CN119390015A - A method for producing high-quality hydrogen by vacuum-induced methane cracking - Google Patents
A method for producing high-quality hydrogen by vacuum-induced methane cracking Download PDFInfo
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Abstract
The invention discloses a method for preparing high-quality hydrogen by vacuum degree induced methane pyrolysis, which comprises the steps of 1) carrying out methane pyrolysis on a transition metal-carrier catalyst in a module methane decomposition reactor under the carrier gas containing CH 4 to generate H 2 and a carbon-transition metal carrier mixture, 2) carrying out decarburization on the carbon-transition metal carrier mixture under a gasifying agent to obtain a transition metal-carrier and CO decarburization gas, preheating imported CO 2 by an outlet high-temperature CO through a heat exchanger to realize multiple heat utilization, recycling the decarburized transition metal-carrier to the step 1), and carrying out cyclic repetition of the steps to realize large-scale continuous methane pyrolysis hydrogen production. The present invention converts excess CO 2 to valuable CO or a mixture of CO 2 and CO. When pure CO 2 is used as a raw material, carbon elements in CO 2 can be stored in the form of high-concentration CO through a reduction process, and the catalyst and carbon are separated efficiently through carbon gasification.
Description
Technical Field
The invention relates to a method for preparing high-quality hydrogen by methane pyrolysis induced by vacuum degree, belonging to the technical field of combustion chemical industry and materials.
Background
Hydrogen is an important feedstock and has long been used in ammonia synthesis and oil refining. Hydrogen is used as an energy carrier and has positive significance for meeting the global partial energy demand and reducing the emission of carbon dioxide (CO 2). The use of fuel cell power generation has made a breakthrough progress, which has also driven the utilization of hydrogen. Methane has the characteristics of high hydrogen-carbon ratio, abundant reserves, easy treatment and the like, and is a hydrogen production source with wide prospect. Currently, common methane hydrogen production/synthesis gas technologies include methane Steam Reforming (SRM), methane Dry Reforming (DRM), methane Partial Oxidation (POM), and methane decomposition, with SRM being the most industrialized method of producing hydrogen. However, the SRM process is complex, including multiple steps of methane desulfurization, reforming, water gas shift, and pressure swing adsorption. The SRM inevitably generates CO 2, and capturing and sequestering CO 2 not only requires a significant amount of energy, but is also costly.
At present, the hydrogen production technology based on SMR, DMR and POM generates COx in the reaction process, which is contrary to the green development principle. The methane catalytic Cracking (CMD) hydrogen production has the advantages of simple method, easy separation of products, no generation of carbon oxides and the like. The produced high-purity hydrogen can be directly used for proton exchange membrane fuel cells without further purification, so that the hydrogen production cost is reduced, and the solid product carbon material can be used for fuel cells or used as an advanced functional material. Methane catalytic pyrolysis becomes an attractive alternative way for obtaining high-purity hydrogen and high-added-value carbon materials, and has wide application prospect.
Kinetic studies have shown that after chemisorption of methane molecules on the active site, the c—h bonds are successively broken. It is generally believed that methyl dehydrogenation is the rate controlling step of the overall process. CMD is a moderately endothermic reaction, and direct thermal cracking of methane requires temperatures above 1200 ℃ to completely decompose into hydrogen and carbon materials. Thus, the methane cracking reaction requires the use of a catalyst to improve the methane cracking process kinetics and reduce the reaction temperature. Optimization of methane cracking catalysts refers not only to higher reactivity and lower reaction temperatures, but also to the ability to maintain thermochemical stability in strong char deposits. The activity and stability of the catalyst and the characteristic of surface carbon deposit play a vital role in the yield of the reaction product.
Disclosure of Invention
Aiming at the problems of lower methane conversion rate, easy sintering of the catalyst and difficult separation of the catalyst and carbon deposit in the existing methane decomposition hydrogen production technology, the invention provides a method for preparing high-quality hydrogen by methane decomposition induced by vacuum degree, which aims at improving the methane decomposition conversion rate, improving the purity of produced hydrogen, realizing the efficient separation of the catalyst and the carbon deposit, converting the carbon deposit into high-concentration CO for storage, and being beneficial to the regeneration and recycling of the catalyst.
