Methane cracking carbon preparation method based on molten medium regulation and control

Abstract

The invention relates to the technical field of methane cracking carbon preparation, in particular to a methane cracking carbon preparation method based on molten medium regulation and control. The method comprises the following steps: placing a molten medium catalyst in a tubular furnace, heating to a reaction temperature at a heating rate of 7-10 DEG C / min, introducing argon in the heating process, introducing methane when the temperature is raised to the reaction temperature, cooling to room temperature in an argon atmosphere after the reaction is finished, and collecting the prepared carbon product, wherein the reaction temperature is 850-1000 DEG C; the molten medium catalyst comprises a modified metal-based material and chlorate; the modified metal-based material comprises modified metal and foam metal.

Description

Technical Field

[0001] This application relates to the technical field of methane cracking to produce carbon, and particularly relates to a method for methane cracking to produce carbon based on molten medium regulation. Background Art

[0002] As one of the cleanest fossil fuels, the high-value clean utilization of natural gas is regarded as one of the key technologies with broad development prospects in the energy transition, and thus has received extensive attention. The utilization method of natural gas is mostly direct combustion for energy supply, generating a large amount of carbon dioxide. At present, in addition to direct combustion, the industrial-scale utilization methods also include steam methane reforming (SMR). In this process, methane and steam are catalyzed to obtain carbon dioxide and hydrogen, and there is still carbon dioxide emission. Methane cracking to produce hydrogen and carbon products not only has no carbon dioxide emission, but also can produce value-added carbon products.

[0003] Catalyzing methane cracking with a molten medium, under the action of bubbles and density, carbon can float on the surface of the melt to achieve long-term continuous reaction. There are problems with molten metal catalysis such as high reaction temperature (greater than 1000 °C) and a large amount of metal impurities remaining in the carbon product; molten salt catalysis can remove a large amount of impurities by simple water washing, but the activity is low. Therefore, it is particularly important to find a way to achieve higher activity of methane cracking at a lower temperature, thereby producing carbon products with less impurity content and how to directly apply the carbon product containing a small amount of metal. Summary of the Invention

[0004] To achieve the purpose mentioned in the background art, this application provides a method for methane cracking to produce carbon based on molten medium regulation, which is characterized in that it includes the following steps: Place the molten medium catalyst in a tubular furnace, heat it to the reaction temperature at a heating rate of 7 - 10 °C / min, and introduce argon during the heating process. When the reaction temperature is reached, introduce methane. After the reaction is completed, cool it to room temperature in an argon atmosphere, and collect the produced carbon product. The reaction temperature is 850 - 1000 °C; The molten medium catalyst includes a modified metal-based material and a chloride salt; The modified metal-based material includes a modified metal and a foam metal. The preparation method of the modified metal includes: Disperse metal particles in ethanol, then add a nano boron nitride dispersion, stir for 2 h, dry at 80 °C, and calcine in an argon atmosphere at 600 °C for 1 h to form a boron nitride adsorption layer to obtain metal-boron nitride. The mass-volume ratio of the metal particles to ethanol is 1 g : 20 mL, the volume of the nano boron nitride dispersion is 40 - 60% of the ethanol, and the concentration of the nano boron nitride dispersion is 0.1 mg / mL; Prepare a 0.1 mol / L NH4VO3 solution, adjust the pH to 3. After adding the metal-boron nitride into it, react at 80 °C for 2 h. After filtration, calcine in a nitrogen atmosphere at 500 °C for 3 h to obtain precursor particles. The mass-volume ratio of the metal-boron nitride to the NH4VO3 solution is 1 g : 20 mL; Immerse the precursor particles in an acetic acid solution of 2 wt% chitosan oligosaccharide, stir at room temperature for 6 h. After filtration and drying, calcine in an argon atmosphere at 700 °C for 2 h to obtain the modified metal. The mass-volume ratio of the precursor particles to the acetic acid solution of 2 wt% chitosan oligosaccharide is 1 g : (15 - 25) mL.

