Bimetallic oxygen carriers and methods of making, two-step hydrogen production method for medium temperature methane chemical looping

Abstract

The application provides a bimetallic oxygen carrier, a preparation method and a method for preparing hydrogen by a two-step methane chemical chain, and belongs to the technical field of hydrogen preparation by a chemical chain. The preparation method of the bimetallic oxygen carrier comprises the following steps: obtaining a mixed powder comprising a metal oxide carrier, an iron oxide active component and an oxide active component of another metal, wherein the another metal is selected from any one of Ni, Co, Mn, Cu and Ce, the metal oxide carrier is selected from any one of Al2O3, MgO, MgAl2O4, SiO2 and 50% Y2O3, the mass percentage ratio of iron and the carrier metal is 40%-70%:60%-30%, and the total is 100%; the mass percentage ratio of the another metal and the carrier metal is 10%-70%:90%-30%, and the total is 100%; adding a binder, a pore-forming agent and water into the mixed powder to stir, to obtain a slurry; extruding the slurry in an extruder to obtain an extrudate, and rolling the extrudate in a rolling machine to obtain spherical particles; and drying and stepwise temperature calcining the spherical particles to obtain the bimetallic oxygen carrier.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical chain hydrogen production and oxygen carrier preparation, and particularly relates to a bimetallic oxygen carrier and a preparation method and a medium-temperature methane chemical chain two-step hydrogen production method. BACKGROUND

[0002] Hydrogen has the advantages of high calorific value, cleanliness, wide application, etc., is an ideal fuel and energy carrier, and has important significance for energy green and low-carbon transformation and realization of the carbon neutralization target. In the chemical chain hydrogen production reaction process, the oxygen carrier is the core of the reaction system, and the preparation and selection of the oxygen carrier are the determining factors of the chemical chain hydrogen production technology. In the traditional chemical chain hydrogen production reaction, the oxygen carrier mostly needs to be driven at 900 DEG C or above to have high performance, which not only needs a high heat source, but also is a great challenge to the material and design of the reactor, and current hydrogen production can only be realized in one step, which reduces the hydrogen production.

[0003] Therefore, how to use the oxygen carrier to carry out the chemical chain hydrogen production reaction in a medium-temperature environment and have high hydrogen production performance is the research focus of popularizing the chemical chain hydrogen production technology. SUMMARY

[0004] In view of the above technical problems, the application provides a bimetallic oxygen carrier and a preparation method and a medium-temperature methane chemical chain two-step hydrogen production method, so as to at least partially solve the above technical problems, wherein the technical solutions provided by the application are as follows:

[0005] As a first aspect of the application, a preparation method of a bimetallic oxygen carrier is provided, comprising:

[0006] obtaining a mixed powder containing a metal oxide carrier, an iron oxide active component and an oxide active component of another metal, wherein the another metal is selected from any one of Ni, Co, Mn, Cu and Ce, the metal oxide carrier is selected from any one of Al2O3, MgO, MgAl2O4, SiO2 and 50% Y2O3, the mass percentage ratio of iron to the carrier metal is 40%-70%:60%-30%, and the total is 100%; the mass percentage ratio of the another metal to the carrier metal is 10%-70%:90%-30%, and the total is 100%;

[0007] adding a binder, a pore former and water to the mixed powder to obtain a slurry;

[0008] extruding the slurry in an extruder to obtain an extrudate, and rolling the extrudate in a roller to obtain spherical particles;

[0009] drying and stepwise temperature calcining the spherical particles to obtain the bimetallic oxygen carrier.

[0010] As a second aspect of the present application, a bimetallic oxygen carrier prepared by the above method is provided, comprising:

[0011] a metal oxide carrier, and

[0012] an iron oxide active component and an oxide active component of another metal supported by the metal oxide carrier;

[0013] wherein the mass percentage ratio of iron to carrier metal is 40%-70%:60%-30%, totaling 100%; the mass percentage ratio of another metal to carrier metal is 10%-70%:90%-30%, totaling 100%.

[0014] As a third aspect of the present application, a method for preparing hydrogen by a two-step process of a medium-temperature methane chemical looping is provided, comprising:

[0015] filling the bimetallic oxygen carrier into a reactor;

[0016] introducing methane and steam into the reactor to perform a medium-temperature methane chemical looping hydrogen production reaction, wherein the temperature of the medium-temperature methane chemical looping hydrogen production reaction is 450-650℃, and the medium-temperature methane chemical looping hydrogen production reaction comprises a methane steam reforming reaction and a steam oxidation reaction;

[0017] in the methane steam reforming reaction, the iron oxide and the oxide of another metal in the bimetallic oxygen carrier are reduced to generate metallic iron and another metal, while the methane and steam are reformed to generate a mixture containing hydrogen of a first stage;

[0018] in the steam oxidation reaction, the metallic iron and another metal are oxidized to iron oxide and the oxide of another metal, while the steam is reduced to generate hydrogen of a second stage.

[0019] Based on the above technical solutions, the bimetallic oxygen carrier, the preparation method thereof, and the method for preparing hydrogen by a methane chemical looping provided by the present application have at least one of the following beneficial effects:

[0020] (1) In the embodiment of the present application, by controlling the proportion of the metal oxide carrier, iron oxide and another metal oxide active component, a mixed powder with different performance and strength is obtained. Subsequently, a binder, a pore-forming agent and water are added to the mixed powder for stirring, by controlling the amount of the added binder, the active component in the mixed powder is tightly combined with the inert carrier, and a slurry with uniform mixing and tight combination is obtained. Then the slurry is placed in an extruder, and the pressure in the extrusion process is used to make the slurry combination more tightly, and an extrudate with certain strength and shaping is obtained. Subsequently, the extrudate is placed in a roller for rolling, and spherical particles are obtained, so that the bimetallic oxygen carrier particles can be applied in the subsequent reactor. Finally, the formed spherical particles are dried to preliminarily remove the water in the spherical particles, and then the dried spherical particles are subjected to stage temperature calcination, on the one hand, it can avoid the cracking of the spherical particles and more energy consumption due to the too fast dispersion of water in the spherical particles, and at the same time make the spherical particles have stronger hardness, on the other hand, in the calcination process, the bimetallic oxygen carrier has higher pore structure and specific surface area by using the pore-forming agent, which can enhance the gas transmission performance of the bimetallic oxygen carrier in the application process.

[0021] (2) In the embodiment of the present application, the active component in the bimetallic oxygen carrier obtained by the above method can be uniformly dispersed on the carrier surface, and by adjusting the proportion of the metal active component, the methane chemical chain hydrogen production reaction in a medium temperature environment can be realized.

[0022] (3) In an embodiment of the present invention, a bimetallic oxygen support is applied to a methane chemical loop hydrogen production reaction. During the methane steam reforming hydrogen production reaction, a bimetallic oxygen support is filled into the reactor and methane and steam are introduced. In the initial stage of the methane steam reforming hydrogen production reaction, the active components of iron oxide and another metal oxide in the bimetallic oxygen support are reduced to generate Fe3O4 and another metal, while a small amount of CO and a small amount of CO2 are generated. As the reaction proceeds, in the middle and later stages of the methane steam reforming hydrogen production reaction, the reduced other metal acts as a catalyst to convert methane and steam into hydrogen and CO in situ in the first stage. At the same time, the hydrogen and CO generated in the first stage are further used to reduce Fe3O4 to metallic iron and FeO. In the steam oxidation reaction, after steam is introduced into the reactor, metallic iron, FeO and another metal in the reactor are oxidized to iron oxide (Fe3O4) and another metal oxide. At the same time, steam is reduced to generate hydrogen in the second stage, thus realizing a two-step hydrogen production reaction. Furthermore, by introducing steam into the methane steam reforming hydrogen production process, the carbon deposition on the surface of the bimetallic oxygen support can be effectively suppressed, and the overall hydrogen yield and purity of the hydrogen produced can be increased. During the oxidation process, the presence of steam can effectively remove the carbon deposits on the surface of the bimetallic oxygen support, maintaining its high activity.