A vacuum degree induced methane pyrolysis high-quality hydrogen method comprises the following steps:
step 1) methane cracking of CH 4 in a methane decomposition reactor;
In a modular methane decomposition reactor, a transition metal-supported catalyst is subjected to methane pyrolysis under a carrier gas containing CH 4 to generate H 2 and a carbon-transition metal support mixture, wherein the temperature of the catalytic methane pyrolysis reaction is 650-850 ℃ and the pressure is 0.03125-1 bar.
The transition metal-supported catalyst is Ni, fe, co, mg, ru or Cu. The carrier adopts Al 2O3、MgO、SiO2, SBA-15 or 13X. The catalyst is preferably Ni-Al 2O3, and the mass content of Ni is 5-40%.
The temperature and pressure of CH 4 are ambient temperature and pressure, namely 20 ℃ and 1atm, and the flow rate of CH 4 is more than 0 and less than or equal to 40kmol/h;
the excess heat of the high heat H 2 generated by the catalytic methane cracking reaction is used for preheating CH 4.
Step 2) decarbonizing the catalyst in a carbon separation reactor;
Decarbonizing the carbon-transition metal carrier mixture under a gasifying agent to obtain a transition metal carrier and CO decarbonizing gas, wherein the gasifying agent is O 2、CO2 or H 2 O. The temperature of the catalyst decarburization reaction is 750-950 ℃.
Preheating the high-temperature CO at the outlet to the inlet CO 2 through a heat exchanger to realize the repeated utilization of heat;
And (3) recycling the decarbonized transition metal-carrier into the step (1), and recycling the steps to realize the large-scale continuous hydrogen production by methane pyrolysis.
The catalyst is preferably a Ni-Al 2O3 catalyst, and the mass content of Ni is 5% -40%. The specific method is preferably as follows:
step 1) methane cleavage of CH 4 in a methane decomposition reactor
In a modular methane decomposition reactor, carrying out methane pyrolysis on a Ni-Al 2O3 catalyst at a temperature of 650-850 ℃ and a pressure of 0-1 bar in a carrier gas containing CH 4 to generate H 2 and a carbon-nickel-aluminum mixture;
The generated high heat H 2 is used for preheating CH 4, so that the heat can be utilized for multiple times;
The Ni content of the Ni-Al 2O3 catalyst is 5% -40%, the temperature and the pressure of CH 4 are the ambient temperature and the ambient pressure (20 ℃ and 1 atm), and the flow rate of CH 4 is 0% -40 kmol/h;
Step 2) decarbonizing the catalyst in a carbon separation reactor
Decarbonizing the carbon-nickel-aluminum mixture at the temperature of 0-100 vol% CO 2 (gasifying agent) and 750-950 ℃ to obtain Ni-Al 2O3 and CO decarbonizing gas;
The decarbonized Ni-Al 2O3 is recycled to step 1).
According to the invention, the CH 4 is subjected to catalytic pyrolysis under the vacuum degree condition for the first time, the high conversion rate of methane is realized based on the cooperative control of the active Ni content, the temperature and the pressure in the treatment process, the pyrolysis reaction does not generate gas except hydrogen, the high-purity hydrogen is obtained, the generated high-heat hydrogen can be used for preheating the raw material CH 4, the energy can be repeatedly utilized, and the high-efficiency separation of carbon deposition and a catalyst is promoted. According to the technical scheme, the method has the advantages of better methane conversion rate and higher hydrogen yield, and the carbon separation process can generate high-concentration CO with higher value, so that the method has better industrial practical value.
According to the technical scheme, the Ni-Al 2O3 catalyst is subjected to methane cracking reaction under the carrier gas containing CH 4, high-quality hydrogen is produced by methane cracking based on the cooperative control of the temperature, the pressure and the CH 4 flow in the methane cracking reaction process, and the carbon deposition catalyst after the reaction is subjected to decarburization in the 100vol% CO 2 gasifying agent atmosphere at the temperature of 750-950 ℃ to realize the repeated cycling hydrogen production of the catalyst.
