must perform. In contrast, in the case of WO 2022 / 241545, the definition of the shape and dimensions of the reactor is very complex (which does not allow for good control of the quality of the fumed silica), as it must allow for both:

[0126] - to sublime quartz to form gaseous silicon monoxide, and - to quench the silicon monoxide gas and oxidize the SiO particles to produce fumed silica.

[0127] The transformations of matter during these stages can be described by the following reactions:

[0128] Q+T°C

[0129] 2SiO2quartz) - > 2SiO gas) + O2(gas) (decomposition of quartz) -Q(tempering~)

[0130] 2SiO (gas) -> 2SiO (particles) (SiO quench)

[0131] Temperature

[0132] 2SiO₂ (particles) + O₂ (gas) → 2SiO₂ (pyrogenic silica) (SiO₂ oxidation)

[0133] The conveying conduit 3 allows the circulation of gases between the sublimation chamber 1 and the quenching and oxidation chamber 2. It may include one (or more) pipe(s) connected on one side to the sublimation chamber 1, and on the other side to the quenching and oxidation chamber 2.

[0134] In some embodiments, the device may also include a thermally insulating structure associated with the conveying conduit 3. Such a thermally insulating structure allows:

[0135] - to reduce heat loss during the passage of gases from sublimation chamber 1 to quenching and oxidation chamber 2, and

[0136] - to limit the parasitic condensation of silicon monoxide on the inner face(s) of the pipe(s) of the conveying line 3 (which reduces the material yield of the reaction and can cause a blockage of the line 3).

[0137] Since such a thermally insulating structure is known to those skilled in the art, it will not be described in further detail hereafter. This thermally insulating structure can, for example, consist of a thick ceramic lining of aluminum oxide (alumina or silicon carbide) placed around or inside the conveying pipe 3.

[0138] 3. Sublimation chamber

[0139] Sublimation chamber 1 allows:

[0140] - on the one hand, to contain the reactants, namely the (homogeneous) mixture of silicon (Si) and quartz (SiO2) particles, and

[0141] - on the other hand, to heat said reagents to high temperature to sublime the mixture in order to form a silicon monoxide (SiO) gas.

[0142] With reference to Figure 1, sublimation chamber 1 comprises:

[0143] - a heating system e 11,

[0144] - a 12-inch waterproof speaker,

[0145] - possibly a reagent supply system 13, and

[0146] - a crucible 14 intended to contain the reagents,

[0147] - an inert gas injection port - such as argon - 121 (to promote the circulation of the produced gases towards the quenching and oxidation chamber 2), the heating system 11 and the crucible 14 being housed in the enclosure 12.

[0148] 3.1. Heating System

[0149] The heating system 11 allows the reactants to be heated to a high temperature (in particular greater than or equal to 1200°C) to induce the decomposition reaction of the mixture of silicon (Si) and its associated oxide (SiCh) in order to produce the gas containing silicon monoxide (SiO) according to the following reaction:

[0150] Si + SiO2 2 SiO (gas). The heating system 11 can be of any type known to a person skilled in the art, such as a plasma arc furnace, an induction furnace, a resistive furnace, a gas furnace, etc.

[0151] In the following, the invention will be described with reference to a plasma arc furnace, it being understood for the person skilled in the art that other types of heating systems may be used for the implementation of the present invention.

[0152] For the formation of a plasma arc allowing the heating of the reactants (Si+SiC), the arc furnace includes electrodes 111, 112 powered either from a direct current source or from an alternating current source.

[0153] Each electrode 111, 112 may consist of a hollow cylindrical graphite bar extending vertically, each cylindrical bar being hollow for the injection of inert gas - such as argon - in order to promote the initiation / ignition of a plasma arc between the electrodes.

