A reactive sintered silicon carbide microchannel reactor and its preparation method

Abstract

The present invention relates to the technical field of fluid mixing and microchannel reaction equipment, and specifically to a reaction-sintered silicon carbide microchannel reactor and a preparation method thereof. The preparation method comprises the following steps: mixing silicon carbide powder, an activated carbon source, a phenolic resin, and an additive to prepare a ceramic slurry; the volume solid content of the ceramic slurry is between 40% and 56%; placing at least one channel mold in the ceramic slurry and performing a heat curing treatment under sealed conditions to control the volume shrinkage to ≤4.5% to obtain a cured green body; then performing a carbonization treatment under a protective atmosphere to obtain a carbonized green body; and then performing a sintering treatment to prepare a reaction-sintered silicon carbide microchannel reactor. Sealing and curing and increasing the solid content of the slurry reduce the shrinkage of the slurry during the curing stage, thereby reducing shrinkage and cracking of the green body during the carbonization process of the phenolic resin. The preparation process is simple and controllable, providing a guarantee for the realization of large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid mixing and microchannel reaction equipment, and particularly relates to a reaction-sintered silicon carbide microchannel reactor and a preparation method thereof. Background Art

[0002] Microreactors are small reaction systems manufactured using micromachining technology. Compared to traditional batch reaction processes, microreactors have the advantages of high-speed mixing, efficient heat transfer, good repeatability, and high safety performance. The submillimeter-scale fluid channels in microreactors have a high specific surface area, which can significantly enhance the heat and mass transfer effects of the reaction, reduce reaction conditions, greatly shorten reaction time, and improve product yield and conversion rate. In recent years, with the rapid development of micromachining technology, microreactors have been widely used in organic synthesis, polymerization reactions, nanomaterial preparation and other fields. In the current situation of increasingly serious environmental problems, microreactors can create a safer, more environmentally friendly, and more efficient way to produce chemical products, which is of great significance to the future development of the chemical industry.

[0003] Currently, commonly used materials for microreactors, such as metal, glass, and single-crystal silicon, can meet the mixing requirements of general fluid products. However, due to their poor thermal conductivity and corrosion resistance, these materials are no longer suitable for specialized reactions involving flammable, explosive, strong acid, and strong base reactions. Patent CN201210098405.4 discloses a method for fabricating a sheet-shaped microchannel reactor, primarily using transparent glass as a substrate. However, due to material limitations, this material is not corrosion-resistant and difficult to use in strong acid and alkali conditions, limiting its application. Patent CN109095927 discloses a method for fabricating a pressureless sintered silicon carbide microchannel reactor chip. However, due to the compression molding process, the complex microchannel structure cannot be fabricated through machining. Chips must be welded together to form a microchannel reactor, which is not only complex but also difficult to weld due to the inherent welding difficulties of silicon carbide ceramics. Patent CN114105645 proposes an intermediate product and method for preparing a silicon carbide microchannel reactor. Although the entire silicon carbide microchannel reactor can be prepared by molding in one step, the molding steps of the microchannel are cumbersome, and the obtained microchannel is incomplete and contains impurities.

[0004] Currently, silicon carbide microchannel reactors, which use silicon carbide as a carrier, have excellent chemical corrosion resistance, high temperature tolerance, and thermal conductivity, making them suitable for a variety of chemical reaction environments. The design of the microchannel reactor allows for efficient chemical reactions, mixing, and heat exchange inside, thus achieving a revolutionary change in industrial production. However, despite the numerous advantages of silicon carbide microchannel reactors, their preparation process still faces some challenges. Among them, the high volume shrinkage rate during the curing stage and the easy cracking of the prepared microchannel reactor are problems that need to be solved urgently.

[0005] Based on this, it is necessary to develop a preparation method for a silicon carbide microreactor suitable for silicon carbide materials with simple steps and complete microstructure, so as to reduce the volume shrinkage rate during the curing stage and avoid cracking problems. Summary of the Invention

[0006] In order to solve the problems that the existing microchannel reactor preparation process is complicated, the volume shrinkage rate is high during the curing stage, and the prepared microchannel reactor is prone to cracking, the purpose of the present invention is to provide a reaction-sintered silicon carbide microchannel reactor and a preparation method thereof.

