A system for directly cracking biogas to produce multi-walled carbon nanotubes and a method thereof

Abstract

The application provides a system for directly cracking biogas to prepare multi-walled carbon nanotubes and a method thereof, and belongs to the technical field of multi-walled carbon nanotube preparation, and solves the problem that multi-walled carbon nanotubes cannot be directly prepared from biogas without deep purification in the prior art. The system comprises a reaction tube, the outer side of the reaction tube is provided with a tube furnace, the inlet end of the reaction tube is connected with a hydrogen gas delivery pipeline, a biogas delivery pipeline and an inert gas delivery pipeline, the outlet end of the reaction tube is connected with an absorption tank for absorbing water and carbon dioxide through a pipeline, and the absorption tank is connected with a gas chromatograph and a hydrogen gas pressure swing adsorption device through a pipeline. According to the application, the biogas containing CH4, CO2, H2S and other components can be directly used as a carbon source without deep purification or reforming of the biogas, multi-walled carbon nanotubes can be efficiently generated under an optimized catalytic system, and high-value conversion of waste is realized.

Description

Technical Field

[0001] This invention belongs to the field of multi-walled carbon nanotube preparation technology, specifically to a system and method for directly preparing multi-walled carbon nanotubes from biogas. Background Technology

[0002] With increasing global focus on sustainable development and green chemistry, the preparation of carbon nanomaterials using renewable carbon sources has become a research hotspot in materials science. Carbon nanomaterials, especially multi-walled carbon nanotubes (MWCNTs), exhibit enormous application potential in numerous fields such as energy storage, composite material reinforcement, electronic devices, and catalyst supports due to their unique electronic structure, excellent mechanical properties, high electrical and thermal conductivity, etc. Traditional methods for preparing carbon nanomaterials largely rely on fossil fuel-derived carbon sources, such as methane and ethylene. This not only exacerbates dependence on non-renewable resources but also contradicts the globally advocated low-carbon and environmentally friendly principles. Therefore, developing carbon nanomaterial preparation technologies based on renewable carbon sources is of great significance for reducing carbon emissions, achieving resource recycling, and promoting the green and sustainable development of the nanomaterials industry.

[0003] Currently, some studies have attempted to convert biomass gasification or biogas reforming into syngas (mainly composed of CO and H2), and use this as a carbon source for the synthesis of carbon materials. However, this type of process faces many significant problems in practical applications: 1. Complex Process Flow: The conversion of biomass or biogas into syngas, and then into carbon nanomaterials, typically involves multiple conversion steps. Each step requires specific reaction conditions and equipment, involving the cascading of multiple unit operations, resulting in a lengthy and complex process flow. This not only increases equipment investment and floor space requirements but also raises operational difficulty and operating costs.

[0004] 2. High energy consumption: Most reaction steps in the multi-step conversion process require harsh conditions such as high temperature and high pressure. For example, biomass gasification usually needs to be carried out at a high temperature of 800-1200℃, and biogas reforming also requires high temperature and catalyst to achieve effective conversion. These high temperature and high pressure conditions require a large amount of energy to maintain, making the energy consumption of the entire process high and failing to meet the development requirements of energy conservation and emission reduction.

[0005] 3. Strict requirements for gas purity: The presence of impurities in the syngas can severely affect the synthesis quality of carbon nanomaterials and the activity of the catalyst. For example, trace amounts of sulfur compounds, chlorides, and other impurities may cause catalyst poisoning and deactivation, thereby reducing the yield and quality of carbon nanotubes. Therefore, in order to obtain high-quality carbon nanomaterials, the syngas needs to be deeply purified, which further increases the complexity and cost of the process.

[0006] 4. Difficulty in Achieving Economical and Efficient Large-Scale Application: Due to the combined effects of the complex process, high energy consumption, and strict requirements for gas purity, the cost of preparing carbon nanomaterials based on syngas is high, making it economically uncompetitive and hindering large-scale industrial application. This presents a significant obstacle to the promotion and popularization of this technology, preventing it from fully realizing its potential advantages in resource utilization and environmental protection.

