CHEMICAL LOOPING SYSTEM COMPOSITION AND METHOD FOR USING La-Co-Al COMPLEX OXIDE IN CHEMICAL LOOPING SYSTEM

Abstract

To provide a composition which improves the efficiency of recovering carbon monoxide while having excellent heat resistance.SOLUTION: There is provided a chemical looping system composition which is a La-Co-Al complex oxide including lanthanum, cobalt, and aluminum. The La-Co-Al complex oxide is in such a form that aluminum forms a solid solution with a La-Co complex oxide having a perovskite-type structure. The La-Co-Al complex oxide has a composition represented by the following chemical formula (1): LaCoyAlxOδ (1) (in the chemical formula (1), x and y are each a number satisfying a condition of 0<x<1, 0<y<1, and x+y=0.5 to 1.5 and δ is a number of 1.5 to 4.5).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a composition for a chemical looping system and a method for using an La-Co-Al based composite oxide in a chemical looping system. [Background technology]

[0002] One known method for recovering carbon monoxide, which is used as a raw material for chemical products such as methanol, is to separate carbon monoxide from a mixed gas containing carbon monoxide and water produced by a reverse shift reaction (H2 + CO2 → CO + H2O) using a catalyst. However, this method requires a process for separating carbon monoxide from the mixed gas, and the reaction temperature required to favorably proceed with the reverse shift reaction is relatively high. Meanwhile, Patent Document 1 discloses a chemical looping system that generates carbon monoxide from carbon dioxide using a complex oxide that functions as an oxygen carrier. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-123519 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, there is still room for improvement in the heat resistance of the composite oxide that functions as an oxygen carrier, and therefore there has been a demand for a composition with excellent heat resistance.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and an object of the present invention is to provide a composition that has excellent heat resistance while improving the carbon monoxide recovery efficiency. [Means for solving the problem]

[0006] The present invention has been made to solve at least a part of the above-described problems and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, a composition for a chemical looping system is provided. This composition for a chemical looping system is a La-Co-Al-based composite oxide containing lanthanum, cobalt, and aluminum, and the La-Co-Al-based composite oxide has a form in which the aluminum is solid-dissolved in a La-Co-based composite oxide having a perovskite-type structure, and has the following chemical formula (1): LaCo y Al x O[[ID=..]] δ ···(1) (In chemical formula (1), x and y are numbers that satisfy the conditions of 0 < x <, 0 < y < 1, and x + y = 0.5 to 1.5, respectively, and δ is a number of 1.5 to 4.5.) It has a composition represented by

[0008] According to this configuration, by using the La-Co-Al-based composite oxide, the reverse shift reaction that simultaneously generates carbon monoxide and water can be divided into a reaction that generates water from hydrogen and a reaction that generates carbon monoxide from carbon dioxide. Therefore, compared with the reverse shift reaction, the recovery of carbon monoxide becomes easier, so that the recovery efficiency of carbon monoxide can be improved. Further, according to this configuration, compared with the reaction temperature at which the reverse shift reaction preferably proceeds, the reaction temperatures at which the water generation reaction and the carbon monoxide generation reaction using the La-Co-Al-based composite oxide each preferably proceed are low, so that the amount of energy required for the generation of carbon monoxide can be reduced. From this aspect as well, the recovery efficiency of carbon monoxide can be improved. Further, according to this configuration, the aluminum contained in the La-Co-Al-based composite oxide can improve the carbon monoxide generation ability. From this aspect as well, the recovery efficiency of carbon monoxide can be improved. Furthermore, according to this configuration, since the La-Co-Al-based composite oxide also has excellent heat resistance, it is possible to provide a composition having excellent heat resistance while improving the recovery efficiency of carbon monoxide compared with the reverse shift reaction.

[0009] (2) According to another aspect of the present invention, there is provided a method for using the La-Co-Al-based composite oxide in a chemical looping system, which comprises alternately performing a step of reacting the La-Co-Al-based composite oxide with hydrogen to produce water and a step of reacting the La-Co-Al-based composite oxide with carbon dioxide to produce carbon monoxide. According to this configuration, since La-Co-Al based composite oxide is used, carbon monoxide can be recovered efficiently and a decrease in the efficiency of the carbon monoxide production reaction can be suppressed even at high temperatures.

