Method for producing high-quality hydrogen by vacuum degree-induced methane cracking

Abstract

The application discloses a method for preparing high-quality hydrogen by vacuum degree induced methane cracking, and comprises the following steps: 1) in a module methane decomposition reactor, a transition metal-carrier catalyst is subjected to methane cracking in a carrier gas containing CH4 to generate H2 and a carbon-transition metal-carrier mixture; 2) the carbon-transition metal-carrier mixture is subjected to decarburization in a gasification agent to obtain a transition metal-carrier and CO decarburization gas; high-temperature CO at an outlet is preheated for inlet CO2 through a heat exchanger to realize multiple utilization of heat; the decarburized transition metal-carrier is recycled to step 1) to realize large-scale continuous hydrogen production by methane cracking through the above steps. The application converts excess CO2 into valuable CO or a mixture of CO2 and CO. When pure CO2 is used as a raw material, carbon elements in the CO2 can be stored in the form of high-concentration CO through a reduction process; and the catalyst and carbon are efficiently separated through carbon gasification.

Description

Technical Field

[0001] This invention relates to a vacuum-induced methane cracking method for producing high-quality hydrogen, belonging to the field of combustion chemistry and materials technology. Background Technology

[0002] Hydrogen is an important raw material, long used in ammonia synthesis and oil refining. As an energy carrier, hydrogen plays a positive role in meeting part of global energy demand and reducing carbon dioxide (CO2) emissions. Breakthroughs in fuel cell power generation have also driven hydrogen utilization. Methane, with its high hydrogen-to-carbon ratio, abundant reserves, and ease of processing, is a promising hydrogen production source. Currently, commonly used methane-to-hydrogen / syngas technologies include steam reforming (SRM), dry reforming (DRM), partial oxidation of methane (POM), and methane decomposition; among these, SRM is the most industrialized hydrogen production method. However, the SRM process is complex, involving multiple steps such as methane desulfurization, reforming, water-gas shift, and pressure swing adsorption. SRM inevitably produces CO2, and capturing and storing CO2 requires significant energy and is costly.

[0003] Currently, hydrogen production technologies based on SMR, DMR, and POM all generate COx during the reaction process, which contradicts the principles of green development. Catalytic cracking of methane (CMD) for hydrogen production offers advantages such as simplicity, easy product separation, and no carbon oxide generation. The resulting high-purity hydrogen can be directly used in proton exchange membrane fuel cells without further purification, reducing hydrogen production costs. The solid product, carbon materials, can be used in fuel cells or as advanced functional materials. Catalytic cracking of methane has become an attractive alternative for obtaining high-purity hydrogen and high-value-added carbon materials, with broad application prospects.

[0004] Kinetic studies show that after chemisorption of methane molecules at active sites, the CH bonds break successively. Methyl dehydrogenation is generally considered the rate-determining step of the entire process. CMD is a moderately endothermic reaction; direct thermal cracking of methane requires temperatures above 1200 °C to completely decompose it into hydrogen and carbon. Therefore, the methane cracking reaction requires catalysts to improve the kinetics of the process and lower the reaction temperature. Optimization of methane cracking catalysts not only refers to higher reactivity and lower reaction temperatures but also includes the ability to maintain thermochemical stability under intense carbon deposition. The catalyst's activity, stability, and the characteristics of surface carbon deposition all play a crucial role in the yield of the reaction products. Summary of the Invention

[0005] To address the problems of low methane conversion rate, easy catalyst sintering, and difficulty in separating catalyst from carbon deposits in existing methane decomposition hydrogen production technologies, this invention proposes a vacuum-induced methane cracking method for producing high-quality hydrogen. The aim is to improve the methane decomposition conversion rate, enhance the purity of the produced hydrogen, and achieve efficient separation of the catalyst and carbon deposits, converting the carbon deposits into high-concentration CO for storage, which facilitates catalyst regeneration and recycling.

[0006] A method for producing high-quality hydrogen from methane through vacuum-induced cracking includes the following steps:

[0007] Step 1): Methane cracking in a methane decomposition reactor;

[0008] In the modular methane decomposition reactor, a transition metal-supported catalyst is used to decompose methane in a carrier gas containing CH4 to produce H2 and a carbon-transition metal support mixture; the temperature of the catalytic methane decomposition reaction is 650℃~850℃ and the pressure is 0.03125bar~1bar.