[0154] Each electrode 111, 112 is mounted in the enclosure 12 at the level of a respective through hole

[0155] As previously mentioned, each electrode 111, 112 is connected to a direct current or alternating current source. One advantage of a direct current supply is that the electrodes are not subjected to the electromagnetic effects experienced by the electrodes of a furnace powered from an alternating current source.

[0156] In the case of a direct current power supply:

[0157] - the mobile electrode(s) 111 can be connected to the positive pole of the direct current source to form an anode,

[0158] - the fixed electrode(s) 112 can be connected to the negative pole of the direct current source and form a cathode. The arc furnace being of a type known in itself to the man skilled in the art, its operation will not be described in more detail in the following.

[0159] 3.2. Enclosure

[0160] The sealed enclosure 12 allows for the definition of an enclosed space in which it is possible to generate a slight overpressure, that is to say, a space in which it is possible to increase the pressure to a value slightly greater than the pressure in the quenching and oxidation chamber 2. Thus, the pressure in the sublimation chamber 1 is greater than the pressure in the quenching and oxidation chamber 2.

[0161] Preferably, for the production of a pyrogenic material, the pressure in sublimation chamber 1 is between 0.1 and 1.1 bar. To ensure a pressure in enclosure 12:

[0162] - between 0.1 and 1.1 bar, and

[0163] - greater than the pressure in the quenching and oxidation chamber 2, the pyrogenic material production device may include a pump.

[0164] Generating a slight overpressure in chamber 12 helps to promote the escape of the gas containing silicon monoxide (formed following the heating of the mixture of silicon and silicon dioxide) towards the quenching and oxidation chamber 2.

[0165] The enclosure 12 includes one (or more) through-hole(s) connected (each) to a gas injection channel 121, each channel 121 being connected to a supply of inert gas, such as argon gas, for:

[0166] - Faci I iter l'allumage de l'arc plasma genere entre les electrodes 111, 112 du four à arc,

[0167] - increase the pressure in chamber 12 (relative to the pressure in the quenching and oxidation chamber 2) in order to promote the escape of the gas containing silicon monoxide towards the quenching and oxidation chamber 2.

[0168] The enclosure 12 also includes through holes for the passage of components of the heating system 11 (such as electrodes 111, 112 in the case of an arc furnace), a high-temperature sealing gasket being provided between the edges of each through hole and its associated component for:

[0169] - avoid excessive air infiltration into enclosure 12 and for

[0170] - to allow the generation of a slight overpressure in the enclosure 12 in order to promote the escape of the gas containing silicon monoxide towards the quenching and oxidation chamber 2.

[0171] Finally, enclosure 12 includes a through outlet connected to the supply line 3 to allow the circulation of the gas containing silicon monoxide between the sublimation chamber 1 and the quenching and oxidation chamber 2.

[0172] Of course, enclosure 12 has one (or more) other light(s) passing through for the passage of means of electrical connection, or to allow the evacuation of reaction waste, etc.

[0173] In some embodiments, the sublimation chamber 1 may include a thermally insulating structure associated with the enclosure 12 to reduce heat loss within the housing. Such a thermally insulating structure may consist of a thick ceramic lining of aluminum oxide (alumina or silicon carbide) arranged around or inside the enclosure 12.

[0174] Since such an enclosure 12 is known to the man of the trade, it will not be described in further detail hereafter.

[0175] 3.3. Feeding System The reagent feeding system 13 allows the crucible 14 to be filled with the mixture of silicon (Si) and silicon dioxide (SiC) particles. This particle mixture can consist of a cluster of pellets with fault sizes between 10 and 100 mm, each pellet being obtained by compacting a homogeneous mixture of metal particles (silicon) and its associated oxide (silicon dioxide) with a particle fault size between 4 and 10 µm.

[0176] Power supply system 13 includes:

[0177] - a receiving bowl 131 intended to contain a reserve of silicon particles (Si) and silicon oxide (SiC>2),

[0178] - a distribution channel 132 for the circulation of the mixture of silicon particles (Si) and silicon oxide (SiC>2), and

[0179] - one (or more) sealed valve(s) 133 to allow or stop the flow of the mixture of silicon particles (Si) and silicon oxide (SiCk).

