Catalyst for hydrogen production through catalytic cracking of methane, preparation method of catalyst, and method for hydrogen production and carbon nanomaterial generation through continuous cracking of methane

Abstract

The invention provides a methane catalytic cracking hydrogen production catalyst and a preparation method thereof, the structural formula of the catalyst is x (Nia-Feb). YA.zB, the catalyst takes nickel-iron alloy nanoparticles as an active center, A is an auxiliary metal element, B is a carrier, x, y and z are the mole numbers of nickel-iron alloy, auxiliary metal and the carrier respectively, a and b are the mole numbers of Ni and Fe, x: z = 1: 1-10: 1, x: y = 5: 1-20: 1, and a: b = 1: 1-9: 1. The invention further provides a method for producing hydrogen through continuous methane cracking and generating a carbon nanomaterial, by adopting the catalyst for producing hydrogen through methane catalytic cracking, catalytic cracking at relatively low temperature and low pressure can be achieved, the method is simple in process (one-step method), high-energy-consumption steam is not needed, and energy consumption and production cost are greatly reduced; the hydrogen and the carbon nanomaterial can be generated by efficiently cracking methane, the methane conversion rate exceeds 60%, and the yield of the carbon nanomaterial exceeds 20 gc / gcat.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation and application, and specifically relates to a methane catalytic cracking hydrogen production catalyst and a preparation method thereof, and also relates to a method for continuously cracking methane to produce hydrogen and generate carbon nanomaterials. Background Art

[0002] Energy is the basic condition for the survival and development of human society. With the development of economy and the progress of society, the reserves of fossil fuels are becoming increasingly scarce, and environmental pollution and global warming are becoming increasingly serious. Clean and efficient energy to replace fossil fuels is urgently needed. Hydrogen has the advantages of abundant sources, high mass energy density (calorific value reaches 143MJ / kg), no carbon emissions, clean and pollution-free, so it is hailed as the "ultimate energy" of the 21st century. Especially under the "dual carbon" goal, hydrogen energy has become an important way to achieve carbon reduction goals in industries such as industry, chemical industry and power. More than a dozen countries have issued national hydrogen energy development strategies, fully recognizing the huge potential value of hydrogen energy in the future energy field.

[0003] The current methods of hydrogen production mainly include fossil fuel hydrogen production, byproduct hydrogen recovery, water electrolysis hydrogen production and biomass hydrogen production, among which natural gas is the main method of hydrogen production in the world, accounting for 48%; and for natural gas hydrogen production, steam reforming hydrogen production is the main method, which includes steam generation section, methane steam reforming section, low-temperature water gas shift section, carbon dioxide removal or pressure swing adsorption and other auxiliary steps; in addition to steam reforming, partial oxidation hydrogen production can also be used, using oxygen as a gasification agent, but it will also produce a large amount of carbon dioxide gas like steam reforming, and the process flow is complex and energy consumption is high. Unlike steam reforming and oxidation hydrogen production processes, methane catalytic cracking converts methane into hydrogen and carbon in one step under anaerobic conditions. The process requires low energy, simple process, and the gas produced has a single component and high purity, which has great prospects for promotion and application.

[0004] Chinese patent document CN101838480A discloses a method for the co-production of carbon black and high-purity hydrogen by high-temperature cracking of methane. The method uses low calorific value fuel gas as fuel, adopts controlled oxygen supply to provide pyrolysis temperature, and realizes methane cracking to produce carbon black and hydrogen through heat storage in the reactor, alternating working mode of methane cracking, and multi-stage group combination of cracking reactors. However, this method firstly requires oxygen to assist in combustion, and the pyrolysis temperature is as high as 1400-1500°C, which has high pyrolysis temperature, high energy consumption, and high cost. Secondly, the purity of the produced hydrogen is poor, and the purification process is complicated.

[0005] Chinese patent document CN111689467A discloses a method for producing hydrogen by catalyzing methane cracking with activated carbon as a catalyst. The method adopts a fixed bed reactor for gas-solid phase catalytic reaction, uses activated carbon as a catalyst, and adds a trace amount of hydrogen sulfide to improve the activity of activated carbon catalyzing methane cracking to produce hydrogen, thereby prolonging the deactivation time of the activated carbon catalyst. However, the conversion efficiency and stability of the carbon catalyst are poor, and the catalyst conversion rate is less than 20% and basically deactivated after only a dozen minutes. At the same time, the fixed bed reactor requires intermittent production, which is not conducive to scale expansion.

[0006] Chinese patent document CN104627960A discloses a method for producing hydrogen by catalyzing methane cracking using modified red mud. The method uses red mud as raw material for modification, and prepares a catalyst through acid washing, alkali washing, drying, roasting and reduction, and is applied to catalytic methane cracking. Although the method realizes the resource utilization of red mud and reduces the cost of the catalyst, a large amount of acid and alkali is used in the modification process, which increases the cost of waste liquid treatment. At the same time, the catalytic effect of the method is poor, and the methane conversion rate is only about 20%, which seriously limits the efficiency of hydrogen production.

[0007] Chinese patent document CN104998654A discloses a nickel-based catalyst and its preparation method and a method for producing hydrogen by catalytic cracking of methane. The method uses a nickel-based catalyst to catalytically crack methane gas. The reactor adopts an improved high-density circulating fluidized bed. The catalyst is separated in the settler and then enters the regenerator for regeneration to produce synthesis gas. The energy of the entire system achieves self-heating balance and can be produced continuously on a large scale. Although the regeneration process of this method can extend the life of the catalyst, it will also cause the composition of the synthesis gas to be complex, resulting in a lower purity of hydrogen and increasing the difficulty of purification.

