Ammonia decomposition device and hydrogen production method

Abstract

To provide an ammonia decomposition device that is capable of decomposing ammonia by efficiently transmitting heat produced from an oxidation catalyst to a decomposition catalyst, as well as a hydrogen production method.SOLUTION: An ammonia decomposition device 10 supplies a raw material gas containing ammonia and oxygen, decomposes ammonia, and produces hydrogen. The ammonia decomposition device includes a reaction part 11 with a flow path 11A to which the raw material gas is supplied, and a catalyst layer 12 containing a catalyst disposed in the flow path 11A. The catalyst layer 12 includes at least two oxidation catalyst layers 12A containing an oxidation catalyst for ammonia decomposition, and at least one decomposition catalyst layer 12B containing a decomposition catalyst for ammonia decomposition, arranged alternately and continuously in this order from the upstream side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ammonia decomposition apparatus for producing hydrogen (H2) by decomposing ammonia (NH3), and a hydrogen production method. [Background technology]

[0002] Ammonia produced using a process that does not emit carbon dioxide (CO2) (known as blue ammonia) is expected to be a decarbonized fuel and hydrogen carrier that can be implemented in society at an early stage. However, when using ammonia as fuel, there are fundamental issues, such as its difficulty in igniting and its extremely slow burning speed. This issue can be resolved by reforming ammonia with a catalyst to produce an ammonia-hydrogen mixed fuel. For example, a mixed gas of 50% ammonia and 50% hydrogen has the same burning speed as methane, improving ignition and combustibility.

[0003] However, the thermal decomposition of ammonia is an endothermic reaction and requires heating. For example, heating with an electric heater is possible, but there are issues such as the need to consider carbon dioxide generated by electricity, the large heat loss, the large power consumption, and the low energy efficiency of mixed gas production.

[0004] Thus, an autothermal reformer (ATR) that burns a portion of ammonia and uses the combustion heat has been known (see, for example, Patent Document 1). Patent Document 1 describes the use of an oxidation catalyst (combustion catalyst) that has the function of burning ammonia and a decomposition catalyst that has the function of decomposing ammonia, in which the decomposition catalyst is packed behind the oxidation catalyst in the reaction gas flow, and the heat generated by the combustion of ammonia is used to decompose the ammonia. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-64282 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, since the decomposition catalyst is simply packed behind the oxidation catalyst (combustion catalyst), there is a problem in that the heat generated by the oxidation catalyst cannot be efficiently transferred to the decomposition catalyst.

[0007] The present invention has been made in light of the above problems, and has an object to provide an ammonia decomposition apparatus and a hydrogen production method capable of efficiently transferring heat generated in an oxidation catalyst to a decomposition catalyst to decompose ammonia. [Means for solving the problem]

[0008] The ammonia decomposition apparatus of the present invention supplies a raw material gas containing ammonia (NH3) and oxygen (O2) and decomposes the ammonia to produce hydrogen (H2). The apparatus comprises a reaction section having a flow path through which the raw material gas is supplied, and a catalyst layer containing a catalyst provided in the flow path. The catalyst layer has two or more oxidation catalyst layers containing an oxidation catalyst that oxidizes ammonia and one or more decomposition catalyst layers containing a decomposition catalyst that decomposes ammonia, arranged alternately in this order from the upstream side.

[0009] The hydrogen production method of the present invention produces hydrogen by supplying a raw material gas containing ammonia and oxygen and decomposing the ammonia. The raw material gas is passed through a catalyst layer having two or more oxidation catalyst layers containing an oxidation catalyst that oxidizes ammonia and one or more decomposition catalyst layers containing a decomposition catalyst that decomposes ammonia, in this order from the upstream side, in an alternating manner, whereby ammonia is oxidized by the oxidation catalyst and the heat generated by the oxidation of ammonia is utilized to decompose the ammonia using the decomposition catalyst to produce hydrogen. Effect of the Invention