[0010] The present invention can be realized in various forms, such as a chemical looping system, a chemical looping plant, a chemical looping combustion apparatus, an apparatus and system including these, a method for producing carbon monoxide, a method for synthesizing carbon monoxide, a computer program for executing these apparatus and methods, a server device for distributing this computer program, and a non-transitory storage medium on which the computer program is stored. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a chemical looping system according to a first embodiment. [Figure 2] FIG. 1 shows the results of measuring the crystalline phases of various composite oxides by X-ray diffraction. [Figure 3] FIG. 1 is a diagram showing the mass change of various composite oxides during a chemical looping reaction. [Figure 4] FIG. 1 is an explanatory diagram showing the rate of carbon monoxide production by various composite oxides. [Figure 5] FIG. 1 is an explanatory diagram showing the carbon monoxide production capacity of various composite oxides. [Figure 6] FIG. 10 is an explanatory diagram showing the configuration of a chemical looping system according to a second embodiment. [Figure 7] FIG. 10 is an explanatory diagram showing the configuration of a chemical looping system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment 1 is an explanatory diagram illustrating the configuration of a chemical looping system 1 according to a first embodiment of the present invention. The chemical looping system 1 is a system for alternately carrying out a reaction to produce water from hydrogen and a reaction to produce carbon monoxide from carbon dioxide using a composite oxide. The chemical looping system 1 includes a reactor R, flow paths F1 to F6, flow rate regulators V1 and V2, and gas switchers S1 and S2.

[0013] One end of the flow path F1 is connected to the flow path F3 via the gas switch S1, and the other end of the flow path F1 is connected to a carbon dioxide supply source (not shown). The flow path F1 is a flow path for sending carbon dioxide to the flow path F3. The flow rate regulator V1 provided in the flow path F1 is an adjustment valve capable of adjusting the flow rate of carbon dioxide circulating in the flow path F1.

[0014] One end of flow path F2 is connected to flow path F3 via gas switch S1, and the other end of flow path F2 is connected to a hydrogen supply source (not shown). Flow path F2 is a flow path for sending hydrogen to flow path F3. A flow rate regulator V2 provided in flow path F2 is an adjustment valve that can adjust the flow rate of hydrogen flowing through flow path F2.

[0015] The gas switch S1 is connected to each of the flow paths F1 to F3. The gas switch S1 is a three-way valve that switches between either the flow path F1 or the flow path F2 and the flow path F3 to allow communication therethrough.

[0016] The flow path F3 is connected to the reactor R. The flow path F3 is a flow path for sending the gas sent from either one of the flow paths F1 and F2 to the reactor R. When the gas switch S1 enables the flow between the flow path F1 and the flow path F3, carbon dioxide is sent from the flow path F1 through the flow path F3 to the reactor R. When the gas switch S1 enables the flow between the flow path F2 and the flow path F3, hydrogen is sent from the flow path F2 through the flow path F3 to the reactor R.

[0017] The reactor R contains a composite oxide that promotes the reaction of generating carbon monoxide and water from carbon dioxide and hydrogen sent through the flow paths F1 to F3. This composite oxide is a La-Co-Al-based composite oxide containing lanthanum, cobalt, and aluminum. More specifically, this composite oxide is in a form in which aluminum is solid-dissolved in a La-Co-based composite oxide having a perovskite-type structure, and has the following chemical formula (1): LaCo y Al x O δ ···(1) (In the chemical formula (1), x and y are numbers that satisfy the conditions of 0 < x < 1, 0 < y <, and x + y = 0.5 to 1.5, respectively, and δ is a number of 1.5 to 4.5.) In this embodiment, since x + y = 1, y = 1 - x, and since δ = 3, the composite oxide contained in the reactor R is represented as LaCo 1-x Al x O3.

