Bimetallic oxygen carriers, methods of making the same, and methods of methane chemical looping hydrogen production

Abstract

The application provides a bimetallic oxygen carrier, a preparation method thereof and a method for hydrogen production by methane chemical looping, and belongs to the technical field of hydrogen production by chemical looping. The preparation method of the bimetallic oxygen carrier comprises the following steps: placing a carrier powder of a predetermined type into a reaction container, heating, keeping warm and vacuumizing; cooling the reaction container and using the vacuum degree of the reaction container to pour a double-metal salt mixed solution composed of iron salt and nickel salt into the reaction container through suction; releasing the vacuum state of the reaction container, mixing the double-metal salt mixed solution and the carrier powder to form an initial mixed solution; and preparing a bimetallic oxygen carrier product based on the initial mixed solution. The bimetallic oxygen carrier comprises a carrier of a predetermined type, and metal iron oxides and metal nickel oxides attached to the surface of the carrier, wherein the metal iron oxides and the metal nickel oxides with a particle size less than 250 nm are obtained by changing the preparation parameters. The application further provides a method for hydrogen production by methane chemical looping using the bimetallic oxygen carrier.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical chaining hydrogen production, and in particular relates to a bimetallic oxygen carrier and a preparation method thereof, and a method for producing hydrogen from methane by chemical chaining. More specifically, it relates to a method for preparing a nano-scale stably dispersed bimetallic oxygen carrier by a hydrothermal method and a method for producing hydrogen from methane by chemical chaining at medium temperature. Background Art

[0002] Methane chemical looping hydrogen production technology is an emerging near-zero carbon emission hydrogen production technology. By introducing metal oxygen carriers into chemical looping combustion technology, the partial oxidation or reforming reaction of methane can be decoupled, resulting in three reactions: oxygen carrier reduction, steam oxidation, and air oxidation. Each reaction produces hydrogen, carbon monoxide (CO), and carbon dioxide (CO2), respectively, achieving near-zero carbon emission "blue hydrogen" production.

[0003] Oxygen carriers are the core of methane chemical looping hydrogen production technology. On the one hand, they can transfer the oxygen required in the fuel reaction process, and on the other hand, they can produce hydrogen through steam oxidation. Currently, bimetallic oxygen carriers composed of two active metal components are often used in the methane chemical looping hydrogen production process, such as the common iron-nickel bimetallic oxygen carriers and iron-cerium bimetallic oxygen carriers. However, these bimetallic oxygen carriers often form micron-sized or larger particles during the traditional mechanical blending, impregnation, and sol-gel methods. The bimetallic components are far apart, which can easily affect the frequent material exchange and oxidation / reduction reactions in the subsequent methane chemical hydrogen production reaction due to uneven mixing of the metal components. If methods such as microwave hydrothermal synthesis are used, the particle size of the oxygen carrier is difficult to control, and ferrites may be formed, causing the bimetallic components to separate, weakening or even losing the advantages of bimetallic oxygen carriers in the field of hydrogen production. In addition, the bimetallic oxygen carriers made using the current method have a reaction temperature of 800-1000°C during the methane chemical chain hydrogen production reaction, which leads to high requirements on the materials and design of the reactor. Moreover, these bimetallic oxygen carriers only produce hydrogen during the oxidation reaction, and have problems such as slow hydrogen production rate or poor selectivity, which limits the potential of bimetallic oxygen carriers in the methane chemical chain hydrogen production reaction. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a bimetallic oxygen carrier and a preparation method thereof, and a method for producing hydrogen from methane chemical chaining, in order to at least partially solve the above technical problems.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] As a first aspect of the present invention, a method for preparing a bimetallic oxygen carrier is provided, comprising:

[0007] Placing a predetermined type of carrier powder in a reaction vessel, heating and keeping the temperature, and evacuating the vessel;

[0008] The reaction vessel loaded with the carrier powder is cooled and the double metal salt mixed solution consisting of iron salt and nickel salt is sucked back into the reaction vessel using the vacuum degree of the reaction vessel;

[0009] releasing the vacuum state of the reaction container, and mixing the bimetallic salt mixed solution and the carrier powder to form an initial mixed solution;

[0010] A bimetallic oxygen carrier product is prepared based on the initial mixed solution, wherein the bimetallic oxygen carrier product includes metal iron oxide, metal nickel oxide, and a predetermined type of carrier.

[0011] As a second aspect of the present invention, a bimetallic oxygen carrier prepared by the above-mentioned preparation method is provided, comprising:

[0012] metallic iron oxides in flaky or granular form;

[0013] Flake or granular metallic nickel oxides are interlaced with metallic iron oxides;

[0014] a predetermined type of carrier;

[0015] The metal iron oxide and the metal nickel oxide are attached to the surface of the carrier, and the particle size of the metal iron oxide and the metal nickel oxide is less than 250 nm.

[0016] As a third aspect of the present invention, a method for producing hydrogen from methane by chemical chaining using the bimetallic oxygen carrier prepared above is provided, comprising:

[0017] Filling the bimetallic oxygen carrier into the reactor, wherein the reactor adopts a fixed bed or a moving bed;

[0018] Water vapor and methane gas are introduced into the reactor to cause a chemical chain hydrogen production reaction between the methane gas, water vapor, and the bimetallic oxygen carrier. The chemical chain hydrogen production reaction includes a reduction reaction and an oxidation reaction, wherein:

[0019] The reduction reaction includes an initial stage reaction and a mid- to late-stage reaction; wherein, in the initial stage reaction, the metallic iron oxide and the metallic nickel oxide in the bimetallic oxygen carrier are reduced to generate Fe3O4 and metallic nickel, and methane is catalyzed under the catalytic action of the metallic nickel to obtain a first-stage product mixture, wherein the first-stage product mixture includes the first-stage hydrogen product, unreacted methane, CO, and CO2; in the mid- to late-stage reaction, Fe3O4 reacts with hydrogen and the first-stage CO to produce metallic iron and FeO; in the oxidation reaction, the metallic iron and FeO are oxidized by water vapor to generate metallic iron oxide, and at the same time, the water vapor is reduced to generate the second-stage hydrogen product, pure hydrogen, wherein the second-stage product mixture obtained after the oxidation reaction includes the second-stage hydrogen product, unreacted water vapor, unreacted methane, CO, and CO2;

[0020] In both the reduction reaction and the oxidation reaction, water vapor is introduced.

[0021] Based on the above technical solution, the present invention provides a bimetallic oxygen carrier and a preparation method thereof, and a method for producing hydrogen from methane chemical chaining, which have at least one of the following beneficial effects:

[0022] (1) In an embodiment of the present invention, a predetermined type of carrier powder is placed in a reaction vessel, heated and kept warm, and vacuumed. The vacuum state is used to remove the air film on the surface of the carrier, so that the predetermined type of carrier can fully contact the bimetallic in the subsequent preparation process. The reaction vessel is then cooled while maintaining the vacuum state, and the iron salt and nickel salt are sucked back into the reaction vessel using the vacuum degree of the reaction vessel. On the one hand, this can avoid the mixing of air during the addition of the bimetallic salt mixed solution, further ensuring that there is no air film on the surface of the carrier before the bimetallic is loaded on the carrier (different from the traditional method of directly mixing the two after removing the vacuum), so that the carrier without air film can directly contact the bimetallic salt mixed solution, which is conducive to the uniform adsorption of bimetallic ions on the carrier surface, ensuring the adhesion and uniform dispersion of the bimetallic components and the predetermined type of carrier. The Fe ions in the iron salt and the Ni ions in the nickel salt can be attached to the microcavities on the surface of the predetermined type of carrier through adsorption, which can further improve the adhesion and uniform dispersion between the carrier and the active component during the precipitation process. Finally, the vacuum state of the reaction container is released, and the bimetallic salt mixed solution is mixed with the carrier powder to obtain an initial mixed solution. The bimetallic oxygen carrier in the product prepared based on this solution is uniformly and stably dispersed, and the reaction performance of the oxygen carrier is improved.

