Reaction medium and treatment method

Abstract

A reaction medium according to the present invention is characterized by having a chemical structure in which Mn is introduced into a composite iron oxide. It is preferable that this reaction medium is used in a method for producing hydrogen by thermally decomposing water. It is preferable that this reaction medium contains a composite metal oxide of Fe, Co, Ni, and Mn, contains a composite metal oxide of Fe, Ni, Mg, and Mn, or contains a composite metal oxide of Fe, Co, Mg, and Mn. A treatment method according to the present invention includes: a first step for thermally reducing the reaction medium; and a second step for bringing the thermally reduced reaction medium into contact with an object to be treated, thereby oxidizing the reaction medium and decomposing the object to be treated.

Description

Reaction medium and treatment method

[0001] The present invention relates to a reaction medium and a processing method.

[0002] As a method for producing hydrogen by thermal decomposition of water using heat obtained by concentrating sunlight, cerium oxide (CeO ２ A two-stage water pyrolysis cycle using a catalyst such as tungsten (e.g., ceria) as a reaction medium is considered promising (see, for example, Non-Patent Documents 1 and 2).

[0003] In this two-step hydrothermal decomposition cycle, heating produces CeO ２ and a step of obtaining hydrogen by reacting the non-stoichiometric oxide with water vapor (water decomposition reaction).

[0004] Cerium oxide (CeO ２ In the two-stage water decomposition cycle using the catalyst, from a thermodynamic viewpoint, the thermal reduction step is carried out at a temperature of 1500°C or higher, and the water decomposition reaction step is carried out at a temperature of 1000°C or lower.

[0005] Regarding the cost of hydrogen production using such a two-stage water thermal decomposition cycle, there are problems such as large heat loss and high reactor material costs when the processing temperature in the thermal reduction step is 1500°C or higher. Furthermore, to achieve a high temperature of 1500°C by concentrating sunlight, a higher concentration is required in the sunlight concentrating system, which requires an increase in the number of reflectors installed and the need to increase the concentration with secondary and tertiary reflectors, resulting in high energy loss and high costs.

[0006] Regarding energy loss in solar reactors, in a conventional two-stage water thermal decomposition cycle using cerium oxide, the temperature difference between the thermal reduction step and the water decomposition reaction step is 500°C or more. Swinging the reactor temperature with such a large temperature difference results in significant heat loss.

[0007] On the other hand, regarding the reaction medium, a research group at Pohang University of Science and Technology (POSTECH) in South Korea developed a composite metal oxide Fe containing equal moles of magnesium, nickel, cobalt, and iron. ０．２５ Co ０．２５ Ni０．２５ Mg ０．２５ O ｘ In the thermal reduction process of MNCFO, the rock salt structure wüstite is generated, and by increasing the entropy, cerium oxide (CeO) is obtained in a two-stage hydrothermal decomposition cycle. ２ It has been reported that this method achieves a reaction activity exceeding that of conventional methods, and that the temperature of the thermal reduction step can be lowered to 1300°C (see, for example, Non-Patent Document 3).

[0008] However, even with such composite metal oxides, it is difficult to say that the reaction activity of the reaction medium or the energy efficiency in hydrogen production is sufficiently high, and there has been a demand for further improvements in the reaction activity of the reaction medium and the efficiency in hydrogen production.

[0009] Furthermore, not only in the production of hydrogen by decomposition of water, but also in the thermal decomposition of the material to be treated to obtain the target substance, the efficiency is not sufficiently high, and there has been a demand for further improvements in the reaction activity of the reaction medium and the efficiency in producing the target substance.

[0010] N. Gokon, T. Suda, T. Kodama “Thermochemical reactivity of 5-15 mol% Fe, Co, Ni, Mn-doped cerium oxides in two-step water-splitting cycle for solar hydrogen production”, Thermochimica Acta, 617 (2015) 179-190.N. Gokon, T. Suda, T. Kodama “Oxygen and hydrogen productivities and repeatable reactivity of 30-mol%-Fe, Co-, Ni-, Mn-doped CeO2-δ for thermochemical two-step water splitting cycle”, Energy, 90 (2015) 1280-1289.Shang Zhai et. al., Energy Environ. Sci., 11, 2018, pp.2172-2178.

[0011] The object of the present invention is to provide a reaction medium that has high reaction activity and can be used to efficiently pyrolyze a material to be treated to obtain a target substance, and to provide a treatment method that can efficiently pyrolyze a material to be treated to obtain a target substance.

[0012] These objects can be achieved by the present invention as set forth in the following (1) to (18): (1) A reaction medium characterized by having a chemical structure in which Mn is introduced into a composite iron oxide.

[0013] (2) The reaction medium according to (1) above, wherein the reaction medium is used in a method for producing hydrogen by thermal decomposition of water.

[0014] (3) The reaction medium according to (1) above, wherein the reaction medium is used in a method for producing carbon monoxide by thermal decomposition of carbon dioxide.

[0015] (4) The reaction medium according to any one of (1) to (3) above, which contains a composite metal oxide of Fe, Co, Ni and Mn.

[0016] (5) The reaction medium according to (4) above, wherein the composite metal oxide contains Fe, Co, Ni, and Mn in substantially the same molar ratio.

[0017] (6) The composite metal oxide is Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ The reaction medium according to claim 5, wherein

[0018] (7) The reaction medium according to any one of (1) to (3) above, which contains a composite metal oxide of Fe, Ni, Mg, and Mn.

[0019] (8) The reaction medium according to (7) above, wherein the composite metal oxide contains Fe, Mn, Ni, and Mg in substantially the same molar ratio.

[0020] (9) The composite metal oxide is Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘThe reaction medium according to (8) above, represented by the formula:

[0021] (10) The reaction medium according to any one of (1) to (3) above, which contains a composite metal oxide of Fe, Co, Mg, and Mn.

[0022] (11) The reaction medium according to (10) above, wherein the composite metal oxide contains Fe, Co, Mn, and Mg in substantially the same molar ratio.

[0023] (12) The composite metal oxide is Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ The reaction medium according to (11) above, represented by the formula:

[0024] (13) A treatment method comprising: a first step of thermally reducing the reaction medium described in any one of (1) to (12) above; and a second step of contacting the thermally reduced reaction medium with a material to be treated to oxidize the reaction medium and decompose the material to be treated.

[0025] (14) The treatment method according to (13) above, wherein the material to be treated is water, and hydrogen is generated in the second step.

[0026] (15) The treatment method according to (13) above, wherein the material to be treated is carbon dioxide, and carbon monoxide is generated in the second step.

[0027] (16) The processing method according to any one of claims (13) to (15), wherein the reaction temperature in the first step is 1200°C or higher and 1400°C or lower.

[0028] (17) The processing method according to any one of claims (13) to (16), wherein the reaction temperature in the second step is 1000°C or higher and 1200°C or lower.

[0029] (18) The processing method according to any one of claims (13) to (17), wherein a series of processes including the first step and the second step are repeatedly performed.

[0030] According to the present invention, it is possible to provide a reaction medium that has high reaction activity and can be used to efficiently pyrolyze a material to be treated to obtain a target substance, and to provide a processing method that can efficiently pyrolyze a material to be treated to obtain a target substance.