In the step 1) of the invention, the high-quality hydrogen production is realized based on a methane cracking mechanism, and the reaction mechanism is as follows:
CH4→2H2+C。
In the invention, the gasifying agent can also be replaced by at least one of water vapor and O 2.
In the present invention, in step 1), it is carried out in a fixed bed reactor;
preferably, the flow rate of methane in the carrier gas is 5 to 20kmol/h, and more preferably 10 to 15kmol/h.
Preferably, in the step 1), the temperature of methane cracking reaction is 700-800 ℃.
Preferably, in the step 1), the reaction pressure is 0.03125bar to 0.5bar.
Preferably, in the step 1), the content of Ni is 10% -20%.
In the present invention, in step 2), the process is performed under an atmosphere containing a CO 2 gasifying agent;
preferably, the concentration of CO 2 in the gasifying agent is 60-100 vol%.
In the invention, in the step 2), the decarburization regeneration temperature of the catalyst is 750-950 ℃. Preferably, the regeneration temperature is 800 ℃ to 900 ℃.
The regeneration reactor in the step 2) adopts solar energy to supply energy or industrial waste heat to supply heat.
In the present invention, the step 2) is performed in a fixed bed or moving bed reactor.
The invention has the beneficial effects that:
1. According to the invention, the first report that Ni-Al 2O3 is used for catalyzing methane to perform catalytic cracking reaction under vacuum degree, and compared with the existing catalytic cracking process of methane and oxygen carrier, the catalytic cracking process is beneficial to improving the methane conversion rate and obtaining better hydrogen yield and quality. The relationship between hydrogen yield and temperature and pressure in methane cracking reaction is shown in fig. 12, and compared with the process under normal pressure, the hydrogen yield can be improved by 12.57% when 10% Ni-Al 2O3 is used for catalyzing methane cracking reaction under vacuum. In addition, the reaction process only generates hydrogen and carbon, does not generate CO 2, and is beneficial to realizing green production of hydrogen production by methane.
2. Based on the catalytic cracking reaction of the Ni-Al 2O3 catalytic methane under the vacuum degree, compared with the existing catalytic cracking process of methane and an oxygen carrier, the catalytic cracking process has better carbon removal performance through the carbon gasification reaction of C+CO 2 →2CO, compared with the process under the normal pressure condition, the carbon deposition catalyst is placed under the CO 2 atmosphere, the change relation of the concentration of carbon monoxide with the temperature and the pressure is shown in figure 4 when the reaction is stable, and the CO is increased by 20.48 percent at the carbon gasification temperature of 650 ℃. In addition, the process also improves the carbon dioxide emission reduction capability.
3. Under the treatment process based on the step 1), the synergistic effect can be generated by further controlling the Ni consumption, the methane flow rate, the treatment temperature and the reaction pressure in a combined way, so that the cracking of methane is facilitated, and the hydrogen selectivity is improved.
Aiming at the analysis, the method for refining the hydrogen based on the Ni-based oxygen carrier catalytic methane cracking method is simple and feasible, convenient to operate, high in quality of produced hydrogen, low in conversion temperature, applicable to industrial application and capable of obtaining high-quality raw materials or energy sources.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a graph showing the concentration of hydrogen at the outlet of the reactor of example 1 as a function of temperature and pressure;
FIG. 3 is a graph showing methane conversion as a function of temperature and pressure for the reaction process of example 1;
FIG. 4 is a graph showing the relationship between carbon monoxide concentration and temperature versus pressure in example 1;
FIG. 5 is a graph of carbon conversion as a function of temperature and pressure for example 1;
FIG. 6 is a graph showing the total heat load as a function of temperature T 1 and pressure P 1 for the methane cracking stage and the carbon gasification stage of example 1;
fig. 7 is a three-dimensional plot of the total amount of heat load for the methane cracking stage and the carbon gasification stage for example 1 at reaction conditions of T 2＝850℃、P2 =0.06 bar;
FIG. 8 is a graph of carbon monoxide yield and concentration as a function of carbon dioxide concentration fed to the gasifier for example 1;
FIG. 9 is a graph showing the total heat load as a function of the carbon gasification temperature T 2 and the pressure P 2 for the methane cracking stage and the carbon gasification stage of example 3;
fig. 10 is a graph of the range of conditions for the system for optimal methane cracking performance at a reaction condition of T 2＝850℃、P2 =0.06 bar in the carbon gasification stage;
FIG. 11 is a graph of the range of conditions for the present system for optimal carbon gasification performance at reaction conditions T 1＝750℃、P1 = 0.06bar in the methane cracking stage;
FIG. 12 is a graph showing the hydrogen yield as a function of temperature and pressure for a methane cracking reaction for a carbon gasification stage of the present system at reaction conditions of T 2＝850℃、P2 =0.06 bar;
Fig. 13 is a graph of carbon monoxide yield as a function of temperature and pressure for the present system in a carbon gasification reaction at a methane cracking stage reaction condition of T 1＝750℃、P1 =0.06 bar.
