Reactor for decomposing NH3 at high temperatures

Abstract

The present invention relates to a reactor and reactor components having good resistance to NH3, N2, and optionally H2O at high temperatures and average pressures, so that they can be used during the catalytic decomposition of NH3 into N2 and H2 on a large scale.

Description

[Technical Field]

[0001] Priority is claimed from Luxembourg Patent Application No. LU103141 dated June 5, 2023.

[0002] The present invention relates to reactors and reactor components that have good resistance to NH3, N2, and possibly H2O at high temperatures and moderate pressures, and therefore can be used for catalytic decomposition of NH3 to N2 and H2 on an industrial scale. [Background technology]

[0003] H2 can be obtained electrolytically from H2O using renewable energy and then converted to NH3 using N2. NH3 can be stored and transported much more safely than H2. NH3 can then be broken down again into H2 and N2. After being separated from N2, H2 becomes available for a wide range of industrial applications.

[0004] The decomposition of NH3 into N2 and H2 is an endothermic reaction in which the molar amount doubles (2NH3 → N2 + 3H2) (ΔH° = 45.9 kJ·mol). -1 Therefore, the reaction is generally favored at high temperature and low pressure. To achieve a satisfactory reaction yield, the higher the pressure, the higher the temperature must be.

[0005] The reaction temperature at which catalytic decomposition of NH3 proceeds is determined, in particular, by the selection of the NH3 decomposition catalyst. Numerous materials have been proposed as catalysts for decomposing NH3, and these are active at different temperatures (see, for example, Il. Lucentini et al., Ind.Eng.Chem.Res.2021,60,18560-18611).

[0006] However, in industrial applications, many of these NH3 decomposition catalysts are not economically feasible on an industrial scale. NH3 decomposition catalysts useful for industrial applications are particularly ruthenium-based and nickel-based catalysts.

[0007] Ruthenium-based NH3 decomposition catalysts have the advantage of achieving conversion rates exceeding 90% at relatively low temperatures. However, because the maximum achievable conversion rate is limited, a considerable amount of undecomposed NH3 residue remains in the product gas, and this amount may need to be separated by additional means.

[0008] Nickel-based NH3 decomposition catalysts have the advantage of being able to achieve significantly higher conversion rates. Therefore, at most, only a small amount of undecomposed NH3 residue remains in the product gas, which can also be separated by conventional methods for H2 purification, particularly pressure swing adsorption, without the need for additional means. However, the temperatures required for nickel-based NH3 decomposition catalysts are clearly high.

[0009] Numerous methods for the catalytic decomposition of NH3 have been described in the prior art, and various reactor types have been proposed (e.g., U.S. Patent No. 4,704,267, U.S. Patent Publication No. 2009 / 280024, U.S. Patent Publication No. 2020 / 0123006, French Patent Publication No. 1469045, British Patent Publication No. 768091, Chinese Patent Publication No. 111957270, Chinese Patent Publication No. 113896168, International Publication No. 201 See publications 1 / 107279, 2012 / 090739, 2020 / 095467, 2021 / 257944, 2022 / 096529, 2022 / 153720, 2022 / 243410, 2022 / 265647, 2022 / 265648, 2022 / 265649, 2022 / 265650, and 2022 / 265651.

[0010] The catalytic decomposition of NH3 is endothermic and requires high temperatures, so heat must be introduced into the reactor. A combustion process that utilizes the heat generated by burning combustion gases for the catalytic decomposition of NH3 has been particularly proposed, similar to an electric heating system.

[0011] A reactor suitable for such a reaction regime is one designed particularly similarly to a primary reformer. The combustion gas and reaction gas are physically separated from each other by the reactor, but they exchange heat with each other. The combustion gas is burned in a combustion chamber using a burner, supplied with combustion air, and there is a heat flow from the combustion chamber to at least one physically separated reaction chamber. The reaction gas flows through an NH3 decomposition catalyst located in the reaction chamber, and the catalytic reaction proceeds. For example, some of the reaction chambers may be designed as tubes, each filled with an NH3 decomposition catalyst, with the reaction gas flowing parallel to each. These tubes are arranged in bundles within the combustion chamber without mixing the combustion gas and reaction gas.

[0012] The materials used to manufacture the reaction chamber and other components of such a reactor must withstand considerable temperatures and loads. The temperature generated by the combustion of the combustion gases in the combustion chamber is far higher than the temperature of the reaction gases in the reaction chamber. This temperature gradient forms the basis for the heat flow from the combustion chamber to the reaction chamber, among other things.

[0013] When such reactors are used for the catalytic decomposition of NH3 via nickel-based NH3 decomposition catalysts, an additional complicating factor is that, due to the high concentrations, pressures, and temperatures of NH3 or N2, many metal alloys corrode as a result of external and / or internal nitriding (often referred to in this context as "nitration").

[0014] RPRubly et al., Oxidation of Metals Vol.35,3-4 (1991), discusses internal nitriding of nickel-chromium alloys. The nitriding properties of nickel-chromium alloys were tested in an ammonia-hydrogen mixture in the range of 700-900°C. Under all exposure conditions, CrN was formed, and Cr2N could not be detected. The transition from internal to external nitride formation at 900°C was 30-40% Cr.

[0015] JJBarnes et al., Journal de Physique III, vol.3, 1993, 167-174, discuss the factors that influence the behavior of Fe-based, Ni-based, and Co-based metal alloys with respect to nitriding at high temperatures (1093°C).

[0016] K. Tjorko et al., Oxidation of Metals Vol. 44, 453-474 (1995), discusses a comparison of internal nitriding in NH3 and N2. Nitriding requires the dissociation of either N2 or NH3. Dissociation of N2 occurs to a considerable extent only above approximately 700°C. Therefore, at temperatures below approximately 700°C, nitriding is determined by the presence of NH3. Even at very high temperatures (1000°C), nitriding with NH3 is more pronounced than nitriding with N2.

[0017] U. Krupp et al., Oxidation of Metals vol.52, 277-298 (1999), describes the internal nitridation of nickel-based alloys, particularly the behavior of binary and ternary alloys of the Ni-Cr-Al-Ti system.

[0018] Similarly, U. Krupp et al., Oxidation of Metals vol.52, 299-320 (1999), also discusses the internal nitriding of nickel-based alloys, particularly the behavior of quaternary Ni-Cr-Al-Ti alloys, and a computer-based explanation referencing thermodynamic data incorporated into FEM diffusion calculations.

[0019] HJ Grabke et al., Materials and Corrosion 2003, 54(11), 895-902, describes a study in which iron, nickel, ferritic 1-18%Cr steel, austenitic 18%Cr-9%Ni and 20%Cr-31%Ni steel, and 16%CrNi alloys were exposed to He-30%H2O and 70%H2O-30%NH3 at 500°C to compare the corrosion properties of materials in steam, such as in conventional power plants, with their behavior in NH3-H2O mixtures, i.e., under "Carina cycle" conditions.

[0020] G.Y. Lai, High-Temperature Corrosion and Materials Applications, ASM International, 2007, Chapter 4: Nitridation describes the reasons for nitridation and the methods of attack on various metals that penetrate deeper than oxidation in some cases. It examines nitridation and its effects on metals and alloys in high-temperature air as well as in NH3-H2O, NH3, H2-N2-NH3 and N2 environments.

[0021] M.O. Cojocaru et al., Materials 2021, 14, 2432 is concerned with the influence of the variation in the activity of the nitriding agent by diluting ammonia with nitrogen.

[0022] E. Wo?owiec-Korecka et al., Coatings 2023, 13, 257, 1-12 is concerned with the stability of layered nitrides in the case of nitridation at low pressure.

[0023] It should also be noted that for reducing the risk of stress corrosion cracking of non-alloy steel, NH3 is frequently spiked with trace amounts of H2O for storage and transportation. This increases the oxygen partial pressure at high temperatures in the reactor, so that not only nitridation but also oxidation can play a role. For example, nitridation of metal alloys in NH3 (or in a mixture of NH3, N2 and H2 formed during the decomposition reaction) at high temperatures in the range of 650 - 750 °C has been little studied to date, especially in the presence of trace amounts of H2O.

[0024] The reverse process is the synthesis of NH3 from N2 and H2 by the Haber-Bosch process.

[0025] American Iron and Steel Institute, A Designer’s Handbook Series No. 9013, 1978, Nickel Institute, 4-23 is concerned with stainless steels for ammonia production.