[0031] FIG. 1 is a schematic diagram showing a preferred embodiment of a hydrogen production device as a treatment device. FIG. 2 is a diagram illustrating a method for producing a reaction medium in an example. FIG. 3 is a diagram showing the TGA weight change when a low-temperature two-stage hydrothermal decomposition cycle is performed on the reaction medium of Example 1. FIG. 4 is a diagram showing the amount of hydrogen and oxygen produced and H in each cycle on the reaction medium of Example 1. ２ / O ２ 5 shows the average production amount per cycle and the molar ratio for the reaction media of Examples 1 to 3 and Comparative Example 1. ２ / O ２ Fig. 6 is a graph showing the TGA weight change when the reaction medium of Example 2 was subjected to a high-temperature two-stage hydrothermal decomposition cycle. Fig. 7 is a graph showing the amount of hydrogen and oxygen produced and the H ２ / O ２ 8 shows the average production amount per cycle and the molar ratio for the reaction media of Examples 1 to 3 and Comparative Examples 1 to 3. ２ / O ２ FIG. 9 is a diagram showing the hydrogen production rate in each cycle when a high-temperature two-stage water pyrolysis cycle was performed for the reaction media of Examples 1 to 3. FIG. 10 is a diagram showing a schematic configuration of a differential scanning calorimeter. FIG. 11 is a diagram showing the results of differential scanning calorimetry for the reaction media of Examples 1 to 3 and Comparative Examples 1 and 4.

[0032] A preferred embodiment of the present invention will be described below. The reaction medium of the present invention is a reaction medium used in a method for producing a target substance by thermally decomposing a material to be treated. The treatment method of the present invention is a method for obtaining a target substance by thermally decomposing a material to be treated.

[0033] [1] Reaction Medium First, the reaction medium of the present invention will be explained.

[0034] The reaction medium of the present invention is characterized by having a chemical structure in which Mn is introduced into a composite iron oxide.

[0035] By introducing Mn into the composite iron oxide in this way, the following effects can be obtained.

[0036] That is, Mn ions can have many valencies, for example, varying from 2 to 4. Furthermore, manganese oxides can have either a rock salt structure or a spinel structure.

[0037] In the present invention, by introducing manganese oxide into a composite iron oxide having high entropy, valence changes due to oxidation-reduction can occur in multiple valences, thereby making it possible to give the composite iron oxide with a rock salt structure a higher entropy and improving its reaction activity.

[0038] As a result, the mixed metal oxide according to the present invention has a greater entropy effect than conventional mixed metal oxides, and has improved reaction activity.

[0039] By using such a reaction medium, the material to be treated can be efficiently pyrolyzed to obtain the target substance. More specifically, for example, by producing hydrogen using such a reaction medium, hydrogen can be produced more efficiently.

[0040] In addition, cerium oxide (CeO), which has conventionally been used as a reaction medium, ２ , ceria), it is advantageous in that the manufacturing cost can be reduced and it has a long life.

[0041] Manganese oxides also have relatively high melting points. For example, the melting point of MnO is 1945°C, and ３ O ４ The melting point of the composite metal oxide (composite iron oxide) is 1567° C. By including Mn in the composite metal oxide (composite iron oxide), it is expected that the composite metal oxide will be prevented from melting or sintering during high-temperature treatment.

[0042] The reaction medium of the present invention is not particularly limited in type to the material to be treated or the target substance, as long as it is used in a method for producing a target substance by thermal decomposition of the material to be treated. Examples of the reaction medium of the present invention include those used in a method for producing hydrogen by thermal decomposition of water, and those used in a method for producing carbon monoxide by thermal decomposition of carbon dioxide.

[0043] In particular, when the reaction medium is one used in a method for producing hydrogen by thermal decomposition of water, hydrogen can be suitably obtained as a non-fossil fuel, clean fuel that is excellent in transportability, storability, etc.

[0044] In the reaction of thermally decomposing water as the material to be treated, hydrogen may be the target substance, oxygen may be the target substance, or both hydrogen and oxygen may be the target substances.

[0045] Furthermore, when the reaction medium is used in a method for producing carbon monoxide by thermal decomposition of carbon dioxide, it can contribute to reducing the amount of carbon dioxide, a substance that causes global warming. The carbon monoxide obtained can be used as an industrial gaseous fuel and as a reducing agent in metallurgy. It can also be used as a main component of synthesis gas, etc., and as a raw material for synthesizing liquid hydrocarbons, methanol, etc.

[0046] In the reaction of thermally decomposing carbon dioxide as the material to be treated, carbon monoxide may be the target substance, oxygen may be the target substance, or both carbon monoxide and oxygen may be the target substances.

[0047] In the following description, the reaction medium will be mainly described as being one used in a method for producing hydrogen by thermal decomposition of water.

[0048] First Embodiment A first embodiment of the reaction medium of the present invention will be described.

[0049] The reaction medium according to this embodiment contains a composite metal oxide of Fe, Co, Ni, and Mn.

[0050] In the present invention, Mn ions are introduced into a composite metal oxide of Fe, Co, Ni and Mg (MNCFO), which is a conventional four-component rock salt-spinel type high-entropy oxide, in place of a specific metal.

[0051] In this embodiment, Mn is introduced in place of Mg in a conventional composite metal oxide of Fe, Co, Ni and Mg (MNCFO).

[0052] As mentioned above, Mn ions can have many valencies, for example, varying from 2 to 4. Furthermore, manganese oxides can have either a rock salt structure or a spinel structure.

[0053] In the present invention, by introducing manganese oxide into a composite iron oxide having high entropy, valence changes due to oxidation-reduction can occur in multiple valences, thereby making it possible to give the composite iron oxide with a rock salt structure a higher entropy and improving its reaction activity.

[0054] As a result, the composite metal oxide according to the present invention has a larger entropy effect and improved reaction activity than conventional composite metal oxides of Fe, Co, Ni, and Mg.

[0055] By producing hydrogen using such a reaction medium, hydrogen can be produced more efficiently.

[0056] The composite metal oxide constituting the reaction medium preferably has a melting point of 1500° C. or higher.

[0057] If the melting point of the composite metal oxide is lower than the treatment temperature (e.g., 1400°C) in the thermal reduction step (first step) in the treatment method described below, the particles of the composite metal oxide will melt due to the temperature during thermal reduction, and furthermore, sintering associated with the thermal reduction will significantly reduce the surface area, resulting in a significant decrease in the reaction activity of the reaction medium.

[0058] When the melting point of the metal oxide constituting the reaction medium is sufficiently high as described above, it is possible to suppress a decrease in the reaction activity of the reaction medium in the thermal reduction step.

[0059] The composite metal oxide of this embodiment is not limited to a specific composition as long as it contains Fe, Co, Ni, and Mn, but it is preferable that the composite metal oxide contains each metal in substantially equimolar amounts, in other words, that the composite metal oxide contains Fe, Co, Ni, and Mn in substantially the same molar ratios, thereby making the above-described effects of the present invention more pronounced.

[0060] In the present invention, "substantially the same proportion" means that, among a plurality of elements to be compared, the ratio of the content of the element with the smallest content to the content of the element with the largest content, in units of mol%, is 95% or more and 100% or less.

[0061] In particular, the composite metal oxide of this embodiment is ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ It is preferable that the formula is represented by the following formula: This makes it possible to further enhance the above-mentioned effects of the present invention.

[0062] In the following description of this embodiment, the composite metal oxide constituting the reaction medium is Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ This section will mainly explain the case where

[0063] The reaction medium of this embodiment has higher reaction activity than conventional reaction media. Therefore, in the two-stage water thermal decomposition cycle described below, even if the treatment temperature in the thermal reduction step is set lower than conventional temperatures, the target reaction can proceed sufficiently. This improves the energy efficiency of hydrogen production.