Detailed Description
The invention will be further illustrated with reference to examples, comparative examples and figures of the specification.
The 10% Ni used in the examples below is 10% nickel by weight of the total mass of the catalyst. The embodiment adopts the flow as shown in fig. 1.
Example 1 test by experiment
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) is fed into a methane decomposition reactor, methane is fed into the methane decomposition reactor as raw material gas (4 kmol/h;20 ℃ C.; 1 atm), the temperature is raised to 750 ℃ at a heating rate of 170 ℃ C.; and the pressure in the reactor is regulated to 0.06bar, the main products are high-quality hydrogen and fiber carbon materials, a small amount of amorphous carbon deposit is contained, the change of the concentration of the hydrogen at the outlet of the reactor along with the temperature and the pressure is shown in FIG. 2, the change of the hydrogen concentration at the outlet of the reactor along with the temperature and the pressure is shown in FIG. 3, the condition range curve when the methane cracking performance is optimal when the carbon gasification temperature T 2＝850℃、P2 = 0.06bar is shown in FIG. 10, the change of the hydrogen yield along with the temperature along with the pressure is shown in FIG. 12, and the hydrogen yield along with the temperature is 7.93kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% CO 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At a high temperature of 850 ℃ and a low pressure of 0.06bar, the amorphous carbon attached to the catalyst is separated from the catalyst, carbon and carbon dioxide react and gasify to generate carbon monoxide, the relationship between the concentration of carbon monoxide and the temperature and the pressure is shown in figure 4, the relationship between the concentration of carbon monoxide and the pressure is 99.59%, the relationship between the conversion rate of carbon and the temperature and the pressure is shown in figure 5, the conversion rate of carbon is 99.99%, when the reaction condition in the methane cracking stage is T 1＝750℃、P1 = 0.06bar, the condition range curve when the carbon gasification performance is optimal is shown in figure 11, the relationship between the yield of carbon monoxide and the temperature and the pressure is shown in figure 13, and the yield of carbon monoxide is 7.93kmol/h.
The gas production was continuously collected in the methane cracking stage and the carbon gasification stage, and the methane cracking stage and the carbon gasification stage were tested for the heat load and the total amount of heat load as a function of the methane cracking temperature T 1 and the pressure P 1 as shown in fig. 6 and 7, the methane cracking stage heat load=27.54 kcal/sec, the carbon gasification stage heat load=48.65 kcal/sec, and the methane cracking stage and the carbon gasification stage heat load total amount was 76.19kcal/sec.
In the carbon gasification stage, the relation between the carbon monoxide yield and the concentration of the carbon dioxide fed into the gasifying agent (taking the decarburization temperature of 850 ℃ as an example) is shown in FIG. 8, the carbon monoxide yield and the concentration of the carbon dioxide are increased along with the increase of the carbon dioxide concentration of the gasifying agent, and when the carbon dioxide concentration reaches 100%, the carbon monoxide yield is increased from 0kmol/h to 7.93kmol/h, and the carbon monoxide concentration reaches 97.15vol%.
Example 2:
the only difference compared to example 1 is the pressure difference during the reaction.