[0026] Regarding metal alloys suitable for the catalytic decomposition of NH3, since the temperature is clearly lower in the Haber-Bosch process, there is little information available from Haber-Bosch process technology. However, temperature has a significant impact on nitridation. In many cases, austenitic steel is sufficient for reactors and components in the Haber-Bosch process. Austenitic steel can be used at temperatures up to about 480 °C, and when the wall thickness is thicker, it can also be used at slightly higher temperatures (up to about 510 °C). A further material suitable for the Haber-Bosch process is Alloy600, but according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Sec II-D, this is only approved up to a temperature of 649 °C.

[0027] There is also little available information regarding metal alloys suitable for the catalytic decomposition of NH3 from technologies using an NH3 atmosphere under supercritical conditions, for example, the recovery of single nitride crystals. Single nitride crystals are typically recovered at clearly low temperatures, for example, about 133 °C, and correspondingly high pressures, for example, 11.3 MPa. Furthermore, on the one hand, the reaction mechanism of electrochemical reactions on the surface (for example, in the case of fluids) and, on the other hand, the diffusion control mechanism in the substrate and reaction layer (for example, in the case of gases) should be distinguished. In supercritical media, the reaction mechanism that progresses can typically be similar to that of fluid reactions or gas reactions. This typically depends on the medium itself and further different parameters. In the case of supercritical water, for example, density is the determining parameter. At low density, the behavior is more similar to that of a gas, and at high density, the behavior of a liquid is dominant (the low-high boundary is about 0.2 g / ml). In the case of supercritical CO2, for example, the water content, impurity content, and temperature are the determining parameters. At high temperatures, conventional high-temperature processes are dominant in dry CO2. Trace amounts of water result in clear material removal corrosion. The supercritical behavior of CO2 and NH3 can be considered equivalent in a first approximation. NH3 often contains trace amounts of water. In that case, similar to the case of supercritical CO2, condensation is possible, and thus it is not only gas-phase reactions.

[0028] In addition to corrosion resistance at high temperatures in the presence of N2, NH3, and possibly H2O, other properties of metal alloys, particularly hardness, tensile strength, elongation, elongation at break, modulus of elasticity, density, electrical resistance, melting range, thermal conductivity, and specific heat capacity, are also important. Another factor is workability, especially weldability.

[0029] There is a need for an improved reactor that can be used economically on an industrial scale to catalytically decompose NH3 into N2 and H2, and that has a satisfactory or longer lifespan compared to conventional reactors used for this purpose at high temperatures (e.g., 650-750°C). The materials used in the manufacture of the reactor should strike a balance between satisfactory properties and procurement costs. [Prior art documents] [Patent Documents]

[0030] [Patent Document 1] U.S. Patent No. 4704267 [Patent Document 2] U.S. Patent Application Publication No. 2009 / 280024 [Patent Document 3] U.S. Patent Application Publication No. 2020 / 0123006 [Patent Document 4] French Patent Application Publication No. 1469045 [Patent Document 5] UK Patent Application Publication No. 768091 [Patent Document 6] Chinese Patent Application Publication No. 111957270 Specification [Patent Document 7] Chinese Patent Application Publication No. 113896168 Specification [Patent Document 8] International Publication No. 2011 / 107279 [Patent Document 9] International Publication No. 2012 / 090739 [Patent Document 10] International Publication No. 2020 / 095467

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Non-licensed literature

[0031] [Non-licensed document 1] Il.Lucentini et al.,Ind.Eng.Chem.Res.2021,60,18560-18611 [Non-licensed document 2] RPRubly et al.,Oxidation of Metals Vol.35,3-4(1991) [Non-licensed document 3] JJBarnes et al.,Journal de Physique III,vol.3,1993,167-174

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[0032] The object of the present invention is to provide an improved reactor for the production of H2 by catalytic decomposition of NH3. The production of H2 must be possible safely, economically, and on an industrial scale. [Means for solving the problem]

[0033] This objective is achieved by the subject matter of the claims.

[0034] A first aspect of the present invention relates to a plant for producing H2 by catalytic decomposition of NH3 to obtain N2 and H2, The plant is equipped with a reactor containing an NH3 decomposition catalyst. The reactor comprises at least one component formed at least partially from a metal alloy, During reactor operation, the metal alloy is in direct contact with NH3 and / or N2 in at least one region of its surface, preferably in direct contact with NH3, N2 and H2O or their dissociation products. The metal alloy contains nickel, chromium, or both nickel and chromium, and the total nickel and / or chromium content is at least 15% by weight based on the total weight of the metal alloy.

[0035] For explanatory purposes, the meaning of the total content of "A and / or B" is that the metal alloy of the present invention (i) contains both A and B, in which case the total content relates to the sum of the two individual content amounts of A and B, or (ii) does not contain B, and the total content relates to the content of A alone, or (iii) does not contain A, and the total content relates to the content of B alone.

[0036] The metal alloy preferably contains nickel and chromium in a total content of at least 15% by weight of nickel and chromium based on the total weight of the metal alloy.

[0037] In preferred embodiments, the metal alloy of the present invention contains at least two metals selected from the group consisting of nickel, cobalt, chromium, iron, molybdenum, manganese, niobium, cerium, aluminum, titanium, silicon, tungsten, copper, boron, zirconium, lanthanum, and yttrium.

[0038] In a preferred embodiment, the metal alloy of the present invention contains at least three metals selected from the group consisting of nickel, cobalt, chromium, iron, molybdenum, manganese, niobium, cerium, aluminum, titanium, silicon, tungsten, copper, boron, zirconium, lanthanum, and yttrium.

[0039] In a preferred embodiment, the metal alloy of the present invention contains at least four metals selected from the group consisting of nickel, cobalt, chromium, iron, molybdenum, manganese, niobium, cerium, aluminum, titanium, silicon, tungsten, copper, boron, zirconium, lanthanum, and yttrium.

[0040] In a preferred embodiment, the metal alloy of the present invention contains at least five metals selected from the group consisting of nickel, cobalt, chromium, iron, molybdenum, manganese, niobium, cerium, aluminum, titanium, silicon, tungsten, copper, boron, zirconium, lanthanum, and yttrium.

[0041] The nickel and, optionally, cobalt content has been found to be important parameters for sufficient resistance to nitriding. This is particularly because nickel and cobalt in iron-based alloys reduce the solubility of nitrogen, making internal nitriding more difficult. To obtain sufficient stability against nitriding, the nickel or the combined nickel and cobalt content is preferably at least 40% by weight based on the total weight of the metal alloy.

[0042] Furthermore, it was found that chromium itself tends to be disadvantageous in terms of resistance to nitriding. This is particularly because chromium increases the solubility of nitrogen in nickel-based alloys, and therefore the tendency to undergo nitriding.

[0043] However, as soon as the gas atmosphere includes H2O in addition to N2 and NH3, other factors, particularly the formation of an outer oxide layer on the surface of the metal alloy, play a crucial role. If the partial pressure of O2 is sufficiently high, an outer oxide layer is formed. The partial pressures of O2 and H2 are thermodynamically determined by the equilibrium 2H2O⇔2H2+O2. If the partial pressure of O2 is lower than the equilibrium pressure of O2 relative to the metal / metal oxide equilibrium, no oxide is formed.

[0044] In the presence of H2O, chromium forms a stable oxide, Cr2O3, and thus chromium has been found to have a favorable effect in terms of corrosion resistance. Unlike iron oxide, Cr2O3 is stable even at very low O2 partial pressures. Even a low content of H2O of a few ppm can result in an outer layer of Cr2O3, which significantly reduces nitriding. This is true, for example, when an NH3 gas mixture contains only 45 ppm of H2O at, for example, 900°C. It has been found that the chromium content must be sufficiently high to form and maintain a sufficiently dense outer layer of Cr2O3. The latter means that chromium replenishment must be ensured to ensure the stable growth of the Cr2O3 outer layer. The chromium content is preferably at least 18% by weight based on the total weight of the metal alloy.

[0045] Therefore, in a preferred embodiment, the metal alloy of the present invention contains at least 30% by weight, preferably at least 33% by weight, of nickel and / or cobalt (total content), and at least 15% by weight, preferably at least 19% by weight, of chromium, based on the total weight of the metal alloy each time. In a preferred embodiment, the metal alloy of the present invention contains at least 40% by weight, of nickel and / or cobalt (total content), and at least 20% by weight, of chromium, based on the total weight of the metal alloy each time.