[0064] For example, as shown in the examples below, the reaction medium (Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ) was used, and the reaction activity was tested in a cycle at a relatively low temperature, such as a thermal reduction temperature of 1200°C and a water decomposition temperature of 1000°C. ０．２５ Co ０．２５ Ni ０．２５ Mg ０．２５ O ｘ This is because the amount of hydrogen produced is about 1.4 times that of conventional cerium oxide (CeO ２ This is about 5.7 times the amount of hydrogen produced when the reaction was carried out in a cycle at high temperatures of 1400°C for thermal reduction and 1000°C for water decomposition.

[0065] Hereinafter, in this specification, specifically, in a treatment method using a two-stage water thermal decomposition cycle as described below, a cycle in which the thermal reduction temperature in the first step is 1200°C and the water decomposition temperature in the second step is 1000°C will be referred to as a "low-temperature cycle," and a cycle in which the thermal reduction temperature in the first step is 1400°C and the water decomposition temperature in the second step is 1000°C will be referred to as a "high-temperature cycle." The terms "low-temperature" and "high-temperature" used here are relative to the thermal reduction temperature and are not based on absolute temperatures.

[0066] In the reaction medium of this embodiment, the treatment temperature in the thermal reduction step can be lower than conventional methods, and the temperature difference in the two-stage water pyrolysis cycle can be reduced, thereby improving the energy efficiency of hydrogen production.

[0067] In particular, the reaction medium (Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ ) to produce hydrogen, hydrogen and oxygen are generated with good cyclical efficiency, and H ２ / O ２ The molar ratio is close to the stoichiometric ratio of 2, and the reaction proceeds stably at a stoichiometric ratio.

[0068] In this way, by using the reaction medium of this embodiment in a method for producing hydrogen by thermal decomposition of water, the amount and efficiency of hydrogen production can be significantly improved.

[0069] The volume-based average particle size of the reaction medium is preferably 10 μm or more and 300 μm or less, which can improve the fluidity and ease of handling of the reaction medium, and also can form appropriate gaps between particles when the reaction medium is stored in a container, allowing for more optimal flow of gases (reaction gas, carrier gas, product gas) in the first step (thermal reduction step) and the second step (water decomposition step) of the treatment method described below.

[0070] The average particle size of the reaction medium can be determined, for example, by adding a sample to methanol, dispersing the resultant dispersion for 3 minutes using an ultrasonic disperser, and measuring the particle size distribution using a Coulter Counter particle size distribution analyzer (TA-II model, manufactured by COULTER ELECTRONICS INS) with a 50 μm aperture.

[0071] The reaction medium of this embodiment may have at least a portion of its surface made of the above-mentioned material (composite metal oxide of Fe, Co, Ni, and Mn), and may have a configuration in which the surface of a base (support) made of a material other than the above-mentioned material (composite metal oxide of Fe, Co, Ni, and Mn) is coated with the above-mentioned material (composite metal oxide of Fe, Co, Ni, and Mn). In this case, zirconia, for example, can be used as the base (support).

[0072] Second Embodiment Next, a second embodiment of the reaction medium of the present invention will be described.

[0073] In the following description, differences from the above-described embodiment will be mainly described, and descriptions of similar matters will be omitted.

[0074] The reaction medium according to this embodiment contains a composite metal oxide of Fe, Ni, Mg, and Mn.

[0075] In this embodiment, Mn is introduced in place of Co in a conventional composite metal oxide of Fe, Co, Ni, and Mg (MNCFO), which results in a composite metal oxide of this embodiment having a larger entropy effect and improved reaction activity than the conventional composite metal oxide of Fe, Co, Ni, and Mg.

[0076] By producing hydrogen using such a reaction medium, hydrogen can be produced more efficiently.

[0077] Co is a rare metal and therefore expensive, and its production areas are concentrated in politically unstable regions, making stable supply difficult. In contrast, Mn is inexpensive and can be supplied stably. By using Mn instead of Co in conventional composite metal oxides, raw material costs can be reduced and stable production of the reaction medium becomes possible.

[0078] The composite metal oxide of this embodiment is not limited to any particular composition as long as it contains Fe, Ni, Mg, and Mn, but it is preferable that the composite metal oxide contains each metal in substantially equimolar amounts, in other words, that the composite metal oxide contains Fe, Ni, Mg, and Mn in substantially the same molar ratios, thereby making the above-described effects of the present invention more pronounced.

[0079] In particular, the composite metal oxide of this embodiment is ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ It is preferable that the formula is represented by the following formula: This makes it possible to further enhance the above-mentioned effects of the present invention.

[0080] In the following description of this embodiment, the composite metal oxide constituting the reaction medium is Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ This section will mainly explain the case where

[0081] As will be shown in the examples below, the reaction medium (Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ ) has particularly high reactivity in a high-temperature cycle such as a thermal reduction temperature of 1400°C and a water decomposition temperature of 1000°C. Specifically, in a high-temperature cycle, it is found that cerium oxide (CeO ２ ) can produce approximately 15 times the amount of hydrogen.

[0082] The reaction medium of this embodiment may have at least a portion of its surface made of the above-mentioned material (composite metal oxide of Fe, Ni, Mg, and Mn), and may have a configuration in which the surface of a base (support) made of a material other than the above-mentioned material (composite metal oxide of Fe, Ni, Mg, and Mn) is coated with the above-mentioned material (composite metal oxide of Fe, Ni, Mg, and Mn). In this case, zirconia, for example, can be used as the base (support).

[0083] Third Embodiment Next, a third embodiment of the reaction medium of the present invention will be described.

[0084] In the following description, differences from the above-described embodiment will be mainly described, and descriptions of similar matters will be omitted.

[0085] The reaction medium according to this embodiment contains a composite metal oxide of Fe, Co, Mg, and Mn.

[0086] In this embodiment, Mn is introduced instead of Ni in a conventional composite metal oxide of Fe, Co, Ni, and Mg (MNCFO), which results in a composite metal oxide of this embodiment having a larger entropy effect and improved reaction activity than the conventional composite metal oxide of Fe, Co, Ni, and Mg.

[0087] By producing hydrogen using such a reaction medium, hydrogen can be produced more efficiently.

[0088] Ni is a rare metal and therefore expensive, and its production areas are concentrated in politically unstable regions, making stable supply difficult. In contrast, Mn is inexpensive and can be supplied stably. By using Mn instead of Ni in conventional composite metal oxides, raw material costs can be reduced and stable production of the reaction medium becomes possible.

[0089] The composite metal oxide of this embodiment is not limited to any particular composition as long as it contains Fe, Co, Mg, and Mn, but it is preferable that the composite metal oxide contains each metal in substantially equimolar amounts, in other words, that the composite metal oxide contains Fe, Co, Mg, and Mn in substantially the same molar ratios, thereby making the above-described effects of the present invention more pronounced.

[0090] In particular, the composite metal oxide of this embodiment is ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ It is preferable that the formula is represented by the following formula: This makes it possible to further enhance the above-mentioned effects of the present invention.

[0091] In the following description of this embodiment, the composite metal oxide constituting the reaction medium is Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ This section will mainly explain the case where

[0092] As will be shown in the examples below, the reaction medium (Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ ) in a high-temperature cycle of thermal reduction temperature: 1400°C - water decomposition temperature: 1000°C, conventional cerium oxide (CeO ２ ) and the initial rate of hydrogen generation in the water decomposition process is particularly high, allowing for a significant reduction in reaction time.

[0093] The reaction medium of this embodiment may have at least a portion of its surface made of the above-mentioned material (composite metal oxide of Fe, Co, Mg, and Mn), and may have a configuration in which the surface of a base (support) made of a material other than the above-mentioned material (composite metal oxide of Fe, Co, Mg, and Mn) is coated with the above-mentioned material (composite metal oxide of Fe, Co, Mg, and Mn). In this case, zirconia, for example, can be used as the base (support).

[0094] [2] Processing Method Next, the processing method of the present invention will be described.