[0009] The transition metal-supported catalyst wherein the transition metal is Ni, Fe, Co, Mg, Ru, or Cu. The support is Al₂O₃, MgO, SiO₂, SBA-15, or 13X. Preferably, a Ni-Al₂O₃ catalyst is used, with a Ni mass content of 5%–40%.

[0010] The temperature and pressure of CH4 are ambient temperature and pressure, i.e., 20℃ and 1 atm, and the CH4 flow rate is greater than 0 and less than or equal to 40 kmol / h.

[0011] The excess heat from the high-temperature H2 generated by the catalytic methane cracking reaction is used to preheat CH4.

[0012] Step 2): The catalyst is decarbonized in the carbon separation reactor;

[0013] The carbon-transition metal support mixture is decarbonized under a gasifying agent to obtain a transition metal-support mixture and decarbonized CO gas; the gasifying agent is O2, CO2, or H2O. The temperature of the catalytic decarbonization reaction is 750℃~950℃.

[0014] The high-temperature CO at the outlet is preheated to the imported CO2 through a heat exchanger, so that the heat can be used multiple times.

[0015] The decarbonized transition metal-support is recycled to step 1), and by repeating the above steps, large-scale continuous cracking of methane to produce hydrogen is achieved.

[0016] The catalyst preferred in this invention is a Ni-Al2O3 catalyst, with a Ni mass content of 5% to 40%. The preferred method is as follows:

[0017] Step 1): Methane cracking of CH4 in a methane decomposition reactor

[0018] In a modular methane decomposition reactor, a Ni-Al2O3 catalyst is used to decompose methane in a carrier gas containing CH4 at a temperature of 650℃~850℃ and a pressure of 0bar~1bar to produce H2 and a carbon-nickel-aluminum mixture.

[0019] The generated high-heat H2 is used to preheat CH4, thus enabling multiple uses of heat.

[0020] The Ni-Al2O3 catalyst has a Ni content of 5% to 40%, the CH4 temperature and pressure are ambient temperature and pressure (20℃ and 1 atm), and the CH4 flow rate is 0 to 40 kmol / h;

[0021] Step 2): Decarbonization of the catalyst in the carbon separation reactor

[0022] A carbon-nickel-aluminum mixture was decarburized at 0%–100 vol% CO2 (gasifying agent) and 750℃–950℃ to obtain Ni-Al2O3 and CO decarburized gas.

[0023] The decarburized Ni-Al2O3 is recycled to step 1).

[0024] This invention reports for the first time a catalytic cracking method for CH4 under vacuum conditions. Furthermore, by synergistically controlling the active Ni content, temperature, and pressure during the process, a high methane conversion rate is achieved. The cracking reaction does not produce gases other than hydrogen, contributing to the production of high-purity hydrogen. The generated high-temperature hydrogen can be used to preheat the feedstock CH4, enabling multiple energy utilization. Moreover, this invention facilitates the efficient separation of carbon deposits from the catalyst. When using CO2 as a gasifying agent for separation, the carbon deposits can be converted into high-concentration CO for storage, and catalyst regeneration can be achieved. This invention offers superior methane conversion and higher hydrogen yield, and the carbon separation process also generates more valuable high-concentration CO, demonstrating greater industrial applicability.

[0025] The technical solution of this invention involves using a Ni-Al2O3 catalyst to perform a methane cracking reaction under a carrier gas containing CH4. Based on the coordinated control of temperature, pressure, and CH4 flow rate during the methane cracking reaction, high-quality hydrogen is produced from methane through cracking. The catalyst, which has carbon deposits after the reaction, is decarbonized in a 100 vol% CO2 gasification agent atmosphere at a temperature of 750℃ to 950℃, thereby achieving multiple hydrogen production cycles from the catalyst.

[0026] In step 1) of this invention, high-quality hydrogen production is achieved based on the mechanism of methane cracking. The reaction mechanism is as follows:

[0027] CH4→2H2+C.