[0005] Preferably, the preparation method of the modified metal-based material comprises the following steps: Immerse the modified metal and the foam metal successively in acetone, deionized water, and ethanol and perform ultrasonic treatment for 30 - 40 min; Continue to immerse the modified metal and the foam metal in a 0.5 - 1 mol / L hydrochloric acid solution and perform ultrasonic treatment for 30 - 50 min; Continue to immerse the modified metal and the foam metal in deionized water and perform ultrasonic treatment for 40 - 50 min, then transfer to a vacuum drying oven for drying treatment. Make the modified metal into a spherical or foil shape, and then place the modified metal and the foam metal in the tube furnace reaction tube in the following manner: Along the length direction of the tube furnace reaction tube, methane gas enters from the bottom end of the tube furnace reaction tube and passes through the foam metal and the modified metal in sequence. The diameter of the foam metal is equal to the inner diameter of the tube furnace reaction tube.

[0006] Preferably, the thickness of the foam metal is 5 mm and the pore size is 60 ppi.

[0007] Preferably, the chloride salt is one or more of KCl, NaCl, NiCl2, and MnCl2.

[0008] Preferably, the metal particles are one or more of copper, nickel, and iron; The foam metal is one or more of copper, nickel, and iron.

[0009] Preferably, when argon is introduced during the heating process, the reaction is carried out at atmospheric pressure, the argon flow rate is 20 - 80 mL / min, and the methane flow rate is 20 - 60 mL / min.

[0010] Preferably, after collecting the prepared carbon product, the following steps are further included: Perform suction filtration and washing of the carbon product with deionized water for 5 - 7 times, and dry to obtain the carbon product; Alternatively, the carbon product is subjected to suction filtration and washing with deionized water 5 - 7 times, transferred into a 200 - 300 mL hydrochloric acid solution with a concentration of 10 - 20% added with a magnetic stirrer, and stirred at a rotation speed of 500 - 700 rpm for 5 - 6 h. Subsequently, it is subjected to suction filtration 3 - 5 times with 200 - 300 mL of deionized water and dried to obtain the carbon product.

[0011] The beneficial effects brought by the technical solution provided in this application include: This application provides a method for methane pyrolysis to produce carbon based on molten medium regulation. The interfacial interaction between the modified metal and the molten chloride can adjust the electron cloud density of the metal, reduce the dissociation energy barrier of the C - H bond, and promote methane pyrolysis. The fluidity of the molten salt can wash away the carbon deposition on the metal surface. At the same time, the high thermal conductivity of the metal can accelerate heat transfer and avoid carbon deposition caused by local overheating. The pore structure of the foam metal pre - disperses the methane gas flow, changes the number and size of the bubbles, increases the gas - liquid contact area, and the chemical inertness of boron nitride and VO2 cooperate to promote methane pyrolysis while protecting the metal and extending the service life of the molten medium catalyst. At the same time, it realizes the production of various carbon products with less metal content at a lower temperature (≤1000°C), and the carbon products containing those obtained by cleaning and etching and those untreated are applied in practice. Description of the Drawings

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 SEM diagrams of the carbon products prepared in Examples 1 - 4, Comparative Example 1, and Comparative Example 2 provided in this application, where Figure 1 (a) - Figure 1 (f) are, in sequence, the SEM diagrams of Examples 1 - 4, Comparative Example 1, and Comparative Example 2. Detailed Embodiments

[0014] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in this application belong to the scope of protection of this application.

[0015] See Figure 1As shown in the figure, the present application provides a method for methane pyrolysis to produce carbon based on molten medium regulation (hereinafter referred to as the methane pyrolysis to carbon method).

