JPWO2020175426A1 - Hydrocarbon low temperature reforming system, and method for producing hydrogen and / or syngas at low temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system capable of modifying a hydrocarbon material in a large amount in a short time by utilizing low temperature waste heat of less than 700 ° C. SOLUTION: In the hydrocarbon low temperature reforming system 1 of the present invention, an oxidized oxygen carrier M (O) and a hydrocarbon-based material are reacted at 600 ° C. or lower, and the reduced oxygen carrier M () and hydrogen are combined with each other. A first reactor 10 that produces a carbon oxide and a second reactor 20 that reacts a reduced oxygen carrier M () with an oxidizing agent to produce an oxidized oxygen carrier M (O) are provided. .. In the system 1, the oxygen carrier M (O) may be a chemical loop type in which the first reactor 10 and the second reactor 20 circulate and flow, or a cyclic operation in which the supplied gas is alternately switched and switched. It may be an expression. [Selection diagram] Fig. 1

Description

The present invention relates to a low temperature hydrocarbon reforming system and a method for producing hydrogen and / or syngas at low temperatures.

So far, a reforming reaction technique has been known as a method for producing hydrogen from a hydrocarbon-based material. There are steam reforming, _{dry reforming using CO 2,} and partial oxidation by air and oxygen.

By the way, the reforming reaction for producing hydrogen and / or CO from a hydrocarbon material and steam or CO ₂ as raw materials is endothermic, and the reaction requires a high temperature to proceed under equilibrium conditions. And. Therefore, conventional methods require extremely high energy inputs resulting from the combustion of fuel, resulting in large CO ₂ emissions.

By lowering the process temperature, the energy required for the reforming reaction from hydrocarbon materials to hydrogen can be reduced. Then, by lowering the process temperature, it may be possible to utilize the energy of low-temperature waste heat as the energy of the reforming reaction from the hydrocarbon material to hydrogen.

So far, it has been proposed to recover waste heat at a high temperature exceeding 500 ° C. and utilize the waste heat energy for other processes (see Non-Patent Document 1). However, low-temperature waste heat of less than 500 ° C is released to the outside of the chemical process system with little use, and there is room for _{energy saving and reduction of CO 2 emissions by proposing a technology for using low-temperature waste heat.} There is.

The total amount of low-temperature waste heat below 500 ° C in Japan is estimated to be 1,018 petajoules (PJ) per year. This corresponds to about 10% of the total energy consumed in Japan (see Non-Patent Document 1). Loss of low temperature waste heat is a common issue not only in Japan but all over the world.

In order to realize the reforming reaction from hydrocarbon materials to hydrogen at low temperature, it is necessary to overcome the problem of chemical equilibrium. For example, the steam reforming reaction using water as an oxidizing agent is based on the following reaction formula.
C _n H _m + H ₂ O → CO (or CO ₂ ) + H ₂

However, the reaction is an endothermic reaction, and, all materials in the same reaction field _{(C n H m, H 2} O, CO, CO 2, H 2) are present. Due to the restriction of reaction equilibrium, it is difficult for the reaction from the hydrocarbon material to hydrogen to proceed unless it is in a high temperature state of 700 ° C. or higher. Although various catalysts have been proposed to promote the reaction, even if a catalyst is added to the reaction system, the reaction equilibrium is still restricted. Therefore, even if low-temperature waste heat of less than 700 ° C., particularly low-temperature waste heat of less than 500 ° C. is used as heat energy, hydrogen cannot be efficiently obtained.

The reforming reaction using carbon dioxide as an oxidizing agent is based on the following reaction formula.
C _n H _m + CO ₂ → CO + H ₂

This reforming reaction is also an endothermic reaction, and, all materials in the same reaction field _{(C n H m, H 2} O, CO, CO 2, H 2) are present. Therefore, due to the restriction of reaction equilibrium, it is subject to the same restrictions as the steam reforming reaction.

In order to solve this problem, it is conceivable to use a membrane reactor. By using a membrane reactor, the reaction field in the reactor can be separated.

The Energy Conservation Center, Japan. Https://www.asiaeec-col.eccj.or.jp/ (accessed 26 December 26, 2018)

However, even if a membrane reactor is used, the membrane reactor is not suitable for mass treatment of hydrocarbon materials, and it is desirable to solve the problem by another approach.

By the way, a method called chemical loop has been known for a long time. This makes it possible to divide the reaction into two and make the product a high-purity gas. There is also a report on the reforming reaction. It is also possible for partial oxidation, which causes weak heat generation as a whole.

However, in order to carry out these reactions at low temperature, an oxygen carrier driven at low temperature is required. Since this has not been achieved, a low temperature endothermic reforming reaction by a low temperature chemical loop has not been investigated.

The present invention has been made in view of such a problem, and an object of the present invention is to modify a hydrocarbon material at a low temperature by utilizing low temperature waste heat of less than 700 ° C.

As a result of diligent research to achieve the above problems, the present inventors have obtained hydrogen and carbon oxides from hydrocarbon-based materials by using oxidized oxygen carriers by using low-temperature driven oxygen nanocarriers. The present invention has been completed by finding that the above object can be achieved by individually executing the reaction for producing oxygen carriers and the reaction for oxidizing oxygen carriers reduced by using an oxidizing agent. Specifically, the present invention provides the following.

The invention according to the first feature comprises a first reactor in which an oxidized oxygen carrier and a hydrocarbon-based material are reacted at 600 ° C. or lower to produce hydrogen and a carbon oxide, and the reduced oxygen carrier. Provided is a chemical loop type hydrocarbon low temperature reforming system including a second reactor that reacts with an oxidizing agent to generate the oxidized oxygen carrier.

According to the invention according to the first feature, in the first reactor, an oxidation reaction of a hydrocarbon-based material and a reduction reaction of oxygen carriers occur. At this time, the lattice oxygen of the oxygen carrier is used for the oxidation reaction of the hydrocarbon-based material, and hydrogen and carbon oxide are produced by the oxidation reaction. In the first reactor, since water is not a raw material, any material that can occur when reacted and water the hydrocarbon material in a single reactor _{(C n H m, H 2} O, CO, CO 2 , H ₂ ) do not exist in the same reaction field. Thus, all materials in the same reaction field constraints _{(C n H m, H 2} O, CO, CO 2, H 2) caused by the presence reaction equilibrium can be avoided.

In the second reactor, the oxygen component contained in the oxidizing agent oxidizes the oxygen carrier.

By the way, the reaction in the second reactor depends on the type of oxygen carrier material (determined by the magnitude of the redox potential with the oxidizing agent), _{but when CeO 2} is used, for example, it is an exothermic reaction, and the second reaction Oxidized oxygen carriers, which are one of the reaction products in the two reactors, can recover the heat generated by the exothermic reaction in terms of heat capacity. Then, the oxygen carrier circulates and flows from the second reactor to the first reactor, and the hydrocarbon material is brought into contact with the oxygen carrier that has absorbed the waste heat in the first reactor. The heat required for the endothermic reaction of is supplied. External waste heat from other processes can also be used. That is, in the invention according to the first feature, it is possible to make the oxygen carrier function not only as a transport source of oxygen but also as a transport source of heat, whereby the oxygen carrier is supplied to the first reactor from the outside. It is possible to suppress the amount of heat.

On the contrary, the same applies to the combination of a material / oxidizing agent that generates heat in the first reactor and absorbs heat in the second reactor. The heat is stored as the heat capacity of the oxygen carrier material, and the heat is endothermic. It will be possible to provide to.

In addition, since a chemical loop system is used instead of a membrane reactor, oxygen transfer can be controlled by the amount of particle circulation without being regulated by the mass transfer rate in the membrane, resulting in a large amount of hydrocarbon material. Can be processed.

Therefore, according to the invention according to the first feature, it is possible to process a large amount of the reforming reaction of the hydrocarbon material in a short time by utilizing the low temperature waste heat of 600 ° C. or lower.

The invention according to the second feature includes a plurality of reactors filled with oxygen carriers, and the plurality of reactors are configured to be capable of introducing a hydrocarbon-based material or an oxidizing agent, and among the plurality of reactors. The hydrocarbon is introduced into the reactor in which the oxygen carrier is in an oxidized state, and the hydrocarbon-based material can be oxidized at 600 ° C. or lower. The oxidant is introduced into the reactor in which the oxygen carrier is in a reduced state, and the oxidant can be reduced, depending on the state of the oxygen carrier filled in each of the plurality of reactors. Provided is a low temperature hydrocarbon reforming system capable of switching the material to be introduced into the reactor between the hydrocarbon-based material and the oxidizing agent.