[0023] Furthermore, the bimetallic oxide support prepared using the mixing-granulation-extrusion-calcination method provided by this invention possesses high strength, making it less prone to breakage during the reaction and maintaining good integrity, thus ensuring the stable activity of the bimetallic oxide support during the reaction. By controlling the proportion of each component in the bimetallic oxide support, the synergistic effect of iron oxide and another metal oxide in the bimetallic oxide support is achieved, which can reduce the reaction temperature of the bimetallic oxide support with methane at the same hydrogen production rate. This allows the bimetallic oxide support to carry out a two-step hydrogen production reaction at a medium temperature (450-650℃) with high hydrogen production yield and rate, avoiding the equipment maintenance and material selection problems caused by high-temperature (above 900℃) hydrogen production. In addition, the particle size of the bimetallic oxide support of this invention meets the requirements for application in moving bed reactors, and can be applied on a large scale in moving bed reactors. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process for preparing bimetallic oxygen carriers using the mechanical solid-phase mixing method in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the process for preparing a bimetallic oxygen support using the sol-gel method in another embodiment of the present invention;

[0026] Figure 3AThe principle diagram of the two-step hydrogen production reaction of the iron-nickel bimetallic oxygen carrier in the embodiment 1 of the present application;

[0027] Figure 3B The principle diagram of the three-step hydrogen production reaction of the iron-nickel bimetallic oxygen carrier in the embodiment 1 of the present application;

[0028] Figure 4 The methane conversion performance diagram of the iron-nickel bimetallic oxygen carrier in the embodiment I of the present application at different reaction temperatures;

[0029] Figure 5 The oxidation degree diagram of the iron-nickel bimetallic oxygen carrier in the embodiment 1 of the present application;

[0030] Figure 6 The methane conversion rate and hydrogen production effect diagram of the iron-nickel bimetallic oxygen carrier in the embodiment 1 of the present application in the fixed bed reaction gas. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the following will further describe the present application in combination with specific embodiments.

[0032] The embodiments of the present application will be described below with reference to the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application. In the following detailed description, many specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, it is apparent that one or more embodiments can be implemented without these specific details. In addition, in the following description, the description of well-known structures and techniques is omitted to avoid unnecessary confusion of the concept of the present application.

[0033] The terms used herein are only used to describe specific embodiments and are not intended to limit the present application. The terms "include", "contain" and the like used herein indicate the existence of the described features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0034] 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 to have meanings consistent with the context of the present specification, and should not be interpreted in an idealized or overly formal manner.

[0035] In the case of using expressions such as "at least one of A, B, and C", it generally means the same as "at least one of A or B; at least one of A or C; at least one of B or C; at least one of A, B, and C; and the like." In the case of using expressions such as "at least one of A, B, or C", it generally means the same as "at least one of A, at least one of B, or at least one of C; and the like."

[0036] Most of the conventional chemical looping hydrogen production reactions need to be carried out at a temperature above 900 DEG C, which requires high energy driving and has a problem of strict requirement for reactor equipment. In addition, the conventional oxygen carriers are mostly powders, which ignores the requirement of the reactor for the particle size of the oxygen carrier, especially the moving bed reactor. Therefore, how to design an oxygen carrier with higher performance and lower temperature of the methane chemical looping hydrogen production reaction is a problem to be solved in the current methane chemical looping hydrogen production reaction.

[0037] Therefore, the present application provides a granular bimetallic oxygen carrier, by controlling the proportion of active components in the bimetallic oxygen carrier and the preparation method, to obtain a mixed powder of bimetallic oxygen carriers with different properties, and combined with the granulation, pore forming and calcination forming process, the prepared bimetallic oxygen carrier has high mechanical strength, and can reduce the equilibrium temperature of the methane chemical looping hydrogen production reaction while maintaining high hydrogen production efficiency.

[0038] Specifically, the first aspect of the present application provides a preparation method of a bimetallic oxygen carrier, comprising: obtaining a mixed powder comprising a metal oxide carrier, an iron oxide active component and an oxide active component of another metal, wherein the another metal is selected from any one of Ni, Co, Mn, Cu and Ce, the metal oxide carrier is selected from any one of Al2O3, MgO, MgAl2O4, SiO2 and 50% Y2O3, the mass percentage ratio of iron to carrier metal is 40%-70%:60%-30%, and the total is 100%; the mass percentage ratio of another metal to carrier metal is 10%-70%:90%-30%, and the total is 100%; adding a binder, a pore forming agent and water to the mixed powder to obtain a slurry; extruding the slurry in an extruder to obtain an extrudate, and rolling the extrudate in a roller to obtain a spherical particle; and drying and stepwise calcining the spherical particle to obtain the bimetallic oxygen carrier.

[0039] In the embodiment of the present application, the metal oxide carrier, iron oxide and the oxide of another metal of Co, Mn, Ni, Cu, Ce are mixed in proportion to obtain a mixed powder with different properties and strength and containing the active components of alumina, iron oxide and the oxide of another metal. The mixed powder is added with a binder, a pore-forming agent and water for stirring, and the amount of the binder added is controlled to tightly bind the metal active components in the mixed powder with the inert metal oxide carrier to obtain a uniformly mixed slurry. Then the slurry is placed in an extruder, and the pressure in the extrusion process is used to make the slurry more tightly bound to obtain an extrudate with certain strength and shape. Subsequently, the extrudate is placed in a roller to be rounded to obtain spherical particles, so that the bimetallic oxygen carrier particles can be applied in the subsequent reactor. Finally, the formed spherical particles are dried to preliminarily remove the water in the spherical particles, and then the dried spherical particles are subjected to stepwise temperature calcination, on the one hand to avoid the cracking of the spherical particles due to the too fast loss of water and to obtain a relatively strong hardness, and on the other hand to make the bimetallic oxygen carrier have a relatively high pore structure and specific surface area to enhance the gas transmission performance of the bimetallic oxygen carrier in the application process.

[0040] In the embodiment of the present application, two methods are provided to obtain the mixed powder containing the metal oxide carrier, the iron oxide active component and the oxide active component of another metal, one of which is to prepare the mixed powder by a mechanical solid-phase mixing method first, and then to prepare the bimetallic oxygen carrier based on the mixed powder; and the other is to prepare the mixed powder by a sol-gel method, and then to prepare the bimetallic oxygen carrier based on the mixed powder.

[0041] Figure 1 The flowchart for preparing the bimetallic oxygen carrier by the mechanical solid-phase mixing method in the embodiment of the present application is shown.

[0042] As shown in Figure 1 , the preparation of the bimetallic oxygen carrier by the mechanical solid-phase mixing method in the present application includes steps S101-S103.

[0043] Step S101: preparing a mixed powder by a mechanical solid-phase mixing method;

[0044] Step S102: stirring the obtained mixed powder with a binder, a pore-forming agent and water, and forming spherical particles from the obtained slurry by an extrusion-rolling method;

[0045] Step S103: obtaining the bimetallic oxygen carrier after drying and stepwise temperature calcination of the obtained spherical particles.