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) was fed into a methane decomposition reactor, methane was fed as a raw material gas (4 kmol/h;20 ℃ C.; 1 atm) into the methane decomposition reactor, the temperature was raised to 750 ℃ C.; at a heating rate of 170 ℃ C.; and the pressure inside the reactor was regulated to 0.5bar, the main products were high-concentration hydrogen and fibrous carbon materials, a small amount of amorphous carbon deposit was contained, the reactor outlet hydrogen concentration was 96.75%, the reaction process methane conversion was 93.70%, and the hydrogen yield was 7.50kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% CO 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At a high temperature of 850 ℃ and a low pressure of 0.5bar, the amorphous carbon attached to the catalyst is separated from the catalyst, carbon and carbon dioxide react and gasify to generate carbon monoxide, the concentration of the carbon monoxide is 96.86%, and the carbon conversion rate is 94.69%.
And continuously collecting gas production in the methane cracking stage and the carbon gasification stage, and testing the change relation of the heat load and the total heat load of the methane cracking stage and the carbon gasification stage along with the temperature and the pressure, wherein the heat load of the methane cracking stage is=26.19 kcal/sec, the heat load of the carbon gasification stage is=45.18 kcal/sec, and the total heat load of the methane cracking stage and the carbon gasification stage is 71.37kcal/sec.
Example 3:
The only difference compared to example 1 is the temperature difference during the reaction.
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) was introduced into a methane decomposition reactor, methane was introduced as a raw material gas (4 kmol/h;20 ℃ C.; 1 atm) into the methane decomposition reactor, the temperature was raised to 850 ℃ C.; at a heating rate of 170 ℃ C.; and the pressure inside the reactor was regulated to 0.06bar, the main products were high-quality hydrogen and fibrous carbon materials, a small amount of amorphous carbon deposit was contained, the reactor outlet hydrogen concentration was 99.84%, the reaction process methane conversion was 99.67%, and the hydrogen yield was 7.97kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% CO 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At a high temperature of 950 ℃ and a low pressure of 0.06bar, the amorphous carbon attached to the catalyst is separated from the catalyst, carbon and carbon dioxide react and gasify to generate carbon monoxide, the concentration of the carbon monoxide is 99.59%, and the carbon conversion rate is 99.99%.
The gas production was continuously collected in the methane cracking stage and the carbon gasification stage, and the relationship between the methane cracking stage and the carbon gasification stage in terms of the heat load and the total amount of heat load with the carbon gasification temperature T 2 and the pressure P 2 was tested as shown in fig. 9, the methane cracking stage heat load=29.89 kcal/sec, the carbon gasification stage heat load=51.02 kcal/sec, and the methane cracking stage and the carbon gasification stage heat load total amount of 80.91kcal/sec.
Example 4:
The only difference compared to example 1 is the temperature difference during the reaction.
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) was fed into a methane decomposition reactor, methane was fed as a raw material gas (4 kmol/h;20 ℃ C.; 1 atm) into the methane decomposition reactor, the temperature was raised to 650 ℃ C., at a heating rate of 170 ℃ C.; and the pressure inside the reactor was regulated to 0.06bar, the main products were high-quality hydrogen and fibrous carbon materials, a small amount of amorphous carbon deposit was contained, the reactor outlet hydrogen concentration was 98.79%, the reaction process methane conversion was 97.19%, and the hydrogen yield was 7.79kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% CO 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At a high temperature of 750 ℃ and a low pressure of 0.06bar, the amorphous carbon attached to the catalyst is separated from the catalyst, carbon and carbon dioxide react and gasify to generate carbon monoxide, the concentration of the carbon monoxide is 97.91%, and the carbon conversion rate is 96.33%.
And continuously collecting gas production in the methane cracking stage and the carbon gasification stage, and testing the change relation of the heat load and the total heat load of the methane cracking stage and the carbon gasification stage along with the temperature and the pressure, wherein the heat load of the methane cracking stage is=25.82 kcal/sec, the heat load of the carbon gasification stage is=44.71 kcal/sec, and the total heat load of the methane cracking stage and the carbon gasification stage is 70.53kcal/sec.
Comparative example 1:
The only difference compared to example 1 is that the carbon gasification process does not add the gasifying agent carbon dioxide, and an O 2 atmosphere is used instead.