[0180] The receiving bowl 131 includes a base in which is provided a through-hole connected to one end of the distribution channel 132, the other end of the distribution channel 132 opening into the crucible 14.

[0181] The valve(s) 133 is / are mounted on the distribution channel 132. A controller (not shown) allows the valve(s) to be switched from an inactive state to an active state (and from an active state to an inactive state):

[0182] - each valve blocks the passage of the mixture (Si + SiC) between the receiving bowl 131 and the crucible 14 in the deactivated state,

[0183] - each valve allowing the passage of the mixture (Si + SiC ) between the receiving bowl 131 and the crucible 14 in the active state.

[0184] When the feeding system 13 includes two valves, these define a sealed compartment between the receiving bowl 131 and the crucible 14 (and more generally between the outside and inside of the chamber 12). For filling the compartment, the controller activates the valve closest to the receiving bowl 131 and deactivates the valve furthest from the receiving bowl 131. The mixture (Si + SiC) flows by gravity from the receiving bowl 131 to the compartment defined between the two valves. When the compartment is full, the controller deactivates the valve closest to the receiving bowl 131, then activates the valve furthest from the receiving bowl 131. The mixture of particles (Si + SiC) flows by gravity from the compartment to the crucible 14. Once the compartment is empty, the controller deactivates the valve furthest from the receiving bowl 131, and a new filling cycle can be initiated.The presence of two valves 133 allows the enclosure 12 to be maintained at a pressure higher than atmospheric pressure during the filling of the crucible 14.

[0185] 3.4. Crucible

[0186] Crucible 14 is intended to contain the mixture of metal particles and metal oxide (Si + SiC). For this purpose, crucible 14 has a base, one (or more) side wall(s), and a top opening.

[0187] The crucible 14 may consist of a graphite frame externally coated with a refractory lining. Alternatively, the crucible 14 may have a coating (e.g., SiC) or be made of alumina, silica, metal, or silicon carbide (SiC).

[0188] 3.5. Operating Principle

[0189] The operating principle of sublimation chamber 1 is as follows.

[0190] In the first step, the silicon and quartz mixture is introduced into the sublimation chamber. The controller activates valve 133 of the feed system 13 to allow the transfer of the mixture from the receiving bowl to the crucible 14. Once the crucible is full, the controller deactivates valve 133.

[0191] The controller then initiates the decomposition reaction of the mixture to form the gas containing silicon monoxide. Specifically, the controller activates the heating system to heat the mixture. For example, when the heating system is an arc furnace, the controller activates the arc furnace electrodes to generate a plasma arc. The controller also activates the inert gas supply to inject said gas into chamber 12 (to facilitate the ignition of the plasma arc in the case of an arc furnace, and) to increase the pressure in sublimation chamber 1 to a value higher than the pressure in quenching and oxidation chamber 2.

[0192] Due to the intense heat produced by the heating system, the mixture of silicon and quartz is sublime and decomposes simultaneously (at the interface between the plasma arc and the molten bath in the case of an arc furnace) according to the following reaction:

[0193] Si + SiO2 → 2 SiO (gas).

[0194] Since this reaction does not produce oxygen, and no oxygen-containing gas is injected into chamber 12, the atmosphere in sublimation chamber 1 exhibits reducing behavior. This limits the risk of premature degradation of sublimation chamber 1, unlike the solution described in WO 2022 / 241 545.

[0195] The decomposition of the (Si+SiO2) mixture allows (under negative pressure) the production of a gas containing silicon monoxide. This gas naturally escapes to the quenching and oxidation chamber 2 via the supply line 3 due to the overpressure between the sublimation chamber 1 and the quenching and oxidation chamber 2.