[0007] To achieve the above objectives, the technical solutions of the present invention are as follows.

[0008] A first aspect of the present invention provides a method for preparing a reaction-sintered silicon carbide microchannel reactor, comprising the following steps:

[0009] Silicon carbide powder, activated carbon source, phenolic resin and additives are mixed to prepare ceramic slurry; the volume solid content of the ceramic slurry is 40-56%;

[0010] At least one channel mold is placed in a ceramic slurry and heat-cured under sealed conditions to control the volume shrinkage rate to ≤4.5% to obtain a solidified green blank; then, a carbonization treatment is performed under a protective atmosphere to obtain a carbonized green blank; and then a sintering treatment is performed to prepare a reaction-sintered silicon carbide microchannel reactor.

[0011] The present invention prepares a green body with microchannels by injecting a ceramic slurry into a mold pre-embedded with a polymer material microchannel mold, solidifying and carbonizing the ceramic slurry through a gel injection molding process, and then producing a complete microchannel reactor after secondary reaction and sintering. Because the ceramic slurry and the microchannel mold shrink differently, if the slurry shrinks significantly during the curing stage, it can cause cracking in the green body. Therefore, by sealing and curing and increasing the slurry's solid content, the shrinkage rate of the slurry during the curing stage is reduced. The polymer mold material is easily volatilized, reducing shrinkage and cracking of the green body during the carbonization process of the phenolic resin, thereby producing a crack-free silicon carbide microchannel reactor.

[0012] To reduce shrinkage during the curing phase, the present invention uses a sealed curing method to reduce solvent volatilization during the curing phase, achieving net-size molding. The preparation process employed in the present invention is simple and controllable. Silicon carbide microchannel reactors can be prepared using a common ceramic preparation process, namely, slurry preparation, injection molding, carbonization, and high-temperature sintering, providing a guarantee for large-scale industrial production.

[0013] In a preferred embodiment, the ceramic slurry has a volume solids content of 42-56%. The volume solids content is further preferably 45-54%. The present invention aims to reduce shrinkage during the curing phase by reducing the volume fraction of ethylene glycol in the slurry. Subsequent experiments have shown that as the volume solids content of the slurry increases, that is, as the volume fraction of ethylene glycol decreases, the shrinkage of the cured product decreases.

[0014] In a preferred embodiment, the viscosity of the ceramic slurry is controlled at 20-30 Pa·s.

[0015] The present invention designs ceramic slurries with different components to obtain ceramic slurries with different volume solid contents and viscosities. The volume solid content is controlled at 40-56%, preferably 42-56%, for example, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, etc. The viscosity is 20-30 Pa·s, for example, 20 Pa·s, 21 Pa·s, 22 Pa·s, 23 Pa·s, 24 Pa·s, 25 Pa·s, 26 Pa·s, 27 Pa·s, 28 Pa·s, 29 Pa·s, 30 Pa·s, etc. By adjusting the volume solid content and viscosity of the ceramic slurry to an appropriate range, the volume shrinkage during the curing stage can be effectively reduced, avoiding the problem of cracking of the ceramic body.

[0016] In a preferred embodiment, heat curing is performed under sealed conditions to control the volume shrinkage to 0.3-4.5%. Because the microchannel mold within the slurry does not shrink during the curing process, it is necessary to reduce the shrinkage of the slurry during the curing stage to avoid cracks caused by shrinkage mismatch. To this end, sealed curing is used to reduce the volatilization of ethylene glycol and the shrinkage of the blank. Preferably, controlling the volume shrinkage of the slurry in a sealed environment to 1.1-4.5% can prevent cracks in the blank.

[0017] In a preferred embodiment, the additives include solvents, dispersants and additives; and the ceramic slurry is made of the following raw materials in parts by weight:

[0018] 13-34 parts of silicon carbide powder, 10-18.2 parts of activated carbon source, 7.3-7.5 parts of phenolic resin, 6.2-7.6 parts of solvent, 0.2-0.6 parts of dispersant, and 0.8-1 part of auxiliary agent.