[0046] In a preferred embodiment, the metal alloy of the present invention contains at least 30% by weight, preferably at least 33% by weight, of nickel and at least 15% by weight, preferably at least 19% by weight, of chromium, based on the total weight of the metal alloy each time. In a preferred embodiment, the metal alloy of the present invention contains at least 40% by weight, of nickel and at least 20% by weight, of chromium, based on the total weight of the metal alloy each time.

[0047] Therefore, in a preferred embodiment, the metal alloy of the present invention contains at least 33% by weight of cobalt and at least 15% by weight of chromium, based on the total weight of the metal alloy each time. In a preferred embodiment, the metal alloy of the present invention contains at least 40% by weight of cobalt and at least 20% by weight of chromium, based on the total weight of the metal alloy each time.

[0048] In preferred embodiments, the metal alloy of the present invention contains nickel, chromium, and iron, and preferably the nickel content is greater than the chromium content.

[0049] In preferred embodiments, the metal alloy of the present invention contains nickel, cobalt, chromium, and iron, and preferably the total content of nickel and cobalt is greater than the chromium content. [Brief explanation of the drawing]

[0050] [Figure 1] Figure 1 is a schematic diagram of a preferred embodiment of the reactor 1 of the present invention. [Modes for carrying out the invention]

[0051] For explanatory purposes, a “reactor” is a device for catalytically decomposing NH3 into N2 and H2. The reactor of the present invention is typically a partitioned space specifically designed and prepared for that purpose to enable and control the catalytic decomposition of NH3 into N2 and H2 under specified conditions.

[0052] For illustrative purposes, “metallic alloy” is a macroscopically homogeneous metallic material generally obtained by co-melting different metals, which may also include nonmetals and / or metalloids. Metals, nonmetals and / or metalloids may be in elemental form, intermetallic phase form and / or other compound form. Metallic alloys may be crystalline, semicrystalline or amorphous. Particularly important metals according to the present invention that may be present in the metallic alloys of the present invention are nickel, cobalt, chromium and iron, but may also be aluminum and titanium. Further metals that may be present in the metallic alloys of the present invention are, for example, molybdenum, tungsten, niobium, copper, aluminum, titanium, silicon, boron, lanthanum, manganese, vanadium, cerium, yttrium, zirconium, lead, etc. Particularly important nonmetals and metalloids according to the present invention that may be present in the metallic alloys of the present invention are boron, carbon, silicon, nitrogen, phosphorus and sulfur, etc.

[0053] For explanatory purposes, the “NH3 decomposition catalyst” catalyzes the decomposition of NH3 into N2 and H2. To achieve a yield of over 90%, typically high temperatures for NH3, preferably at least 500°C, are required.

[0054] For explanatory purposes, "direct contact with NH3 and / or N2" means that there is no further material present in at least one region between the metal alloy and the NH3 and / or N2, and that the NH3 and / or N2 can interact with the surface of the metal alloy in at least this region. However, modification of the surface of the metal alloy, such as the formation of an outer layer of oxides and nitrides, is permissible in the context of the present invention for direct contact. The metal alloy or its surface does not need to be in complete contact with NH3 and / or N2 over its entire surface. For example, it is sufficient if there is at least one region in which the NH3 and / or N2 can interact with the surface of the metal alloy. Since NH3 decomposes in the reactor of the present invention on its way from the inlet to the outlet, the amount of NH3 at the reactor inlet is clearly greater than the amount of NH3 at the reactor outlet during reactor operation. The amount of N2 formed by the decomposition of NH3 is the reverse. Preferably, the metal alloy is in direct contact with NH3, N2, and H2O or their dissociation products (N2, H2, or O2) at least in a surface area during the operation of the reactor.

[0055] Unless otherwise specified, all percentages are based on weight [weight %]. For ranges defined by "±", such as A±B, the numerical lower limit of the range is AB, and the numerical upper limit of the range is A+B. If the value of B is the same as the value of A, the lower limit is 0, and therefore, neither component may be present at all. Unless otherwise specified, the weight % content data will not add up to 100 weight %; that is, other unmentioned components may be present in addition to the components mentioned.

[0056] The plant of the present invention includes a reactor in which NH3 is catalytically decomposed during plant operation to form a product gas containing N2, H2, and optionally undecomposed NH3.

[0057] In a preferred embodiment of the present invention, the plant of the present invention comprises one or fewer devices fluidly connected to one another. (i) Apparatus for storing liquid NH3, (ii) Apparatus for heating and evaporating liquid NH3, (iii) Reactor of the present invention, (iv) Apparatus for purifying H2 from the generated gas, (v) Apparatus for recovering process heat Includes.

[0058] The reactor of the present invention preferably comprises several chambers that are physically separated from each other. The reactor preferably comprises at least one reaction chamber and at least one combustion chamber.

[0059] The reactor of the present invention is preferably designed similarly to a primary reformer.

[0060] The reactor of the present invention is - One or more combustion chambers for burning combustion gases to generate combustion heat and flue gas (off-gas), -One or more reaction chambers for catalytic decomposition of NH3 to produce a product gas containing N2, H2, and possibly undecomposed NH3 It is preferable to include the following.

[0061] The combustion chambers (one or more) and reaction chambers (one or more) are preferably physically separated from each other so as not to mix the combustion gas of one with the NH3 (reaction gas) or product gas of the other during the operation of the reactor.

[0062] The (one or more) combustion chambers and (one or more) reaction chambers are preferably configured such that, during reactor operation, there is a heat flow from the (one or more) combustion chambers to the (one or more) reaction chambers. During reactor operation, this heat flow is preferably useful in maintaining the endothermic catalytic decomposition of NH3.

[0063] In preferred embodiments of the present invention, one or more reaction chambers are tubular, i.e., have a cylindrical shape. Preferably, a plurality of such tubular reaction chambers are arranged in a bundle parallel to each other within a common combustion chamber.

[0064] Each combustion chamber preferably includes one or more burners for burning combustion gases. The flame formed here is preferably spatially close to the outer wall of at least one reaction chamber containing the NH3 decomposition catalyst during reactor operation. During reactor operation, the heat of combustion then preferably flows from the inside of the combustion chamber through the wall of at least one reaction chamber, thus introducing heat to the NH3 decomposition catalyst, through which the NH3 flows and the endothermic decomposition of NH3 proceeds.

[0065] The reactor of the present invention also comprises at least one component that is at least partially formed from a metal alloy that is in direct contact with NH3 and / or N2 during the operation of the reactor.

[0066] Preferably, the component is a reaction chamber or an element of a reaction chamber, and the NH3 decomposition catalyst is located inside the reaction chamber. Next, the reactor of the present invention preferably comprises a reaction chamber containing the component and the NH3 decomposition catalyst.

[0067] In a preferred embodiment of the present invention, the components are formed entirely from the metal alloy of the present invention; that is, the components consist entirely of a metal alloy.

[0068] If the component formed entirely from the metal alloy of the present invention is a reaction chamber in which the NH3 decomposition catalyst is located, then the walls of the reaction chamber consist of that component and are therefore entirely made of the metal alloy. The inner surface of the reaction chamber walls faces the NH3 decomposition catalyst, and the metal alloy constituting the reaction chamber walls is in direct contact with NH3 and / or N2 in at least one region during the operation of the reactor.

[0069] If a component formed entirely from the metal alloy of the present invention is an element of a reaction chamber in which the NH3 decomposition catalyst is located, it is preferable that the wall of the reaction chamber includes that component. For example, the component may be tubular, or it may be concentrically arranged within another tubular element that together forms the wall of the reaction chamber. The inner surface of the component faces the NH3 decomposition catalyst, and the metal alloy constituting the internal component of the wall is in direct contact with NH3 and / or N2 in at least one region during the operation of the reactor.

[0070] In other preferred embodiments, the components are formed only partially from the metal alloy of the present invention. For example, the components may be multilayered, in which case one of the layers of the components, preferably the outer layer, is formed from the metal alloy of the present invention, i.e., this layer of the component is made of a metal alloy, and the other layers of the component may be made of other materials and / or the same or different compositions of the alloy of the present invention.

[0071] If the component formed only partially from the metal alloy of the present invention is a reaction chamber in which an NH3 decomposition catalyst is located, the component may be a reaction chamber having a multilayer wall, the multilayer wall having an inner layer and an outer layer. The inner surface of the inner layer of the component faces the NH3 decomposition catalyst, and the metal alloy constituting the inner layer is in direct contact with NH3 and / or N2 in at least one region during the operation of the reactor.

