System and method for preparing composite carbon material and hydrogen by cracking low-carbon hydrocarbon

Abstract

The invention provides a system and method for preparing a composite carbon material and hydrogen through cracking of low-carbon hydrocarbons, and relates to the technical field of hydrogen production through cracking of low-carbon hydrocarbons, the system comprises a multi-stage bubbling bed reaction device with at least one built-in porous gas distribution plate, the device is filled with a molten alloy catalyst, and the molten alloy catalyst is filled with a molten alloy catalyst. Carrying out catalytic cracking reaction on the low-carbon hydrocarbon bubbles and the molten alloy catalyst; the molten alloy catalyst comprises molten active metal and a molten medium; the molten active metal is selected from at least two of Ni, Cu, Co, Fe and Mo; the molten medium is selected from at least one of Sn, Bi, Ga, Zn, Al, Pb, Bi and In; the molar ratio of the molten active metal to the molten alloy catalyst is 10%-60%. According to the present invention, the efficient conversion of the low-carbon hydrocarbon is achieved, the catalytic activity is ensured, the reaction temperature for hydrogen production through cracking of the low-carbon hydrocarbon is significantly reduced, the reaction safety is improved, and the nanotube graphite composite carbon material with the high added value is obtained.

Description

Technical Field

[0001] This invention relates to the field of low-carbon hydrocarbon cracking for hydrogen production technology, and in particular to a system and method for preparing composite carbon materials and hydrogen by low-carbon hydrocarbon cracking. Background Technology

[0002] Against the backdrop of rapidly increasing global energy demand and a shift in the energy structure towards low-carbon, clean, and efficient energy, the development and utilization of new energy sources are crucial. Hydrogen energy is considered an ideal clean energy source due to its high energy density, wide availability, and zero carbon emissions during combustion. Previous hydrogen production methods mainly included: hydrogen production via water electrolysis (patent CN202510180654.5), hydrogen production via industrial by-product purification (patent CN202510054902.1), and hydrogen production via biomass (patent CN202410710941.8). These processes often suffer from low product purity, high energy consumption, and limitations imposed by cost and resources. Natural gas, as a clean energy source, can be cracked to produce high-purity hydrogen and high-value-added carbon materials, playing a significant role in promoting the shift towards a zero-carbon, clean energy structure and becoming a focal point in energy transition.

[0003] Methane, as a major component of natural gas, is considered a highly efficient feedstock for hydrogen production due to its high hydrogen-to-carbon ratio. Current mainstream technologies for methane-to-hydrogen production include methane steam reforming, high-temperature thermal cracking of methane, catalytic cracking of methane, and molten metal methane cracking. The methane steam reforming technology disclosed in patent application CN202410499236.8 is the most widely used and relatively mature, but it suffers from problems such as high reaction temperatures (600~900 ℃), catalyst deactivation due to carbon buildup, and high carbon emissions. High-temperature thermal cracking of methane disclosed in patent CN201010160179.9 is an emerging hydrogen production technology that directly cracks methane into hydrogen and solid carbon in a high-temperature reactor (>1200 ℃) without the intervention of a catalyst. Compared to methane steam reforming, this reaction process has near-zero carbon emissions. Furthermore, it eliminates the need for catalysts, avoiding the deactivation and replacement issues associated with metal catalysts. However, the reaction temperature needs to be maintained above 1200 °C, leading to increased energy consumption. Carbon deposition can cause decreased heat transfer efficiency and pipeline blockage, affecting the long-term stable operation of the system. Patent application CN202311420810.8 discloses a methane catalytic cracking hydrogen production technology, which involves the direct decomposition of methane into hydrogen and solid carbon under the action of a catalyst. With the assistance of Ni-based, Fe-based, and other solid catalyst systems, the reaction temperature can be reduced to 600-800 °C. However, the lower temperature results in a relatively low single-pass conversion rate of methane. In addition, the catalyst suffers from rapid deactivation due to carbon deposition, poor stability, and inability to operate for extended periods. The catalyst exists in solid form during the cracking reaction, and the generated carbon material is also solid; the mixture of the two is difficult to separate and recover, preventing the realization of carbon material as a byproduct and reducing the process's economic efficiency. Compared to methane thermal cracking and solid-state catalytic cracking, the molten metal methane cracking hydrogen production process disclosed in patent application CN202410818737.8 is an innovative thermochemical hydrogen production process. Catalytic cracking is achieved by passing methane through a high-temperature molten metal medium. This technology utilizes molten metal (such as Sn, Bi, or their alloys) as the reaction medium, decomposing methane molecules into hydrogen and solid carbon in the molten metal at an operating temperature of 1000–1100 °C. Compared to traditional thermal cracking, the molten metal system has better thermal conductivity and temperature uniformity, significantly improving reaction efficiency. The reaction principle is mainly that methane bubbles crack as they pass through the molten metal layer, generating hydrogen that escapes from the melt surface, while solid carbon floats on the metal surface due to density differences, achieving in-situ product separation. The molten metal not only acts as a heat carrier, but its surface properties also lower the reaction activation energy, playing a catalytic role. However, the metal medium experiences evaporation and entrainment losses during long-term operation, the high-temperature molten metal can corrode reactor materials, and carbon products may affect system flowability, causing a risk of blockage. In addition, the reaction energy consumption of this technology is still relatively high, it is difficult to control costs on a large scale, and there are limited ways to utilize carbon products for high value.