[0095] The treatment method of the present invention comprises a first step of thermally reducing the above-mentioned reaction medium, and a second step of contacting the thermally reduced reaction medium with the material to be treated to oxidize the reaction medium and decompose the material to be treated.

[0096] In the present invention, by introducing the above-mentioned manganese oxide into the composite metal oxide, the entropy effect is increased, and the material to be treated can be efficiently pyrolyzed using a reaction medium with improved reaction activity, thereby efficiently obtaining the target substance.

[0097] The treatment method of the present invention may be any method that includes a first step and a second step, and the type of the object to be treated or the target substance is not particularly limited. Examples of the object to be treated include water, carbon dioxide, etc.

[0098] When the material to be treated is water, hydrogen is generated in the second step, and when the material to be treated is carbon dioxide, carbon monoxide is generated in the second step.

[0099] In particular, when the material to be treated is water and hydrogen is generated in the second step, hydrogen can be suitably obtained as a non-fossil fuel that is clean and has excellent transportability and storability.

[0100] Furthermore, when the treated material is carbon dioxide and carbon monoxide is generated in the second step, it can contribute to reducing the amount of carbon dioxide, a substance that causes global warming. The carbon monoxide obtained can be used as an industrial gaseous fuel and as a reducing agent in metallurgy. It can also be used as a main component of synthesis gas, etc., and as a raw material for synthesizing liquid hydrocarbons, methanol, etc.

[0101] In the following description, the treatment method of the present invention will be mainly described in the case where water is used as the material to be treated and hydrogen is generated in the second step.

[0102] A hydrogen production method as an example of the treatment method of the present invention includes a first step (thermal reduction step) of thermally reducing the above-mentioned reaction medium, and a second step (water decomposition step) of contacting the thermally reduced reaction medium with water to oxidize the reaction medium and generate hydrogen.

[0103] In the present invention, by introducing the above-described manganese oxide into the composite metal oxide, the entropy effect is increased, and hydrogen is produced using a reaction medium with improved reaction activity, thereby enabling efficient production of hydrogen.

[0104] In the treatment method of the present invention, the heat used in the reaction may be any type, and does not have to be heat obtained by concentrating sunlight. However, the following description will mainly focus on the case where heat is obtained by concentrating sunlight.

[0105] In the present invention, the first step and the second step each need only be carried out at least once, but it is preferable to repeatedly carry out a series of treatments including the first step and the second step.

[0106] This allows the overall amount of water (steam) to be processed as the treated material to be increased, further improving the productivity of hydrogen as the target substance, and since the effect of reducing the temperature difference between the two processes is repeatedly exerted, the effects described above are more pronounced.

[0107] In the present invention, a pre-treatment step may be included in the first step, an intermediate treatment step may be included between the first step and the second step, or a post-treatment step may be included in the second step. The pre-treatment step and the post-treatment step may or may not be included in the series of treatments.

[0108] When the above-described series of treatments is repeated, the treatment conditions may be changed in at least one step in each cycle.

[0109] [2-1] First Step In the first step (thermal reduction step), a reaction medium containing the above-mentioned composite metal oxide is thermally reduced.

[0110] This improves the reaction activity in the first step and the second step, and improves the energy efficiency of hydrogen production and hydrogen productivity.

[0111] The reaction in this step can be represented by the following formula (1-1), formula (1-2), or formula (1-3).

[0112] Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ (Spinel structure) → Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ－σ (rock salt structure) + σO ２ ... (1-1)

[0113] Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ (Spinel structure) → Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ－σ (rock salt structure) + σO ２ ... (1-2)

[0114] Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ (spinel structure) → Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ－σ (rock salt structure) + σO ２ ... (1-3)

[0115] The reaction temperature (T1) in this step is preferably 1200°C or higher and 1400°C or lower, more preferably 1200°C or higher and 1370°C or lower, and even more preferably 1200°C or higher and 1350°C or lower.

[0116] This makes it possible to increase the reaction rate in this step and further improve the energy efficiency of the entire treatment method of the present invention.

[0117] In particular, the reaction medium of the present invention described above has higher reaction activity than conventional reaction media, and therefore, by using the reaction medium of the present invention, the temperature of the thermal reduction step can be lowered below the temperature in conventional thermal reduction steps, for example, 1500°C.

[0118] This makes it possible to reduce the temperature difference between the thermal reduction step (first step) and the water decomposition step (second step), resulting in better energy efficiency.

[0119] More specifically, if the temperature difference between the two processes is large, for example, the energy loss during temperature cycling in the reactor increases, resulting in reduced energy efficiency. However, in the present invention, the temperature difference between the two processes can be suitably reduced, so that such problems do not arise and the energy efficiency in hydrogen production can be made particularly excellent.

[0120] By lowering the processing temperature in the thermal reduction process compared to conventional methods, heat loss due to re-radiation, heat conduction, and convection is reduced, and cheaper materials can be used as reactor construction materials. Furthermore, by lowering the processing temperature, the reaction can be carried out at a lower concentration in the solar concentrating system compared to conventional high temperatures (over 1500°C), reducing the number of reflectors installed and eliminating the need for secondary and tertiary reflectors. This improves energy efficiency and reduces costs.

[0121] Furthermore, the temperature difference in the temperature swing of the two-stage water pyrolysis cycle can be reduced, and by cycling the temperature of the reactor with a small temperature difference, heat loss due to the temperature swing can also be significantly reduced.

[0122] As a result, the present invention can greatly increase the amount of hydrogen produced and the energy efficiency.

[0123] Furthermore, by reducing the temperature difference between the two steps, the time required to adjust the temperature to a suitable level in each step can be shortened, thereby improving hydrogen productivity.

[0124] Furthermore, the small temperature difference between the two processes reduces the burden on the equipment (reactor) used to produce hydrogen, which results in stable hydrogen production over a long period of time, as well as extending the life of the equipment used to produce hydrogen and simplifying maintenance.

[0125] Furthermore, since high resistance to shocks caused by repeated large temperature changes is not required, the range of materials from which the reactor can be constructed can be expanded, and even with a relatively simple device configuration rather than a special one (for example, a configuration in which two processes are performed in different parts of different reactors), the energy efficiency during hydrogen production and hydrogen productivity can be made sufficiently excellent, thereby making it possible to reduce the manufacturing costs of the hydrogen production device (processing device).

[0126] It can also contribute to reducing the running costs of the hydrogen production device (processing device).

[0127] Furthermore, by carrying out the thermal reduction reaction at a lower temperature than in conventional two-stage water pyrolysis cycles that use sunlight, hydrogen can be suitably produced by the two-stage water pyrolysis cycle even in regions outside the sunbelt (regions with relatively little sunlight), which were previously unsuitable for implementing the two-stage water pyrolysis cycle. In other words, the number of regions where hydrogen can be suitably produced can be expanded compared to conventional regions.

[0128] Furthermore, compared to conventional solar-powered two-stage water thermal decomposition cycles, the thermal reduction reaction is carried out at a lower temperature, which shortens the time required to raise the temperature of the reaction medium to a suitable temperature, further improving hydrogen productivity and reducing the burden on the equipment (reactor) used for hydrogen production.

[0129] In addition, when the treatment temperature in this step changes with time, the highest treatment temperature in this step can be used as T1.

[0130] The treatment time in this step (when the series of treatments is repeated, the treatment time in one first step) is preferably 20 minutes or more and 180 minutes or less, more preferably 20 minutes or more and 120 minutes or less, and even more preferably 20 minutes or more and 30 minutes or less.

[0131] This allows the thermal reduction reaction of the reaction medium to proceed sufficiently, and also enables hydrogen to be produced in a short period of time, thereby further improving hydrogen productivity.