[0016] Example 1 The methane pyrolysis to carbon method provided in this example includes the following steps: A modified Cu metal foil with a size of 0.25 mm * 60 mm * 200 mm (thickness * width * length), copper foam with a diameter equal to the inner diameter of the reaction tube of the tubular furnace (15 mm), a thickness of 5.0 mm, and 60 ppi, and a chloride salt covering the top of the modified Cu metal foil are used. The chloride salt used is a mixed salt of KCl and NiCl2 (mass ratio 3:1); The modified Cu metal foil and the copper foam are successively immersed in acetone, deionized water, and ethanol and ultrasonically treated for 30 min; The modified Cu metal foil and the copper foam are continuously immersed in a 1 mol / L hydrochloric acid solution and ultrasonically treated for 30 min; The modified Cu metal foil and the copper foam are continuously immersed in deionized water and ultrasonically treated for 40 min, then transferred to a vacuum drying oven for drying. The modified Cu metal foil is made into a roll shape with a spacing of 2 mm along the width direction, and then the copper foam is placed under the modified Cu metal foil to obtain a modified metal matrix material; The modified metal matrix material and the above-mentioned chloride salt are used as a molten medium catalyst and placed in a tubular furnace. It is heated to the reaction temperature of 1000 °C at a heating rate of 7 °C / min. During the heating process, 70 mL / min of argon is introduced. After reaching the reaction temperature, the argon flow rate is reduced to 45.5 mL / min, and 24.5 mL / min of methane is introduced, and the reaction is carried out for 8 h; after the reaction is completed, it is cooled to room temperature in an argon atmosphere, and the prepared carbon product is collected. The collected carbon product is filtered and washed 5 times with deionized water and dried to obtain a carbon product; the washed carbon product can be used as a working electrode for electrocatalytic oxygen evolution reaction.

[0017] Specifically, the modified metal matrix material in this example includes a modified Cu metal foil and copper foam. The modified Cu metal foil, and the preparation method of the modified Cu metal foil includes: After dispersing 40 g of copper particles (100 nm) in 800 mL of ethanol, 400 mL of a nano-boron nitride dispersion with a concentration of 0.1 mg / mL is added. After stirring for 2 h, it is dried at 80 °C and calcined in an argon atmosphere at 600 °C for 1 h to form a boron nitride adsorption layer, obtaining a metal-boron nitride; Prepare 800 mL of NH4VO3 solution with a concentration of 0.1 mol / L, adjust the pH to 3, add 40 g of metal-boron nitride into it, react at 80 °C for 2 h, filter, and then calcine in a nitrogen atmosphere at 500 °C for 3 h to obtain precursor particles; Immerse 40 g of precursor particles into an acetic acid solution of 2 wt% chitosan oligosaccharide, stir at room temperature for 6 h, filter and dry, and then calcine in an argon atmosphere at 700 °C for 2 h to obtain a modified Cu metal foil with a foil thickness of 0.25 mm; the composition of the 2 wt% chitosan oligosaccharide acetic acid solution is 16 g of chitosan oligosaccharide, 80 mL of acetic acid, and 720 mL of deionized water.

[0018] Example 2 The method for methane cracking to produce carbon provided in this example includes the following steps: Use a modified Fe metal foil with dimensions of 0.25 mm * 10 mm * 200 mm (thickness * width * length), foam iron with a diameter equal to the inner diameter of the reaction tube of the tubular furnace (15 mm), a thickness of 5.0 mm, and 60 ppi, and a chloride salt that covers the top of the modified Fe metal foil, where NaCl is used as the chloride salt; Immerse the modified Fe metal foil and the foam iron successively in acetone, deionized water, and ethanol and ultrasonically treat for 40 min; Continue to immerse the modified Fe metal foil and the foam iron in a 0.5 mol / L hydrochloric acid solution and ultrasonically treat for 50 min; Continue to immerse the modified Fe metal foil and the foam iron in deionized water and ultrasonically treat for 50 min, then transfer to a vacuum drying oven for drying. Make the modified Fe metal foil into a tube with the width as the circumference, and then place the foam iron below the modified Fe metal foil to obtain a modified metal matrix material; Place the modified metal matrix material and the chloride salt as a molten medium catalyst in a tubular furnace, heat to the reaction temperature of 1000 °C at a heating rate of 7 °C / min. During the heating process, introduce 80 mL / min of argon. After reaching the reaction temperature, reduce the argon flow rate to 56 mL / min, introduce 24 mL / min of methane, and react for 8 h; after the reaction, cool to room temperature in an argon atmosphere, collect the prepared carbon product, wash the collected carbon product by suction filtration with deionized water 7 times, transfer it to 300 mL of a 20% hydrochloric acid solution containing a magnetic stirrer, stir at 500 rpm for 6 h, then filter 5 times with 300 mL of deionized water, and dry to obtain a carbon product; the washed carbon product can be used as an electrode material for supercapacitors.

