Ammonia production unit and production method

Abstract

A method for producing NH3, the method executing a production process that includes: a first step in which an exhaust gas that is discharged from a facility and contains NOx and O2 is supplied into N reaction tubes (N is an integer of 2 or more) in each of which a catalyst material containing platinum, aluminum oxide (Al2O3), and one or more alkaline earth metals selected from among barium (Ba), calcium (Ca) and strontium (Sr) is contained, so that the catalyst material absorbs NOx in the exhaust gas; and a second step in which NH3 is produced from NOx, which has been absorbed by the catalyst material, by supplying a reducing gas into the reaction tubes after stopping the supply of the exhaust gas. The time duration for which the second step is executed is equal to or longer than the time duration for which the first step is executed; the reducing gas contains H2; and the temperature of the catalyst material is 200°C to 350°C in the first step and the second step.

Description

[Technical Field]

[0001] The present invention relates to a technology for producing ammonia (NH3) from nitrogen oxides (NOx). [Background technology]

[0002] The Haber-Bosch (HB) process is known as a method for producing ammonia (NH3). In the HB process, NH3 is produced using nitrogen (N2) and hydrogen (H2) as raw materials. However, this process requires a large input of energy, as H2 must be produced by steam reforming methane (CH4) at high temperatures (up to 1000°C), and NH3 must then be produced under high temperatures and pressures (400-600°C, 200-400 atmospheres).

[0003] Meanwhile, nitrogen oxides (so-called thermal NOx) resulting from air combustion are generated in the exhaust gases within the combustors of high-temperature combustion equipment. The generated nitrogen oxides are detoxified into N2 and released into the atmosphere. Therefore, if NH3 could be generated from the NOx in the exhaust gases, harmful chemicals could be used as chemical raw materials. Furthermore, increasing the temperature of the heat engine to improve its energy efficiency would further increase the amount of thermal NOx generated. If the generated thermal NOx could be recovered as NH3, it may be possible to improve the energy efficiency of the heat engine without increasing the amount of nitrogen oxides released into the atmosphere.

[0004] Here, for example, a technology has been proposed in which air is plasma-oxidized to generate nitric oxide (NO) from N2 and oxygen (O2), and the NOx is then stored through a NOx storage reduction (NSR) catalyst (Ba / Pt / Al2O3), after which H2 is supplied as a reducing agent to generate NH3 (Non-Patent Documents 1 and 2). That is, the technologies in Non-Patent Documents 1 and 2 do not anticipate the use of exhaust gas, and require the installation of a separate device for generating NO. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] L. Hollevoet et al., Angew. Chem. Int. Ed., 59 (2020) 23825. doi.org / 10.1002 / anie.202011676 [Non-patent document 2] L. Hollevoet et al., ChemSusChem, 15 (2022) e202102526. doi.org / 10.1002 / cssc.202102526 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technologies of Non-Patent Documents 1 and 2 disclose that the efficiency of ammonia production drops significantly when the catalyst temperature becomes high (e.g., 200°C or higher). Therefore, it would be difficult to produce NH3 from high-temperature exhaust gas, such as that emitted from a combustion facility, using the technologies of Non-Patent Documents 1 and 2. If an attempt were made to produce NH3 from exhaust gas, temperature control (e.g., significantly lowering the temperature of the exhaust gas) would be necessary, which would likely require a huge amount of energy. Taking these circumstances into consideration, the present invention aims to improve the efficiency of NH3 production in high-temperature environments in a technology for producing NH3 from NOx contained in exhaust gas emitted from various facilities (e.g., waste incineration facilities, high-temperature combustion facilities such as thermal power plants, and chemical plants). [Means for solving the problem]

[0007] [1] A method for producing NH3, comprising the steps of: (a) supplying exhaust gas discharged from a facility and containing NOx and O2 to the reaction tubes, each containing a catalytic material containing one or more alkaline earth metals selected from barium (Ba), calcium (Ca), and strontium (Sr), platinum, and aluminum oxide (Al2O3), and (b) supplying a reducing gas to the reaction tubes after stopping the supply of the exhaust gas to produce NH3 from the NOx occluded in the catalytic material; (c) supplying a reducing gas to the reaction tubes after stopping the supply of the exhaust gas to the reaction tubes; and (d) producing NH3 from the NOx occluded in the catalytic material; wherein the time for which the second step is performed is equal to or longer than the time for which the first step is performed, the reducing gas contains H2, and the temperature of the catalytic material is 200°C or higher and 350°C or lower during the first step and the second step.

[0008] [2] The manufacturing method of [1], wherein the first step is completed when the concentration of NOx in the gas released from the reaction tube is 50% or less of the concentration of NOx in the exhaust gas supplied to the reaction tube.

[0009] [3] The production method according to [1] or [2], further comprising a third step of recovering NH3 from the NH3-containing product gas produced in the second step.

[0010] [4] The manufacturing method of [3], wherein the NH3 recovered in the third step is used to purify the NOx in the exhaust gas supplied to the reaction tube in the first step that was not occluded by the catalytic material.

[0011] [5] The NH3 recovered in the third step is used to purify NOx contained in the exhaust gas discharged from the facility that was not supplied to the reaction tube. [3]

[0012] [6] The manufacturing method according to [3], wherein the recovered gas remaining after recovering NH3 from the generated gas in the third step contains H2, which is one of the reducing gases and was not used in the production of NH3 in the second step, and the recovered gas is supplied to the reaction tube as the reducing gas in the second step.

[0013] [7] The method according to any one of [1] to [6], wherein N in the N number of reaction tubes is set according to a time period during which the first step is performed and a time period during which the second step is performed, and the first step is performed in at least one reaction tube among the N number of reaction tubes while an exhaust gas is being discharged from the facility.

[0014] [8] The manufacturing method according to any one of [1] to [7], wherein the aluminum oxide is porous, the mode of the pore size distribution in the catalytic material is 1 nm or more and 200 nm or less in diameter, and the average particle size of the platinum is 10 nm or more and 50 nm or less.

[0015] [9] A manufacturing method according to any one of [1] to [8], wherein the aluminum oxide is porous, the platinum is contained inside the aluminum oxide, and the alkaline earth metal is supported on the aluminum oxide containing the platinum inside.

[0016]

[10] The manufacturing method according to any one of [1] to [9], further comprising a step of supplying an inert gas to the reaction tube between the first step and the second step.

[0017]

[11] A unit for producing NH3, comprising: N (N is an integer of 2 or more) reaction tubes each containing a catalytic material containing one or more alkaline earth metals selected from barium (Ba), calcium (Ca), and strontium (Sr), platinum, and aluminum oxide (Al2O3); a production apparatus having N first supply lines for supplying exhaust gases discharged from a facility and containing NOx and oxygen to the N reaction tubes, respectively; and N second supply lines for supplying reducing gases to the N reaction tubes, respectively; a control device for controlling the production apparatus; and a supplyer for supplying the reducing gas to each of the N reaction tubes via the second supply lines, wherein the control device controls each of the N reaction tubes. and making the manufacturing apparatus execute a manufacturing process including: a first step of supplying the exhaust gas to the reaction tube to cause the NOx in the exhaust gas to be occluded in the catalytic material; and a second step of generating and recovering NH3 from the NOx occluded in the catalytic material by supplying the reducing gas to the reaction tube after stopping the supply of the exhaust gas, wherein a time period during which the second step is executed is equal to or longer than a time period during which the first step is executed, and the first step is executed in at least one reaction tube out of the N reaction tubes U during a period during which the manufacturing process is executed for the N reaction tubes U, the reducing gas contains H2, and the temperature of the catalytic material is 200°C or more and 350°C or less during the first step and the second step.

[0018]

[12] The production unit according to

[11] , comprising a recovery device for recovering NH3 from the product gas containing NH3 produced in the second step. [Effects of the Invention]

[0019] The production method and production device according to the present invention improve the efficiency of NH3 production in a high-temperature environment in a technology for producing NH3 from exhaust gas. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is a configuration diagram of a manufacturing unit according to the first embodiment. [Figure 2] 1 is a conceptual diagram of a manufacturing process executed by a manufacturing apparatus according to a first embodiment. [Figure 3] FIG. 2 is a configuration diagram of a manufacturing unit (unit period T1) according to the first embodiment. [Figure 4] FIG. 2 is a configuration diagram of a manufacturing unit (unit period T2) according to the first embodiment. [Figure 5] FIG. 10 is a configuration diagram of a manufacturing unit (unit period T3) according to the first embodiment. [Figure 6] FIG. 10 is a configuration diagram of a manufacturing unit according to another aspect of the first embodiment. [Figure 7] FIG. 10 is a configuration diagram of a manufacturing unit according to a second embodiment. [Figure 8] 1 is a graph showing the relationship between the average particle size of platinum and the NH3 conversion rate for each temperature of the catalyst material in accordance with an example. DETAILED DESCRIPTION OF THE INVENTION

[0021] [First embodiment] 1 is a configuration diagram illustrating a manufacturing unit 100 for manufacturing NH3 according to the first embodiment. The manufacturing unit 100 includes a manufacturing device 20, a control device 30, and a supplier 50.