[0019] In a preferred embodiment, the solvent is ethylene glycol; the dispersant is polyethylene glycol 400; the auxiliary agent is benzenesulfonyl chloride; the activated carbon source is a mixture of nanocarbon black and diamond; and the mass ratio of nanocarbon black to diamond is 3.2-10.5:5.4-7.7. The present invention promotes the curing of the ceramic slurry by adding benzenesulfonyl chloride as a curing accelerator.

[0020] In a preferred embodiment, the ceramic slurry is made of the following raw materials in parts by weight:

[0021] 13-34 parts of silicon carbide powder, 3.2-10.5 parts of nano carbon black, 5.4-7.7 parts of diamond, 7.3-7.5 parts of phenolic resin, 6.2-7.6 parts of ethylene glycol, 0.2-0.6 parts of dispersant, and 0.8-1 part of auxiliary agent.

[0022] In a preferred embodiment, the ceramic slurry is prepared as follows:

[0023] Phenolic resin and solvent are mixed to obtain a premixed liquid; silicon carbide powder, activated carbon source, and dispersant are mixed to obtain a mixed material; the mixed material and premixed liquid are stirred and mixed, and then an auxiliary agent is added. The stirring and mixing is continued, and the mixture is filtered and defoamed to obtain a ceramic slurry. The defoaming time of the slurry is 0.5 to 1 hour.

[0024] In the present invention, ethylene glycol is used as a solvent to dissolve the phenolic resin, uniformly dispersing the phenolic resin in the premix. The addition of ethylene glycol can adjust the viscosity of the premix to control the viscosity of the ceramic slurry between 20 and 30 Pa·s, improve the volume shrinkage during the curing stage, and improve the wettability of the phenolic resin with other solid particles, reducing agglomeration.

[0025] In a preferred embodiment, the channel mold is made of a polymer material with a decomposition temperature below 800° C., and the polymer material is polytetrafluoroethylene or polyvinyl chloride.

[0026] The channel mold is made of a polymer material with a decomposition temperature below 800°C, lower than the carbonization temperature of the phenolic resin, and decomposes to form channels before carbonization. The resulting microchannel mold decomposes to form channels before the phenolic resin carbonizes. By varying the shape and size of the microchannel mold, ceramic blanks with microchannels of varying shapes and sizes can be produced, preventing shrinkage during carbonization that could cause cracking. The channel mold is prepared using machining, casting, or polymer processing techniques. When there is one channel mold, it is a microchannel mold, used to simulate the reactor microchannels. When there are two channel molds, they comprise a microchannel mold and a heat channel mold. The shapes of the microchannel and heat channel molds simulate the reactor microchannels and heat exchange channels, and are shaped using machining, casting, or polymer processing techniques.

[0027] In a preferred embodiment, the conditions for thermal curing treatment are: curing temperature 140-160°C, curing time 12-18h; curing temperature examples include 140°C, 145°C, 150°C, 155°C, 160°C, etc.; curing time examples include 12h, 14h, 16h, 18h, etc.

[0028] The conditions for carbonization treatment are: carbonization temperature of 750-850°C, carbonization time of 2-5h; protective atmosphere is flowing nitrogen atmosphere; carbonization temperature, for example, is 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 710°C, 820°C, 830°C, 840°C, 850°C, etc.; carbonization time, for example, is 2h, 3h, 4h, 5h, etc.

[0029] The sintering conditions are: a sintering temperature of 1700-1800°C and a sintering time of 2-5 hours. Examples of sintering temperatures include 1700°C, 1720°C, 1740°C, 1750°C, 1760°C, 1780°C, and 1800°C; and sintering times include 2 hours, 3 hours, 4 hours, and 5 hours. Sintering involves transferring the carbonized green blank into a graphite crucible containing silicon powder and then sintering it in a vacuum siliconizing furnace.

[0030] The second aspect of the present invention provides a reaction-sintered silicon carbide microchannel reactor prepared by the preparation method described in the first aspect.