[0019] Specifically, the modified metal-based material in this embodiment includes modified Fe metal foil and iron foam. For the modified Fe metal foil, the preparation method thereof includes: After dispersing 30 g of iron particles (100 nm) in 600 mL of ethanol, 300 mL of a nano boron nitride dispersion with a concentration of 0.1 mg / mL is added. After stirring for 2 h, it is dried at 80°C and calcined in an argon atmosphere at 600°C for 1 h to form a boron nitride adsorption layer, obtaining metal-boron nitride. Prepare 600 mL of an NH4VO3 solution with a concentration of 0.1 mol / L, adjust the pH to 3. After adding 30 g of metal-boron nitride into it, react at 80°C for 2 h. After filtration, calcine in a nitrogen atmosphere at 500°C for 3 h to obtain precursor particles. Immerse 30 g of the precursor particles in an acetic acid solution of 2 wt% chitosan oligosaccharide, stir at room temperature for 6 h, filter and dry, then calcine in an argon atmosphere at 700°C for 2 h to obtain the modified Fe metal foil with a foil thickness of 0.25 mm. The composition of the 2 wt% chitosan oligosaccharide acetic acid solution is 12 g of chitosan oligosaccharide, 60 mL of acetic acid, and 540 mL of deionized water.

[0020] Example 3 The method for methane cracking to produce carbon provided in this embodiment includes the following steps: Use a modified Ni metal foil with dimensions of 0.25 mm * 60 mm * 200 mm (thickness * width * length), nickel foam with a diameter equal to the inner diameter of the reaction tube of the tubular furnace (15 mm), a thickness of 5.0 mm, and 60 ppi, and a chloride salt that covers the top of the modified Ni metal foil. The chloride salt used is a mixed salt of NaCl and MnCl2 (mass ratio 3:1). Immerse the modified Ni metal foil and nickel foam successively in acetone, deionized water, and ethanol and perform ultrasonic treatment for 30 min. Continue to immerse the modified Ni metal foil and nickel foam in a 1 mol / L hydrochloric acid solution and perform ultrasonic treatment for 30 min. Continue to immerse the modified Ni metal foil and nickel foam in deionized water and perform ultrasonic treatment for 40 min, then transfer them to a vacuum drying oven for drying treatment. Roll the modified Ni metal foil into a roll along the width direction with a spacing of 2 mm, and then place the nickel foam below the modified Ni metal foil to obtain the modified metal-based material. The modified metal-based material and chloride salt are used as a molten medium catalyst and placed in a tubular furnace. It is heated to the reaction temperature of 900 °C at a heating rate of 10 °C / min. During the heating process, argon is introduced at a flow rate of 70 mL / min. After reaching the reaction temperature, the argon flow rate is reduced to 45.5 mL / min, and methane at 24.5 mL / min is introduced, and the reaction lasts for 8 h. After the reaction, it is cooled to room temperature in an argon atmosphere, and the prepared carbon product is collected. The collected carbon product is filtered and washed 7 times with deionized water, transferred to 300 mL of a 10% hydrochloric acid solution containing a magnetic stir bar, and stirred at 500 rpm for 5 h. Subsequently, it is filtered 3 times with 200 mL of deionized water and dried to obtain the carbon product. The washed carbon product can be used in industrial coatings.

[0021] Specifically, the modified metal-based material in this example includes modified Ni metal foil and nickel foam. For the modified Ni metal foil, the preparation method thereof includes: After dispersing 30 g of nickel particles (100 nm) in 600 mL of ethanol, 300 mL of a nano-boron nitride dispersion with a concentration of 0.1 mg / mL is added. After stirring for 2 h, it is dried at 80 °C and calcined in an argon atmosphere at 600 °C for 1 h to form a boron nitride adsorption layer, obtaining metal-boron nitride. Prepare 600 mL of an NH4VO3 solution with a concentration of 0.1 mol / L, adjust the pH to 3. After adding 30 g of metal-boron nitride into it, react at 80 °C for 2 h. After filtration, calcine in a nitrogen atmosphere at 500 °C for 3 h to obtain precursor particles. Immerse 30 g of precursor particles in an acetic acid solution of 2 wt% chitosan oligosaccharide, stir at room temperature for 6 h, filter and dry, and then calcine in an argon atmosphere at 700 °C for 2 h to obtain the modified Ni metal foil with a foil thickness of 0.25 mm. The composition of the 2 wt% chitosan oligosaccharide acetic acid solution is 15 g of chitosan oligosaccharide, 30 mL of acetic acid, and 675 mL of deionized water.