[0022] The production apparatus 20 is an apparatus that produces NH3 from NOx (e.g., NO, NO2, N2O, and N2O3) in exhaust gas. Schematically, the production apparatus 20 supplies an exhaust gas G1 containing NOx to a catalyst material Q, stops the supply of the exhaust gas G1, and then supplies a reducing gas G2 to the catalyst material Q, thereby producing NH3 (hereinafter referred to as the "production process").

[0023] The catalytic material Q is a catalyst that absorbs and reduces NOx in the exhaust gas G1. Details of the catalytic material Q will be described later.

[0024] The exhaust gas G1 is a gas containing NOx and O2. The exhaust gas G1 is a gas discharged from various facilities (for example, waste incineration facilities, high-temperature combustion facilities such as thermal power plants, and chemical plants). In other words, the present invention is applicable to various facilities that discharge the exhaust gas G1. The NOx concentration in the exhaust gas G1 is, for example, 100 ppm or more and 2% or less. The O2 concentration in the exhaust gas G1 is, for example, 1% or more and 20% or less. In addition to NOx and O2, the exhaust gas G1 may also contain CO2, water vapor (H2O), N2, etc.

[0025] The reducing gas G2 is a gas that reduces the NOx stored (adsorbed) in the catalytic material Q. Specifically, the reducing gas G2 is a gas containing a reducing agent. The reducing gas G2 is preferably a gas that does not contain NOx. Note that the fact that the reducing gas G2 does not contain NOx also includes the case where the reducing gas G2 contains NOx at an extremely low concentration (for example, 10 ppm or less) that does not affect the reduction of the NOx stored (adsorbed) in the catalytic material Q and does not have an impact on the environment.

[0026] In the first embodiment, H2 is used as the reducing agent from the viewpoint of improving the efficiency of NH3 generation in a high-temperature environment. That is, the reducing gas G2 contains H2. The concentration of H2 in the reducing gas G2 is, for example, 0.5% or more and 100% or less, preferably 1% or more and 50% or less, and more preferably 5% or more and 40% or less. When the concentration of H2 in the reducing gas G2 is in the above range, the efficiency of NH3 generation in a high-temperature environment can be further improved. In addition to the reducing agent (H2), the reducing gas G2 may contain H2O, N2, and reducing agents other than H2 (for example, CH4 and ethane (C2H6)).

[0027] As illustrated in FIG. 1, the production apparatus 20 of the first embodiment includes N (N is an integer of 2 or greater) reaction tubes U[1] to U[N], N first supply paths R1[1] to R1[N], N second supply paths R2[1] to R2[N], N first on-off valves V1[1] to V1[N], N second on-off valves V2[1] to V2[N], and N recovery paths R3[1] to R3[N]. In other words, each reaction tube U[n] (n = 1 to N) is provided with a first supply path R1[n], a second supply path R2[n], a first on-off valve V1[n], a second on-off valve V2[n], and a recovery path R3[n]. The first on-off valve V1, the second on-off valve V2, and the recovery path R3 may be omitted depending on the configuration of the production apparatus 20.

[0028] The reaction tube U is a hollow structure in which a catalyst material Q is accommodated.

[0029] The first supply path R1 is a flow path for supplying the exhaust gas G1 to the catalytic material Q (reaction tube U). Specifically, the first supply path R1 is a tubular member, and its downstream side is connected to the reaction tube U. The upstream side of the first supply path R1 is connected to, for example, a facility that discharges the exhaust gas G1. In the first embodiment, assuming the exhaust gas G1 from a high-temperature combustion facility, a configuration is exemplified in which the upstream side of the first supply path R1 is connected to a combustor (combustion chamber) 40 of the high-temperature combustion facility. However, the equipment of the facility to which the upstream side of the first supply path R1 is connected (i.e., the equipment in the facility that discharges the exhaust gas G1) is not limited to the combustor 40 and may vary appropriately depending on the type of the facility. Note that the upstream side of the first supply path R1 may be directly connected to the combustor 40 or indirectly connected to the combustor 40 via other piping or devices, as long as it can supply the exhaust gas G1 to the reaction tube U.

[0030] 1 illustrates a configuration in which the upstream sides (opposite sides to the reaction tube U) of the N first supply passages R1[1] to R1[N] are connected to the combustor 40 via a first common passage K1. In other words, the N first supply passages R1[1] to R1[N] are flow paths branching from the first common passage K1 toward the N reaction tubes U[1] to U[N]. The upstream side of the first common passage K1 is connected to the combustor 40. An exhaust gas G1 is supplied to each of the N first supply passages R1[1] to R1[N] via the first common passage K1.

[0031] The second supply path R2 is a flow path for supplying the reducing gas G2 to the catalyst material Q (reaction tube U). Specifically, the second supply path R2 is a tubular member, and its downstream side is connected to the reaction tube U. The upstream side of the second supply path R2 is connected to, for example, a supply device 50 containing the reducing gas G2. Note that the upstream side of the second supply path R2 may be directly connected to the supply device 50 or indirectly connected to the supply device 50 via another pipe or device, as long as it can supply the reducing gas G2 to the reaction tube U.

[0032] In FIG. 1, the upstream sides (opposite side to the reaction tube U) of the N second supply paths R2[1] to R2[N] are connected to a supply unit 50 via a second common path K2. In other words, the N second supply paths R2[1] to R2[N] are flow paths branching from the second common path K2 toward the N reaction tubes U[1] to U[N]. The upstream side of the second common path K2 is connected to the supply unit 50. A reducing gas G2 is supplied to each of the N second supply paths R2[1] to R2[N] via the second common path K2. An on-off valve may also be provided in each of the first common path K1 and the second common path K2.

[0033] As can be understood from the above explanation, the first embodiment illustrates a configuration in which the exhaust gas G1 and the reducing gas G2 have separate supply sources, and the exhaust gas G1 and the reducing gas G2 are each supplied from independent mechanisms (combustor 40 and supplier 50).

[0034] The first on-off valve V1 is a valve that opens and closes the first supply path R1. That is, the first on-off valve V1 switches between opening and closing the first supply path R1. When an exhaust gas G1 is supplied to the reaction tube U (when a first step described later is performed), the first on-off valve V1 is opened. On the other hand, when a reducing gas G2 is supplied to the reaction tube U (when a second step described later is performed), the first on-off valve V1 is closed.

[0035] The second on-off valve V2 is a valve that opens and closes the second supply path R2. That is, the second on-off valve V2 switches between opening and closing the second supply path R2. When a reducing gas G2 is supplied to the reaction tube U (when a second step described later is performed), the second on-off valve V2 is opened. On the other hand, when an exhaust gas G1 is supplied to the reaction tube U (when a first step described later is performed), the second on-off valve V2 is closed. Note that, for convenience, FIG. 1 illustrates a case where both the first on-off valve V1 and the second on-off valve V2 are open.

[0036] The recovery line R3 is a flow path for recovering NH3 produced in the reaction tube U. Specifically, the recovery line R3 is a tubular member, and an upstream side of the recovery line R3 is connected to the reaction tube U. An on-off valve may be provided in the recovery line R3. NH3 produced in the reaction tube U is released from the recovery line R3.

[0037] The supply unit 50 is a device for supplying the reducing gas G2 to each reaction tube U. Specifically, the supply unit 50 supplies the reducing gas G2 to each of the N reaction tubes U via the second supply path R2.

[0038] The control device 30 is a computer system for controlling each element of the manufacturing device 20 in an integrated manner, and includes, for example, one or more processors (for example, CPU: Central Processing Unit) that control each element of the manufacturing device 20.

[0039] The control device 30 of the first embodiment causes the manufacturing apparatus 20 to execute a manufacturing process. Specifically, the control device 30 causes the manufacturing apparatus 20 to execute a manufacturing process by controlling the supply of exhaust gas G1 and reducing gas G2. The control device 30 of the first embodiment controls the supply of exhaust gas G1 by switching the opening and closing of a first on-off valve V1, for example, and controls the supply of reducing gas G2 by switching the opening and closing of a second on-off valve V2. The control device 30 also controls the flow rates of the exhaust gas G1 from the combustor 40 and the reducing gas G2 from the supply device 50.

[0040] Specifically, the manufacturing process of the first embodiment includes a first step and a second step. In the first step, exhaust gas G1 is supplied to a reaction tube U, and NOx in the exhaust gas is occluded by the catalytic material Q. In the following description, the gas released from the reaction tube U in the first step is referred to as "used exhaust gas." The used exhaust gas of the first embodiment is the gas that passes through the catalytic material Q in the first step and is released from the recovery line R3. The concentration of NOx in the used exhaust gas is lower than the concentration of NOx in the exhaust gas supplied to the reaction tube U.

[0041] The second step is a step of producing NH3 from NOx occluded in the catalytic material Q by supplying a reducing gas G2 to the reaction tube U after stopping the supply of the exhaust gas G1 (i.e., after the first step). In the first embodiment, a configuration is exemplified in which the production process is repeatedly executed for each of the N reaction tubes U. That is, the first step and the second step are alternately and repeatedly executed in each reaction tube U (first step → second step → first step → second step → first step → second step → . . .).

