Silicon carbide-boron nitride composite ceramic microchannel reactor, preparation method and application

Abstract

This invention provides a silicon carbide-boron nitride composite ceramic microchannel reactor with a unidirectional flow structure of three-dimensional channels. The raw materials of the microchannel reactor include, by mass fraction: 75%-90% silicon carbide powder; 5%-18% boron nitride powder; and 3%-8% sintering aid. A method for preparing the silicon carbide-boron nitride composite ceramic microchannel reactor is also proposed, including slurry preparation, green body forming, pre-oxidation treatment, and sintering. An application of the silicon carbide-boron nitride composite ceramic microchannel reactor is also proposed, which can be used in continuous flow processes with strong exothermic reactions, highly corrosive media, or high thermal shock loads. This invention allows silicon carbide and boron nitride, two materials that cannot be effectively combined, to form a compact integral structure, combining the chemical corrosion resistance, high thermal conductivity, and high-temperature strength of silicon carbide with the high in-plane thermal conductivity, lubricity, and excellent thermal shock stability of boron nitride. Therefore, it can be more widely applied in various chemical production processes.

Description

Technical Field

[0001] This invention relates to the field of microchannel reactor technology, and more particularly to silicon carbide-boron nitride composite ceramic microchannel reactors, their preparation methods, and applications. Background Technology

[0002] In the chemical industry, reaction equipment is the core factor determining production efficiency, safety, and product quality. Currently, the mainstream production methods can be divided into two main categories: traditional macroscopic reaction vessels and emerging microchannel reactors.

[0003] Traditional batch or semi-continuous reactors (such as stirred tank reactors and tower reactors used for ammonia synthesis, bulk chemicals, and some pharmaceutical intermediates) have a series of fundamental problems that are difficult to overcome, such as low mixing and transfer efficiency, significant scale-up effect, poor safety, large footprint, and high energy consumption.

[0004] Therefore, with the development of materials science, microchannel reactors are gradually being used more and more widely in the chemical industry. As a representative of process intensification technology, microchannel reactors can improve mass and heat transfer efficiency by several orders of magnitude by miniaturizing the reaction space (channel characteristic scale at the submicron to millimeter level), achieving continuous, safe, and efficient production, and showing a significant improvement in efficiency and purity compared to traditional reactors.

[0005] In current applications, microchannel reactors are increasingly revealing limitations in material properties: Metals are the current market mainstream, and while easy to process, their corrosion resistance is limited, making them unsuitable for long-term use in highly corrosive media such as hydrofluoric acid, concentrated alkalis, and halides; their thermal conductivity is generally low, potentially leading to thermal bottlenecks when handling extremely exothermic reactions; and the surface characteristics of metals may catalyze certain unwanted side reactions. Glass / quartz materials offer excellent corrosion resistance and visibility, but are inherently brittle, have poor thermal shock resistance and pressure resistance, making them unsuitable for rapid temperature increases / decreases or high-pressure processes. Polymer materials are low-cost and easy to process, but their poor temperature, pressure, and solvent resistance limit their applications.

[0006] Silicon carbide ceramics are considered ideal microreactor materials for demanding chemical processes due to their excellent chemical corrosion resistance, extremely high thermal conductivity, and superior high-temperature strength. However, their industrial application still faces two major obstacles: First, molding is difficult. SiC is a strongly covalent compound, making it difficult to sinter, which prevents traditional ceramic molding processes (such as dry pressing and slip casting) from processing complex three-dimensional internal channels. Second, insufficient strength. The inherent high brittleness and relatively limited thermal shock resistance of pure SiC ceramics make them susceptible to failure when subjected to severe temperature fluctuations or mechanical impacts.

[0007] Therefore, a microchannel reactor based on silicon carbide ceramics is needed to overcome the aforementioned difficulties in processing and the material's brittleness and thermal shock resistance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a silicon carbide-boron nitride composite ceramic microchannel reactor, its preparation method, and its application. This invention solves the problem that existing microchannel reactors suffer from material defects, making it difficult to unify their technical characteristics such as corrosion resistance, thermal shock resistance, and structural strength.