[0022] Example 4 The method for producing carbon by methane cracking provided in this example includes the following steps: Use modified Cu balls with a diameter of 3 mm and a filling height of 20 cm, nickel foam with a diameter equal to the inner diameter of the reaction tube of the tubular furnace (15 mm), a thickness of 5.0 mm, and 60 ppi, and chloride salt covering the top of the modified Cu balls. The chloride salt used is a mixed salt of KCl and NiCl2 (mass ratio 3:1). Immerse the modified Cu balls and nickel foam successively in acetone, deionized water, and ethanol and ultrasonically treat for 30 min. Continue to immerse the modified Cu spheres and nickel foam in a 1 mol / L hydrochloric acid solution and ultrasonically treat for 30 min; Continue to immerse the modified Cu spheres and nickel foam in deionized water and ultrasonically treat for 40 min, then transfer to a vacuum drying oven for drying. Place the nickel foam under the modified Cu spheres to obtain the modified metal matrix material; Place the modified metal matrix material and chloride salt as the molten medium catalyst in a tubular furnace, heat to the reaction temperature of 1000 °C at a heating rate of 7 °C / min. During the heating process, introduce argon at a flow rate of 70 mL / min. After reaching the reaction temperature, reduce the argon flow rate to 45.5 mL / min and introduce methane at a flow rate of 24.5 mL / min, and react for 8 h; After the reaction, cool to room temperature in an argon atmosphere, collect the prepared carbon product. The collected carbon product is filtered and washed 6 times with deionized water, transferred to a 300 mL hydrochloric acid solution with a concentration of 10% containing a magnetic stir bar, and stirred at 500 rpm for 5 h. Subsequently, filter 3 times with 200 mL of deionized water and dry to obtain the carbon product; The washed carbon product can be used in industrial coatings.

[0023] Specifically, the modified metal matrix material in this example includes modified Cu spheres and nickel foam, and modified Cu spheres. The preparation method of the modified Cu spheres includes: Disperse 200 g of copper particles (100 nm) in 4 L of ethanol, then add 1.6 L of a nano-boron nitride dispersion with a concentration of 0.1 mg / mL, stir for 2 h, dry at 80 °C, and calcine in an argon atmosphere at 600 °C for 1 h to form a boron nitride adsorption layer to obtain metal-boron nitride; Prepare 4 L of an NH4VO3 solution with a concentration of 0.1 mol / L, adjust the pH to 3, add 200 g of metal-boron nitride into it, react at 80 °C for 2 h, filter, and calcine in a nitrogen atmosphere at 500 °C for 3 h to obtain precursor particles; Immerse 200 g of precursor particles in an acetic acid solution of 2 wt% chitosan oligosaccharide, stir at room temperature for 6 h, filter and dry, and calcine in an argon atmosphere at 700 °C for 2 h to obtain modified Cu spheres; The composition of the 2 wt% chitosan oligosaccharide acetic acid solution is 80 g of chitosan oligosaccharide, 400 mL of acetic acid, and 3.6 L of deionized water.

[0024] Comparative Example 1 The difference from Example 1 is that in the modified metal matrix material of the molten medium catalyst, instead of adding modified Cu metal foil, an equal amount of Cu metal foil is used for replacement.

[0025] Comparative Example 2 The difference from Example 1 is that the modified Cu metal foil in the modified metal matrix material is replaced with an unmodified Cu metal foil, and copper foam is not added.

[0026] Comparative Example 3 The difference from Example 1 is that after raising the reaction temperature, the argon gas is turned off, and methane is introduced at 55 mL / min for 8 h; the collected carbon product is also filtered and washed with deionized water 5 times and dried to obtain a carbon product; the washed carbon product can be used as the anode material of a fuel cell.

[0027] It should be noted that in the above examples and comparative examples, the size of the reaction tube of the tube furnace used is 15 mm×600 mm, and the positional relationship between the modified metal and the foam metal is as follows: along the length direction of the reaction tube of the tube furnace, methane gas enters from the bottom end of the reaction tube of the tube furnace and passes through the foam metal and the modified metal in sequence.