[0018] When hydrogen is sent from the flow path F2 through the flow path F3 to the reactor R, in the reactor R, due to the containment of the La-Co-Al-based composite oxide, the reaction represented by the following formula (2) proceeds. LaCo 1-x Al x O3 + δH2 → LaCo 1-x Al x O 3-δ + δH2O ···(2) When carbon dioxide is sent from flow path F1 to reactor R via flow path F3, the reaction represented by the following formula (3) proceeds in reactor R because the reactor R contains a La-Co-Al-based composite oxide. LaCo 1-x Al x O 3-δ +δCO2 → LaCo 1-x Al x O3 + δCO···(3) That is, the La-Co-Al-based composite oxide contained in the reactor R corresponds to a composition for a chemical looping system that advances two reactions that alternately occur in the chemical looping system 1, namely, the reaction of producing water from hydrogen represented by the above formula (2) and the reaction of producing carbon monoxide from carbon dioxide represented by the above formula (3).

[0019] The flow path F4 is connected to the reactor R. The flow path F4 is a flow path for sending the gas sent from the reactor R to either the flow path F5 or the flow path F6.

[0020] The gas switch S2 is connected to each of the flow paths F4 to F6. The gas switch S2 is a three-way valve that switches between either the flow path F5 or the flow path F6 and the flow path F4 to allow communication therebetween.

[0021] One end of flow path F5 is connected to flow path F4 via gas switch S2, and the other end of flow path F5 is open to the outside of the chemical looping system 1. Flow path F5 is a flow path for sending the gas containing carbon monoxide and carbon dioxide sent from reactor R to the outside of the chemical looping system 1. That is, when carbon dioxide is sent from flow path F1 to reactor R via flow path F3, gas switch S2 allows communication between flow paths F4 and F5, and sends the gas containing carbon monoxide and unreacted carbon dioxide generated by the above formula (3) to the outside of the chemical looping system 1.

[0022] One end of flow path F6 is connected to flow path F4 via gas switch S2, and the other end of flow path F6 is open to the outside of the chemical looping system 1. Flow path F6 is a flow path for sending the gas containing water and hydrogen sent from reactor R to the outside of the chemical looping system 1. That is, when hydrogen is sent from flow path F2 to reactor R via flow path F3, gas switch S2 allows communication between flow paths F4 and F6, and sends the gas containing water and unreacted hydrogen generated by the above formula (2) to the outside of the chemical looping system 1.

[0023] Next, the La-Co-Al composite oxide (LaCo 1-x Al x This section explains the manufacturing method of O3. The materials used were lanthanum nitrate La(NO3)3·6H2O (purity 99.9%), cobalt nitrate Co(NO3)2·6H2O (purity 99.9%), aluminum nitrate Al(NO3)3·9H2O (purity 98%), citric acid (purity 98%), and ethylene glycol (purity 99%). All five of these materials are manufactured by Wako Pure Chemical Industries, Ltd.

[0024] First of all, LaCo 1-x Al x Stoichiometric ratios of lanthanum nitrate, cobalt nitrate, and aluminum nitrate are dissolved in a minimum amount of pure water at room temperature so that x in O3 is the target value. After confirming that the solution is transparent, citric acid and ethylene glycol (6 equivalents relative to the total amount of cations) are added to the solution to obtain a solution containing a metal citrate complex. The solution containing the metal citrate complex is then heated to 150°C and maintained for 30 minutes to obtain a polymer gel in which the metal citrate complex is dispersed. The resulting polymer gel is then transferred to an alumina crucible and heat-treated in a degreasing furnace at 400°C for 2 hours in air to thermally decompose the polymer gel, yielding a metal oxide precursor in which the metal elements (lanthanum, cobalt, and aluminum) are uniformly dispersed. The resulting metal oxide precursor is then transferred to an electric furnace and calcined at 800°C for 5 hours in air to obtain a polycrystalline powder of La-Co-Al composite oxide.

[0025] Figure 2 shows the results of X-ray diffraction analysis of the crystalline phases of various composite oxides obtained by the above-mentioned manufacturing methods. Measurements by X-ray diffraction were performed using a RINT-Ultima (Rigaku Corporation) X-ray diffractometer with a CuKα radiation source under conditions of 40 kV, 40 mA, and 2θ = 5° / min. Figure 2(a) shows the full-width XRD pattern, and Figure 2(b) shows the pattern at 2θ = 32 to 35°.