[0023] (2) In the embodiment of the present invention, during the entire process of adding the alkaline precipitant to the initial mixed solution (i.e., the bimetallic salt mixed solution is sucked back into the solution), vigorous stirring is maintained to form an initial mother solution that is not layered and exists in the form of a slurry. This can avoid the local enrichment of iron and nickel oxides, and is conducive to the subsequent acquisition of nano-scale, uniformly dispersed bimetallic oxygen carriers.

[0024] (3) In the embodiment of the invention, the active components of the metal iron oxide and metal nickel oxide in the bimetallic oxygen carrier prepared by the hydrothermal method of the bimetallic oxygen carrier are loaded on the carrier surface in a nanometer-scale, stable and uniform manner, wherein the reaction process of the hydrothermal method is easy to control, and by changing the time and temperature of the hydrothermal reaction, the particle size of the active components of the metal iron oxide and metal nickel oxide can be controlled at the nanometer scale (such as the particle size is less than 250nm, and the particle size of the active component gradually increases with the reaction time). Compared with the impregnation method, that is, the method of directly drying and calcining the initial mixed solution to obtain the bimetallic oxygen carrier, the hydrothermal method can prepare nanometer-scale dispersed particles, while the impregnation method cannot effectively control the particle size; compared with the more complex and faster microwave hydrothermal method, the reaction rate of the ordinary hydrothermal method is moderate and easy to control, and the particle size control strategy is richer. Therefore, under the appropriate nanoparticle size, the nanoscale size effect of the bimetallic oxygen carrier and the synergistic effect of the bimetallic active components can be enhanced, thereby obtaining a bimetallic oxygen carrier with better performance. The hydrothermal method solves the technical problem in the related art that the oxygen carrier particle size cannot be effectively controlled.

[0025] (4) In an embodiment of the present invention, the prepared bimetallic oxygen carrier is filled in a reactor and water vapor and methane gas are introduced into the reactor, so that a chemical chain hydrogen production reaction including an oxidation reaction and a reduction reaction is carried out between the methane gas, water vapor and the bimetallic oxygen carrier. In the initial stage of the reduction reaction, the nickel oxide and iron oxide in the bimetallic oxygen carrier first react with methane and water vapor to produce metallic nickel, Fe3O4, a small amount of CO and a small amount of CO2; in the middle and late stages of the reduction reaction, nickel acts as a catalyst to convert methane and water vapor into first-stage hydrogen and CO in situ, while Fe3O4 is further reduced to metallic iron and FeO by the first-stage hydrogen and the first-stage CO. In other words, after the reduction reaction, methane is oxidized into CO, CO2 and first-stage hydrogen (H2), while the bimetallic oxygen carrier is reduced to metallic nickel, metallic iron, FeO and Fe3O4. In addition, the introduction of water vapor during the reduction reaction can not only effectively avoid the problem of excessive oxidation of methane and carbon accumulation on the surface of the bimetallic oxygen carrier, but also improve the total hydrogen production and hydrogen purity of the reduction reaction. Subsequently, in the oxidation reaction, metallic iron and FeO are oxidized by water vapor to form Fe3O4, and the introduced water vapor is reduced to hydrogen in the second stage, thereby realizing the two-step hydrogen production process of methane chemical chain and improving hydrogen production and hydrogen production rate; by introducing water vapor during the oxidation process, high-purity hydrogen is produced, and hydrogen can be used to oxidize FeO back to Fe3O4 at a lower temperature, returning to the state at the end of the initial reduction reaction, so that the bimetallic oxygen carrier is regenerated and maintains a high activity.

[0026] Through the above process, the synergistic effect of iron oxide and nickel oxide in the bimetallic oxygen carrier is achieved, and the NiO active component is used to reduce the reaction temperature of the bimetallic oxygen carrier with methane at the same hydrogen production rate. In other words, the bimetallic oxygen carrier of the present invention can realize the methane chemical chaining hydrogen production reaction in the medium temperature range (500-600°C), while simultaneously improving hydrogen production and hydrogen production rate, avoiding the equipment maintenance and design issues associated with high temperatures, and also avoiding the low conversion rate and high energy consumption of the outlet product gas separation caused by methane steam reforming hydrogen production at lower temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the process for preparing a bimetallic oxygen carrier by a precipitation-hydrothermal method according to an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the principle of a method for producing hydrogen from methane using a bimetallic oxygen carrier in an embodiment of the present invention;

[0029] Figure 3 Graph showing the methane conversion rate and hydrogen production rate of the bimetallic oxygen carrier in Example 1 of the present invention in a methane chemical chaining hydrogen production reaction at different temperatures;

[0030] Figure 4 This is a graph showing the degree of oxidation of the bimetallic oxygen carrier in Example 1 of the present invention after 70 cycles of stability testing;

[0031] Figure 5A This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention before the methane chemical chaining reaction to produce hydrogen, with a scale of 200 nm;

[0032] Figure 5B This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention after 150 cycles of methane chemical chaining hydrogen production reactions, with a scale of 200 nm;

[0033] Figure 6A This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical looping hydrogen production cycles;

[0034] Figure 6B This is an energy spectrum analysis diagram of all elements of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles;

[0035] Figure 6C This is an energy spectrum analysis diagram of the oxygen element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles;

[0036] Figure 6DThis is an energy spectrum analysis diagram of the aluminum element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles;

[0037] Figure 6E This is an energy spectrum analysis diagram of the iron element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles;

[0038] Figure 6F This is an energy spectrum analysis diagram of nickel element in the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles;

[0039] Figure 7 is the X-ray diffraction pattern of the bimetallic oxygen carrier in Example 1 of the present invention;

[0040] Figure 8 This is a comparison chart of the methane conversion rate and hydrogen production rate of the bimetallic oxygen carrier in Example 2 of the present invention and the bimetallic oxygen carrier prepared by the mechanical mixing method in the methane chemical chaining hydrogen production reaction at different temperatures. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0042] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0043] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0044] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0045] When expressions such as “at least one of A, B, and C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (e.g., “a system having at least one of A, B, and C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.). When expressions such as “at least one of A, B, or C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (e.g., “a system having at least one of A, B, or C” should include but is not limited to systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.).