[0132] The treatment time in this step can be the time during which no gas containing water vapor (gas with a water vapor partial pressure of 10 kPa or more) is supplied and the temperature of the reaction medium is 1100°C or higher.

[0133] This step is usually carried out in an atmosphere with a low oxygen gas partial pressure. Specifically, the oxygen gas partial pressure in the atmosphere during this step is preferably 1 kPa or less, and more preferably 0.1 kPa or less.

[0134] This allows the reduction reaction of the reaction medium to proceed favorably, and also effectively prevents the reaction medium that has been reduced once from being unintentionally re-oxidized in this step.

[0135] This step is usually carried out while supplying an inert gas such as argon or nitrogen gas into a vessel (reactor) containing a reaction medium.

[0136] This allows oxygen generated by the reduction reaction of the reaction medium to be efficiently discharged from the system containing the reaction medium, and more effectively prevents the reaction medium from being unintentionally oxidized once reduced by the oxygen. Furthermore, when the reaction medium is in a particulate form, the reaction medium can be efficiently flowed within the vessel containing the reaction medium, thereby further improving the reaction efficiency in this step.

[0137] This step may be carried out in a vacuum environment or a reduced pressure environment (for example, an environment of 10 kPa or less).

[0138] [2-2] Second Step In the second step (water decomposition step), the reaction medium thermally reduced in the first step is brought into contact with water to oxidize the reaction medium and generate hydrogen.

[0139] The reaction in this step can be represented by the following formula (2-1), formula (2-2), or formula (2-3).

[0140] Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ－σ (rock salt structure) + δH ２ O → Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ (Spinel structure) + δH ２ ...(2-1) (wherein, 1≦x≦2, 0<δ≦x.)

[0141] Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ－σ (rock salt structure) + δH ２ O → Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ (Spinel structure) + δH ２ ...(2-2) (wherein, 1≦x≦2, 0<δ≦x.)

[0142] Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ－σ (rock salt structure) + δH ２ O → Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ (Spinel structure) + δH ２ ...(2-3) (wherein, 1≦x≦2, 0<δ≦x.)

[0143] The reaction temperature (T2) in this step is preferably 800°C or higher and 1200°C or lower, more preferably 900°C or higher and 1200°C or lower, and even more preferably 1000°C or higher and 1200°C or lower.

[0144] This makes it possible to sufficiently increase the reaction rate in this step and further improve the energy efficiency of the entire treatment method of the present invention.

[0145] In addition, when the treatment temperature in this step changes with time, the highest treatment temperature in this step can be used as T2.

[0146] The treatment time in this step (when the series of treatments is repeated, the treatment time in one second step) is preferably 10 minutes or more and 150 minutes or less, more preferably 10 minutes or more and 100 minutes or less, and even more preferably 10 minutes or more and 80 minutes or less.

[0147] This allows the water decomposition reaction (hydrogen production, oxidation reaction of the reaction medium) to proceed sufficiently, and also makes it possible to produce hydrogen in a short period of time, thereby further improving hydrogen productivity.

[0148] The treatment time in this step can be the time during which the gas containing water vapor is supplied and the temperature of the reaction medium is 950° C. or higher.

[0149] This step is usually carried out while supplying water vapor into a vessel (reactor) containing the reaction medium. This allows the reaction between the thermally reduced reaction medium and water to proceed more stably, resulting in more efficient hydrogen generation. It also facilitates the recovery of generated hydrogen. Furthermore, when the reaction medium is particulate, the reaction medium can be efficiently flowed within the vessel containing the reaction medium, further improving the reaction efficiency of this step.

[0150] The partial pressure of water vapor in the atmosphere during this step is preferably 1 kPa or more and 1 MPa or less, and more preferably 10 kPa or more and 100 kPa or less.

[0151] This allows the target reaction to proceed more favorably, and hydrogen productivity to be further improved.

[0152] This step is preferably carried out while supplying a gas (carrier gas) that is inert to the reaction in this step, such as an inert gas or nitrogen gas, together with water vapor, into a vessel (reactor) that contains the reaction medium.

[0153] This allows the reaction between the thermally reduced reaction medium and water to proceed more stably, improving the efficiency of hydrogen generation and making it easier to recover the generated hydrogen.

[0154] In this step, when the partial pressure of water vapor in the gas supplied into the vessel (reactor) containing the reaction medium is P1 [Pa] and the partial pressure of the carrier gas is P2 [Pa], it is preferable to satisfy the relationship 0.2≦P1 / P2≦0.999, and it is more preferable to satisfy the relationship 0.3≦P1 / P2≦0.995.

[0155] This allows the target reaction to proceed more favorably, and hydrogen productivity to be further improved.

[0156] This step is usually carried out in an atmosphere with a low oxygen gas partial pressure. Specifically, the oxygen gas partial pressure in the atmosphere during this step is preferably 1 kPa or less, and more preferably 0.1 kPa or less.

[0157] This effectively prevents the thermally reduced reaction medium from being oxidized by an oxidation reaction (oxidation reaction by oxygen gas) that does not contribute to the generation of hydrogen, and allows the reaction between the thermally reduced reaction medium and water to proceed more smoothly.

[0158] [3] Production Apparatus A treatment apparatus that can be used in the treatment method of the present invention will be described below. In the following description, a hydrogen production apparatus used in a method of producing hydrogen by thermal decomposition of water will be mainly described as an example of a treatment apparatus. Figure 1 is a schematic diagram showing a preferred embodiment of the hydrogen production apparatus as a treatment apparatus.

[0159] The hydrogen production device 100 as a processing device includes a ground reflector (sunlight concentrating means) 20 called a heliostat installed on the ground, a tower reflector (sunlight concentrating means) 30 installed in a tower (not shown), and a reactor (container) 10 into which light reflected by the tower reflector 30 enters and the reaction of the reaction medium described above takes place.

[0160] In the illustrated hydrogen production device 100, a ground reflector 20 and a tower reflector 30 constitute a beam-down type light collection system.

[0161] This beam-down type light collecting system is configured to collect sunlight S and irradiate the central portion of the upper surface of the fluidized bed 2 contained in the reactor 10.

[0162] The reactor 10 is made of a heat-resistant material that can withstand the temperatures in the first and second steps. Examples of the reactor 10 include those made of stainless steel alloys and Inconel alloys. The reactor 10 accommodates the fluidized bed 2 containing the reaction medium.

[0163] In addition, a gas introduction plate 3 is provided at the bottom of the reactor 10, which can retain the reaction medium particles that constitute the fluidized bed 2 within the reactor 10 and introduce gases introduced from gas introduction means 4 and 5 into the reactor 10.

[0164] A large number of minute openings are provided in the gas introduction plate 3. The gas introduction means (low oxygen partial pressure gas introduction means) 4 is a flow path (pipe) for introducing the gas used in the first step into the reactor 10, and the gas introduction means (water vapor-containing gas introduction means) 5 is a flow path (pipe) for introducing the gas used in the second step into the reactor 10.

[0165] A light-transmitting and heat-resistant window 6 is provided at the top of the reactor 10 so that sunlight can pass through. Examples of materials for the window 6 include quartz.

[0166] At the sides of the upper part of the reactor 10, outlets 8 and 9 are provided for taking out gas that has passed through the flow.

[0167] More specifically, the reactor 10 is provided with an outlet (oxygen-containing gas outlet) 8 for extracting the gas that has passed through the fluidized bed 2 in the first step (gas containing oxygen gas produced by the reaction), and an outlet (hydrogen-containing gas outlet) 9 for extracting the gas that has passed through the fluidized bed 2 in the second step (gas containing hydrogen gas produced by the reaction).