[0072] It is preferable that the entire inner surface area of ​​the reaction chamber facing the NH3 decomposition catalyst and in direct contact with NH3 and / or N2 during reactor operation be formed from a metal alloy.

[0073] It is preferable that the entire inner surface area of ​​the reaction chamber, which comes into direct contact with NH3 and / or N2 during reactor operation, be formed from a metal alloy.

[0074] The reactor of the present invention includes an NH3 decomposition catalyst. When NH3 flows through the NH3 decomposition catalyst under reaction conditions, it catalyzes the decomposition of NH3 into N2 and H2.

[0075] Useful NH3 decomposition catalysts according to the present invention include various materials. The reaction temperature at which the catalytic decomposition of NH3 proceeds is determined particularly by the selection of the NH3 decomposition catalyst.

[0076] In a preferred embodiment of the present invention, the NH3 decomposition catalyst is catalytically active with respect to the decomposition of NH3 at a temperature in the range of at least 500 °C, preferably at least 520 °C, more preferably at least 540 °C, even more preferably at least 550 °C, most preferably at least 580 °C, and particularly at least 600 °C. Here, "catalytically active" means that a conversion rate of at least 90% of the decomposition products N2 and H2 is obtained in relation to the amount of NH3 used (measured under standard conditions in pure NH3 at a pressure of 1013 hPa and a space velocity of 36 Lg cat -1 .

[0077] In a preferred embodiment of the present invention, the NH3 decomposition catalyst for the decomposition of NH3 has an apparent activation energy E app of at least 50 kJ·mol -1 , more preferably at least 75 kJ·mol -1 , even more preferably at least 100 kJ·mol -1 , most preferably at least 125 kJ·mol -1 , and particularly at least 150 kJ·mol -1 . The method for determining the apparent activation energy E app is known to those skilled in the art and is determined, for example, from an Arrhenius plot based on measurements under standard conditions in pure NH3 at a pressure of 1013 hPa and a space velocity of 36 Lg cat -1 .

[0078] In preferred embodiments of the present invention, a nickel-based NH3 decomposition catalyst is used. The reaction temperature determines the equilibrium conversion rate. At 900°C and a pressure of 20 bar, the decomposition of NH3 proceeds almost quantitatively. At 650°C, the conversion rate of NH3 is about 98.5%, and at 500°C, it is only about 95%. According to the present invention, to achieve a high conversion rate, it is preferable to establish a reaction temperature in the range of about 600°C to about 900°C, preferably about 600°C to about 700°C. In terms of energy balance and conversion rate, the optimal reaction temperature is in the range of about 630°C to 640°C. Nickel-based NH3 decomposition catalysts are advantageous despite relatively high reaction temperatures. Due to the high conversion rate, the residual content of undecomposed NH3 in the product gas is relatively low, so it is preferable to omit the separate separation of undecomposed NH3 for recovery. Instead, the combined separation of N2 and undecomposed NH3 from the product gas is combined by pressure swing adsorption during the purification of H2.

[0079] The NH3 decomposition catalyst preferably contains supported nickel. Preferred support materials include Al2O3, MgO, SiO2, mesoporous SiO2 (e.g., MCF-17, MCM-41, SBA-15), zeolite (e.g., HY, H-ZSM-5), BaMnO3, BaTiO3, BaZrO3, CaMnO3, CaTiO3, CaZrO3, CeO2, Gd2O3, GdAlO3, KNbO3, La2O3, LaAlO3, MnO2, and N The group is selected from aNbO3, Nb2O5, Sm2O3, SmAlO3, SrMnO3, SrTiO3, SrZrO3, TiO2, Y2O3, ZrO2, carbon (e.g., CNT, SWCNT, AX-21, MSC-30, MESO-C, GNP, activated carbon, graphene, graphene oxide), attapulgite, hydrocalmite, sepiolite, and mixtures thereof.

[0080] The metal alloy of the present invention contains nickel and chromium in a total content of at least 15% by weight of nickel and chromium based on the total weight of the metal alloy.

[0081] In preferred embodiments of the present invention, the total content of nickel and chromium is, on a case-by-case basis, at least 15.5% by weight, preferably at least 16.0% by weight, preferably at least 16.5% by weight, more preferably at least 17.0% by weight, even more preferably at least 17.5% by weight, most preferably at least 18.0% by weight, and in particular at least 18.5% by weight.

[0082] In preferred embodiments of the present invention, the total content of nickel and chromium is, on a case-by-case basis, at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight, even more preferably at least 35% by weight, most preferably at least 40% by weight, and in particular at least 45% by weight.

[0083] In preferred embodiments of the present invention, the total content of nickel and chromium is, on a case-by-case basis, at least 50% by weight, preferably at least 55% by weight, more preferably at least 60% by weight, even more preferably at least 65% by weight, most preferably at least 70% by weight, and in particular at least 75% by weight.

[0084] In preferred embodiments of the present invention, the total content of nickel and chromium is at least 80% by weight, preferably at least 85% by weight, and more preferably at least 90% by weight, based on the total weight of the metal alloy each time.

[0085] In preferred embodiments of the present invention, the total content of nickel and chromium is, on a case-by-case basis, up to 85% by weight, preferably up to 80% by weight, more preferably up to 75% by weight, even more preferably up to 70% by weight, most preferably up to 65% by weight, and particularly up to 60% by weight.

[0086] The metal alloy of the present invention contains nickel.

[0087] In preferred embodiments of the present invention, the nickel content is at least 5.0% by weight, preferably at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, most preferably at least 30% by weight, and in particular at least 35% by weight, based on the total weight of the metal alloy each time.

[0088] In preferred embodiments of the present invention, the nickel content is at least 40% by weight, preferably at least 45% by weight, more preferably at least 50% by weight, even more preferably at least 55% by weight, most preferably at least 60% by weight, and in particular at least 65% by weight, based on the total weight of the metal alloy each time.

[0089] In a preferred embodiment of the present invention, the nickel content is at least 70% by weight, preferably at least 75% by weight, based on the total weight of the metal alloy each time.

[0090] In preferred embodiments of the present invention, the nickel content is in the range of 20±15% by weight, 20±10% by weight, or 20±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0091] In preferred embodiments of the present invention, the nickel content is in the range of 30±25% by weight, 30±20% by weight, 30±15% by weight, 30±10% by weight, or 30±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0092] In preferred embodiments of the present invention, the nickel content is in the range of 40±35% by weight, 40±30% by weight, 40±25% by weight, 40±20% by weight, 40±15% by weight, 40±10% by weight, or 40±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0093] In preferred embodiments of the present invention, the nickel content is in the range of 50±30% by weight, 50±25% by weight, 50±20% by weight, 50±15% by weight, 50±10% by weight, or 50±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0094] In preferred embodiments of the present invention, the nickel content is in the range of 60±20% by weight, 60±15% by weight, 60±10% by weight, or 60±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0095] In preferred embodiments of the present invention, the nickel content is in the range of 70 ± 10% by weight or 70 ± 5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0096] In preferred embodiments of the present invention, the nickel content is, on a case-by-case basis, up to 60% by weight, preferably up to 55% by weight, more preferably up to 50% by weight, even more preferably up to 45% by weight, most preferably up to 40% by weight, and particularly up to 35% by weight.

[0097] The metal alloy of the present invention contains chromium.

[0098] In preferred embodiments of the present invention, the chromium content is, on a case-by-case basis, up to 40% by weight, preferably up to 38% by weight, more preferably up to 36% by weight, even more preferably up to 35% by weight, most preferably up to 34% by weight, and particularly up to 32% by weight.

[0099] In preferred embodiments of the present invention, the chromium content is, on a case-by-case basis, up to 30% by weight, preferably up to 28% by weight, more preferably up to 26% by weight, even more preferably up to 24% by weight, most preferably up to 22% by weight, and particularly up to 20% by weight.

[0100] In other preferred embodiments, the chromium content is at least 12% by weight, preferably at least 15% by weight, more preferably at least 18% by weight, even more preferably at least 21% by weight, most preferably at least 24% by weight, and in particular at least 27% by weight, based on the total weight of the metal alloy each time.