Similar to the invention according to the first feature, the invention according to the second feature also makes it possible to process a large amount of the modification reaction of the hydrocarbon material in a short time by utilizing the low temperature waste heat of 600 ° C. or lower. It is possible.

The invention according to the third feature provides a system in which the oxidizing agent contains water in the invention according to the first or second feature.

According to the invention according to the third feature, steam reforming of a hydrocarbon-based material can be realized, and as a result, high-purity hydrogen and a mixed gas of _{CO (CO 2} ) and H _{2 can be recovered.}

The invention according to the fourth feature provides a system in which the oxidizing agent contains carbon dioxide in the invention according to the first or second feature.

According to the invention according to the fourth feature, CO ₂ dry reforming of a hydrocarbon-based material can be realized, and as a result, high-purity CO and a mixed gas of _{CO (CO 2} ) and H _{2 can be recovered.}

The invention according to the fifth feature provides a system in which the oxidizing agent contains oxygen and / or air in the invention according to the first or second feature.

According to the invention according to the fifth feature, partial oxidation of the hydrocarbon-based material can be realized. In this case, since air oxidation and partial hydrocarbon oxidation can be separated, high-concentration CO that is not diluted with air and CO ₂ and H ₂ can be recovered.

In the invention according to the sixth feature, the oxygen carrier in the invention according to any one of the first to sixth features is cerium oxide (CeO ₂ ), chromium-doped cerium oxide (Cr-CeO ₂ ), iron oxide-zirconia-based composite. Oxide (FeOx-ZrO ₂ ), iron oxide (Fe ₂ O ₃ ), indium oxide (In ₂ O ₃ ), yttrium-stabilized zirconium oxide (YSZ), scandium oxide-doped zirconium oxide (ScSZ), scandium oxide (Sc ₂₎ O ₃ ), lanthanum gallium oxide (LaGaO ₃ ), lanthanum strontium manganite (LSM), gadolinium-doped cerium oxide (Gd-CeO ₂ ), molybdenum oxide (MoO ₃ ), manganese oxide (MnO ₃ ), lanthanum strontium cobalt ferrite (O 3). LSCF), lanthanum strontium ferrite (LSF), tricobalt tetraoxide (Co ₃ O ₄ ), cobalt oxide II (CoO), vanadium oxide (V ₂ O ₅ ), and ceria zirconia solid solution selected from the group 1 Provide a system containing more than seeds.

In the reforming reaction of hydrocarbon materials, it is known that the reaction rate is low in a low temperature state. If the reaction rate is low, a larger reactor is required, so it is preferable to increase the reaction rate as much as possible even in a low temperature state.

According to the invention according to the sixth feature, the oxygen carrier is a specific material, and even in a low temperature region of 600 ° C. or lower, the oxygen transfer of the oxygen carrier, that is, the reduction reaction of the oxygen carrier in the first reactor, and the second. 2 Oxidation reaction of oxygen carriers in the reactor can be realized. As a result, according to the invention according to the third feature, the low-temperature waste heat generated by a known exothermic reaction such as methanol synthesis or ammonia synthesis can be used for the modification reaction of the hydrocarbon material, thereby saving energy and CO. _{2 This} will lead to a reduction in emissions.

The invention according to the seventh feature is the invention according to any one of the first to sixth features, wherein the oxygen carrier and the metal co-catalyst coexist inside the reactor, and / or the oxygen carrier. Provided is a system in which a metal co-catalyst is supported.

According to the invention according to the seventh feature, the reforming reaction of the hydrocarbon-based material can be promoted more efficiently by the action of the metal co-catalyst.

The invention according to the eighth feature provides a system in which the average primary particle size of the oxygen carrier in the invention according to any one of the first to seventh features is 1 μm or less.

According to the invention according to the eighth feature, the exposed surface area (contact possibility) between the hydrocarbon-based material which is the reactant in the first reactor and the oxidizing agent which is the reactant in the second reactor is increased. Therefore, the efficiency of oxygen transfer of the oxygen carrier is improved, and the reforming reaction of the hydrocarbon material can be promoted even at a low temperature, resulting in energy saving and reduction of _{CO 2 emissions.}

The invention according to the ninth feature provides a system in which the shape of the oxygen carrier in the invention according to any one of the first to eighth features has the most active exposed surface.

For example, in _{the case of CeO 2} , if the shape of the oxygen carrier is a substantially octahedron and / or a substantially cube, the oxygen carrier has a (111) plane and / or a (100) plane as a main exposed plane. The (100) plane of the oxygen carrier is unstable and has greater oxygen mobility (oxygen storage and release capacity). Therefore, according to the invention according to the ninth feature, the reforming reaction from the hydrocarbon material to hydrogen can proceed even at a low temperature, resulting in energy saving and reduction of _{CO 2 emissions.}

Further, for example, when the oxygen carrier is Fe ₃ O ₄ , the most unstable and most active surface is the (110) surface, and the same effect can be obtained by exposing that surface.

The invention according to the tenth feature corresponds to a category difference from the invention according to the first feature. Further, the invention according to the eleventh feature corresponds to a category difference from the invention according to the second feature. According to the inventions according to the tenth and eleventh features, it is possible to process a large amount of the reforming reaction of the hydrocarbon material in a short time by utilizing the low temperature waste heat of 600 ° C. or lower.

According to the present invention, it is possible to process a large amount of modification of a hydrocarbon material in a short time by utilizing low temperature waste heat of 600 ° C. or lower.

FIG. 1 is a configuration example of the hydrogen production system 1 according to the present embodiment. FIG. 2 is a schematic schematic diagram of a synthesizer 30 used when synthesizing chromium-doped cerium oxide (Cr-CeO _2). FIG. 3 is a diagram showing the results of evaluation of oxygen storage / release capacity (OSC) in a low temperature region in Test Example 1. FIG. 4 is a diagram showing the relationship between the doping amount and the oxygen storage / release capacity (OSC) in Test Example 2. FIG. 5 is a diagram showing the relationship between the atomic column of the cerium element and the oxygen vacancies forming property in the particles in Test Example 3. FIG. 6 shows a TEM image of the cerium element in Test Example 3. FIG. 7 is a diagram showing the rate at which the voids of the cerium element in Test Example 3 expand. FIG. 8 is a diagram showing the relationship between the rate at which lattice expansion is observed in the cerium nanoparticles in Test Example 3 and the energy required to form oxygen vacancies between cerium atoms. FIG. 9A is a schematic diagram of a chemical looping system, and FIG. 9B is a schematic diagram of a cyclic operation process. FIG. 9B is the system used in Test Example 4. FIG. 10 is a diagram showing the results of reaction rate evaluation of the oxygen carrier (CeO _{2 nanocube) in Test Example 4.} FIG. 11 is a diagram showing the results of reaction rate evaluation of the oxygen carrier (chromium-doped cerium oxide (Cr-CeO _{2)) in Test Example 4.} Repeated 3 times, it is shown that the reproducibility and the oxygen carrier are not deteriorated. FIG. 12 is a diagram showing the relationship between the number of repetitions of the oxygen carrier (chromium-doped cerium oxide (Cr-CeO ₂ )) and the oxygen storage / release capacity (OSC) in Test Example 4. Even if it is repeated 25 times, the deterioration rate is about 10%. FIG. 13 is a diagram showing the results of reaction rate evaluation of an oxygen carrier (iron oxide-zirconia-based composite oxide (FeOx-ZrO _{2)) in Test Example 4.} The reaction is completed in about 20 minutes. FIG. 14 is a diagram showing the results of reaction rate evaluation of an oxygen carrier (CeO _{2 nanocube carrying palladium) in Test Example 4.} It is produced at a stoichiometric ratio of H ₂ : CO ₂ = 2: 1. FIG. 15 is a diagram showing the relationship between the OSC of the oxygen carrier (CeO _{2 nanocube carrying palladium) and the reaction rate in Test Example 4.} FIG. 16 is a diagram showing the effect of compounding with the metal co-catalyst in Test Example 5. FIG. 17 is a diagram showing changes over time in the amounts of carbon dioxide and hydrogen produced in Test Example 6. 18, in Test Example 7, the oxygen carrier methane in a batch reactor at a CeO ₂ nano cube - a diagram showing the results when performing an oxygen carrier response experiments. FIG. 19 is a diagram showing the results of a methane-oxygen carrier reaction experiment in a batch reactor when the oxygen carrier is iron oxide-zirconia-based composite oxide (FeOx-ZrO _{2) in Test Example 7.} Is.

Hereinafter, specific embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and the present invention is carried out with appropriate modifications within the scope of the object of the present invention. can do.