[0046] Oxygen carriers are the core of methane chemical looping hydrogen production technology. Currently, commonly used bimetallic oxygen carriers are iron-nickel oxide mixed oxygen carriers or iron-cerium oxide mixed oxygen carriers. The iron-nickel oxide mixed oxygen carrier is composed of Fe2O3, NiO, and an inert Al2O3 carrier. However, the Fe2O3 and NiO prepared in the related art often have particle sizes of microns or even larger, and the mixing process suffers from uneven mixing of the components. The reaction temperature for its application in methane chemical looping hydrogen production is generally above 800°C, which places high demands on the reactor material and design. Furthermore, the unevenly mixed iron-nickel oxide bimetallic oxygen carriers are prone to phase separation of the bimetallic components during frequent iron oxide and nickel oxide material exchange and oxidation / reduction reactions. In other words, the iron-nickel oxide bimetallic elements are no longer evenly mixed, but precipitate and form large iron oxide and nickel oxide particles at the micron or even submillimeter level. This reduces the specific surface area of ​​the bimetallic oxygen carrier and increases the distance between the bimetallic elements, reducing the efficiency of product exchange and thus affecting the hydrogen production rate and hydrogen yield during the methane chemical looping hydrogen production reaction. Another iron-cerium oxide mixed oxygen carrier is generally composed of Fe2O3, CeO2 and an inert Al2O3 carrier. It is used in the methane chemical chain hydrogen production reaction. The reaction temperature is generally around 700-1000°C. In addition to the common problems mentioned above with the iron-nickel oxide bimetallic oxygen carrier, the methane conversion rate of this bimetallic oxygen carrier does not exceed 91%, and the hydrogen selectivity does not exceed 86%.

[0047] The present invention addresses the problems in the prior art of bimetallic oxygen carriers in the methane chemical chaining hydrogen production reaction, such as high reaction temperature, slow hydrogen production rate, low hydrogen production selectivity, and large active species particle size and non-uniform dispersion. A bimetallic oxygen carrier, a preparation method thereof, and a method for methane chemical chaining hydrogen production are proposed. By utilizing the advantage of the easy control of the hydrothermal reaction process and changing the time and temperature of the hydrothermal reaction, a nano-scale bimetallic oxygen carrier with uniform grain size distribution can be obtained. The bimetallic oxygen carrier is applied to the methane chemical chaining hydrogen production reaction, which can significantly reduce the reaction temperature while increasing the hydrogen production rate and amount.

[0048] Specifically, the present invention provides a method for preparing a bimetallic oxygen carrier, comprising: placing a predetermined type of carrier powder in a reaction vessel, heating and keeping the temperature constant, and evacuating the vessel; cooling the reaction vessel, and utilizing the vacuum degree of the reaction vessel to suck a bimetallic salt mixed solution composed of an iron salt and a nickel salt into the reaction vessel; releasing the vacuum state of the reaction vessel, mixing the bimetallic salt mixed solution and the carrier powder to form an initial mixed solution; and preparing a bimetallic oxygen carrier product based on the initial mixed solution, wherein the bimetallic oxygen carrier product comprises metal iron oxide, metal nickel oxide, and a predetermined type of carrier.

[0049] In an embodiment of the present invention, a predetermined type of carrier powder is placed in a reaction vessel, heated and kept warm, and vacuumed, and the air film on the surface of the carrier is removed by the vacuum state so that the predetermined type of carrier can fully contact the bimetallic. Subsequently, the reaction vessel is cooled while maintaining a vacuum state, and the vacuum degree of the reaction vessel is used to suck the iron salt and nickel salt back into the reaction vessel. On the one hand, it can avoid mixing with air during the addition of the bimetallic salt mixed solution, further ensuring that there is no air film on the surface of the carrier before the bimetallic is loaded on the carrier, so that the carrier without air film can directly contact the bimetallic salt mixed solution, which is conducive to the uniform adsorption of the bimetallic ions on the carrier surface, ensuring the adhesion and uniform dispersion of the bimetallic components and the predetermined type of carrier. The Fe ions of the iron salt and the Ni ions of the nickel salt can be attached to the microcavities on the surface of the predetermined type of carrier through adsorption, which can further improve the adhesion and uniformity of the dispersion between the carrier and the active component during the precipitation process. Finally, the vacuum state of the reaction vessel is released, and the bimetallic salt mixed solution is mixed with the carrier powder to obtain an initial mixed solution and the bimetallic oxygen carrier in the product prepared based on this solution is uniformly and stably dispersed, and the reaction performance of the oxygen carrier is improved.

[0050] According to an embodiment of the present invention, placing a predetermined type of carrier powder in a reaction vessel, heating and keeping it warm and evacuating it includes: placing a predetermined type of carrier powder in a reaction vessel, heating it to 100°C to 150°C, keeping it warm for 2-8 hours and evacuating it, wherein the vacuum degree of the reaction vessel is less than 0.05atm. In an embodiment of the present invention, it is preferred to select a carrier with a certain mechanical strength as the predetermined type of carrier powder so that its morphology does not change during the application process of methane chemical chain hydrogen production. Preferably, the predetermined type of carrier powder is selected from any one of Al2O3 micron powder, Al2O3 porous microspheres, SBA-15 molecular sieve, and zeolite molecular sieve, wherein the diameter of the Al2O3 porous microspheres is 1-3mm, Al2O3 can be γ-Al2O3 or β-Al2O, and the shape of the carrier can be spherical or cylindrical. In an embodiment of the present invention, by vacuum degassing the carrier powder, it is helpful to make the formed active components directly contact with the carrier and stably and evenly dispersedly attached to the carrier.

[0051] The iron salt is one of the following: ferric nitrate and ferric chloride; the nickel salt is one of the following: nickel nitrate and nickel acetate. The bimetallic oxygen carrier includes a metal iron oxide, a metal nickel oxide, or a predetermined type of carrier, wherein the metal iron oxide is Fe2O3 and the metal nickel oxide is NiO.

[0052] According to an embodiment of the present invention, mixing a bimetallic salt mixed solution and a carrier powder to form an initial mixed solution includes: stirring at a first stirring speed to uniformly mix the bimetallic salt solution and the carrier powder to form an initial mixed solution, wherein the bimetallic salt mixed solution is an acidic concentrated solution and the pH value of the bimetallic salt mixed solution is 0.2-0.5. Preparing a bimetallic oxygen carrier product based on the initial mixed solution includes: adding an alkaline precipitant to the initial mixed solution to form an initial mother liquor in the form of a slurry, wherein the alkaline precipitant is an 8 mol / L NaOH solution or 23-25 ​​wt% ammonia water. While adding the alkaline precipitant to the initial mixed solution, it also includes: stirring at a second stirring speed to mix the initial mixed solution and the alkaline precipitant to form an initial mother liquor containing metal hydroxide in the form of a slurry, wherein the initial mother liquor formed after adding the alkaline precipitant to the initial mixed solution is an alkaline solution, such as a pH value of 9.5-12.0. Before transferring the initial mother liquor from the reaction vessel to the hydrothermal reactor, it also includes: placing the reaction vessel loaded with the initial mother liquor in an ultrasonic cleaning machine for ultrasonic treatment. The initial mother liquor is transferred from the reaction vessel to a hydrothermal reactor, heated and kept warm to obtain a finished mother liquor, wherein the initial mother liquor is transferred to the hydrothermal reactor for stirring, sealed and heated to 110°C to 200°C, and kept warm for 2-12 hours, the pressure in the hydrothermal reactor is 1-1.5MPa, and the finished mother liquor presents a red solid-liquid stratification state. While the initial mother liquor is transferred from the reaction vessel to the hydrothermal reactor for heating, the method further comprises: stirring the initial mother liquor at a third stirring speed; cooling the finished mother liquor to separate the solid precipitated product in the finished mother liquor; drying and grinding the solid precipitated product to obtain a bimetallic oxygen carrier product, wherein, after cooling the finished mother liquor and separating the solid precipitated product in the finished mother liquor, the method further comprises: washing the solid precipitated product with deionized water and / or anhydrous ethanol.

