Mixing system and method for producing a precursor composition

Abstract

The invention relates to a mixing system (1) for producing a precursor composition, the mixing system (1) comprising: - a mixing chamber (2), - a mixer (4) arranged in the mixing chamber (2), - a comminutor (3) located in the mixing chamber (2), and - a heating device (5) designed to heat a material to be mixed located in the mixing chamber (2).

Description

[0001] Mixing plant and process for producing a precursor composition

[0002] The invention relates to a mixing plant and a method for producing a precursor composition and the use of a precursor composition.

[0003] Silicon carbide can be used, for example, for the manufacture of electrodes. To produce silicon carbide, a silicon-containing component and a carbon-containing component can be reacted with each other. For example, silicon carbide can be produced by reacting silicon dioxide with a carbon source comprising a carbohydrate at elevated temperature, as described in EP 2 334 597 A1.

[0004] Furthermore, WO 2008 / 061521 A2 discloses a method for producing an object at least partially with a silicon carbide structure from a blank made of a carbon-containing material. In a first step, the object is produced from the carbon-containing material essentially according to its desired final shape and / or final dimensions and is at least partially coated with carbon-rich silicon dioxide granules. Annealing then takes place in a protective gas atmosphere, with the silicon dioxide granules releasing silicon carbide-containing gas, which penetrates the object and partially or completely converts the carbon-containing material into silicon carbide.

[0005] However, both of the described manufacturing processes are only suitable to a limited extent for the large-scale production of silicon carbide. Furthermore, the resulting silicon carbide contains a certain amount of nitrogen, which can be detrimental depending on the intended application or require complex purification of the silicon carbide.

[0006] The object of the present invention is to provide a mixing device that enables improved production of a precursor composition, in particular for the production of silicon carbide (SiC). A further object of the invention is to provide a method for producing such a precursor composition. This object is achieved by the subject matter of the independent claims. The dependent claims relate to embodiments.

[0007] A first aspect of the invention relates to a mixing system for producing a precursor composition, in particular for producing a precursor composition for producing silicon carbide. Preferably, silicon carbide with high purity, in particular nitrogen-free silicon carbide, can be produced.

[0008] The present invention and particularly preferred embodiments of the present invention are described in more detail in a non-limiting manner with reference to a figure. It shows the figure representation according to

[0009] Fig. 1 shows a schematic representation of a preferred embodiment of the device according to the invention, particularly suitable for carrying out a method according to the present invention. The mixing system 1 comprises a mixing chamber 2, a mixer 4 arranged in the mixing chamber 2, a comminutor 3, e.g., a chopper, arranged in the mixing chamber 2, and a heating device 5 designed to heat a mixture located in the mixing chamber 2.

[0010] Mixer 4 ensures uniform mixing of the reactants so that a reactant mixture that is as homogeneous as possible can be obtained.

[0011] The shredder 3 enables the introduction of shear energy into the reactant mixture. For example, by controlling the shredder 3 accordingly, shear energy can be introduced into the reactant mixture in a targeted manner, e.g., at specific times.

[0012] The heating device 5 enables heating of the reactant mixture. By appropriately controlling the heating device 5, the reactant mixture can be heated to a predeterminable temperature. A temperature profile according to which the reactant mixture is heated can also be defined. The heating device 5 can, for example, be designed as an electric heating device. A key advantage of the proposed mixing system 1 is that many process steps can be carried out in a controlled manner in a predeterminable sequence in one unit. After the reactants have been introduced into the mixing chamber 2, the precursor composition can be produced automatically without the need for further intervention. This enables cost-effective large-scale production of the precursor composition. Furthermore, no hazardous substances are used in the production process.Advantageously, reactants with a very high degree of purity can be used, which means that only minimal post-purification of the resulting precursor composition is necessary or post-purification can even be omitted entirely.

[0013] According to various embodiments, the mixing system 1 can have a filter device 5 designed to filter exhaust gases escaping from the mixing chamber 2.

[0014] By means of the filter device 5, pollutants such as dust and pyrolysis degradation products can be advantageously removed from the exhaust gas, so that the purified exhaust gas can then be released into the environment. This increases operational reliability and improves environmental friendliness.

[0015] According to further embodiments, the mixing system can have a cooling device 7 designed to cool the exhaust gases.