<< Hydrocarbon reforming system >>
The reforming system (hereinafter, also simply referred to as “system”) in the present embodiment includes a first reactor and a second reactor. The system may be a chemical loop type system in which the oxygen carrier circulates and flows between the first reactor and the second reactor, or may be a cyclic operation system in which the gas is alternately switched and switched.

The form of the system is not particularly limited, and may be a two-column circulating fluidized bed or a form in which a stationary phase reactor is switched and operated. Above all, since it is possible to process a larger amount of modification from the hydrocarbon material to hydrogen, the form of the system is preferably a two-column circulating fluidized bed.

Hereinafter, as an example, a case where the system is a chemical loop type two-column circulating fluidized bed contact reactor will be described with reference to the drawings, but the present invention is not limited to this. FIG. 1 shows a configuration example of the system 1 when the system 1 is a two-tower circulation type fluidized bed contact reactor. The system 1 includes a first reactor 10 and a second reactor 20.

<First reactor 10>
The first reactor 10 has a first inlet 11 and a first outlet 12. A hydrocarbon-based material is supplied from the first inlet 11. Then, as the hydrocarbon-based material moves from the first inlet 11 to the first outlet 12, the hydrocarbon-based material reacts with the oxidized oxygen carrier M (O) inside the first reactor 10. Then, the reduced oxygen carrier M (), hydrogen, and carbon oxide are produced. Then, hydrogen and carbon oxide are discharged from the first outlet 12. On the other hand, the reduced oxygen carrier M () circulates and flows toward the second inlet 21 of the second reactor 20.

For the sake of simplicity, the case where the hydrocarbon-based material is methane will be described. In the first reactor 10, the following reaction proceeds.
mM (O) + CH ₄ → mM () + 2H ₂ + CO ₂

In the above formula, M (O) represents an oxidized oxygen carrier and M () represents a reduced oxygen carrier.

According to the invention described in this embodiment, an oxidation reaction of a hydrocarbon-based material and a reduction reaction of oxygen carriers occur in the first reactor 10. At this time, the lattice oxygen of the oxygen carrier is used for the oxidation reaction of the hydrocarbon-based material, and hydrogen and carbon oxide are produced by the oxidation reaction. In the first reactor 10, since water is not a raw material, any material that can occur when reacted and water the hydrocarbon material in a single reactor _{(C n H m, H 2} O, CO, CO _{2, H 2)} will not be present in the same reaction field. Thus, all materials in the same reaction field constraints _{(C n H m, H 2} O, CO, CO 2, H 2) caused by the presence reaction equilibrium can be avoided.

[Oxygen carrier]
In this embodiment, the redox cycle of oxygen carriers is utilized. The oxygen carrier is preferably a solid electrolyte in order to make the redox cycle feasible below 700 ° C.

The solid electrolyte is preferably a material finely divided into nanoparticle size, and in the long periodic table, Group IIIB boron (B) -Group IVB silicon (Si) -Group VB arsenic (As). -The elements on the line of the group Teruru (Te) of the VIB group as a boundary and the elements on the left side or the lower side of the boundary can be exemplified in the long periodic table. Specifically, the elements of Group VIII are Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, etc., the elements of Group IB are Cu, Ag, Au, etc., and the elements of Group IIB are Zn. , Cd, Hg, etc. for Group IIIB elements such as B, Al, Ga, In, Tl, etc., Group IVB elements such as Si, Ge, Sn, Pb, etc., Group VB elements such as As, Sb, Bi, etc. , Elements of Group VIB include Te, Po and the like, and elements of Groups IA to VIIA and the like.

Specific examples of oxygen carriers include cerium oxide (CeO ₂ ), chromium-doped cerium oxide (Cr-CeO ₂ ), iron oxide-zirconia composite oxide (FeOx-ZrO ₂ ), iron oxide (Fe ₂ O ₃ ), and indium oxide. (In ₂ O ₃ ), Ittium Stabilized Zirconium Oxide (YSZ), Scandium Oxide Doped Zirconium Oxide (ScSZ), Scandium Oxide (Sc ₂ O ₃ ), Lantern Gallium Oxide (LaGaO ₃ ), Lantern Strontium Manganite (LSM), Gadrinium-doped cerium oxide (Gd-CeO ₂ ), molybdenum oxide (MoO ₃ ), manganese oxide (MnO ₃ ), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF), tricobalt tetraoxide (Co ₃ O ₄ ) , Cobalt oxide II (CoO), vanadium oxide (V ₂ O ₅ ), and one or more selected from the group consisting of solid solutions of ceria and zirconia. When these oxygen carriers are used, low-temperature waste heat generated by a known exothermic reaction such as methanol synthesis or ammonia synthesis can be used as a heat supply source from the outside to the first reactor 10, thus saving energy and CO. _{2 This} will lead to a reduction in emissions.

Among them, the oxygen carriers are cerium oxide (CeO ₂ ), chromium-doped cerium oxide (Cr-CeO ₂ ), iron oxide-zirconia composite oxide (FeOx-ZrO ₂ ), lanthanum strontium manganite (LSM) and lanthanum strontium cobalt ferrite. It is preferable to include one or more selected from the group consisting of (LSCF).

These oxygen carriers may be used alone or in combination of two or more.

Here, it is preferable that the oxygen carrier and the metal co-catalyst coexist inside the first reactor 10, or that the metal co-catalyst is supported on the oxygen carrier. In the reaction in the first reactor 10, as a modification reaction from the hydrocarbon-based material, in addition to the production of _{H 2 which is a reaction product, a reaction in which H 2} is further oxidized to _{produce H 2} O also occurs. The presence of the metal co-catalyst allows H ₂ to escape to the metal, suppresses the oxidation of _{H 2} to H ₂ O, and increases the amount of _{H 2 recovered.}

The type of metal co-catalyst is not particularly limited, and transition metals, precious metals and alloys thereof can be exemplified. Specifically, Ni, Co, Rh, Pt, FeCo, FeNi, NiCo and the like can be exemplified.

[Average primary particle size]
The upper limit of the average primary particle size of the oxygen carrier is not particularly limited, but it should be 1 μm or less from the viewpoint of maximizing the exposed surface area (contact possibility) with the reactant and the easiness of forming oxygen vacancies due to lattice strain. It is more preferably 100 nm or less, further preferably 50 nm or less, further preferably 30 nm or less, and particularly preferably 10 nm or less.

The lower limit of the average primary particle size of the oxygen carrier is also not particularly limited. Generally, the nanoparticles are converted into secondary particles by powder molding, and the secondary particles are used in a packed bed reactor for cyclic operation or as circulating fluidized bed particles.

In the present embodiment, the average primary particle size of the oxygen carrier is a value obtained by imaging an image of oxygen carrier particles with a TEM (transmission electron microscope) and analyzing the TEM image with image analysis / image measurement software. It shall be.

[shape]
Since the shape of the oxygen carrier has greater oxygen mobility (OSC) at low temperatures, it is necessary to expose the most active surface, which determines the particle shape. The most active surface differs depending on the type of oxygen carrier material, but it is the most thermodynamically unstable surface, and its information can be easily obtained from a material database or the like. For example, in _{the case of CeO 2} , the shape of the oxygen carrier is substantially a cube, and it is preferable that the (100) plane is the main exposed plane. In _{the case of Fe 3} O ₄ , it is preferable that the (110) surface is the main exposed surface.

As an example, the case where the _{oxygen carrier is a nanoparticle of CeO 2 will be described.} The CeO ₂ nanoparticle catalyst can take the form of an octahedron or a cube. Further, at this time, _{the nanoparticle catalyst of CeO 2} has the (111) plane, the 110 plane and / or the (100) plane as the main exposed planes.

Here, as the oxygen carrier, metal oxide nanoparticles having an active surface exposed on 30% or more of the particle surface are preferable. The active surface is the most energetically unstable surface, and is the (100) surface in _{CeO 2.} As a result, oxygen transfer at low temperature becomes possible.

Ratio of the surface of CeO ₂ nanoparticles (100) plane is exposed is preferably 30% or more, more preferably 50% or more, further preferably 70% or more. The ratio of the (100) surface exposed on the surface of the CeO _{2 nanoparticles is measured by TEM.}

In order to increase the activity, _{it is preferable that the CeO 2} nanoparticles are doped with a transition element. Examples of transition elements doped in CeO ₂ nanoparticles include Cr, Gd, and Zr. Of these, Cr and Gd are preferable.