[0053] In an embodiment of the present invention, to obtain a nanoscale, uniformly mixed bimetallic oxide carrier, a first stirring speed is used during the process of mixing the bimetallic salt mixed solution with the carrier powder to form an initial mixed solution. This allows the iron salt and nickel salt to be evenly dispersed on the carrier, thereby improving the bonding strength between the bimetallic salt and the carrier and reducing the particle size of the subsequently prepared bimetallic oxide carrier. Subsequently, an alkaline precipitant is added to the initial mixed solution to precipitate the iron salt and nickel salt, forming an initial, non-stratified mother solution in the form of a slurry. This prevents localized enrichment of iron and nickel oxides and facilitates the subsequent production of a nanoscale, uniformly dispersed bimetallic oxide carrier. However, due to the high viscosity of the slurry, it is necessary to vigorously stir at a second, higher stirring speed while adding the alkaline precipitant to ensure that the slurry is fully mixed and evenly dispersed on the carrier, thereby facilitating the subsequent production of a nanoscale bimetallic oxide carrier. Before transferring the initial mother liquor from the reactor to the hydrothermal reactor, the initial mother liquor is ultrasonically treated to fully break up and evenly disperse any lumps (precipitated material) in the slurry, preventing agglomeration and the resulting impact on the particle size of the bimetallic oxide carrier produced by the hydrothermal reaction. After the initial mother liquor is transferred to the hydrothermal reactor, since the bimetallic components and carrier are already uniformly dispersed and loaded, the initial mother liquor only needs to be stirred at a gentle third stirring rate for the hydrothermal reaction. The gentle stirring method prevents sedimentation of the initial mother liquor during the hydrothermal process, which could affect the particle size and degree of incorporation of the iron oxide and nickel oxide produced by the hydrothermal reaction, while also preventing vigorous stirring from affecting the formation of iron oxide and nickel oxide nanoparticles. Furthermore, by controlling the time and temperature of the hydrothermal reaction, the particle size of the active components of the metallic iron oxide and metallic nickel oxide is controlled to the nanometer scale. After the hydrothermal reaction, a finished product mother liquor containing nanoscale metallic iron oxide and metallic nickel oxide is obtained. After cooling the finished mother liquor and separating the solid precipitate from the finished mother liquor, the product is dried and ground to obtain a nano-scale bimetallic oxygen carrier with a smaller particle size. It should be noted that the present invention employs a design of the stirring speeds during different mixing processes, i.e., a stirring scheme in which the third stirring speed is less than the first stirring speed, and the first stirring speed is less than the second stirring speed. The third stirring speed is 90-120 r / min; the first stirring speed is 900-1300 r / min; and the second stirring speed is 1300-1500 r / min. This facilitates obtaining nano-scale particles of the bimetallic oxygen carrier that are uniformly mixed. During the hydrothermal reaction process, the particle size of the bimetallic oxygen carrier product can be regulated by controlling the hydrothermal reaction temperature. For example, the initial mother liquor is added to the hydrothermal reactor and the hydrothermal reaction is carried out at 120°C, 150°C, 180°C, and 200°C, respectively, and the hydrothermal reaction time is 8h, 10h, and 12h, to obtain bimetallic oxygen carrier nanoparticles with an average particle size of about 150nm, about 200nm, and about 250nm.

[0054] Therefore, the present invention prepares an iron-nickel bimetallic oxygen carrier with iron oxide nanoparticles and nickel oxide nanoparticles as active components and uniformly loaded on the carrier through degassing-precipitation-hydrothermal method-high-pressure digestion-growth, and the preparation method of the present invention solves the problem in the related art that the particle size of the bimetallic oxygen carrier cannot be effectively controlled.

[0055] As a second aspect of the present invention, a bimetallic oxygen carrier prepared by the preparation method of the bimetallic oxygen carrier described in the above embodiment comprises: flaky or granular metal iron oxide, flaky or granular metal nickel oxide, and a predetermined type of carrier; wherein the metal iron oxide and the metal nickel oxide are attached to the surface of the carrier, the flaky or granular metal nickel oxide is interlaced with the metal iron oxide, and the particle size of the metal iron oxide and the metal nickel oxide is less than 250 nm.

[0056] In an embodiment of the invention, a bimetallic oxygen carrier prepared using the hydrothermal method of the bimetallic oxygen carrier described in the above embodiment is prepared. The bimetallic active components of metal iron oxide and metal nickel oxide are stably and uniformly supported on the carrier surface, and the metal iron oxide and metal nickel oxide have nanoscale particle sizes. This allows the nanoscale size effect of the bimetallic oxygen carrier and the synergistic effect of the bimetallic active components to reduce the reaction temperature during use of the bimetallic oxygen carrier while simultaneously improving the reaction activity. In this embodiment of the invention, the particle size of the metal iron oxide and metal nickel oxide is less than 250 nm, preferably 100-250 nm.

[0057] According to an embodiment of the present invention, the metallic iron oxide is Fe2O3, the metallic nickel oxide is NiO, and the carrier is any one of Al2O3 micron powder, Al2O3 porous microspheres, SBA-15 molecular sieve, and zeolite molecular sieve, wherein the diameter of the Al2O3 porous microspheres is 1-3 mm. Furthermore, the mass fraction of the metallic nickel oxide is 5-25%, and the mass fraction of the metallic iron oxide is 75-95%. Furthermore, the metallic iron oxide and metallic nickel oxide are active components of the bimetallic oxide carrier, with a mass ratio of active components to carrier of 3:2 to 5:4, and the mass fraction of NiO relative to Fe2O3 can be 10%-30%.

[0058] In embodiments of the present invention, the nickel doping ratio is adjusted during the preparation of the bimetallic oxygen carrier to produce bimetallic oxygen carriers with different effects. For example, a higher nickel oxide ratio results in better reduction performance and higher methane conversion during the methane chemical chaining reaction, while a higher iron oxide ratio increases the oxidation reaction rate and hydrogen production during the methane chemical chaining reaction.

[0059] As a third aspect of the present invention, a method for chemically looping hydrogen production from methane using a bimetallic oxygen carrier is provided, comprising: filling the bimetallic oxygen carrier into a reactor, wherein the reactor utilizes a fixed bed or a moving bed; introducing water vapor and methane gas into the reactor, causing a chemical looping hydrogen production reaction to occur between the methane gas, water vapor, and the bimetallic oxygen carrier, wherein the chemical looping hydrogen production reaction includes a reduction reaction and an oxidation reaction, and the reduction reaction includes an initial stage reaction and a mid- to late-stage reaction. In the initial stage reaction, the metallic iron oxide and metallic nickel oxide in the bimetallic oxygen carrier are reduced to form Fe3O4 and metallic nickel, and methane is catalyzed by the catalytic action of the metallic nickel to produce a first-stage product mixture, the first-stage product mixture comprising a first-stage hydrogen product, unreacted methane, CO, and CO2; in the mid- to late-stage reaction, the Fe3O4 reacts with the hydrogen and the first-stage CO to produce metallic iron and FeO. In the oxidation reaction, metallic iron and FeO are oxidized by water vapor to form metallic iron oxides, and at the same time, the water vapor is reduced to form the second-stage hydrogen product, pure hydrogen. The second-stage product mixture obtained after the oxidation reaction includes the second-stage hydrogen product, unreacted water vapor, unreacted methane, CO, and CO2. Water vapor is introduced in both the reduction reaction and the oxidation reaction.