[0031] Beneficial effects of the present invention:

[0032] 1. The present invention injects ceramic slurry into a mold pre-embedded with a polymer microchannel mold for gel casting. Furthermore, through cross-linking and curing in a sealed environment, the curing shrinkage is controlled, eliminating cracks caused by shrinkage mismatch between the green body and the solid microchannel mold. The cured green body is carbonized under a flowing protective atmosphere and cracked to produce a reaction-sintered green body with microchannels. After secondary reaction sintering, a complete microchannel reactor is obtained. The present invention primarily reduces the shrinkage of the ceramic slurry during the curing stage through sealed curing and increasing the solids content of the slurry, thereby reducing shrinkage cracking of the green body during the carbonization process of the phenolic resin.

[0033] 2. The preparation method of the present invention eliminates the need for mechanical processing of the microchannel structure of the silicon carbide microreactor and welding of the silicon carbide wafers, directly producing a complete silicon carbide microchannel reactor. Furthermore, this preparation method utilizes abundant raw materials at low cost, and the preparation process is simple and controllable, making it promising for large-scale industrial production.

[0034] 3. The silicon carbide microchannel reactor prepared by the present invention utilizes secondary reaction to reduce residual silicon, has the performance characteristics of high thermal conductivity and corrosion resistance, and also has a complex microchannel structure, and parameters such as shape and size are controllable, which is suitable for use in high-risk working conditions with flammable and explosive, strong acid and strong alkali. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the silicon carbide microchannel reactor prepared in Example 3.

[0036] Figure 2 This is the macroscopic morphology of the silicon carbide microchannel reactor prepared in Example 1.

[0037] Figure 3 This is a macroscopic morphology of the channel cross section of the silicon carbide microchannel reactor prepared in Example 1.

[0038] Figure 4 This is the XRD spectrum of the polished surface of the silicon carbide microchannel reactor prepared in Example 1.

[0039] In the figure, 1. Silicon carbide blank; 2. Microchannel mold; 3. Heat exchange channel mold. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] During the preparation and research process of the silicon carbide microchannel reactor, the inventor's research group discovered that silicon carbide materials are prone to volume shrinkage during the curing process due to changes in internal stress and reorganization of the material structure. If the shrinkage rate is too high and the internal microchannel mold does not shrink during the curing stage, it will cause a mismatch between the shrinkage of the internal microchannel mold and the internal microchannel mold, resulting in structural deformation, dimensional instability, cracks, and even affecting the performance and service life of the reactor.

[0044] Based on this, and to address the existing problems of complex microchannel reactor preparation processes, high volume shrinkage during the curing phase, and the resulting cracking, the present invention reduces the shrinkage of the slurry during the curing phase by sealing and curing and increasing the solids content of the slurry, thereby reducing shrinkage and cracking of the green body during the carbonization process of the phenolic resin. Furthermore, the preparation process is simple and controllable, providing a guarantee for large-scale industrial production.

[0045] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0046] Unless otherwise specified, the methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified. The phenolic resins described in the following examples are commercially available phenolic resins.

[0047] Example 1

[0048] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0049] S1. Weigh 7.5g of phenolic resin and 6.2g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 34g of silicon carbide powder, 10.5g of nanocarbon black, 7.7g of diamond, and 0.6g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 1g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 56%.

[0050] S2. Preparation of Microchannel Mold 2 Using Polytetrafluoroethylene (PTFE) Rods: The microchannel mold used in this experiment was prepared by heating and shaping a 1 mm diameter polytetrafluoroethylene rod. The polytetrafluoroethylene rod was heated and shaped at 100-120°C to obtain a microchannel shape, thereby forming the microchannel mold.

[0051] S3. Place the microchannel mold prepared with polytetrafluoroethylene as raw material in the ceramic slurry mold, then pour in the defoamed ceramic slurry, then seal it in a sealed container, and put it in a 150°C oven for curing for 15 hours to obtain a cured sample.

[0052] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep the temperature for 4 hours to obtain a carbonized green blank.