[0010] According to the present invention, the oxidation catalyst layer and the decomposition catalyst layer are alternately arranged in this order from the upstream side, with two or more oxidation catalyst layers and one or more decomposition catalyst layers. This allows the heat generated in the oxidation catalyst layer to be efficiently transferred to the decomposition catalyst layer, thereby increasing the ammonia decomposition rate. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of an ammonia decomposition device according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing a modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] Fig. 1 shows the configuration of an ammonia decomposition apparatus 10 according to one embodiment of the present invention. Fig. 2 shows a modified example of the ammonia decomposition apparatus 10. This ammonia decomposition apparatus 10 is supplied with a raw material gas containing ammonia and oxygen, and decomposes the ammonia to produce hydrogen, and includes a reaction section 11 having a flow path 11A to which the raw material gas is supplied, and a catalyst layer 12 containing a catalyst provided in the flow path 11A.

[0014] The catalyst layer 12 has an oxidation catalyst layer 12A containing an oxidation catalyst that oxidizes ammonia, and a decomposition catalyst layer 12B containing a decomposition catalyst that decomposes ammonia. The amount of heat required for the decomposition of ammonia in the decomposition catalyst layer 12B is supplied by the combustion of ammonia in the oxidation catalyst layer 12A. The exothermic oxidation reaction of ammonia is shown in formula (1), and the endothermic decomposition reaction of ammonia is shown in formula (2). Exothermic oxidation reaction: NH3+(3 / 4)O2→ 0.5N2+1.5H2O-316.6kJ / mol (1) Endothermic decomposition reaction: NH3 → 0.5N2+1.5H2+46.1kJ / mol (2) From the above formulas (1) and (2), the amount of heat required for decomposition can be supplied by burning (46.1 / 316.6) x 100 = 14.6% of ammonia.

[0015] The catalyst layer 12 has two or more oxidation catalyst layers 12A and one or more decomposition catalyst layers 12B alternately arranged in this order from the upstream side. That is, the catalyst layer 12 has at least a first oxidation catalyst layer 12A, a first decomposition catalyst layer 12B, and a second oxidation catalyst layer 12A arranged in this order from the upstream side. "Continuously" means that the oxidation catalyst layer 12A and the decomposition catalyst layer 12B are in contact with each other.

[0016] The reason why the oxidation catalyst layer 12A is provided continuously (i.e., in contact) on the upstream and downstream sides of the decomposition catalyst layer 12B in this manner is as follows. For example, if the oxidation catalyst layer 12A is provided only on the upstream side of the decomposition catalyst layer 12B, an intense exothermic oxidation reaction occurs on the upstream side of the oxidation catalyst layer 12A, and heat is efficiently transferred to the upstream part of the decomposition catalyst layer 12B located downstream of the oxidation catalyst layer 12A, but heat is not transferred to the downstream part of the decomposition catalyst 12B. Also, for example, if the oxidation catalyst layer 12A is provided only on the downstream side of the decomposition catalyst layer 12B, an intense exothermic oxidation reaction occurs on the upstream side of the oxidation catalyst layer 12A, and heat can be efficiently transferred to the downstream part of the decomposition catalyst layer 12B, but heat is not transferred to the upstream part of the decomposition catalyst 12B. Therefore, in this ammonia decomposition device 10, the oxidation catalyst layer 12A is provided on the upstream and downstream sides of the decomposition catalyst layer 12B, so that the heat generated in the oxidation catalyst layer 12A can be efficiently transferred to the entire decomposition catalyst layer 12B.

[0017] The catalyst layer 12 may have the first oxidation catalyst layer 12A, the first decomposition catalyst layer 12B, and the second oxidation catalyst layer 12A in sequence from the upstream side. For example, a decomposition catalyst layer 12B may be provided downstream of the second oxidation catalyst layer 12A. In addition, one or more decomposition catalyst layers 12B and oxidation catalyst layers 12A may be provided alternately and continuously downstream of the second oxidation catalyst layer 12A. In addition, one or more decomposition catalyst layers 12B and oxidation catalyst layers 12A may be provided alternately and continuously, and one decomposition catalyst layer 12B may be provided downstream of the decomposition catalyst layers 12B and oxidation catalyst layers 12A. In this way, the layer located at the most downstream side downstream of the second oxidation catalyst layer 12A may be the decomposition catalyst layer 12B. This is because the generated mixed gas is at a sufficient temperature due to the heat generated in the oxidation catalyst layer 12A. In addition, heat may be supplied supplementarily by a heating means 13 described later, if necessary.