[0046] According to the embodiment of the present application, in step S101, the method for obtaining the mixed powder containing the metal oxide carrier, the iron oxide active component and the oxide active component of another metal by mechanical solid phase mixing method comprises: pre-calcining the iron oxide powder and the oxide powder of another metal respectively, and obtaining the active powder after grinding and screening, wherein the another metal is selected from any one of Ni, Co, Mn, Cu and Ce, and the metal oxide carrier is selected from any one of Al2O3, MgO, MgAl2O4, SiO2 and 50% Y2O3; mixing the obtained two active powders with the metal oxide carrier in proportion to obtain the mixed powder. The pre-calcination temperature of the iron oxide powder and the oxide powder of another metal is 300-500°C; the particle size of the active powder obtained after grinding and screening is less than 50 microns; the mixing proportion of the two active powders and the metal oxide carrier can be the mass percentage ratio of iron to carrier metal, which is 40%-70%:60%-30%, totaling 100%; the mass percentage ratio of another metal to carrier metal is 10%-70%:90%-30%, totaling 100%. Further, in order to mix the two active components and the inert carrier uniformly, the obtained mixed powder is ball milled after mixing the two active powders with the metal oxide carrier in proportion, so as to obtain the mixed powder with uniform mixing and smaller particle size, wherein the ball milling speed is 100-800 r / min, and the ball milling time is 0.25-5 h.

[0047] For example: the iron oxide and nickel oxide solid powders are put into a reaction container for pre-calcination at 300-500°C, and the calcination time is 1-2 h, so as to improve the initial mechanical strength of the solid powders. Then, the solid powders with certain mechanical strength are respectively ball milled to crush the lumps in the pre-calcination process and reduce the particle size of the calcined solid powders, and the solid particles with particle size less than 50 microns are obtained after screening, which can avoid affecting the activity in the application process of methane chemical chain hydrogen production due to the excessively large particle size of the prepared double-metal oxide carrier. Subsequently, the iron oxide active component, the nickel oxide active component and the metal oxide carrier with particle size less than 50 microns are mixed in the proportion of the mass percentage ratio of iron to metal carrier (such as alumina carrier, aluminum component) being 60%:40%, totaling 100%, and the mass percentage ratio of nickel to metal in the metal oxide carrier (such as alumina carrier, aluminum component) being 20%:80%, totaling 100%, and constant stirring is performed after mixing to obtain the uniformly mixed powder. In order to further ensure that the iron oxide, the nickel oxide and the metal oxide carrier are mixed more uniformly and the particle size of the powder is smaller, the uniformly mixed powder is put into a ball mill, and ball milling is performed at a speed of 100-800 r / min for 0.5-5 h to obtain the mixed powder.

[0048] In the embodiments of the present application, the initial mechanical strength of the solid powder is improved by pre-calcining the iron oxide powder and the oxide powder of another metal, and then the solid powder is ground to obtain an active solid powder with smaller particle size and certain mechanical strength. Then, the metal active component and the metal oxide carrier are mixed in proportion, and the mixed powder is stirred and ball milled to obtain a mixed powder with smaller particle size and more uniform mixing of the active component, so that the mixed powder can be uniformly dispersed in the subsequent granulation process, and the growth of the bimetallic particles in the subsequent calcination process is avoided.

[0049] According to the embodiments of the present application, in step S102, the mixed powder obtained in step S101 is stirred with a binder, a pore-forming agent and water, and the obtained slurry is formed into spherical particles by an extrusion-spheronization method, including: adding the binder, the pore-forming agent and water to the mixed powder to stir and obtain a slurry; placing the slurry in an extruder to form an extrudate; and placing the extrudate in a spheronizer to obtain spherical particles.

[0050] Specifically, 2-15 wt.% of the binder, 2-15 wt.% of the pore-forming agent and 20-50 wt.% of water are added to the mixed powder, and the mixed powder is stirred while the binder, the pore-forming agent and water are added, to obtain a uniformly mixed and slightly viscous slurry, wherein the binder is selected from kaolin or attapulgite, the pore-forming agent is selected from cellulose or graphite, and the water can be deionized water, and other materials with the same properties as kaolin and cellulose can also be used. Then, the uniformly mixed slurry is placed in an extruder (E-25), and is extruded at a speed of 20-150 r / min to obtain an extrudate with a diameter of 0.5-6 mm, wherein different diameters of the extrudate can be obtained by changing the size of the hole plate of the extruder. Finally, the extrudate with a diameter of 0.5-6 mm is sheared and placed in a spheronizer (mini S) to be spheronized at a spheronization speed of 500-1000 r / min. After spheronization into spherical particles, the extrudate is sheared with scissors to obtain spherical particles with a length of 0.5-6 mm.

[0051] In the embodiments of the present application, the uniformly mixed mixed powder is mixed with a binder, a pore-forming agent and water, the binder is used to enhance the binding ability between the inert carrier and the active component in the mixed powder, so as to avoid phase separation of the components in the particles due to frequent material exchange in the application process; and the pore-forming agent is used to provide a loose structure, so that a loose and porous bimetallic oxygen carrier can be obtained in the subsequent calcination process, so as to enhance the gas transmission and improve the hydrogen production performance.

[0052] According to the embodiments of the present application, in step S103, the spherical particles obtained in step S102 are dried and subjected to stepwise temperature calcination to obtain a bimetallic oxygen carrier.

[0053] Specifically, the spherical particles are first placed in a crucible, and then the crucible is placed in a drying box for drying, wherein the drying time is 6-12h, and the drying temperature is 50-120℃. Subsequently, the dried spherical particles are placed in a muffle furnace, and the calcination temperature of the spherical particles is increased from room temperature to 700-900℃ under an air atmosphere for first-stage calcination, and the calcination time is 4-10h. After the first-stage calcination is completed, the calcination temperature is continuously increased to 1100-1300℃ for second-stage calcination, and the calcination time is 1-2h, wherein the calcination increase rates of the first stage and the second stage are both 2-10℃ / min.

[0054] In the embodiments of the present application, the spherical particles are first dried to preliminarily remove the moisture in the spherical particles, so as to avoid the cracking of the spherical particles due to the too fast moisture loss in the subsequent calcination process, and reduce the energy consumption. Subsequently, the dried spherical particles are subjected to two-stage stepwise calcination, so as to avoid the too fast moisture loss and the too intense reaction caused by the once increase of the calcination temperature to the highest calcination temperature, and avoid the collapse of the particles. By using the two-stage stepwise calcination, the too fast moisture loss can be avoided, and the particles are preliminarily hardened, and then the temperature is increased to completely harden the particles, so as to strengthen the strength of the particles.

[0055] Thus, the present application obtains a mixed powder composed of a metal oxide active component and a metal oxide carrier by a mechanical solid-phase mixing method, and forms a slurry of the mixed powder with a binder, a pore-forming agent, etc. Then, the spherical bimetallic oxide carrier particles are formed by an extrusion-spheronization method and calcination, and the preparation method has the characteristics of wide material sources, simple preparation process flow and strong repeatability, and can be prepared on a large scale.

[0056] According to the embodiments of the present application, a method for obtaining a mixed powder containing a metal oxide carrier, an iron oxide active component and an oxide active component of another metal by a sol-gel method is also provided, which comprises the following steps:

[0057] The iron oxide / metal oxide carrier powder and the oxide of another metal / metal oxide carrier powder are mixed in proportion to obtain a mixed powder, wherein the iron oxide / metal oxide carrier powder and the oxide of another metal / metal oxide carrier powder are prepared by a sol-gel method, and the particle size of the iron oxide / metal oxide carrier powder and the oxide of another metal / metal oxide carrier powder is nanometer or micrometer, such as 50nm-10μm. Specifically, the iron oxide / metal oxide carrier powder and the oxide of another metal / metal oxide carrier powder are obtained by the following methods, respectively:

[0058] Step 1: dissolving the carrier metal salt and the metal salt in an aqueous solvent to obtain a mixed solution, wherein the metal salt includes any one of an iron salt and another metal salt, and the aqueous solvent includes a mixture of water and isopropyl alcohol;

[0059] Step 2: drying the mixed solution to remove the solvent to obtain a solid mixed salt containing metal ions and carrier metal ions;

[0060] Step 3: calcining the solid mixed salt in an air atmosphere to obtain a metal oxide / metal oxide carrier powder.