[0028] The types of carbon products and conversion rates and other results obtained by the preparation methods provided in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0029] Table 1

[0030] It should be noted that the conversion rate in Table 1 is the peak conversion rate during the reaction process of the preparation method. In Examples 1-4, after the carbon product is prepared, the present application provides two ways to wash and obtain the carbon product. Among them, the carbon product obtained by washing in the way of "filtering and washing with deionized water 5-7 times and drying to obtain the carbon product" can be used for the electrocatalytic oxygen evolution reaction (OER); the carbon product obtained by washing in the way of "filtering and washing the carbon product with deionized water 5-7 times, transferring it to 200-300 mL of hydrochloric acid solution with a concentration of 10-20% added with a magnetic stirrer, and stirring at a rotation speed of 500-700 rpm for 5-6 h, and then filtering 3-5 times with 200-300 mL of deionized water and drying to obtain the carbon product" can be used for electronic devices and batteries, and can also be used for coatings and lubricants. The obvious difference is whether the washed carbon product contains metal impurities. One of the carbon applications is selected and filled in Table 1.

[0031] The carbon products prepared in Examples 1-4 and Comparative Examples 1 and 2 were characterized by scanning electron microscopy (SEM), and the characterization results are as Figure 1 shown, where Figure 1 (a)~ Figure 1 (f) are, in order, the SEM images of Examples 1-4, Comparative Example 1, and Comparative Example 2.

[0032] Example 2: The modified Fe metal foil was made into a tube. Compared with making the modified Cu metal foil into a roll in Example 1, the conversion rate decreased slightly. In Example 3, the modified Ni metal foil and nickel foam were used as part of the molten medium catalyst, and its conversion rate was significantly higher than that in Example 1 and Example 4, indicating that nickel as the modified metal has a good cooperation effect with chitosan. At the same time, the comparison results between Example 3 and Example 4 show that Example 4 reduced the dosage ratio of chitosan compared with Example 3, indicating that the decrease in the chitosan ratio will weaken its chelating effect.

[0033] In Example 1 and Example 4, the ratio of metal to chitosan is the same. The difference is that in Example 1, the modified metal is the modified Cu metal foil and the foam metal is copper foam; in Example 4, the modified metal is the modified Cu ball and the foam metal is nickel foam. It shows that the modified Cu metal made into a ball has a higher conversion rate in catalytic methane pyrolysis than the modified Cu metal made into a foil. The reason is that the bubbles deform in the spherical Cu metal, increasing the contact area between the bubbles and the molten medium catalyst, and the reaction is more complete.

[0034] Compared with Comparative Example 1, the methane conversion rate in Example 1 is relatively high because Comparative Example 1 only uses Cu foil and copper foam. Due to its low thermal conductivity, on the one hand, it will reduce the reaction rate, and on the other hand, it will reduce the catalytic activity.

[0035] Compared with Comparative Example 2, the methane conversion rate in Example 1 is relatively high because the addition of copper foam disperses the bubbles and promotes the full contact between the bubbles and the molten medium catalyst. At the same time, in Comparative Example 2, unmodified Cu is used, and its C-H bond dissociation energy barrier is 420 kJ / mol, which requires a temperature above 1100 °C to achieve efficient pyrolysis. In the absence of copper foam and without the modification of boron nitride and chitosan on the surface of the Cu metal foil, the carbon deposition rate increases and side reactions increase, resulting in a significant decrease in the methane conversion rate.

[0036] Compared with Comparative Example 2, the methane conversion rate in Comparative Example 1 is relatively high because the addition of copper foam disperses the bubbles and promotes the full contact between the bubbles and the molten medium catalyst.

[0037] Compared with Comparative Example 3, in Comparative Example 3, the total inlet gas flow rate is reduced and the inlet gas is pure methane, which increases the contact time between the bubbles and the molten medium catalyst and promotes the full contact between the bubbles and the molten medium catalyst. Therefore, the peak value of the methane conversion rate is increased. However, due to the high pyrolysis rate under pure methane conditions, the surface of the thin film carbon cannot relax evenly, resulting in carbon growth stacking. Therefore, in the second half of the reaction, the conversion rate will show a downward trend.