[0060] In an embodiment of the present invention, the prepared bimetallic oxygen carrier is filled in a reactor and water vapor and methane gas are introduced into the reactor, so that a chemical chain two-step hydrogen production reaction is carried out between methane gas, water vapor and bimetallic oxygen carrier, thereby increasing hydrogen production and hydrogen production rate. The chemical chain two-step hydrogen production reaction includes an oxidation reaction and a reduction reaction. The introduction of water vapor during the reduction reaction can not only effectively avoid the problem of excessive oxidation of methane and carbon accumulation on the surface of the bimetallic oxygen carrier, but also improve the total hydrogen production and hydrogen purity of the reduction reaction; the introduction of water vapor during the oxidation reaction can not only achieve hydrogen production, but also remove carbon deposited on the bimetallic surface. In addition, the main component of the product of the present invention is hydrogen, and the rest is water vapor, CO, CO2 and a small amount of unreacted methane, and the gas separation energy consumption is low, which is less than the methane reforming hydrogen production reaction.

[0061] According to an embodiment of the present invention, the amount of water vapor introduced into the reactor satisfies a predetermined ratio, wherein the predetermined ratio is a water-to-carbon ratio of 1:1 to 6.5:1 in the water vapor and methane mixture. By reducing the water-to-carbon ratio, the methane conversion rate of the chemical chaining hydrogen production reaction is increased while the average hydrogen production rate of the chemical chaining hydrogen production reaction is reduced; alternatively, by increasing the water-to-carbon ratio, the average hydrogen production rate of the chemical chaining hydrogen production reaction is increased while the methane conversion rate of the chemical chaining hydrogen production reaction is reduced.

[0062] According to an embodiment of the present invention, the reaction temperature in the reactor where the chemical chaining hydrogen production reaction occurs is 525°C to 600°C.

[0063] According to an embodiment of the present invention, the method for methane chemical chaining hydrogen production using a bimetallic oxygen carrier also includes: increasing the mass content of metal iron oxide in the bimetallic oxygen carrier to increase the average hydrogen production rate of the chemical chaining hydrogen production reaction, increasing the proportion of hydrogen production by the oxidation reaction in the total hydrogen production, and reducing the methane conversion rate of the chemical chaining hydrogen production reaction; or increasing the mass content of metal nickel oxide in the bimetallic oxygen carrier to increase the methane conversion rate of the chemical chaining hydrogen production reaction, while reducing the average hydrogen production rate of the chemical chaining hydrogen production reaction and reducing the proportion of hydrogen production by the oxidation reaction in the total hydrogen production.

[0064] In an embodiment of the present invention, a degassing-precipitation-hydrothermal method is used to obtain a bimetallic oxygen carrier with Fe2O3 and NiO as the main active components. Because Fe2O3 and NiO are both nanoscale uniformly mixed, they can maintain their nano-mixing after frequent oxidation / reduction cycles, inhibiting the phase separation process of particle agglomeration to form large-sized particles, and having good cyclic stability. In the process of preparing the bimetallic oxygen carrier using the precipitation-hydrothermal method, the proportion of the active components can be controlled by controlling the ratio of the bimetallic salts, and the nanoparticle size of the active components can be controlled by controlling the time and temperature of the hydrothermal reaction. The bimetallic oxygen carrier obtained in this way can achieve a high methane conversion rate and hydrogen production rate, while reducing the reaction temperature.

[0065] The bimetallic oxygen carrier and its preparation method and the methane chemical chaining hydrogen production method of the present invention are described in detail below with reference to specific examples and drawings. It should be noted that the embodiments provided in the present invention are only for illustration and are not limited thereto.

[0066] Example 1

[0067] The method for preparing bimetallic oxygen carriers by precipitation-hydrothermal method is as follows:

[0068] 1) Al2O3 carrier powder is placed in a reaction vessel, heated to 90°C for 8 hours and evacuated, wherein the vacuum degree of the reaction vessel is 0.05 atm.

[0069] 2) Maintaining the vacuum state, after the Al2O3 carrier powder is cooled to room temperature, 1 unit volume of a mixed solution of iron nitrate and nickel nitrate bimetallic salts with a pH of 0.3 is sucked into the reaction vessel using the vacuum degree of the reaction vessel. Figure 1 As shown in step S101 in .

[0070] 3) Release the vacuum state of the reaction container, stir vigorously at a speed of 900-1300 revolutions per minute, and mix the iron-nickel bimetallic salt mixed solution and the Al2O3 carrier powder to form an initial mixed solution, such as Figure 1 As shown in step S102 in .

[0071] 4) Adding an alkaline precipitant to the initial mixed solution to form an initial mother solution in the form of a slurry. Since the addition of the alkaline precipitant increases the viscosity of the initial mother solution, a higher speed of 1300-1500 r / min is required for stirring to ensure that the initial mixed solution and the alkaline precipitant are evenly mixed and not separated. The alkaline precipitant is an 8 mol / L NaOH solution, such as Figure 1 As shown in step S103 in .

[0072] 5) Before transferring the initial mother liquor from the reaction vessel to the hydrothermal reactor, the reaction vessel loaded with the initial mother liquor is placed in an ultrasonic cleaning machine for ultrasonic treatment to fully break up and disperse the lumps in the initial mother liquor, and to prevent the lumps from agglomerating to form larger lumps, which would affect the particle size of the hydrothermally prepared bimetallic oxygen carrier. Subsequently, the initial mother liquor after ultrasonic treatment is transferred from the reaction vessel to the hydrothermal reactor, heated to 120°C and kept warm for 10 hours. While heating, it is stirred at a speed of 120 r / min to maintain uniform mixing of the initial mother liquor, ensuring that the finished mother liquor is uniformly mixed with iron oxide and nickel oxide, such as Figure 1 As shown in step S104 in .

[0073] 6) After the hydrothermal reactor cools to room temperature, i.e., after the finished product mother liquor cools, the solid precipitate product in the finished product mother liquor is separated and the solid precipitate is washed with deionized water and / or anhydrous ethanol. The solid precipitate product is dried in a vacuum drying oven at 60°C and then ground into a powdered Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier product, wherein the bimetallic oxygen carrier product comprises an Al2O3 carrier and Fe2O3 and NiO attached to the Al2O3 carrier, wherein the Fe2O3 and NiO are alternately distributed, and the mass of the Al2O3 carrier accounts for 40% of the total mass of the Fe2O3 and NiO active components; of the total mass of the active components, the mass of Fe2O3 accounts for 85-95%, and the mass of NiO accounts for 5-15%.

[0074] The bimetallic oxygen carrier prepared by the method provided by the present invention has a particle size of about 100nm-250nm and a uniform grain size distribution, which is conducive to enhancing the transfer of CO and H2 between Fe2O3 and NiO, and can improve the reduction degree and the hydrogen production rate in a single cycle.

[0075] The following combination Figure 2 The principle of methane chemical chaining hydrogen production using a bimetallic oxygen carrier in an embodiment of the present invention is described in detail.

[0076] Figure 2 Schematic diagram of the principle of methane chemical chaining hydrogen production using a bimetallic oxygen carrier in an embodiment of the present invention.