[0026] Examples C1 to C3 and Comparative Examples E1 and E2, listed side by side on the right side of FIG. 2(b), show various composite oxides obtained by the above-mentioned manufacturing method. Example C1 shows the composite oxide (LaCo) obtained when the amount of various nitrates was adjusted with x=0.25 as the target value. 0.75 Al 0.25 O δ ) Example C2 is a composite oxide (LaCo) when the amount of various nitrates is adjusted with x = 0.50 as the target value. 0.50 Al 0.50 O δ ) Example C3 shows the composite oxide (LaCo) when the amount of various nitrates was adjusted with x = 0.75 as the target value. 0.75 Al 0.25 O δ On the other hand, Comparative Example E1 is a composite oxide (LaCoAlO) obtained by adjusting the amount of various nitrates with x=0 as the target value. δ ), which is a La-Co based composite oxide. Comparative Example E2 is a composite oxide (LaCoAlO) obtained by adjusting the amounts of various nitrates with x=1 as the target value. δ 2(a) and 2(b) are the patterns of Examples C1 to C3 and Comparative Examples E1 and E2 shown at the positions corresponding to the respective patterns.

[0027] As is clear from Figure 2(a), it was confirmed that a single-phase composite oxide having a perovskite structure, which is a rhombohedral structure, was obtained for all of the La-Co-Al composite oxides of Examples C1 to C3, the La-Co composite oxide of Comparative Example E1, and the La-Al composite oxide of Comparative Example E2. Furthermore, as shown in Figure 2(b), the main peak near 2θ = 33° shifted to the higher angle side as the amount of aluminum in the composite oxide increased (the larger the value of x), confirming that the lattice constant became smaller. Comparing the ionic radii of the hexacoordinated structures, it was confirmed that Al 3+ (0.535Å) is Co 3+ Since the lattice constant is smaller than (0.60 Å), the decrease in the lattice constant supports the substitution of cobalt by aluminum.

[0028] FIG. 3 shows the results of measuring the mass change during the chemical looping reaction in various complex oxides. The chemical looping reaction refers to the reaction of producing water from hydrogen, as expressed by the above formula (2), and the reaction of producing carbon monoxide from carbon dioxide, as expressed by the above formula (3). The horizontal axis of FIG. 3 represents time, and the vertical axis of FIG. 3 represents the mass loss rate of the complex oxide. Lines c1 to c3 represent the mass change in the complex oxides of Examples C1 to C3. Lines e1 and e2 represent the mass change in the complex oxides of Comparative Examples E1 and E2. The mass change was measured using a thermogravimetric analyzer "TGA-50" (Shimadzu Corporation) at 400°C by alternately supplying nitrogen gas containing 5% hydrogen (H2 (5% by volume) + N2 (balance)) and nitrogen gas containing 5% carbon dioxide (CO2 (5% by volume) + N2 (balance)) to 20 mg of the complex oxide to be measured at 30-minute intervals.

[0029] As shown in Figure 3, the greater the amount of aluminum in the composite oxide, the smaller the rate of mass loss when hydrogen-containing nitrogen gas was supplied. Furthermore, as shown by line e2, the rate of mass loss in the composite oxide of Comparative Example E2 when hydrogen-containing nitrogen gas was supplied was almost zero. This result indicates that the cobalt in the composite oxide contributes to the reaction of producing water from hydrogen, as expressed by the above formula (2), and that the greater the amount of aluminum in the composite oxide (the greater the value of x), the less oxygen can be released from the composite oxide.

[0030] As shown in Figure 3, when Co was contained in the composite oxide, the mass increased when nitrogen gas containing carbon dioxide was supplied. That is, as shown by lines c1 to c3 and e1, the mass of the composite oxides of Examples C1 to C3 and the composite oxide of Comparative Example E1 increased when nitrogen gas containing carbon dioxide was supplied, while as shown by line e2, the mass increase of the composite oxide of Comparative Example E2 was almost zero when nitrogen gas containing carbon dioxide was supplied. This result indicates that in the composite oxide of Comparative Example E2, which does not contain Co, the reaction of the above formula (2) does not proceed easily, and LaCo 1-x Al x O 3-δ It is presumed that this is because the mass is unlikely to increase even if nitrogen gas containing carbon dioxide is supplied, since the