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) was fed into a methane decomposition reactor, methane was fed as a raw material gas (4 kmol/h;20 ℃ C.; 1 atm) into the methane decomposition reactor, the temperature was raised to 750 ℃ C.; at a heating rate of 170 ℃ C.; and the pressure inside the reactor was regulated to 0.06bar, the main products were high-quality hydrogen and fibrous carbon materials, a small amount of amorphous carbon deposit was contained, the reactor outlet hydrogen concentration was 99.57%, the reaction process methane conversion was 99.14%, and the hydrogen yield was 7.93kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% O 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At a high temperature of 850 ℃ and a low pressure of 0.06bar, the amorphous carbon attached to the catalyst is not separated from the catalyst, the carbon monoxide yield is 0kmol/h, and the carbon monoxide concentration is 0.02%.
The gas production was continuously collected in the methane cracking stage and the carbon gasification stage, and the methane cracking stage and the carbon gasification stage were tested for heat load and the total amount of heat load as a function of temperature and pressure, and methane cracking stage heat load=27.54 kcal/sec.
The methane conversion rate and the outlet hydrogen concentration in the methane cracking stage and the carbon monoxide concentration in the carbon gasification stage of the comparative example 1 and the comparative example 1 are basically unchanged, the reaction performance in the methane cracking stage is basically unchanged, carbon deposition in the comparative carbon gasification stage is not reacted, the carbon monoxide conversion rate is reduced by 100%, the carbon monoxide concentration is reduced by 99.98%, the catalyst cannot be regenerated and decarbonized, and the catalyst is seriously influenced to be recycled.
Comparative example 2:
The only difference compared to example 1 is that atmospheric pressure was used during the reaction.
1) Ni-Al 2O3 catalyst (0.4 kmol/h;20 ℃ C.; 1atm; ni content in Ni-Al 2O3 is 10% of total mass of catalyst) was introduced into a methane decomposition reactor, methane was introduced as a raw material gas (4 kmol/h;20 ℃ C.; 1 atm) into the methane decomposition reactor, the temperature was raised to 750 ℃ C., at a heating rate of 170 ℃ C.; and the pressure inside the reactor was adjusted to 1bar, the main products were high-concentration hydrogen and fibrous carbon materials, a small amount of amorphous carbon deposit was contained, the reactor outlet hydrogen concentration was 93.87%, the reaction process methane conversion was 88.45%, and the hydrogen yield was 7.08kmol/h.
2) After catalytic cracking of methane, the decarbonization stage was switched to atmosphere 100vol% CO 2 at a flow rate of 4kmol/h and entered the carbon separation stage. At high temperature of 850 ℃ and low pressure of 1bar, the amorphous carbon attached to the catalyst is separated from the catalyst, carbon and carbon dioxide react and gasify to generate carbon monoxide, the concentration of the carbon monoxide is 94.08%, and the carbon conversion rate is 89.55%.
And continuously collecting gas production in the methane cracking stage and the carbon gasification stage, and testing the change relation of the heat load and the total heat load of the methane cracking stage and the carbon gasification stage along with the temperature and the pressure, wherein the heat load of the methane cracking stage is= 24.88kcal/sec, the heat load of the carbon gasification stage is= 44.09kcal/sec, and the total heat load of the methane cracking stage and the carbon gasification stage is 68.97kcal/sec.
The reaction conditions and results of the examples and comparative examples are specifically shown in Table 1.
TABLE 1
The methane conversion rate and the outlet hydrogen concentration in the methane cracking stage, the carbon monoxide concentration in the carbon gasification stage and the carbon conversion rate in the comparison example 1 and the comparison example 2 are reduced, the methane cracking performance in the methane cracking stage is reduced, the outlet hydrogen concentration is reduced by 5.70%, the methane conversion rate in the reaction process is reduced by 10.69%, the carbon deposition gasification performance in the comparison carbon gasification stage is reduced, the carbon monoxide concentration is reduced by 5.51%, the carbon conversion rate is reduced by 10.44%, high-quality hydrogen and carbon monoxide cannot be generated in the reaction process, and the waste phenomenon exists in the raw materials at the reaction inlet.