[0042] In the following description, the time for performing the first step will be referred to as the "first time", and the time for performing the second step will be referred to as the "second time". The first time is the time for occluding NOx in the catalytic material Q (i.e., the time for supplying exhaust gas G1 to the reaction tube U). The second time is the time for generating NH3 from the NOx occluded in the catalytic material (i.e., the time for supplying reducing gas G2 to the reaction tube U). The first time and the second time will be described in detail later.

[0043] Here, the inventors of the present invention have newly discovered that the efficiency of NH3 generation is improved if NH3 generation is started at a stage where too much NOx is not stored in the catalytic material Q (i.e., at a stage where the catalytic material Q has a margin in its storage capacity). Therefore, the first time period (the time period during which NOx is stored in the catalytic material Q) is set to a time length such that the first step ends at a point where there is a margin in the NOx storage capacity.

[0044] Specifically, the first time is, for example, 10 minutes to 1 hour, preferably 10 minutes to 40 minutes, and more preferably 15 minutes to 30 minutes, from the viewpoint of allowing the catalytic material Q to sufficiently adsorb NOx. Furthermore, from the viewpoint of completing the first step with a margin in the adsorption capacity of the catalytic material Q, the first step is completed when the NOx concentration in the used exhaust gas (NOx concentration in the used exhaust gas / NOx concentration in the exhaust gas) is, for example, 50% or less, preferably 30% or less, and more preferably 10% or less, relative to the NOx concentration in the exhaust gas supplied to the reaction tube U. In other words, the first time is the length of time for completing the first step with a margin in the adsorption capacity of the catalytic material Q. Note that a higher NOx concentration in the used exhaust gas indicates a decrease in the adsorption capacity. The NOx concentration in the used exhaust gas is measured, for example, by a gas sensor near the outlet of the reaction tube U (upstream of the recovery line R3).

[0045] On the other hand, the inventors of the present invention have newly discovered that if most of the NOx occluded in the catalytic material Q is converted to NH3 during the second time period, the amount of NOx occluded in the first step of the subsequent manufacturing process increases. In consideration of the above, the second time period is set to be equal to or longer than the first time period. Specifically, the second time period is, for example, equal to or longer than one and equal to or shorter than three times the first time period, from the viewpoint of converting most of the NOx occluded in the catalytic material Q into NH3.

[0046] The concentration of H2 in the reducing gas G2 does not need to be constant throughout the manufacturing process and may vary during the second step. For example, immediately after the start of the second step, a reducing gas G2 containing a reducing agent at a concentration close to 100% may be supplied, and the reducing agent concentration may be decreased as the second step approaches its end. Furthermore, the concentration of H2 in the reducing gas G2 is preferably a concentration that can convert all of the NOx occluded in the catalytic material Q to NH3. When the alkaline earth metal is Ba, for example, the ratio is 8 mol or more of H2 per 1 mol of Ba(NO3)2 (Ba(NO3)2 + 8H2 → BaO + 2NH3 + 5H2O), and preferably 10 times that amount (80 mol or more) of H2 can be supplied by adjusting the concentration of H2 in the reducing gas G2 and the time for supplying the reducing gas G2.

[0047] Here, it is assumed that the exhaust gas G1 from various facilities is continuously discharged without stopping while the facility (combustor 40) is in operation. Therefore, when NH3 is produced using the exhaust gas G1 as a raw material, it is necessary to continuously supply the exhaust gas G1 to the catalyst material Q without stopping. Therefore, while the exhaust gas G1 is being discharged from the combustor 40 (i.e., while the combustor 40 is in operation), it is preferable that the first step (supply of the exhaust gas G1) is performed in at least one reaction tube out of the N reaction tubes U.

[0048] Hereinafter, an example of a specific configuration for performing the first step in at least one reaction tube U out of the N reaction tubes U will be described.

[0049] For convenience, it is assumed that the second time is twice the first time (for example, the first time is 1 hour and the second time is 2 hours). First, in order to perform the first step in at least one reaction tube U in the repeated production process, the number of reaction tubes (i.e., N) needs to be set according to the first time and the second time.

[0050] Fig. 2 is a table schematically showing the operation of each reaction tube U when the first time is 1 hour, the second time is 2 hours, and there are three reaction tubes U[1] to U[3]. Fig. 2 shows a time series of a unit period T (1 hour).

[0051] As illustrated in FIG. 2, the start time of the production process (first step) is set to be different among the three reaction tubes U[1] to [3], so that one of the three reaction tubes U[1] to [3] performs the first step in turn. For example, the first step of the reaction tube U[2] starts when the first step of the reaction tube U[1] is completed, and the first step of the reaction tube U[3] starts when the first step of the reaction tube U[2] is completed. In this way, there is one reaction tube U that performs the first step among the three reaction tubes U[1] to [3]. Therefore, the exhaust gas G1 continuously discharged from the facility can be continuously supplied to the production apparatus 20.

[0052] The number (N) of the reaction tubes U is set according to the first time and the second time so that the first step is performed in at least one reaction tube U among the N reaction tubes U while the exhaust gas G1 is being discharged from the combustor 40. For example, N is set according to a value obtained by dividing the sum of the first time and the second time by the first time, that is, [(first time + second time) / first time]. In other words, N is set according to the ratio of the first time and the second time (first time:second time). Specifically, N is set to a value equal to or greater than the value obtained by dividing the sum of the first time and the second time by the first time. For example, in the example of FIG. 3, [(first time + second time) / first time] is 3, so N is set to 3. Furthermore, when [(first time + second time) / first time] includes a decimal point (e.g., 2.5), N is set to an integer obtained by rounding up the decimal point (i.e., 3).

[0053] As can be understood from the above description, the number N of the reaction tubes U is set depending on the time for performing the first step and the time for performing the second step, and it is preferable that the first step is performed in at least one reaction tube U among the N reaction tubes U while the exhaust gas G1 is being discharged from the combustor 40.

[0054] In addition, as long as the first step is performed in one reaction tube U while the exhaust gas G1 is being discharged from the combustor 40, for example, a configuration in which the length of the first time (or the second time) is made different among a plurality of reaction tubes U, a configuration in which the length of the first time and the second time is made different for each production process in any one reaction tube U, or a configuration in which the number of reaction tubes U performing the first step per unit period T is made different may also be adopted.

[0055] The following describes the operation of the manufacturing process in the manufacturing apparatus 20 for the unit periods T1 to T3 in Fig. 2. Fig. 3 to Fig. 5 are state diagrams of the manufacturing apparatus 20 for the unit periods T1 to T3.

[0056] 3, in a unit period T1, the first step is carried out in the reaction tube U[1], and the second step is carried out in the reaction tubes U[2] and U[3]. Note that the operations of the first on-off valve V1 and the second on-off valve V2 when the first step and the second step are carried out in each reaction tube U are as described above.

[0057] Specifically, in the unit period T1, the exhaust gas G1 is supplied to the reaction tube U[1], and NOx in the exhaust gas is converted to NO2 - or NO3 - The NOx is occluded (adsorbed) in the catalytic material Q. The exhaust gas G1e after use released from the recovery line R3 has a reduced NOx concentration compared to the exhaust gas G1 (exhaust gas before being supplied to the catalytic material Q) discharged from the combustor 40.

[0058] On the other hand, in the reaction tubes U[2] and U[3], reducing gas G2 is supplied to the catalytic material Q, whereby reduction of NOx progresses in the catalytic material Q where NOx is stored, and NH3 is produced. The produced gas containing NH3 (hereinafter referred to as "produced gas") G2e is recovered from the recovery line R3.

[0059] As shown in FIG. 4, in the unit period T2, the first step is performed in the reaction tube U[2], and the second step is performed in the reaction tubes U[1] and U[3]. As for the reaction tube U[2], by supplying the exhaust gas G1, NOx in the exhaust gas is converted to NO2 -or NO3 - The exhaust gas G1e is then absorbed (adsorbed) into the catalytic material Q. The exhaust gas G1e is then recovered, for example, via a recovery line R3. In the reaction tubes U[1] and U[3], a reducing gas G2 is supplied to the catalytic material Q, whereby the reduction of NOx progresses in the catalytic material Q where NOx has been absorbed, producing NH3. The product gas G2e containing the generated NH3 is then recovered via the recovery line R3.

[0060] As shown in FIG. 5, in the unit period T3, the first step is performed in the reaction tube U[3], and the second step is performed in the reaction tubes U[1] and U[2]. As for the reaction tube U[3], the exhaust gas G1 is supplied, and NOx in the exhaust gas is converted to NO2 - or NO3 - The exhaust gas G1e is then absorbed (adsorbed) into the catalytic material Q. The exhaust gas G1e is then recovered, for example, via a recovery line R3. In the reaction tubes U[1] and U[2], a reducing gas G2 is supplied to the catalytic material Q, whereby the reduction of NOx progresses in the catalytic material Q where NOx has been absorbed, producing NH3. The produced product gas G2e containing the produced NH3 is then recovered via the recovery line R3.