[0031] FIG. 4 is an explanatory diagram showing the measurement results of the carbon monoxide production rate for various complex oxides. The horizontal axis of FIG. 4 represents the cobalt to aluminum content (value x) in the various complex oxides. The vertical axis on the left side of FIG. 4 represents the production rate per weight of the complex oxide, and the vertical axis on the right side of FIG. 4 represents the production rate per substance amount of cobalt in the complex oxide. Since line LG represents the production rate per weight of the various complex oxides, the left vertical axis of FIG. 4 is referred to. Since line LM represents the production rate per substance amount of cobalt in the various complex oxides, the right vertical axis of FIG. 4 is referred to.

[0032] FIG. 5 is an explanatory diagram showing the measurement results of the carbon monoxide production capacity by various composite oxides. The horizontal axis of FIG. 5, like the horizontal axis of FIG. 4, indicates the content ratio of cobalt to aluminum (value of x) in various composite oxides. The vertical axis on the left side of FIG. 5 indicates the production capacity per weight of composite oxide, and the vertical axis on the right side of FIG. 5 indicates the production capacity per substance amount of cobalt in the composite oxide. Since line segment Lg indicates the production capacity per weight of various composite oxides, the left vertical axis of FIG. 5 is referred to. Since line segment Lm indicates the production capacity per substance amount of cobalt in various composite oxides, the right vertical axis of FIG. 5 is referred to.

[0033] The carbon monoxide production rates and carbon monoxide production capacities shown in Figures 4 and 5 were measured using a thermogravimetric analyzer "TGA-50" (Shimadzu Corporation) under the same conditions as those used to obtain the measurement results shown in Figure 3. The carbon monoxide production rates for various complex oxides shown in Figure 4 correspond to the average of three carbon monoxide production rates measured over a 30-second period from the start of supplying nitrogen gas containing carbon dioxide. The carbon monoxide production capacities for various complex oxides shown in Figure 5 correspond to the average of three total volumes of carbon monoxide produced over a 30-minute period from the start of supplying nitrogen gas containing carbon dioxide.

[0034] As shown by line LG in Figure 4 and line LG in Figure 5, it was confirmed that the carbon monoxide production rate and production capacity per weight of various composite oxides increased up to a certain level as the aluminum content in the composite oxide increased (the value of x increased), even though the cobalt content in the composite oxide decreased. In detail, as shown by line LG in Figure 4, the carbon monoxide production rate per weight of various composite oxides increased at x = 0.75 (i.e., LaCo 0.75 Al 0.25 O δ = the composite oxide of Example C1). As shown by the line segment Lg in FIG. 4, the production capacity per weight of various composite oxides was maximum when x = 0.50 (i.e., LaCo 0.50 Al 0.50 O δ The maximum was observed when the composite oxide of Example C2 was used.

[0035] As shown by line LM in Figure 4 and line Lm in Figure 5, it was confirmed that the rate and capacity of carbon monoxide production per unit amount of cobalt in various composite oxides both increased as the amount of aluminum in the composite oxide increased (the larger the value of x). This result indicates that the reaction of carbon dioxide to produce carbon monoxide proceeds more easily with more aluminum.

[0036] A heat resistance test was also conducted on the composite oxides of Examples 1 to 3. In the heat resistance test, using a thermogravimetric analyzer "TGA-50" (manufactured by Shimadzu Corporation), the composite oxides of Examples 1 to 3 were heated to 800°C in nitrogen gas containing 5% hydrogen (H (5% by volume) + N (balance)), and then cooled to room temperature. X-ray diffraction measurements were then conducted on the composite oxides of Examples 1 to 3 cooled to room temperature under the same conditions as those used to obtain the measurement results shown in FIG. 2 . As a result, it was confirmed that the composite oxides of Examples 1 to 3 maintained a single phase exhibiting a perovskite structure without thermal decomposition, even after being exposed to a reducing atmosphere at 800°C. This heat resistance is presumably due to the fact that, in the composite oxides of Examples 1 to 3, a portion of the easily reducible cobalt was replaced with less reducible aluminum while maintaining the perovskite structure. When the same heat resistance test was carried out on the composite oxide of Comparative Example 1, it was confirmed that the composite oxide was separated into cobalt (Co) and lanthanum oxide (La2O3).

