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

Abstract

The invention discloses a method for preparing high-quality hydrogen by vacuum degree induced methane cracking, which comprises the following steps: 1) in a module methane decomposition reactor, performing methane cracking on a transition metal-carrier catalyst under carrier gas containing CH4 to generate H2 and a carbon-transition metal carrier mixture; 2) decarbonizing the carbon-transition metal carrier mixture in the presence of a gasifying agent to obtain a transition metal-carrier and CO decarbonized gas; high-temperature CO at an outlet is used for preheating CO2 at an inlet through a heat exchanger, so that heat can be utilized for many times; and circulating the decarbonized transition metal-carrier to the step (1), and circulating the steps to realize large-scale continuous cracking of methane to produce hydrogen. According to the invention, redundant CO2 is converted 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 efficient separation of the catalyst and carbon is realized through carbon gasification.

Description

Technical Field

[0001] The invention relates to a method for preparing high-quality hydrogen by cracking methane induced by vacuum, and belongs to the technical field of combustion chemical industry and materials. Background Art

[0002] Hydrogen is an important raw material that has long been used for ammonia synthesis and oil refining. As an energy carrier, hydrogen has positive significance for meeting part of the global energy demand and reducing carbon dioxide (CO2) emissions. Breakthrough progress has been made in the application of fuel cell power generation, which has also promoted the use of hydrogen. Methane has the characteristics of high hydrogen-to-carbon ratio, abundant reserves, and easy handling, making it a promising source of hydrogen production. At present, the commonly used methane hydrogen / syngas technologies include methane steam reforming (SRM), methane dry reforming (DRM), methane partial oxidation (POM) and methane decomposition; among them, SRM is the most industrialized hydrogen production method. However, the SRM process is complex, including multiple steps such as methane desulfurization, reforming, water gas shift and pressure swing adsorption. SRM inevitably produces CO2, and capturing and storing CO2 not only requires a lot of energy but also is costly.

[0003] At present, hydrogen production technologies based on SMR, DMR and POM all produce COx during the reaction process, which is contrary to the principle of green development. Methane catalytic cracking (CMD) hydrogen production has the advantages of simple method, easy separation of products and no carbon oxides. The high-purity hydrogen produced can be directly used in proton exchange membrane fuel cells without further purification, reducing the cost of hydrogen production, and the solid product carbon material can be used in fuel cells or as advanced functional materials. Methane catalytic cracking has become an attractive alternative way to obtain high-purity hydrogen and high-value-added carbon materials, with broad application prospects.

[0004] Kinetic studies have shown that after the methane molecules are chemically adsorbed on the active sites, the CH bonds are broken one after another. It is generally believed that methyl dehydrogenation is the rate-controlling step of the entire process. CMD is a moderately endothermic reaction, and the direct thermal cracking of methane requires a temperature of more than 1200°C to completely decompose into hydrogen and carbon materials. Therefore, the methane cracking reaction requires the use of catalysts to improve the kinetics of the methane cracking process and reduce the reaction temperature. The optimization of methane cracking catalysts refers not only to higher reaction activity and lower reaction temperature, but also to the ability to maintain thermochemical stability in strong carbon deposition. The activity and stability of the catalyst and the characteristics of the surface carbon deposition play a crucial role in the yield of the reaction products. Summary of the invention

[0005] In view of the problems of low methane conversion rate, easy sintering of catalyst and difficulty in separating catalyst from carbon deposits in the existing methane decomposition hydrogen production technology, the present invention proposes a method for producing high-quality hydrogen by vacuum-induced methane cracking, aiming to improve the methane decomposition conversion rate, improve the purity of produced hydrogen, and realize efficient separation of catalyst and carbon deposits, convert the carbon deposits into high-concentration CO for storage, which is conducive to the regeneration and recycling of the catalyst.

[0006] A method for producing high-quality hydrogen by vacuum-induced methane cracking comprises the following steps:

[0007] Step 1): methane cracking of CH4 in a methane decomposition reactor;

[0008] In the modular methane decomposition reactor, a transition metal-supported catalyst is used to crack methane in 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°C to 850°C and the pressure is 0.03125 bar to 1 bar.

[0009] The transition metal-carrier catalyst has a transition metal of Ni, Fe, Co, Mg, Ru or Cu. The carrier is Al2O3, MgO, SiO2, SBA-15 or 13X. The preferred catalyst is Ni-Al2O3, with a Ni content of 5% to 40%.

[0010] The temperature and pressure of CH4 are the ambient temperature and pressure, i.e., 20°C 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 of the high-temperature H2 generated by the catalytic methane cracking reaction is used to preheat CH4.