[0196] 4. Quenching and Oxidation Chamber

[0197] The quenching and oxidation chamber 2 allows:

[0198] - to rapidly cool the silicon (II) monoxide contained in the gas from sublimation chamber 1 to obtain solid particles;

[0199] - to oxidize the excess silicon (Si) contained in the solid particles, and - to (simultaneously or successively) functionalize the surface of the solid particles to obtain the desired properties of the final product and thus produce the pyrogenated silica (pyrogenated SiO2).

[0200] The quenching and oxidation chamber 2 comprises:

[0201] - a precipitation box 21, and

[0202] - a set of injection nozzles 22, 23.

[0203] 4.1. Precipitation chamber

[0204] The precipitation caisson 21 can be tubular in shape and include a lateral partition defining upstream and downstream access points:

[0205] - The upstream access is connected to the supply line 3 for the introduction of the gas containing silicon monoxide into the precipitation chamber, and

[0206] - The downstream access is connected to a collection unit (not shown) to collect the pyrogenated silica particles obtained at the outlet of the quenching and oxidation chamber 2.

[0207] Advantageously, the side wall (or all the walls) of the precipitation chamber 21 may include a layer of smooth, non-adherent material such as a ceramic layer, a layer of metal oxides, or a layer of fluoropolymer. This facilitates / simplifies the removal of solidified particles that may settle on the inner surface of the side wall.

[0208] The precipitation chamber 21 may also include a cooling unit (not shown) consisting, for example, of a heat exchanger (such as a coil surrounding the side wall) through which a heat transfer fluid (such as water) circulates. The integration of a cooling unit accelerates the cooling of the gas (containing silicon monoxide) exiting the sublimation chamber. 1.4.2. Injection nozzle assembly

[0209] The set of injection nozzles 22, 23 allows the introduction of different gases into the precipitation chamber 21.

[0210] Each nozzle typically includes a body configured to disperse a jet of gas inside the precipitation chamber.

[0211] The complete set of injection nozzles includes:

[0212] - the first 22 nozzles connected to a quenching and oxidation gas supply source - such as air (O2+N2) or dioxygen (O2) or argon (Ar) - for:

[0213] to rapidly cool the silicon monoxide gas from the sublimation chamber 1 in order to form solid particles, and to oxidize the excess silicon contained in the solid particles, and - from the second nozzles 23 connected to a functionalizing gas supply source - such as water vapor (H2O).

[0214] The first nozzles 22 are closer to the upstream access of the precipitation caisson 21 than the second nozzles 23.

[0215] The first and second nozzles define two zones in the precipitation chamber 21:

[0216] - a first zone - called the "solid condensation" zone - in which the gaseous silicon monoxide is rapidly cooled and oxidized, under the action of the quenching and oxidation gas (air (O2+N2), or dioxygen (O2), and / or possibly water in vapor phase H2O (to quench, oxidize and functionalize simultaneously)) ejected through the first nozzles 22, to form silica particles (SiC>2) according to the following reaction: 2 SiO + O2 → 2 SiO2 (solid), and

[0217] - a second zone - called "functionalization" - in which the silica particles are functionalized, under the action of the functionalization gas (water vapor, etc.) ejected by the second nozzles 23 to produce the pyrogenated silica (pyrogenic SiO2).

[0218] Due to the injection of one (or more) gas containing oxygen molecules (air or dioxygen in the first zone, water vapor in the second zone) into the precipitation chamber 21, the atmosphere in the quenching and oxidation chamber 2 exhibits an oxidizing behavior.

[0219] 4.3. Operating Principle

[0220] The operating principle of the quenching and oxidation chamber 2 is as follows.

[0221] In a first step, the gas containing silicon monoxide from the sublimation chamber 1 is conveyed to the quenching and oxidation chamber 2 via the conveying pipe 3, the pressure difference between the sublimation chamber 1 and the quenching and oxidation chamber 2 (the pressure in the sublimation chamber 1 being greater than the pressure in the quenching and oxidation chamber 2) favoring the movement of the gas containing silicon monoxide towards the quenching and oxidation chamber 2.