[0009] In a first aspect, the present invention proposes a silicon carbide-boron nitride composite ceramic microchannel reactor, wherein the microchannel reactor is a unidirectional flow structure with three-dimensional flow channels, and the raw materials of the microchannel reactor include, by mass fraction:

[0010] Silicon carbide powder 75%-90%;

[0011] Boron nitride powder 5%-18%;

[0012] Sintering aids: 3%-8%.

[0013] Preferably, the silicon carbide powder is submicron α-SiC, and the boron nitride powder is plate-shaped hexagonal boron nitride.

[0014] Preferably, the sintering aid comprises a mixture of aluminum nitride and yttrium oxide, wherein the molar ratio of aluminum nitride to yttrium oxide is 1-1.5:1.

[0015] Preferably, the three-dimensional flow channel structure of the microchannel reactor includes interlaced, spiral, and fractal structures.

[0017] Secondly, this invention proposes a method for preparing a silicon carbide-boron nitride composite ceramic microchannel reactor, comprising the following steps:

[0018] S1. Slurry preparation: Silicon carbide powder, boron nitride powder and sintering aid are prepared as raw materials according to volume percentage, placed in a ball mill jar, dispersant and deionized water are added, and ball milling is carried out to obtain a uniform premix; then water-based gel binder is added to the premix and high-speed stirring is carried out to form a ceramic slurry with a solid content ≥50 vol%.

[0019] S2. Green body forming: The ceramic slurry is loaded into the barrel of the direct writing printer, and a green body component is printed according to the preset three-dimensional digital model of the microchannel reactor; the green body is immediately placed at -30℃ to -50℃ for freezing and shaping, and then transferred to a freeze dryer to sublimate the ice crystals in a vacuum environment to completely remove moisture and obtain a dried green body;

[0020] S3. Pre-oxidation treatment: Place the dried green billet in a sintering furnace with an air atmosphere, heat it to 850℃-950℃ at a slow heating rate of 1-3℃ / min, and hold it at that temperature for 1-3 hours.

[0021] S4. Sintering: The pre-oxidized green body is transferred to an atmosphere sintering furnace and sintered at 1450℃-1550℃ and 1900℃-2000℃ under the protection of flowing inert gas to prepare the required silicon carbide-boron nitride composite ceramic microchannel reactor.

[0022] Preferably, the dispersant in step S1 includes ammonium polyacrylate, ammonium polymethacrylate, or ammonium polycarboxylate.

[0023] Preferably, the aqueous gel binder in step S1 includes agarose, sodium alginate, or methylcellulose.

[0024] Furthermore, in step S4, the sintering process specifically includes:

[0025] First stage: Increase the temperature to 1450℃-1550℃ at a rate of 3-5℃ / min, and hold for 0.5-1.5 hours;

[0026] Second stage: Increase the temperature to 1900℃-2000℃ at a rate of 5-8℃ / min, and hold for 0.5-1 hour;

[0027] It was then cooled to room temperature in the furnace.

[0028] Furthermore, it also includes the following steps:

[0029] S5. Post-processing: Precision grinding is performed on the fluid inlet and outlet connection parts of the microchannel reactor, and standard interface flanges are assembled.

[0031] Thirdly, this invention also proposes an application of a silicon carbide-boron nitride composite ceramic microchannel reactor for continuous flow processes involving strongly exothermic reactions, highly corrosive media, or high thermal shock loads, including:

[0032] High-purity nano-calcium carbonate and high-purity ammonium sulfate are produced by co-producing phosphogypsum.

[0033] Ammonia synthesis process based on electrochemical nitrogen reduction reaction;

[0034] High-purity silicon preparation process based on chemical vapor deposition;

[0035] Synthesis of pharmaceutical intermediates;

[0036] Processing of composite ceramic materials.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention represents a significant improvement in material properties compared to traditional metal / glass microreactors. Compared to metallic materials, the SiC-BN composite ceramic material used in this invention inherits the all-around corrosion resistance of silicon carbide ceramics, allowing for wide application in areas where traditional metallic microreactors cannot operate, such as those handling hydrofluoric acid and strong alkalis. Furthermore, its thermal conductivity (>120 W·m) is superior. -1 ·K -1 Several times stronger than metals, enabling extreme temperature control; finally, the composite ceramic material used in this invention has extremely low chemical activity, almost eliminating any side reactions that would affect product purity. For glass materials, the introduction of boron nitride increases the fracture toughness of the composite ceramic microreactor in this invention by more than 30% compared to pure SiC (reaching 5.8-6.2 MPa·m). 1 / 2 The thermal shock resistance is significantly improved. In addition, the lubricity of boron nitride helps reduce the adhesion of solid materials, expanding its application in systems such as slurry catalysis.