[0004] In summary, the process of producing carbon materials as a byproduct of methane cracking for hydrogen production generally requires operation at high temperatures (1000~1200℃). This process is energy-intensive, and the co-produced carbon materials are mainly low-value graphite and carbon black, resulting in poor economic viability. Therefore, a method for producing high-value carbon materials by cracking molten metallic methane under mild conditions is still lacking. Summary of the Invention

[0005] To address the issue that existing technologies require high temperatures and produce low-value graphite and carbon black as byproducts when cracking low-carbon hydrocarbons to produce hydrogen, the present invention aims to provide a system and method for preparing composite carbon materials and hydrogen through the cracking of low-carbon hydrocarbons, thereby achieving the technical effect of cracking low-carbon hydrocarbons to produce hydrogen and co-producing high-value carbon materials under mild conditions.

[0006] This invention provides a system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons (C1-C3 gaseous hydrocarbons and their mixtures), including a multi-stage bubble bed reactor with at least one built-in porous gas distribution plate. The multi-stage bubble bed reactor is filled with a molten alloy catalyst, so that the low-carbon hydrocarbon bubbles undergo a catalytic cracking reaction with the molten alloy catalyst. The molten alloy catalyst comprises a molten active metal and a molten medium; The molten active metal is selected from at least two of Ni, Cu, Co, Fe, and Mo; The molten medium is selected from at least one of Sn, Bi, Ga, Zn, Al, Pb, Bi, and In; The amount of the molten active metal accounts for 10% to 60% of the amount of the molten alloy catalyst.

[0007] This invention provides a system for preparing composite carbon materials and hydrogen through the cracking of low-carbon hydrocarbons. Addressing the problems of high operating temperatures and low value of co-produced carbon materials in existing low-carbon hydrocarbon cracking processes, this system enhances the gas-liquid interface reaction in a multi-stage bubbling bed reactor with at least one built-in porous gas distribution plate by selecting a specific ratio of multi-element molten alloy catalyst. This achieves efficient conversion of low-carbon hydrocarbons while maintaining catalytic activity, significantly reducing the reaction temperature for hydrogen production from low-carbon hydrocarbon cracking, improving reaction safety, and simultaneously obtaining high-value-added nanotube graphite composite carbon materials.

[0008] Preferably, in the multi-stage bubbling bed reactor, the number of porous gas distribution plates is 1 to 5, and more preferably 1 to 3.

[0009] In this multi-stage bubbling bed reactor, the number of porous gas distribution plates is controlled to be 1 to 3. This ensures that there are enough porous gas distribution plates to effectively reduce the size of the low-carbon hydrocarbon feed bubbles, thereby increasing their contact area with the molten alloy catalyst and enhancing the conversion of low-carbon hydrocarbons. At the same time, it avoids the problem of excessive pressure drop in the bed caused by too many porous gas distribution plates, thus achieving a continuous, stable, and low-pressure reaction process.

[0010] Preferably, the porous gas distribution plate has uniform or non-uniform pore sizes, each of which is 1 μm to 10 mm, and more preferably 10 μm to 1 mm.

[0011] This scheme controls the pore size of the porous gas distribution plate to be uniform and 10 μm to 1 mm. This preferred pore size range can ensure that the pore size is small enough to effectively reduce the size of the low-carbon hydrocarbon feed bubbles, so as to increase the contact area with the molten alloy catalyst and enhance the conversion of low-carbon hydrocarbons. At the same time, it can avoid the problems of easy blockage caused by the pore size being too small and the bed pressure drop being too high.