[0008] Chinese patent document CN110963481A discloses a method for producing hydrogen and carbon nanotubes by cracking methane with two catalysts in series. The method connects two reactors in series. The upstream reactor first pyrolyzes the methane and nitrogen mixed raw gas to form hydrogen and carbon materials, and the downstream reactor further pyrolyzes the methane in the upstream tail gas into hydrogen and carbon nanotubes. The method produces high value-added carbon nanotubes through a two-step process, but due to the low methane concentration in the raw gas, the purification cost of the hydrogen-rich mixed gas is also increased, and the processing volume per unit time is too small, making it difficult to produce on a large scale.

[0009] Currently, the method of preparing hydrogen and carbon materials by cracking methane has problems such as high pyrolysis temperature (>800℃), poor catalyst performance, complex process, poor quality of carbon materials, and low processing volume per unit time, which limit its large-scale production and industrial application. Summary of the invention

[0010] In view of the defects of the prior art, the object of the present invention is to provide a methane catalytic cracking hydrogen production catalyst and a preparation method thereof, wherein the prepared catalyst has high catalytic performance and long service life.

[0011] Another object of the present invention is to provide a method for continuously cracking methane to produce hydrogen and generate carbon nanomaterials. By using the catalyst of the present invention, the methane cracking method is simple to operate, the cracking temperature is low, the hydrogen obtained is of high purity, the carbon added value of the carbon nanomaterials is large, and it is easy to produce on a large scale.

[0012] To achieve the above purpose, the solution adopted by the present invention is as follows:

[0013] In a first aspect, the present invention provides a methane catalytic cracking hydrogen production catalyst, the structural formula of the catalyst is x(Nia-Feb)·yA·zB, the catalyst has nickel-iron alloy nanoparticles as the active center, A is an auxiliary metal element, and B is a carrier, wherein x, y, and z are the molar numbers of the nickel-iron alloy, the auxiliary metal, and the carrier, respectively, a and b are the molar numbers of Ni and Fe, x:z=1:1-10:1, x:y=5:1-20:1, a:b=1:1-9:1; preferably, x:y=10:1-20:1;

[0014] Wherein, the catalyst is prepared by a precipitation method, and its preparation method comprises the following steps:

[0015] Step (1), preparation of catalyst precursor: dissolving nickel salt, iron salt, auxiliary metal salt and carrier or carrier precursor salt in water, adding the obtained mixed solution dropwise into an alkaline solution for precipitation reaction, standing for stratification, removing the supernatant to obtain a solid precipitate;

[0016] Step (2), placing the solid precipitate in an ethanol aqueous solution, stirring and washing, filtering, and drying;

[0017] Step (3), calcining, grinding and sieving the dried filter cake to obtain the catalyst.

[0018] Preferably, the additive metal A is selected from one or more metals and / or oxides thereof of Cu, Zn, Co, Mn, Sr and Ce; preferably, the additive metal A is Cu.

[0019] Preferably, the carrier B is selected from one or more of Al2O3, SiO2, MgO, TiO2, ZrO2, graphite and activated carbon; preferably, the carrier B is Al2O3.

[0020] Preferably, the particle size of the carrier B is 100-420 μm.

[0021] Preferably, the particle size of the catalyst is 60 to 200 μm.

[0022] Preferably, in step (1), in step (1), the nickel salt, iron salt, auxiliary metal salt and carrier precursor salt are nitrates, acetates, oxalates or chlorides of nickel, iron, auxiliary metal and carrier precursor, and the alkaline solution is selected from one or more of sodium carbonate, sodium hydroxide, potassium hydroxide, sodium bicarbonate and ammonia solution.

[0023] Preferably, in step (1), the temperature of the precipitation reaction is 25 to 80° C., preferably 35 to 65° C., and the pH value is 8.5 to 10.5; in step (2), the mass concentration of the ethanol aqueous solution is 0.1% to 10%, preferably 1% to 3%, and after washing, the pH value is 6.8 to 7.2, and the washed filter cake is dried at 60 to 100° C., and the drying temperature is 60 to 100° C., preferably 60 to 80° C.; in step (3), the roasting conditions are: the roasting temperature is 450 to 700° C., the roasting time is 2 to 5 hours, and the roasting gas atmosphere is air.

[0024] In a second aspect, the present invention also provides a method for continuously cracking methane to produce hydrogen and generate carbon nanomaterials, comprising the following steps: adding the methane catalytic cracking hydrogen production catalyst and the raw methane gas as described above into a circulating fluidized bed reaction device respectively to carry out cracking reactions, catalytically cracking methane into hydrogen and carbon nanomaterials, purifying the hydrogen through a purification system and collecting it, and depositing the carbon nanomaterials on the catalyst surface and collecting it.

[0025] Preferably, in the circulating fluidized bed reaction device, the temperature of the methane catalytic cracking reaction is 550-850°C, preferably 600-700°C, the pressure of the catalytic cracking reaction is 0.1-1 MPa; the space velocity of the catalyst is 10-200 L / (h·g cat ), preferably 50 to 100 L / (h·g cat ).

[0026] Preferably, the methane catalytic cracking hydrogen production catalyst is added to the circulating fluidized bed reaction device by means of a spiral feeding method. After the methane is catalytically cracked, the deposited carbon nanomaterial is discharged from the bottom of the circulating fluidized bed reaction device by means of a spiral discharging method. A detection end is set at the end of the hydrogen purification system to monitor the methane conversion rate. When the methane conversion rate is lower than a given value, a new catalyst is added to realize a continuous reaction of the reaction device.

[0027] Preferably, the methane conversion rate exceeds 60%, the hydrogen selectivity exceeds 80%, and the carbon nanomaterial yield exceeds 20gc / g cat .