[0007] Furthermore, residual sulfides and carbon dioxide in biogas can easily deactivate catalysts, further increasing the technical difficulty. Therefore, developing a technology that can directly utilize unrefined biogas (such as biogas from kitchen waste fermentation) to efficiently prepare high-quality multi-walled carbon nanotubes under simplified process conditions not only helps to enhance the resource value of organic waste but also provides a new pathway for the production of green, low-carbon nanomaterials. Currently, there is a lack of an integrated technical solution that combines biogas-adaptive pretreatment, anti-poisoning catalyst design, and efficient CVD in-situ conversion. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to provide a system and method for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes. This application eliminates the need for deep purification or reforming of biogas, and can directly use raw biogas containing components such as CH4, CO2, and H2S as a carbon source to efficiently generate multi-walled carbon nanotubes under an optimized catalytic system, thereby achieving high-value conversion of waste.

[0009] The technical solution adopted in this invention is as follows: A system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes includes a reaction tube with a tubular furnace on its outer side. The inlet end of the reaction tube is connected to a hydrogen delivery pipeline, a biogas delivery pipeline, and an inert gas delivery pipeline. The outlet end of the reaction tube is connected to an absorption box for absorbing water and carbon dioxide via a pipeline. The absorption box is connected to a gas chromatograph and a hydrogen pressure swing adsorption device via a pipeline.

[0010] Preferably, the absorption box is provided with a porous mesh, on which adsorbent material is placed, and the pipe connecting the reaction tube and the absorption box extends below the porous mesh.

[0011] Preferably, a gas injection device is provided on the pipeline between the absorption box and the gas chromatograph. The gas injection device includes a piston outer cylinder, a piston head is movably sealed in the piston outer cylinder, the piston head is connected to a push rod, an exhaust pipe is provided at the bottom of the piston outer cylinder, a first one-way valve is provided in the exhaust pipe to allow gas to flow from the piston outer cylinder to the gas chromatograph, an inlet pipe is provided on the side wall of the piston outer cylinder and the inlet pipe is close to the bottom of the piston outer cylinder, a second one-way valve is provided in the inlet pipe to allow gas to flow from the absorption box to the piston outer cylinder.

[0012] Preferably, a pressure control valve is installed on the pipeline between the absorption box and the hydrogen pressure swing adsorption device.

[0013] Preferably, the hydrogen delivery pipeline, biogas delivery pipeline, and inert gas delivery pipeline are all equipped with valves and mass flow controllers. The hydrogen delivery pipeline is connected to a hydrogen generator, the biogas delivery pipeline is connected to a biogas tank, and the inert gas delivery pipeline is connected to an inert gas tank.

[0014] A method for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes, using the aforementioned system, the method comprising the following steps: S1: Place the catalyst in the middle of the reaction tube, introduce inert gas into the reaction tube through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device to evacuate the reaction tube, and control the tube furnace to heat the reaction tube to the reaction temperature. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen delivery pipeline to pre-activate the catalyst in the reaction tube. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph for preheating. The biogas pipeline supplies biogas to the reaction tube, and at the same time, the gas chromatograph is turned on for online detection of tail gas. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph and cool down. Adjust the tubular furnace to perform the cooling program, continue to supply inert gas, and collect the product after cooling.

[0015] Preferably, in step S1, the reaction temperature is 500-1050℃ and the flow rate of the inert gas is 0-60L / h.

[0016] Preferably, in step S2, the pre-activation time of hydrogen is 30-120 min, and the gas flow rate is 0-60 L / h.

[0017] Preferably, the biogas contains 60-70% methane and 30-40% carbon dioxide.

[0018] Preferably, in step S4, the cooling program of the tubular furnace is set to 10-20℃ / min.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This application does not require deep purification or reforming of biogas. It can directly use raw biogas containing components such as CH4, CO2, and H2S as a carbon source to efficiently generate multi-walled carbon nanotubes under an optimized catalytic system, thereby achieving high-value conversion of waste. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart provided for an embodiment of the present invention; Figure 2 This is a schematic diagram of the gas injection device provided in an embodiment of the present invention; Figure 3 This is a morphology diagram of the carbon nanotubes provided in Embodiment 1 of the present invention; Figure 4 This is a diameter distribution diagram of the carbon nanotubes provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the methane conversion rate provided in Example 1 of the present invention; Figure 6 This is a morphology diagram of the carbon nanotubes provided in Embodiment 2 of the present invention; Figure 7 This is a diameter distribution diagram of the carbon nanotubes provided in Embodiment 2 of the present invention; Figure 8 This is a schematic diagram of the methane conversion rate provided in Example 2 of the present invention; Figure 9 This is a morphology diagram of the carbon nanotubes provided in Example 3 of the present invention; Figure 10 This is a diameter distribution diagram of the carbon nanotubes provided in Embodiment 3 of the present invention; Figure 11 This is a schematic diagram of the methane conversion rate provided in Example 3 of the present invention; Figure 12 This is a morphology diagram of the carbon nanotubes provided in Example 4 of the present invention; Figure 13 This is a diameter distribution diagram of the carbon nanotubes provided in Embodiment 4 of the present invention; Figure 14 This is a schematic diagram of the methane conversion rate provided in Example 4 of the present invention.