[0061] In the embodiments of the present application, the metal oxide / metal oxide carrier active powder is prepared by the sol-gel method, which can make the bimetallic oxide carrier smaller in size, and the water phase mixing method can make the active component and the carrier metal salt mix more uniformly and firmly, which is helpful to obtain a bimetallic oxide carrier of micron or nanometer level and with more excellent reaction performance. By the calcination treatment of the solid mixed salt, the mechanical strength of the metal oxide / metal oxide carrier active powder can be enhanced, and the impurities such as salt contained in the powder can be removed.

[0062] According to the embodiments of the present application, the method for obtaining the iron oxide / metal oxide carrier powder and the oxide of another metal / metal oxide carrier powder further comprises: ball milling and mixing the metal oxide / metal oxide carrier powder obtained by calcination, wherein the ball milling speed is 100-800 r / min, and the ball milling time is 0.5-5 h, so as to further reduce the particle size of the mixed powder.

[0063] According to the embodiments of the present application, in step 1, the mass percentage ratio of iron to the carrier metal is 40%-70%: 60%-30%, and the total is 100%; and / or, the mass percentage ratio of the other metal to the carrier metal is 10%-70%: 90%-30%, and the total is 100%, by controlling the ratio of iron, the carrier metal and the other metal, the strength of the prepared bimetallic oxide carrier and the performance in application are controlled. In step 2, the mixed solution is dried to remove the solvent, wherein the drying is staged drying, and the temperature of the staged drying is 40-80℃. In step 3, the calcination temperature for calcining the dried solid mixed salt is 400-600℃, and the calcination time is 2-4 h, so as to remove the impurities in the solid mixed salt and obtain the metal oxide / metal oxide carrier powder.

[0064] According to the embodiments of the present application, the metal salt is selected from any one of cobalt salt, manganese salt, nickel salt, copper salt and cerium salt; and the iron salt is selected from iron nitrate. Further, the metal salt is selected from metal nitrate, such as any one of nickel nitrate, cobalt nitrate, manganese nitrate and copper nitrate.

[0065] Hereinafter, taking iron and another metal Ni as examples, and taking the metal oxide carrier as alumina, the process for preparing the nickel oxide / alumina inert carrier powder and the iron oxide / alumina inert carrier powder by the sol-gel method, and preparing the bimetallic oxide carrier is described in detail as follows.

[0066] Figure 2 Figure 2 shows a flowchart of a process for preparing a bimetallic oxygen carrier according to another embodiment of the present application.

[0067] As shown in Figure 2, the process for preparing a bimetallic oxygen carrier according to the embodiment of the present application comprises steps S201-S207. Figure 2

[0068] Steps S201-S205: preparing a mixed powder by a sol-gel method;

[0069] Step S206: based on the obtained mixed powder, a binder, a pore-forming agent and water are stirred to obtain a slurry, and the slurry is formed into spherical particles by an extrusion-spheronization method;

[0070] Step S207: the obtained spherical particles are dried and subjected to a stepwise temperature increase calcination to obtain a bimetallic oxygen carrier.

[0071] According to the embodiment of the present application, in steps S201-S205, the process for preparing a mixed powder by a sol-gel method comprises the following steps: first, preparing an iron oxide / aluminum oxide inert carrier powder and a nickel oxide / aluminum oxide inert carrier powder, and then mixing the two powders to obtain a mixed powder after ball milling.

[0072] More specifically, the process for preparing an iron oxide / aluminum oxide carrier powder by a sol-gel method comprises the following steps:

[0073] In step S201: according to the mass ratio of metal oxides, a corresponding mass of iron nitrate and aluminum nitrate is dissolved in an isopropanol aqueous solution to obtain a mixed solution containing aluminum ions and iron ions;

[0074] In step S202: the mixed solution is dried to obtain a solid mixed salt containing iron ions and aluminum ions, and the solid mixed salt is calcined in an air atmosphere to obtain an iron oxide / aluminum oxide carrier powder (Fe2O3 / Al2O3).

[0075] Similarly, the process for preparing a nickel oxide / aluminum oxide carrier powder by a sol-gel method comprises the following steps:

[0076] In step S203: according to the mass ratio of metal oxides, a corresponding mass of nickel nitrate and aluminum nitrate is dissolved in an isopropanol aqueous solution to obtain a mixed solution containing aluminum ions and nickel ions;

[0077] In step S204: the mixed solution is dried to obtain a solid mixed salt containing nickel ions and aluminum ions, and the solid mixed salt is calcined in an air atmosphere to obtain a nickel oxide / aluminum oxide carrier powder (NiO / Al2O3).

[0078] ​In step S205, the iron oxide / alumina carrier powder and the nickel oxide / alumina carrier powder are mixed and ground by a ball mill to obtain a mixed powder (Fe2O3 / Al2O3 powder + NiO / Al2O3 powder).

[0079] In step S206, the obtained mixed powder is stirred with a binder, a pore-forming agent and water, and the obtained slurry is formed into spherical particles by an extrusion-spheronization method, including: adding the binder, the pore-forming agent and water to the mixed powder to obtain a slurry; placing the slurry in an extruder to form an extrudate; and placing the extrudate in a spheronizer to obtain spherical particles.

[0080] Specifically, the iron oxide / alumina carrier powder and the nickel oxide / alumina carrier powder are mixed according to the mass ratio of iron oxide to nickel oxide, and a mixed powder is obtained, wherein the mixing ratio can be 4:1. Based on the mass of the mixed powder (Fe2O3 / Al2O3 powder + NiO / Al2O3 powder), 2-15 wt.% of a binder, 2-15 wt.% of a pore-forming agent and 20-50 wt.% of water (such as deionized water) are added to the mixed powder while stirring to obtain a uniform and slightly viscous slurry, wherein the binder is selected from kaolin or attapulgite, and the pore-forming agent is selected from cellulose or graphite. Then, the uniformly mixed slurry is placed in an extruder (E-25), and the extruder is used to form an extrudate with a diameter of 0.5-6 mm at a rotating speed of 20-150 r / min, wherein different diameters of the extrudate can be obtained by changing the size of the hole plate of the extruder. Finally, the obtained extrudate with a diameter of 0.5-6 mm is sheared and placed in a spheronizer (mini S) to be spheronized at a spheronization rotating speed of 500-1000 r / min. After spheronization into spherical particles, the extrudate is sheared by scissors to spherical particles with a length of 0.5-6 mm.

[0081] According to the embodiment of the present application, in step S207, the obtained spherical particles are dried and subjected to stepwise temperature rising calcination to obtain a bimetallic oxygen carrier.

[0082] Specifically, the spherical particles are first placed in a crucible, and then the crucible is placed in a drying oven for drying, wherein the drying time is 6-12 h and the drying temperature is 50-120℃. Subsequently, the dried spherical particles are placed in a muffle furnace, and the calcination temperature of the spherical particles is raised from room temperature to 700-900℃ under an air atmosphere for first stage calcination, and the calcination time is 4-10 h. After the first stage calcination is completed, the calcination temperature is continuously raised to 1100-1300℃ for second stage calcination, and the calcination time is 1-2 h, wherein the calcination temperature rising rate of the first stage and the second stage is 2-10℃ / min.

[0083] Thus, the present application prepares a mixed powder of Fe2O3 / Al2O3 powder + NiO / Al2O3 powder by a sol-gel method, and then forms a spherical particle by an extrusion-spheronization method. By refining the preparation method of the mixed powder, a bimetallic oxygen carrier particle with higher porosity and smaller particle size can be obtained, and more excellent reaction performance can be provided.