[0061] After the unit period T4, the same operations as those of the manufacturing apparatus 20 in the unit periods T1 to T3 are repeatedly performed in parallel with the discharge of the exhaust gas G1 in the combustor .

[0062] As described above, the exhaust gas G1 is supplied to at least one reaction tube U among the N reaction tubes U, so that the exhaust gas G1 continuously discharged from the combustor 40 can be continuously supplied to the production apparatus 20 without interruption.

[0063] The configuration of the manufacturing apparatus 20 is not limited to the above example. FIG. 6 is a configuration diagram of another embodiment of the manufacturing apparatus 20. For convenience, FIG. 6 illustrates the configuration of the manufacturing apparatus 20 (when N=3) during the unit period T1 in FIG. 2. As illustrated in FIG. 6, the manufacturing apparatus 20 may include, for example, a recovery line R3 for recovering the generated gas G2e containing NH3 and an exhaust line R4 for recovering the used exhaust gas G1e from the reaction tube U, separately for each reaction tube U. Furthermore, the manufacturing apparatus 20 may include, for each reaction tube U, a third on-off valve V3 for opening and closing the recovery line R3 and a fourth on-off valve V4 for opening and closing the exhaust line R4. During the first step, the third on-off valve V3 is closed, and the fourth on-off valve V4 is open. During the second step, the third on-off valve V3 is open, and the fourth on-off valve V4 is closed. The third on-off valve V3 and the fourth on-off valve V4 are switched between open and closed states under the control of the control device 30.

[0064] The catalytic material Q is heated to 200°C or higher and 350°C or lower, preferably 200°C or higher and 300°C or lower, in the first and second steps. In other words, the first and second steps are performed with the catalytic material Q within the above temperature range. By maintaining the catalytic material Q at 200°C or higher and 350°C or lower in both the first and second steps, the efficiency of NH3 production can be improved. When the temperature of the exhaust gas G1 itself from the combustor 40 is within the range of 200°C or higher and 350°C or lower, the catalytic material Q is maintained within the above temperature range by supplying the exhaust gas G1 to the reaction tube U. When temperature control of the catalytic material Q is required, the temperature of the catalytic material Q may be controlled by adjusting the temperature of the exhaust gas G1 or the reducing gas G2, or by heating the reaction tube U.

[0065] The temperature of the catalyst material Q in the first step and the temperature of the catalyst material Q in the second step need only be within the above-mentioned ranges, and do not need to be the same. However, in the first embodiment, it is preferable that the temperature of the catalyst material Q in the first step and the temperature of the catalyst material Q in the second step are substantially the same (the temperature difference between the two is, for example, within a range of ±30°C, preferably within a range of ±10°C). The configuration in which the temperature of the catalyst material Q in the first step and the temperature of the catalyst material Q in the second step are substantially the same has the advantage that the temperature of the catalyst material Q in the first step and the second step does not need to be different.

[0066] <Catalyst materials> The catalyst material will be described in detail below: The catalyst material according to the first embodiment contains one or more alkaline earth metals selected from Ba, Ca, and Sr, platinum, and aluminum oxide (Al2O3).

[0067] It is preferable that the aluminum oxide (alumina) is porous. Specifically, for example, it is more preferable to use particulate porous alumina (mesoporous alumina) having a crystalline structure as the aluminum oxide. Porous alumina is produced by a process described below, in which a precursor solution containing alumina or its hydrate monomer or oligomer species and amphiphilic organic molecules is dried and sintered. During sintering, the amphiphilic organic molecules disappear, resulting in a porous structure with regularly arranged pores. However, the aluminum oxide is not limited to mesoporous alumina.

[0068] The alumina content of the entire catalyst material is, for example, 40% by mass to 99% by mass, preferably 45% by mass to 98% by mass, and more preferably 65% ​​by mass to 95% by mass. Typically, the catalyst material is preferably composed of an alkaline earth metal, platinum, and alumina.

[0069] The average particle size of the platinum contained in the catalytic material is, for example, 0.1 nm to 100 nm, preferably 10 nm to 50 nm. In particular, for NH3 production at a catalytic material temperature in the range of 250°C to 300°C, the average particle size of the platinum is more preferably 17 nm to 30 nm, and particularly preferably 20 nm to 25 nm. Platinum is in the form of nanoparticles, and these nanoparticles are contained in the catalytic material. By setting the average particle size of the platinum and platinum compound within the above range, it is possible to achieve both the oxidation reaction characteristics of the gas being circulated and the durability of the catalyst. Furthermore, by appropriately selecting the average particle size of the platinum and platinum compound within the above range, it is possible to obtain a high NH3 conversion rate within the desired temperature range.

[0070] The average particle size of platinum is the mode diameter determined by measuring the particle sizes of a predetermined number of particles (for example, 100 particles) through observation with a transmission electron microscope.

[0071] The platinum is contained in the catalyst material in a state where it is supported on the surface of alumina or in a state where it is contained inside the alumina. The state where it is contained inside the alumina refers to a state where particulate platinum is enclosed inside spherical particles of alumina to form a composite. From the viewpoint of improving the efficiency of ammonia production, it is preferable that the platinum is contained inside the alumina.

[0072] In the following description, alumina containing platinum inside is referred to as “platinum-containing alumina.” In platinum-containing alumina, platinum nanoparticles are exposed in some parts of the porous structure and embedded in the alumina skeleton in other parts.

[0073] Platinum may be contained in alumina as platinum alone, as a platinum compound containing platinum, or both. In the following description, when "platinum" is used, it includes both platinum alone and platinum in a platinum compound. In addition to platinum, other precious metals (e.g., palladium, rhodium, etc.) may also be contained in the catalyst material.

[0074] The platinum content (platinum element in the catalyst material) is 0.01 to 20 mass % of the entire catalyst material, preferably 0.1 to 10.0 mass %, and more preferably 0.3 to 5.0 mass %. By keeping the platinum content within the above range, it is possible to improve catalytic activity while reducing the amount of expensive platinum used.

[0075] As described above, the alkaline earth metal contained in the catalyst material is one or more selected from Ba, Ca, and Sr. The alkaline earth metal is supported on alumina (or platinum-containing alumina) as, for example, a compound containing the alkaline earth metal (hereinafter referred to as an "alkaline earth metal compound"). Examples of the alkaline earth metal compound include an oxide, peroxide, carbonate, and hydroxide of the alkaline earth metal. However, the alkaline earth metal may also be supported on alumina as a single element.

[0076] From the viewpoint of improving the efficiency of NH production, the alkaline earth metal is preferably contained in the catalyst material in a state supported on platinum-containing alumina. The alkaline earth metal supported on the platinum-containing alumina is coated on the already formed porous structure, and is mainly present on the surfaces of the alumina and platinum.

[0077] The total amount of alkaline earth metals (alkaline earth metal elements in the catalyst material) is 0.1% to 50% by mass, preferably 0.5% to 40% by mass, and more preferably 1% to 30% by mass, of the entire catalyst material. By keeping the alkaline earth metal content within the above range, it is possible to improve the NOx reduction efficiency while maintaining a uniformly arranged pore structure.

[0078] The average particle size of the catalyst material is, for example, 0.01 μm to 500 μm, preferably 0.1 μm to 100 μm, and more preferably 0.5 μm to 50 μm. The average particle size of the catalyst material is the cumulative average particle size (median diameter) on a volume basis measured using a particle size distribution measuring device. However, the catalyst material may also be molded into pellets or coated on a molded body.

[0079] The specific surface area of ​​the catalyst material is, for example, 100 m 2 / g or more 350m 2 / g or less, preferably 120m 2 / g or more 330m 2 / g or less, and more preferably 150m 2 / g or more 300m 2 / g or less. When the specific surface area of ​​the catalyst material is within the above range, for example, the adsorption rate of gases (e.g., nitrogen oxides) is improved. The specific surface area of ​​the catalyst material is measured by the BET multipoint method.

[0080] The mode of the pore size distribution of the catalyst material is, for example, 1 nm to 200 nm, preferably 1 nm to 50 nm, and more preferably 2 nm to 20 nm. When the mode of the pore size distribution of the catalyst material is within the above range, for example, gas can be adsorbed with high efficiency.

[0081] The pore volume of the catalyst material is, for example, 0.2 cm 3 / g or more 1.5cm 3 / g or less, preferably 0.3 cm 3 / g or more 1.2cm 3 / g or less, and more preferably 0.5 cm 3 / g or more 0.9cm 3 When the pore volume of the catalyst material is within the above range, for example, gases can be adsorbed with high efficiency.

[0082] The mode of the pore size distribution in the catalyst material is measured, for example, by the NLDFT method using gas adsorption. The pore volume of the catalyst material is also measured, for example, by gas adsorption.