[0022] Reference numerals in the attached figures: 1-Hydrogen generator; 2-Biogas tank; 3-Inert gas tank; 4-Reaction tube; 5-Tube furnace; 6-Absorption box; 7-Porous mesh; 8-Injection device; 801-Piston outer cylinder; 802-Push rod; 803-Piston head; 804-Exhaust pipe; 805-First one-way valve; 806-Inlet pipe; 807-Second one-way valve; 9-Gas chromatograph; 10-Pressure control valve; 11-Hydrogen pressure swing adsorption device; 12-Valve; 13-Mass flow controller. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] In the description of this invention, it should be noted that if terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use, they are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0026] The following is combined with Figures 1-14 The present invention will be described in detail below.

[0027] Example: A system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes includes a reaction tube 4, a tubular furnace 5 disposed outside the reaction tube 4, a hydrogen delivery pipeline, a biogas delivery pipeline and an inert gas delivery pipeline connected to the inlet end of the reaction tube 4, and an absorption box 6 for absorbing water and carbon dioxide connected to the outlet end of the reaction tube 4 via a pipeline. The absorption box 6 is connected to a gas chromatograph 9 and a hydrogen pressure swing adsorption device 11 via a pipeline.

[0028] This application is based on the direct pyrolysis of kitchen waste fermentation biogas using the CVD method; the reaction tube 4 is horizontally set up for easy placement of the catalyst; a hydrogen delivery pipeline outputs hydrogen to activate the catalyst, ensuring its performance; an inert gas is used to isolate oxygen and reduce the concentration of biogas, preventing explosions caused by contact between biogas and oxygen in the reaction tube 4; biogas enters the reaction tube 4 along with the inert gas, and under high temperature and the action of the catalyst, the biogas is pyrolyzed to produce multi-walled carbon nanotubes, which accumulate in the reaction tube 4; the absorption box 6 absorbs water and carbon dioxide in the tail gas, preventing water vapor from damaging the internal metal components of the gas chromatograph 9 and preventing carbon dioxide from interfering with the methane conversion rate test (carbon dioxide and methane have similar peaks detected in the gas chromatograph 9); the gas chromatograph 9 performs online detection of the tail gas, analyzes the tail gas components, and thus determines the methane conversion rate; a hydrogen pressure swing adsorption device 11 (hydrogen pressure swing adsorption device 11 is existing technology) adsorbs and reuses hydrogen in the tail gas, reducing hydrogen waste.

[0029] This application does not require deep purification or reforming of biogas. It can directly use raw biogas containing components such as CH4, CO2, and H2S as a carbon source to efficiently generate multi-walled carbon nanotubes under an optimized catalytic system, thereby achieving high-value conversion of waste.

[0030] A porous mesh 7 is installed in the absorption chamber 6, on which adsorbent material is placed. The pipe connecting the reaction tube 4 and the absorption chamber 6 extends below the porous mesh 7. The adsorbent material used in this application is an alkaline molecular sieve (calcium oxide can be selected as the alkaline molecular sieve). The exhaust gas in the reaction tube 4 is introduced below the porous mesh 7, passes through the porous mesh 7 and contacts the adsorbent material, adsorbing water and carbon dioxide. The exhaust gas is then discharged from the top pipe of the absorption chamber 6.