[0101] In preferred embodiments of the present invention, the chromium content is in the range of 10 ± 7.5% by weight, 10 ± 5.0% by weight, or 10 ± 2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0102] In preferred embodiments of the present invention, the chromium content is in the range of 12.5 ± 10% by weight, 12.5 ± 7.5% by weight, 12.5 ± 5.0% by weight, or 12.5 ± 2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0103] In preferred embodiments of the present invention, the chromium content is in the range of 15±12.5% ​​by weight, 15±10% by weight, 15±7.5% by weight, 15±5.0% by weight, or 15±2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0104] In preferred embodiments of the present invention, the chromium content is in the range of 17.5±15% by weight, 17.5±12.5% ​​by weight, 17.5±10% by weight, 17.5±7.5% by weight, 17.5±5.0% by weight, or 17.5±2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0105] In preferred embodiments of the present invention, the chromium content is in the range of 19±17.5% by weight, 19±15% by weight, 19±12.5% ​​by weight, 19±10% by weight, 19±7.5% by weight, 19±5.0% by weight, or 19±2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0106] In preferred embodiments of the present invention, the chromium content is in the range of 20±17.5% by weight, 20±15% by weight, 20±12.5% ​​by weight, 20±10% by weight, 20±7.5% by weight, 20±5.0% by weight, or 20±2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0107] In preferred embodiments of the present invention, the chromium content is in the range of 22.5±20% by weight, 22.5±17.5% by weight, 22.5±15% by weight, 22.5±12.5% ​​by weight, 22.5±10% by weight, 22.5±7.5% by weight, 22.5±5.0% by weight, or 22.5±2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

[0108] In preferred embodiments of the present invention, the chromium content is in the range of 25±22.5% by weight, 25±20% by weight, 25±17.5% by weight, 25±15% by weight, 25±12.5% ​​by weight, 25±10% by weight, 25±7.5% by weight, 25±5.0% by weight, or 25±2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

[0109] In preferred embodiments of the present invention, the chromium content is in the range of 27.5±25% by weight, 27.5±22.5% by weight, 27.5±20% by weight, 27.5±17.5% by weight, 27.5±15% by weight, 27.5±12.5% ​​by weight, 27.5±10% by weight, 27.5±7.5% by weight, 27.5±5.0% by weight, or 27.5±2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

[0110] In preferred embodiments of the present invention, the chromium content is in the range of 30±27.5% by weight, 30±25% by weight, 30±22.5% by weight, 30±20% by weight, 30±17.5% by weight, 30±15% by weight, 30±12.5% ​​by weight, 30±10% by weight, 30±7.5% by weight, 30±5.0% by weight, or 30±2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

[0111] In preferred embodiments of the present invention, the chromium content is in the range of 32.5±30% by weight, 32.5±27.5% by weight, 32.5±25% by weight, 32.5±22.5% by weight, 32.5±20% by weight, 32.5±17.5% by weight, 32.5±15% by weight, 32.5±12.5% ​​by weight, 32.5±10% by weight, 32.5±7.5% by weight, 32.5±5.0% by weight, or 32.5±2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

[0112] Preferred embodiments Z1 to Z72 each have the following nickel and chromium content in weight percent based on the total weight of the metal alloy. [Table 1] Preferably, the metal alloy of the present invention further contains cobalt.

[0113] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is, on a case-by-case basis, at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight, even more preferably at least 35% by weight, most preferably at least 40% by weight, and in particular at least 45% by weight.

[0114] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is at least 50% by weight, preferably at least 54% by weight, more preferably at least 58% by weight, even more preferably at least 62% by weight, most preferably at least 66% by weight, and in particular at least 70% by weight, based on the total weight of the metal alloy on a case-by-case basis. In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is at least 70% by weight, preferably at least 75% by weight, based on the total weight of the metal alloy on a case-by-case basis.

[0115] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 20 ± 15% by weight, 20 ± 10% by weight, or 20 ± 5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0116] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 30±25% by weight, 30±20% by weight, 30±15% by weight, 30±10% by weight, or 30±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0117] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 40±35% by weight, 40±30% by weight, 40±25% by weight, 40±20% by weight, 40±15% by weight, 40±10% by weight, or 40±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0118] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 50±30% by weight, 50±25% by weight, 50±20% by weight, 50±15% by weight, 50±10% by weight, or 50±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0119] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 60±20% by weight, 60±15% by weight, 60±10% by weight, or 60±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0120] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is in the range of 70 ± 10% by weight or 70 ± 5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0121] In preferred embodiments of the present invention, the total content of nickel and optionally cobalt is, on a case-by-case basis, up to 60% by weight, preferably up to 55% by weight, more preferably up to 50% by weight, even more preferably up to 45% by weight, most preferably up to 40% by weight, and particularly up to 35% by weight.

[0122] For explanatory purposes, the meaning of “total content of nickel and optionally cobalt” is that (i) the metal alloy of the present invention contains both nickel and cobalt, in which case the total content relates to the sum of the two individual contents of nickel and cobalt, or (ii) it does not contain cobalt, and the total content relates to the content of nickel alone.

[0123] In preferred embodiments of the present invention, the cobalt content is at least 4.0% by weight, preferably at least 8.0% by weight, more preferably at least 12% by weight, even more preferably at least 16% by weight, most preferably at least 20% by weight, and in particular at least 24% by weight, based on the total weight of the metal alloy each time.

[0124] In other preferred embodiments, the cobalt content is, on a case-by-case basis, up to 15% by weight, preferably up to 12.5% ​​by weight, more preferably up to 10% by weight, even more preferably up to 7.5% by weight, most preferably up to 5.0% by weight, and particularly up to 2.5% by weight.

[0125] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of cobalt, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably, cobalt is nominally absent.

[0126] In each of the preferred embodiments A1 to A72, nickel, and optionally cobalt and chromium, are present in the following amounts by weight percentage based on the total weight of the metal alloy. [Table 2] The nickel content or the combined nickel and cobalt content in the metal alloy of this invention has been found to have a significant effect on nitrogen solubility and, consequently, nitriding. As the nickel content or the combined nickel and cobalt content increases, the solubility of nitrogen in the metal alloy decreases. Lower nitrogen solubility is associated with a lower tendency for (internal) nitriding.

[0127] Furthermore, it was found that the higher the solubility of nitrogen in austenitic steel, the more susceptible it is to (internal) nitriding than nickel-based materials. In nickel-based materials, satisfactory resistance to nitriding can be ensured with a nickel content in the range of 40-50% by weight.

[0128] High chromium content likely has a facilitating effect on internal nitriding at relatively high temperatures, even after prolonged exposure. Therefore, a high chromium content can be disadvantageous.

[0129] When NH3 is spiked with trace amounts of water, or when NH3 contains trace amounts of O2, the partial pressure of O2 increases, which can have a beneficial effect on the stability of the outer oxide layer on the surface of the metal alloy. Chromium has been found to have a favorable effect in this regard.

[0130] The metal alloy of the present invention may further contain aluminum and / or titanium. Although aluminum and titanium are undesirable in themselves, it may be advantageous to use raw materials that can contain relatively small amounts of aluminum and / or titanium to produce the metal alloy of the present invention, for example, for strength reasons. Although aluminum and titanium are undesirable in themselves, certain amounts may be acceptable.

[0131] Both aluminum and titanium are often present in industrial metal alloys, though not necessarily in large quantities, to enhance mechanical strength and creep resistance. Aluminum can further improve oxidation resistance. Both metals have a remarkable tendency to form nitrides, particularly deep within the material, upon contact with nitrogen at high temperatures (internal nitriding). The depth of internal nitriding in metal alloys containing aluminum and / or titanium has been found to be increased compared to metal alloys that do not contain either aluminum or titanium. It has also been found that higher chromium content further promotes internal nitriding in aluminum and titanium.

[0132] It was found that the relatively large amount of nitrides (nitride precipitates) formed leads to undesirable embrittlement of the metal alloy.

[0133] Furthermore, it has been found that volumetric stresses associated with internal nitriding and / or embrittlement can cause delamination of the outer layer on the surface of the metal alloy. This outer layer may consist of oxides and / or nitrides. Delamination of the outer layer results in a localized loss of its protective effect and increases the rate of undesirable nitriding. Subsequently, nitrogen absorption is promoted due to the absence of the outer layer.

[0134] Water (or trace amounts of oxygen) appears to increase the ductility of the outer nitride layer and reduce the risk of delamination. Therefore, if NH3 is contaminated with trace amounts of water, it may have a favorable effect on the stability of the nitride outer layer, thus suppressing or reducing internal nitriding.