[0084] According to an embodiment of the present application, in addition to the mechanical solid-phase mixing method and the sol-gel method, the bimetallic oxygen carrier can also be prepared by a solution precipitation method in cooperation with the extrusion-spheronization-calcination process.

[0085] As a second aspect of the present application, a bimetallic oxygen carrier prepared by the method in the above embodiments is also provided, which includes a metal oxide carrier, and an iron oxide active component and another metal oxide active component supported by the metal oxide carrier; wherein the mass percentage ratio of iron to the carrier metal is 40%-70%: 60%-30%, and the total is 100%; and the mass percentage ratio of another metal to the carrier metal is 10%-70%: 90%-30%, and the total is 100%.

[0086] According to an embodiment of the present application, the bimetallic oxygen carrier is a Fe-Ni bimetallic oxygen carrier, wherein the particle size of the active component in the Fe-Ni bimetallic oxygen carrier is micron level, the strength of the micron level Fe-Ni bimetallic oxygen carrier is 60-90 N, the specific surface area is 1-10 m 2 / g, and the porosity is 30-50%. The particle size of the active component in the Fe-Ni bimetallic oxygen carrier is nanometer level, the strength of the nanometer level Fe-Ni bimetallic oxygen carrier is 30 N-50 N, the specific surface area is 5-20 m 2 / g, and the porosity is 40-60%.

[0087] As a third aspect of the present application, a method for preparing hydrogen by a medium-temperature methane chemical looping two-step process using a bimetallic oxygen carrier is provided, which includes: filling the bimetallic oxygen carrier into a reactor; introducing methane and steam into the reactor to perform a medium-temperature methane chemical looping hydrogen production reaction, wherein the temperature of the medium-temperature methane chemical looping hydrogen production reaction is 450-650°C, and the medium-temperature methane chemical looping hydrogen production reaction includes a methane steam reforming reaction and a steam oxidation reaction; in the methane steam reforming reaction process, the iron oxide and another metal oxide in the bimetallic oxygen carrier are reduced to generate metallic iron and another metal, and at the same time, the methane and steam are reformed to generate a mixture containing hydrogen of a first stage; in the steam oxidation reaction process, the metallic iron and another metal are oxidized to iron oxide and another metal oxide, and at the same time, the steam is reduced to generate hydrogen of a second stage.

[0088] In the embodiment of the present application, in the methane steam reforming reaction, methane and steam are introduced into the reactor, the metal active component in the bimetallic oxygen carrier is reduced to metal by the methane steam reforming reaction, and at the same time, methane is decomposed into CO, CO2 and H2, thereby realizing the first-stage hydrogen production. In the steam oxidation process, the reduced metal is oxidized to metal oxide, and the introduced steam is reduced to the second-stage hydrogen, thereby realizing the two-step hydrogen production by the methane chemical looping and improving the hydrogen production and the hydrogen production rate. In addition, the introduction of steam in the methane steam reforming reaction can not only inhibit the carbon deposition on the surface of the bimetallic oxygen carrier, but also improve the hydrogen production. In the oxidation process, the introduction of steam can carry away part of the carbon deposited on the surface of the bimetallic oxygen carrier. In addition, by controlling the proportion of the active component in the bimetallic oxygen carrier and using the bimetallic oxygen carrier prepared by the mechanical mixing method or the sol-gel method, the bimetallic oxygen carrier has the characteristics of small particle size, can realize the hydrogen production in the medium-temperature environment (450-650 ℃) and has excellent hydrogen production performance, and the problems of equipment maintenance and material selection caused by the high-temperature (above 900 ℃) hydrogen production are avoided.

[0089] According to the embodiment of the present application, the steam-to-carbon ratio of the steam to methane is 1:1-3:1.

[0090] According to the embodiment of the present application, the method for producing hydrogen by the methane chemical looping further comprises: by increasing the content of another metal oxide active component in the bimetallic oxygen carrier, the methane conversion rate in the two-step hydrogen production by the methane chemical looping is increased, and at the same time, the hydrogen production rate of the two-step hydrogen production by the methane chemical looping and the proportion of the hydrogen production amount of the steam oxidation reaction in the total hydrogen production amount are reduced; or by increasing the content of the iron oxide active component in the bimetallic oxygen carrier, the hydrogen production amount in the two-step hydrogen production by the methane chemical looping and the proportion of the hydrogen production amount of the steam oxidation reaction in the total hydrogen production amount are increased, and at the same time, the methane conversion rate in the two-step hydrogen production by the methane chemical looping is reduced.

[0091] For example, taking Ni as another metal, the iron-nickel bimetallic oxygen carrier is formed by adjusting the active component of nickel oxide. Since nickel oxide can react with methane at a lower temperature, and the reduced metal nickel also has a certain performance of catalyzing the methane cracking, the addition of the active component of nickel oxide reduces the reaction temperature of the iron-nickel bimetallic oxygen carrier with methane. In other words, the formed iron-nickel bimetallic oxygen carrier has excellent performance in the hydrogen production reaction at medium temperature. Further, increasing the content of the active component of nickel oxide can promote the decomposition of methane to produce CO and H2, and reduce the hydrogen production amount in the two-step hydrogen production by the methane chemical looping. If the content of the active component of iron oxide is increased, the hydrogen production amount in the hydrogen production by the methane chemical looping can be increased.

[0092] According to the embodiment of the present application, the reactor used is a moving bed reactor. In the moving bed reactor, the bimetallic oxygen carrier particles prepared by mechanical solid phase mixing or sol-gel and in combination with the extrusion-spheronization method have strong mechanical properties and are spherical, which helps to reduce the wear rate of the bimetallic oxygen carrier in the moving bed reactor, maintain a high degree of integrity, and thus maintain a high reaction activity. In addition, the same technical effects can also be achieved by using a fixed bed reactor.

[0093] According to the embodiment of the present application, the method for preparing hydrogen by the two-step process of the medium-temperature methane chemical looping also includes: air oxidation of the bimetallic oxygen carrier after the two-step hydrogen production reaction of the medium-temperature methane chemical looping, to increase the oxygen carrying capacity of the bimetallic oxygen carrier, and the heat released is used to supply heat to the two-step hydrogen production reaction of the medium-temperature methane chemical looping or to supply heat to the outside.

[0094] In the embodiment of the present application, the bimetallic oxygen carrier after the water vapor oxidation reaction is subjected to air oxidation treatment, the partially oxidized bimetallic oxygen carrier is fully oxidized by air (containing oxygen and nitrogen), the oxygen carrying capacity of the oxygen carrier is increased, and the hydrogen production rate in the two-step hydrogen production process is improved; the high heat released can provide heat to the two-step hydrogen production reaction or provide a reaction heat source for the outside.

[0095] The bimetallic oxygen carrier, the preparation method thereof, and the method for preparing hydrogen by methane chemical looping of the present application will be described in detail below in combination with specific embodiments and the accompanying drawings. It should be noted that the embodiments provided by the present application are only for illustration and are not limited thereto.

[0096] Embodiment 1

[0097] The steps for preparing the iron-nickel bimetallic oxygen carrier by mechanical solid phase mixing are as follows:

[0098] 1) Obtain mixed powder: Put the iron oxide and nickel oxide solid powders into a reactor respectively, and pre-calcine at 500℃ for 2h. After calcination, grind and sieve to obtain active powders with a particle size of less than 50μm. Mix the micron-sized iron oxide, nickel oxide active powders, and aluminum oxide carrier according to the mass percentage ratio of iron to aluminum of 60%:40% and the mass percentage ratio of nickel to aluminum of 30%:70%. After mixing, continuously stir to obtain uniformly mixed powder. Then, put the powder into a ball mill and ball mill at a speed of 500r / min for 2h to obtain mixed powder.