[0077] The Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier prepared by the above method is used to carry out two-step hydrogen production from methane chemical chain, wherein the method and principle of two-step hydrogen production from methane chemical chain are as follows: Figure 2 Shown, including:

[0078] 1) filling a bimetallic oxygen carrier into a reactor, wherein the reactor is a fixed bed or a moving bed, and a reforming reactor and an oxidation reactor are arranged in the fixed bed or the moving bed;

[0079] 2) Water vapor and methane gas are introduced into the reactor to cause a chemical chain reaction of hydrogen production between the methane gas, water vapor, and the bimetallic oxygen carrier, wherein the chemical chain reaction of hydrogen production includes a reduction reaction and an oxidation reaction. During the reduction reaction, water vapor and methane are introduced into the reforming reactor to reduce the metal iron oxide and metal nickel oxide in the bimetallic oxygen carrier to generate Fe3O4 and metal nickel, while nickel acts as a catalyst to convert methane and water vapor in situ into hydrogen and CO in the first stage, and Fe3O4 is further reduced to metal iron and FeO by the first stage hydrogen and the first stage CO. In other words, in the reforming reactor, the metal iron oxide and metal nickel oxide in the bimetallic oxygen carrier are reduced to generate metal iron, FeO and metal nickel, while methane and water vapor are oxidized to obtain the first stage hydrogen product, CO and CO2 and some unreacted methane. During the oxidation reaction, water vapor is introduced to oxidize metallic iron, FeO, and metallic nickel to produce metallic iron oxide (Fe3O4) and metallic nickel oxide. At the same time, the water vapor is reduced to obtain the second-stage hydrogen product, as well as unreacted water vapor, unreacted methane, CO, and CO2, thus realizing the two-step hydrogen production process of methane chemical chain. Among them, the water-carbon ratio of the introduced water vapor and methane is 1:1, the reaction temperature of the methane chemical chain hydrogen production is 525-600℃, and the space velocity is 150h -1 , residence time 24s; reduction reaction duration is 5min, oxidation reaction duration is 10min, where the space velocity is the ratio of the volume of methane introduced to the volume of the bimetallic oxygen carrier.

[0080] Furthermore, introducing water vapor during the reduction reaction effectively suppresses excessive oxidation and carbon deposition on the surface of the bimetallic oxygen carrier, while also increasing the overall hydrogen production and purity of the reduction reaction. This reduces the reaction issues associated with methane chemical chaining and enables hydrogen production at a moderate temperature of 500-600°C. In the oxidation reactor (oxidation reaction), the introduced water vapor is reduced to generate the second-stage hydrogen product and removes carbon deposits on the surface of the bimetallic oxygen carrier, helping to maintain its high activity and stability.

[0081] A methane chemical chaining hydrogen production reaction was carried out at 450-600° C. using a bimetallic oxygen carrier in which the mass of the Fe 2 O 3 active component in Example 1 accounted for 85-95% and the mass of the NiO active component accounted for 5-15%.

[0082] Figure 3 Graph showing the methane conversion rate and hydrogen production rate of the bimetallic oxygen carrier in Example 1 of the present invention in a methane chemical chaining hydrogen production reaction at different temperatures.

[0083] like Figure 3 As shown, when the reaction temperature is greater than 500°C, the methane conversion rate is higher than 80% and the single-cycle hydrogen production rate is higher than 10 mL / g. When the reaction temperature is greater than 575°C, the methane conversion rate is higher than 90% and the single-cycle hydrogen production rate is higher than 16 mL / g.

[0084] Furthermore, the bimetallic oxygen carrier in Example 1 was placed in a thermogravimetric analyzer, and a cyclic stability test was performed by switching the gas path to perform oxidation reaction and reduction reaction, wherein the conditions of the cyclic stability test were the same as those of the methane chemical chain hydrogen production reaction.

[0085] Figure 4 This is a graph showing the degree of oxidation of the bimetallic oxygen carrier in Example 1 of the present invention after 70 cycles of stability testing.

[0086] like Figure 4 As shown in the methane chemical chain hydrogen production reaction, the bimetallic oxygen carrier provided by the present invention can still maintain a large oxygen loss limit after 70 cycles, indicating that the bimetallic oxygen carrier in this application has high activity, wherein the limit oxygen loss is not much different from the initial value. The average oxygen loss in 100 cycles can reach 55%, and the oxygen loss is calculated as (m1-m i ) / (m1-m2)×100%, where m1 refers to the mass of the bimetallic oxygen carrier at the beginning of the reduction reaction, m j It refers to the mass of the bimetallic oxygen carrier at the end of the reduction reaction, and m2 refers to the mass of the bimetallic oxygen carrier after the metal iron oxide and metal nickel oxide are reduced to metal iron and metal nickel.

[0087] Furthermore, scanning electron microscopy (SEM) was used to characterize the bimetallic oxygen carrier before and after the methane chemical chaining reaction to hydrogen at medium temperature.

[0088] Figure 5A This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention before the methane chemical chaining reaction to produce hydrogen, with a scale of 200 nm; Figure 5B This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention after 150 methane chemical chaining hydrogen production reactions, with a scale of 200 nm.

[0089] like Figure 5A-5B As shown, the morphology of the bimetallic oxygen carrier in Example 1 of the present invention is a nano-granular structure with a diameter of 150-250nm, and the Fe2O3 nanoparticles and NiO nanoparticles in the active components are characterized by stable dispersion with Al2O3 and uniform grain size distribution. During the methane chemical chaining hydrogen production reaction under medium temperature conditions (600°C), after 150 cycles, the surface of the bimetallic oxygen carrier can still maintain more than 80% of the nanostructure and is dispersed at the nanometer level, without forming micron or even sub-millimeter large particles. This shows that the bimetallic oxygen carrier obtained by the precipitation-hydrothermal method-high-pressure digestion-growth process of the present invention achieves uniform mixing of Fe2O3 and NiO at the nanometer level during the preparation process, and Fe2O3 and NiO grow together on Al2O3 particles, and the length and width of the Fe and Ni element enrichment area do not exceed 5μm. Therefore, the present invention utilizes nano-scale blending to ensure sufficient material transfer between the iron and nickel components, deepen the degree of Fe2O3 reduction, resist carbon deposition, and improve hydrogen selectivity. Furthermore, after the frequent oxidation and reduction reaction cycles of the methane chemical chain hydrogen production reaction, uniform blending at the nano-particle level is still maintained, thereby suppressing the phase separation process of agglomeration to form large grains, and stably maintaining a high methane conversion rate and hydrogen production rate.

[0090] Furthermore, scanning electron microscopy (SEM) was used to characterize the bimetallic oxygen carrier after 300 cycles of methane chemical chaining reaction to hydrogen production at medium temperature.

[0091] Figure 6A This is a scanning electron microscope image of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chain hydrogen production cycles. Figure 6B This is an energy spectrum analysis diagram of all elements of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chain hydrogen production cycles. Figure 6C This is an energy spectrum analysis diagram of the oxygen element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chain hydrogen production cycles. Figure 6D This is an energy spectrum analysis diagram of the aluminum element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chain hydrogen production cycles. Figure 6E This is an energy spectrum analysis diagram of the iron element of the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chain hydrogen production cycles. Figure 6F This is an energy spectrum analysis diagram of the nickel element in the bimetallic oxygen carrier in Example 1 of the present invention after 300 methane chemical chaining hydrogen production cycles.