[0222] The gas containing silicon monoxide (SiO) enters the precipitation box 21 through the upstream access and moves towards the downstream access.

[0223] During its movement through the first zone (i.e., the quenching zone) of the precipitation chamber 21, the gas containing silicon monoxide is rapidly cooled and oxidized by the quenching and oxidation gas ejected from the first injection nozzles. As previously indicated, this quenching and oxidation gas can be:

[0224] - of air, to limit the costs associated with the production of fumed silica,

[0225] - dioxygen (O2) or an inert gas (such as Argon Ar), to limit the risks of reaction between the nitrogen (N2) contained in the air and the gas containing silicon monoxide.

[0226] In all cases, the rapid cooling and oxidation of the gas from the sublimation chamber 1 induces the reaction of silicon monoxide (SiO) with the dioxygen (O2) contained in the quenching and oxidation chamber 2, so that solid silica particles are produced:

[0227] 2 SiO + O2 → 2 SiO2 (solid).

[0228] Since the silica particles thus produced are volatile, they move towards the downstream access of the precipitation chamber 21.

[0229] During their movement in the second zone (i.e. the functionalization zone) of the precipitation chamber 21, the silica particles (SiO2) can be functionalized by the functionalization gas ejected from the second injection nozzles (modification of the surface of the particles).

[0230] This produces the pyrogenated silica particles. These are collected at the downstream access point of precipitation chamber 21.

[0231] 5. Conclusions

[0232] The device described above allows, thanks to a sublimation chamber 1 and a separate quenching and oxidation chamber 2, the production of a pyrogenic material - from a metal and its associated oxide - such as:

[0233] - a pyrogenated alumina powder (pyrogenic Al2O3) from a mixture of aluminum (Al) particles and aluminum oxide (Al2O3) particles, - a pyrogenated titanium dioxide (pyrogenic TiO2) powder, from a mixture of titanium (Ti) particles and titanium oxide (TiC) particles, - a pyrogenated magnesia (pyrogenic MgO) powder, from a mixture of magnesium (Mg) particles and magnesium oxide (MgO) particles,

[0234] - a pyrogenated silica powder (pyrogenic SiO2) from a mixture of silicon and quartz (SiO2).

[0235] In the case of the production of a pyrogenic material other than fumed magnesia (MgO), due to the separation between the chambers on the one hand, and the use of a metal-oxide mixture on the other hand:

[0236] - the sublimation chamber - which must withstand high temperatures - has a reducing atmosphere (which limits the risk of premature degradation of said sublimation chamber), while

[0237] - the quenching and oxidation chamber - which is less stressed from a thermal point of view - presents an oxidizing atmosphere (to allow the formation of the pyrogenated material from the gaseous metal monoxide from the sublimation chamber).

[0238] The reader will appreciate that, in the case of the production of fumed magnesia, the sublimation chamber presents an oxidizing atmosphere due to the need to inject oxygen (O2) gas for the reactants (a mixture of magnesium (Mg) and magnesium oxide (MgO) particles) to be completely consumed. Indeed, given the stoichiometry of the magnesium oxide (MgO) molecule, a mixture of magnesium (Mg) and magnesium oxide (MgO) particles contains an excess of the metal (Mg). Thus, for the production of fumed magnesia (fumigation of MgO), the sublimation chamber presents an oxidizing atmosphere (presence of O2).

[0239] Finally, the fact that the pressure in the sublimation chamber 1 is greater than the pressure in the quenching and oxidation chamber 2 facilitates the circulation of gases between the sublimation chamber 1 and the quenching and oxidation chamber 2. The reader will have understood that many modifications can be made to the invention described above without materially departing from the new lessons and advantages described here.