[0083] When the catalyst material is irradiated with X-rays, at least one of a diffraction peak and a scattering peak corresponding to a lattice spacing of 1 nm to 200 nm is observed. The diffraction peak is measured by X-ray diffraction. The scattering peak is measured by small-angle X-ray scattering. Specifically, in measurements using X-ray diffraction, one or more diffraction peaks corresponding to a lattice spacing of 1 nm to 200 nm are observed, and in measurements using small-angle X-ray scattering, one or more scattering peaks corresponding to a lattice spacing of 1 nm to 200 nm are observed.

[0084] It is desirable to use Fe as the tube that generates the X-rays, as the wavelength of the characteristic X-rays is long and the diffraction or scattering peaks appear at high angles, making them easy to detect, and their intensity is sufficient for the detector, but tubes made of other elements (such as Cu) are also acceptable. The presence of these diffraction and scattering peaks indicates the regular arrangement of pores in the porous structure.

[0085] A catalyst material in which one or more diffraction peaks or scattering peaks corresponding to lattice spacings of 1 nm or more and 200 nm or less are observed can be expected to have a high specific surface area and uniform gas diffusion behavior within the pores due to the presence of a regular arrangement of pores with uniform pore diameters in the porous structure.

[0086] In the present invention, the use of a catalytic material containing one or more alkaline earth metals selected from Ba, Ca, and Sr, platinum, and aluminum oxide can improve the efficiency of NH3 production (particularly in high-temperature environments). In the first embodiment, the use of a catalytic material in which platinum is contained within aluminum oxide and an alkaline earth metal is supported on aluminum oxide containing platinum therein (i.e., platinum-containing alumina) improves the efficiency of NH3 production, particularly in high-temperature environments of 250°C or higher.

[0087] <Method of manufacturing catalyst material> An example of a method for producing a catalytic material will be described. In the following description, a method for producing a catalytic material in which an alkaline earth metal is supported on platinum-containing alumina will be exemplified. In general, the catalytic material is produced by synthesizing porous alumina containing platinum (platinum-containing alumina) and supporting an alkaline earth metal on the platinum-containing alumina.

[0088] <1> Preparation of precursor solution The platinum-containing precursor solution (hereinafter simply referred to as "precursor solution") is a solution containing an alumina source, a platinum source, an amphiphilic organic molecule, an acid, and a solvent.

[0089] The alumina source (aluminum compound) used in the precursor solution is one that becomes a transition alumina (alumina with a crystal structure other than α) such as γ-alumina upon calcination. Specific examples of the alumina source include aluminum hydroxide, aluminum nitrate, aluminum sulfate, aluminum chloride (including hydrates), and aluminum alkoxides, with aluminum alkoxides being preferred. Examples of aluminum alkoxides include aluminum tri-sec-butoxide, aluminum tri-n-butoxide, aluminum tri-tert-butoxide, aluminum tri-isopropoxide, aluminum tri-ethoxide, and aluminum tri-phenoxide. Among these, aluminum chloride (including hydrates), aluminum tri-sec-butoxide, and aluminum tri-n-butoxide are preferred, with aluminum tri-sec-butoxide being particularly preferred, from the standpoints of reactivity to hydrolysis, availability, and raw material cost.

[0090] Examples of platinum sources contained in the precursor solution include platinum oxide, hydroxide, chloride, carbonate, acetate, nitrate, oxalate, phosphate, and chloride complexes.

[0091] Examples of platinum sources that can be used include inorganic platinum compounds such as chloroplatinic acid (including hydrates), dinitrodiammine platinum, hexahydroxyplatinic acid, platinous chloride, platinic chloride, tetraammineplatinum dichloride, potassium tetrachloroplatinate, and potassium hexachloroplatinate, as well as organic platinum compounds such as bis(acetylacetonato)platinum, dichloro(cyclohexane)platinum dimer, dichloro(η-ethylene)Pt dimer, dichloro(η-cycloocta-1,5-diene)platinum, tetrakis(triphenylphosphite)platinum, cis-dichlorobis(triphenylphosphine)platinum, bis(benzonitrile)dichloroplatinum, trans-d-cyclohexanediaminedichloroplatinum, and trans-l-cyclohexanediaminedichloroplatinum. These may be used alone or in combination. Among these, chloroplatinic acid (including hydrate) or bis(acetylacetonato)platinum is particularly preferred from the viewpoint of solubility in the solvent when preparing the precursor solution.

[0092] The amphiphilic organic molecules used in the precursor solution may be one or more of polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymers (trade name: Pluronic (registered trademark)), alkylammonium salts, polystyrene-polyethylene oxide block copolymers, etc. Among these, from the viewpoint of forming a regularly arranged porous structure, at least one of polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymers and polystyrene-polyethylene oxide block copolymers is particularly preferred, with Pluronic P123 and F127 being more preferred.

[0093] The pore size of the resulting platinum-containing alumina varies significantly depending on the type of amphiphilic organic molecule. For example, when a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer is used as the amphiphilic organic molecule, the mode of the pore size distribution is 2 nm to 30 nm. Furthermore, when a polystyrene-polyethylene oxide block copolymer is used as the amphiphilic organic molecule, the mode of the pore size distribution is 25 nm to 200 nm (see Bulletin of the Chemical Society of Japan, 2019, 92, 1859-1866, and Dalton Transactions, 2021, 50, 7191-7197).

[0094] The acid used in the precursor solution may be an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid, or an organic acid such as carboxylic acid or sulfonic acid. Among these, from the viewpoint of forming a regularly arranged porous structure, it is particularly preferable that the precursor solution contains at least one of hydrochloric acid and nitric acid.

[0095] The solvent used in the precursor solution may be alcohol, ether, water, ketone, or the like. In particular, various alcohols, including ethanol, methanol, n-butanol, sec-butanol, tert-butanol, n-propanol, and isopropanol, can be used. Among these, ethanol is particularly preferred from the viewpoint of optimizing the evaporation rate of the solvent to form a regular porous structure.

[0096] The content of the alumina source (aluminum compound) in the precursor solution is 5% by mass or more and 25% by mass or less, preferably 8% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less.

[0097] The content of the platinum source in the precursor solution is 0.01% by mass or more and 0.20% by mass or less, preferably 0.03% by mass or more and 0.20% by mass or less, and more preferably 0.05% by mass or more and 0.10% by mass or less.

[0098] The content of the amphiphilic organic molecules in the precursor solution is 1% by mass to 20% by mass, preferably 2% by mass to 15% by mass, and more preferably 3% by mass to 10% by mass.

[0099] The content of the acid in the precursor solution is 0.1% by mass to 3.0% by mass, preferably 0.3% by mass to 2.0% by mass, and more preferably 0.5% by mass to 1.5% by mass.

[0100] The content of the solvent in the precursor solution is 50% by mass or more and 93% by mass or less, preferably 60% by mass or more and 90% by mass or less, and more preferably 70% by mass or more and 80% by mass or less.

[0101] An example of a specific method for preparing the precursor solution is as follows (1) to (3).

[0102] (1) After adding the amphiphilic organic molecule to a solvent, a platinum source is further added. (2) An aluminum source is added to a solvent to prepare a dispersion. While stirring the dispersion, an acid is added dropwise over a predetermined period of time (e.g., 10 minutes or more). The dispersion is stirred for a predetermined period of time (e.g., 3 hours). (3) The dispersion liquid of (2) is added to the solution prepared in (1) to prepare a precursor solution.

[0103] <2> Synthesis of platinum-containing alumina Examples of methods for synthesizing platinum-containing alumina are as follows (1) and (2).

[0104] (1) First, a precursor (powder) of platinum-containing alumina is recovered from the precursor solution. Specifically, the solvent and water are removed from the precursor solution by drying. The method for drying the precursor solution is not particularly limited, but examples include one or a combination of two or more of any known methods such as spray drying, freeze drying, heat drying, hot air drying, reduced pressure drying, and natural drying. Among these, spray drying is particularly preferred from the viewpoints of productivity and reproducibility. The precursor solution is dried, and a precursor (powder) of platinum-containing alumina is recovered.

[0105] (2) Next, the recovered precursor is calcined to synthesize platinum-containing alumina. Specifically, calcining the precursor removes the amphiphilic organic molecules that formed the pores, resulting in porosity, while also thermally decomposing the platinum source and crystallizing the alumina. The precursor is calcined by holding it at a desired temperature (e.g., 800-900°C) under a nitrogen stream for a predetermined time (e.g., 1-3 hours), and then holding it at that temperature under an oxygen stream for an additional predetermined time (e.g., 2-3 hours). It is preferable to increase the temperature stepwise (e.g., 1-3°C per minute) until the desired temperature is reached under a nitrogen stream.

[0106] <3> Alkaline earth metal loading The synthesized platinum-containing alumina is made to support an alkaline earth metal. Specifically, an alkaline earth metal compound is made to support the platinum-containing alumina. As described above, the alkaline earth metal is one or more selected from Ba, Ca, and Sr.

[0107] To support alkaline earth metals on platinum-containing alumina, compounds containing alkaline earth metals, such as acetates, nitrates, carbonates, hydroxides, halides, oxides, and hydrides (hereinafter referred to as "precursor compounds"), are used. Among these, at least one of acetates and nitrates is preferred from the viewpoints of solubility and thermal decomposition temperature. The precursor compounds are converted into alkaline earth metal compounds by thermal decomposition through heating.