[0018] The amount of oxidation catalyst in the catalyst layer 12 is preferably in the range of 1 to 1.5 times the minimum amount required to supply the amount of heat required for decomposition of ammonia by oxidation of ammonia, more preferably in the range of 1 to 1.3 times the minimum amount, and even more preferably in the range of 1.1 to 1.2 times the minimum amount. The amount of oxidation catalyst may be greater than this, but if the thickness of the oxidation catalyst layer 12A becomes thicker, the amount of heat transferred to the decomposition catalyst layer 12B decreases, reducing efficiency, and more oxidation catalyst than necessary is wasteful. The amount of oxidation catalyst in the catalyst layer 12 is the total amount of oxidation catalyst contained in the multiple oxidation catalyst layers 12A provided in the catalyst layer 12.

[0019] For example, when 1.0 mol of ammonia is supplied, the amount of oxidation catalyst in the catalyst layer 12 is preferably within a range of 1 to 1.5 times, more preferably 1 to 1.3 times, and even more preferably 1.1 to 1.2 times the minimum amount of oxidation catalyst capable of oxidizing 1.0 x 0.146 = 0.146 mol of ammonia. When the oxidation catalyst layer 12A has two layers, it is preferable to arrange them, for example, half on the upstream side and half on the downstream side. The minimum amount of oxidation catalyst can be determined by a simple experiment.

[0020] In addition, when 1.0 mol of ammonia is supplied, the minimum amount of decomposition catalyst in the catalyst layer 12 is, for example, an amount that can decompose 1.0-1.0×0.146=0.854 mol of ammonia at atmospheric pressure and 500° C. The amount of decomposition catalyst may be more than the minimum amount necessary to decompose ammonia that can be decomposed by the amount of heat supplied by the oxidation of ammonia, but it is preferable to set it within a range of 1 to 1.5 times, further 1 to 1.3 times, and further 1.1 to 1.2 times the minimum amount. This is because if the decomposition catalyst is used more than necessary, it will be wasted. The minimum amount of decomposition catalyst can be obtained by a simple experiment.

[0021] The oxidation catalyst is not particularly limited, and examples thereof include vanadium oxide, tungsten oxide, molybdenum oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, perovskite oxide, palladium (Pd), and platinum (Pt). Noble metals such as palladium and platinum can also be used by supporting them on a support having a high specific surface area such as alumina, silica, zirconia, titania, and zeolite. The oxidation catalyst may be used alone or in combination of two or more.

[0022] The decomposition catalyst is not particularly limited, and examples thereof include transition metals such as iron (Fe), cobalt (Co), nickel (Ni), and molybdenum (Mo), rare earths such as lanthanum (La), cerium (Ce), and neodymium (Nd), and ruthenium (Ru). Transition metals can be used as alloys, nitrides, carbides, oxides, and composite oxides, and rare earths can be used as oxides. All of these can be supported on a support having a high specific surface area such as alumina, silica, zirconia, titania, and zeolite. The decomposition catalyst may be used alone or in combination of two or more.

[0023] The oxidation catalyst and the decomposition catalyst can be prepared by a general preparation method. The oxidation catalyst and the decomposition catalyst may be in the form of spherical particles or pellets formed from particles, or may be supported on a honeycomb made of cordierite or stainless steel.

[0024] The raw gas supplied to the reaction section 11 may contain one or more other gases in addition to ammonia and oxygen. Examples of the other gases include hydrogen and a gas inert to the reaction (such as nitrogen (N2)). If hydrogen is added to the raw gas, the temperature of the raw gas can be increased to a temperature at which oxidation of ammonia begins by burning hydrogen, so that ammonia can be decomposed without using a heating means. The oxygen may be mixed into the raw gas, or air may be mixed. When oxygen is mixed, for example, (3 / 4)×0.146=0.11 mol is supplied to 1.0 mol of ammonia, and when air is mixed, for example, 0.11 / 0.21=0.52 mol is supplied to 1.0 mol of ammonia, which is the stoichiometric value of formula (1).