[0039] 2. h-BN possesses a graphite-like layered structure, combining high in-plane thermal conductivity, lubricity, and excellent thermal shock resistance. However, the extremely stable chemical properties of h-BN are severely mismatched with the sintering kinetics of SiC, making it impossible to achieve integrated, dense molding of the complex structures of both using traditional powder metallurgy or existing additive manufacturing methods.

[0040] Therefore, the preparation method of the present invention includes a pre-oxidation treatment and a sintering step. In the pre-oxidation treatment, the surface of h-BN and SiC particles is selectively and mildly oxidized by slow heating and low temperature preheating, so that amorphous boron oxide (B2O3) thin layer and silicon dioxide (SiO2) thin layer are generated on their surfaces, respectively.

[0041] Subsequently, the sintering process is divided into two steps at different temperatures: During sintering at 1450℃-1550℃, the surface-generated B2O3 and SiO2 react with the composite sintering aid AlN / Y2O3, forming a boroaluminosilicate liquid phase with a low eutectic temperature at a temperature far lower than that of pure SiC. This liquid phase can fully wet and encapsulate SiC and h-BN particles, driving particle rearrangement through capillary forces to achieve initial densification. During sintering at 1900℃-2000℃, with the assistance of the high temperature and the boroaluminosilicate liquid phase, SiC achieves grain densification growth through a dissolution-precipitation mechanism. Simultaneously, h-BN lamellar crystals are firmly "pinned" to the SiC grain boundaries, forming an interlocked multiphase microstructure. This solves the problem of kinetic mismatch between SiC and h-BN, two difficult-to-sinter materials, and achieves integrated densification of complex structures.

[0042] This invention combines silicon carbide and boron nitride, two materials that are not normally effectively bonded, into a tightly integrated structure. This structure combines the chemical corrosion resistance, high thermal conductivity, and high-temperature strength of silicon carbide with the high in-plane thermal conductivity, lubricity, and excellent thermal shock resistance of boron nitride. Therefore, it can be more widely applied in various chemical production processes.

[0043] 3. This invention employs direct-write molding technology for 3D printing ceramic green bodies, exhibiting strong adaptability to slurries and eliminating the need for expensive photosensitive resins or laser systems. It enables the integrated net-shape forming of truly complex three-dimensional flow channels (such as internal spirals and three-dimensional interlaced meshes) that are impossible to achieve through traditional machining or etching, providing limitless possibilities for optimizing reaction performance through flow channel design. The entire process is streamlined, avoiding multiple cycles of the PIP method, significantly shortening the production cycle and reducing costs. Attached Figure Description

[0044] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0045] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] Example 1:

[0047] The silicon carbide-boron nitride composite ceramic microchannel reactor in this embodiment was prepared using the following steps:

[0048] (1) Slurry preparation: 75% α-SiC powder with an average particle size of 0.5 μm, 17% h-BN powder with a flake size of 3-5 μm, and 8% composite additive of AlN and Y2O3 mixed at a molar ratio of 1.2:1 were taken as raw materials. 2% ammonium polyacrylate was added as a dispersant. Deionized water was added to control the water-to-powder ratio (by mass) at 0.4:1. The mixture was ball-milled for 24 hours. Then, 4% agarose was added as a gel binder after preheating to 60°C. The mixture was then vigorously stirred at 60°C for 2 hours to form a uniform slurry with good extrusion flowability and a solid content ≥50 vol%.

[0049] (2) Green body forming: Using a direct-write 3D printing equipment equipped with a 410μm diameter conical nozzle, a reactor green body with an external dimension of 50mm × 50mm × 20mm and containing continuous staggered serrated microchannels (channel cross-section of approximately 0.5mm × 1mm) was printed. After printing, the green body was placed in a -40℃ freezer for 12 hours to set, and then transferred to a freeze dryer for vacuum drying for 24 hours.