[0028] In this invention, the vaporizing agent can also be replaced by at least one of water vapor and O2.

[0029] In this invention, step 1) is carried out in a fixed-bed reactor;

[0030] Preferably, the flow rate of methane in the carrier gas is 5–20 kmol / h; more preferably, it is 10–15 kmol / h.

[0031] Preferably, in step 1), the temperature of the methane cracking reaction is 700℃~800℃.

[0032] Preferably, in step 1), the reaction pressure is 0.03125 bar to 0.5 bar.

[0033] Preferably, in step 1), the Ni content is 10% to 20%.

[0034] In this invention, step 2) is carried out in an atmosphere containing a CO2 vaporizing agent;

[0035] Preferably, the concentration of CO2 in the gasifying agent is 60 vol% to 100 vol%.

[0036] In this invention, in step 2), the catalyst decarbonization regeneration temperature is 750℃~950℃. Preferably, the regeneration temperature is 800℃~900℃.

[0037] In step 2), the regeneration reactor is powered by solar energy or industrial waste heat.

[0038] In this invention, step 2) is carried out in a fixed-bed or moving-bed reactor.

[0039] The beneficial effects of this invention are as follows:

[0040] 1. This invention reports for the first time that Ni-Al2O3 catalyzes the catalytic cracking reaction of methane under vacuum. Compared with existing catalytic cracking processes using methane and oxygen carriers, this method helps to improve methane conversion and obtain better hydrogen yield and quality. The relationship between hydrogen yield and temperature and pressure in the methane cracking reaction is as follows: Figure 12 As shown, compared to the process under normal pressure, the hydrogen yield can be increased by 12.57% when 10% Ni-Al2O3 catalyzes the methane cracking reaction under vacuum. Furthermore, this process only produces hydrogen and carbon, without generating CO2, which helps to achieve green production of hydrogen from methane.

[0041] 2. Based on this invention, Ni-Al2O3 catalyzes the catalytic cracking reaction of methane under vacuum. Compared with existing catalytic cracking processes using methane and oxygen carriers, this invention, through the C+CO2→2CO carbon gasification reaction, exhibits superior carbon removal performance. Compared to processes under atmospheric pressure, placing the carbon-deposited catalyst in a CO2 atmosphere, the relationship between carbon monoxide concentration and temperature and pressure when the reaction is stable is as follows: Figure 4 As shown, CO emissions increased by 20.48% at a carbonization temperature of 650℃. Furthermore, this process also improved carbon dioxide emission reduction capabilities.

[0042] 3. Based on the processing technology in step 1) of this invention, further control of Ni dosage, methane flow rate, processing temperature and reaction pressure can produce a synergistic effect, which is beneficial to methane cracking and improves hydrogen selectivity.

[0043] Based on the above analysis, it can be seen that the method of refining hydrogen by catalytic methane cracking based on Ni-based oxygen carrier is simple, easy to operate, produces high-quality hydrogen, and has a low conversion temperature, making it suitable for industrial applications and yielding high-quality raw materials or energy. Attached Figure Description

[0044] Figure 1 This is a flowchart of the method of the present invention;

[0045] Figure 2 The graph shows the relationship between the concentration of hydrogen at the reactor outlet and temperature and pressure in Example 1.

[0046] Figure 3 This is a graph showing the relationship between methane conversion rate and temperature and pressure during the reaction process in Example 1.

[0047] Figure 4 This is a graph showing the relationship between carbon monoxide concentration and temperature and pressure in Example 1.

[0048] Figure 5 This is a graph showing the relationship between carbon conversion rate and temperature and pressure in Example 1.

[0049] Figure 6 This is a graph showing the relationship between the heat load and total heat load during the methane cracking and carbonization stages in Example 1, and the changes in temperature T1 and pressure P1.

[0050] Figure 7 The three-dimensional diagram shows the total heat load of the methane cracking and carbonization stages when the reaction conditions for the carbonization stage in Example 1 are T2 = 850°C and P2 = 0.06 bar.

[0051] Figure 8 This is a graph showing the relationship between carbon monoxide yield and concentration as a function of the concentration of carbon dioxide in the gasifying agent in Example 1.