[0025] The ammonia decomposition apparatus 10 may also include a heating means 13 for heating the catalyst layer 12. This is for heating the catalyst layer 12 to a temperature at which oxidation of ammonia begins. The heating temperature varies depending on the type of oxidation catalyst, and is, for example, 150° C. when platinum is used as the oxidation catalyst. When hydrogen is added to the raw material gas, the heating means 13 does not need to be provided, and when the heating means 13 is provided, hydrogen does not need to be added to the raw material gas. The heating means 13 is, for example, an electric heater, and is preferably provided so as to cover the periphery of the reaction section 11 in correspondence with the catalyst layer 12.

[0026] The ammonia decomposition apparatus 10 further includes a gas supplying means 14 such as a pipe for supplying a raw gas (e.g., ammonia and air) to the reaction section 11, and a gas recovery means 15 such as a pipe for recovering the product mixed gas generated in the reaction section 11. The gas supplying means 14 may be provided with, for example, a heat exchanger 16 for exchanging heat between the product mixed gas and the raw gas. This is to preheat the raw gas by utilizing the heat of the product mixed gas. In addition, for example, as shown as a modified example in FIG. 2, a product mixed gas adding means 17 such as a pipe for adding a part of the product mixed gas to the raw gas may be provided, and a part of the product mixed gas may be reused to add hydrogen to the raw gas.

[0027] Using this ammonia decomposition apparatus 10, hydrogen can be produced as follows. First, for example, the catalyst layer 12 is heated by the heating means 13 to a temperature at which oxidation of ammonia begins. Next, the raw material gas is adjusted and flowed into the catalyst layer 12. As a result, ammonia is burned in the oxidation catalyst layer 12A to generate heat, and this heat is used to decompose ammonia in the decomposition catalyst layer 12B. In this ammonia decomposition apparatus 10, the oxidation catalyst layer 12A and the decomposition catalyst layer 12B are alternately arranged in succession from the upstream side, with two or more oxidation catalyst layers 12A and one or more decomposition catalyst layers 12B, so that the heat generated in the oxidation catalyst layer 12A is efficiently transferred to the decomposition catalyst layer 12B.

[0028] In the reaction section 11, a product mixed gas containing, for example, hydrogen, nitrogen, and ammonia is generated by decomposition of ammonia. Since the temperature of this product mixed gas is high, for example, 400° C., it is preferable to introduce the product mixed gas into the heat exchanger 16 and exchange heat with the raw material gas to preheat the raw material gas. In addition, it is preferable to measure the temperature of the decomposition catalyst layer 12B and the hydrogen concentration at the outlet of the reaction section 11, and adjust the output of the heating means 13 so as to achieve a desired hydrogen concentration. In addition, when hydrogen is added to the raw material gas, it is not necessary to heat it with the heating means 13. In addition, as shown in the modified example of FIG. 2, a part of the product mixed gas may be added to the raw material gas. It is preferable to stop adding the product mixed gas to the raw material gas when the hydrogen concentration at the outlet of the reaction section 11 reaches a desired value.

[0029] As described above, according to this embodiment, the oxidation catalyst layer 12A and the decomposition catalyst layer 12B are provided alternately in this order from the upstream side, with two or more oxidation catalyst layers 12A and one or more decomposition catalyst layers 12B. Therefore, the heat generated in the oxidation catalyst layer 12A can be efficiently transferred to the decomposition catalyst layer 12B, and the ammonia decomposition rate can be increased with minimal energy consumption.

[0030] In addition, the calorific value of hydrogen obtained from 1 mol of ammonia and the amount of carbon dioxide discharged from the electric heater, which is the heating means 13, when decomposing 1 mol of ammonia, were compared between the case where ammonia is decomposed according to this embodiment and the case where ammonia is decomposed only by the decomposition catalyst layer 12B without providing the oxidation catalyst layer 12A. In this embodiment, the calorific value of hydrogen obtained from 1 mol of ammonia is 310 kJ / mol-NH3, whereas in the case where ammonia is decomposed only by the decomposition catalyst layer 12B, 550°C is required to obtain an ammonia decomposition rate of 99%, and the calorific value of hydrogen obtained from 1 mol of ammonia is 284 kJ / mol-NH3. That is, according to this embodiment, the efficiency can be improved by about 10% compared to the case where only the decomposition catalyst layer 12B is used. Also, the amount of carbon dioxide discharged from the electric heater when decomposing 1 mol of ammonia is 2 g in this embodiment, whereas it is 256 g in the case where only the decomposition catalyst layer 12B is used, and thus can be significantly reduced according to this embodiment. EXAMPLES