[0050] (3) Pre-oxidation treatment: The dried green billet is placed in a muffle furnace and heated to 900°C at a rate of 2°C / min in an air atmosphere. It is then held at this temperature for 2 hours and then cooled to room temperature with the furnace.

[0051] (4) Sintering: The pre-oxidized green body is placed in a graphite sintering furnace, and after vacuuming, high-purity argon is introduced as a protective atmosphere. First, the temperature is raised to 1500℃ at 4℃ / min and held for 1 hour; then the temperature is raised to 1950℃ at 6.5℃ / min and held for 45 minutes; finally, the temperature is cooled to room temperature under program control.

[0053] Example 2:

[0054] The silicon carbide-boron nitride composite ceramic microchannel reactor in this embodiment was prepared using the following steps:

[0055] (1) Slurry preparation: 79% α-SiC powder with an average particle size of 0.5 μm, 18% h-BN powder with a flake size of 3-5 μm, and 3% composite additive of AlN and Y2O3 mixed in a molar ratio of 1:1 were taken as raw materials. 1.0% of the raw material mass of ammonium polymethacrylate was added as a dispersant. Deionized water was added to control the water-to-powder ratio (mass) at 0.35:1. The mixture was ball-milled for 24 hours. Subsequently, 2% of the raw material mass of sodium alginate aqueous solution was added as a gel binder after preheating to 60°C. The mixture was then vigorously stirred at 60°C for 2 hours to form a uniform slurry with good extrusion flowability and a solid content ≥50 vol%.

[0056] (2) Green body forming: Using a direct-write 3D printing equipment equipped with a 410μm diameter conical nozzle, a reactor green body with an external dimension of 50mm × 50mm × 20mm was printed. The green body contained continuously interlaced serrated (interlaced, spiral, fractal structure) microchannels (channel cross-section approximately 0.5mm × 0.5mm). After printing, the green body was placed in a -30℃ freezer for 12 hours to set, and then transferred to a freeze dryer for vacuum drying for 24 hours.

[0057] (3) Pre-oxidation treatment: The dried green billet is placed in a muffle furnace and heated to 850℃ at a rate of 1℃ / min in an air atmosphere, and held at this temperature for 1 hour, and then cooled to room temperature with the furnace.

[0058] (4) Sintering: The pre-oxidized green body is placed in a graphite sintering furnace, and after evacuation, high-purity argon is introduced as a protective atmosphere. First, the temperature is increased to 1450℃ at 3℃ / min and held for 0.5 hours; then the temperature is increased to 1900℃ at 5℃ / min and held for 0.5 hours; finally, the temperature is cooled to room temperature under program control.

[0060] Example 3:

[0061] The silicon carbide-boron nitride composite ceramic microchannel reactor in this embodiment was prepared using the following steps:

[0062] (1) Slurry preparation: 90% of α-SiC powder with an average particle size of 0.5 μm, 5% of h-BN powder with a flake size of 3-5 μm, and 5% of composite additives of AlN and Y2O3 mixed at a molar ratio of 1.5:1 were taken as raw materials. 2.5% of the raw material mass of polycarboxylate ammonium salt was added as a dispersant. Deionized water was added to control the water-to-powder ratio (mass) at 0.45:1. The mixture was ball-milled for 24 hours. Subsequently, 6% of the raw material mass of methylcellulose aqueous solution was added as a gel binder after preheating to 60°C. The mixture was then vigorously stirred at 60°C for 2 hours to form a uniform slurry with good extrusion flowability and a solid content ≥50 vol%.

[0063] (2) Green body forming: Using a direct-write 3D printing equipment equipped with a 410μm diameter conical nozzle, a reactor green body with an external dimension of 50mm × 50mm × 20mm was printed. The green body contained continuously interlaced serrated (interlaced, spiral, fractal structure) microchannels (channel cross-section approximately 1.0mm × 1.0mm). After printing, the green body was placed in a -50℃ freezer for 12 hours to set the shape, and then transferred to a freeze dryer for vacuum drying for 24 hours.