[0037] According to the chemical looping system 1 of the first embodiment described above, the La-Co-Al composite oxide (LaCo 1-x Al xBy using La-Co-Al composite oxide (LaCo), the reverse shift reaction, which simultaneously produces water and carbon monoxide from hydrogen and carbon dioxide, can be divided into two reactions: one that produces water from hydrogen and the other that produces carbon monoxide from carbon dioxide. This makes it easier to recover carbon monoxide than the reverse shift reaction, improving the efficiency of carbon monoxide recovery. In detail, to recover carbon monoxide from the mixed gas (a mixture of water and carbon monoxide) generated by the reverse shift reaction, it is necessary to separate water and carbon monoxide. However, the use of La-Co-Al composite oxide (LaCo 1-x Al x O3), the reverse shift reaction is split into two reactions, eliminating the need to separate water and carbon monoxide, making it easier to recover carbon monoxide.

[0038] Furthermore, in the chemical looping system 1 of the first embodiment, the reaction temperatures at which the water production reaction and the carbon monoxide production reaction using the La-Co-Al composite oxide each proceed favorably (approximately 500°C) are lower than the reaction temperature at which the reverse shift reaction proceeds favorably (700°C or higher), which reduces the amount of energy required to produce carbon monoxide, thereby improving the carbon monoxide recovery efficiency.

[0039] Furthermore, according to the chemical looping system 1 of the first embodiment, the aluminum contained in the La-Co-Al-based composite oxide can improve the carbon monoxide production capacity (the production rate and production capacity described in FIGS. 4 and 5), which also improves the carbon monoxide recovery efficiency.

[0040] Furthermore, according to the chemical looping system 1 of the first embodiment, the La-Co-Al-based composite oxide has excellent heat resistance, and therefore can be said to be a composition that improves the carbon monoxide recovery efficiency compared to the reverse shift reaction while also having excellent heat resistance.

[0041] The La-Co-Al-based composite oxide described above has been found to have an unknown attribute: the ability to promote a reaction that produces water from hydrogen and a reaction that produces carbon monoxide from carbon dioxide. This attribute has made it suitable for use in a chemical looping system that alternates between these two reactions. In other words, the La-Co-Al-based composite oxide described above is a so-called application invention. Japanese Patent No. 6670880 discloses that the La-Co-Al-based composite oxide has the oxygen storage capacity to store oxygen when the ambient oxygen concentration is high and to release oxygen when the ambient oxygen concentration is low. However, this application differs from the application of the La-Co-Al-based composite oxide described in the first embodiment. Specifically, while Japanese Patent No. 6670880 discloses that the La-Co-Al-based composite oxide stores or releases oxygen depending on the ambient oxygen concentration, the first embodiment demonstrates that the La-Co-Al-based composite oxide stores oxygen and produces carbon monoxide when carbon dioxide is supplied, and produces water when hydrogen is supplied. That is, when comparing Japanese Patent No. 6670880 with the first embodiment, the reactants that react with the La-Co-Al-based composite oxide are different, and the first embodiment shows that carbon monoxide and water are produced as products by reaction with the La-Co-Al-based composite oxide (Japanese Patent No. 6670880 does not disclose the production of carbon monoxide or water), so the uses of the La-Co-Al-based composite oxide disclosed in Japanese Patent No. 6670880 are different from the uses of the La-Co-Al-based composite oxide shown in the first embodiment.

[0042] Second Embodiment 6 is an explanatory diagram illustrating the configuration of a chemical looping system 1a according to a second embodiment of the present invention. The chemical looping system 1a of the second embodiment differs from the chemical looping system 1 of the first embodiment in that it includes gas switchers s1 and s2 instead of gas switchers S1 and S2, flow paths Fa3 and Fb3 instead of flow path F3, reactors Ra and Rb instead of reactor R, and flow paths Fa4 and Fb4 instead of flow path F4.

[0043] The gas switch s1 is connected to each of the flow paths F1 and F2 and the flow paths Fa3 and Fb3. The gas switch s1 is a four-way valve that switches between either the flow path F1 or the flow path F2 and either the flow path Fa3 or the flow path Fb3 to allow communication therethrough.