[0012] Preferably, the porosity of the porous gas distribution plate is 0.01% to 10%, more preferably 0.1% to 1%.

[0013] This scheme controls the porosity of the porous gas distribution plate to be 0.1%~1%. This preferred porosity range can effectively reduce the size of the low-carbon hydrocarbon feed bubbles to increase their contact area with the molten alloy catalyst and enhance the conversion of low-carbon hydrocarbons, while avoiding problems such as leakage of the molten alloy catalyst below the distribution plate due to excessive porosity, which would cause pipeline blockage.

[0014] Preferably, the distribution plate is in the form of a perforated plate, a sieve plate, or a grid plate.

[0015] Preferably, the amount of the molten active metal accounts for 20% to 40% of the amount of the molten alloy catalyst.

[0016] This scheme controls the amount of molten active metal to account for 20% to 40% of the amount of molten alloy catalyst, which can effectively reduce the reaction activation energy of the low-carbon hydrocarbon cracking hydrogen production process, improve the single-pass conversion rate of low-carbon hydrocarbons, and at the same time regulate the type of co-produced carbon materials to generate high-value-added carbon nanotubes and graphite composite materials, thereby improving the economic efficiency of the process.

[0017] Preferably, the molten active metal is Ni and Cu, and the molar ratio of Ni to Cu is (0.5~2):1; the molten medium is selected from at least one of Sn, Bi, and Ga, preferably Bi and Sn, and / or Bi and Ga; When the molten medium is Bi and Sn, and / or Bi and Ga, the amount of Bi accounts for 50% to 80% of the amount of the molten medium.

[0018] More preferably, the molten active metal is Ni and Cu, and the molar ratio of Ni to Cu is (0.8~1.5):1; the molten medium is Bi and Sn, and / or Bi and Ga, and the amount of Bi accounts for 60%~80% of the amount of the molten medium.

[0019] This invention provides a method for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons, wherein the method is carried out in the system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons; The method includes the following steps: introducing low-carbon hydrocarbon bubbles to carry out a catalytic cracking reaction with the molten alloy catalyst in the multi-stage bubble bed reactor.

[0020] Preferably, the gas velocity of the low-carbon hydrocarbon passing through the porous gas distribution plate is 0.01 m / s to 10 m / s, and more preferably 0.1 to 2.0 m / s.

[0021] More preferably, the gas velocity of the low-carbon hydrocarbon passing through the porous gas distribution plate is 0.2~1.0 m / s.

[0022] Preferably, the residence time of the low-carbon hydrocarbon feed bubbles in the molten alloy catalyst is 0.01 min to 10 h, and more preferably 0.1 min to 1 h.

[0023] In this scheme, the residence time of the low-carbon hydrocarbon feed bubbles in the molten alloy catalyst is controlled to be 0.1 min to 1 h, which can achieve both efficient conversion of low-carbon hydrocarbons and ensure a high feed processing capacity.

[0024] Preferably, the temperature of the catalytic cracking reaction is 500~1500 ℃, more preferably 700~1100 ℃.

[0025] This scheme controls the temperature of the catalytic cracking reaction to 700~1100 ℃, which improves the safety of the reaction while ensuring catalytic activity.

[0026] Preferably, the pressure of the catalytic cracking reaction is 0.01 atm to 3 MPa, and more preferably 0.1 atm to 5 atm.

[0027] This scheme controls the pressure of the catalytic cracking reaction to be 0.1 atm ~ 5 atm, which ensures catalytic activity while avoiding the limitation of methane cracking equilibrium by excessive pressure, and at the same time improves the safety of the reaction.

[0028] Preferably, the method for preparing composite carbon materials and hydrogen by low-carbon hydrocarbon cracking includes the following steps: loading a molten alloy catalyst into a multi-stage bubble bed reactor with 1 to 3 built-in porous gas distribution plates, introducing low-carbon hydrocarbon bubbles to carry out a catalytic cracking reaction with the molten alloy catalyst at 700 to 1100 °C, wherein the residence time of the low-carbon hydrocarbon feed bubbles in the molten alloy catalyst is 0.1 min to 1 h, more preferably 2 min to 20 min; The porous gas distribution plate has uniform pore size, which is 50~500 μm. The porosity of the porous gas distribution plate is 0.1~0.5%; The molten alloy catalyst comprises a molten active metal and a molten medium; The molten active metal is Ni and Cu, with a molar ratio of Ni to Cu of 0.5 to 2; the molten medium is Bi and Sn, and / or Bi and Ga, with the amount of Bi accounting for 50% to 80% of the amount of the molten medium. The amount of the molten active metal accounts for 20% to 40% of the amount of the molten alloy catalyst.