[0031] Example 1 Ammonia was decomposed using the ammonia decomposition apparatus 10 shown in FIG. 1. The flow path 11A was provided with a first oxidation catalyst layer 12A of 15 cm length in the following order from the upstream side. 3 , the first decomposition catalyst layer 12B is 20 cm 3 The second oxidation catalyst layer 12A is 10 cm 3The oxidation catalyst layer 12A was filled. That is, the oxidation catalyst layer 12A was provided on the upstream side and downstream side of the single decomposition catalyst layer 12B in succession. Platinum was used as the oxidation catalyst, and ruthenium was used as the decomposition catalyst. The total amount of oxidation catalyst in the oxidation catalyst layer 12A was 2.8 times the minimum amount required to supply the heat required for the decomposition of ammonia by the oxidation of ammonia. The raw material gas was a mixed gas of 12 vol% ammonia, 6 vol% oxygen, 4 vol% hydrogen, and 78 vol% nitrogen, and was flowed through the flow path 11A at a flow rate of 3.2 L / min. The heating means 13 was not used, and the temperature of the raw material gas was raised to a temperature at which the oxidation of ammonia began by the combustion of hydrogen. The temperature of the decomposition catalyst layer 12B during ammonia decomposition was 450°C, and the decomposition rate of ammonia was 49%. The results are shown in Table 1.

[0032] Example 2 The filling volume of the first and second oxidation catalyst layers 12A is 5 cm 3 Ammonia was decomposed in the same manner as in Example 1, except that the amount of oxidation catalyst in the oxidation catalyst layer 12A was changed to 1.1 times the minimum amount required to supply the amount of heat required for the decomposition of ammonia by the oxidation of ammonia. The temperature of the decomposition catalyst layer 12B during ammonia decomposition was 500°C, and the decomposition rate of ammonia was 99%. The results are also shown in Table 1.

[0033] Comparative Example 1 The oxidation catalyst layer 12A was not provided downstream of the decomposition catalyst layer 12B, and the filling volume of the oxidation catalyst layer 12A on the upstream side was set to 20 cm 3 Ammonia was decomposed in the same manner as in Example 1, except that the above was changed to the above. That is, the oxidation catalyst layer 12A and the decomposition catalyst layer 12B were packed in this order from the upstream side of the flow path 11A. The temperature of the decomposition catalyst layer 12B during ammonia decomposition was 320°C, and the decomposition rate of ammonia was 10%. The results are also shown in Table 1.

[0034] Comparative Example 2 The oxidation catalyst layer 12A was not provided upstream of the decomposition catalyst layer 12B, and the filling volume of the oxidation catalyst layer 12A on the downstream side was set to 20 cm 3Ammonia was decomposed in the same manner as in Example 1, except that the above was changed to the above. That is, the decomposition catalyst layer 12B and the oxidation catalyst layer 12A were packed in this order from the upstream side of the flow path 11A. The temperature of the decomposition catalyst layer 12B during ammonia decomposition was 500°C, and the decomposition rate of ammonia was 28%. The results are also shown in Table 1.

[0035] [Table 1]

[0036] As shown in Table 1, this embodiment was able to improve the ammonia decomposition rate compared to the comparative example. That is, it was found that by providing the oxidation catalyst layer 12A and the decomposition catalyst layer 12B alternately and continuously in this order from the upstream side, with two or more oxidation catalyst layers 12A and one or more decomposition catalyst layers 12B, the heat generated in the oxidation catalyst layer 12A can be efficiently transferred to the decomposition catalyst layer 12B, and the ammonia decomposition rate can be increased.