[0108] An example of a method for supporting an alkaline earth metal on platinum-containing alumina is as follows (1) to (3): For example, an alkaline earth metal is supported on platinum-containing alumina by impregnation support.

[0109] (1) Platinum-containing alumina is dispersed in distilled water, and an aqueous solution of the precursor compound is added dropwise while vigorously stirring.

[0110] The aqueous solution of the precursor compound is added dropwise so that the content of alkaline earth metal elements in the catalyst material becomes, for example, 0.1% by mass to 50% by mass, preferably 0.5% by mass to 40% by mass, and more preferably 1% by mass to 30% by mass. By adding the aqueous solution of the precursor compound dropwise so that the content of alkaline earth metal elements falls within the above range, the NOx storage characteristics and reduction efficiency can be improved.

[0111] (2) The dispersion liquid of (1) is heated under reduced pressure to remove the distilled water, thereby obtaining a powder. For example, the distilled water is removed from the dispersion liquid by distillation under reduced pressure at 30 to 80°C.

[0112] (3) The powder obtained in (2) is dried and then calcined to obtain the catalyst material according to the present invention. The powder obtained in (2) is dried, for example, at 80 to 120°C for 6 to 20 hours. The dried powder is calcined, for example, in a tubular furnace at 400 to 700°C for 2 to 5 hours.

[0113] The above-described manufacturing method produces a catalytic material in which an alkaline earth metal is supported on platinum-containing alumina. The manufacturing method according to the present invention has the advantage that the catalytic material can be produced in a short period of time with high productivity, compared to a method in which a precursor solution is spread in a container such as a petri dish and dried at a predetermined temperature for several days.

[0114] When a catalytic material in which an alkaline earth metal is supported on platinum-containing alumina is produced using the above-described production method, the mode in the pore size distribution is 1 nm or more and 200 nm or less in diameter. Furthermore, a catalytic material with a mode in the pore size distribution of 1 nm or more and 200 nm or less can smoothly diffuse and store NOx in the gas phase. Furthermore, the pore size distribution of the catalytic material can be controlled depending on the type of amphiphilic organic molecule selected and the synthesis conditions, and the balance between NOx diffusion in the pores and the specific surface area of ​​the catalytic material can also be adjusted.

[0115] A catalytic material in which an alkaline earth metal is supported on platinum-containing alumina can improve the NOx reduction efficiency while increasing the amount of NOx adsorbed. Furthermore, a catalytic material in which an alkaline earth metal is supported on platinum-containing alumina can maintain a regularly arranged pore structure. Therefore, the specific surface area can be maintained at a high level.

[0116] In the above explanation, a method for producing a catalytic material in which an alkaline earth metal is supported on platinum-containing alumina has been exemplified. However, the catalytic material used in the present invention may be any material as long as it contains platinum, one or more alkaline earth metals selected from Ba, Ca, and Sr, and aluminum oxide. For example, a catalytic material in which platinum and Ba are supported on the surface of alumina may be used. The catalytic material in which an alkaline earth metal and platinum are supported on the surface of alumina may be produced by any method. For example, first, alumina (γ-alumina) and a solution of a platinum compound (e.g., an ethanol solution of chloroplatinic acid hexahydrate) are mixed, evaporated to dryness, and then calcined to produce platinum-supported alumina. Then, an alkaline earth metal is supported on the platinum-supported alumina, thereby producing alumina supporting both platinum and alkaline earth metals. The method for supporting an alkaline earth metal on platinum-supported alumina can be, for example, the above-mentioned " <3> The same method as in "Supporting alkaline earth metals" is adopted.

[0117] The present invention can also be conceived as a method for producing NH3, which includes a production process including: a first step in which exhaust gas discharged from a facility (for example, a high-temperature combustion facility such as a waste incineration facility or a thermal power plant, or a chemical plant) containing NOx and O2 is supplied to the reaction tube, causing the NOx in the exhaust gas to be occluded by the catalytic material, and a second step in which a reducing gas is supplied to the reaction tube after the supply of the exhaust gas is stopped, thereby producing NH3 from the NOx occluded in the catalytic material, for N (N is an integer of 2 or more) reaction tubes, each containing a catalytic material containing one or more alkaline earth metals selected from Ba, Ca, and Sr, platinum, and aluminum oxide; and a second step in which a reducing gas is supplied to the reaction tube after the supply of the exhaust gas is stopped, thereby producing NH3 from the NOx occluded in the catalytic material, the second step being performed for a time period equal to or longer than the time period for which the first step is performed, the reducing gas containing H2, and the temperature of the catalytic material being 200°C or more and 350°C or less in the first and second steps.

[0118] In the first embodiment, the production method and production device described above make it possible to improve the production efficiency of NH3 even in a high-temperature environment when producing NH3 using exhaust gas.

[0119] [Second embodiment] A second embodiment will be described. In the following examples, elements that have the same functions as those in the first embodiment will be designated by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be omitted where appropriate.

[0120] The method for producing NH3 according to the second embodiment includes, in addition to the first and second steps, a third step of recovering NH3 from the product gas G2e containing NH3 produced in the second step.

[0121] FIG. 7 is a configuration diagram illustrating a production unit 100 according to the second embodiment. For convenience, FIG. 7 illustrates a configuration diagram of the production apparatus 20 (when N=3) in the unit period T1 of FIG. 2. As illustrated in FIG. 7, the production unit 100 according to the second embodiment has a configuration in which, for example, a recovery device 60 for recovering NH3 is provided downstream of the production apparatus 20 in the production unit 100 of FIG. 6. The recovery device 60 is connected to, for example, a recovery line R3. Note that, although FIG. 6 illustrates a configuration in which a recovery device 60 is provided for each reaction tube U, a common reaction tube U may be provided for multiple reaction tubes U.

[0122] 1 (configuration in which the used exhaust gas G1e and the generated gas G2e are commonly discharged from the recovery path R3) may also be adopted. However, in the manufacturing unit 100 of the second embodiment, the configuration of the manufacturing apparatus 20 is not limited to the above example.

[0123] Any mechanism for recovering NH3 from the product gas G2e can be used as the recovery device 60. For example, a device that extracts NH3 from the product gas G2e by cooling the product gas G2e using a cooler to liquefy NH3, or an adsorption device that adsorbs only NH3 through a chemical reaction, can be appropriately used as the recovery device 60.

[0124] The NH3 recovered in the third step is used as a resource for various purposes. For example, the recovered NH3 is used for the following purposes 1 and 2.

[0125] (1)Application 1 In the first step, not all of the NOx in the exhaust gas G1 supplied to the reaction tube U may be occluded by the catalytic material Q. That is, the used exhaust gas G1e may contain NOx. Therefore, the NH3 recovered in the third step may be used to purify the NOx in the exhaust gas G1 supplied to the reaction tube U in the first step that was not occluded by the catalytic material Q. In purifying NOx, for example, NH3 is introduced as a reducing agent into an NH3-SCR (Selective Catalytic Reduction) catalyst. For example, the used exhaust gas G1e and the NH3 recovered in the third step are supplied to a purification device containing an NH3-SCR catalyst.

[0126] Furthermore, if the molar ratio (NH3 / NOx) of the NH3 recovered in the third step to the NOx contained in the used exhaust gas G1e is greater than 1, it becomes possible to purify all of the NOx contained in the used exhaust gas G1e with the recovered NH3.

[0127] In application 1, the production unit 100 includes, in addition to the production apparatus 20, the control device 30, and the recovery device 60, a purification device (not shown) for purifying NOx in the used exhaust gas G1e using NH3 produced by the production apparatus 20.

[0128] In application 1, the NH3 produced by the production apparatus 20 can be used to further reduce the concentration of NOx in the exhaust gas G1e after consumption.

[0129] (2)Application 2 A part of the exhaust gas G1 discharged from the combustor 40 may be used to produce NH3 (i.e., supplied to the production apparatus 20), and the remainder of the exhaust gas G1 discharged from the combustor 40 may be purified with the NH3 produced in the production apparatus 20. That is, the NH3 recovered in the third step is used to purify NOx contained in the exhaust gas G1 discharged from the combustor 40 that has not been supplied to the reaction tube U.

[0130] Specifically, the exhaust gas G1 from the combustor 40 is discharged not only through the first common passage K1 but also through one or more other passages (hereinafter referred to as "discharge passages"). Therefore, the exhaust gas G1 discharged through the first common passage K1 is supplied to the production apparatus 20 (reaction tube U) and used to produce NH3. The NH3 produced in the production apparatus 20 is then used to purify NOx in the exhaust gas G1 discharged through a discharge passage (not shown). For example, an NH3-SCR catalyst is used to purify NOx using NH3, as in the case of application 1 described above.

[0131] In Use 2, the production unit 100 includes, in addition to the production apparatus 20, the control device 30, and the recovery device 60, a purification device (not shown) for purifying the exhaust gas G1 discharged from the exhaust path using NH3 produced by the production apparatus 20. The purification device used may be, for example, the same as that in Use 1.