[0052] Figure 9 This is a graph showing the relationship between the heat load and total heat load during the methane cracking and carbonization stages in Example 3, and the changes in carbonization temperature T2 and pressure P2.

[0053] Figure 10 This is a curve showing the range of conditions under which the methane cracking performance of this system is optimal when the reaction conditions during the carbonization stage are T2 = 850℃ and P2 = 0.06 bar.

[0054] Figure 11 This is a curve showing the range of conditions under which the carbon gasification performance of this system is optimal when the reaction conditions in the methane cracking stage are T1 = 750℃ and P1 = 0.06 bar.

[0055] Figure 12 The graph shows the relationship between hydrogen yield and temperature and pressure in the methane cracking reaction of this system under the reaction conditions of T2 = 850℃ and P2 = 0.06 bar during the carbonization stage.

[0056] Figure 13 The graph shows the relationship between carbon monoxide yield and temperature and pressure during the carbon gasification reaction in this system under the reaction conditions of T1 = 750℃ and P1 = 0.06 bar during the methane cracking stage. Detailed Implementation

[0057] The present invention will be further described below with reference to embodiments, comparative examples, and the accompanying drawings.

[0058] In the following examples, 10% Ni refers to nickel comprising 10% of the total mass of the catalyst. The examples use... Figure 1 The process is shown below.

[0059] Example 1: Experimental Testing

[0060] 1) A Ni-Al₂O₃ catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al₂O₃ is 10% of the total catalyst mass) is fed into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) is fed into the reactor as feed gas. The temperature is increased to 750℃ at a heating rate of 170℃ / min, and the internal pressure of the reactor is adjusted to 0.06 bar. The main products are high-quality hydrogen and fibrous carbon material, containing a small amount of amorphous carbon deposits. The relationship between the hydrogen concentration at the reactor outlet and temperature and pressure is shown in the figure. Figure 2 As shown, the hydrogen concentration at the reactor outlet is 99.57%. The relationship between the methane conversion rate and temperature and pressure during the reaction process is shown in the figure. Figure 3 As shown, the condition range curve for optimal methane cracking performance when the carbonization temperature T2 = 850℃ and P2 = 0.06 bar is shown in the figure. Figure 10As shown, the methane conversion rate in the reaction process was 99.14%, and the relationship between hydrogen yield and temperature and pressure is shown in the figure. Figure 12 As shown, the hydrogen yield is 7.93 kmol / h.

[0061] 2) After the catalytic cracking of methane, the atmosphere for the decarbonization stage is switched to 100 vol% CO2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 850℃ and a low pressure of 0.06 bar, the amorphous carbon adhering to the catalyst separates from the catalyst, and the carbon reacts with carbon dioxide to vaporize and generate carbon monoxide. The relationship between carbon monoxide concentration and temperature and pressure is shown in [Figure showing the relationship between carbon monoxide concentration and temperature and pressure]. Figure 4 As shown, the carbon monoxide concentration is 99.59%, and the relationship between carbon conversion rate and temperature and pressure is shown in the figure. Figure 5 As shown, the carbon conversion rate is 99.99%. The optimal carbon gasification performance is achieved under the following conditions: T1 = 750℃ and P1 = 0.06 bar. Figure 11 As shown, the relationship between carbon monoxide yield and temperature and pressure is given in the figure. Figure 13 As shown, the carbon monoxide yield is 7.93 kmol / h.

[0062] During the methane cracking and gasification stages, produced gas was continuously collected. The relationship between the heat load and total heat load during the methane cracking and gasification stages and the changes in methane cracking temperature T1 and pressure P1 was tested. Figure 6 , Figure 7 As shown, the heat load of the methane cracking stage is 27.54 kcal / sec, the heat load of the carbon gasification stage is 48.65 kcal / sec, and the total heat load of the methane cracking and carbon gasification stages is 76.19 kcal / sec.

[0063] The relationship between carbon monoxide yield and concentration during the carbon gasification stage and the concentration of carbon dioxide in the introduced gasifying agent (taking a decarbonization temperature of 850℃ as an example) is as follows: Figure 8 As shown, with the increase of carbon dioxide concentration in the gasifying agent, both the carbon monoxide yield and concentration increase. When the carbon dioxide concentration reaches 100%, the carbon monoxide yield increases from 0 kmol / h to 7.93 kmol / h, and the carbon monoxide concentration reaches 97.15 vol.