[0168] A shutter (not shown) is provided at each of the outlets 8 and 9. This allows the gas that has passed through the fluidized bed 2 in the first step and the gas that has passed through the fluidized bed 2 in the second step to be collected separately.

[0169] More specifically, in the first step, outlet 8 is left open and outlet 9 is left closed, so that gas containing oxygen gas produced by the reaction is recovered from outlet 8, and in the second step, outlet 8 is left closed and outlet 9 is left open, so that gas containing hydrogen gas produced by the reaction is recovered from outlet 9.

[0170] This makes it possible to effectively prevent the gas containing oxygen gas and the gas containing hydrogen gas from being unintentionally mixed together in the recovered gas.

[0171] The production of hydrogen using the hydrogen production apparatus 100 will be described below. First, before the start of the first step described above, a low oxygen partial pressure gas introduced from a gas introduction means (low oxygen partial pressure gas introduction means) 4 is introduced into the reactor 10 containing the reaction medium via the gas introduction plate 3, and the fluidized bed 2 is fluidized to form an internal circulation flow.

[0172] Next, while a low-oxygen partial pressure gas is flowed into the reactor 10, sunlight S concentrated by the sunlight concentrating means 20, 30 is irradiated through the window 6 onto the inside of the reaction medium (fluidized bed 2) in the reactor 10, thereby heating the fluidized bed 2 to a desired temperature and allowing the reaction in the first step to proceed.

[0173] Next, the amount of sunlight S (amount per unit time) input into the reactor 10 is reduced to lower the temperature of the particle reaction medium (fluidized bed 2) to a desired temperature, and the gas supplied to the inside of the reactor 10 is switched from the low oxygen partial pressure gas to a water vapor-containing gas. That is, the supply of gas from the gas introduction means 4 is stopped, and a water vapor-containing gas is supplied from the gas introduction means 5 to the inside of the reactor 10 via the gas introduction plate 3. This allows the second step to proceed.

[0174] Thereafter, a series of processes including the first and second steps is repeated a desired number of times. When the first step is performed again after the second step, the amount of sunlight S (amount per unit time) input into the reactor 10 is increased to raise the temperature of the particle reaction medium (fluidized bed 2) to a desired temperature, and the gas supplied into the reactor 10 is switched from the water vapor-containing gas to the low oxygen partial pressure gas. That is, the supply of gas from the gas introduction means 5 is interrupted, and the low oxygen partial pressure gas is supplied into the reactor 10 from the gas introduction means 4 via the gas introduction plate 3.

[0175] As described above, by performing the first step and the second step in the same container (particularly, performing them in the same location in the same container), the configuration of the hydrogen production device (processing device) can be simplified, the manufacturing costs of the hydrogen production device can be reduced, and installation of the hydrogen production device can be made easier.

[0176] Furthermore, as described above, by carrying out the first and second steps while circulating the fluidized bed 2 containing the powdered reaction medium within the reaction vessel, it is possible to further improve the productivity of hydrogen.

[0177] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these.

[0178] For example, the processing method of the present invention is not limited to being performed using the processing apparatus described above, and may be performed using processing apparatuses of other configurations. More specifically, in the above-described embodiment, the first step and the second step are mainly performed in the same part of the processing apparatus (reactor), but for example, the first step and the second step may be performed in different parts of the processing apparatus (reactor).

[0179] In the above-described embodiment, the reaction medium is mainly described as being in particulate (powder) form, but the reaction medium may be in any shape, such as a molded body made of a porous body (e.g., a foam). This allows the reaction medium and gas to be brought into contact with each other in the first and second steps, and the target reaction to proceed smoothly.

[0180] Furthermore, in the above-described embodiment, the explanation has been centered on the case where the reaction is carried out using heat from sunlight, but in the present invention, heat from sources other than sunlight may be used as at least a part of the heat used in the reaction.

[0181] The present invention will be described in detail below based on specific examples, but the present invention is not limited to these examples.

[0182] In the following description, treatments for which no particular temperature conditions are specified were performed at room temperature (23°C) and a relative humidity of 50%. Furthermore, for various measurement conditions, values ​​for which no particular temperature conditions are specified are those at room temperature (23°C) and a relative humidity of 50%.

[0183] [4] Production of reaction medium A reaction medium was produced as follows. Figure 2 is a diagram illustrating the production method of the reaction medium. (Example 1) First, equimolar amounts of iron nitrate, cobalt nitrate, nickel nitrate, and manganese nitrate were weighed and mixed to obtain a mixture.

[0184] Next, 100 parts by mass of the mixture was dissolved in 400 parts by mass of ion-exchanged water to obtain an aqueous solution.

[0185] Ethylenediaminetetraacetic acid (EDTA) was added to the aqueous solution in an amount of 60% of the total molar amount of metal ions, and then citric acid was added in an amount of 75% of the total molar amount of metal ions. Then, while stirring with a stirrer rotating at 300 rpm, an aqueous ammonium hydroxide solution was added to adjust the pH to 11. Then, while continuing to stir at 300 rpm, the aqueous solution was heated at 200°C. Stirring was stopped when the aqueous solution gelled. The heating time at 200°C was approximately 5 hours.

[0186] The gelled aqueous solution was dried overnight at 300° C., which resulted in the gel becoming almost solid. The solidified gel was then heated at 300° C. for 1 hour in a box furnace.

[0187] The mixture was then fired in air using an electric furnace. The temperature was increased to 800°C at a rate of 10°C / min, then increased from 800°C to 1000°C at a rate of 5°C / min, and held at 1000°C for 1 hour.

[0188] Thereafter, the temperature was decreased to 800°C at a rate of 5°C / min, and then the material was naturally cooled to obtain Fe. ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ A reaction medium consisting of

[0189] When XRD measurement was performed, the obtained Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ was a single phase with a spinel structure.

[0190] Example 2: Fe nitrate was prepared in the same manner as in Example 1, except that iron nitrate, manganese nitrate, nickel nitrate, and magnesium nitrate were used as the metal nitrates. ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ A reaction medium consisting of

[0191] When XRD measurement was performed, the obtained Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５O ｘ was a single phase with a spinel structure.

[0192] Example 3: Fe nitrate was prepared in the same manner as in Example 1, except that iron nitrate, cobalt nitrate, manganese nitrate, and magnesium nitrate were used as the metal nitrates. ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ A reaction medium consisting of

[0193] When XRD measurement was performed, the obtained Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ was a single phase with a spinel structure.

[0194] Comparative Example 1: Fe nitrate was prepared in the same manner as in Example 1, except that iron nitrate, cobalt nitrate, nickel nitrate, and magnesium nitrate were used as the metal nitrates. ０．２５ Co ０．２５ Ni ０．２５ Mg ０．２５ O ｘ A reaction medium composed of (MNCFO) was obtained.

[0195] XRD measurement revealed that Fe ０．２５ Co ０．２５ Ni ０．２５ Mg ０．２５ O ｘ was a complex phase consisting of rock salt and spinel structures.

[0196] (Comparative Example 2) First, a predetermined amount of Ce(NO ３ ) ３ ・6H ２ O and MnSO ４ ・5H ２ O was added to water and stirred at room temperature to obtain a solution.

[0197] Next, while stirring this aqueous solution, an aqueous sodium hydroxide solution was added dropwise to this aqueous solution to adjust the pH to 8.5, thereby forming a precipitate.

[0198] The precipitate was then collected by centrifugation, washed with purified water and acetone, and dried at room temperature for 24 hours.

[0199] Then, a firing treatment was performed at 900°C for 2 hours to obtain Mn-doped CeO ２ A reaction medium consisting of

[0200] The reaction medium thus obtained contains CeO ２ The substitution rate of Mn for Ce constituting the alloy was 15 mol %.