[0029] Advantages compared to existing technologies: This invention provides a method for producing high-value carbon materials as a byproduct of hydrogen production from low-carbon hydrocarbon cracking. The method utilizes a multi-component molten alloy catalyst to effectively reduce the activation energy of the hydrogen production process. A multi-stage bubbling bed reactor inhibits the coalescence and growth of low-carbon hydrocarbon bubbles, reducing bubble size and thus enhancing the gas-liquid interface reaction between low-carbon hydrocarbon molecules and the multi-component molten metal catalyst. The synergistic enhancement effect of the highly active multi-component molten alloy catalyst and the multi-stage bubbling bed reactor on the gas-liquid interface reaction not only reduces the reaction operating temperature (reducing energy consumption) and increases the single-pass conversion rate of low-carbon hydrocarbons, but also allows for the control of the type of carbon materials co-produced, generating high-value-added carbon nanotubes and graphite composite materials, thereby improving the economic efficiency of the process. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 The process flow diagram for preparing composite carbon materials and hydrogen by methane cracking in Example 1 is shown.

[0032] Figure 2The image shows a scanning electron microscope (SEM) image of the composite carbon material prepared by methane cracking in Example 1.

[0033] Figure 3 The image shows the Raman spectrum of the composite carbon material prepared by methane cracking in Example 1.

[0034] Figure 1 The correspondence between each label and component name is as follows: 1-Multi-stage bubbling bed reactor, 2-Gas-solid separator, 3-High-purity carbon material storage tank, 4-Pressure swing adsorption unit, 5-Low-purity carbon material recovery unit, 6-Lower gas redistribution plate, 7-Upper gas redistribution plate, 8-Lower molten metal bed, 9-Middle molten metal bed, 10-Upper molten metal bed, 11-Carbon material layer, 12-Top free space, 13-Raw material inlet, 14-Gas-solid product outlet, 15-Gas product outlet, 16-Solid carbon material outlet, 17-High-purity hydrogen outlet, 18-Unreacted methane, 19-Liquid-solid product outlet, 20-Molten metal reflux. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Example 1 This embodiment provides a Ni molten alloy catalyst. 0.15 Cu 0.15 Bi 0.7 The specific preparation method includes the following steps: Ni, Cu, and Bi metal powders were mechanically mixed and ground in a molar ratio of 0.15:0.15:0.70, and then subjected to a nitrogen atmosphere at 1200 °C. o C calcination forms an alloy phase, which is further processed at 1100 °C. o C. Pre-reduced under a pure hydrogen atmosphere and then used as a catalyst material for later use.

[0037] This embodiment provides a method for preparing composite carbon materials and hydrogen through methane cracking (process flow is as follows) Figure 1 (As shown), including the following steps: S1. The multi-component molten alloy catalyst Ni prepared in this embodiment, with a height of 20 cm, was packed into a multi-stage bubbling bed reactor with an inner diameter of 5 cm. 0.15 Cu 0.15 Bi 0.7Methane, fed through the inlet, undergoes a cracking reaction to produce hydrogen and co-produce high-value carbon materials. In the multi-stage bubbling bed reactor 1, methane is fed from the bottom up. Besides the gas feed distributor at the bottom, the reactor is divided into multiple reaction beds 8, 9, and 10 by two porous gas distribution plates 6 and 7 in the lower part of the reactor. The porous gas distribution plates have a pore size of 50 μm and an opening ratio of 0.1%. The porous plate design effectively reduces the size of the feed bubbles and enhances their conversion. The methane gas velocity through the holes is 0.5 m / s, the residence time of the methane feed bubbles in the bubbling bed is 5 min, and the reaction temperature is 1100 °C. o C, reaction pressure 1.1 atm. Methane cracked in the molten bed to produce gaseous and solid products. After the reaction stabilized, the gaseous product was passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate was 82%, and the hydrogen selectivity was 99.9% (see Table 1 for details). The solid product was a composite material of carbon nanotubes and multilayer graphite.