[0028] Preferably, in the methane catalytic cracking hydrogen production catalyst, when the auxiliary metal A is Cu, the methane conversion rate exceeds 80%, the hydrogen selectivity exceeds 90%, and the carbon nanomaterial yield exceeds 30gc / g cat .

[0029] Preferably, in the methane catalytic cracking hydrogen production catalyst, the auxiliary metal A is Cu, and when x:y=10:1-20:1, the methane conversion rate exceeds 80%, the hydrogen selectivity exceeds 90%, and the carbon nanomaterial yield exceeds 45gc / g cat .

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention uses nickel-iron alloy nanoparticles as active centers, and prepares a catalyst by adding auxiliary metals and carriers. The catalyst active metal is uniformly dispersed on the carrier and the active center particle size is small, the catalyst has a large specific surface area, a high methane conversion rate, good hydrogen selectivity, and a large added value of carbon materials; and by adding auxiliary metals, the migration rate of carbon is increased and the catalyst life is extended; the method for continuous cracking of methane to produce hydrogen and generate carbon nanomaterials provided by the present invention, using the methane catalytic cracking hydrogen production catalyst provided by the present invention, can achieve catalytic cracking at relatively low temperature and low pressure, the method is simple in process (one-step method), does not require high-energy steam, and greatly reduces energy consumption and production costs; the present invention adopts a circulating fluidized bed reactor and a spiral feed (discharge), which can enable the cracking reaction to proceed continuously, and is suitable for continuous large-scale production and application. At the same time, the methane catalytic cracking hydrogen production catalyst of the present invention can achieve efficient cracking of methane to produce hydrogen and carbon nanomaterials, the byproduct carbon material is of high quality and high added value, the generated carbon nanomaterials are controllable, excellent in performance, and widely used, and can be used in batteries, supercapacitors, carriers, absorbing materials, composite materials and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a schematic structural diagram of a method and device for continuously cracking methane to produce hydrogen and generate carbon nanomaterials.

[0033] Figure 2 Graph showing the relationship between the methane conversion rate of the catalyst and time in an embodiment of the present invention.

[0034] Figure 3 Graph showing the relationship between hydrogen selectivity and time of the catalyst in the embodiment of the present invention.

[0035] Figure 4 This is a morphology diagram of the carbon nanomaterial prepared by methane cracking in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The invention provides a catalyst for producing hydrogen by catalytic cracking of methane.

[0037] Compared with other traditional hydrogen production methods, methane catalytic cracking reaction can directly produce pure hydrogen because there is no oxygen factor in the reaction. The reaction equation is CH4+2H2O→CO2+4H2. Moreover, compared with other alkanes (such as ethane, propane, etc.), the amount of carbon oxides produced for every 1KgH2 produced is the least, so it has become the first choice for hydrogen production.

[0038] Methane molecules are very stable. In the absence of a catalyst, gas phase cracking can only be carried out effectively above 1473K. Therefore, a highly active catalyst must be used to crack methane under relatively mild conditions. At present, the catalysts used for methane cracking reactions are mainly 3d subgroup metal supported catalysts, such as Fe, Co, Ni, etc.

[0039] Methane can be cracked to produce hydrogen under the action of a catalyst at a relatively low temperature. For example, the cracking reaction temperature of Ni and Co catalysts is between 450-800°C, and Fe catalysts can obtain a high reaction activity at above 700°C. During the cracking process of the catalyst, methane is adsorbed on the catalyst surface and dehydrogenated to obtain carbon. Carbon will continue to accumulate on the catalyst surface, causing the catalyst surface to be continuously covered with metal catalytic active components or blocking the catalyst pores, resulting in reduced catalyst activity or even complete deactivation. By designing specific catalyst types, catalyst preparation conditions, cracking reaction conditions and equipment, carbon deposition can be avoided and the conversion rate of methane can be improved. Therefore, the conversion rate of methane is an important indicator for catalyst evaluation.

[0040] While avoiding carbon deposition, methane continuously grows carbon materials during the cracking process of the catalyst. Therefore, the methane cracking reaction process includes: methane molecules dissociate on the crystal plane of the catalyst metal grains to generate hydrogen, while carbon atoms diffuse, precipitate, and grow into carbon tubes or carbon fibers on the surface or inside the grains. Therefore, in addition to obtaining pure hydrogen, the methane cracking reaction can also be used to prepare various nano-carbon materials, such as carbon nanotubes, carbon nanofibers, carbon nanospheres, or nano-onion carbon. During the preparation process, the morphology of the nano-carbon material is affected by many conditions such as the type of catalyst, the preparation conditions of the catalyst, the cracking reaction conditions, and the cracking equipment.

[0041] In order to obtain a higher methane conversion rate and a better morphology of nano-carbon materials, the present invention provides a methane catalytic cracking hydrogen production catalyst, the structural formula of the catalyst is x(Nia-Feb)·yA·zB, the catalyst uses nickel-iron alloy nanoparticles as active centers, A is an auxiliary metal element, and B is a carrier, wherein x, y, and z are respectively the molar numbers of the nickel-iron alloy, the auxiliary metal and the carrier, a and b are the molar numbers of Ni and Fe, x:z=1:1-10:1, x:y=5:1-20:1, and a:b=1:1-9:1.

[0042] <Catalyst active component>

[0043] As mentioned above, Fe, Co, Ni and other metal supported catalysts are well-known catalysts that can be used for methane cracking reactions. These Fe, Co, Ni and other metal catalysts play a dual role of catalytic activation and carbon atom migration in the form of metal grains during the catalytic cracking of methane. The structure and size of these metal grains during the reaction determine the activity of the catalyst and the duration of the activity. According to existing literature reports, the catalytic activity of these metal catalysts is Ni>Co>Fe. In the methane catalytic cracking hydrogen production catalyst provided by the present invention, the composite alloy nanoparticles of Ni and Fe are used as the catalyst active component. It is confirmed by the embodiments of the present invention that the catalytic activity is better than that of Ni or Fe alone.