[0132] In application 2, a portion of the exhaust gas G1 discharged from the combustor 40 is used to produce NH3, and the remaining exhaust gas G1 is purified with the produced NH3. Therefore, compared to a configuration in which all of the exhaust gas G1 is used to produce ammonia, it is possible to purify all of the exhaust gas G1 discharged from the combustor 40 while reducing the amount of exhaust gas G1 to be treated by the production apparatus 20.

[0133] [Third embodiment] Here, the gas remaining after NH3 is recovered from the product gas G2e in the third step (hereinafter referred to as "recovered gas") may contain H2 that was not used in the production of NH3 from the reducing gas G2. Therefore, the recovered gas may be supplied to the reaction tube U as the reducing gas G2 in the second step.

[0134] In the above configuration, the production unit 100 further includes a path for returning the recovered gas discharged from the recovery device 60 for recovering NH to the supply device 50. Note that, in the third embodiment as well, the specific configuration of the production device 20 is arbitrary.

[0135] The configuration of the third embodiment has the advantage that H2, which is part of the reducing gas G2 and has not been used to produce NH3, can be reused.

[0136] The production method according to this embodiment may include other steps in addition to the first and second steps. For example, it is also possible to perform a step (hereinafter referred to as the "fourth step") of supplying an inert gas (e.g., N2) to the reaction tube U between the first and second steps. The period between the first and second steps refers to one or both of the following in a repeated production process: after the completion of the first step and before the start of the second step, and after the completion of the second step and before the start of the first step. The time period for which the fourth step is performed is, for example, sufficiently shorter than the time period for which the first step is performed (first time), and is expected to be, for example, approximately 30 seconds to 10 minutes. Because the exhaust gas G1 contains O2 and the reducing gas G2 contains H2, performing the fourth step of supplying an inert gas between the first and second steps has the advantage of improving safety in the production of NH3. [Example]

[0137] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0138] First, the following catalyst materials 1 to 3 were prepared.

[0139] <Catalyst material 1> The catalyst material 1 is a catalyst material in which Ba is supported on platinum-containing porous alumina. The mass ratio of platinum, Ba, and porous alumina (platinum:Ba:porous alumina) is 1:10:100.

[0140] Catalyst material 1 is the following <1> - <3> It was prepared as follows.

[0141] <1> Preparation of platinum-containing alumina precursor solution (1) 15 g of Pluronic P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer) was weighed into a stoppered Erlenmeyer flask, 120 mL of ethanol was added, and 0.135 g of chloroplatinic acid hexahydrate was then added, followed by stirring with a magnetic stirrer and a stirring bar.

[0142] (2) 60 mL of ethanol and 24.6 g of aluminum tri-sec-butoxide were added to a three-neck flask to prepare a dispersion. While continuing to stir the dispersion, concentrated hydrochloric acid (14.5 mL) was added dropwise over 10 minutes, and the mixture was stirred for 3 hours.

[0143] (3) The dispersion liquid of (2) was added to the solution of (1) to prepare a platinum-containing alumina precursor solution.

[0144] <2> Synthesis of platinum-containing alumina (1) The platinum-containing alumina precursor solution was introduced into a spray dryer (Yamato Scientific ADL311), and the precursor solution was sprayed and the water content, including ethanol, was removed by hot air drying. The inlet temperature of the spray dryer was set to 170°C. The platinum-containing alumina precursor was then recovered using a cyclone separator.

[0145] (2) The precursor recovered by the cyclone separator was calcined in a tubular furnace to remove the Pluronic P123 that formed the pores, and to make it porous. The platinum compound (chloroplatinic acid hexahydrate) was thermally decomposed and alumina crystallized. The calcination was carried out by heating the material to 850°C at a rate of 2°C per minute under a nitrogen stream, holding it at that temperature for 1 hour, and then holding it at that temperature for another 2 hours under an oxygen stream.

[0146] <3> Supporting Ba species on platinum-containing alumina

[0147] As described above, Ba is supported on platinum-containing alumina as a barium compound (in catalytic material 1, it is a barium compound generated by thermal decomposition of barium acetate, such as barium carbonate, barium oxide, or barium hydroxide).

[0148] Specifically, the barium compound was supported on the platinum-containing alumina by impregnation.

[0149] (1) Platinum-containing alumina was dispersed in distilled water, and an aqueous solution of barium acetate was added dropwise to the dispersion while vigorously stirring. The barium acetate solution was added dropwise so that the mass ratio of the platinum-containing alumina to Ba in the aqueous solution (platinum-containing alumina:Ba) was 101:10.

[0150] (2) After shaking the dispersion from (1) for 1 hour, the dispersion was transferred to an eggplant-shaped flask, and the distilled water was removed under reduced pressure at 60°C using a rotary evaporator to recover the powder. The powder was further dried at 110°C for 10 hours or more, and then calcined in a tubular furnace at 500°C for 3 hours (heating rate: 10°C per minute, under a dry air stream) to obtain a catalytic material consisting of platinum-containing alumina supported on a barium compound.

[0151] The average particle size of the platinum (nanoparticles) contained in catalyst material 1 was 21 nm. The average particle size of platinum was determined by observation with a transmission electron microscope using a JEOL JEM-2010, measuring the size of platinum nanoparticles at 100 points, and determining the most frequent particle size (mode diameter). Observation with a transmission electron microscope also confirmed that platinum was contained in alumina.

[0152] <Catalyst material 2> The catalyst material 2 is a catalyst material in which Ca species are supported on platinum-containing porous alumina. The mass ratio of platinum, Ca, and porous alumina (platinum:Ca:porous alumina) is 0.96:5.6:100.

[0153] The catalyst material was the same as catalyst material 1, except that an aqueous solution of calcium acetate monohydrate was used instead of the aqueous solution of barium acetate. The aqueous solution of calcium acetate monohydrate was added dropwise so that the mass ratio of platinum-containing alumina to Ca in calcium acetate monohydrate (platinum-containing alumina:Ca) was 100.96:5.6.

[0154] For catalyst material 2, Ca was supported as a calcium compound on platinum-containing alumina by impregnation. Transmission electron microscopy of the resulting catalyst confirmed that platinum was contained in the alumina. The average particle size of the platinum (nanoparticles) contained in catalyst material 2 was 24 nm. The average particle size of platinum was measured using the same method as described above for catalyst material 1.

[0155] The catalyst material 1 and the catalyst material 2 are examples of catalyst materials in which an alkaline earth metal is supported on platinum-containing alumina.

[0156] <Catalyst material 3> The catalyst material was a material in which both platinum (nanoparticles) and Ba species were supported on commercially available gamma alumina (manufactured by Strem Chemicals). The mass ratio of platinum, Ba, and porous alumina (platinum:Ba:porous alumina) was 1:10:100. The catalyst material was prepared as follows (1)-(4).

[0157] (1) Gamma alumina was pretreated in a dry air stream at 500°C for 2 hours. (2) An ethanol solution of chloroplatinic acid hexahydrate was used and mixed with the gamma alumina of (1) and platinum so that the mass ratio was 100:1. (3) After evaporating the ethanol to dryness, the mixture was calcined in a dry air stream at 600°C for 3 hours to prepare platinum-supported gamma alumina. (4) Ba species were supported on the platinum-supported γ-alumina obtained in (3) in the same manner as in catalyst material 1. The mass ratio of platinum-supported γ-alumina to Ba was 101:10.

[0158] The average particle size of the platinum (nanoparticles) contained in the catalyst material 3 was 13 nm. The average particle size of the platinum was measured in the same manner as described above for the catalyst material 1.

[0159] <1> Mode of pore size distribution The mode of the pore size distribution was measured for catalyst materials 1 and 2 (catalysts in which alkaline earth metals are supported on platinum-containing alumina). The samples were heated at 110°C for 6 hours under reduced pressure to remove adsorbed moisture and other substances, and then nitrogen adsorption isotherms were measured using a Quantachrome Autosorb-iQ. The pore size distribution was calculated from the desorption side of the adsorption / desorption isotherm using the BJH (Barrett-Joyner-Halenda) method, and the mode of the pore size distribution was identified.

[0160] <2> X-ray diffraction measurements The samples (catalyst materials 1 and 2) were subjected to X-ray diffraction measurement using a Rigaku RINT 2100 (Fe beam source, scanning angle: 0.6 to 12 degrees, scanning speed: 2 degrees per minute) to confirm whether diffraction peaks corresponding to lattice spacings of 1 nm or more and 200 nm or less could be detected.

[0161] Table 1 shows the mode of the pore size distribution and the lattice spacing indicated by the diffraction peaks obtained by X-ray diffraction measurement.

[0162] [Table 1]

[0163] As can be seen from Table 1, for catalyst materials 1 and 2, the mode of the pore size distribution was in the diameter range of 1 nm to 200 nm, and a diffraction peak corresponding to a lattice spacing of 1 nm to 200 nm was observed. In other words, it was confirmed that catalyst materials 1 and 2 have regularly arranged pores. It is thought that the regularly arranged pores in catalyst materials 1 and 2 are the result of the self-organization of amphiphilic organic molecules that have chemically interacted with the alumina source, followed by the removal of the amphiphilic organic molecules by calcination.