[0064] Example 2:

[0065] The only difference from Example 1 is the pressure during the reaction process.

[0066] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al2O3 is 10% of the total catalyst mass) was introduced into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) was introduced into the methane decomposition reactor. The temperature was increased to 750℃ at a heating rate of 170℃ / min. The pressure inside the reactor was adjusted to 0.5 bar. The main products were high-concentration hydrogen and fibrous carbon materials, containing a small amount of amorphous carbon deposits. The hydrogen concentration at the reactor outlet was 96.75%. The methane conversion rate during the reaction was 93.70%, and the hydrogen yield was 7.50 kmol / h.

[0067] 2) After the catalytic cracking of methane, the atmosphere for the decarbonization stage is switched to 100 vol% CO2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 850℃ and a low pressure of 0.5 bar, the amorphous carbon attached to the catalyst separates from the catalyst, and the carbon reacts with carbon dioxide to gasify into carbon monoxide, with a carbon monoxide concentration of 96.86% and a carbon conversion rate of 94.69%.

[0068] Gas was continuously collected during the methane cracking and carbonization stages. The heat load and total heat load of the methane cracking and carbonization stages were tested in relation to temperature and pressure. The heat load of the methane cracking stage was 26.19 kcal / sec, the heat load of the carbonization stage was 45.18 kcal / sec, and the total heat load of the methane cracking and carbonization stages was 71.37 kcal / sec.

[0069] Example 3:

[0070] The only difference from Example 1 is that the temperature is different during the reaction process.

[0071] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al2O3 is 10% of the total catalyst mass) is fed into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) is fed into the methane decomposition reactor. The temperature is increased to 850℃ at a heating rate of 170℃ / min. The pressure inside the reactor is adjusted to 0.06 bar. The main products are high-quality hydrogen and fibrous carbon materials, containing a small amount of amorphous carbon deposits. The hydrogen concentration at the reactor outlet is 99.84%. The methane conversion rate during the reaction is 99.67%, and the hydrogen yield is 7.97 kmol / h.

[0072] 2) After the catalytic cracking of methane, the atmosphere for the decarbonization stage is switched to 100 vol% CO2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 950℃ and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst separates from the catalyst, and the carbon reacts with carbon dioxide to gasify into carbon monoxide, with a carbon monoxide concentration of 99.59% and a carbon conversion rate of 99.99%.

[0073] Gas was continuously collected during the methane cracking and gasification stages. The relationship between the heat load and total heat load during the methane cracking and gasification stages and the changes in gasification temperature T2 and pressure P2 was tested. Figure 9 As shown, the heat load of the methane cracking stage is 29.89 kcal / sec, the heat load of the carbon gasification stage is 51.02 kcal / sec, and the total heat load of the methane cracking stage and the carbon gasification stage is 80.91 kcal / sec.

[0074] Example 4:

[0075] The only difference from Example 1 is that the temperature is different during the reaction process.

[0076] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al2O3 is 10% of the total catalyst mass) was introduced into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) was introduced into the methane decomposition reactor. The temperature was increased to 650℃ at a heating rate of 170℃ / min. The pressure inside the reactor was adjusted to 0.06 bar. The main products were high-quality hydrogen and fibrous carbon materials, containing a small amount of amorphous carbon deposits. The hydrogen concentration at the reactor outlet was 98.79%. The methane conversion rate during the reaction was 97.19%, and the hydrogen yield was 7.79 kmol / h.

[0077] 2) After the catalytic cracking of methane, the atmosphere for the decarbonization stage is switched to 100 vol% CO2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 750℃ and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst separates from the catalyst, and the carbon reacts with carbon dioxide to gasify into carbon monoxide, with a carbon monoxide concentration of 97.91% and a carbon conversion rate of 96.33%.

[0078] Gas was continuously collected during the methane cracking and carbonization stages. The heat load and total heat load of the methane cracking and carbonization stages were tested in relation to temperature and pressure. The heat load of the methane cracking stage was 25.82 kcal / sec, the heat load of the carbonization stage was 44.71 kcal / sec, and the total heat load of the methane cracking and carbonization stages was 70.53 kcal / sec.