[0044] In the methane catalytic cracking hydrogen production catalyst provided by the present invention, composite alloy nanoparticles of Ni and Fe act as catalyst active components, and the molar number of Ni and Fe in the alloy nanoparticles of Ni and Fe is a:b=1:1-9:1. If the molar number of Ni and Fe exceeds or falls below this numerical range, the activity of the catalyst and the conversion rate of methane will be reduced.

[0045] <Auxiliary Metal Components>

[0046] Adding auxiliary metal components to the above-mentioned metal-loaded catalyst will affect the state of the metal catalyst particles, and the addition of auxiliary metal components also increases the mobility of hydrogen atoms and reduces the growth rate of the carbon atom layer on the surface of the metal catalyst, thereby slowing down the process of the catalyst particles being wrapped by the carbon layer, thereby improving the stability of the metal catalyst, and increasing the reaction activity of the catalyst for methane cracking, and significantly increasing the amount of carbon deposition on the catalyst, thereby obtaining a better morphology of the nanocarbon material.

[0047] In the methane catalytic cracking hydrogen production catalyst provided by the present invention, the auxiliary metal component A includes but is not limited to one or more metals selected from Cu, Zn, Co, Mn, Sr and Ce and / or their oxides, and the total molar number of alloy nanoparticles of Ni and Fe to the molar number of the auxiliary metal component A is x:y=5:1 to 20:1. Exceeding or falling below this numerical range will reduce the activity and stability of the catalyst.

[0048] It is further confirmed by the examples of the present invention that when the auxiliary metal component A is Cu, the methane conversion rate and carbon nanomaterial yield obtained by the catalyst in the process of catalytic cracking of methane to produce hydrogen are higher than the methane conversion rate and carbon nanomaterial yield when other auxiliary metal components are used, thereby showing that Cu as an auxiliary metal component has better reaction activity of assisting the catalyst active components Ni and Fe.

[0049] <Carrier Components>

[0050] Adding a carrier on the basis of the above-mentioned metal-loaded catalyst will also have an important influence on the activity of the catalyst. The present invention loads the catalyst active components and auxiliary metal components of the composite alloy nanoparticles of Ni and Fe on the carrier, which can significantly improve the activity of the catalyst and extend the life of the catalyst.

[0051] In the methane catalytic cracking hydrogen production catalyst provided by the present invention, the carrier B includes but is not limited to one or more of Al2O3, SiO2, MgO, TiO2, ZrO2, graphite and activated carbon. In the embodiment of the present invention, Al2O3 is used as an example of carrier B to illustrate the scheme of the present invention. The ratio of the total molar number of Ni and Fe alloy nanoparticles to the molar number of carrier B is x:z=1:1~10:1. Exceeding or falling below this numerical range will reduce the activity and life of the catalyst.

[0052] In the catalyst for producing hydrogen from catalytic cracking of methane provided by the present invention, the carrier B exists in the form of powder, and its particle size may be 100 to 420 μm.

[0053] <Preparation of Catalyst>

[0054] The methane catalytic cracking hydrogen production catalyst provided by the present invention is prepared by a precipitation method, comprising the following steps:

[0055] Step (1), preparation of catalyst precursor: dissolving nickel salt and iron salt in water, then adding auxiliary metal salt and carrier or carrier precursor salt, adding the obtained mixed solution dropwise into alkaline solution for precipitation reaction, standing for stratification, removing the supernatant to obtain a solid precipitate;

[0056] In this step, the nickel salt, iron salt, auxiliary metal salt and carrier precursor salt are nitrates, acetates, oxalates or chlorides of nickel, iron, auxiliary metal and carrier precursor, and the alkaline solution includes but is not limited to one or more of sodium carbonate, sodium hydroxide, potassium hydroxide, sodium bicarbonate and ammonia solution.

[0057] In this step, the temperature of the precipitation reaction may be 25 to 80° C., preferably 35 to 65° C., and the pH value may be 8.5 to 10.5.

[0058] Step (2), adding the solid precipitate into an ethanol aqueous solution, stirring, washing, filtering, and drying;

[0059] In this step, the mass concentration of the ethanol aqueous solution can be 0.1% to 10%, preferably 1% to 3%. After washing, the pH value of the washing liquid is 6.8 to 7.2, and the washed filter cake is dried at 60 to 100° C. (preferably 60 to 80° C.).

[0060] Step (3), calcining, grinding and screening the dried filter cake to obtain the methane catalytic cracking hydrogen production catalyst of the present invention.

[0061] In this step, the calcination conditions are as follows: the calcination temperature may be 450-700° C., the calcination time is 2-5 hours, and the calcination gas atmosphere is air.

[0062] The powdered methane catalytic cracking hydrogen production catalyst prepared by the above preparation method has a particle size of 60 to 200 μm. In the prepared catalyst, the catalyst active metal is evenly dispersed on the carrier, and the active center particle size is small. The catalyst has a large specific surface area, which can greatly improve the methane conversion rate.

[0063] At the same time, the powdered methane catalytic cracking hydrogen production catalyst prepared by the above preparation method can obtain a catalyst with a higher loading rate on the carrier because the active metal, the auxiliary metal and the carrier precursor are directly blended and then precipitated through a solvent reaction. In addition, the active metal components of the catalyst are more evenly dispersed in the carrier, the active center particle size of the prepared catalyst is smaller, and the catalyst has more reaction active sites, thereby greatly improving the reaction activity of the catalyst and improving the conversion rate of methane catalytic cracking.