[0164] <3> NH3 production test from nitrogen oxides (NOx) Using the above catalyst material 1-3, a production test of NH3 was carried out using a fixed-bed flow reactor (Examples 1-6). Table 2 shows the conditions of the production test (Examples 1-6) carried out using catalyst material 1-3. The details of the production test for Examples 1-6 are as follows.

[0165] 100 mg of catalyst material (200 mg in Example 6) was placed inside a quartz reaction tube, and both ends were fixed with quartz wool. Throughout the test, the gas flow rate was fixed at 100 mL / min (50 mL / min in Example 6). The specific test method is as follows.

[0166] In the pretreatment step, the catalyst material was heated to 300°C and held in a nitrogen gas stream containing 1% H2 for 1 hour. Next, in the NOx adsorption step, the catalyst material was heated to the catalyst temperature shown in Table 2 and held in a nitrogen gas stream (simulated exhaust gas) containing 1000 ppm NO and 10% O2 for the first step time shown in Table 2, thereby occluding NO in the catalyst material (first step). Then, the catalyst material was held in a nitrogen gas stream containing H2 at the concentration shown in Table 2 for the second step time shown in Table 2 to produce NH3 (second step).

[0167] In the second and subsequent tests, the pretreatment process was not performed, and only the NOx adsorption process and NH3 production process were repeated three or more times. The amount of NOx adsorption and the amount of NH3 produced were quantified using a Thermo Fisher Scientific Nicolet iS 20 infrared spectrophotometer and a PIKE Technologies multi-reflection gas cell.

[0168] Table 2 shows the results from the third run onwards when the NH3 production test from NOx was repeated three or more times, including the amount of NOx adsorbed, the amount of NH3 produced from NOx, the amount of N2O produced, the NH3 conversion rate (amount of NH3 produced / amount of NOx adsorbed), and the maximum NH3 concentration. Note that the amount of NOx adsorbed and the amount of NH3 produced per mass were calculated from the catalyst weight after the NH3 production test.

[0169] [Table 2]

[0170] As shown in Examples 1-6, an NH3 conversion rate of 70% or more was achieved at 200 to 350°C. Examples 1 and 2 showed that the NH3 conversion rate was higher when the H2 concentration in the reducing gas was 5% than when it was 1%. Furthermore, in Examples 1-6, no generation of N2O, a greenhouse gas (whose greenhouse effect is about 300 times that of CO2), was confirmed.

[0171] As can be understood from the above explanation, it has been confirmed that the efficiency of NH3 production is good when the time for which the second step of producing NH3 is carried out is longer than the time for which the first step of absorbing NOx is carried out, a reducing gas containing H2 is used, and the temperature of the catalyst material is 200°C or higher and 350°C or lower in the first and second steps.

[0172] Fig. 8 is a graph showing the relationship between the average particle size of platinum used in the catalyst material and the NH3 conversion rate for each temperature of the catalyst material. Specifically, Fig. 8 shows the NH3 conversion rate versus the average particle size of platinum when an NH3 production test was conducted using catalyst materials (catalyst materials 1, 2, and 3) with different average platinum particle sizes under the same conditions as in Examples 1-3 (except that 1% H2 was used as the reducing agent and the catalyst temperature was changed from 200°C to 300°C).

[0173] Figure 8 shows that catalytic material 3, with an average particle size of 13 nm, at 200°C, catalytic material 1, with an average particle size of 21 nm, and catalytic material 2, with an average particle size of 24 nm, achieved high NH conversion rates at 200°C, 250°C, and 300°C, respectively. This finding suggests that increasing the average platinum particle size increases the NH conversion rate at higher temperatures. Thus, for NH production at catalytic material temperatures between 200°C and 350°C, an average platinum particle size of 10 nm to 50 nm is preferred. For NH production at catalytic material temperatures between 250°C and 300°C, an average platinum particle size of 17 nm to 30 nm is more preferred, with an average platinum particle size of 20 nm to 25 nm being particularly preferred. It was confirmed that by appropriately using catalytic materials with different average platinum particle sizes, high NH conversion rates can be achieved even at catalytic material temperatures above 200°C.

[0174] In addition, although Non-Patent Documents 1 and 2 do not use exhaust gas (they use NO generated by plasma oxidation), the NH3 production efficiency is 80% at 175°C, but gradually decreases above 200°C, dropping to 20% at 300°C. In other words, Non-Patent Documents 1 and 2 not only require a device for producing NO separate from the NH3 production device, but are also difficult to use in high-temperature environments such as those using exhaust gas. If used in a high-temperature environment, temperature control becomes necessary, and it can be said that more energy is required to produce NH3 than in the present invention. [Explanation of symbols]

[0175] 20: Manufacturing equipment 30: Control device 40: Combustor 50:Supplier 60: Recovery device 100: Manufacturing units G1: Exhaust gas G1e: Post-use exhaust gas G2: Reducing gas G2e: Produced gas K1: 1st common road K2: 2nd common road Q: Catalyst material R1: 1st supply path R2: 2nd supply path R3: Recovery route R4: Exhaust duct U: Reaction tube V1: First shut-off valve V2: Second shut-off valve V3: Third shut-off valve V4: 4th shut-off valve

Claims

1. NH ３ A method for producing One or more alkaline earth metals selected from barium (Ba), calcium (Ca) and strontium (Sr), platinum and aluminum oxide (Al ２ O ３ For each of N (N is an integer of 2 or more) reaction tubes each containing a catalyst material including NOx and O ２ a first step of supplying an exhaust gas containing the above to the reaction tube, thereby causing the NOx in the exhaust gas to be occluded by the catalytic material; After the supply of the exhaust gas is stopped, a reducing gas is supplied to the reaction tube, whereby NH is converted from NOx stored in the catalytic material. ３ and a second step of producing The time for which the second step is performed is equal to or longer than the time for which the first step is performed, The reducing gas is H ２ Including, The temperature of the catalyst material is 200° C. or higher and 350° C. or lower in the first step and the second step. Manufacturing method.

2. The first step is completed when the concentration of NOx in the gas released from the reaction tube is 50% or less of the concentration of NOx in the exhaust gas supplied to the reaction tube. The method of claim 1.

3. NH produced in the second step ３ From the product gas containing NH ３ and a third step of recovering The method of claim 1.

4. NH recovered in the third step ３ is used to purify the NOx in the exhaust gas supplied to the reaction tube in the first step that has not been occluded in the catalytic material. The method of claim 3.

5. NH recovered in the third step ３ is used to purify NOx contained in the exhaust gas discharged from the facility that has not been supplied to the reaction tube. The method of claim 3.

6. In the third step, NH ３ The recovered gas after recovering NH ３ H that was not used in the production of ２ Including, The recovered gas is supplied to the reaction tube as the reducing gas in the second step. The method of claim 3.

7. N in the N number is set according to the time during which the first step is performed and the time during which the second step is performed, While exhaust gas is being discharged from the facility, the first step is carried out in at least one reaction tube out of the N reaction tubes. The method of claim 1.

8. The aluminum oxide is porous, the mode of the pore size distribution in the catalyst material is a diameter of 1 nm or more and 200 nm or less; The average particle size of the platinum is 10 nm or more and 50 nm or less. The method of claim 1.

9. The aluminum oxide is porous, The platinum is contained within the aluminum oxide, The alkaline earth metal is supported on the aluminum oxide containing the platinum therein. The method of claim 1.

10. Between the first step and the second step, a step of supplying an inert gas to the reaction tube is included. The method of claim 1.

11. NH ３ A unit for manufacturing One or more alkaline earth metals selected from barium (Ba), calcium (Ca) and strontium (Sr), platinum and aluminum oxide (Al ２ O ３ N (N is an integer of 2 or more) reaction tubes each containing a catalyst material including N first supply passages for supplying an exhaust gas discharged from a facility and containing NOx and oxygen to the N reaction tubes, respectively; a manufacturing apparatus having N second supply passages for supplying a reducing gas to the N reaction tubes, respectively; a control device that controls the manufacturing device; a supplier for supplying the reducing gas to each of the N reaction tubes through the second supply line, The control device For each of the N reaction tubes, a first step of supplying the exhaust gas to the reaction tube to cause the catalytic material to occlude NOx in the exhaust gas; After the supply of the exhaust gas is stopped, the reducing gas is supplied to the reaction tube, whereby NH is converted from NOx occluded in the catalytic material. ３ and a second step of generating and recovering the The time for which the second step is performed is equal to or longer than the time for which the first step is performed, The reducing gas is H ２ Including, The temperature of the catalyst material is 200° C. or higher and 350° C. or lower in the first step and the second step. Manufacturing unit.

12. NH produced in the second step ３ From the product gas containing NH ３ A recovery device is provided for recovering the 12. The manufacturing unit of claim 11.

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