[0038] S2. The gaseous product at the gas-solid product outlet 14 mainly consists of hydrogen and some unreacted methane. It passes sequentially through the gas-solid separator 2 and the gaseous product outlet 15 to obtain the gaseous product. After passing through the pressure swing adsorption unit 4, high-purity hydrogen product 17 is obtained. The unreacted methane 18 is recycled as reaction feed. The solid product has a low density and is suspended in the free space 12 above the multi-component molten alloy catalyst, gradually accumulating to form a carbon material layer 11. The carbon material is transferred via vacuum to the low-purity carbon material recovery unit 5 via pipeline 19, along with the liquid metal. The molten metal is returned to the bottom of the multi-stage bubbling bed reactor via pipeline 20, while the solid carbon material undergoes acid washing and water washing to obtain high-purity carbon material. In addition, the gaseous product also carries some solid carbon material with low metal content. After passing through the gas-solid separator 2, high-purity carbon material can be directly obtained and collected in the high-purity carbon material storage tank 3.

[0039] Example 2 This embodiment provides a Ni molten alloy catalyst. 0.15 Co 0.15 Bi 0.7 The specific preparation method includes the following steps: Ni, Co, and Bi metal powders were mechanically mixed and ground in a molar ratio of 0.15:0.15:0.70, and then subjected to a nitrogen atmosphere at 1200 °C. o C calcination forms an alloy phase, which is further processed at 1100 °C. o C. Pre-reduced under a pure hydrogen atmosphere and then used as a catalyst material for later use.

[0040] The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that the multi-component molten alloy catalyst Ni prepared in this embodiment is loaded into the multi-stage bubble bed reactor. 0.15 Co 0.15 Bi 0.7 After the reaction stabilized, the product was passed into a gas chromatograph for online analysis of its composition. The methane conversion rate was 79%, and the hydrogen selectivity was 99.9%. Specific results are shown in Table 1. The solid-phase product was a carbon nanotube and multilayer graphite composite material.

[0041] Example 3 This embodiment provides a Ni molten alloy catalyst. 0.15 Cu 0.15 Bi 0.5 Ga 0.2 The specific preparation method includes the following steps: Ni, Cu, Bi, and Ga metal powders were mechanically mixed and ground in a molar ratio of 0.15:0.15:0.50:0.20, and then subjected to a nitrogen atmosphere at 1200 °C. o C calcination forms an alloy phase, which is further processed at 1100 °C. o C. Pre-reduced under a pure hydrogen atmosphere and then used as a catalyst material for later use.

[0042] The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that the multi-component molten alloy catalyst Ni prepared in this embodiment is loaded into the multi-stage bubble bed reactor. 0.15 Cu 0.15 Bi 0.5 Ga 0.2 After the reaction stabilized, the product was passed into a gas chromatograph for online analysis of its composition. The methane conversion rate was 87%, and the hydrogen selectivity was 99.9%. Specific results are shown in Table 1. The solid-phase product was a composite material of carbon nanotubes and multilayer graphite.

[0043] Example 4 This embodiment provides a Ni molten alloy catalyst. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 The specific preparation method includes the following steps: Ni, Cu, Bi, and Sn metal powders were mechanically mixed and ground in a molar ratio of 0.15:0.15:0.50:0.20, and then subjected to a nitrogen atmosphere at 1200 °C. o C calcination forms an alloy phase, which is further processed at 1100 °C. o C. Pre-reduced under a pure hydrogen atmosphere and then used as a catalyst material for later use.

[0044] The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that the multi-component molten alloy catalyst Ni prepared in this embodiment is loaded into the multi-stage bubble bed reactor. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 After the reaction stabilized, the product was passed into a gas chromatograph for online analysis of its composition. The methane conversion rate was 91%, and the hydrogen selectivity was 99.9%. Specific results are shown in Table 1. The solid-phase product was a composite material of carbon nanotubes and multilayer graphite.

[0045] Example 5 The molten alloy catalyst provided in this embodiment is the same as that in Example 4, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that a porous gas distribution plate is installed in the lower part of the reaction apparatus. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 83%, and the hydrogen selectivity is 99.9%, as shown in Table 1. The solid-phase product is a composite material of carbon nanotubes and multilayer graphite.

[0046] Example 6 The molten alloy catalyst provided in this embodiment is the same as that in Example 4, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that three porous gas distribution plates are installed in the lower part of the reaction apparatus. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 95%, and the hydrogen selectivity is 99.9%, as shown in Table 1. The solid-phase product is a composite material of carbon nanotubes and multilayer graphite.

[0047] Example 7 The molten alloy catalyst provided in this embodiment is the same as that in Example 4, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 1 in that four porous gas distribution plates are installed in the lower part of the reaction apparatus. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 96%, and the hydrogen selectivity is 99.9%, as shown in Table 1. The solid-phase product is a composite material of carbon nanotubes and multilayer graphite.