[0201] (Comparative Example 3) MnSO ４ ・5H ２ A reaction medium was prepared in the same manner as in Comparative Example 2 above, except that O was not used.

[0202] The reaction medium thus obtained contains CeO ２ (not doped with any metal other than Ce).

[0203] (Comparative Example 4) Commercially available Fe ３ O ４ was prepared as a reaction medium.

[0204] [5] Production of Hydrogen Using the reaction media produced in each Example and Comparative Example, hydrogen was produced as follows: A thermobalance (TG8120, manufactured by Rigaku Corporation) was used for hydrogen production.

[0205] First, a predetermined amount (33 mg to 38 mg) of the reaction medium obtained above was prepared and filled into a platinum cup having a diameter of 5 mm and a depth of 5 mm, which was then placed in a heating furnace, and the atmosphere in the electric furnace was replaced with nitrogen gas. ２ Since the reactivity of is low and the weight change is small, the sample amount for Comparative Example 3 was set to 66 mg.

[0206] Next, while nitrogen gas was flowing into the electric furnace at 300 mL / min, the temperature was increased to 1000°C at a rate of 30°C / min, and then increased to the thermal reduction temperature (1200°C) at a rate of 20°C / min, and held at 1200°C for 10 minutes. At this time, the pressure inside the electric furnace was adjusted to 100 kPa. The nitrogen gas used here had a purity of 99.9% or higher, and the partial pressures of water vapor and oxygen gas in the electric furnace were both 0.1 kPa or less.

[0207] The temperature in the electric furnace was then cooled to 1000°C at a rate of 20°C / min. When the water decomposition temperature (1000°C) was reached, the gas flowing into the electric furnace was switched to a mixed gas of water vapor and nitrogen gas. The inflow rate of nitrogen gas in the mixed gas was 50 mL / min. At this time, the pressure in the electric furnace was adjusted to 100 kPa. At this time, the partial pressure of nitrogen gas in the electric furnace was 70 kPa, the partial pressure of water vapor was 30 kPa, and the partial pressure of oxygen gas was 0.1 kPa or less.

[0208] The heat treatment under the nitrogen gas atmosphere (particularly, heat treatment at 1100°C or higher) is the first step in which the thermal reduction reaction of the reaction medium is carried out, and the heat treatment under an atmosphere of a mixed gas of water vapor and nitrogen gas is the second step in which the water decomposition reaction is carried out.

[0209] After the second step was performed for 60 minutes, the gas flowing into the electric furnace was switched to nitrogen gas, the same as in the first step (thermal reduction step), and the temperature was raised to the thermal reduction temperature (1200°C). The same treatment as above was then repeated, and the first step and the second step were each performed four times in total. In other words, the set of the first step and the second step was repeated four times.

[0210] The amounts of hydrogen and oxygen produced in the thermal reduction step and the water decomposition step were calculated from the weight change of the obtained sample. The reaction activity (amount of hydrogen produced) was evaluated in four consecutive cycles.

[0211] In the above measurements, PtPAN was used as a blank sample, and about 33 mg of Pt plate was used as a reference sample. ２ ) the sample amount was 66 mg, so the amount of the blank sample was also 66 mg.

[0212] [6] Results and Discussion [6-1] Comparison of Reaction Activity in a Low-Temperature Two-Stage Water Pyrolysis Cycle The reaction activity (amount of hydrogen produced) in a low-temperature two-stage water pyrolysis cycle with a thermal reduction temperature of 1200°C and a water decomposition temperature of 1000°C was examined for the reaction media of each Example and Comparative Example using thermogravimetric analysis (TGA).

[0213] FIG. 3 shows the TGA weight change when the reaction medium of Example 1 was subjected to a low-temperature two-stage hydrothermal decomposition cycle.

[0214] During the thermal reduction step, weight loss occurs due to the release of lattice oxygen as molecular oxygen, while the subsequent water decomposition step results in the loss of reduced Fe. ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ is oxidized by water vapor, in other words, hydrogen is produced, resulting in an increase in weight.

[0215] As described above, it was found that in the present invention, the target reaction proceeds favorably in the first and second steps in the low-temperature cycle.

[0216] From this weight change, the amounts of hydrogen and oxygen produced in each of the second to fourth cycles were calculated. ２ / O ２ The molar ratio was also calculated.

[0217] FIG. 4 shows the amounts of hydrogen and oxygen produced and H ２ / O ２ In the first cycle, the amount of oxygen generated is greater than in a normal cycle reaction because the sample before the reaction is reduced in the thermal reduction step, and therefore this was excluded from the data.

[0218] From FIG. 4, it can be seen that hydrogen and oxygen are produced in the reaction medium of Example 1 with good cyclical efficiency, and H ２ / O ２ The molar ratio was close to the stoichiometric ratio of 2, suggesting that the reaction proceeded almost stoichiometrically.

[0219] FIG. 5 shows the average production amount per cycle and H for the reaction media of Examples 1 to 3 and Comparative Example 1. ２ / O ２ The molar ratio of hydrogen and oxygen produced and H ２ / O ２ The molar ratio is the average value of the second to fourth cycles.

[0220] As a result, it was found that in the present invention, both of the catalysts exhibited high reaction activity, and the target reactions proceeded favorably in the first and second steps.

[0221] In particular, the reaction medium of Example 1 produced about 1.4 times as much hydrogen as that of Comparative Example 1. ２ / O ２ The average molar ratio is about 1.9, which is closer to the stoichiometric ratio than the other reaction media, and it is clear that the reaction proceeds more stably at the stoichiometric ratio.

[0222] The reaction medium of Example 2 also exhibited a high reaction activity (amount of hydrogen produced) exceeding that of Comparative Example 1. ２ / O ２ The average molar ratio was also about 1.7, which was closer to the stoichiometric ratio than Comparative Example 1.

[0223] In addition, no measurable weight change was observed in the reaction medium (cerium oxide) of Comparative Example 3. In other words, cerium oxide (CeO ２ ) hardly reacted in such a low-temperature cycle, and the amount of hydrogen produced was almost zero.

[0224] The average hydrogen production amount per cycle in the low-temperature cycle of the reaction medium of Example 1, 425 μmol / g, exceeds the average hydrogen production amount in the high-temperature cycle of the reaction medium of Comparative Example 2, 376 μmol / g, shown in FIG. 8, and is about 5.7 times the average hydrogen production amount in the high-temperature cycle of the reaction medium of Comparative Example 3.

[0225] From the above, it can be seen that by using the reaction medium of the present invention, particularly the reaction medium of Example 1, a high amount of hydrogen can be produced even when the treatment temperature in the thermal reduction step is reduced from the conventional high temperature of 1500° C. or higher to a low temperature of 1200° C. Therefore, in the present invention, the temperature difference in the temperature swing can be significantly reduced while the cycle temperature is lowered.

[0226] [6-2] Comparison of reaction activity in a high-temperature two-stage water pyrolysis cycle The reaction media of each example and comparative example were examined by thermogravimetric analysis (TGA) for reaction activity (amount of hydrogen produced) in a high-temperature two-stage water pyrolysis cycle with a thermal reduction temperature of 1400°C and a water decomposition temperature of 1000°C.

[0227] In the high-temperature two-stage water pyrolysis cycle, hydrogen was produced in the same manner as above, except that the treatment temperature in the first step was set to 1400°C.

[0228] FIG. 6 shows the TGA weight change when the reaction medium of Example 2 was subjected to a high-temperature two-stage hydrothermal decomposition cycle.