[0064] <Method and device for continuous cracking of methane to produce hydrogen and generate carbon nanomaterials>

[0065] The methane catalytic cracking hydrogen production catalyst prepared by the present invention is applied to methane catalytic cracking, and Figure 1 A schematic structural diagram of a reactor for producing hydrogen by catalytic cracking of methane is given in one embodiment.

[0066] like Figure 1As shown, the device for producing hydrogen and generating carbon nanomaterials by catalytic cracking of methane includes a screw feeding device 1, a circulating fluidized bed reaction device 2, a screw discharging device 3, a cyclone separation device 4, a return chute 5, a gas preheating device 6, a hopper collecting barrel 7, a heat exchange device 8, a gas purification device 9, a gas detection device 10 and a hydrogen collecting device 11.

[0067] In the device for producing hydrogen and generating carbon nanomaterials by catalytic cracking of methane, the circulating fluidized bed reaction device 2 is a reaction device for catalytic cracking of methane. The above-mentioned catalyst prepared by the present invention is added to the circulating fluidized bed reaction device 2 by means of a spiral feeding device 1. The raw gas methane gas is preheated and then introduced into the circulating fluidized bed reaction device 2. In the circulating fluidized bed reaction device 2, the catalyst and methane are efficiently contacted, and the methane gas undergoes a cracking reaction to generate hydrogen. The carbon nanomaterial is deposited on the surface of the catalyst to generate carbon material particles. The carbon material particles and the catalyst inactivated by the reaction are spirally discharged from the bottom of the circulating fluidized bed reaction device 2 through a spiral discharging device 3 and transported to a hopper collecting barrel 7. The hydrogen and solid mixture flows to the cyclone separation device 4 for gas-solid separation, and the solid mixture returns to the reactor through the return chute 5 to continue the reaction to provide utilization. The separated hydrogen is discharged from the top of the cyclone separation device 4, and the discharged hydrogen enters the heat exchange device 8. The waste heat of the hydrogen is replaced by the heat exchange device 8 and brought into the gas preheating device 6 to return to the circulating fluidized bed reaction device 2 to preheat the raw gas to improve the energy utilization efficiency. At the same time, it can also have a higher catalytic activity when reacting with the catalyst; the hydrogen cooled by the heat exchange device 8 is then purified by the gas purification device 9, and the purified hydrogen enters the hydrogen collection device 11 for collection to obtain pure hydrogen. In the pipeline from the heat exchange device 8 to the gas purification device 9, a branch is separated to connect the gas detection device 10, which is used to detect the gas composition and proportion, analyze the catalyst efficiency and methane conversion rate, and judge the catalyst replenishment time, that is, when the methane conversion rate is detected to be lower than a given value, a new catalyst is added from the upper feed port.

[0068] Combination Figure 1 The present invention further provides a method for continuously cracking methane to produce hydrogen and generate carbon nanomaterials, comprising the following steps:

[0069] (1) nitrogen is introduced into the reactor to exhaust the air, so that the reactor is in an anaerobic condition, the reactor is heated to 550-850° C., preferably 600-700° C., and the above-mentioned catalyst prepared by the present invention is added into the reactor by a screw feeding device 1 in a screw feeding manner;

[0070] (2) After the temperature stabilizes, the nitrogen gas is switched to preheated methane gas. The reaction pressure and space velocity are controlled according to different catalyst adaptations. The pressure range is 0.1 to 1 MPa, and the space velocity is 10 to 200 L / (h·gcat). In the initial stage, the catalyst is reduced to an active metal alloy by the reducing gas generated by the raw gas and the initial cracking. The reduction time is 0 to 40 min.

[0071] The reduced activated catalyst catalytically cracks the reaction gas methane into hydrogen and carbon nanomaterials, the hydrogen and unreacted methane flow to the cyclone separation device 4 for gas-solid separation, and the carbon nanomaterials are deposited on the catalyst surface;

[0072] (3) After the reaction, the mixed gas passes through the cyclone separation device 4 to remove the trace catalyst and carbon material carried by it, and the mixed gas enters the subsequent gas purification device 9. The hydrogen purified by the gas purification device 9 is purified and flows to the hydrogen collection device 11 for collection; the solid re-enters the reactor for recycling through the return chute 5;

[0073] As the reaction proceeds, after the catalyst deposits a certain amount of carbon nanomaterials, it is discharged from the discharge port at the lower end of the reactor and discharged through the spiral discharge device 3 into the hopper collection barrel 7.

[0074] When the methane conversion rate at the detection end is lower than a given value, new catalyst is added from the upper feed port to allow the reaction device to react continuously and maintain a high methane conversion rate.

[0075] Methane conversion rate calculation formula: X% = (F1-F2) / F1*100%;

[0076] Among them, F1 and F2 are the methane inlet flow rate and methane outlet flow rate respectively.

[0077] The formula for calculating hydrogen selectivity is: H% = H1 / [2*(F1-F2)]*100%;

[0078] Among them, F1 and F2 are the methane inlet flow rate and methane outlet flow rate respectively, and H1 is the hydrogen outlet flow rate.