The invention discloses a method for preparing high-quality hydrogen by methane pyrolysis induced by vacuum degree. The process requires two recycle reactors, including a methane decomposition reactor and a carbon separation reactor (carbon separation reactor). Methane is decomposed into solid carbon and high-purity hydrogen in a methane decomposition reactor under the condition of high-temperature vacuum degree. The carbon produced is then sent to a carbon separation reactor along with a catalyst, followed by gasification of the introduced carbon dioxide/oxygen. The design heat of the method is provided by solar energy and combustion. The essence of this process is the production of H 2 and CO from CH 4 and CO 2, respectively. Compared with the existing methane catalysis technology, the method is mainly characterized in that:
1) In the methane catalytic cracking reaction process, the catalysis of a Ni-Al 2O3 system (CH 4→C+2H2) is combined with the synergistic regulation and control of ultralow pressure and proper temperature, so that the methane conversion rate is improved, and better hydrogen yield and quality are obtained. The hydrogen yield with temperature and pressure changes when the methane catalytic reaction pressure was reduced from 1bar to 0.03125bar, as shown in fig. 12, can be improved by 18.64%, and the methane conversion rate is improved by 27.64%. In addition, the reaction process only generates hydrogen and carbon, does not generate CO 2, and is beneficial to realizing green production of hydrogen production by methane.
2) In the carbon gasification stage, through the C+CO 2 - & gt 2CO carbon gasification reaction, the carbon removal performance is better, a carbon deposition catalyst is placed in a reactor, decarburization is carried out in the CO 2 gasifying agent atmosphere, the carbon dioxide emission reduction is positively influenced, and when the concentration of CO 2 is increased from 0vol% to 100vol%, the CO yield is increased from 0kmol/h to 7.93kmol/h.
3) The composition of the product is controlled by controlling the Ni content of the catalyst, the reaction temperature, the reaction pressure, the type and the concentration of the gasifying agent and other conditions, so that methane pyrolysis is directionally regulated to produce high-quality hydrogen, carbon separation of the carbon deposition catalyst under the action of the gasifying agent is realized, and low-loss recycling of the catalyst is realized.
Claims (8)
1. The vacuum degree induced methane pyrolysis method for preparing high-quality hydrogen is characterized by comprising the following steps of:
step 1) methane cracking of CH 4 in a methane decomposition reactor;
In a modular methane decomposition reactor, subjecting a transition metal-supported catalyst to methane cracking in a carrier gas containing CH 4 to produce H 2, and a carbon-transition metal support mixture;
step 2) decarbonizing the catalyst in a carbon separation reactor;
decarbonizing the carbon-transition metal carrier mixture under a gasifying agent to obtain a transition metal carrier and CO decarbonizing gas;
Preheating the high-temperature CO at the outlet to the inlet CO 2 through a heat exchanger to realize the repeated utilization of heat;
And (3) recycling the decarbonized transition metal-carrier into the step (1), and recycling the steps to realize the large-scale continuous hydrogen production by methane pyrolysis.
2. The method for producing high-quality hydrogen by vacuum induced methane pyrolysis according to claim 1, wherein in step 1), the transition metal is Ni, fe, co, mg, ru or Cu.
3. The method for preparing high-quality hydrogen by methane pyrolysis under the induction of vacuum degree according to claim 1, wherein the transition metal-carrier catalyst is Al 2O3、MgO、SiO2, SBA-15 or 13X.
4. The method for preparing high-quality hydrogen by methane pyrolysis induced by vacuum degree according to claim 1, wherein the transition metal-carrier catalyst is a Ni-Al 2O3 catalyst, and the mass content of Ni is 5% -40%.
5. The method for preparing high-quality hydrogen by methane pyrolysis induced by vacuum degree according to claim 1, wherein in the step 1), the temperature of the catalytic methane pyrolysis reaction is 650-850 ℃, and the pressure is 0.03125-1 bar.
6. The method for producing high-quality hydrogen by vacuum induced methane pyrolysis according to claim 1, wherein in step 1), excess heat of high heat H 2 generated by catalytic methane pyrolysis reaction is used for preheating CH 4.
7. The method for producing high-quality hydrogen by vacuum induced methane pyrolysis according to claim 1, wherein in the step 2), the gasifying agent is O 2、CO2 or H 2 O.
8. The method for preparing high-quality hydrogen by methane pyrolysis under vacuum degree induction according to claim 1, wherein in the step 2), the temperature of the catalyst decarburization reaction is 750-950 ℃.
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