The doping amount of the transition element in the CeO ₂ nanoparticles is preferably 0.1 mol% or more, more preferably 4 mol% or more, further preferably 10 mol% or more, still more preferably 15 mol% or more, based on the total mass of _{CeO 2.} , 20 mol% or more is more preferable, and 25 mol% or more is particularly preferable. The larger the doping amount of the transition element, the better, but the doping amount is up to 50 mol%.

Regarding the nanostructure of CeO ₂ , it has been clarified that the six (100) planes have the largest surface energy among the low index crystal planes. This high surface energy is due to the instability of oxygen in the top layer, which is the cross-linking position between cerium ions. It is believed that this oxygen instability achieves a high conversion rate of organic matter. Oxygen in the top layer of the cube CeO ₂ is released depending on temperature and pressure. This oxygen species can move to the reactants and decompose it into products. Due to the reaction in the first reactor 10, the Ce in the 4+ valence state is converted to the Ce in the 3+ valence state and becomes unstable. Since the vacancy of ceria oxygen is generated by Ce3 +, in the reaction in the second reactor described later, the vacancy formed on the surface of the reduced ceria causes a reaction with water molecules, which combines with oxygen to have a 4+ valence. It becomes Ce in the state. In some cases, the released hydrogen molecules are transferred to the degrading compound to cause a hydrogenation reaction.

(Manufacturing method of oxygen carrier)
The method for producing the oxygen carrier is not particularly limited, but when the oxygen carrier is metal oxide nanoparticles, for example, it is disclosed in Japanese Patent No. 3047110 (one of the inventors of the patent is the present inventor). It can be manufactured by the methods used.

The documents include metal salts (IB metal, IIA metal, IIB metal, IIIA metal, IIIB metal, IVA metal, IVB metal, VA metal, VB metal, VIB metal, VIIB metal. An aqueous solution of a metal salt such as a metal or a transition metal) is continuously supplied to a flow reactor as a reaction zone having a temperature of 200 ° C. or higher and a pressure of 160 kg / cm ^{2 or higher, which are subcritical to supercritical conditions of water.} At the same time, it is disclosed that metal oxide fine particles are produced by introducing a reducing gas (for example, hydrogen) or an oxidizing gas (for example, oxygen) into an aqueous solution of this metal salt.

As an example of another method for producing fine particles, for example, the method disclosed in Japanese Patent No. 3663408 (one of the inventors of the patent is the inventor of the present application) can be mentioned.

In the document, water is made into supercritical or subcritical high-temperature and high-pressure water via a pressurizing means and a heating means, and the fluid raw material is subjected to the critical temperature of water before being merged with the high-temperature and high-pressure water. Also disclosed is a method for producing fine particles using high temperature and high pressure water, which is cooled to a low temperature, and then the high temperature and high pressure water and a fluid raw material are merged and mixed at a mixing portion and then guided to a reactor.

Further, the metal oxide nanoparticles can be collected and collected after production by, for example, the method disclosed in Japanese Patent No. 3925936 (one of the inventors of the patent is the inventor of the present application).

According to the method described in the document.
(I) Using high-temperature and high-pressure water as a reaction field, a metal compound is subjected to a hydrothermal reaction to form metal oxide nanoparticles such as _{CeO 2.}
(Ii) Using high-temperature and high-pressure water as a reaction field, the surface of metal oxide nanoparticles is reacted with an organic modifier, and a hydrocarbon group which may be substituted or unsubstituted is covalently bonded or ether. Selected from the group consisting of bonds, ester bonds, N-atom-mediated bonds, S-atom-mediated bonds, metal-C- bonds, metal-C = bonds and metal- (C = O) -bonds. The surface of the nanoparticles is organically modified by binding to the surface of the nanoparticles through an object.
(Iii) (1) Precipitating and recovering metal oxide nanoparticles dispersed in an aqueous solution, (2) Transferring metal oxide nanoparticles dispersed in an aqueous solution into an organic solvent and recovering, or (3) Metal oxide nanoparticles are obtained by collecting metal oxide nanoparticles at the organic solvent phase-aqueous phase interface.

Hereinafter, the synthesis of nanoparticles of _{CeO 2} , which is a typical oxygen carrier, will be described.

Octahedral CeO ₂ nanoparticles can be synthesized by known methods.

For cubic CeO ₂ nanoparticles, (1) prepare a raw material solution in toluene, (2) use an organic modifier to synthesize _{cubic CeO 2 nanoparticles under supercritical water conditions, and} (3) It is synthesized by a method including removing the organic modifier without changing the morphology of the cube CeO2.

Specifically, _{the nanoparticles of cube CeO 2} can be prepared as follows. This is a non-limiting example.

A nanoparticle precursor solution of cubic cerium oxide is prepared by dissolving hexanoic acid and Ce (OH) _{4 as organic modifiers in toluene.} The precursor solution is then mixed with continuous stirring to obtain a clear solution. The precursor solution is mixed with deionized water and rapidly heated to 600-700 K using a furnace. The mixture is then cooled. Nanoparticles of cubic cerium oxide are obtained as a dispersion in a mixture of water, toluene and unreacted raw materials. Ethanol is added to the nanoparticles in the toluene phase and purified by centrifugation and tilting, thereby removing unreacted organic molecules. The particles are dispersed in cyclohexane and then lyophilized under vacuum. In order to remove any organic ligand from the surface of the particles, the collected nanoparticles are calcined in air for several hours at a high temperature of about 300 ° C. The calcined nanoparticles are cleaned by centrifugation and tilting and then dried under reduced pressure, whereby _{the nanoparticles of cubic CeO 2} can be obtained.

[Hydrocarbon materials]
The hydrocarbon-based material refers to a compound containing carbon and hydrogen in the molecule or a mixture thereof, and may contain other elements such as oxygen in the molecule. Examples of hydrocarbon-based materials include hydrocarbons, alcohols, ethers, biofuels and the like.

Hydrocarbons are materials containing alicyclic hydrocarbons, cyclic or acyclic aliphatic hydrocarbons as a single component or a mixed component. Examples of the alicyclic hydrocarbon include monocyclic alicyclic compounds such as cyclohexane, methylcyclohexane, dimethylcyclohexane, 1,3,5-trimethylcyclohexane, decalin, methyldecalin, tetralin (tetrahydronaphthalene), methyltetraline and the like. The bicyclic alicyclic compound of the above, a tricyclic alicyclic compound such as tetradecahydroanthracene, and the like are included. Acyclic aliphatic hydrocarbons include alkanes composed of CH (methane, ethane, propane, butane, etc.). Examples of hydrocarbons include natural gas, LPG (liquefied petroleum gas), city gas, gasoline, naphtha, kerosene, and light oil.

Examples of alcohols include methanol, ethanol, 2-propanol and the like. Examples of ethers include dimethyl ether and the like. Examples of biofuel include biogas, bioethanol, biodiesel, biojet and the like.

[Reaction temperature in the first reactor 10]
The upper limit of the reaction temperature is not particularly limited, but since low temperature waste heat is used, the upper limit is preferably 600 ° C. or lower, more preferably 550 ° C. or lower, and further preferably 500 ° C. or lower. , 450 ° C. or lower is even more preferable, and 400 ° C. or lower is particularly preferable.

The lower limit of the reaction temperature may be such that the oxygen carrier has sufficient oxygen mobility (oxygen storage / release capacity), and from the viewpoint of effectively utilizing low-temperature waste heat, the lower the reaction temperature, the more preferable. Examples of the lower limit of the reaction temperature include room temperature or higher, 100 ° C. or higher, 150 ° C. or higher, 200 ° C. or higher, 250 ° C. or higher, and the like.

[Reaction time in the first reactor 10]
The upper limit of the reaction time is not particularly limited, but in order to realize further shortening, the reaction time is preferably 50 minutes or less, more preferably 33 minutes or less, and more preferably 25 minutes or less. Is even more preferable, 20 minutes or less is even more preferable, and 10 minutes or less is particularly preferable.

The lower limit of the reaction time is not particularly limited, but the reaction time is preferably 4 minutes or more, and more preferably 5 minutes or more, in order to surely proceed with the reaction in the first reactor 10.

[Material of the first reactor 10]
The material of the first reactor 10 is not particularly limited, and is not limited to a material having high temperature resistance such as chromium-molybdenum steel and stainless steel, and may be ordinary steel.

Conventionally, the reaction from a hydrocarbon material to hydrogen requires a high temperature state of 700 ° C. or higher, and the material of the reactor is also a material having high temperature resistance such as chromium-molybdenum steel and stainless steel. It takes. However, in the invention described in this embodiment, low temperature waste heat can be used, and ordinary steel having a relatively small temperature resistance can also be used.