[0053] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0054] The silicon carbide green body was solidified in a sealed container, and the volume shrinkage during the solidification stage was 0.3%. Compared with the sample solidified in a non-sealed environment, the volume shrinkage of the ceramic slurry during the solidification stage was reduced. The surface of the silicon carbide microchannel reactor obtained in Example 1 was intact and had no obvious defects, such as Figure 2 As shown. The silicon carbide microchannel reactor was cut open to observe the channel. The channel completely retained the shape and size of the microchannel mold, as shown Figure 3 shown.

[0055] Example 2

[0056] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0057] S1. Weigh 7.5g of phenolic resin and 6.2g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 22g of silicon carbide powder, 10.5g of nanocarbon black, 7.7g of diamond, and 0.6g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 1g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then, transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 50%.

[0058] S2. Preparation of Microchannel Mold 2 Using Meltable Polytetrafluoroethylene (PTFE): The microchannel mold used in this experiment was prepared using injection molding. Meltable polytetrafluoroethylene was evenly poured into the injection molding machine and heated to 380°C. The mold was then heated to 200°C using a hydraulic press. The injection rate was controlled at 10 mm / s to ensure that the molten material evenly and completely filled the mold. The pressure was maintained at 40 MPa for 10 seconds. After cooling and solidification, the mold was removed from the mold and polished to a thickness of 2 mm to complete the microchannel mold.

[0059] S3. Place the microchannel mold prepared with polytetrafluoroethylene as raw material in the ceramic slurry mold, then pour in the defoamed ceramic slurry, then seal it in a sealed container, and put it in a 150°C oven for curing for 15 hours to obtain a cured sample.

[0060] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep the temperature for 4 hours to obtain a carbonized green blank.

[0061] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0062] The silicon carbide green body solidified in a sealed container, with a volume shrinkage of 1.1% during the solidification phase; this volume shrinkage was higher than that of a ceramic slurry with a higher solids content. The silicon carbide microchannel reactor obtained in Example 2 had an intact surface, free of obvious defects. When the silicon carbide microchannel reactor was cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel mold.

[0063] Example 3

[0064] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0065] S1. Weigh 7.4g of phenolic resin and 7.6g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 20g of silicon carbide powder, 3.2g of nanocarbon black, 6.8g of diamond, and 0.2g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 0.8g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 42%.

[0066] S2. Preparation of Microchannel Mold 2 and Heat Exchange Channel Mold 3 Using Polyvinyl Chloride (PVC): The microchannel mold and heat exchange channel mold used in this experiment were cut from 2mm thick PVC sheets. After precisely positioning the PVC sheet in the cutting area, the cutting parameters and path were adjusted. After selecting the cutting tool, the polymer sheet was automatically cut using the cutting tool. The cut samples were inspected for dimensional accuracy and surface quality, and then ground and polished to create the microchannel molds.

[0067] S3, placing the microchannel mold and heat exchange channel mold made of polyvinyl chloride as raw material into the ceramic slurry mold, such as Figure 1 , then pour in the defoamed ceramic slurry, then place it in a sealed container, seal it, and put it in a 150°C oven for curing for 15 hours to obtain a cured sample.

[0068] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep the temperature for 4 hours to obtain a carbonized green blank.

[0069] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0070] The silicon carbide green body was solidified in a sealed container, and the volume shrinkage during the solidification stage was 2.6%. Example 3 A silicon carbide microchannel reactor with two channels inside was prepared, such as Figure 1 One channel can be used as a reaction channel and the other as a heat exchange channel. The resulting silicon carbide microchannel reactor has a complete surface with no obvious defects. When the silicon carbide microchannel reactor is cut open to observe the channels, both channels fully retain the shape and size of the microchannel mold.

[0071] Example 4

[0072] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0073] S1. Weigh 7.3g of phenolic resin and 6.4g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 13g of silicon carbide powder, 5.9g of nanocarbon black, 5.4g of diamond, and 0.2g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 1g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 40%.

[0074] S2. Microchannel Mold 2 Using Polyvinyl Chloride (PVC): The microchannel mold used in this experiment was prepared by heating and shaping a 2mm diameter PVC tube. The PVC tube was heated at 100-120°C to form the microchannel shape, creating the microchannel mold.