[0031] A gas injection device 8 is installed on the pipeline between the absorption chamber 6 and the gas chromatograph 9. The gas injection device 8 includes a piston outer cylinder 801, a piston head 803 is movably sealed in the piston outer cylinder 801, and a push rod 802 is connected to the piston head 803. An exhaust pipe 804 is provided at the bottom of the piston outer cylinder 801. A first one-way valve 805 is provided in the exhaust pipe 804 to allow gas to flow from the piston outer cylinder 801 to the gas chromatograph 9. An inlet pipe 806 is provided on the side wall of the piston outer cylinder 801, and the inlet pipe 806 is close to the bottom of the piston outer cylinder 801. A second one-way valve 807 is provided in the inlet pipe 806 to allow gas to flow from the absorption chamber 6 to the piston outer cylinder 801. The gas chromatograph 9 of this application is an intermittent gas injection detection system to avoid long-term operation of the gas chromatograph 9. Therefore, the gas injection device 8 is provided to select whether to inject tail gas into the gas chromatograph 9 for detection as needed. Specifically: The operator can control the piston head 803 to move within the piston outer cylinder 801 via the push rod 802. When the piston head 803 is at the bottom of the piston outer cylinder 801, the piston head 803 blocks the air inlet pipe 806, preventing air from entering the air inlet pipe 806. When air injection is required, the piston head 803 is controlled to move upward, opening the air inlet pipe 806. Due to the setting of the first one-way valve 805 and the second one-way valve 807, a negative pressure is generated in the piston outer cylinder 801, forcing the exhaust gas in the air inlet pipe 806 into the piston outer cylinder 801. Then, the piston head 803 is pushed downward, and the exhaust gas in the piston outer cylinder 801 enters the gas chromatograph 9 through the first one-way valve 805 for detection.

[0032] A pressure control valve 10 is installed on the pipeline between the absorption tank 6 and the hydrogen pressure swing adsorption device 11. The pressure control valve 10 can display the pipeline pressure and can be controlled to adjust the pressure of the exhaust gas.

[0033] Each of the hydrogen, biogas, and inert gas delivery pipelines is equipped with a valve 12 and a mass flow controller 13. The hydrogen delivery pipeline is connected to a hydrogen generator 1, the biogas delivery pipeline is connected to a biogas tank 2, and the inert gas delivery pipeline is connected to an inert gas tank 3. The valve 12 controls the opening and closing of the relevant pipelines, and the mass flow controller 13 controls the delivery volume of the relevant gases.

[0034] A method for preparing multi-walled carbon nanotubes by directly pyrolyzing biogas includes the following steps: S1: Place the catalyst in the middle of the reaction tube 4, introduce inert gas into the reaction tube 4 through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device 11 to evacuate the reaction tube 4. Control the tube furnace 5 to heat the reaction tube 4 to the reaction temperature; the reaction temperature is 500-1050℃, and the inert gas flow rate is 0-60L / h. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen supply pipeline to pre-activate the catalyst in reaction tube 4; the pre-activation time of hydrogen is 30-120 min, and the gas flow rate is 0-60 L / h. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph 9 for preheating. Simultaneously, supply biogas to the reaction tube 4 via the biogas pipeline, and turn on the gas chromatograph 9 for online detection of the tail gas. The biogas contains 60-70% methane and 30-40% carbon dioxide. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph 9 and cool down, adjust the cooling program of the tubular furnace 5, continue to supply inert gas, and collect the product (a mixture of catalyst and carbon nanotubes) after cooling down; the cooling program of the tubular furnace 5 is set to 10-20℃ / min.

[0035] The gas chromatograph 9 uses intermittent gas inlet detection; the catalyst particle size is 5–50 nm; the inert gas is one or more combinations of argon, nitrogen, and helium.

[0036] Example 1: Multi-walled carbon nanotubes were prepared according to the following parameters: S1: Place the catalyst in the middle of the reaction tube 4, introduce inert gas into the reaction tube 4 through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device 11 to evacuate the reaction tube 4. Control the tube furnace 5 to heat the reaction tube 4 to the reaction temperature; the reaction temperature is 650℃, and the inert gas flow rate is 0-60L / h. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen supply pipeline to pre-activate the catalyst in reaction tube 4; the pre-activation time of hydrogen is 30 min, and the flow rate is 20-60 L / h. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph 9 for preheating. The biogas pipeline supplies biogas to the reaction tube 4, and at the same time, turn on the gas chromatograph 9 for online detection of tail gas. The proportion of methane in biogas is 70%, the proportion of carbon dioxide is 30%, and the detection frequency of the gas chromatograph 9 is 10 min / time. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph 9 and cool it down. Adjust the tubular furnace 5 to perform the cooling program, continue to supply inert gas, and collect the product after cooling. The cooling program of the tubular furnace 5 is set to 10℃ / min.

[0037] The carbon nanotubes prepared by catalytic biogas pyrolysis have an average diameter of 34 nm, and the biogas conversion rate reached 70%, indicating that the equipment can effectively convert biogas to produce carbon nanotubes with an average diameter of 34 nm.