[0044] The flow paths Fa3 and Fb3 are connected to the reactors Ra and Rb, respectively. The flow path Fa3 (Fb3) is a flow path for sending gas sent from either the flow path F1 or the flow path F2 to the reactor Ra (Rb). When the gas switch s1 allows communication between the flow path F1 and the flow path Fa3 (Fb3), carbon dioxide is sent from the flow path F1 to the reactor Ra (Rb) via the flow path Fa3 (Fb3). When the gas switch s1 allows communication between the flow path F2 and the flow path Fa3 (Fb3), hydrogen is sent from the flow path F2 to the reactor Ra (Rb) via the flow path Fa3 (Fb3).

[0045] The reactors Ra and Rb contain a composite oxide that promotes a reaction to produce carbon monoxide and water from carbon dioxide and hydrogen sent through the flow paths Fa3 and Fb3, respectively. This composite oxide is a La-Co-Al composite oxide (LaCo), which is the same as the composite oxide contained in the reactor R of the first embodiment. y Al x O δ ) In this embodiment, since x + y = 1, y = 1 - x, and δ is 3, the composite oxide contained in the reactors Ra and Rb is LaCo 1-x Al x It is represented as O3.

[0046] When hydrogen is sent from flow path F2 to reactor Ra (Rb) via flow path Fa3 (Fb3), the reaction represented by the above formula (2) proceeds in reactor Ra (Rb), similar to the reactor R of the first embodiment, to produce water. On the other hand, when carbon dioxide is sent from flow path F1 to reactor Ra (Rb) via flow path Fa3 (Fb3), the reaction represented by the above formula (3) proceeds in reactor Ra (Rb), similar to the reactor R of the first embodiment, to produce carbon monoxide.

[0047] The flow paths Fa4 and Fb4 are connected to the reactors Ra and Rb. The flow path Fa4 (Fb4) is a flow path for sending the gas sent from the reactor Ra (Rb) to either the flow path F5 or the flow path F6.

[0048] The gas switch s2 is connected to each of the flow paths Fa4, Fb4 and the flow paths F5, F6. The gas switch s2 is a four-way valve that switches between either the flow path Fa4 or the flow path Fb4 and either the flow path F5 or the flow path F6 to allow communication therethrough.

[0049] The chemical looping system 1a of the second embodiment described above can efficiently recover carbon monoxide, as in the first embodiment. Furthermore, since the chemical looping system 1a of the second embodiment includes two reactors Ra and Rb, carbon monoxide can be continuously recovered by alternately supplying carbon dioxide to one of the reactors Ra and Rb and hydrogen to the other. To avoid mixing of the gas containing carbon monoxide and unreacted carbon dioxide generated during carbon dioxide supply with the gas containing water and unreacted hydrogen generated during hydrogen supply, a step of supplying an inert gas to the target reactor or a step of evacuating the target reactor may be inserted between the steps of supplying carbon dioxide and supplying hydrogen. Furthermore, even if carbon monoxide and hydrogen are mixed in the raw gas when producing chemical products, such a mixture is acceptable if the chemical product being produced is, for example, methanol. Therefore, the steps of supplying an inert gas and evacuating the target reactor may be unnecessary.

[0050] Third Embodiment 7 is an explanatory diagram illustrating the configuration of a chemical looping system 1b according to a third embodiment of the present invention. In the chemical looping system 1b of the third embodiment, La-Co-Al-based composite oxides similar to the composite oxides described in the first and second embodiments function as particles circulating within the system. The chemical looping system 1b includes a first production column HT, a second production column CT, and circulation pipes FC and FH.

[0051] The first production tower HT is a tower that produces water by reacting hydrogen with the La-Co-Al composite oxide particles circulating within the system. The first production tower HT is provided with a supply port for supplying hydrogen to the inside and an outlet port (not shown) for discharging the produced water and a gas containing unreacted hydrogen to the outside.

[0052] The second production tower CT is a tower that produces carbon monoxide by reacting carbon dioxide with the La-Co-Al-based composite oxide particles circulating within the system. The second production tower CT is provided with a supply port for supplying carbon dioxide to the inside and an outlet port for discharging gas containing the produced carbon monoxide and unreacted carbon dioxide to the outside (not shown).