[0099] 2) Extrusion-spheronization: A binder (kaolin, 10 wt.%) and a pore-forming agent (cellulose, 8 wt.%) and deionized water (50 wt.%) were added to the obtained mixed powder while stirring to obtain a uniform viscous slurry. Subsequently, the slurry was placed in an extruder to be extruded at 150 r / min to obtain an extrudate having a diameter of 1.5 ± 0.2 mm. Next, the obtained extrudate was cut and placed in a spheronizer to be spheronized at 500 r / min to obtain spherical particles having a diameter of 1.5 ± 0.2 mm.

[0100] 3) Drying, calcination and molding: The spherical particles were placed in a drying oven and dried at 80 °C for 6 h, and then placed in a muffle furnace for stepwise temperature calcination in an air atmosphere. The calcination temperature was first increased from room temperature to 700 °C for first-stage calcination, and the calcination time was 5 h. Finally, the calcination temperature was further increased to 1200 °C for second-stage calcination, and the calcination time was 2 h to harden the powder.

[0101] The strength of the Fe-Ni bimetallic oxygen carrier prepared by the method in Example 1 was 50.26 N, the specific surface area was 6.841 m 2 / g, the porosity was 40 ± 5%, and the bulk density was 1.50 g / cm 3 . Thus, it is shown that the bimetallic oxygen carrier has high mechanical strength and high specific surface area and porosity.

[0102] Further, the Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier prepared in Example 1 was used in a method for preparing hydrogen by a two-step methane chemical looping, which comprises:

[0103] 1) The Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier was filled in a reactor;

[0104] 2) Water vapor and methane gas were introduced into the reactor, so that a chemical looping hydrogen production reaction occurred between the methane gas, the water vapor, and the Fe2O3 / NiO / Al2O3 bimetallic oxygen carrier. The temperature of the methane chemical looping hydrogen production reaction was 600 °C, and the methane chemical looping hydrogen production reaction included a methane steam reforming reaction and a water vapor oxidation reaction.

[0105] In the methane steam reforming reaction process, water vapor and methane were introduced into the reactor. In the reaction process, the iron oxide and nickel oxide in the bimetallic oxygen carrier were reduced to generate metallic iron and metallic nickel, and the methane and water vapor were reformed to generate a first-stage hydrogen-containing mixture, wherein the first-stage hydrogen-containing mixture includes a small amount of CO and CO2, and a first-stage H2.

[0106] In the water vapor oxidation reaction process, water vapor is introduced into the reactor, and the metal iron and metal nickel in the reactor are oxidized into iron oxide and nickel oxide, while the water vapor is reduced to generate the second stage hydrogen. Among them, the water carbon ratio of the introduced water vapor and methane is 1.5:1, the space velocity is 200h -1 ; the duration of the reduction reaction is 5min, and the duration of the oxidation reaction is 10min, wherein the space velocity is the ratio of the volume of the introduced methane to the volume of the bimetallic oxygen carrier.

[0107] Figure 3A The principle diagram of the methane chemical chain two-step hydrogen production reaction is carried out on the iron-nickel bimetallic oxygen carrier in Example 1 of the present application.

[0108] As shown in Figure 3A , the reactor includes a reforming reactor and an oxidation reactor. The iron-nickel bimetallic oxygen carrier is filled into the reforming reactor and methane and water vapor are introduced to carry out the methane steam reforming reaction. In the initial stage of the methane steam reforming reaction, the active components of nickel oxide and iron oxide in the iron-nickel bimetallic oxygen carrier are reduced to Fe3O4 and metal nickel, while a small amount of CO and a small amount of CO2 are generated. As the reaction proceeds, in the later stage of the methane steam reforming reaction, the reduced metal nickel acts as a catalyst to convert methane and water vapor in situ into the first stage hydrogen (H2) and CO, which can promote the deep reduction of Fe3O4 to Fe and FeO. In the water vapor oxidation reaction process, water vapor is introduced, and the metal nickel, metal iron (Fe) and FeO entering the oxidation reactor are oxidized by the water vapor to generate iron oxide and nickel oxide, while the water vapor is reduced to H2, realizing the effective transfer of CO and H2 between Fe2O3 and NiO, and realizing two-step hydrogen production. In addition, the introduction of water vapor in the methane steam reforming reaction can inhibit the surface carbon deposition of the iron-nickel bimetallic oxygen carrier and improve the hydrogen production; and the introduction of water vapor in the water vapor oxidation reaction process can remove part of the carbon deposited on the surface of the oxygen carrier, so that the bimetallic oxygen carrier maintains a high activity. In addition, the present application uses nickel oxide as the active component, which can carry out the methane chemical chain hydrogen production reaction at a lower temperature, thereby reducing the reaction temperature; on the other hand, the nickel oxide has the ability to take away the oxygen atoms in water, so that water vapor can be used in the oxidation reaction process, and the purposes of hydrogen production and carbon removal can be achieved.

[0109] Therefore, the iron-nickel bimetallic oxygen carrier provided by the present application can reduce the methane reforming reaction temperature to 450-600℃, realize the two-step hydrogen production of the reduction reaction (methane steam reforming hydrogen production reaction) and the oxidation reaction (water vapor oxidation reaction), and the corresponding hydrogen production purity of the two-step hydrogen production is 80% and 99%, respectively. It should be noted that other types of metals, such as Mn, Cu, Co, Ce, also have the same performance as Ni, i.e. two-step hydrogen production in a medium temperature environment.

[0110] Figure 3B This is a schematic diagram illustrating the principle of the three-step chemical chain reaction for hydrogen production from methane using an iron-nickel bimetallic oxygen support in Example 1 of this invention.

[0111] like Figure 3B As shown, in this embodiment of the invention, the bimetallic oxygen support, in addition to participating in the above-mentioned intermediate-temperature methane chemical chain two-step hydrogen production reaction, also includes the partially oxidized bimetallic oxygen support after the water vapor oxidation reaction in the methane chemical chain two-step hydrogen production reaction. The bimetallic oxygen carrier is introduced into an air oxidation reactor, where it is partially oxidized by the oxygen in the air. It is completely oxidized to a bimetallic oxygen carrier (MeO), which increases the oxygen carrying capacity of the bimetallic oxygen carrier and releases heat, nitrogen and a small amount of oxygen, and then enters a new round of methane chemical chain hydrogen production reaction.

[0112] Figure 4 The graph shows the methane conversion performance of the iron-nickel bimetallic oxygen support in Example 1 of this invention at different reaction temperatures.

[0113] like Figure 4 As shown, the iron-nickel bimetallic oxygen support provided by this invention can achieve a methane conversion rate of over 85% (approximately 92%) at a reaction temperature of 600℃, realizing hydrogen production under medium temperature conditions with a high methane conversion rate, and a unit hydrogen production rate of 46.3 mL / g.

[0114] Figure 5 The diagram shows the oxidation degree of the iron-nickel bimetallic oxygen support in Example 1 of this invention. The stability test method is as follows: the iron-nickel bimetallic oxygen support is placed in a differential thermogravimetric analyzer to carry out oxidation and reduction reactions. The oxidation reaction is used to simulate the water vapor oxidation reaction in the methane chemical chain hydrogen production reaction. The oxidation reaction temperature is 600°C, and the oxidizing gas is air or oxygen. The reduction reaction is used to simulate the methane water vapor reforming reaction in the methane chemical chain hydrogen production reaction. The reduction reaction temperature is 600°C, and 50% methane is introduced as the reduction reaction gas.

[0115] like Figure 5 As shown, after a long-term cyclic stability test (200 cycles), the iron-nickel bimetallic oxygen carrier provided by the present invention showed no significant change in the oxygen gain and loss rates, indicating that it has high cyclic stability and a long lifespan.