[0135] Furthermore, internal nitriding can lead to depletion, and therefore reduced creep and nitriding resistance. Due to the depletion of outer layer-forming elements such as Cr, Si, or Al, the protective outer layer may fail.

[0136] Therefore, internal nitriding should be suppressed as much as possible, or at best, allowed to proceed to a relatively small extent.

[0137] In preferred embodiments of the present invention, the total content of aluminum and / or titanium is, on a case-by-case basis, up to 5.5% by weight, preferably up to 5.0% by weight, more preferably up to 4.5% by weight, even more preferably up to 4.0% by weight, most preferably up to 3.5% by weight, and particularly up to 3.0% by weight.

[0138] For explanatory purposes, the meaning of “total content of aluminum and / or titanium” is that the metal alloy of the present invention (i) contains both aluminum and titanium, in which case the total content relates to the sum of the two individual contents of aluminum and titanium, or (ii) does not contain aluminum, and the total content relates to the content of titanium alone, or (iii) does not contain titanium, and the total content relates to the content of aluminum alone.

[0139] In preferred embodiments of the present invention, the metal alloy contains at most very small amounts of aluminum and / or titanium, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably nominally, aluminum and titanium are absent.

[0140] The metal alloy of the present invention may further contain aluminum.

[0141] In preferred embodiments of the present invention, the aluminum content is preferably up to 6.0% by weight, preferably up to 5.5% by weight, more preferably up to 5.0% by weight, even more preferably up to 4.5% by weight, most preferably up to 4.0% by weight, and particularly up to 3.5% by weight, based on the total weight of the metal alloy each time.

[0142] In preferred embodiments of the present invention, the aluminum content is preferably up to 3.0% by weight, preferably up to 2.5% by weight, more preferably up to 2.0% by weight, even more preferably up to 1.5% by weight, most preferably up to 1.0% by weight, and particularly up to 0.5% by weight, based on the total weight of the metal alloy each time.

[0143] Similar to Cr2O3, Al2O3 is very stable even at low O2 partial pressures. However, because the formation of Al2O3 is kinetically inhibited at relatively low temperatures, the outer oxide layer of Al2O3 grows even more slowly than that of Cr2O3. Furthermore, it has been found that relatively high aluminum content (>5 wt%) makes the metal alloy difficult to weld and also has a significant tendency to form highly brittle nitrides.

[0144] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of aluminum, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably nominally no aluminum.

[0145] The metal alloy of the present invention may further contain titanium.

[0146] In preferred embodiments of the present invention, the titanium content is preferably up to 4.5% by weight, preferably up to 4.0% by weight, more preferably up to 3.5% by weight, even more preferably up to 3.0% by weight, most preferably up to 2.5% by weight, and particularly up to 2.0% by weight, based on the total weight of the metal alloy each time.

[0147] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of titanium, preferably up to 1.0% by weight, more preferably up to 0.6% by weight, even more preferably up to 0.5% by weight, and most preferably up to 0.1% by weight, in particular, titanium is nominally absent.

[0148] Preferably, the metal alloy of the present invention further contains iron.

[0149] In a preferred embodiment of the present invention, the metal alloy of the present invention is steel, preferably austenitic steel.

[0150] In preferred embodiments of the present invention, the iron content is, on a case-by-case basis, up to 85% by weight, preferably up to 80% by weight, more preferably up to 75% by weight, even more preferably up to 70% by weight, most preferably up to 65% by weight, and particularly up to 50% by weight.

[0151] In preferred embodiments of the present invention, the iron content is, on a case-by-case basis, up to 45% by weight, preferably up to 40% by weight, more preferably up to 35% by weight, even more preferably up to 30% by weight, most preferably up to 25% by weight, and particularly up to 20% by weight.

[0152] In a preferred embodiment of the present invention, the iron content is a maximum of 15% by weight, preferably a maximum of 10% by weight, and more preferably a maximum of 5.0% by weight, based on the total weight of the metal alloy each time.

[0153] In a preferred embodiment of the present invention, the iron content is in the range of 10 ± 5% by weight, based on the total weight of the metal alloy.

[0154] In preferred embodiments of the present invention, the iron content is in the range of 20±15% by weight, 20±10% by weight, or 20±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0155] In preferred embodiments of the present invention, the iron content is in the range of 30±25% by weight, 30±20% by weight, 30±15% by weight, 30±10% by weight, or 30±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0156] In preferred embodiments of the present invention, the iron content is in the range of 40±35% by weight, 40±30% by weight, 40±25% by weight, 40±20% by weight, 40±15% by weight, 40±10% by weight, or 40±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0157] In preferred embodiments of the present invention, the iron content is in the range of 50±30% by weight, 50±25% by weight, 50±20% by weight, 50±15% by weight, 50±10% by weight, or 50±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0158] In preferred embodiments of the present invention, the iron content is in the range of 60±20% by weight, 60±15% by weight, 60±10% by weight, or 60±5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0159] In preferred embodiments of the present invention, the iron content is in the range of 70 ± 10% by weight or 70 ± 5.0% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

[0160] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of iron, preferably up to 1.5% by weight, more preferably up to 1.0% by weight, even more preferably up to 0.5% by weight, and most preferably up to 0.1% by weight, in particular, iron is nominally absent.

[0161] Preferably, the metal alloy of the present invention contains silicon.

[0162] SiO2 is known to be thermodynamically more stable than Cr2O3. Therefore, firstly, in a low-oxygen atmosphere, SiO2 can form on the surface instead of Cr2O3, thus preventing nitriding. Secondly, the silicon content is metallurgically limited. Therefore, the formation of a dense SiO2 layer is usually absent, and the protective effect is reduced. If Cr2O3 is stable, SiO2 can form at the internal phase boundary, which similarly reduces the tendency to nitrid. However, even here, the SiO2 layer is usually not continuous, or mixed oxides are formed.

[0163] In preferred embodiments of the present invention, the silicon content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0164] The addition of silicon is known to improve the stability of certain metal alloys against oxidation. However, experimental evidence suggests that silicon does not appear to increase stability against nitriding.

[0165] In preferred embodiments of the present invention, the silicon content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0166] Preferably, the metal alloy of the present invention contains carbon.

[0167] In preferred embodiments of the present invention, the carbon content is at least 0.010% by weight, preferably at least 0.020% by weight, more preferably at least 0.030% by weight, even more preferably at least 0.040% by weight, most preferably at least 0.050% by weight, and in particular at least 0.060% by weight, based on the total weight of the metal alloy each time.

[0168] In preferred embodiments of the present invention, the carbon content is in the range of 0.1 to 0.5% by weight based on the total weight of the metal alloy. This is particularly preferred in the case of cast alloys.

[0169] In preferred embodiments of the present invention, the carbon content is, on a case-by-case basis, up to 0.10% by weight, preferably up to 0.09% by weight, more preferably up to 0.08% by weight, even more preferably up to 0.07% by weight, most preferably up to 0.06% by weight, and particularly up to 0.05% by weight.

[0170] In iron-based alloys, atomic hydrogen can react with carbides such as iron carbide to form methane. Low-alloy chromium steels and chromium-molybdenum steels become increasingly stable against this form of high-temperature embrittlement (HTHA) as the Cr content increases, because chromium carbide is far more stable than iron carbide. Therefore, austenitic steels and nickel-based alloys have good stability against high-temperature embrittlement. However, nickel-based alloys can become brittle as a result of hydrogen being "trapped" on chromium carbide during the thermal aging process.

[0171] Preferably, the metal alloy of the present invention contains molybdenum.

[0172] In preferred embodiments of the present invention, the molybdenum content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0173] In preferred embodiments of the present invention, the metal alloy contains molybdenum, and the molybdenum content is at least 1.0% by weight, preferably at least 2.0% by weight, more preferably at least 3.0% by weight, even more preferably at least 4.0% by weight, most preferably at least 5.0% by weight, and particularly at least 6.0% by weight, based on the total weight of the metal alloy each time.

[0174] In preferred embodiments of the present invention, the molybdenum content is, on a case-by-case basis, up to 12% by weight, preferably up to 11% by weight, more preferably up to 10% by weight, even more preferably up to 9.0% by weight, most preferably up to 8.0% by weight, and particularly up to 7.0% by weight.