[0229] As a result, it was found that in the present invention, the target reaction proceeds favorably in the first and second steps even in the high-temperature cycle.

[0230] From this weight change, the amounts of hydrogen and oxygen produced in each of the second to fourth cycles were calculated, and the ratio (H ２ / O ２ The molar ratio was also calculated.

[0231] FIG. 7 shows the amounts of hydrogen and oxygen produced and H ２ / O ２ FIG. 1 is a diagram showing the molar ratio.

[0232] As a result, in the present invention, hydrogen and oxygen were produced with good cyclic properties in both cases, and the average ratio was close to the stoichiometric ratio of 2, suggesting that the reaction proceeded almost stoichiometrically.

[0233] FIG. 8 shows the average production amount per cycle and H for the reaction media of Examples 1 to 3 and Comparative Examples 1 to 3. ２ / O ２ The amounts of hydrogen and oxygen produced and the H ２ / O ２ The molar ratio is the average value of each of the second to fourth cycles.

[0234] As a result, it was found that in the present invention, the target reaction proceeded favorably in both the first and second steps even in the high-temperature cycle.

[0235] Furthermore, compared to MNCFO of Comparative Example 1, the reaction medium of Example 1 yielded a particularly high amount of hydrogen, approximately 1.1 times, and the reaction medium of Example 2 yielded a particularly high amount of hydrogen, approximately 2 times.

[0236] Compared to the cerium oxide of Comparative Example 3, the reaction medium of Example 1 produced approximately 8.6 times as much hydrogen, the reaction medium of Example 3 produced approximately 8.1 times as much, and the reaction medium of Example 2 produced approximately 15 times as much hydrogen, which is a particularly high amount.

[0237] [6-3] Study on reaction rate For the reaction media of Examples 1 to 3, the hydrogen production rate in each cycle of the high-temperature two-stage water pyrolysis cycle was studied.

[0238] 9(A) is a graph showing the hydrogen production rate in each cycle when a high-temperature, two-stage water pyrolysis cycle was performed for the reaction medium of Example 1. FIG. 9(B) is a graph showing the hydrogen production rate in each cycle when a high-temperature, two-stage water pyrolysis cycle was performed for the reaction medium of Example 2. FIG. 9(C) is a graph showing the hydrogen production rate in each cycle when a high-temperature, two-stage water pyrolysis cycle was performed for the reaction medium of Example 3. In FIGS. 9(A) to 9(C), data from 10 minutes after the start of the reaction in each water pyrolysis step is used as the initial reaction rate.

[0239] 9 shows that the reaction medium of Example 3 has a particularly fast initial reaction rate of hydrogen production in the water decomposition step in the high-temperature cycle compared to Examples 1 and 2.

[0240] [6-4] Investigation of Melting Point A differential scanning calorimetry (DSC) apparatus was used to investigate the melting points of the reaction media of Examples 1 to 3. Fig. 10 is a diagram showing a schematic configuration of a differential scanning calorimetry (DSC) apparatus.

[0241] The conditions for the heat flow difference measurement were as follows: Pt cup: diameter 5 mm, depth 2.5 mm Sample: approximately 2 mg Reference sample: Al３ O ３ Approximately 2 mg Temperature: Room temperature to 1500°C Atmosphere: N ２ Gas Retention time: 0 [min] Temperature increase rate: 20 [°C / min] N ２ Gas flow rate: 50 mL / min

[0242] 11 is a diagram showing the results of differential scanning calorimetry measurements of the reaction media of Examples 1 to 3 and Comparative Examples 1 and 4. In Comparative Example 4, a normal Fe ３ O ４ When heated, Fe ３ O ４ →An endothermic peak appears due to the melting of FeO produced by the reduction of FeO, but no endothermic peak was observed in any of the reaction media of Examples 1 to 3.

[0243] These results show that none of the reaction media in Examples 1 to 3 melts at a temperature lower than 1500° C. In other words, the melting points of the reaction media in Examples 1 to 3 are all 1500° C. or higher.

[0244] Furthermore, when the material to be treated was treated in the same manner as described above, except that carbon dioxide was used instead of water, it was confirmed that carbon monoxide and oxygen were efficiently produced when the reaction medium according to the present invention was used.

[0245] The reaction medium of the present invention is characterized by having a chemical structure in which Mn is introduced into a composite iron oxide, and therefore provides a reaction medium that has high reaction activity and can be used to efficiently pyrolyze a material to be treated and obtain a target substance.

[0246] The treatment method of the present invention comprises a first step of thermally reducing the reaction medium and a second step of contacting the thermally reduced reaction medium with a material to be treated to oxidize the reaction medium and decompose the material to be treated. Therefore, a treatment method can be provided that can efficiently thermally decompose the material to be treated and obtain a target substance.

[0247] Therefore, the reaction medium of the present invention and the processing method of the present invention have industrial applicability.

[0248] DESCRIPTION OF SYMBOLS 100... Hydrogen production device 10... Reactor (container) 2... Fluidized bed 3... Gas introduction plate 4... Gas introduction means (low oxygen partial pressure gas introduction means) 5... Gas introduction means (water vapor-containing gas introduction means) 6... Window 8... Outlet (oxygen-containing gas outlet) 9... Outlet (hydrogen-containing gas outlet) 20... Ground reflector (sunlight collecting means) 30... Tower reflector (sunlight collecting means) S... Sunlight

Claims

1. A reaction medium characterized by having a chemical structure in which Mn is introduced into a composite iron oxide.

2. The reaction medium according to claim 1, which is used in a method for producing hydrogen by thermal decomposition of water.

3. The reaction medium according to claim 1, which is used in a process for producing carbon monoxide by thermal decomposition of carbon dioxide.

4. The reaction medium of claim 1 containing a complex metal oxide of Fe, Co, Ni and Mn.

5. The reaction medium according to claim 4, wherein said composite metal oxide comprises Fe, Co, Ni and Mn in substantially equal molar proportions.

6. The composite metal oxide is Fe ０．２５ Co ０．２５ Ni ０．２５ Mn ０．２５ O ｘ The reaction medium according to claim 5, wherein 7. The reaction medium of claim 1 comprising a complex metal oxide of Fe, Ni, Mg and Mn.

8. The reaction medium according to claim 7, wherein said complex metal oxide comprises Fe, Mn, Ni and Mg in substantially equal molar proportions.

9. The composite metal oxide is Fe ０．２５ Mn ０．２５ Ni ０．２５ Mg ０．２５ O ｘ The reaction medium according to claim 8, wherein 10. The reaction medium of claim 1 comprising a complex metal oxide of Fe, Co, Mg and Mn.

11. The reaction medium of claim 10, wherein the complex metal oxide comprises Fe, Co, Mn and Mg in substantially equal molar proportions.

12. The composite metal oxide is Fe ０．２５ Co ０．２５ Mn ０．２５ Mg ０．２５ O ｘ The reaction medium according to claim 11, 13. A treatment method comprising: a first step of thermally reducing a reaction medium according to any one of claims 1 to 12; and a second step of contacting the thermally reduced reaction medium with a workpiece to oxidize the reaction medium and decompose the workpiece.

14. The processing method according to claim 13, wherein the material to be processed is water, and hydrogen is generated in the second step.

15. The method according to claim 13, wherein the substance to be treated is carbon dioxide and carbon monoxide is generated in the second step.

16. The method according to claim 13, wherein the reaction temperature in the first step is 1200°C or higher and 1400°C or lower.

17. The method according to claim 13, wherein the reaction temperature in the second step is 1000°C or higher and 1200°C or lower.

18. The processing method according to claim 13, wherein a series of processes including the first step and the second step is repeatedly performed.

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