[0079] Specifically, the reactor includes a bottom storage section, a reaction section and an expansion section. The storage section is provided with a discharge port connected to a spiral discharge device 3, and the spiral discharge port is connected to a hopper collecting barrel 7 for collecting the catalyst and carbon material after the reaction. The bottom of the reaction section is provided with an air inlet connected to an air outlet of a gas preheating device 6, and a return port is connected to a cyclone separation device 4 through a return chute 5. The expansion section is provided with a feed port connected to a spiral feed device 1, and an air outlet connected to a cyclone separation device 4; the air outlet of the cyclone separator reactor 4 is connected to the inlet end of the first heat exchange channel in the heat exchange device 8, and the outlet end of the first heat exchange channel in the heat exchange device 8 is connected to the inlet of a gas purification device 9, and a branch is separated to connect to a gas detection device 10 for detecting gas composition and proportion, the inlet end of the second heat exchange channel in the heat exchange device 8 is connected to a raw gas delivery pipeline, and the outlet end of the second heat exchange channel in the heat exchange device 8 is the same as the air inlet end of the gas preheating device 6; the air outlet of the gas purification device 9 is connected to a hydrogen collection device 11.

[0080] The present invention adopts a circulating fluidized bed reactor and a spiral feeding and discharging method, which can enable the methane catalytic cracking reaction to proceed continuously, and is provided with a preheating and material circulation device to improve the conversion efficiency and economy, and is suitable for continuous large-scale production and application.

[0081] At the same time, the methane catalytic cracking hydrogen production catalyst, as well as the method and device for continuous cracking of methane to produce hydrogen and generate carbon nanomaterials of the present invention can achieve catalytic cracking at relatively low temperature (600-700°C) and low pressure (0.1-1Mpa), and no high-energy steam is required, which greatly reduces energy consumption and production costs. The methane conversion rate exceeds 60%, and the carbon nanomaterial output exceeds 20gc / g cat ; and further confirmed by the examples of the present invention, when the auxiliary metal component A is Cu, the methane conversion rate obtained by the catalyst in the process of catalytic cracking of methane to produce hydrogen exceeds 80%, and the carbon nanomaterial yield exceeds 30gc / g cat , the methane conversion rate and carbon nanomaterial output are higher than those using other auxiliary metal components.

[0082] The technical solution of the present invention is further described below in conjunction with specific embodiments and drawings, but the protection scope of the present invention is not limited to these embodiments. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the protection scope of the present invention.

[0083] Embodiment 1:

[0084] 1) Dissolution: Weigh 4.2749 g of Ni(NO3)2·6H2O, 1.2726 g of Fe(NO3)3·9H2O, 0.5908 g of Cu(NO3)2, and 1.3130 g of Al(NO3)3·9H2O respectively, place them in a beaker filled with 100 ml of distilled water, stir and dissolve them thoroughly;

[0085] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 2 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 35°C water bath for 15 hours with stirring overnight, and then aged for 5 hours;

[0086] 3) Washing and drying: After the precipitate is aged, it is filtered to obtain a filter cake, and the precipitate is dissolved with a 0.5% ethanol aqueous solution under constant stirring to make a suspension, and then it is repeatedly filtered and washed until the pH value is 7±0.2, and the filter cake is filtered to obtain a filter cake, and the filter cake is dried at 60°C to make it completely dry;

[0087] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 600°C at 3°C / min for 5 hours. After calcination, the solid is ground and sieved into catalysts with a particle size of 100-200 μm, thereby obtaining the desired catalyst.

[0088] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 650° C. cracking temperature. The evaluation results are shown in Table 1.

[0089] Embodiment 2:

[0090] 1) Dissolution: Weigh 3.6642g of Ni(NO3)2·6H2O, 1.6968g of Fe(NO3)3·9H2O, 0.2626g of Cu(NO3)2, and 1.3130g of Al(NO3)3·9H2O respectively, place them in a beaker filled with 100ml of distilled water, stir and dissolve them thoroughly;

[0091] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 2 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 45°C water bath for 15 hours with stirring overnight, and then aged for 5 hours;

[0092] 3) Washing and drying: After the precipitate is aged, it is filtered to obtain a filter cake, and the precipitate is dissolved with a 1% ethanol aqueous solution under constant stirring to make a suspension, and then it is repeatedly filtered and washed until the pH value is 7±0.2, and the filter cake is filtered to obtain a filter cake, and the filter cake is dried at 60°C to make it completely dry;

[0093] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 550°C at a rate of 3°C / min for 3 hours. After calcination, the solid is ground and sieved into catalysts with a particle size of 75-150 μm, thereby obtaining the desired catalyst.

[0094] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 650° C. cracking temperature. The evaluation results are shown in Table 1.

[0095] Embodiment 3:

[0096] 1) Dissolution: Weigh 3.0535 g of Ni(NO3)2·6H2O, 1.414 g of Fe(NO3)3·9H2O, 1.0412 g of Zn(NO3)2·6H2O, and 1.3130 g of Al(NO3)3·9H2O respectively, place them in a beaker filled with 100 ml of distilled water, stir and dissolve them thoroughly;

[0097] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 2 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 35°C water bath for 15 hours with stirring overnight, and then aged for 5 hours;

[0098] 3) Washing and drying: After the precipitate is aged, filter to obtain a filter cake, dissolve the precipitate with a 1% ethanol aqueous solution under constant stirring to make a suspension, then filter and wash repeatedly until Ph = 7 ± 0.2, filter to obtain a filter cake, and dry the filter cake at 80 ° C to make it completely dry;

[0099] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 550°C at 3°C / min for 5 hours. After calcination, the solid is ground and the catalyst with a particle size of 75-150 μm is sieved to obtain the desired catalyst.

[0100] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 600° C. cracking temperature. The evaluation results are shown in Table 1.

[0101] Embodiment 4:

[0102] 1) Dissolution: Weigh 3.6642g of Ni(NO3)2·6H2O, 1.6968g of Fe(NO3)3·9H2O, 1.2223g of Co(NO3)2·6H2O, and 0.5191g of Mg(NO3)2 respectively, place them in a beaker filled with 100ml of distilled water, stir and dissolve them thoroughly;

[0103] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 1 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 55°C water bath for 12 hours with stirring overnight, and then aged for 5 hours.