[0075] S3. Place the microchannel mold prepared with polyvinyl chloride as raw material in the ceramic slurry mold, then pour in the defoamed ceramic slurry, then seal it in a sealed container, and put it in a 150°C oven for curing for 15 hours to obtain a cured sample.

[0076] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep it at that temperature for 4 hours to obtain a carbonized green blank.

[0077] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0078] The silicon carbide green body solidified in a sealed container, with a volume shrinkage of 4.5% during the solidification phase; this volume shrinkage was higher than that of a ceramic slurry with a higher solids content. The silicon carbide microchannel reactor prepared in Example 4 had an intact surface, free of obvious defects. When the silicon carbide microchannel reactor was cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel mold.

[0079] Example 5

[0080] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0081] S1. Weigh 7.3g of phenolic resin and 6.4g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 13g of silicon carbide powder, 5.9g of nanocarbon black, 5.4g of diamond, and 0.2g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 1g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 40%.

[0082] S2. Preparation of Microchannel Mold 2 Using Polyvinyl Chloride (PVC): The microchannel mold used in this experiment was prepared using injection molding. PVC was evenly poured into the injection molding machine and heated to 200°C. A hydraulic press was used to heat the mold to 50°C. The injection rate was controlled at 10 mm / s to ensure that the melt filled the mold evenly and completely. The pressure was maintained at 20 MPa for 10 seconds. After cooling and solidification, the mold was removed from the mold and polished to a thickness of 2 mm. This completed the microchannel mold.

[0083] S3: A microchannel mold made of polyvinyl chloride (PVC) was placed inside a ceramic slurry mold. The defoamed ceramic slurry was then poured into the mold. The mold was then placed directly into a 150°C oven for curing for 15 hours to obtain a cured sample. During the curing of the silicon carbide green body, the ceramic slurry was placed directly into the oven for curing, without controlling its shrinkage during the curing stage.

[0084] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep the temperature for 4 hours to obtain a carbonized green blank.

[0085] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0086] The silicon carbide green body of Example 5, due to not curing in a sealed container and the low solids content of the slurry, exhibited a significant volume shrinkage of 7.4% during the curing stage. The silicon carbide microchannel reactor prepared in Example 5 exhibited cracks at the point where the surface contacted the microchannel mold. When the silicon carbide microchannel reactor was cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel mold, but significant cracks were observed around the channels.

[0087] Example 6

[0088] A method for preparing a reaction-sintered silicon carbide microchannel reactor comprises the following steps:

[0089] S1. Weigh 7.4g of phenolic resin and 7.6g of ethylene glycol and stir for 0.5h to obtain a well-mixed premix. Weigh 15g of silicon carbide powder, 3.2g of nanocarbon black, 6.8g of diamond, and 0.2g of polyethylene glycol 400 and mix to obtain a mixture. Add the mixture to the premix and stir for 6h to obtain a well-mixed ceramic slurry. Add 0.8g of benzenesulfonyl chloride to the ceramic slurry and stir for 0.5h. Then transfer the mixture to a suction flask and connect a vacuum pump to perform vacuum defoaming for 1h while using magnetic stirring to obtain a defoamed ceramic slurry. The volume solids content of the ceramic slurry for preparing the silicon carbide green body is 41%.

[0090] S2. Preparation of Microchannel Mold 2 Using Polyethylene (PE): The microchannel mold used in this experiment was prepared by cutting 2 mm thick polyethylene sheet. After precisely positioning the polyethylene sheet in the cutting area, the cutting parameters and path were adjusted. After selecting the cutting tool, the polymer sheet was automatically cut using the cutting tool. The cut sample was inspected for dimensional accuracy and surface quality, and then ground and polished to create the microchannel mold.

[0091] S3: A microchannel mold made of polyethylene was placed inside a ceramic slurry mold, followed by the defoamed ceramic slurry. The mold was then placed in a 150°C oven for curing for 15 hours to obtain a cured sample. During the curing of the silicon carbide green body, the ceramic slurry was placed directly into the oven for curing, without controlling its shrinkage during the curing stage.