[0012] Step 2): decarbonizing the catalyst in a carbon separation reactor;

[0013] The carbon-transition metal carrier mixture is decarbonized in the presence of a gasifying agent to obtain a transition metal-carrier and CO decarbonized gas; the gasifying agent is O2, CO2 or H2O. The temperature of the catalyst decarbonization reaction is 750°C to 950°C.

[0014] The high-temperature CO at the outlet is used to preheat the inlet CO2 through a heat exchanger to achieve multiple utilization of heat;

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

[0016] The catalyst of the present invention is preferably a Ni-Al2O3 catalyst, and the Ni content is 5% to 40%. The specific method is preferably:

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

[0018] In a modular methane decomposition reactor, a Ni-Al2O3 catalyst is used to crack methane in a carrier gas containing CH4 at a temperature of 650°C to 850°C and a pressure of 0 bar to 1 bar to generate H2 and a carbon-nickel-aluminum mixture;

[0019] The generated high-heat H2 is used to preheat CH4, realizing multiple utilization of heat;

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

[0021] Step 2): Catalyst decarbonization in the carbon separation reactor

[0022] Decarburizing the carbon-nickel-aluminum mixture at 0% to 100 vol% CO2 (gasifying agent) at 750° C. to 950° C. to obtain Ni-Al2O3 and CO decarburized gas;

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

[0024] The present invention reports for the first time that CH4 is catalytically cracked under vacuum conditions, and further based on the coordinated control of active Ni content, temperature, and pressure during the treatment process, a high conversion rate of methane is achieved. The cracking reaction does not produce gases other than hydrogen, which helps to obtain high-purity hydrogen. The generated high-heat hydrogen can be used for preheating raw material CH4 to achieve multiple energy utilization. In addition, the present invention also helps to promote the efficient separation of carbon deposits and catalysts, and when using gasifying agent CO2 for separation, carbon deposits can be converted into high-concentration CO for storage, and catalyst regeneration can be achieved. The technical solution of the present invention has a better methane conversion rate and a higher hydrogen yield. The carbon separation process can also generate more valuable high-concentration CO, which has better industrial practical value.

[0025] According to the technical solution of the present invention, a Ni-Al2O3 catalyst performs a methane cracking reaction in a carrier gas containing CH4, and based on the coordinated control of the temperature, pressure and CH4 flow rate of the methane cracking reaction process, methane cracking is achieved to produce high-quality hydrogen, and the carbon-deposited catalyst after the reaction is decarbonized in a 100 vol% CO2 gasifying agent atmosphere at a temperature of 750°C to 950°C, thereby achieving multiple cycles of catalyst hydrogen production.

[0026] In step 1) of the present invention, high-quality hydrogen production is achieved based on the mechanism of methane cracking, and its reaction mechanism is:

[0027] CH4→2H2+C.

[0028] In the present invention, the gasifying agent may also be replaced by at least one of water vapor and O2.

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

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

[0031] Preferably, in step 1), the temperature of the methane cracking reaction is 700°C to 800°C.

[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 the present invention, step 2) is carried out in an atmosphere containing a CO2 gasifying agent;

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

[0036] In the present invention, in step 2), the catalyst decarbonization regeneration temperature is 750°C to 950°C. Preferably, the regeneration temperature is 800°C to 900°C.

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

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

[0039] The present invention has the beneficial effects:

[0040] 1. The present invention reports for the first time that Ni-Al2O3 catalyzes the catalytic cracking reaction of methane under vacuum, which helps to improve the methane conversion rate and obtain better hydrogen yield and quality compared with the existing catalytic cracking process of methane and oxygen carrier. The relationship between the hydrogen yield in the methane cracking reaction and the temperature and pressure is as follows Fig.12 As shown, compared with the process under normal pressure conditions, the hydrogen yield can be increased by 12.57% when 10% Ni-Al2O3 catalyzes the methane cracking reaction under vacuum. In addition, the process only produces hydrogen and carbon, and no CO2, which helps to achieve green production of methane hydrogen.

[0041] 2. Based on the catalytic cracking reaction of methane in vacuum catalyzed by Ni-Al2O3 of the present invention, compared with the existing catalytic cracking process of methane and oxygen carrier, the present invention has better carbon removal performance through C+CO2→2CO carbon gasification reaction. Compared with the process under normal pressure conditions, the carbon-deposited catalyst is placed in a CO2 atmosphere. When the reaction is stable, the relationship between the change of carbon monoxide concentration with temperature and pressure is as follows: Figure 4 As shown in the figure, CO increased by 20.48% at a carbon gasification temperature of 650°C. In addition, the process also improves the carbon dioxide emission reduction capability.