[0064] (3) Pre-oxidation treatment: The dried green billet is placed in a muffle furnace and heated to 950°C at a rate of 3°C / min in an air atmosphere. It is then held at this temperature for 3 hours and then cooled to room temperature with the furnace.

[0065] (4) Sintering: The pre-oxidized green body is placed in a graphite sintering furnace, and after evacuation, high-purity argon is introduced as a protective atmosphere. First, the temperature is increased to 1550℃ at 5℃ / min and held for 1.5 hours; then the temperature is increased to 2000℃ at 8℃ / min and held for 1 hour; finally, the temperature is cooled to room temperature under program control.

[0067] The silicon carbide-boron nitride composite ceramic microchannel reactors prepared in Examples 1-3 were compared with the SiC ceramic microchannel reactors prepared by the reaction sintering method in the prior art. The three-point bending strength, fracture toughness (single-sided notched beam method), and thermal conductivity (laser flash method) were measured respectively. The results are shown in Table 1:

[0068]

[0069] As shown in Table 1, the three-point bending strength of the present invention is not much different from that of the existing SiC ceramic microchannel reactor, but it is far superior to the existing technology in terms of fracture toughness and thermal conductivity. This fully demonstrates that the technical solution of the present invention overcomes the shortcomings of high brittleness and low thermal shock resistance of SiC ceramic materials in the existing technology while retaining the advantage of high inherent strength of SiC materials.

[0071] Example 4:

[0072] This embodiment is used to specifically illustrate the application of the silicon carbide-boron nitride composite ceramic microchannel reactor of the present invention in the high-purity silicon preparation process based on chemical vapor deposition.

[0073] The silicon carbide-boron nitride composite ceramic microchannel reactor prepared in Example 1 was encapsulated in a 316L stainless steel shell, and a 3 mm wide annular sealed jacket was precision machined to serve as an independent temperature-controlled flow channel. Standardized quick-install flanges were integrated at both ends of the module, and high-precision temperature sensors (PT100, accuracy ±0.1℃) were installed at the inlet and outlet. The microchannel reactor itself served as a direct heating resistor, equipped with an independent multi-stage heater and thermocouple. The jacket was used for emergency cooling, thus creating a standard reaction module.

[0074] During operation, the temperature of the eight parallel standard reaction modules is controlled at 850℃±2℃. Temperature data from each module is uploaded in real time. The central controller runs a temperature field equalization algorithm to compare the average temperature of each module and analyze the gradient of multiple temperature measurement points within each module. When a module is found to be dissipating heat slightly faster due to its location at the system edge, the controller fine-tunes the heating power of that module and coordinates the cooling flow of the jackets of adjacent modules to reduce its thermal radiation impact, thus achieving thermal environment equalization at the system level.

[0076] Example 5:

[0077] This embodiment is used to specifically illustrate the application of the silicon carbide-boron nitride composite ceramic microchannel reactor of the present invention in the synthesis of intermediates for nitrated high-risk drugs.

[0078] The silicon carbide-boron nitride composite ceramic microchannel reactor prepared in Example 2 was encapsulated in a 316L stainless steel shell, and a 2 mm wide annular sealed jacket was precision-machined to serve as an independent temperature-controlled flow channel. Standardized quick-install flanges were integrated at both ends of the module, and high-precision temperature sensors (PT100, accuracy ±0.1℃) were installed at the inlet and outlet. An embedded online analysis probe was seamlessly integrated into the outlet flow path. This probe was connected via fiber optic to a UV-Vis spectrometer, Raman spectrometer, or near-infrared spectrometer to achieve in-situ, real-time, and continuous monitoring of the concentration or characteristic spectral signals of key components in the reaction liquid flow under flowing conditions. This forms a standard reaction module, and two of these standard reaction modules were connected in series to form a reaction unit.

[0079] During the process, an acetonitrile solution containing dissolved aromatic substrates and a pre-cooled mixture of concentrated nitric acid and concentrated sulfuric acid were respectively introduced into the reaction unit for reaction. Online ultraviolet spectroscopy continuously displayed the absorbance at 310 nm as a function of time (i.e., along the reactor flow path).