[0016] The exhaust gases can be cooled, for example, at least until the pollutants contained in the exhaust gas reach their boiling point, so that the pollutants condense and can be separated in liquid form. For this purpose, the cooling device 7 can be designed, for example, as a condenser. The exhaust gases can be cooled before, after, or simultaneously with filtration.

[0017] According to further embodiments, the mixing plant 1 can have a suction device 8 designed to remove the exhaust gases from the mixing chamber 2.

[0018] By means of the extraction device 8, process gases, i.e., gases present in the mixing chamber 2 during the preparation of the precursor composition, can be efficiently and controllably removed from the mixing chamber 2 as exhaust gases. For example, a constant outflow of exhaust gases can be enabled. According to further embodiments, the mixing system 1 can have a supply device 9 designed to supply an inert gas to the mixing chamber 2.

[0019] This enables the production of the precursor composition under inert gas conditions. The produced precursor composition can also be removed from the mixing chamber 2 under inert gas and, for example, packaged and further processed. This allows a high-quality precursor composition to be produced. Argon, for example, can be used as the inert gas. The inert gas is preferably nitrogen-free, which prevents the chemical incorporation of nitrogen into the precursor composition. Furthermore, the use of an inert gas can increase safety.

[0020] According to further embodiments, the mixing system 1 can have a control unit 10 designed to control a mixing process taking place in the mixing chamber 2.

[0021] The control unit 10 receives sensor signals from sensors, such as pressure sensors, temperature sensors, etc., processes these sensor signals based on instructions or code programmed in the control unit 10 according to one or more routines, and sends control signals to actuators, such as the heater, mixer, chopper, etc. in response to the processed sensor signals.

[0022] The control unit 10 can be implemented in hardware and / or software and can be physically constructed in one or more parts. The control unit 10 is in a signal-based connection with the sensors and actuators.

[0023] The control unit 10 can also be designed as a closed-loop control unit, which, in addition to controlling the mixing process, also enables closed-loop control of the mixing process taking place in the mixing chamber 2. This allows process parameters such as pressures and temperatures to be continuously monitored and adjusted as needed.

[0024] According to further design variants, mixer 4 can be designed as a horizontal mixer. A horizontal mixer enables particularly thorough mixing of the reactants and even heat distribution. Furthermore, sealing the mixer or agitator is easy with a horizontal mixer.

[0025] A further aspect of the invention relates to a process for producing a precursor composition, in particular for producing a precursor composition for producing silicon carbide. The process is particularly well suited for the large-scale production of such precursor compositions.

[0026] The process can be carried out, for example, using the mixing plant described above. Therefore, the above explanations of the mixing plant also serve to describe the proposed process. The advantages of the mixing plant are correspondingly linked to the process.

[0027] The method comprises the following steps: introducing liquid reactants into the mixing chamber, mixing the reactants in the mixing chamber to obtain a reactant mixture, heating the reactant mixture to evaporate solvents contained in the reactant mixture, heating the solvent-free reactant mixture while introducing shear energy until a pyrolysis temperature is reached and carrying out a pyrolysis while comminuting the solvent-free reactant mixture to obtain the precursor composition.

[0028] The above-mentioned procedural steps can be carried out in the order in which they are mentioned, but also in a different order or with overlapping times.

[0029] The reactants can, for example, be a first reactant that provides silicon, i.e., a silicon source, and a second reactant that provides carbon, a carbon source. For example, silica, e.g., fumed silica, can be used as the silicon source. A carbohydrate or a mixture of carbohydrates, such as sugar, for example, a mixture of glucose and fructose, e.g., invert sugar, can be used as the carbon source. The process can be carried out as a batch process. The total duration of the process can, for example, be between 8 and 12 hours.

[0030] According to various embodiments, the method may comprise removing the precursor composition from the mixing chamber under inert gas conditions.

[0031] According to further embodiments, the process may include removing exhaust gases from the mixing chamber. The removed exhaust gases may be cooled and / or filtered.

[0032] According to further embodiments, the pyrolysis temperature can be higher than 300 °C.

[0033] According to further embodiments, the process can be carried out at least partially under inert gas conditions. In particular, the mixing of the reactants, the heating of the reactant mixture, and the pyrolysis can be carried out under inert gas conditions.