[0104] 3) Washing and drying: After aging, the precipitate is filtered to obtain a filter cake, which is washed with a 0.5% ethanol aqueous solution under constant stirring to form a suspension, which is then repeatedly filtered and washed until the pH value is 7±0.2, and the filter cake is filtered to obtain a filter cake, which is dried at 60°C to make it completely dry.

[0105] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 550°C at 3°C / min for 5 hours. After calcination, the solid is ground and the catalyst with a particle size of 75-150 μm is sieved to obtain the desired catalyst.

[0106] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 600° C. cracking temperature. The evaluation results are shown in Table 1.

[0107] Comparative Example 1:

[0108] 1) Dissolution: Weigh 3.6642 g of Ni(NO3)2·6H2O and 1.3130 g of Al(NO3)3·9H2O respectively, place them in a beaker filled with 100 ml of distilled water, stir and dissolve them thoroughly;

[0109] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 2 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 35°C water bath for 15 hours with stirring overnight, and then aged for 5 hours;

[0110] 3) Washing and drying: After the precipitate is aged, it is filtered to obtain a filter cake, and the precipitate is washed with a 0.5% ethanol aqueous solution under constant stirring to make it into a suspension, and then it is repeatedly filtered and washed until the pH value is 7±0.2, and the filter cake is filtered to obtain a filter cake, and the filter cake is dried at 60°C to make it completely dry;

[0111] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 600°C at 3°C / min for 5 hours. After calcination, the solid is ground and the catalyst with a particle size of 75-150 μm is sieved to obtain the desired catalyst.

[0112] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 650° C. cracking temperature. The evaluation results are shown in Table 1.

[0113] Comparative Example 2:

[0114] 1) Dissolution: Weigh 3.6642 g of Ni(NO3)2·6H2O, 1.6968 g of Fe(NO3)3·9H2O, and 1.3130 g of Al(NO3)3·9H2O respectively, place them in a beaker filled with 100 ml of distilled water, stir and dissolve them thoroughly;

[0115] 2) Co-precipitation: Take 100 ml of the prepared 1 mol / L Na2CO3 aqueous solution and place it in a 250 ml round-bottom flask. Use a constant pressure funnel to drop 100 ml of the fully dissolved nitrate mixed solution into the round-bottom flask for precipitation reaction. Use 2 mol / L NaOH solution to control the pH value of the solution between 9-10. The entire precipitation process is carried out in a 35°C water bath for 15 hours with stirring overnight, and then aged for 5 hours;

[0116] 3) Washing and drying: After the precipitate is aged, it is filtered to obtain a filter cake, and the precipitate is washed with a 0.5% ethanol aqueous solution under constant stirring to make it into a suspension, and then it is repeatedly filtered and washed until the pH value is 7±0.2, and the filter cake is filtered to obtain a filter cake, and the filter cake is dried at 60°C to make it completely dry;

[0117] 4) Calcination: The completely dried filter cake is placed in a muffle furnace and calcined at 600°C at 3°C / min for 5 hours. After calcination, the solid is ground and the catalyst with a particle size of 75-150 μm is sieved to obtain the desired catalyst.

[0118] The catalyst was evaluated using the above catalyst evaluation method, and the evaluation conditions were: 0.2 g catalyst, 100 ml / min methane flow, 300° C. preheating temperature, and 650° C. cracking temperature. The evaluation results are shown in Table 1.

[0119] The evaluation results of the catalysts x(Nia-Feb)·yA·zB obtained in Examples 1-4 and Comparative Examples 1-2 are listed in Table 1.

[0120] Table 1

[0121]

[0122] Figure 2 and Figure 3 The relationship graphs of methane conversion rate and time of the catalysts obtained in Examples 1-4 and Comparative Examples 1-2 and the relationship graphs of hydrogen selectivity and time of the catalysts are given.

[0123] from Figure 2 and Figure 3 It can be seen that the catalysts obtained by Examples 1-4 of the present invention have a reaction time at which the methane conversion rate of the catalysts begins to decrease later than that of the catalysts of Comparative Examples 1-2 as the reaction time progresses, indicating that the catalysts obtained by Examples 1-4 of the present invention have a later failure time point, a longer catalyst life, a higher methane conversion rate, and a better hydrogen selectivity. In particular, the catalysts of Examples 1 and 2 have a methane conversion rate as high as about 80% or about 70% compared with the catalysts of other Examples and Comparative Examples, and can be maintained at about 80% or about 70% for a relatively long time, and the catalyst life is better, indicating that the use of Cu as a promoter metal in the catalyst can better assist the reaction activity of the catalyst active components Ni and Fe than other types of promoter metals, reflecting a higher methane conversion rate and hydrogen average selectivity.

[0124] Compared with Example 1 and Example 2, under similar conditions, Example 2 uses less auxiliary metal (x:y=12:1). Although it will reduce the methane conversion rate, the average hydrogen selectivity and carbon nanomaterial yield will increase significantly. This shows that when Cu is used as an auxiliary metal, only a small amount of addition is needed to assist in promoting the reaction activity of the active components Ni and Fe, and the selectivity of methane catalytic cracking to generate hydrogen and carbon nanomaterials is better, and less other undesirable substances such as olefins are produced. Therefore, even if a part of the methane conversion rate is sacrificed, the average hydrogen selectivity and carbon nanomaterial yield are higher, and the increase in the amount of auxiliary metal Cu is not conducive to the generation of hydrogen and carbon nanomaterials. At the same time, it is shown in Figure 2 and Figure 3 The catalyst of Example 2 can maintain a constant value for a longer time than the catalyst of Example 1, indicating that the methane conversion rate and the life of the catalyst of Example 2 are better than those of Example 1.