[0038] Example 2: Multi-walled carbon nanotubes were prepared according to the following parameters: S1: Place the catalyst in the middle of the reaction tube 4, introduce inert gas into the reaction tube 4 through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device 11 to evacuate the reaction tube 4. Control the tube furnace 5 to heat the reaction tube 4 to the reaction temperature; the reaction temperature is 650℃, and the inert gas flow rate is 0-60L / h. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen supply pipeline to pre-activate the catalyst in reaction tube 4; the pre-activation time of hydrogen is 60 min, and the flow rate is 10-30 L / h. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph 9 for preheating. The biogas pipeline supplies biogas to the reaction tube 4, and at the same time, turn on the gas chromatograph 9 for online detection of tail gas. The proportion of methane in biogas is 70%, the proportion of carbon dioxide is 30%, and the detection frequency of the gas chromatograph 9 is 10 min / time. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph 9 and cool it down. Adjust the tubular furnace 5 to perform the cooling program, continue to supply inert gas, and collect the product after cooling. The cooling program of the tubular furnace 5 is set to 20℃ / min.

[0039] The carbon nanotubes prepared by catalytic biogas pyrolysis have an average diameter of 27 nm, and the biogas conversion rate reaches 70-80%, indicating that the equipment can effectively convert biogas to produce carbon nanotubes with an average diameter of 27 nm.

[0040] Example 3: Multi-walled carbon nanotubes were prepared according to the following parameters: S1: Place the catalyst in the middle of the reaction tube 4, introduce inert gas into the reaction tube 4 through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device 11 to evacuate the reaction tube 4. Control the tube furnace 5 to heat the reaction tube 4 to the reaction temperature; the reaction temperature is 650℃, and the inert gas flow rate is 0-60L / h. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen supply pipeline to pre-activate the catalyst in reaction tube 4; the pre-activation time of hydrogen is 80 min, and the gas flow rate is 40-60 L / h. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph 9 for preheating. The biogas pipeline supplies biogas to the reaction tube 4, and at the same time, turn on the gas chromatograph 9 for online detection of tail gas. The proportion of methane in biogas is 70%, the proportion of carbon dioxide is 30%, and the detection frequency of the gas chromatograph 9 is 20 min / time. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph 9 and cool it down. Adjust the tubular furnace 5 to perform the cooling program, continue to supply inert gas, and collect the product after cooling. The cooling program of the tubular furnace 5 is set to 20℃ / min.

[0041] The carbon nanotubes prepared by catalytic biogas pyrolysis have an average diameter of 22 nm, and the biogas conversion rate reaches 60-70%, indicating that the equipment can effectively convert biogas to prepare carbon nanotubes with an average diameter of 22 nm.

[0042] Example 4: Multi-walled carbon nanotubes were prepared according to the following parameters: S1: Place the catalyst in the middle of the reaction tube 4, introduce inert gas into the reaction tube 4 through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device 11 to evacuate the reaction tube 4. Control the tube furnace 5 to heat the reaction tube 4 to the reaction temperature; the reaction temperature is 650℃, and the inert gas flow rate is 0-60L / h. S2. After the temperature reaches the reaction temperature, hydrogen is supplied through the hydrogen supply pipeline to pre-activate the catalyst in reaction tube 4; the pre-activation time of hydrogen is 120 min, and the gas flow rate is 20-60 L / h. S3. After pre-activation is complete, stop supplying hydrogen and turn on the gas chromatograph 9 for preheating. The biogas pipeline supplies biogas to the reaction tube 4, and at the same time, turn on the gas chromatograph 9 for online detection of tail gas. The proportion of methane in biogas is 60%, the proportion of carbon dioxide is 40%, and the detection frequency of the gas chromatograph 9 is 10 min / time. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph 9 and cool it down. Adjust the tubular furnace 5 to perform the cooling program, continue to supply inert gas, and collect the product after cooling. The cooling program of the tubular furnace 5 is set to 15℃ / min.

[0043] The carbon nanotubes prepared by catalytic biogas pyrolysis have an average diameter of 28 nm, and the biogas conversion rate reached 70%, indicating that the equipment can effectively convert biogas to produce carbon nanotubes with an average diameter of 28 nm.

[0044] Advantages of this application: (1) High-value-added multi-walled carbon nanotubes are prepared directly from biogas fermented from kitchen waste, which greatly enhances the resource value of organic waste and reduces raw material costs.