[0079] Comparative Example 1:

[0080] Compared with Example 1, the only difference is that carbon dioxide is not added as a gasifying agent in the carbon gasification process; instead, an O2 atmosphere is used.

[0081] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al2O3 is 10% of the total catalyst mass) is fed into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) is fed into the methane decomposition reactor. The temperature is increased to 750℃ at a heating rate of 170℃ / min. The pressure inside the reactor is adjusted to 0.06 bar. The main products are high-quality hydrogen and fibrous carbon materials, containing a small amount of amorphous carbon deposits. The hydrogen concentration at the reactor outlet is 99.57%. The methane conversion rate during the reaction is 99.14%, and the hydrogen yield is 7.93 kmol / h.

[0082] 2) After the catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% O2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 850℃ and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst does not separate from the catalyst, the carbon monoxide yield is 0 kmol / h, and the carbon monoxide concentration is 0.02%.

[0083] Gas was continuously collected during the methane cracking and carbonization stages. The relationship between the heat load and total heat load during the methane cracking and carbonization stages and the changes in temperature and pressure was tested. The heat load during the methane cracking stage was 27.54 kcal / sec.

[0084] Comparing the methane conversion rate and outlet hydrogen concentration in the methane cracking stage and the carbon monoxide concentration in the carbon gasification stage of Example 1 and Comparative Example 1, the reaction performance in the methane cracking stage remained basically unchanged; in contrast, no reaction occurred in the carbon gasification stage, the carbon monoxide conversion rate decreased by 100%, the carbon monoxide concentration decreased by 99.98%, the catalyst could not be regenerated and decarbonized, which seriously affected the recycling of the catalyst.

[0085] Comparative Example 2:

[0086] The only difference from Example 1 is that atmospheric pressure is used during the reaction.

[0087] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20℃; 1 atm; Ni content in Ni-Al2O3 is 10% of the total catalyst mass) was introduced into a methane decomposition reactor. Methane (4 kmol / h; 20℃; 1 atm) was introduced into the methane decomposition reactor as feed gas. The temperature was increased to 750℃ at a heating rate of 170℃ / min. The pressure inside the reactor was adjusted to 1 bar. The main products were high-concentration hydrogen and fibrous carbon materials, containing a small amount of amorphous carbon deposits. The hydrogen concentration at the reactor outlet was 93.87%. The methane conversion rate during the reaction was 88.45%, and the hydrogen yield was 7.08 kmol / h.

[0088] 2) After the catalytic cracking of methane, the atmosphere for the decarbonization stage is switched to 100 vol% CO2 at a flow rate of 4 kmol / h, entering the carbon separation stage. At a high temperature of 850℃ and a low pressure of 1 bar, the amorphous carbon attached to the catalyst separates from the catalyst, and the carbon reacts with carbon dioxide to gasify into carbon monoxide, with a carbon monoxide concentration of 94.08% and a carbon conversion rate of 89.55%.

[0089] Gas was continuously collected during the methane cracking and carbonization stages. The heat load and total heat load of the methane cracking and carbonization stages were tested in relation to temperature and pressure. The heat load of the methane cracking stage was 24.88 kcal / sec, the heat load of the carbonization stage was 44.09 kcal / sec, and the total heat load of the methane cracking and carbonization stages was 68.97 kcal / sec.

[0090] The reaction conditions and results of the examples and comparative examples are shown in Table 1.

[0091] Table 1

[0092]

[0093] Comparing the methane conversion rate and outlet hydrogen concentration in the methane cracking stage of Example 1 and Comparative Example 2, and the carbon monoxide concentration and carbon conversion rate in the carbon gasification stage, the methane cracking performance decreased in the methane cracking stage, the outlet hydrogen concentration decreased by 5.70%, and the methane conversion rate decreased by 10.69% in the reaction process. In contrast, the carbon gasification performance decreased in the carbon deposition stage, the carbon monoxide concentration decreased by 5.51%, and the carbon conversion rate decreased by 10.44%. The reaction process failed to generate high-quality hydrogen and carbon monoxide, and there was a waste of the imported raw materials.