[0125] Figure 4 The morphology of the carbon nanomaterial obtained by using the catalyst obtained in Examples 1-4 in the methane cracking hydrogen production process is given. Figure 4It can be seen that the catalysts obtained in Examples 1-4 of the present invention are used in the methane cracking hydrogen production process to obtain carbon nanomaterials with relatively good morphological characteristics. In particular, the carbon nanofibers of the carbon nanomaterials obtained in the methane cracking hydrogen production process using the catalysts in Examples 1 and 2, which have good methane conversion rates and catalyst lifespans, are finer and denser, and the quality of the carbon nanomaterials is better.

[0126] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A catalyst for producing hydrogen by catalytic cracking of methane, It is characterized in that The structural formula of the catalyst is x(Nia-Feb)·yA·zB, wherein the catalyst uses nickel-iron alloy nanoparticles as the active center, A is an auxiliary metal element, and B is a carrier, wherein x, y, and z are the molar numbers of the nickel-iron alloy, the auxiliary metal, and the carrier, respectively, and a and b are the molar numbers of Ni and Fe, x:z=1:1-10:1, x:y=5:1-20:1, and a:b=1:1-9:1; preferably, x:y=10:1-20:1; Wherein, the catalyst is prepared by a precipitation method, and its preparation method comprises the following steps: Step (1), preparation of catalyst precursor: dissolving nickel salt, iron salt, auxiliary metal salt and carrier or carrier precursor salt in water, adding the obtained mixed solution dropwise into an alkaline solution for precipitation reaction, standing for stratification, removing the supernatant to obtain a solid precipitate; Step (2), placing the solid precipitate in an ethanol aqueous solution, stirring and washing, filtering, and drying; Step (3), calcining, grinding and sieving the dried filter cake to obtain the catalyst.

2. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 1, It is characterized in that The additive metal A is selected from one or more metals and / or oxides thereof of Cu, Zn, Co, Mn, Sr and Ce; preferably, the additive metal A is Cu.

3. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 1, It is characterized in that The carrier B is selected from Al 2 O 3 、SiO 2 ,MgO,TiO 2 、ZrO 2 , graphite and activated carbon; preferably, the carrier B is Al 2 O 3 .

4. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 3, It is characterized in that The particle size of the carrier B is 100 to 420 μm.

5. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 1, It is characterized in that The particle size of the catalyst is 60 to 200 μm.

6. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 1, It is characterized in that In step (1), the nickel salt, iron salt, auxiliary metal salt and carrier precursor salt are nitrates, acetates, oxalates or chlorides of nickel, iron, auxiliary metal and carrier precursor, and the alkaline solution is selected from one or more of sodium carbonate, sodium hydroxide, potassium hydroxide, sodium bicarbonate and ammonia solution.

7. The catalyst for producing hydrogen from catalytic cracking of methane according to claim 1, It is characterized in that In step (1), the temperature of the precipitation reaction is 25 to 80° C., preferably 35 to 65° C., and the pH value is 8.5 to 10.5; in step (2), the mass concentration of the ethanol aqueous solution is 0.1% to 10%, preferably 1% to 3%, and after washing, the pH value is 6.8 to 7.2, and the washed filter cake is dried at 60 to 100° C., and the drying temperature is 60 to 100° C., preferably 60 to 80° C.; in step (3), the roasting conditions are: the roasting temperature is 450 to 700° C., the roasting time is 2 to 5 hours, and the roasting gas atmosphere is air.

8. A method for continuously cracking methane to produce hydrogen and carbon nanomaterials, It is characterized in that The method comprises the following steps: adding the methane catalytic cracking hydrogen production catalyst as described in any one of claims 1 to 7 and the raw material methane gas into a circulating fluidized bed reaction device to perform cracking reactions, catalytically cracking the methane into hydrogen and carbon nanomaterials, purifying the hydrogen through a purification system and collecting the hydrogen, and depositing the carbon nanomaterials on the catalyst surface and collecting the carbon nanomaterials.

9. The method according to claim 8, It is characterized in that In the circulating fluidized bed reaction device, the temperature of the methane catalytic cracking reaction is 550-850°C, preferably 600-700°C, the pressure of the catalytic cracking reaction is 0.1-1 MPa; the space velocity of the catalyst is 10-200 L / (h·g cat ), preferably 50 to 100 L / (h·g cat ).

10. The method according to claim 8, It is characterized in that The methane catalytic cracking hydrogen production catalyst is added to a circulating fluidized bed reaction device by means of a spiral feeding method. After the methane is catalytically cracked, the deposited carbon nanomaterial is discharged from the bottom of the circulating fluidized bed reaction device by means of a spiral discharging method. A detection end is arranged at the end of the hydrogen purification system to monitor the methane conversion rate. When the methane conversion rate is lower than a given value, a new catalyst is added to realize a continuous reaction of the reaction device.

11. The method according to any one of claims 8 to 10, It is characterized in that Methane conversion rate exceeds 60%, hydrogen selectivity exceeds 80%, and carbon nanomaterial output exceeds 20gc / g cat .

12. The method according to claim 11, It is characterized in that In the methane catalytic cracking hydrogen production catalyst, when the auxiliary metal A is Cu, the methane conversion rate exceeds 80%, the hydrogen selectivity exceeds 90%, and the carbon nanomaterial yield exceeds 30gc / g cat .

13. The method according to claim 11, It is characterized in that In the methane catalytic cracking hydrogen production catalyst, the auxiliary metal A is Cu, and when x:y=10:1-20:1, the methane conversion rate exceeds 80%, the hydrogen selectivity exceeds 90%, and the carbon nanomaterial yield exceeds 45gc / g cat .

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