[0175] In preferred embodiments of the present invention, the molybdenum content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0176] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of molybdenum, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably nominally no molybdenum.

[0177] In preferred embodiments of the present invention, the metal alloy contains molybdenum, and the total content of nickel, chromium, and molybdenum is, on a case-by-case basis, up to 85% by weight, preferably up to 80% by weight, more preferably up to 75% by weight, even more preferably up to 70% by weight, most preferably up to 65% by weight, and particularly up to 60% by weight.

[0178] Preferably, the metal alloy of the present invention contains vanadium.

[0179] In preferred embodiments of the present invention, the vanadium content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0180] In preferred embodiments of the present invention, the vanadium content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0181] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of vanadium, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably vanadium is nominally absent.

[0182] Preferably, the metal alloy of the present invention contains manganese.

[0183] Manganese has been found to have a tendency to form spinel (MnCr2O4) in the presence of chromium, and spinel is thermodynamically more stable than Cr2O3, especially at low oxygen partial pressures. The growth rate of spinel is faster than that of Cr2O3.

[0184] In preferred embodiments of the present invention, the manganese content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0185] In preferred embodiments of the present invention, the manganese content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0186] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of manganese, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.2% by weight, and most preferably nominally no manganese.

[0187] Preferably, the metal alloy of the present invention contains zirconium.

[0188] In preferred embodiments of the present invention, the zirconium content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy on a case-by-case basis.

[0189] In preferred embodiments of the present invention, the zirconium content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0190] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of zirconium, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably nominally no zirconium.

[0191] Preferably, the metal alloy of the present invention contains copper.

[0192] In preferred embodiments of the present invention, the copper content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0193] In preferred embodiments of the present invention, the copper content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0194] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of copper, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably, copper is nominally absent.

[0195] Preferably, the metal alloy of the present invention contains niobium.

[0196] In preferred embodiments of the present invention, the niobium content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0197] In preferred embodiments of the present invention, the niobium content is, on a case-by-case basis, up to 5.5% by weight, preferably up to 5.0% by weight, more preferably up to 4.5% by weight, even more preferably up to 4.0% by weight, most preferably up to 3.5% by weight, and particularly up to 3.0% by weight.

[0198] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of niobium, preferably up to 1.5% by weight, more preferably up to 1.0% by weight, even more preferably up to 0.5% by weight, and most preferably nominally no niobium.

[0199] Preferably, the metal alloy of the present invention contains tungsten.

[0200] In preferred embodiments of the present invention, the tungsten content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0201] In preferred embodiments of the present invention, the metal alloy contains tungsten, and the tungsten content is at least 1.0% by weight, preferably at least 2.0% by weight, more preferably at least 3.0% by weight, even more preferably at least 4.0% by weight, most preferably at least 5.0% by weight, and particularly at least 6.0% by weight, based on the total weight of the metal alloy each time.

[0202] In a preferred embodiment of the present invention, the tungsten content is, on a case-by-case basis, up to 20% by weight, preferably up to 19% by weight, more preferably up to 18% by weight, even more preferably up to 17% by weight, most preferably up to 16% by weight, and particularly up to 15% by weight.

[0203] In preferred embodiments of the present invention, the tungsten content is, on a case-by-case basis, up to 5.0% by weight, preferably up to 4.0% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0204] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of tungsten, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably, tungsten is nominally absent.

[0205] In preferred embodiments of the present invention, the metal alloy contains tungsten, and the total content of nickel, chromium, and tungsten is, on a case-by-case basis, up to 95% by weight, preferably up to 90% by weight, more preferably up to 85% by weight, even more preferably up to 80% by weight, most preferably up to 75% by weight, and particularly up to 70% by weight.

[0206] Preferably, the metal alloy of the present invention contains molybdenum and tungsten.

[0207] In preferred embodiments of the present invention, the metal alloy contains molybdenum and tungsten, and the total content of nickel, chromium, molybdenum, and tungsten is, on a case-by-case basis, up to 95% by weight, preferably up to 90% by weight, more preferably up to 85% by weight, even more preferably up to 80% by weight, most preferably up to 75% by weight, and particularly up to 70% by weight.

[0208] In a preferred embodiment of the present invention, the amount of {[(molybdenum content) + 0.5 x (tungsten content)]} is less than 1.5% by weight.

[0209] In preferred embodiments of the present invention, the amount of {[(molybdenum content) + 0.5 x (tungsten content)]} is, on a case-by-case basis, up to 1.4% by weight, preferably up to 1.2% by weight, more preferably up to 1.0% by weight, even more preferably up to 0.8% by weight, most preferably up to 0.6% by weight, and especially up to 0.4% by weight.

[0210] In a preferred embodiment of the present invention, the amount of {[(molybdenum content) + 0.5 x (tungsten content)]} is greater than 8.5% by weight.

[0211] In preferred embodiments of the present invention, the amount of {[(molybdenum content) + 0.5 x (tungsten content)]} is, on a case-by-case basis, at least 8.6% by weight, preferably at least 8.8% by weight, more preferably at least 9.0% by weight, even more preferably at least 10% by weight, most preferably at least 13% by weight, and in particular at least 16% by weight.

[0212] In a preferred embodiment of the present invention, the amount of (1.8x chromium / {[(molybdenum content)+0.5x(tungsten content)]}) is less than 3.0% by weight.

[0213] In preferred embodiments of the present invention, the amount of (1.8x chromium / {[(molybdenum content)+0.5x(tungsten content)]}) is, on a case-by-case basis, up to 2.9% by weight, preferably up to 2.6% by weight, more preferably up to 2.3% by weight, even more preferably up to 2.0% by weight, most preferably up to 1.7% by weight, and particularly up to 1.4% by weight.

[0214] In a preferred embodiment of the present invention, the amount of (1.8x chromium / {[(molybdenum content)+0.5x(tungsten content)]}) is greater than 10% by weight.

[0215] In preferred embodiments of the present invention, the amount of (1.8x chromium / {[(molybdenum content)+0.5x(tungsten content)]}) is, on a case-by-case basis, at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 75% by weight, most preferably at least 80% by weight, and in particular at least 85% by weight.

[0216] Preferably, the metal alloy of the present invention contains rare earth metals selected from the group consisting of scandium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, and more preferably from the group consisting of scandium, lanthanum, cerium, neodymium, and yttrium. It has been found that rare earth metals (especially cerium and yttrium) in the case of external nitriding (low oxygen partial pressure) can improve the adhesion of the nitride.

[0217] In preferred embodiments of the present invention, the total content of rare earth metals is, on a case-by-case basis, at least 0.01% by weight, preferably at least 0.02% by weight, more preferably at least 0.03% by weight, even more preferably at least 0.04% by weight, most preferably at least 0.05% by weight, and in particular at least 0.06% by weight.

[0218] In preferred embodiments of the present invention, the total content of rare earth metals is, on a case-by-case basis, up to 0.6% by weight, preferably up to 0.5% by weight, more preferably up to 0.4% by weight, even more preferably up to 0.3% by weight, most preferably up to 0.2% by weight, and particularly up to 0.1% by weight.

[0219] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of rare earth metals, preferably up to 0.10% by weight, more preferably up to 0.09% by weight, and even more preferably up to 0.08% by weight, and most preferably nominally no rare earth metals.

[0220] Preferably, the metal alloy of the present invention contains cerium.

[0221] In preferred embodiments of the present invention, the cerium content is at least 0.01% by weight, preferably at least 0.02% by weight, more preferably at least 0.03% by weight, even more preferably at least 0.04% by weight, most preferably at least 0.05% by weight, and in particular at least 0.06% by weight, based on the total weight of the metal alloy each time.

[0222] In preferred embodiments of the present invention, the cerium content is, on a case-by-case basis, up to 0.6% by weight, preferably up to 0.5% by weight, more preferably up to 0.4% by weight, even more preferably up to 0.3% by weight, most preferably up to 0.2% by weight, and particularly up to 0.1% by weight.

[0223] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of cerium, preferably up to 1.0% by weight, more preferably up to 0.5% by weight, and even more preferably up to 0.1% by weight, and most preferably nominally no cerium.

[0224] Preferably, the metal alloy of the present invention contains yttrium.

[0225] In preferred embodiments of the present invention, the yttrium content is at least 0.01% by weight, preferably at least 0.02% by weight, more preferably at least 0.03% by weight, even more preferably at least 0.04% by weight, most preferably at least 0.05% by weight, and in particular at least 0.06% by weight, based on the total weight of the metal alloy each time.