[0092] S4. Place the solidified sample in an atmosphere furnace and carbonize it under a N2 protective atmosphere. Raise the temperature to 800°C at a heating rate of 3°C / min and keep the temperature for 4 hours to obtain a carbonized green blank.

[0093] S5. Place the carbonized blank into a graphite crucible, place silicon powder at the bottom of the graphite crucible, place it in a vacuum resistance furnace, heat it to 1600°C and keep it warm for 6 hours, wherein the heating rate from room temperature to 1100°C is 15°C / min, and the heating rate from 1100°C to 1600°C is 4°C / min, to obtain a silicon carbide microreactor.

[0094] The silicon carbide green body of Example 6, due to not being cured in a sealed container and the low solids content of the slurry, exhibited a significant volume shrinkage of 7.1% during the curing stage. The silicon carbide microchannel reactor prepared in Example 6 exhibited cracks at the point where the surface contacted the microchannel mold. When the silicon carbide microchannel reactor was cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel mold intact, but significant cracks were observed around the channels.

[0095] The raw material ratios of the ceramic slurries with different solid contents in the above embodiments are shown in Table 1. The solid content of the ceramic slurry is adjusted by changing the ratio of the raw materials, thereby regulating the shrinkage of the ceramic slurry during the curing stage.

[0096] Table 1 Raw material ratios of ceramic slurries with different solid contents in various embodiments

[0097]

[0098] Note: The dispersant is polyethylene glycol 400. The auxiliary agent is benzenesulfonyl chloride.

[0099] Figure 1 Schematic diagram of the silicon carbide microchannel reactor prepared in Example 3. Figure 1 The silicon carbide body 1 is prepared using a gel-casting process, with the microchannel mold 2 and heat exchange channel mold 3 symmetrically positioned within the body. The microchannel mold 2 or heat exchange channel mold 3 is made of a polymer material with a decomposition temperature below 600°C. The microchannel mold 2 and heat exchange channel mold 3 are placed within the silicon carbide body 1 and cured, carbonized, and sintered in a sealed container to produce a reaction-sintered silicon carbide microchannel reactor.

[0100] Figure 2 This is a macroscopic morphology of the silicon carbide microchannel reactor prepared in Example 1. Figure 2 As shown, there are no obvious defects on the surface of the reaction-sintered silicon carbide microchannel reactor.

[0101] Figure 3 This is a macroscopic morphology of the cross section of the channel of the silicon carbide microchannel reactor prepared in Example 1. Figure 3 for Figure 2 Macroscopic morphology along the cross section of the channel. Figure 3 As shown, the channels of the reactive sintered silicon carbide microchannel reactor remain intact.

[0102] Figure 4 This is an XRD spectrum of the polished surface of the silicon carbide microchannel reactor prepared in Example 1. As can be seen from the XRD spectrum, the phase composition of the reaction-bonded silicon carbide microchannel reactor prepared by the method of Example 1 is mainly β-phase silicon carbide and α-phase silicon carbide, as well as a small amount of silicon phase, indicating that it has good corrosion resistance.

[0103] Table 2 Effects of curing conditions and slurry volume solid content on the shrinkage of the cured body and the macroscopic morphology of the green body

[0104]

[0105] Note: Because the methods described in the above examples incorporate corresponding channel molds within the slurry, such as microchannel molds and heat exchange channel molds, the slurry surrounding the channel molds may crack due to shrinkage mismatch. Therefore, it is necessary to reduce the shrinkage of the slurry solidification to prevent excessive shrinkage and cracking of the ceramic green body. The shrinkage of the slurry solidification is measured based on the volume change of the green body before and after curing.

[0106] The results in Table 2 show that the silicon carbide green bodies of Examples 1-4 were all cured in sealed containers with slurry volume solids contents ranging from 40% to 56%. The volume shrinkage of the silicon carbide green bodies during the curing stage ranged from 0.3% to 4.5%. This indicates that as the volume solids content of the slurry decreases, the volume shrinkage of the silicon carbide green bodies during the curing stage increases. However, the silicon carbide microchannel reactors prepared in Examples 1-4 exhibited intact surfaces with no apparent defects. When the silicon carbide microchannel reactors were cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel mold and the heat exchange channel mold.