[0094] This invention discloses a vacuum-induced methane cracking method for producing high-quality hydrogen. The method requires two circulating reactors: a methane decomposition reactor and a carbon separation reactor. Under high-temperature vacuum conditions, methane is cracked into solid carbon and high-purity hydrogen in the methane decomposition reactor. The resulting carbon, along with a catalyst, is then fed to the carbon separation reactor, where it is subsequently vaporized by introduced carbon dioxide / oxygen. The heat for this method is provided by solar energy and combustion. Essentially, this method produces H2 and CO from CH4 and CO2, respectively. The innovation compared to existing methane catalytic technologies mainly lies in:

[0095] 1) In the catalytic cracking reaction of methane, the catalytic effect of the Ni-Al2O3 system (CH4→C+2H2), combined with the synergistic regulation of ultra-low pressure and suitable temperature, helps to improve the methane conversion rate and obtain better hydrogen yield and quality. The relationship between hydrogen yield and temperature and pressure when the pressure of the methane catalytic reaction decreases from 1 bar to 0.03125 bar is as follows: Figure 12 As shown, the hydrogen yield can be increased by 18.64%, and the methane conversion rate can be increased by 27.64%. In addition, this process only produces hydrogen and carbon, and does not produce CO2, which helps to achieve green production of hydrogen from methane.

[0096] 2) In the carbon gasification stage, this invention has superior carbon removal performance through the C+CO2→2CO carbon gasification reaction. The carbon-deposited catalyst is placed in the reactor and decarbonized under the atmosphere of CO2 gasification agent, which has a positive impact on carbon dioxide emission reduction. When the CO2 concentration increases from 0 vol% to 100 vol%, the CO yield increases from 0 kmol / h to 7.93 kmol / h.

[0097] 3) By controlling the composition of the products in combination with conditions such as catalyst Ni content, reaction temperature, reaction pressure, gasifying agent type and concentration, the high-quality hydrogen produced by methane cracking can be directionally adjusted, and carbon separation of carbon deposited catalyst under the action of gasifying agent can be achieved, thus realizing low-loss recycling of catalyst.

Claims

1. A method for producing high-quality hydrogen gas by vacuum degree-induced methane cracking, characterized by, The method comprises the following steps: Step 1): CH4 is cracked in a methane decomposition reactor; In the module methane decomposition reactor, a transition metal-support catalyst is subjected to methane cracking under a carrier gas containing CH4 to generate H2 and a carbon-transition metal-support mixture; the temperature of the catalytic methane cracking reaction is 650-850 DEG C, and the pressure is 0.03125 bar-1 bar; Step 2): the catalyst is decarburized in a carbon separation reactor; The carbon-transition metal-support mixture is subjected to decarburization under a gasifying agent to obtain a transition metal-support and a CO decarburization gas; The outlet high-temperature CO is preheated by a heat exchanger for the inlet CO2 to realize multiple utilization of heat; The decarburized transition metal-support is recycled to step 1), and the above steps are repeatedly circulated to realize large-scale continuous cracking of methane to produce hydrogen.

2. A method of producing high quality hydrogen from vacuum induced methane cracking as claimed in claim 1, wherein, In step 1), the transition metal-support catalyst, the transition metal is Ni, Fe, Co, Mg, Ru or Cu.

3. A method of producing high quality hydrogen from vacuum induced methane cracking as claimed in claim 1, wherein, The transition metal-support catalyst, the support uses Al2O3, MgO, SiO2, SBA-15 or 13X.

4. The method of claim 1, wherein the method is characterized by, The transition metal-support catalyst is a Ni-Al2O3 catalyst, and the mass content of Ni is 5%-40%.

5. The method of claim 1, wherein the method is characterized by, In step 1), the excess heat of the high-temperature H2 generated by the catalytic methane cracking reaction is used for preheating CH4.

6. The method of claim 1, wherein the method is characterized by, In step 2), the gasifying agent is O2, CO2 or H2O.

7. The method of claim 1, wherein the method is characterized by, In step 2), the temperature of the catalyst decarburization reaction is 750-950 DEG C.

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