[0037] Furthermore, the temperature of the decomposition catalyst layer 12B was higher in Example 2 than in Example 1, and the decomposition rate of ammonia was significantly improved. This is believed to be because the heat generated in the oxidation catalyst layer 12A can be more efficiently transferred to the decomposition catalyst layer 12B by using an appropriate amount of oxidation catalyst. Therefore, it was found that it is preferable to set the amount of oxidation catalyst in the catalyst layer 12 within a range of 1 to 1.5 times the minimum amount required to supply the amount of heat required for the decomposition of ammonia by the oxidation of ammonia.

[0038] Although the present invention has been described above with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples and can be modified in various ways. For example, in Figs. 1 and 2 and Examples 1 and 2, a case where the first oxidation catalyst layer 12A, the first decomposition catalyst layer 12B, and the second oxidation catalyst layer 12A are successively provided in the catalyst layer 12 from the upstream side is specifically described, but the present invention also includes a case where the second decomposition catalyst layer is successively provided downstream of the second oxidation catalyst layer 12A. If the second decomposition catalyst layer is supplementarily heated by the heating means 13, the decomposition rate is considered to reach 99.8%, and the supplementary temperature of the heating means 13 is estimated to be about 450°C.

[0039] Furthermore, the present invention also includes a case in which a second decomposition catalyst layer and a third oxidation catalyst layer are provided in succession downstream of the first oxidation catalyst layer 12A, the first decomposition catalyst layer 12B, and the second oxidation catalyst layer 12A. Even with this configuration, the same effects can be obtained because the oxidation catalyst layers 12A are provided in succession upstream and downstream of the decomposition catalyst layer 12B, as described in the above embodiment and example.

[0040] In addition, the present invention also includes cases in which the decomposition catalyst layers and oxidation catalyst layers are arranged alternately and consecutively, such as when the second decomposition catalyst layer, the third oxidation catalyst layer, and the third decomposition catalyst layer are arranged in succession downstream of the first oxidation catalyst layer 12A, the first decomposition catalyst layer 12B, and the second oxidation catalyst layer 12A, or when the second decomposition catalyst layer, the third oxidation catalyst layer, the third decomposition catalyst layer, and the fourth oxidation catalyst layer are arranged in succession. [Explanation of symbols]

[0041] 10... ammonia decomposition device, 11... reaction section, 11A... flow path, 12... catalyst layer, 12A... oxidation catalyst layer, 12B... decomposition catalyst layer, 13... heating means, 14... gas supply means, 15... gas recovery means, 16... heat exchanger, 17... product mixed gas adding means

Claims

1. An ammonia decomposition apparatus that supplies a raw material gas containing ammonia and oxygen, and decomposes the ammonia to produce hydrogen, a reaction section having a flow path through which the raw material gas is supplied, and a catalyst layer including a catalyst provided in the flow path, The catalyst layer includes an oxidation catalyst layer containing an oxidation catalyst that oxidizes ammonia and a decomposition catalyst layer containing a decomposition catalyst that decomposes ammonia, the oxidation catalyst layer having two or more layers and the decomposition catalyst layer having one or more layers being alternately arranged in this order from the upstream side. An ammonia decomposition apparatus comprising:

2. 2. The ammonia decomposition apparatus according to claim 1, wherein the amount of the oxidation catalyst in the catalyst layer is within a range of 1 to 1.5 times the minimum amount required to supply the amount of heat required for decomposing ammonia by oxidation of ammonia.

3. A hydrogen production method comprising: supplying a raw material gas containing ammonia and oxygen, and producing hydrogen by decomposing the ammonia, the method comprising the steps of: The raw material gas is passed through a catalyst layer in which an oxidation catalyst layer containing an oxidation catalyst that oxidizes ammonia and a decomposition catalyst layer containing a decomposition catalyst that decomposes ammonia are provided alternately and continuously in this order from the upstream side, and the oxidation catalyst layer has two or more layers and the decomposition catalyst layer has one or more layers. This causes ammonia to be oxidized by the oxidation catalyst, and the heat generated by the oxidation of ammonia is utilized to decompose ammonia by the decomposition catalyst to produce hydrogen. A method for producing hydrogen.

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