[0042] 3. Based on the treatment process of step 1) of the present invention, further by jointly controlling the Ni dosage, methane flow rate, treatment temperature and reaction pressure, a synergistic effect can be produced, which is beneficial to the cracking of methane and improves the hydrogen selectivity.

[0043] Based on the above analysis, it can be seen that the refining of hydrogen based on the Ni-based oxygen carrier catalytic methane cracking method is simple and easy to operate, has high hydrogen quality and low conversion temperature, is suitable for industrial applications, and can obtain high-quality raw materials or energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart of the method of the present invention;

[0045] Figure 2 The graph is a graph showing the relationship between the concentration of hydrogen at the outlet of the reactor of Example 1 and the temperature and pressure;

[0046] Figure 3 This is a graph showing the relationship between the methane conversion rate and the temperature and pressure during the reaction process of 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 the total heat load in the methane cracking stage and the carbon gasification stage in Example 1 and the temperature T1 and the pressure P1;

[0050] Figure 7 This is a three-dimensional diagram of the total heat load of the methane cracking stage and the carbon gasification stage when the reaction conditions of the carbon gasification stage in Example 1 are T2=850°C and P2=0.06bar;

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

[0052] Fig. 9 This is a graph showing the relationship between the heat load and the total heat load in the methane cracking stage and the carbon gasification stage and the carbon gasification temperature T2 and the pressure P2 of Example 3;

[0053] Fig.10 This is a curve diagram of the condition range when the methane cracking performance is optimal when the reaction conditions of the system in the carbon gasification stage are T2 = 850 ° C and P2 = 0.06 bar;

[0054] Fig.11 This is a curve diagram of the condition range when the carbon gasification performance is optimal when the reaction conditions of the system in the methane cracking stage are T1=750℃, P1=0.06bar;

[0055] Fig.12 This is the relationship between the hydrogen yield in the methane cracking reaction and the temperature and pressure when the reaction conditions in the carbon gasification stage of this system are T2 = 850 ° C and P2 = 0.06 bar;

[0056] Fig.13 This is a graph showing the relationship between the carbon monoxide yield in the carbon gasification reaction and the temperature and pressure when the reaction conditions are T1 = 750°C and P1 = 0.06 bar in the methane cracking stage of this system. DETAILED DESCRIPTION

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

[0058] The 10% Ni used in the following examples means that nickel accounts for 10% of the total mass of the catalyst. Figure 1 The process shown.

[0059] Example 1: Experimental testing

[0060] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20°C; 1 atm; the Ni content in the Ni-Al2O3 is 10% of the total mass of the catalyst) is introduced into a methane decomposition reactor, and methane is introduced into the methane decomposition reactor as a raw gas (4 kmol / h; 20°C; 1 atm), and the temperature is increased to 750°C at a heating rate of 170°C / min, and 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 relationship between the concentration of hydrogen at the reactor outlet and the change of temperature and pressure is shown in Figure 2 As shown, the hydrogen concentration at the reactor outlet is 99.57%, and the relationship between the methane conversion rate and the temperature and pressure during the reaction process is shown in Figure 3 As shown in Figure 2, when the carbon gasification temperature T2 = 850 ° C and P2 = 0.06 bar, the condition range curve for the best methane cracking performance is shown in Figure 2. Fig.10As shown, the methane conversion rate in the reaction process is 99.14%, and the relationship between the hydrogen yield and the temperature and pressure is shown in Fig.12 As shown, the hydrogen production rate is 7.93 kmol / h.

[0061] 2) After catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% CO2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 850°C and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst is separated from the catalyst, and the carbon reacts with carbon dioxide to gasify into carbon monoxide. The relationship between the concentration of carbon monoxide and the temperature and pressure is shown in 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 Figure 5 As shown, the carbon conversion rate is 99.99%. When the reaction conditions of the methane cracking stage are T1 = 750 ° C and P1 = 0.06 bar, the condition range curve for the best carbon gasification performance is shown in Fig.11 As shown in Figure 2, the relationship between carbon monoxide yield and temperature and pressure is shown in Figure 2. Fig.13 As shown, the carbon monoxide production rate is 7.93 kmol / h.

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

[0063] In the carbonization stage, the relationship between the carbon monoxide yield and concentration and the concentration of carbon dioxide introduced into the gasification agent (taking the decarbonization temperature of 850℃ as an example) is as follows: Figure 8 As shown, as the carbon dioxide concentration of the gasifying agent increases, the carbon monoxide yield and concentration both 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] Embodiment 2:

[0065] Compared with Example 1, the only difference is that the pressure during the reaction is different.