In general, a material having high temperature resistance has a large load on the environment when the material is manufactured. For example, the greenhouse gas emissions in the life cycle (LC-GHG) of manufacturing chrome molybdenum steel and stainless steel are 2.42 and 4.35 _{kg-CO 2} equivalent / kg-steel, respectively (Non-Patent Document 2). reference). On the other hand, greenhouse gas emissions in the life cycle (LC-GHG) of ordinary steel production are limited to 2.11 _{kg-CO 2} equivalents / kg-steel (see Non-Patent Document 2).
[Non-Patent Document 2] Inventory Database for Environmental Analysis (IDEA), TCO2 Co. Ltd., 2017. http://idea-lca.com/?lang=en (accessed 26 December 2018)

By realizing the low temperature of the first reaction, in addition to utilizing the low temperature waste heat, it is possible to realize the reduction of the environmental load by reviewing the material of the first reactor 10.

[Second reactor 20]
The second reactor 20 has a second inlet 21 and a second outlet 22. An oxidizing agent is supplied from the second inlet 21. Then, as the oxidant moves from the second inlet 21 to the second outlet 22, the oxidant reacts with the reduced oxygen carrier M () inside the second reactor 20 to be oxidized. It produces an oxygen carrier M (O) and a reduction product of the oxidant. Then, the reduction product of the oxidizing agent is discharged from the second outlet 22. On the other hand, the oxidized oxygen carrier M (O) circulates and flows toward the first inlet 11 of the first reactor 10.

[Oxidant]
The oxidizing agent is not particularly limited as long as it is a material capable of oxidizing the reduced oxygen carrier M (). Examples of oxidants include water, carbon dioxide, oxygen and / or air.

(water)
When the oxidant is water, steam reforming of the hydrocarbon-based material can be realized in the second reactor 20.

For the sake of simplicity, the case where the hydrocarbon-based material is methane will be described. In the second reactor 20, the following reaction proceeds.
M () + H ₂ O → M (O) + H ₂

In the above formula, M () represents a reduced oxygen carrier and M (O) represents an oxidized oxygen carrier. In the second reactor 20, the vacant position formed by the reduced oxygen carrier causes a reaction with water molecules and combines with oxygen to become an oxidized oxygen carrier. Then, the released hydrogen molecules are transferred to the decomposing compound and cause a hydrogenation reaction.

Therefore, since hydrogen is discharged from the outlet of the second reactor 20, high-purity hydrogen and a mixed gas of _{CO (CO 2} ) and H _{2 can be recovered as a whole system.}

It is also preferable that the oxygen carrier and the metal co-catalyst coexist inside the second reactor 20 or that the metal co-catalyst is supported on the oxygen carrier. The presence of the metal co-catalyst allows H ₂ to escape to the metal, suppresses the oxidation of _{H 2} to H ₂ O, and increases the amount of _{H 2 recovered.}

(carbon dioxide)
When the oxidant is carbon dioxide, CO ₂ dry reforming of the hydrocarbon-based material can be realized in the second reactor 20.

Therefore, since carbon monoxide is discharged from the outlet of the second reactor 20, high-purity CO and a mixed gas of _{CO (CO 2} ) and H _{2 can be recovered as a whole system.}

Also in this case, it is preferable that the oxygen carrier and the metal co-catalyst coexist, or that the metal co-catalyst is supported on the oxygen carrier. The presence of the metal co-catalyst allows CO to escape to the metal, _{suppresses the oxidation of CO to CO 2} , and increases the amount of CO recovered.

(Oxygen and / or air)
When the oxidizing agent is oxygen and / or air, partial oxidation of the hydrocarbon-based material can be realized in the second reactor 20.

Therefore, since air oxidation and partial hydrocarbon oxidation can be separated as a whole system, high-concentration CO that is not diluted with air, and CO ₂ and H ₂ can be recovered.

Also in this case, it is preferable that the oxygen carrier and the metal co-catalyst coexist, or that the metal co-catalyst is supported on the oxygen carrier. The presence of the metal co-catalyst allows CO to escape to the metal, _{suppresses the oxidation of CO to CO 2} , and increases the amount of CO recovered.

[Reaction temperature in the second reactor 20]
In the second reactor 20, the oxygen component contained in the oxidant oxidizes the oxygen carrier, thereby producing a reduction product of the oxidant. The reaction in the second reactor 20 is an exothermic reaction, and the reaction proceeds suitably even at a low temperature. Therefore, in the second reactor 20, the reaction temperature is not particularly limited.

By the way, the reaction in the second reactor 20 is an exothermic reaction, and the oxidized oxygen carrier M (O), which is one of the reaction products in the second reactor 20, dissipates the waste heat generated by the exothermic reaction. It can be recovered. Then, the oxygen carrier M (O) circulates and flows from the second reactor 20 to the first reactor 10, and the oxygen carrier M (O) and the hydrocarbon-based material absorb the waste heat in the first reactor 10. The heat required for the endothermic reaction of the hydrocarbon-based material is supplied by contacting with. That is, the system 1 described in the present embodiment can not only function the oxygen carrier as a transport source of oxygen, but also function as a transport source of heat, thereby causing the first reactor 10 to function from the outside. It is possible to reduce the amount of heat supplied.

Hereinafter, the present invention will be specifically described with reference to the test examples in the present embodiment, but the present invention is not limited thereto.

<Test Example 1> Evaluation of oxygen storage and release ability in a low temperature range [Example 1-1] Commercially available cerium oxide nanoparticles As an oxygen carrier, cerium oxide nanoparticles (primary particle size: <25 nm, product number: 544841-25G, CAS) Number: 1306-38-3, Aldrich) was used.

Then, _{the oxygen storage and release capacity (OSC) of the CeO 2} nanocubes was measured at 200 ° C., 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C. and 500 ° C., respectively. The results are shown in FIG. The OSC refers to the number of moles of oxygen contained in a unit mass of oxygen carriers.

Here, the OSC of the oxygen carrier shall be measured by the following method.

(1) He gas is flowed into the measurement system at 500 ° C.
_{(2) O 2} gas is flowed through the measurement system at 500 ° C., and a sufficient amount is adsorbed on the sample.
(3) He gas is flowed into the measurement system at 500 ° C.
_{(4) H 2} gas is passed through the measurement system at 500 ° C. to reduce the sample and remove the _{adsorbed O 2.}
(5) He gas is flowed into the measurement system at 500 ° C.
(6) He gas is flowed into the measurement system at the reaction temperature, that is, the detection temperature (200 ° C., 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C. and 500 ° C.) (up to this point is the pretreatment).
(7) At the above-mentioned detection temperature, He gas is used as a carrier gas, and O ₂ gas is pulsed into the measurement system.
(8) to the O ₂ gas flow pulse is no longer detected by the detector, flow O ₂ gas in the measuring system with a pulse.
(9) _{O 2} minus the total detected amount from the total outflow of gas is estimated as the total amount of adsorption of _{O 2} gas (cm ^3).
(10) The unit adsorption amount (cm ³ _{/ g) of O 2} gas is calculated from the total adsorption amount (cm ³ _{) of O 2} gas and the charge amount (g) of the sample obtained in (9) above, and per 1 g of sample. The number of moles of oxygen is calculated and used as OSC.

[Example 1-2] (100) CeO _{2 nanocube with exposed surface A caproic acid-modified CeO 2} nanocube synthesized by a supercritical method as an oxygen carrier (manufactured by Aitec Co., Ltd., CASNo. 1306-38-3, Average primary particle size: 10 nm ± 3 nm) was used. In order to enhance oxygen mobility (oxygen storage and release ability), the nanocube is controlled by using an organic modifier (caproic acid in this example) so that the (100) surface becomes the main exposed surface. Therefore, the nanocubes were burned at 300 ° C. for 2 hours to remove the organic modifier from the nanocubes. Hereinafter, the CeO ₂ which (100) face after organic modifier removed is exposed as CeO ₂ nano cube.

Then, the OSC of the oxygen carrier was measured by the same method as in Example 1-1 except that the oxygen carrier was the CeO _{2 nanocube.} The results are shown in FIG.

[Example 1-3] Chromium-doped cerium oxide (Cr-CeO ₂ )
[Synthesis of Cr-CeO _2]
Chromium-doped cerium oxide (Cr-CeO ₂ ) was synthesized by the reported supercritical hydrothermal synthesis method. In synthesizing Cr-CeO _2, the apparatus 30 shown in FIG. 2 was used.

The device 30 cools the raw material supply unit 31, the supercritical water supply unit 32, the mixing unit 33 that mixes the raw material and supercritical water, and the cooling unit 34 that cools the mixed liquid of the raw material and supercritical water and stores them in a container. And.