[0048] Example 8 The molten alloy catalyst provided in this embodiment is the same as that in Example 6, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 6 in that the reaction temperature is 1000 °C. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 92%, and the hydrogen selectivity is 99.8%, as shown in Table 1. The solid-phase product is a composite material of carbon nanotubes and multilayer graphite.

[0049] Example 9 The molten alloy catalyst provided in this embodiment is the same as that in Example 6, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this embodiment differs from that in Example 6 in that the reaction temperature is 900 °C. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 92%, and the hydrogen selectivity is 99.8%, as shown in Table 1. The solid-phase product is a composite material of carbon nanotubes and multilayer graphite.

[0050] Comparative Example 1 The molten alloy catalyst provided in this embodiment is the same as that in Example 6, namely Ni. 0.15 Cu 0.15 Bi 0.5 Sn 0.2 , The method for preparing composite carbon materials and hydrogen by methane cracking provided in this comparative example differs from that in Example 1 in that a porous gas distribution plate is not installed in the lower part of the reaction apparatus. After the reaction stabilizes, the product is passed into a gas chromatograph for online analysis of the product composition. The methane conversion rate is 78%, and the hydrogen selectivity is 99.9%. Specific results are shown in Table 1. The solid-phase product is graphite carbon material.

[0051] Table 1

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons, characterized in that, The device includes a multi-stage bubble bed reactor with at least one built-in porous gas distribution plate. The multi-stage bubble bed reactor is filled with a molten alloy catalyst, which causes low-carbon hydrocarbon bubbles to undergo a catalytic cracking reaction with the molten alloy catalyst. The molten alloy catalyst comprises a molten active metal and a molten medium; The molten active metal is selected from at least two of Ni, Cu, Co, Fe, and Mo; The molten medium is selected from at least one of Sn, Bi, Ga, Zn, Al, Pb, Bi, and In; The amount of the molten active metal accounts for 10% to 60% of the amount of the molten alloy catalyst.

2. The system for preparing composite carbon materials and hydrogen by low-carbon hydrocarbon cracking according to claim 1, characterized in that, In the multi-stage bubbling bed reactor, the number of porous gas distribution plates is 1 to 5, preferably 1 to 3.

3. The system for preparing composite carbon materials and hydrogen by low-carbon hydrocarbon cracking according to claim 1 or 2, characterized in that, The porous gas distribution plate has uniform or non-uniform pore sizes, and each pore size is independently 1 μm to 10 mm, preferably 10 μm to 1 mm.

4. The system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 1 or 3, characterized in that, The porosity of the porous gas distribution plate is 0.01% to 10%, preferably 0.1% to 1%.

5. The system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 1 or 4, characterized in that, The amount of the molten active metal accounts for 20% to 40% of the amount of the molten alloy catalyst.

6. The system for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 1 or 5, characterized in that, The molten active metal is Ni and Cu, and the molar ratio of Ni to Cu is (0.5~2):1; the molten medium is selected from at least one of Sn, Bi, and Ga, preferably Bi and Sn, and / or Bi and Ga; When the molten medium is Bi and Sn, and / or Bi and Ga, the amount of Bi accounts for 50% to 80% of the amount of the molten medium.

7. A method for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons, characterized in that, The method is carried out in the system for preparing composite carbon materials and hydrogen by low-carbon hydrocarbon cracking as described in any one of claims 1 to 6; The method includes the following steps: introducing low-carbon hydrocarbon bubbles to carry out a catalytic cracking reaction with the molten alloy catalyst in the multi-stage bubble bed reactor.

8. The method for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 7, characterized in that, The gas velocity of the low-carbon hydrocarbon through the porous gas distribution plate is 0.01 m / s to 10 m / s, preferably 0.1 to 2.0 m / s, and / or the residence time of the low-carbon hydrocarbon feed bubbles in the molten alloy catalyst is 0.01 min to 10 h, preferably 0.1 min to 1 h.

9. The method for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 7 or 8, characterized in that, The temperature of the catalytic cracking reaction is 500~1500 ℃, preferably 900~1100 ℃.

10. The method for preparing composite carbon materials and hydrogen by cracking low-carbon hydrocarbons according to claim 7 or 9, characterized in that, The pressure of the catalytic cracking reaction is 0.01 atm to 30 atm, preferably 0.1 atm to 5 atm.

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