[0080] Initially, the control system observed that the absorbance decay rate was slightly lower than the simulation expectation. The system automatically reduced the reactor jacket temperature slightly from 5°C to 3°C while keeping other parameters constant. Subsequently, the absorbance decay curve matched the expected trajectory. When the ultraviolet signal reached the endpoint threshold, the control system confirmed the reaction was complete. The reaction solution immediately entered the ceramic membrane module, while the quenching alkali solution was automatically injected in proportion, achieving simultaneous quenching and filtration of by-product salts on the membrane surface. The filtrate, containing the target nitro compound, was collected directly in a designated container.

[0081] In this embodiment, the nitration reaction was carried out safely at 5°C, the product yield was consistently above 95% (HPLC purity > 99%), and the batch-to-batch variation was minimal.

[0083] Example 6:

[0084] This embodiment is used to specifically illustrate the application of the silicon carbide-boron nitride composite ceramic microchannel reactor of the present invention in the co-production of high-purity nano-calcium carbonate and high-purity ammonium sulfate from phosphogypsum.

[0085] The silicon carbide-boron nitride composite ceramic microchannel reactor prepared in Example 3 was encapsulated in a 316L stainless steel shell, and a 1.5 mm wide annular sealed jacket was precision machined to serve as an independent temperature-controlled flow channel. Standardized quick-install flanges were integrated at both ends of the module to unify the interfaces for materials, temperature control media, and sensors. This resulted in a standard reaction module.

[0086] Ammoniation reaction unit: Two standard modules (R1-A, R1-B) connected in parallel above are used as ammoniation reactors.

[0087] Carbonization reaction unit: Two standard modules (R2-A, R2-B) connected in parallel above are used as carbonization reactors.

[0088] The specific process flow is as follows:

[0089] Raw material pretreatment: Phosphogypsum powder (D50=15 μm) was mixed with deionized water and 0.5 wt% polycarboxylate dispersant to form a 20 wt% homogeneous slurry. The slurry was diluted to 4.0 mol / L with concentrated ammonia. Carbon dioxide gas (purity ≥99.5%) was metered using a mass flow controller.

[0090] Continuous cogeneration operation: Start the entire system, preheat to the set temperature, and establish a stable circulation. Phosphogypsum slurry and ammonia water are pumped into parallel R1-A and R1-B at a total flow rate of 100 mL / min, with a Ca:NH3 molar ratio of 1:2.1. The temperature is controlled at 30.0±0.5℃ and the pressure at 0.3 MPa. After the reaction, the slurry immediately enters the ceramic membrane microfiltration unit. The transmembrane pressure is controlled to obtain a clear ammonium sulfate filtrate (concentration ~20%) with a turbidity <1 NTU and a calcium hydroxide filter cake with a solid content >40%. When the pH at the R1-A outlet is monitored to be 11.2 and that at R1-B to be 10.8, the controller closes the R1-A ammonia water valve by 1.5% and opens the R1-B valve by 1.5% within 2 seconds. After 1 minute, the pH of both outlets stabilizes at 11.0±0.05.

[0091] Carbonization reaction: Calcium hydroxide slurry and 5% excess CO2 are introduced into parallel reactors R2-A and R2-B. The temperature is controlled at 25.0±0.3℃ and the pressure at 0.5 MPa. When the temperature in R2-A rises to 26.5℃ due to disturbance, the controller increases the jacket cooling oil flow rate by 40% within 20 seconds, causing its temperature to quickly return to 25.0℃, while the temperature of R2-B remains unchanged.

[0092] Ammonium sulfate refining: The liquid is adsorbed by activated carbon and concentrated by evaporation to a density of 1.25 g / cm³. 3 The solution was then cooled from 50°C to 20°C in a crystallizer at a rate of 0.5°C / min for crystallization. 90% of the mother liquor was reused.

[0093] Product collection: After carbonization, the slurry is aged, washed, and dried to obtain nano-calcium carbonate. Ammonium sulfate wet crystals are dried to obtain the finished product.