The raw material supply unit 31 has a raw material storage container 31A in which the raw material is stored, and a pump 31B for pumping the raw material stored in the raw material storage container 31A toward the mixing unit 33. The raw material storage container 31A and the pump 31B are connected by piping, and the pump 31B and the mixing portion 33 are connected by piping.

The raw material container 31A contains an aqueous solution containing 0.010 mol / l Ce (OH) ₄ / Cr (OH) ₃ (Ce: Cr = 9: 1 (molar ratio)). Further, in order to modify the surface of the nanoparticles and induce their anisotropic growth, 0.13 g of decanoic acid is also contained in the raw material container 31A.

The supercritical water supply unit 32 is located between the water storage container 32A in which water is stored, the pump 32B that pumps the water contained in the water storage container 32A toward the mixing unit 33, and the pump 32B and the mixing unit 33. It is provided and has a heating unit 32C that puts water in a supercritical state. The water storage container 32A and the pump 32B, the pump 32B and the heating unit 32C, and the heating unit 32C and the mixing unit 33 are connected by pipes, respectively.

In this embodiment, since water is brought into a supercritical state and then supercritical water is supplied to the mixing unit 33, the mixture of the raw material and water is not gradually heated to finally reach the supercritical state. By bringing supercritical water into direct contact with the raw material, the temperature of the raw material is raised to the supercritical state at a mixing rate for an extremely short time, thereby suppressing the formation and growth of particles during the temperature rise and in the supercritical field. Nanoparticles can be synthesized with a high degree of supersaturation.

In the mixing unit 33, the temperature and pressure can be controlled.

In this embodiment, the supercritical water preheated by the supercritical water supply unit 32 is supplied to the mixing unit 33 from a pipe different from the pipe provided in the raw material storage container 31A, and the raw material and the supercritical water are combined. Was rapidly mixed to raise the temperature of the raw material to a supercritical state. Despite the fact that the raw material contains decanoic acid, which is an organic molecule, both the organic molecule and the inorganic aqueous solution form a uniform phase in the supercritical state, and particle synthesis occurs there. At the outlet of the reaction tube in the mixing section 33, the reaction tube was rapidly cooled by an external water cooling device 34A provided in the cooling section 34, and the pressure was subsequently controlled by a back pressure valve (not shown). The reaction temperature in the mixing unit 33 was 400 ° C., the reaction pressure was 30 MPa, and the reaction time was 2 seconds or less. After the hydrothermal reaction, the container 34B containing the post-reaction liquid was cooled in a water bath at room temperature. Nanoparticles (hexane phase) were extracted from the decanoic acid denaturing product using 5 ml of hexane. Then, 10 ml of ethanol was added to the hexane phase as a poor solvent reagent to precipitate a precipitate from the hexane phase. Then, centrifugation was performed to obtain _{cubic Cr-doped CeO 2 nanoparticles.}

By this non-equilibrium system synthesis method, Cr, which can be doped only by a few mol% in the equilibrium system synthesis by an autoclave at a normal low-speed temperature rise, can be increased to several tens of mol%.

[Measurement of OSC]
The OSC of the oxygen carrier was measured by the same method as in Example 1-1 except that the oxygen carrier was the above-mentioned cubic Cr-doped CeO _{2 nanoparticles.} The results are shown in FIG.

[Example 1-4] Iron oxide-zirconia-based composite oxide (FeOx-ZrO ₂ )
[Synthesis of FeOx-ZrO ₂ ]
The case where the oxygen carrier was an iron oxide-zirconia-based composite oxide (FeOx-ZrO ₂ ) was also synthesized by the same distribution system as in FIG. _{FeSO 4 · 7H 2 O (0.45M} ) and _{ZrO (NO 3)} an aqueous solution containing 2 · 2H 2 O (0.18M) was supplied at room temperature, supplies a supercritical water from the other flow path, A rapid temperature rise reaction was carried out. The reaction temperature was 400 ° C., the reaction pressure was 30 MPa, and the reaction time was 2 seconds or less.

The obtained nanoparticles were recovered, and the nanoparticles were washed by repeating the cycle of centrifugation and decantation three times using deionized pure water. Then, the recovered product was freeze-dried for 48 hours to obtain _{FeOx-ZrO 2.}

[Measurement of OSC]
The OSC of the oxygen carrier was measured by the same method as in Example 1-1 except that the oxygen carrier was the iron oxide-zirconia-based composite oxide particles described above. The results are shown in FIG.

〔result〕
FIG. 3 is a diagram showing the results of evaluation of oxygen storage / release capacity (OSC) in a low temperature region in Test Example 1. Compared to the commercially available CeO _{2 of} Example 1-1, the exposed surface controlled cerium oxide (Example 1-2) was higher, the Cr-doped cerium oxide (Example 1-3) was even higher, and iron zirconia (Example 1-2). In 1-4), the value is as high as nearly four digits.

Further, it was confirmed that all oxygen carriers had an OSC exceeding 10 μmol-O / g-cat in the temperature range of 400 ° C. or higher. In particular, it was confirmed that Examples 1-2 to 1-4 had an OSC exceeding 10 μmol-O / g-cat even at 200 ° C.

Further, it was confirmed that _{FeOx-ZrO 2} was particularly excellent in OSC in the temperature range of 250 ° C. or higher, followed by chromium-doped cerium oxide (Cr-CeO ₂ ) and CeO _{2 nanocube in that order.}

Oxygen mobility is related to the strain of the crystal lattice, and the _{lattice strain is formed by doping CeO 2} with Cr, which facilitates the formation of oxygen vacancies. It is presumed that this is the reason why the chrome dope provided higher oxygen mobility than _{the undoped CeO 2.}

Then, it is known that the transition between the divalent and trivalent values of Fe having a magnetite structure is more likely to occur as compared with _{CeO 2, and the reduction is reduced to 0 valence in the reduction field.} This was also found in the development of automobile catalysts, but it is presumed that the doping of Zr makes it easier for oxygen vacancies to occur.

From the above results, it can be said that all of the oxygen carriers of the examples can obtain sufficient OSC even at a low temperature waste heat level of 600 ° C. or lower.

<Test Example 2> Relationship between doping amount and OSC [Test method]
_{Cr-CeO 2} having Cr doping amounts of 7 mol%, 23 mol%, 29 mol%, and 30 mol% was synthesized by the same method as in Examples 1-3.

The oxygen storage and release capacity (OSC) of these four types of Cr-CeO ₂ was measured at 300 ° C., 400 ° C., and 500 ° C., respectively. The results are shown in FIG.

〔result〕
From FIG. 4, it can be said that all the oxygen carriers used in Test Example 2 can obtain sufficient OSC even at a low temperature waste heat level of 600 ° C. or lower. Further, from FIG. 4, it was confirmed that the larger the doping amount of _{Cr to CeO 2, the larger the oxygen mobility can be obtained.} As shown in FIG. 3, the exposed surface control CeO ₂ obtained a high OSC, that is, oxygen mobility even at a low temperature, as compared with a commercially available product. The points on the vertical axis of Cr 0% in FIG. 4 indicate the results of Examples 1-3. Very high OSC can be obtained by Dope of Cr. In a batch type reactor using a normal autoclave, the amount of Cr Dope was several percent. However, according to the non-equilibrium system synthesis method by the distribution type rapid temperature rise synthesis method, a high Dope rate of several tens of percent could be achieved. This resulted in a very high OSC.

<Test Example 3> Relationship between average primary particle size in oxygen carrier and oxygen vacancies forming property in particles [Test method]
_{For the CeO 2} nanocube used in Example 1-2, an image of oxygen carrier particles is imaged by a TEM (transmission electron microscope), and the TEM image is analyzed by image analysis / image measurement software to obtain an average primary particle. The relationship between the diameter and the oxygen vacancies forming property in the particles was investigated. The results are shown in FIGS. 5 to 8.

〔result〕
FIG. 5 shows an atomic column (horizontal axis) of cerium element when the average primary particle diameter is 11 nm, 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, and 5 nm from the upper row, and Ce ³⁺ / (Ce ³⁺ + Ce ⁴⁺ ), that is, The relationship with the oxygen vacancies forming property (vertical axis) in the particles is shown. According to FIG. 5, when the average primary particle size is 11 nm, oxygen defects appear near the surface, whereas as the average primary particle size becomes smaller, oxygen defects appear even in the center of the cerium element. You can see that. The expansion of oxygen vacancies to the inside of the cerium element means that oxygen atoms are moving and oxygen is used not only on the surface of the nanoparticles but also in the entire particle. As a result, it can be said that the smaller the average primary particle size of the oxygen carrier, the more the exposed surface area (contact possibility) with the reactant can be maximized and the oxygen vacancy easily formed by the lattice strain. And here is the reason why the high OSC was obtained.