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

[0067] 2) After catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% CO2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 850°C and a low pressure of 0.5 bar, the amorphous carbon attached to the catalyst is separated 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 production was continuously collected during the methane cracking stage and the carbon gasification stage, and the heat load and the total heat load of the methane cracking stage and the carbon gasification stage were tested in relation to temperature and pressure. The heat load of the methane cracking stage = 26.19 kcal / sec, the heat load of the carbon gasification stage = 45.18 kcal / sec, and the total heat load of the methane cracking stage and the carbon gasification stage was 71.37 kcal / sec.

[0069] Embodiment 3:

[0070] Compared with Example 1, the only difference is that the temperature during the reaction is different.

[0071] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20°C; 1 atm; the Ni content in Ni-Al2O3 is 10% of the total mass of the catalyst) is introduced into a methane decomposition reactor, and methane is introduced into the methane decomposition reactor as a raw gas (4 kmol / h; 20°C; 1 atm), and the temperature is increased to 850°C at a heating rate of 170°C / min, and 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 catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% CO2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 950°C and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst is separated 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] The gas production was continuously collected during the methane cracking stage and the carbon gasification stage, and the relationship between the heat load and the total heat load in the methane cracking stage and the carbon gasification stage and the carbon gasification temperature T2 and the pressure P2 was tested. Fig. 9 As shown, the heat load of the methane cracking stage = 29.89 kcal / sec, the heat load of the carbon gasification stage = 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] Embodiment 4:

[0075] Compared with Example 1, the only difference is that the temperature during the reaction is different.

[0076] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20°C; 1 atm; the Ni content in Ni-Al2O3 is 10% of the total mass of the catalyst) is introduced into a methane decomposition reactor, and methane is introduced into the methane decomposition reactor as a raw gas (4 kmol / h; 20°C; 1 atm), and the temperature is increased to 650°C at a heating rate of 170°C / min, and 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 98.79%, the methane conversion rate during the reaction is 97.19%, and the hydrogen yield is 7.79 kmol / h.

[0077] 2) After catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% CO2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 750°C and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst is separated 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 production was continuously collected during the methane cracking stage and the carbon gasification stage, and the heat load and the total heat load of the methane cracking stage and the carbon gasification stage were tested in relation to temperature and pressure. The heat load of the methane cracking stage = 25.82 kcal / sec, the heat load of the carbon gasification stage = 44.71 kcal / sec, and the total heat load of the methane cracking stage and the carbon gasification stage was 70.53 kcal / sec.

[0079] Comparative Example 1:

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

[0081] 1) A Ni-Al2O3 catalyst (0.4 kmol / h; 20°C; 1 atm; the Ni content in Ni-Al2O3 is 10% of the total mass of the catalyst) is introduced into a methane decomposition reactor, and methane is introduced into the methane decomposition reactor as a raw gas (4 kmol / h; 20°C; 1 atm), and the temperature is increased to 750°C at a heating rate of 170°C / min, and 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 catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% O2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 850°C and a low pressure of 0.06 bar, the amorphous carbon attached to the catalyst is not separated from the catalyst, the carbon monoxide yield is 0 kmol / h, and the carbon monoxide concentration is 0.02%.

[0083] The produced gas was continuously collected during the methane cracking stage and the carbon gasification stage, and the relationship between the heat load and the total heat load of the methane cracking stage and the carbon gasification stage and the temperature and pressure was tested. The heat load of the methane cracking stage = 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 in Example 1 and Comparative Example 1, the reaction performance in the methane cracking stage is basically unchanged; in contrast, the carbon deposition in the carbon gasification stage does not react, the carbon monoxide conversion rate is reduced by 100%, the carbon monoxide concentration is reduced by 99.98%, and the catalyst cannot be regenerated for decarbonization, which seriously affects the recycling of the catalyst.

[0085] Comparative Example 2:

[0086] Compared with Example 1, the only difference is that normal pressure is used during the reaction.

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

[0088] 2) After catalytic cracking of methane, the atmosphere of the decarbonization stage is switched to 100 vol% CO2 with a flow rate of 4 kmol / h, and the carbon separation stage is entered. At a high temperature of 850°C and a low pressure of 1 bar, the amorphous carbon attached to the catalyst is separated 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 production was continuously collected during the methane cracking stage and the carbon gasification stage, and the heat load and the total heat load of the methane cracking stage and the carbon gasification stage were tested in relation to temperature and pressure. The heat load of the methane cracking stage = 24.88 kcal / sec, the heat load of the carbon gasification stage = 44.09 kcal / sec, and the total heat load of the methane cracking stage and the carbon gasification stage was 68.97 kcal / sec.