[0045] (2) Realize solid-state storage of biomass carbon to reduce greenhouse gas emissions; clean hydrogen is produced simultaneously in the reaction to help achieve the "dual carbon" goal.

[0046] (3) No need for deep purification or reforming of biogas, the process is integrated and easy to operate, suitable for distributed and large-scale applications, promoting the circular economy and the self-reliance of high-end materials.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes, characterized in that, The system includes a reaction tube (4), a tubular furnace (5) is provided on the outside of the reaction tube (4), the inlet end of the reaction tube (4) is connected to a hydrogen delivery pipeline, a biogas delivery pipeline and an inert gas delivery pipeline, and the outlet end of the reaction tube (4) is connected to an absorption box (6) for absorbing water and carbon dioxide through a pipeline. The absorption box (6) is connected to a gas chromatograph (9) and a hydrogen pressure swing adsorption device (11) through a pipeline.

2. The system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes according to claim 1, characterized in that, The absorption box (6) is provided with a porous mesh (7), on which adsorbent material is placed. The pipe connecting the reaction tube (4) and the absorption box (6) extends into the bottom of the porous mesh (7).

3. The system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes according to claim 1, characterized in that, A gas injection device (8) is provided on the pipeline between the absorption box (6) and the gas chromatograph (9). The gas injection device (8) includes a piston outer cylinder (801), a piston head (803) is movably sealed in the piston outer cylinder (801), a push rod (802) is connected to the piston head (803), an exhaust pipe (804) is provided at the bottom of the piston outer cylinder (801), a first one-way valve (805) is provided in the exhaust pipe (804) to allow gas to flow from the piston outer cylinder (801) to the gas chromatograph (9), an inlet pipe (806) is provided on the side wall of the piston outer cylinder (801) and the inlet pipe (806) is close to the bottom of the piston outer cylinder (801), and a second one-way valve (807) is provided in the inlet pipe (806) to allow gas to flow from the absorption box (6) to the piston outer cylinder (801).

4. The system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes according to claim 1, characterized in that, A pressure control valve (10) is installed on the pipeline between the absorption box (6) and the hydrogen pressure swing adsorption device (11).

5. The system for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes according to claim 1, characterized in that, The hydrogen delivery pipeline, biogas delivery pipeline and inert gas delivery pipeline are all equipped with valves (12) and mass flow controllers (13). The hydrogen delivery pipeline is connected to a hydrogen generator (1), the biogas delivery pipeline is connected to a biogas tank (2), and the inert gas delivery pipeline is connected to an inert gas tank (3).

6. A method for directly pyrolyzing biogas to prepare multi-walled carbon nanotubes, characterized in that, The method using the system according to any one of claims 1-5 includes the following steps: S1: Place the catalyst in the middle of the reaction tube (4), introduce inert gas into the reaction tube (4) through the inert gas delivery pipeline, and at the same time turn on the hydrogen pressure swing adsorption device (11) to evacuate the reaction tube (4), and control the tube furnace (5) to heat the reaction tube (4) to the reaction temperature. S2. After the temperature reaches the reaction temperature, hydrogen is transported through the hydrogen pipeline to pre-activate the catalyst in the reaction tube (4). S3. After pre-activation is completed, stop supplying hydrogen and turn on the gas chromatograph (9) for preheating. The biogas pipeline supplies biogas to the reaction tube (4), and at the same time, the gas chromatograph (9) is turned on for online detection of tail gas. S4. After the reaction is complete, stop the biogas supply, turn off the gas chromatograph (9) and cool down, adjust the tubular furnace (5) to perform the cooling program, continue to supply inert gas, and collect the product after cooling down.

7. The method for preparing multi-walled carbon nanotubes by direct pyrolysis of biogas according to claim 6, characterized in that, In step S1, the reaction temperature is 500-1050℃ and the flow rate of the inert gas is 0-60L / h.

8. The method for preparing multi-walled carbon nanotubes by direct pyrolysis of biogas according to claim 6, characterized in that, In step S2, the pre-activation time of hydrogen is 30-120 min, and the gas flow rate is 0-60 L / h.

9. The method for preparing multi-walled carbon nanotubes by direct pyrolysis of biogas according to claim 6, characterized in that, The biogas contains 60-70% methane and 30-40% carbon dioxide.

10. The method for preparing multi-walled carbon nanotubes by direct pyrolysis of biogas according to claim 6, characterized in that, In step S4, the cooling program of the tubular furnace (5) is set to 10-20℃ / min.

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