[0092] like Figures 6A-6FAs shown in the figure, after 300 methane chemical chain hydrogen production cycles, the Fe and Ni bimetallic elements still maintain mixing uniformity at the nanometer level, and no phase separation occurs, that is, no bimetallic elements precipitate, and large Fe2O3 and NiO particles of micron or even submillimeter level are formed.

[0093] Furthermore, X-ray diffraction (XRD) was used to analyze the phase of the bimetallic oxygen carrier in Example 1 of the present invention. Figure 7 shown.

[0094] Figure 7 This is the X-ray diffraction pattern of the bimetallic oxygen carrier in Example 1 of the present invention.

[0095] At room temperature and pressure, the bimetallic oxygen carrier appears as a dark red / brown powder with a density of 0.9g / cm 3 .like Figure 7 As shown, the XRD pattern is a combined pattern of α-Fe2O3, Al2O3, and cubic NiO, with α-Fe2O3 and Al2O3 being predominant, along with small amounts of NiO and NiFe2O4. α-Fe2O3 exhibits high reactivity for breaking carbon-hydrogen bonds in methane and exhibits excellent redox cycle stability. Its high surface area and low density facilitate the transfer of matter and energy during chemical chain reactions. Al2O3 serves as a chemically stable matrix material, while NiO promotes the strengthening of carbon-hydrogen bonds in methane, thereby enhancing the degree of reduction in the reaction between α-Fe2O3 and methane.

[0096] Example 2

[0097] The Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier was prepared by the same method as in Example 1, with the only difference being that the mass of the Fe2O3 active component accounted for 60-80% and the mass of the NiO active component accounted for 20-40%, and the methane chemical chaining hydrogen production reaction was carried out at 500-600°C.

[0098] Figure 8 This is a comparison chart of the methane conversion rate and hydrogen production rate of the bimetallic oxygen carrier in Example 2 of the present invention and the bimetallic oxygen carrier prepared by the mechanical mixing method in the methane chemical chaining hydrogen production reaction at different temperatures, wherein the bimetallic oxygen carrier prepared by the mechanical mixing method using the same proportion of components as in Example 2.

[0099] like Figure 8As shown, the bimetallic oxygen carrier in Example 2 of the present invention has a methane conversion rate of more than 62% and a single-cycle hydrogen production rate of more than 10 mL / g at a reaction temperature of 500°C. Above 500°C, the hydrogen production rate of the bimetallic oxygen carrier powder is more than 43 mL / g oxygen carrier, and above 550°C is more than 48 mL / g oxygen carrier; when the reaction temperature is greater than 575°C, the methane conversion rate is more than 85%, and the single-cycle hydrogen production rate is more than 8 mL / g. Therefore, by appropriately increasing the NiO mass fraction to 20-40% and reducing the Fe2O3 mass fraction to 60-80%, the methane conversion rate in the range of 500-600°C can be increased, but the hydrogen production rate may be reduced. In contrast, the bimetallic oxygen carrier prepared by the mechanical mixing method has a methane conversion rate of 50% at a reaction temperature of 500°C, and a methane conversion rate of more than 60% when the reaction temperature is greater than 575°C. This shows that the method provided by the present invention can achieve a high methane conversion rate and hydrogen production under medium temperature conditions, thereby reducing the reaction temperature of methane chemical chain hydrogen production.

[0100] Furthermore, it can be seen from Examples 1 and 2 that by controlling the composition of the bimetallic oxygen carrier particles, the selectivity and hydrogen production rate of the water-based chemical chain methane hydrogen production reaction can be controlled, so that the selectivity and / or hydrogen production rate reach the maximum value at the same reaction temperature, pressure and space velocity.

[0101] According to an embodiment of the present invention, the present invention can also adopt a moving bed reactor, wherein an oxidation reactor and a reforming reactor are provided in the moving bed reactor. By adopting a moving bed reactor, the reforming reactor and the oxidation reactor can be arranged in sequence, and a methane chemical chain hydrogen production reaction can be carried out. Because the bimetallic oxygen carrier particles flow continuously in the moving bed, when preparing the bimetallic oxygen carrier, spherical or cylindrical millimeter-scale porous alumina particles are preferably used. In addition, in addition to preparing the bimetallic oxygen carrier using the method provided by the present invention, Fe2O3 and NiO can be loaded on alumina by an impregnation / hydrothermal method to obtain an oxygen carrier with high mechanical strength, granular, and not easy to sinter, so as to be used on a moving bed reactor while reducing its wear. The bimetallic oxygen carrier obtained by the impregnation / hydrothermal method is applied to methane. In the medium-temperature methane chemical chain hydrogen production method, it is also possible to achieve a higher methane conversion rate and hydrogen production rate while lowering the reaction temperature, while achieving the purpose of resisting sintering and extending the life of the reactor. For example, when the reaction temperature drops to 550°C, the methane conversion rate can still be guaranteed to be >80%, and the hydrogen production rate is >53mL / g. 氧载体 .

[0102] In summary, in the examples of the present invention, a degassing-precipitation-hydrothermal method was used to obtain a mixed structure of Fe2O3 and NiO nanoparticles with a size of 100nm-250nm. This bimetallic oxygen carrier exhibited high dispersion of the active components and facilitated the transfer of reactants and products. By varying the hydrothermal reaction conditions and feed ratios, Fe2O3 / NiO bimetallic oxygen carriers of varying sizes and mass ratios were obtained. This allowed the methane conversion rate and oxygen carrier hydrogen production rate to be regulated to their maximum values, and the process was scalable, meeting the practical application needs of methane chemical chaining for hydrogen production.

[0103] Furthermore, in the process of methane chemical looping hydrogen production using a bimetallic oxygen carrier, the original single hydrogen production reaction is replaced by a two-step dual water-based methane chemical looping reaction, while the reaction temperature is simultaneously reduced from over 800°C to 500-600°C. This increases the hydrogen production rate in both the reduction and oxidation stages, which has beneficial effects on reactor design and manufacturing, as well as hydrogen production efficiency. Furthermore, the bimetallic oxygen carrier does not agglomerate or phase separate even after 150 cycles, improving its stability and service life, reducing investment and operating costs, and also contributing to the cost reduction of water-based methane chemical looping hydrogen production methods.

[0104] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic oxygen carrier, comprising: Placing a predetermined type of carrier powder in a reaction vessel, heating and keeping the temperature, and evacuating the vessel; The reaction container is cooled and the double metal salt mixed solution consisting of iron salt and nickel salt is sucked back into the reaction container by utilizing the vacuum degree of the reaction container; releasing the vacuum state of the reaction container, and mixing the bimetallic salt mixed solution and the carrier powder to form an initial mixed solution; A bimetallic oxygen carrier product is prepared based on the initial mixed solution, wherein the bimetallic oxygen carrier product includes metal iron oxide, metal nickel oxide, and a predetermined type of carrier, the metal iron oxide is Fe2O3, and the metal nickel oxide is NiO; The bimetallic oxygen carrier product prepared based on the initial mixed solution includes: adding an alkaline precipitant to the initial mixed solution to form an initial mother solution in the form of a slurry; Transferring the initial mother liquor from the reaction vessel to a hydrothermal reactor, heating and keeping the temperature constant to obtain a finished mother liquor; Cooling the finished product mother liquor to separate the solid precipitated product from the finished product mother liquor; The solid precipitated product is dried and ground to obtain the bimetallic oxygen carrier product.