Claims

DEMANDS 1. Device for the production of a pyrogenic material, characterized in that the device comprises: - a sublimation chamber (1) for the generation, by high-temperature heating, of a mixture of particles including: o metal particles, and o particles of associated metallic oxide, of a gas containing metal monoxide, - a quenching and oxidation chamber (2), separate from the sublimation chamber (1), for the generation: o of amorphous nanoparticles by cooling the gas containing metal monoxide, and o of pyrogenic material by oxidation of amorphous nanoparticles.

2. Device according to claim 1, wherein the quenching and oxidation chamber (2) is further configured for the generation of a pyrogenic material functionalized by modification of the surface of the pyrogenic material.

3. Device according to claim 1 or 2, wherein: - the pyrogenic material is pyrogenated silica, a mixture of particles comprising silicon particles (Si) and silicon dioxide particles (SiC2), or in which - the pyrogenic material is pyrogenated alumina, a mixture of particles comprising aluminum particles (Al) and aluminum oxide particles (Al2O3), or in which - the pyrogenic material is pyrogenic titanium dioxide, the mixture of particles comprising titanium particles (Ti) and titanium oxide particles (TiC), or in which - the pyrogenic material is pyrogenic magnesia, the mixture of particles comprising magnesium particles (Mg) and magnesium oxide particles (MgO).

4. Device according to any one of claims 1 to 3, wherein: - the quantity of metal particles is between 1 and 50% by moles of the particle mixture, preferably between 10% and 40% by moles, and even more preferably between 20% and 30% by moles, in particular on the order of 25% by moles of the particle mixture, and - the quantity of metal oxide is between 50 and 99% by moles of the mixture of particles, preferably between 60% and 90% by moles, and even more preferably between 70% and 80% by moles, in particular of the order of 75% by moles of the mixture of particles.

5. Device according to any one of claims 1 to 4, comprising means for: - maintain the sublimation chamber (1) at a pressure between 0.1 and 1.1 bar, and - maintain the quenching chamber (2) at a pressure lower than the pressure in the sublimation chamber (1).

6. Device according to any one of claims 1 to 5, further comprising a delivery line (3) connected to the sublimation chamber (1) on the one hand and to the quenching chamber (2) on the other hand, the pressure in the sublimation chamber (1) being greater than the pressure in the quenching chamber (2) to facilitate the circulation of the gas containing the metal monoxide between the sublimation chamber (1) and the quenching chamber (2) via the delivery line (3).

7. Device according to any one of claims 1 to 6, wherein: - the sublimation chamber (1) comprises: o an enclosure (12) containing the particle mixture, and o a heating system (11) allowing the particle mixture to be heated to a high temperature to form the gas containing the metal monoxide, and - the quenching chamber (2) comprises: o a precipitation chamber (21) through which the gas containing metal monoxide circulates, o an assembly of injection nozzles including quenching and oxidation nozzles configured to inject into the precipitation chamber, a quenching and oxidation gas, such as air or dioxygen, for the generation of amorphous nanoparticles.

8. Device according to claim 7, wherein the sublimation chamber (1) is configured so that the atmosphere in the enclosure (12) has a reducing behavior, and the quenching chamber (2) is configured so that the atmosphere in the precipitation box (21) has an oxidizing behavior.

9. Device according to any one of claims 7 or 8, wherein: - The enclosure (12) includes at least one through orifice connected to an injection channel for an inert gas, such as Argon, the enclosure being devoid of a through orifice for the injection of gas containing reactive species such as hydrogen (H2), oxygen (O2), or water vapor (H2O). - the precipitation chamber (21) includes o the first nozzles configured to inject a quenching and oxidation gas chosen from air, oxygen (O2), water vapor (H2O), or a mixture thereof in order to: ■ to cool the gas containing the metal monoxide from the sublimation chamber (1) to obtain the amorphous nanoparticles, and ■ to oxidize the amorphous nanoparticles to obtain the pyrogenic material.

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