[0038] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for methane cracking to produce carbon based on molten medium regulation, characterized in that, It includes the following steps: Place the molten medium catalyst in a tubular furnace, heat it to the reaction temperature at a heating rate of 7 - 10 °C / min, and introduce argon during the heating process. When the reaction temperature is reached, introduce methane. After the reaction ends, cool it to room temperature in an argon atmosphere, and collect the prepared carbon product. The reaction temperature is 850 - 1000 °C; Among them, the molten medium catalyst includes a modified metal-based material and a chloride salt; The modified metal-based material includes a modified metal and a foam metal. The preparation method of the modified metal includes: Disperse metal particles in ethanol, then add a nano-boron nitride dispersion liquid, stir for 2 h, dry at 80 °C, and calcine in an argon atmosphere at 600 °C for 1 h to form a boron nitride adsorption layer, obtaining metal-boron nitride. The mass-volume ratio of the metal particles to ethanol is 1 g : 20 mL. The volume of the nano-boron nitride dispersion liquid is 40 - 60% of that of the ethanol, and the concentration of the nano-boron nitride dispersion liquid is 0.1 mg / mL; Prepare a 0.1 mol / L NH4VO3 solution, adjust the pH to 3, put the metal-boron nitride into it, react at 80 °C for 2 h, filter, and calcine in a nitrogen atmosphere at 500 °C for 3 h to obtain precursor particles. The mass-volume ratio of the metal-boron nitride to the NH4VO3 solution is 1 g : 20 mL; Immerse the precursor particles in a 2 wt% acetic acid solution of chitosan oligosaccharide, stir at room temperature for 6 h, filter and dry, and then calcine in an argon atmosphere at 700 °C for 2 h to obtain the modified metal. The mass-volume ratio of the precursor particles to the 2 wt% acetic acid solution of chitosan oligosaccharide is 1 g : (15 - 25) mL.

2. The method for producing carbon by methane cracking regulated by a molten medium according to claim 1, characterized in that: The preparation method of the modified metal-based material includes the following steps: Immerse the modified metal and the foam metal successively in acetone, deionized water, and ethanol and perform ultrasonic treatment for 30 - 40 min; Continue to immerse the modified metal and the foam metal in a 0.5 - 1 mol / L hydrochloric acid solution and perform ultrasonic treatment for 30 - 50 min; Continue to immerse the modified metal and the foam metal in deionized water and perform ultrasonic treatment for 40 - 50 min, then transfer them to a vacuum drying oven for drying treatment. Make the modified metal into a spherical shape, a rolled shape, or a tubular shape, and then place the modified metal and the foam metal in the reaction tube of the tubular furnace in the following manner: Along the length direction of the reaction tube of the tubular furnace, methane gas enters from the bottom end of the reaction tube of the tubular furnace, and successively passes through the foam metal and the modified metal. The diameter of the foam metal is equal to the inner diameter of the reaction tube of the tubular furnace.

3. The method for producing carbon by methane cracking regulated by a molten medium according to claim 2, characterized in that: The thickness of the foam metal is 5 mm and the pore size is 60 ppi.

4. The method for producing carbon by methane cracking regulated by a molten medium according to claim 1, characterized in that: The chloride salt is one or more of KCl, NaCl, NiCl2, and MnCl2.

5. The method for producing carbon by methane cracking regulated by a molten medium according to claim 1, wherein: The metal particles are one or more of copper, nickel, and iron; The metal foam is one or more of copper, nickel, and iron.

6. The method for producing carbon by methane cracking regulated by a molten medium according to claim 1, wherein: When argon is introduced during the heating process, the reaction is carried out at atmospheric pressure, the argon flow rate is 20 - 80 mL / min, and the methane flow rate is 20 - 60 mL / min.

7. The method for producing carbon by methane cracking regulated by a molten medium according to claim 1, wherein: After collecting the produced carbon product, the following steps are further included: The carbon product is subjected to suction filtration and washing with deionized water 5 - 7 times, and then dried to obtain a carbon product; Alternatively, the carbon product is subjected to suction filtration and washing with deionized water 5 - 7 times, transferred to a 200 - 300 mL hydrochloric acid solution with a concentration of 10 - 20% containing a magnetic stirrer, and stirred at a rotation speed of 500 - 700 rpm for 5 - 6 h. Subsequently, it is suction filtered 3 - 5 times with 200 - 300 mL of deionized water and dried to obtain a carbon product.

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