[0034] A further aspect of the invention relates to the use of a precursor composition prepared according to a process as described above for producing silicon carbide.

[0035] Example:

[0036] A horizontal mixer is essentially used for production. This ensures uniform mixing of the reactants. A chopper is also built into the mixer, which introduces shear energy into the mixture at specific times. The exhaust gases from the mixer must be filtered and cooled. This requires a filter and a condenser. An extraction system ensures the constant outflow of the process gases. Process parameters such as pressures and temperatures of the heaters and the product temperature must be continuously monitored. A preferred system suitable for carrying out the process according to the invention is also shown in Figure 1. A test, which takes place in batch mode, lasts between 8 and 12 hours. Several process phases are run through. To ensure safety at all times, an inerting system is installed.

[0037] The product temperature determines which phase the mixing process is in. It should be noted that, depending on the temperature, a portion of the reactants used passes into the gas phase. This loss varies depending on the control of the process parameters. The loss must be determined and taken into account when adding reactants.

[0038] 1st phase: The two liquid reactants are mixed together in the mixer. In the first step, mixing takes place using a defined shear energy.

[0039] 2nd phase: The solvent added through the liquid phase is evaporated at a certain temperature.

[0040] Phase 3: The mixture is now heated under constant shearing. This results in a sharp increase in viscosity, which must be overcome by electrically controlling the agitator.

[0041] 4th phase: As the temperature increases, pyrolysis begins at T > 300°C. The material is crushed, particularly with the chopper, with strong gas evolution. Pressure monitoring ensures process stability. The process is operated in phases under overpressure. 5th phase: The temperature in the mixer is continuously increased with constant stirring until the final temperature is reached.

[0042] Phase 6: The powder is now transferred to a container. The high product temperature must be taken into account. This process step takes place under inert gas conditions. The container is transferred to the next process step under inert conditions.

[0043] List of reference symbols: Mixing plant 6 Filter device Mixing chamber 7 Cooling device Crusher 8 Extraction device Mixer 9 Feeding device Heating device 10 Control unit

Claims

Patent claims:

1. Mixing plant (1) for producing a precursor composition, the mixing plant (1) comprising: a mixing chamber (2), a mixer (4) arranged in the mixing chamber (2), a comminutor (3) arranged in the mixing chamber (2) and a heating device (5) designed to heat a mixture located in the mixing chamber (2).

2. Mixing system (1) according to claim 1, comprising: a filter device (6) designed to filter exhaust gases escaping from the mixing chamber (2).

3. Mixing plant (1) according to one of the preceding claims, comprising: a cooling device (7) designed to cool the exhaust gases.

4. Mixing plant (1) according to one of the preceding claims, comprising: a suction device (8) designed to remove the exhaust gases from the mixing chamber (2).

5. Mixing plant (1) according to one of the preceding claims, comprising: a supply device (9) designed to supply an inert gas to the mixing chamber (2).

6. Mixing plant (1) according to one of the preceding claims, comprising: a control unit (10) designed to control a mixing process taking place in the mixing chamber (2).

7. Mixing plant (1) according to one of the preceding claims, wherein the mixer (4) is designed as a horizontal mixer.

8. A process for preparing a precursor composition, the process comprising: Introducing liquid reactants into the mixing chamber, mixing the reactants in the mixing chamber to obtain a reactant mixture, Heating the reactant mixture to evaporate solvents contained in the reactant mixture, Heating the solvent-free reactant mixture by applying shear energy until a pyrolysis temperature is reached and Carrying out a pyrolysis with comminution of the solvent-free reactant mixture to obtain the precursor composition.

9. The method according to claim 8, comprising: Removing the precursor composition from the mixing chamber under inert gas conditions.

10. The method according to claim 8 or 9, comprising: Removing exhaust gases from the mixing chamber.

11. The method according to claim 10, comprising: Cooling and / or filtering the exhaust gases.

12. Process according to one of claims 8 to 11, wherein the pyrolysis temperature is higher than 300 °C.

13. A process according to any one of claims 8 to 12, wherein the process is carried out at least partially under inert gas conditions.

14. A process according to any one of claims 8 to 13, wherein the process is carried out in a mixing plant according to any one of claims 1 to 7.

15. Use of a method according to any one of claims 8 to 14 prepared precursor composition for the production of silicon carbide.

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