FIG. 6A shows a TEM image of the cerium element in Test Example 3. FIG. 12B shows the distortion between atoms. The part that looks bright is the part that has a large distortion.

In FIG. 6A, the left image is a TEM image of a cerium element having an average primary particle diameter of 11 nm, and the right image is a TEM image of a cerium element having an average primary particle diameter of 6 nm. The points on the left and right TEM images indicate cerium atoms, and the region surrounded by four cerium atoms is the region where oxygen can be taken into the molecule.

FIG. 6B is a visualization of the strain between cerium atoms by analyzing the TEM image shown in FIG. 6A. When the color is gray (when the numerical value is close to 0), it indicates that the distortion between atoms is small. Then, the lighter the color (closer to white), the more the voids between atoms expand, indicating that oxygen can be easily taken into the voids. On the other hand, the darker the color (closer to black), the smaller the voids between atoms, indicating that it is difficult to take oxygen into the voids. According to FIG. 6 (B), in the cerium nanoparticles having an average primary particle size of 11 nm, expansion of interatomic voids is observed on the surface of the particles, while expansion of interatomic voids is hardly observed at the center of the particles. .. On the other hand, in the cerium nanoparticles having an average primary particle size of 6 nm, expansion of voids between atoms is observed throughout the particles. As a result, it can be said that the smaller the average primary particle size of the oxygen carriers, the easier it is to form oxygen vacancies due to lattice strain.

FIG. 7 shows the rate of expansion of the lattice of the cerium element from left to right with respect to the TEM image shown in FIG. 6 (A). FIG. 7A shows a state for a cerium element having an average primary particle size of 11 nm, and FIG. 7B shows a state for a cerium element having an average primary particle size of 6 nm. From FIG. 7, it is confirmed that the smaller the average primary particle size of the oxygen carriers, the more the lattice expansion between atoms is recognized, and the oxygen vacancy easy formation property due to the lattice strain can be realized.

FIG. 8 is a diagram showing the relationship between the rate at which lattice expansion is observed in cerium nanoparticles and the energy required to form oxygen vacancies between cerium atoms. According to FIG. 8, it can be seen that the larger the rate at which the lattice expansion is observed, the smaller the energy required to form oxygen vacancies between the cerium atoms. Therefore, it can be said that the smaller the average primary particle size of the oxygen carrier and the wider the expansion of the lattice between the cerium atoms is recognized in the whole element, the easier it is to form oxygen vacancies between the cerium atoms. This is the reason why the extremely high OSC was obtained in FIGS. 3 and 4.

If the strain confirmed in FIGS. 5 and 6 is formed, it indicates that oxygen vacancies are easily formed and oxygen is easily moved, and the high OSC shown in FIGS. 3 and 4 is obtained on the exposed surface. It can be seen that as the controlled nano-sized particles become smaller, distortion occurs throughout the particles, which promotes oxygen transfer.

<Test Example 4> Evaluation of Reaction Rate of Oxygen Carrier As shown in (B) of FIG. 9, a cyclic operation system including a first reactor R1 and a second reactor R1 that alternately switches and switches gas. Was used to evaluate the reaction rate of oxygen carriers by simulating the chemical loop reaction shown in FIG. 9 (A).

[Example 4-1] When the oxygen carrier is a CeO ₂ nanocube The two reactors R1 and R2 were filled _{with the CeO 2} nanocube used in Example 1-2 as an oxygen carrier. Reactors R1 and R2 are _{configured so that CH 4} or water can be introduced, and in a reactor in which oxygen carriers are oxidized, CH ₄ is introduced to _{oxidize CH 4} while oxidizing oxygen carriers. The first reaction step of reducing was carried out. On the other hand, water was introduced into the reactor in which the oxygen carriers were reduced, and a second reaction step of reducing the water while oxidizing the reduced oxygen carriers was performed. Depending on the state of the oxygen carriers filled in each of the two reactors R1 and R2, the materials to be introduced into the reactors R1 and R2 were alternately switched between _{CH 4 and water.} Then, the reaction temperature was set to 400 ° C. and 350 ° C., and the change over time in the amount of _{CO 2 produced was measured.} The results are shown in FIG.

_{When CH 4 is} passed through the reactors R1 and R2 _{, CO 2} is generated, and the amount of CO 2 produced decreases with the reduction of _{CeO 2.} Since this reaction is completed in 20 to 30 minutes, it can be seen that the oxygen transfer of _{CeO 2} is completed in such a short time even though the reaction temperature is in the low temperature range of 400 ° C. and 350 ° C.

Example 4-2] oxygen carrier is a chromium-doped cerium oxide was used (Cr-CeO ₂₎ in chromium-doped cerium oxide (Cr-CeO ₂₎ when the oxygen carrier in Example 1-3, the reaction temperature of 300 ° C., The change over time in the amount of _{CO 2} produced was measured by the same method as in Example 4-1. Furthermore, this measurement was repeated 25 times. The results are shown in FIGS. 11 and 12.

According to FIG. 11, when the oxygen carrier is chromium-doped cerium oxide (Cr-CeO ₂ ), the reaction temperature is 300 ° C., which is a lower temperature region than that of Example 4-1 in about 20 to 30 minutes. It was confirmed that the reaction was completed. In addition, the activity of chromium-doped cerium oxide (Cr-CeO _{2) was maintained even when repeated three times.}

FIG. 12 shows the number of repetitions and the stability of the OSC. When the amount of OSC obtained at the first time is 100%, it is about 95% after 5 repetitions, about 90% after 10 repetitions, about 86% after 15 repetitions, and after 20 repetitions. About 84%, about 80% OSC could be obtained after 25 repetitions.

Example 4-3] oxygen carrier iron oxide - zirconia composite oxide iron oxide was used in (FeOx-ZrO ₂₎ when carrying out the oxygen carrier Example 1-4 - zirconia composite oxide (FeOx-ZrO ₂ ), The reaction temperature was set to 500 ° C., and the change over time in the amount of _{CO 2 produced was measured by the same method as in Example 4-1.} The results are shown in FIG.

It was also confirmed that the reaction was completed in an extremely short time of about 20 minutes even when the oxygen carrier was an iron oxide-zirconia-based composite oxide (FeOx-ZrO _2).

[Example 4-4] In _{the case of cerium oxide (CeO 2} ) in which the oxygen carrier carries an co-catalyst 0.1 mass by mass as an co-catalyst with _{respect to 100 parts by mass of cerium oxide (CeO 2} ) used in Example 1-1. The Pd of the portion was supported. Then, with Pd-supported CeO ₂ as an oxygen carrier and a reaction temperature of 400 ° C., the change over time in the amount of _{CO 2} produced is measured by the same method as in Example 4-1 and the change over time in the amount of _{H 2 produced is also measured.} bottom. The results are shown in FIG.

According to FIG. 14, it was confirmed that the reaction was completed in an extremely short time of about 20 minutes even when the oxygen carrier was Pd-supported CeO _2. In addition, the ratio of the amount of H _{2 produced to the amount of CO 2} produced was 2.22, and it was confirmed that _{H 2} was produced, which was close to the stoichiometric ratio.

In addition, the amount of oxygen consumed in _{CeO 2} can be calculated from the amount _{of CO 2 produced.} Initially, it is in an oxidized state and oxygen for OSC is accumulated. The OSC conversion rate X can be evaluated for each reaction time from the integrated amount of oxygen consumption and the amount of OSC. This rate of change dX / dt is the reaction rate, and the relationship between the oxygen residual rate (1-X) and the reaction rate was investigated. FIG. 15A is a diagram showing the reaction rate on the solid side (oxygen carrier side). The horizontal axis is 1-X [−], and the vertical axis is dX / dt. Note that X is the OSC conversion rate. Since the CO ₂ concentration is _{obtained by dividing the CO 2} generation rate by the gas flow velocity, the reaction rate of methane on the gas side can also be evaluated. FIG. 15B is a diagram showing the reaction rate on the gas side (methane decomposition reaction side). The horizontal axis is 1-X [−], and the vertical axis is CH ₄ consumption rate [μmol / min].

From FIG. 15, it was confirmed that the reaction rate decreased as the oxygen carrier concentration decreased, regardless of whether it was on the solid side (oxygen carrier side) or the gas side (methane decomposition reaction side).