[0094] The nano-calcium carbonate product prepared in this embodiment has an average particle size of 42±6 nm and a specific surface area of ​​29.8 m². 2 / g, CaCO3 content >99.2%. Ammonium sulfate product: 20-60 mesh particles ≥92%, (NH4)2SO4 content ≥99.6%, nitrogen content ≥21.0%; moisture ≤0.15%; free acid (as H2SO4) ≤0.03%; heavy metals (as Pb) <3 ppm; phosphorus and fluorine content both <8 ppm. Overall: calcium conversion rate >98.5%, ammonia utilization rate >97%, carbon dioxide utilization rate >96%.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A silicon carbide-boron nitride composite ceramic microchannel reactor, characterized in that, The microchannel reactor is a unidirectional flow structure with three-dimensional flow channels. The raw materials for the microchannel reactor include, by mass fraction: Silicon carbide powder 75%-90%; Boron nitride powder 5%-18%; Sintering aids: 3%-8%.

2. The silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 1, characterized in that: The silicon carbide powder is submicron α-SiC, and the boron nitride powder is plate-shaped hexagonal boron nitride.

3. The silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 1, characterized in that: The sintering aid comprises a mixture of aluminum nitride and yttrium oxide, wherein the molar ratio of aluminum nitride to yttrium oxide is 1-1.5:

1.

4. The silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 1, characterized in that: The three-dimensional flow channel structure of the microchannel reactor includes interlaced, spiral, and fractal structures.

5. A method for preparing a silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 1, characterized in that, Includes the following steps: S1. Slurry preparation: Silicon carbide powder, boron nitride powder and sintering aid are prepared as raw materials according to volume percentage, placed in a ball mill jar, dispersant and deionized water are added, and ball milling is carried out to obtain a uniform premix; then water-based gel binder is added to the premix and high-speed stirring is carried out to form a ceramic slurry with a solid content ≥50 vol%. S2. Green body forming: The ceramic slurry is loaded into the barrel of the direct writing printer, and a green body component is printed according to the preset three-dimensional digital model of the microchannel reactor; the green body is immediately placed at -30℃ to -50℃ for freezing and shaping, and then transferred to a freeze dryer to sublimate the ice crystals in a vacuum environment to completely remove moisture and obtain a dried green body; S3. Pre-oxidation treatment: Place the dried green billet in a sintering furnace with an air atmosphere, heat it to 850℃-950℃ at a slow heating rate of 1-3℃ / min, and hold it at that temperature for 1-3 hours. S4. Sintering: The pre-oxidized green body is transferred to an atmosphere sintering furnace and sintered at 1450℃-1550℃ and 1900℃-2000℃ under the protection of flowing inert gas to prepare the required silicon carbide-boron nitride composite ceramic microchannel reactor.

6. The method for preparing the silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 5, characterized in that: The dispersant in step S1 includes ammonium polyacrylate, ammonium polymethacrylate, or ammonium polycarboxylate.

7. The method for preparing the silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 5, characterized in that: The aqueous gel binder in step S1 includes agarose, sodium alginate, or methylcellulose.

8. The method for preparing the silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 5, characterized in that, In step S4, the sintering process specifically includes: First stage: Increase the temperature to 1450℃-1550℃ at a rate of 3-5℃ / min, and hold for 0.5-1.5 hours; Second stage: Increase the temperature to 1900℃-2000℃ at a rate of 5-8℃ / min, and hold for 0.5-1 hour; It was then cooled to room temperature in the furnace.

9. The method for preparing the silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 5, characterized in that, It also includes the following steps: S5. Post-processing: Precision grinding is performed on the fluid inlet and outlet connection parts of the microchannel reactor, and standard interface flanges are assembled.

10. An application of the silicon carbide-boron nitride composite ceramic microchannel reactor as described in claim 1, characterized in that, Continuous flow processes used for strongly exothermic reactions, highly corrosive media, or high thermal shock loads include: High-purity nano-calcium carbonate and high-purity ammonium sulfate are produced by co-producing phosphogypsum. Ammonia synthesis process based on electrochemical nitrogen reduction reaction; High-purity silicon preparation process based on chemical vapor deposition; Synthesis of pharmaceutical intermediates; Processing of composite ceramic materials.

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