2. The preparation method according to claim 1, before transferring the initial mother liquor to the hydrothermal reactor, further comprising: The reaction container containing the initial mother solution is placed in an ultrasonic cleaning machine for ultrasonic treatment.

3. The preparation method according to claim 1, wherein mixing the bimetallic salt mixed solution and the carrier powder comprises: The double metal salt mixed solution and the carrier powder are mixed by stirring at a first stirring speed.

4. The preparation method according to claim 3, further comprising: adding an alkaline precipitant to the initial mixed solution; The mixture is stirred at a second stirring speed to mix the initial mixed solution and the alkaline precipitant.

5. The preparation method according to claim 4, further comprising: while transferring the initial mother liquor from the reaction vessel to a hydrothermal reactor for heating; The initial mother liquor is stirred at a third stirring speed.

6. The preparation method according to claim 5, wherein: The third stirring speed is less than the first stirring speed; The first stirring speed is less than the second stirring speed.

7. The preparation method according to claim 6, wherein: The third stirring speed is: 90~120r / min; The first stirring speed is: 900~1300r / min; The second stirring speed is: 1300~1500r / min.

8. The preparation method according to claim 1, wherein: The predetermined type of carrier powder is one of the following: Al2O3 micron powder, Al2O3 porous microspheres, SBA-15 molecular sieve, zeolite molecular sieve, wherein the diameter of the Al2O3 porous microspheres is 1-3 mm; The iron salt is one of the following: ferric nitrate, ferric chloride; The nickel salt is one of the following: nickel nitrate and nickel acetate.

9. The preparation method according to claim 1, wherein: The alkaline precipitant is one of the following: 8 mol / L NaOH solution, 23-25 ​​wt% ammonia water.

10. The preparation method according to claim 1, wherein Placing a predetermined type of carrier powder in a reaction vessel, heating, keeping the temperature, and evacuating the vessel comprises: Place the predetermined type of carrier powder in a reaction vessel, heat to 100°C~150°C, keep warm for 2-8 hours and evacuate; Wherein, the vacuum degree of the reaction container is less than 0.05atm.

11. The preparation method according to claim 1, wherein: The double metal salt mixed solution is an acidic concentrated solution, and the pH value of the double metal salt mixed solution is 0.2-0.5; The initial mother liquor formed after adding the alkaline precipitant to the initial mixed liquor is an alkaline concentrated solution.

12. The preparation method according to claim 1, wherein The initial mother liquor is transferred from the reaction vessel to a hydrothermal reactor, heated and kept warm to obtain a finished mother liquor comprising: The initial mother liquor is transferred to a hydrothermal reactor, sealed and heated to 110°C~200°C, and kept warm for 2-12 hours to obtain a finished mother liquor, wherein the finished mother liquor presents a red solid-liquid stratification state, and the pressure in the hydrothermal reactor is 1-1.5MPa.

13. The preparation method according to claim 1, after separating the solid precipitated product from the finished product mother liquor, further comprising: The solid precipitated product is washed with deionized water and / or anhydrous ethanol.

14. A bimetallic oxygen carrier prepared by the method according to any one of claims 1 to 13, comprising: Flake or granular metallic iron oxide, the metallic iron oxide is Fe2O3; Flake or granular metal nickel oxide, staggeredly distributed with the metal iron oxide, the metal nickel oxide is NiO; a predetermined type of carrier; Wherein, the metal iron oxide and the metal nickel oxide are attached to the surface of the carrier, and the particle size of the metal iron oxide and the metal nickel oxide is 100-250 nm.

15. The bimetallic oxygen carrier according to claim 14, wherein: The metal iron oxide is: Fe2O3; The metal nickel oxide is: NiO; The carrier is one of the following: Al2O3 micron powder, Al2O3 porous microspheres, SBA-15 molecular sieve, zeolite molecular sieve, wherein the diameter of the Al2O3 porous microspheres is 1-3 mm.

16. The bimetallic oxygen carrier according to claim 15, wherein: Of the total mass of active ingredients: The mass proportion of the metal nickel oxide is 5-25%; the mass proportion of the metal iron oxide is 75-95%.

17. The bimetallic oxygen carrier according to claim 16, wherein: In the bimetallic oxygen carrier, the metal iron oxide and the metal nickel oxide are active components, and the mass ratio of the active components to the carrier is 3:2 to 5:

4.

18. A method for producing hydrogen from methane by chemical chaining using the bimetallic oxygen carrier according to any one of claims 14 to 17, comprising: Filling the bimetallic oxygen carrier into a reactor, wherein the reactor adopts a fixed bed or a moving bed; Water vapor and methane gas are introduced into the reactor to cause a chemical chain hydrogen production reaction between the methane gas, the water vapor, and the bimetallic oxygen carrier, wherein the chemical chain hydrogen production reaction includes a reduction reaction and an oxidation reaction, wherein: The reduction reaction includes an initial stage reaction and a mid- to late-stage reaction; wherein, in the initial stage reaction, the metal iron oxide and the metal nickel oxide in the bimetallic oxygen carrier are reduced to generate Fe3O4 and metal nickel, and methane is catalyzed under the catalytic action of the metal nickel to obtain a first-stage product mixture, wherein the first-stage product mixture includes the first-stage hydrogen product, unreacted methane, CO, and CO2; in the mid- to late-stage reaction, Fe3O4 reacts with hydrogen and the first-stage CO to produce metal iron and FeO; In the oxidation reaction, metallic iron and FeO are oxidized by water vapor to generate metallic iron oxides, and at the same time, the water vapor is reduced to generate a second-stage hydrogen product, wherein the second-stage product mixture obtained after the oxidation reaction includes the second-stage hydrogen product, unreacted water vapor, unreacted methane, CO, and CO2; During the reduction reaction and the oxidation reaction, water vapor is introduced.

19. The method according to claim 18, wherein: The amount of water vapor introduced into the reactor satisfies a predetermined ratio condition, wherein the predetermined ratio condition is that the water-to-carbon ratio in the mixture of water vapor and methane is 1:1-6.5:

1.

20. The method of claim 18, wherein: The reaction temperature in the reactor where the chemical chaining hydrogen production reaction occurs is 525°C to 600°C.

21. The method of claim 18, further comprising: By increasing the mass content of the metal iron oxide in the bimetallic oxygen carrier, the average hydrogen production rate of the chemical chaining hydrogen production reaction is increased, the proportion of the hydrogen production of the oxidation reaction in the total hydrogen production is increased, and the methane conversion rate of the chemical chaining hydrogen production reaction is reduced; or By increasing the mass content of the metal nickel oxide in the bimetallic oxygen carrier, the methane conversion rate of the chemical chaining hydrogen production reaction is increased, while the average hydrogen production rate of the chemical chaining hydrogen production reaction is reduced and the proportion of the hydrogen production of the oxidation reaction in the total hydrogen production is reduced.

22. The method of claim 19, further comprising: By reducing the water-to-carbon ratio, the methane conversion rate of the chemical chaining hydrogen production reaction is increased, while the average hydrogen production rate of the chemical chaining hydrogen production reaction is reduced; or By increasing the water-to-carbon ratio, the average hydrogen production rate of the chemical chaining hydrogen production reaction is increased, while the methane conversion rate of the chemical chaining hydrogen production reaction is reduced.

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