[0053] The circulation pipes FC and FH are both pipes that circulate the La-Co-Al-based composite oxide between the first production tower HT and the second production tower CT. The circulation pipe FC connects the first production tower HT and the second production tower CT and is a flow path for sending the La-Co-Al-based composite oxide from the first production tower HT to the second production tower CT. The circulation pipe FH connects the first production tower HT and the second production tower CT and is a flow path for sending the La-Co-Al-based composite oxide from the second production tower CT to the first production tower HT. In addition to the circulation pipes FC and FH, a loop seal may be provided between the first production tower HT and the second production tower CT to limit the movement of gas between the first production tower HT and the second production tower CT.

[0054] According to the chemical looping system 1b of the third embodiment described above, similar to the first and second embodiments, carbon monoxide can be efficiently recovered. Further, in the chemical looping system 1b of the third embodiment, the La-Co-Al-based composite oxide circulates between the first production tower HT and the second production tower CT, enabling continuous recovery of carbon monoxide.

[0055] In the chemical looping systems 1 and 1a of the first and second embodiments described above, hydrogen and carbon dioxide are alternately supplied to the La-Co-Al-based composite oxide accommodated in the reactors R, Ra, and Rb, whereby the reaction of generating water from hydrogen and the reaction of generating carbon monoxide from carbon dioxide are alternately carried out. On the other hand, in the chemical looping system 1b of the third embodiment, the La-Co-Al-based composite oxide circulates between the first production tower HT to which hydrogen is supplied and the second production tower CT to which carbon monoxide is supplied, whereby the reaction of generating water from hydrogen and the reaction of generating carbon monoxide from carbon dioxide are alternately carried out. Thus, the chemical looping system for alternately carrying out the two reactions includes a form in which the La-Co-Al-based composite oxide, which is a composition for the chemical looping system, is used in a retained state, and a form in which the La-Co-Al-based composite oxide is used in a state of circulating within the same system.

[0056] <Modifications of this embodiment> The present invention is not limited to the above-described embodiments, and can be implemented in various aspects without departing from the gist thereof. For example, the following modifications are possible.

[0057] In the above-described embodiments, in the composite oxide (LaCo y Al x O δ ), x + y was set to 1, but it is not limited thereto. x and y may be any values as long as they satisfy the conditions of 0 < x < 1, 0 < y < 1, and x + y = 0.5 to 1.5. In addition, x is preferably 0.1 to 0.5, y is preferably 0.5 to 0.9, and x + y is preferably 1.

[0058] In the above-described embodiment, the composite oxide (LaCo y Al x O δ In the above, δ was set to 3, but is not limited to this. δ may be any value as long as it is a number between 1.5 and 4.5. δ is preferably between 2 and 4, and particularly preferably 3.

[0059] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0060] 1, 1a, 1b...Chemical Looping System R: reactor F1~F6...flow path S1, S2...Gas switch V1,V2…Flow rate regulator Ra, Rb...reactor Fa3, Fa4, Fb3, Fb4...flow path s1, s2...Gas switch HT…First generation tower CT…Second generation tower FH…Circulation piping FC...Circulation piping

Claims

1. A composition for a chemical looping system, which is a La-Co-Al based composite oxide containing lanthanum, cobalt, and aluminum, The La—Co—Al-based composite oxide has a form in which the aluminum is dissolved in a La—Co-based composite oxide having a perovskite structure, and is represented by the following chemical formula (1): LaCo ｙ Al ｘ O δ ・・・(1) (In chemical formula (1), x and y are numbers that satisfy the conditions 0<x<1, 0<y<1, and x+y=0.5 to 1.5, and δ is a number from 1.5 to 4.5.) A composition for a chemical looping system having a composition represented by the formula:

2. A method for using the La-Co-Al-based composite oxide according to claim 1 in a chemical looping system, comprising: a step of reacting the La—Co—Al-based composite oxide with hydrogen to produce water; and a step of reacting the La-Co-Al based composite oxide with carbon dioxide to produce carbon monoxide.

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