[0116] Figure 6 The graph shows the methane conversion rate and hydrogen production effect of the iron-nickel bimetallic oxygen carrier in the fixed-bed reaction gas in Example 1 of the present invention.

[0117] like Figure 6 As shown, the iron-nickel bimetallic oxygen support provided by this invention maintains an average methane conversion rate of 87% and a hydrogen production rate of 8.5 mL / min / g after 20 cycles.oc It is shown that the bimetallic oxygen carrier has high methane conversion rate and hydrogen production rate, and stable performance.

[0118] Example 2

[0119] The iron-nickel bimetallic oxygen carrier was prepared by the same method as in Example 1, and was subjected to the two-step hydrogen production reaction by methane chemical looping at the same reaction conditions, except that the type of metal oxide carrier was different, i.e., the metal oxide carriers used were SiO2, MgO, MgAl2O4, and YSZ (50% Y2O3). The bulk density, mechanical strength, specific surface area, methane conversion rate, and hydrogen production amount of the iron-nickel bimetallic oxygen carrier prepared using different metal oxide carriers are shown in Table 1.

[0120] Table 1. Related test data of iron-nickel bimetallic oxygen carriers prepared using different metal oxide carriers

[0121]

[0122] As can be seen from Table 1, the iron-nickel bimetallic oxygen carriers prepared using different metal oxide carriers all have high methane conversion rate and hydrogen production amount.

[0123] Example 3

[0124] The iron-nickel bimetallic oxygen carrier was prepared by the same method as in Example 1, and was subjected to the two-step hydrogen production reaction by methane chemical looping at the same reaction conditions, except that the type of metal active component was different, i.e., the metal was any one combination of Fe, Ni, Co, Mn, and Cu. The bulk density, mechanical strength, specific surface area, methane conversion rate, and hydrogen production amount of the iron-nickel bimetallic oxygen carrier prepared using different metal oxide carriers are shown in Table 2.

[0125] Table 2. Related test data of iron-nickel bimetallic oxygen carriers prepared using different metal active components

[0126]

[0127] As can be seen from Table 2, the methane conversion rate and hydrogen production amount of the bimetallic active component using the Fe-Ni and Ni-Co combination are significantly better than those of the Fe-Co, Fe-Mn, and Fe-Cu combinations under a medium-temperature environment.

[0128] Comparative Example

[0129] The different bimetallic oxygen carriers were used for methane chemical looping hydrogen production reaction, and the specific comparison results are shown in Table 3. The bimetallic oxygen carrier in Comparative Example 1 is 10mol% NiO-Fe2O3 / MgAl2O4 (from "Ni, Co and Cu-promoted iron-based oxygen carriers in methane-fueled chemical looping hydrogen generation process"), and the bimetallic oxygen carrier in Comparative Example 2 is 5wt% NiO-red mud (from "Ni-enhanced red mud oxygen carrier for chemical looping steam methane reforming").

[0130] Table 3. Comparison of methane chemical looping hydrogen production performance of different bimetallic oxygen carriers

[0131]

[0132] As can be seen from Table 3, the existing bimetallic oxygen carriers have the problems of not producing hydrogen during the reduction reaction process, failing to realize two-step hydrogen production, and the temperature of the methane chemical looping hydrogen production reaction being relatively high, generally at 900℃, i.e. failing to realize hydrogen production at a medium temperature environment.

[0133] Example 4

[0134] The steps of preparing the iron-nickel bimetallic oxygen carrier by the sol-gel-hydrothermal method are as follows:

[0135] Step 1: a mixed solution of deionized water and isopropyl alcohol is used to dissolve a certain mass of iron nitrate nonahydrate, and the corresponding mass of aluminum nitrate nonahydrate is mixed and dissolved according to the mass percentage ratio of active ingredient iron oxide to aluminum oxide carrier of 60%:40%, to obtain a mixed solution containing aluminum ions and iron ions;

[0136] Step 2: the mixed solution containing aluminum ions and iron ions in step (1) is placed in a constant temperature drying box, and isopropanol and water are removed by staged drying to obtain a solid nitrate containing iron ions and aluminum ions. The solid nitrate containing iron ions and aluminum ions is calcined in an air atmosphere at 500℃ for 3h to obtain an iron oxide / aluminum oxide carrier powder (Fe2O3 / Al2O3);

[0137] Similarly, in step 3, a mixed solution of deionized water and isopropyl alcohol is used to dissolve a certain mass of nickel nitrate nonahydrate, and the corresponding mass of aluminum nitrate nonahydrate is mixed and dissolved according to the mass percentage ratio of active ingredient nickel oxide to aluminum oxide carrier of 60%:40%, to obtain a mixed solution containing aluminum ions and nickel ions;

[0138] Step 4: The mixed solution containing aluminum ions and nickel ions in step (3) was placed in a constant temperature drying oven, and isopropanol and water were removed by stepwise drying to obtain a solid nitrate containing nickel ions and aluminum ions. The solid nitrate containing nickel ions and aluminum ions was calcined in an air atmosphere at 500°C for 3h to obtain a nickel oxide / alumina carrier powder (NiO / Al2O3), and further ground into a nano powder by a ball mill;

[0139] Step 5: The iron oxide / alumina carrier powder and the nickel oxide / alumina carrier powder were mixed in a ratio of 4:1 of the mass ratio of iron oxide to nickel oxide, and the powder was placed in a ball mill at a ball milling speed of 500r / min for 2h to obtain a mixed powder (Fe2O3 / Al2O3 powder + NiO / Al2O3 powder).

[0140] Step 6: A binder (kaolin, 10wt.%) and a pore-forming agent (cellulose, 8wt.%) and deionized water (50wt.%) were added to the mixed powder of step (5) while stirring to obtain a uniform thick slurry. Subsequently, the slurry was placed in an extruder to be extruded at 150r / min to obtain an extrudate, and the obtained extrudate was cut into 1.2-1.5mm in length and placed in a rounding machine at 500-1000r / min to be rounded to obtain spherical particles with a diameter of 1.2-1.5mm.

[0141] Step 7: The spherical particles were placed in a drying oven and dried at 80°C for 6h, and then placed in a muffle furnace for stepwise temperature calcination in an air atmosphere. The calcination temperature was first increased from room temperature to 700°C for the first stage calcination, and the calcination time was 5h. Finally, the calcination temperature was further increased to 1200°C for the second stage calcination, and the calcination time was 2h to harden the powder.

[0142] The strength of the iron-nickel bimetallic oxygen carrier prepared by the method in Example 4 was 32.46±6N, the specific surface area was 13.839±2m 2 / g, the porosity was 40±5%, and the bulk density was 1.40±0.3g / cm 3 The iron-nickel bimetallic oxygen carrier in Example 4 was applied to the methane chemical chain hydrogen production reaction, and the conversion rate of methane was 95% and the unit hydrogen production was 51.6mL / g under the reaction conditions of 600°C. Thus, the sol-gel method can prepare a nano powder and improve the specific surface area and reaction performance of the bimetallic oxygen carrier.

[0143] In summary, the preparation process of the bimetallic oxygen carrier provided by the application is relatively simple, the preparation parameters are easy to control, and the repeatability is strong, and the bimetallic oxygen carrier is suitable for being used as an oxygen carrier of a chemical looping reaction of a large-scale reactor such as a moving bed. In the process of preparing the mixed powder of the bimetallic oxygen carrier, the mechanical solid-phase mixing method and the sol-gel method can be flexibly replaced, so that a simpler and more flexible preparation process is realized. After the mixed powder containing the metal oxide carrier, the iron oxide active component and the oxide active component of another metal is obtained, the extrusion-rounding and calcination molding process is used, the pore size of the molded particles is adjusted by changing the pore diameter of the extruder, and the mechanical strength and the porosity of the particles are adjusted by adjusting the calcination temperature. The higher the calcination temperature is, the higher the mechanical strength of the molded particles is, and the oxygen carrier abrasion rate in the application process of the moving bed reactor is correspondingly reduced. The lower the calcination temperature is, the porosity of the molded particles is increased, the contact area of the particles and the reaction gas is increased, and the reaction performance is improved.