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

[0091] Table 1

[0092]

[0093] Comparing the methane conversion rate and the outlet hydrogen concentration in the methane cracking stage, and the carbon monoxide concentration and the carbon conversion rate in the carbon gasification stage in Example 1 and Comparative Example 2, the methane cracking performance in the methane cracking stage is reduced, the outlet hydrogen concentration is reduced by 5.70%, and the methane conversion rate in the reaction process is reduced by 10.69%; compared with the carbon gasification stage, the carbon deposition gasification performance is reduced, the carbon monoxide concentration is reduced by 5.51%, and the carbon conversion rate is reduced by 10.44%. High-quality hydrogen and carbon monoxide cannot be generated in the reaction process, and there is a waste of the imported raw materials in the reaction.

[0094] The present invention discloses a method for producing high-quality hydrogen by vacuum-induced methane cracking. The method requires two circulating reactors, including a methane decomposition reactor and a carbon separation reactor (carbon separation reactor). Under high-temperature vacuum conditions, methane is cracked into solid carbon and high-purity hydrogen in the methane decomposition reactor. The produced carbon is then sent to the carbon separation reactor together with the catalyst, and then gasified by the introduced carbon dioxide / oxygen. The designed heat of the method is provided by solar energy and combustion. The essence of the method is to produce H2 and CO from CH4 and CO2, respectively. Compared with the existing methane catalytic technology, the creativity is mainly reflected in:

[0095] 1) During the methane catalytic cracking reaction, the catalytic effect of the Ni-Al2O3 system (CH4→C+2H2), combined with ultra-low pressure and appropriate temperature synergistic regulation, helps to improve the methane conversion rate and obtain better hydrogen yield and quality. The relationship between the hydrogen yield and temperature and pressure when the methane catalytic reaction pressure is reduced from 1 bar to 0.03125 bar is shown in the figure. Fig.12 As shown in the figure, the hydrogen yield can be increased by 18.64% and the methane conversion rate can be increased by 27.64%. In addition, the process only produces hydrogen and carbon, but no CO2, which helps to achieve green production of methane to hydrogen.

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

[0097] 3) By controlling the Ni content of the catalyst, reaction temperature, reaction pressure, gasification agent type and concentration and other conditions, the composition of the product is jointly controlled, the methane cracking is directionally adjusted to produce high-quality hydrogen, and the carbon separation of the carbon deposited catalyst under the action of the gasification agent is realized, so as to realize the low-loss recycling of the catalyst.

Claims

1. A method for producing high-quality hydrogen by vacuum-induced methane cracking, characterized in that: The following steps are involved: Step 1): methane cracking of CH4 in a methane decomposition reactor; In a modular methane decomposition reactor, a transition metal-supported catalyst is used to crack methane in a carrier gas containing CH4 to generate H2 and a carbon-transition metal support mixture; Step 2): decarbonizing the catalyst in a carbon separation reactor; Decarburizing the carbon-transition metal carrier mixture in the presence of a gasifying agent to obtain a transition metal-carrier and CO decarburized gas; The high-temperature CO at the outlet is used to preheat the inlet CO2 through a heat exchanger to achieve multiple utilization of heat; The decarbonized transition metal-support is recycled to step 1), and the above steps are repeated to achieve large-scale continuous cracking of methane to produce hydrogen.

2. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: In step 1), the transition metal-support catalyst, the transition metal is Ni, Fe, Co, Mg, Ru or Cu.

3. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: The transition metal-carrier catalyst uses Al2O3, MgO, SiO2, SBA-15 or 13X as the carrier.

4. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: The transition metal-carrier catalyst is a Ni-Al2O3 catalyst, and the Ni mass content is 5% to 40%.

5. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: In step 1), the temperature of the catalytic methane cracking reaction is 650° C. to 850° C., and the pressure is 0.03125 bar to 1 bar.

6. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: In step 1), the excess heat of the high-temperature H2 generated by the catalytic methane cracking reaction is used to preheat CH4.

7. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: In step 2), the gasifying agent is O2, CO2 or H2O.

8. The method for producing high-quality hydrogen by vacuum-induced methane cracking according to claim 1, characterized in that: In step 2), the temperature of the catalyst decarbonization reaction is 750°C to 950°C.

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