[0107] Compared to Examples 1-4, Examples 5-6 exhibited a greater volumetric shrinkage due to the fact that the silicon carbide green bodies were not cured in a sealed container and the slurry had a lower solids content. The volumetric shrinkage of the silicon carbide green bodies during the curing stage was 7.1-7.4%, which was greater than that of Examples 1-4. Furthermore, cracks were present on the surface of the silicon carbide microchannel reactors prepared in Examples 5-6 where they contacted the microchannel mold. When the silicon carbide microchannel reactors were cut open to inspect the channels, the channels retained the shape and dimensions of the microchannel molds, but significant cracks were present around the channels.

[0108] The above analysis shows that by adjusting the solids content of the ceramic slurry to 42-56% by varying the raw material ratio and curing the silicon carbide green body in a sealed container, the volume shrinkage of the silicon carbide green body during the curing stage can be effectively reduced. This ensures that the surface of the prepared silicon carbide microchannel reactor is intact and free of obvious defects, and the internal channels are intact, preserving the shape and size of the microchannel mold and heat exchange channel mold. The above test results show that reducing the shrinkage of the cured slurry can prevent the ceramic body from cracking.

[0109] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a reaction-sintered silicon carbide microchannel reactor, characterized in that: The following steps are involved: Silicon carbide powder, activated carbon source, phenolic resin and additives are mixed to prepare ceramic slurry; the volume solid content of the ceramic slurry is 40-56%; Placing at least one channel mold in the ceramic slurry and performing a heat curing treatment under a sealed condition to control the volume shrinkage to be ≤4.5% to obtain a cured green blank; Then, a carbonization treatment is performed under a protective atmosphere to obtain a carbonized green blank; and then a sintering treatment is performed to prepare a reaction-sintered silicon carbide microchannel reactor.

2. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, characterized in that: The volume solid content of the ceramic slurry is 42-56%.

3. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, characterized in that: The viscosity of the ceramic slurry is controlled at 20-30 Pa·s.

4. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, wherein: The heat curing treatment is carried out under sealing conditions to control the volume shrinkage rate to 0.3 to 4.5%.

5. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, characterized in that: The additives include solvents, dispersants and additives; The ceramic slurry is made from the following raw materials in parts by weight: 13-34 parts of silicon carbide powder, 10-18.2 parts of activated carbon source, 7.3-7.5 parts of phenolic resin, 6.2-7.6 parts of solvent, 0.2-0.6 parts of dispersant, and 0.8-1 part of auxiliary agent.

6. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 5, characterized in that: The solvent is ethylene glycol; the dispersant is polyethylene glycol 400; the auxiliary agent is benzenesulfonyl chloride; the activated carbon source is a mixture of nano-carbon black and diamond; and the mass ratio of nano-carbon black to diamond is 3.2-10.5:5.4-7.

7.

7. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 5, characterized in that: The ceramic slurry is prepared as follows: Phenolic resin and solvent are mixed to obtain a premixed liquid; silicon carbide powder, an activated carbon source and a dispersant are mixed to obtain a mixed material; the mixed material and the premixed liquid are stirred and mixed, an auxiliary agent is added, stirring and mixing is continued, filtering and defoaming are performed to obtain a ceramic slurry.

8. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, characterized in that: The channel mold is made of a polymer material with a decomposition temperature below 800° C., and the polymer material is polytetrafluoroethylene or polyvinyl chloride.

9. The method for preparing a reaction-sintered silicon carbide microchannel reactor according to claim 1, characterized in that: The conditions for heat curing treatment are: curing temperature 140-160°C, curing time 12-18h; The carbonization treatment conditions are as follows: carbonization temperature is 750-850°C, carbonization time is 2-5h, and protective atmosphere is flowing nitrogen atmosphere; The sintering conditions are: sintering temperature 1700-1800°C, sintering time 2-5h.

10. A reaction-bonded silicon carbide microchannel reactor prepared by the preparation method according to any one of claims 1 to 9.

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