[0144] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the application, and it should be understood that the above description is only for specific embodiments of the application and is not used to limit the application, and any modification, equivalent replacement, improvement and the like made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for preparing a bimetallic oxygen carrier for a two-step hydrogen production by a medium-temperature methane chemical looping, comprising: obtaining a mixed powder comprising a metal oxide carrier, an iron oxide active component and an oxide active component of another metal, wherein the another metal is selected from any one of Ni, Co, Mn, Cu and Ce, the metal oxide carrier is selected from any one of Al2O3, MgO, MgAl2O4, SiO2 and 50% Y2O3, the mass percentage ratio of iron to the carrier metal is 40%-70%:60%-30%, and the total is 100%; the mass percentage ratio of the another metal to the carrier metal is 10%-70%:90%-30%, and the total is 100%; adding a binder, a pore-forming agent and water to the mixed powder to obtain a slurry; extruding the slurry in an extruder to obtain an extrudate, and rolling the extrudate in a roller to obtain spherical particles; drying and stepwise calcining the spherical particles to obtain a bimetallic oxygen carrier. The method for obtaining the mixed powder comprising the metal oxide carrier, the iron oxide active component and the oxide active component of the another metal comprises: respectively pre-calcining iron oxide powder and oxide powder of the another metal, and grinding and screening the pre-calcined powder to obtain active powder; mixing the two kinds of active powder obtained in the above step with the metal oxide carrier in a certain proportion; or mixing iron oxide / metal oxide carrier powder with oxide of the another metal / metal oxide carrier powder in a certain proportion, and the particle size of the iron oxide / metal oxide carrier powder and the oxide of the another metal / metal oxide carrier powder is nano or micron.

2. The method of claim 1, wherein, The pre-calcination temperature is 300-500℃, and the particle size of the active powder is less than 50 microns.

3. The method of claim 2, wherein, The method for obtaining the mixed powder further comprises: ball-milling the mixture obtained after mixing the two kinds of active powder with the metal oxide carrier to obtain the mixed powder.

4. The method of claim 1, wherein, The iron oxide / metal oxide carrier powder and the oxide of the another metal / metal oxide carrier powder are respectively obtained by a method comprising the following steps: Step 1: dissolving carrier metal salt and metal salt in an aqueous solvent to obtain a mixed solution, wherein the metal salt comprises any one of iron salt and another metal salt, and the aqueous solvent comprises a mixture of water and isopropyl alcohol; Step 2: drying the mixed solution to remove the solvent to obtain a solid mixed salt containing metal ions and carrier metal ions; Step 3: calcining the solid mixed salt in an air atmosphere to obtain metal oxide / metal oxide carrier powder.

5. The method of claim 4, wherein, The method for obtaining the mixed powder comprising the iron oxide / metal oxide carrier powder and the oxide of the another metal / metal oxide carrier powder further comprises: ball-milling and mixing the metal oxide / metal oxide carrier powder obtained by calcination. 6.The method according to claim 3 or 5, wherein: the ball-milling rotation speed is 100-800 r / min, and the ball-milling time is 0.5-5 h.

7. The method of claim 4, wherein, The drying in the step 2 is stepwise drying, and the stepwise drying temperature is 40-80℃. The calcination temperature in step 3 is 400-600℃.

8. The method of claim 4, wherein: The other metal salt is selected from any one of cobalt salt, manganese salt, nickel salt, copper salt, cerium salt; The iron salt is selected from ferric nitrate.

9. The method of claim 1, wherein: The weight ratio of the mixed powder, the binder, the pore-forming agent, and water is 1: (2-15%) : (2-15%) : (20-50%); The binder is selected from kaolin or attapulgite; The pore-forming agent is selected from cellulose or graphite.

10. The method of claim 1, wherein: The rotation speed of the extruder is 20-150 r / min, and the diameter of the extrudate is 0.5-6 mm; The rotation speed of the spheroidizer is 500-100 r / min, and the particle size of the spherical particles is 0.5-6 mm.

11. The method of claim 1, wherein: The drying temperature of the spherical particles is 50-120℃; The step of calcining the dried spherical particles comprises: In an air atmosphere, the calcination temperature of the spherical particles is increased from room temperature to 700-900℃ for the first stage of calcination, and then increased to 1100-1300℃ for the second stage of calcination after holding for 4-10 h, wherein the heating rate is 2-10℃ / min.

12. A bimetallic oxygen carrier prepared by the method of any one of claims 1-11, comprising: a metal oxide carrier, and an iron oxide active component and an oxide active component of another metal supported by the metal oxide carrier; wherein the mass percentage ratio of iron to carrier metal is 40%-70%: 60%-30%, and the mass percentage ratio of the other metal to carrier metal is 10%-70%: 90%-30%, with a total of 100%.

13. The bimetallic oxygen carrier of claim 12, wherein: the bimetallic oxygen carrier is an iron-nickel bimetallic oxygen carrier, The particle size of the active component in the iron-nickel bimetallic oxygen carrier is micron level, the strength of the micron level iron-nickel bimetallic oxygen carrier is 60-90 N, the specific surface area is 1-10 m 2 / g, and the porosity is 30-50%; or The particle size of the active component in the iron-nickel bimetallic oxygen carrier is nanometer level, the strength of the nanometer level iron-nickel bimetallic oxygen carrier is 30N-50N, the specific surface area is 5-20 m 2 / g, and the porosity is 40-60%.

14. A method for medium-temperature methane chemical looping two-step hydrogen production using the bimetallic oxygen carrier of any one of claims 12-13, comprising: filling the bimetallic oxygen carrier into a reactor; introducing methane and steam into the reactor to perform a medium-temperature methane chemical looping hydrogen production reaction, wherein the temperature of the medium-temperature methane chemical looping hydrogen production reaction is 450-650℃, and the medium-temperature methane chemical looping hydrogen production reaction comprises a methane steam reforming reaction and a steam oxidation reaction; during the methane steam reforming reaction, the iron oxide and the oxide of another metal in the bimetallic oxygen carrier are reduced to form metallic iron and another metal, while the methane and steam are reformed to produce a mixture containing first-stage hydrogen; during the steam oxidation reaction, the metallic iron and another metal are oxidized to form iron oxide and another metal oxide, while the steam is reduced to produce second-stage hydrogen.

15. The method of claim 14, wherein: the water-carbon ratio of steam to methane is 1:1-3:

1.

16. The method of claim 14, further comprising: increasing the content of another metal oxide active component in the bimetallic oxygen carrier to increase the methane conversion rate of the methane steam reforming reaction for hydrogen production, while decreasing the hydrogen production rate of the methane steam reforming reaction for hydrogen production and the proportion of hydrogen production of the oxidation reaction in the total hydrogen production rate; or increasing the content of the iron oxide active component in the bimetallic oxygen carrier to increase the hydrogen production rate of the steam oxidation reaction and the proportion of hydrogen production of the oxidation reaction in the total hydrogen production rate, while decreasing the methane conversion rate of the methane steam reforming reaction for hydrogen production. The reactor is a moving bed reactor or a fixed bed reactor.

17. The method of claim 14, wherein, 18. The method of claim 14, further comprising: air-oxidizing the bimetallic oxygen carrier after the medium-temperature methane chemical looping two-step hydrogen production reaction to increase the oxygen carrying capacity of the bimetallic oxygen carrier, while releasing heat, which is used to supply heat to the medium-temperature methane chemical looping two-step hydrogen production reaction or to supply heat to the outside. ​

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