And <Test Example 5> metal promoter and cerium oxide effect compounding Example 5-1] oxygen carrier is used in the case of Example 1-1 cerium oxide (CeO ₂₎ of a (CeO ₂₎ in the oxidation state One reactor was filled. Then, CH ₄ was introduced, CH ₄ was oxidized at 300 ° C., and the change over time in the amount of carbon dioxide and hydrogen produced was measured. At that time, the reaction pressure was 0.15 MPa. The results are shown in FIG. 16 (A).

[Example 5-2] In _{the case of cerium oxide (CeO 2} ) in which the oxygen carrier carries an co-catalyst 10 parts by mass as an co-catalyst with respect to 100 parts by mass of cerium oxide (CeO _{2) used in Example 1-1.} Ni was supported. Then, using Ni-supported CeO ₂ as an oxygen carrier, changes over time in the amounts of carbon dioxide and hydrogen produced were measured by the same method as in Example 5-1. The results are shown in FIG. 16 (B).

〔result〕
With respect to Example 5-1 in _{the reaction with CeO 2} , theoretically, H ₂ should be produced in an amount twice as much as that of CO _{2 , but the amount of H 2} produced is larger than the amount of CO _{2 produced.} There are few. It is presumed that the reason is that the generated H ₂ was burned to _{become H 2 O.}

On the other hand, when a metal co-catalyst is supported on the oxygen carrier, _{much more H 2} is produced (Example 5-2). It is presumed that the reason is that the presence of the metal co-catalyst allowed H ₂ to escape to the metal, suppressed the oxidation of _{H 2} to H _{2 O, and increased the amount of H 2 recovered.}

<Test Example 6> Relationship between reaction pressure and gas production amount The Ni-supported CeO ₂ used in Example 5-2 was used as an oxygen carrier, and the reaction pressures were 0.15 MPa, 0.3 MPa, 0.6 MPa, and 0.9 MPa. As four types, the time course of the amount of carbon dioxide and hydrogen produced was measured by the same method as in Example 5-1. The reaction time was 20 minutes each. The results are shown in FIG.

From FIG. 17, it was confirmed that the amount of carbon dioxide and hydrogen produced, that is, the reaction rate between methane and the oxygen carrier increased in the first order with respect to the methane concentration (pressure).

<Test Example 7> Methane-oxygen carrier reaction experiment in a batch reactor [Test Example 7-1] When the oxygen carrier is cerium oxide (CeO ₂ ) [CO ₂ generation]
The cerium oxide (CeO ₂ ) used in Example 1-1 was brought into an oxidized state and filled in one reactor. Then, CH _{4 was introduced, CH 4} was oxidized at 300 ° C., and the change over time in the amount of carbon dioxide produced was measured. At that time, the reaction pressure was 0.6 MPa. The results are shown in FIG. 18 (A).

[H ₂ generation]
The cerium oxide used in Example 1-1 was reduced and filled in one reactor. Then, water vapor was introduced to oxidize the reduced cerium oxide at 300 ° C., and the change over time in the amount of hydrogen produced was measured. At that time, the reaction pressure was 8 MPa. The results are shown in FIG. 18 (B).

[Test Example 7-2] When the oxygen carrier is an iron oxide-zirconia-based composite oxide (FeOx-ZrO ₂ ) [CO ₂ formation]
The iron oxide-zirconia-based composite oxide (FeOx-ZrO ₂ ) used in Example 4-3 was put into an oxidized state and filled in one reactor. Then, CH _{4 was introduced, CH 4} was oxidized at 400 ° C., and the change over time in the amount of carbon dioxide produced was measured. At that time, the reaction pressure was 0.6 MPa. The results are shown in FIG. 19 (A).

[H ₂ generation]
The iron oxide-zirconia-based composite oxide used in Example 4-3 was reduced and filled in one reactor. Then, water vapor was introduced, the composite oxide in the reduced state was oxidized at 400 ° C., and the change over time in the amount of hydrogen produced was measured. At that time, the reaction pressure was 8 MPa. The results are shown in FIG. 19 (B).

〔result〕
When the oxygen carrier is cerium oxide (CeO ₂ ), the reaction rate constant k in the reaction for producing carbon dioxide from _{CH 4} ^{is 0.060 [min -1} ], and the reaction rate constant k in the reaction for producing hydrogen from water vapor is , 0.044 [min ^-1 ]. On the other hand, when the oxygen carrier is an iron oxide-zirconia-based composite oxide, the reaction rate constant k in the reaction for producing carbon dioxide from _{CH 4} ^{is 0.07 [min -1} ], and in the reaction for producing hydrogen from water vapor. The reaction rate constant k was 0.135 [min ^-1 ]. This also supports that the iron oxide-zirconia-based composite oxide is particularly excellent as an oxygen carrier in this reaction system.

1 Hydrocarbon low temperature reforming system 10 1st reactor 11 1st inlet 12 1st outlet 20 2nd reactor 21 2nd inlet 22 2nd outlet

Claims (11)

A first reactor that produces hydrogen and carbon oxide by reacting an oxidized oxygen carrier with a hydrocarbon-based material at 600 ° C. or lower.
A chemical loop type low temperature reforming system for hydrocarbons, comprising a second reactor that reacts the reduced oxygen carrier with an oxidizing agent to generate the oxidized oxygen carrier. Equipped with multiple reactors filled with oxygen carriers,
The plurality of reactors are configured to be capable of introducing a hydrocarbon-based material or an oxidizing agent.
Among the plurality of reactors, the hydrocarbon is introduced into the reactor in which the oxygen carrier is in an oxidized state, and the hydrocarbon-based material can be oxidized at 600 ° C. or lower.
Among the plurality of reactors, the oxidant can be introduced into the reactor in which the oxygen carrier has been reduced to reduce the oxidant.
A hydrocarbon low-temperature reforming system capable of switching between the hydrocarbon-based material and the oxidizing agent depending on the state of the oxygen carriers filled in each of the plurality of reactors. .. The system according to claim 1 or 2, wherein the oxidizing agent contains water. The system according to claim 1 or 2, wherein the oxidizing agent contains carbon dioxide. The system according to claim 1 or 2, wherein the oxidizing agent contains oxygen and / or air. The oxygen carriers include cerium oxide (CeO ₂ ), chromium-doped cerium oxide (Cr-CeO ₂ ), iron oxide-zirconia composite oxide (FeOx-ZrO ₂ ), iron oxide (Fe ₂ O ₃ ), and indium oxide (In). ₂ O ₃ ), yttrium-stabilized zirconium oxide (YSZ), scandium oxide-doped zirconium oxide (ScSZ), scandium oxide (Sc ₂ O ₃ ), lanthanum gallium oxide (LaGaO ₃ ), lanthanum strontium manganate (LSM), gadolinium dope Cerium oxide (Gd-CeO ₂ ), molybdenum oxide (MoO ₃ ), manganese oxide (MnO ₃ ), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF), tricobalt tetraoxide (Co ₃ O ₄ ), oxidation The system according to any one of claims 1 to 5, comprising one or more selected from the group consisting of cobalt II (CoO), vanadium oxide (V ₂ O _{5), and ceria zirconia solid solution.} The system according to any one of claims 1 to 6, wherein the oxygen carrier and the metal co-catalyst coexist inside the reactor, and / or the metal co-catalyst is supported on the oxygen carrier. The system according to any one of claims 1 to 7, wherein the average particle size of the primary particles of the oxygen carrier is 1 μm or less. The system according to any one of claims 1 to 8, wherein the shape of the oxygen carrier has the most active exposed surface. The first reaction step of reacting an oxidized oxygen carrier with a hydrocarbon-based material at 600 ° C. or lower to produce hydrogen and carbon oxide, and
A method for producing hydrogen and / or syngas at a low temperature, which comprises a second reaction step of reacting the reduced oxygen carrier with an oxidizing agent to produce the oxidized oxygen carrier. Equipped with multiple reactors filled with oxygen carriers,
The plurality of reactors are configured to be capable of introducing a hydrocarbon-based material or an oxidizing agent.
Among the plurality of reactors, in the reactor in which the oxygen carrier is in an oxidized state, the hydrocarbon is introduced, and the first reaction step of oxidizing the hydrocarbon-based material at 600 ° C. or lower is performed.
Among the plurality of reactors, the oxidant is introduced into the reactor in which the oxygen carrier is reduced, and a second reaction step of reducing the oxidant is performed.
Hydrogen and / or synthesis comprising a switching step of switching between the hydrocarbon-based material and the oxidizing agent depending on the state of the oxygen carrier filled in each of the plurality of reactors. A method for producing gas at low temperature.

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