[0226] In preferred embodiments of the present invention, the yttrium content is, on a case-by-case basis, up to 0.6% by weight, preferably up to 0.5% by weight, more preferably up to 0.4% by weight, even more preferably up to 0.3% by weight, most preferably up to 0.2% by weight, and particularly up to 0.1% by weight.

[0227] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of yttrium, preferably up to 0.10% by weight, more preferably up to 0.09% by weight, and even more preferably up to 0.08% by weight, and most preferably nominally no yttrium is present.

[0228] Preferably, the metal alloy of the present invention contains lanthanum.

[0229] In preferred embodiments of the present invention, the lanthanum content is at least 0.01% by weight, preferably at least 0.02% by weight, more preferably at least 0.03% by weight, even more preferably at least 0.04% by weight, most preferably at least 0.05% by weight, and in particular at least 0.06% by weight, based on the total weight of the metal alloy each time.

[0230] In preferred embodiments of the present invention, the lanthanum content is, on a case-by-case basis, up to 0.6% by weight, preferably up to 0.5% by weight, more preferably up to 0.4% by weight, even more preferably up to 0.3% by weight, most preferably up to 0.2% by weight, and particularly up to 0.15% by weight.

[0231] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of lanthanum, preferably up to 0.10% by weight, more preferably up to 0.09% by weight, and even more preferably up to 0.08% by weight, and most preferably nominally no lanthanum.

[0232] Preferably, the metal alloy of the present invention contains boron.

[0233] In preferred embodiments of the present invention, the boron content is at least 0.1% by weight, preferably at least 0.2% by weight, more preferably at least 0.3% by weight, even more preferably at least 0.4% by weight, most preferably at least 0.5% by weight, and in particular at least 0.6% by weight, based on the total weight of the metal alloy each time.

[0234] In preferred embodiments of the present invention, the boron content is, on a case-by-case basis, up to 4.0% by weight, preferably up to 3.5% by weight, more preferably up to 3.0% by weight, even more preferably up to 2.5% by weight, most preferably up to 2.0% by weight, and particularly up to 1.5% by weight.

[0235] In other preferred embodiments, the metal alloy of the present invention contains at most very small amounts of boron, preferably up to 0.1% by weight, more preferably up to 0.01% by weight, and even more preferably up to 0.001% by weight, and most preferably nominally no boron.

[0236] Preferably, Each time, based on the total weight of the metal alloy, -The total content of nickel and, optionally, cobalt is at least 54% by weight. -The chromium content is up to 24% by weight. - The total content of aluminum and / or titanium is 2.1% by weight or less.

[0237] Preferably, Each time, based on the total weight of the metal alloy, -The total content of nickel and, optionally, cobalt is at least 57% by weight. - The chromium content is at least 26% by weight.

[0238] Preferably, Each time, based on the total weight of the metal alloy, -The total content of nickel and, optionally, cobalt is at least 30% by weight. -The chromium content is in the range of 15-35% by weight. - The aluminum content is up to 2.5% by weight. - The titanium content is up to 0.6% by weight.

[0239] Preferably, Each time, based on the total weight of the metal alloy, -The total content of nickel and, optionally, cobalt is at least 30% by weight. -The chromium content is in the range of 19-35% by weight. - The aluminum content is up to 2.5% by weight. - The titanium content is up to 0.6% by weight.

[0240] Preferably, the metal alloy is selected from the group consisting of metal alloys A1-A12, B1-B17, C1-C17, D1-D17, or E1-E17, each containing the following chromium and nickel content in weight percent based on the total weight of the metal alloy, and further components not listed in the table may be present in each case. [Table 3] [Table 4] Preferably, the metal alloy is selected from the group consisting of metal alloys F1-F12, G1-G17, H1-H17, I1-I17, or J1-J17, each containing, in weight percent based on the total weight of the metal alloy, the following amounts of iron, chromium, and nickel, and further components not listed in the table may be present in each case.

Table 5

Table 6

Table 7

[0241]

Table 8

Table 9

Table 10

Table 11

Table 12

Table 13

Table 14

[0242] Preferably, the metal alloy of the present invention is selected from the group consisting of the following material classes: DIN No.1.4820, 1.4821, 1.4822, 1.4823, 1.4824, 1.4825, 1.4826, 1.4827, 1.4828, 1.4829, 1.4830, 1.4831, 1.4832, 1.4833, 1.4834, 1.4835, 1.4 836, 1.4837, 1.4838, 1.4839, 1.4840, 1.4841, 1.4842, 1.4843, 1.4844 , 1.4845, 1.4846, 1.4847, 1.4848, 1.4849, 1.4850, 1.4851, 1.4852, 1.4 853, 1.4854, 1.4855, 1.4856, 1.4857, 1.4858, 1.4859, 1.4860, 1.4861, 1.4862, 1.4863, 1.4864, 1.4865, 1.4866, 1.4867, 1.4868, 1.4869, 1.4870, 1.4871, 1.4872, 1.4873, 1.4874, 1.4875, 1.4876, 1.4877, 1.4878, 1.4879, 1.4880, 1.4881, 1.4882, 1.4883, 1.4884, 1.4885, and 1.4886.

[0243] Preferably, the metal alloy of the present invention is selected from the group consisting of the following material classes: DIN No. 1.4948, 1.4949, 1.4950, 1.4951, 1.4952, 1.4953, 1.4954, 1.4955, 1.4956, 1.4957, 1.4958, 1.4959, 1.4960, 1.4961, 1.4962, 1.4963, 1.4964, 1.4965, 1.4966, 1.4967, 1.4968, 1.4969, 1.4970, and 1.4971.

[0244] Preferably, the metal alloy of the present invention is selected from the group consisting of the following material classes: DIN No. 2.4630, 2.4633, 2.4650, 2.4653, 2.4654, 2.4655, 2.4656, 2.4657, 2.4658, 2.4659, 2.4660, 2.4661, 2.4662, 2.4663, 2.4664, 2.4665, 2.4666, 2.4667, 2.4668, 2.4669, 2.4670, 2.4671, 2.4672, and 2.4673.

[0245] Preferably, the metal alloy of the present invention is selected from the group consisting of the following material classes: DIN No. 2.4723, 2.4724, 2.4725, 2.4726, 2.4727, 2.4728, 2.4729, 2.4730, 2.4731, 2.4732, 2.4733, 2.4734, 2.4735, 2.4736, 2.4737, 2.4738, 2.4739, 2.4740, 2.4741, 2.4742, and 2.4743.

[0246] Preferably, the metal alloy of the present invention is selected from the group consisting of the following material classes: DIN No. 2.4806, 2.4807, 2.4808, 2.4809, 2.4810, 2.4811, 2.4812, 2.4813, 2.4814, 2.4815, 2.4816, 2.4817, 2.4818, 2.4819, 2.4820, 2.4821, 2.4822, 2.4823, 2.4824, 2.4825, 2.4826, 2.4827, 2.4828, 2.4829, 2.4830, 2.4831, 2.4832, 2.4833, 2.4834, 2.4835, 2.4836, 2.4837 , 2.4838, 2.4839, 2.4840, 2.4841, 2.4842, 2.4843, 2.4844, 2.4845, 2.4846, 2.4847, 2.4848, 2.4849, 2.4850, 2.4851, 2.4852, 2.4853, 2.4854, 2.4855, 2.4856, 2.4857, 2.4858, 2.4859, 2.4860, 2.4861, 2.4862, 2.4863, 2.4864, 2.4865, 2.4866, 2.4867, 2.4868 and 2.4879.

[0247] Preferably, the metal alloy is in direct contact with gaseous NH3.

[0248] Preferably, the metal alloy is not in direct contact with NH3 in a supercritical state.

[0249] A further aspect of the present invention relates to a method for catalytic decomposition of NH3 to N2 and H2 in a plant of the present invention as described above, wherein NH3 is introduced into the reactor at a temperature of at least 500 °C, more preferably at least 530 °C, even more preferably at least 560 °C, most preferably at least 590 °C, particularly at least 620 °C.

[0250] Preferably, the component is exposed to a temperature of at least 500 °C, more preferably at least 530 °C, even more preferably at least 560 °C, most preferably at least 590 °C, particularly at least 620 °C. Preferably, the component is exposed to a temperature of at least 650 °C, more preferably at least 680 °C, even more preferably at least 710 °C, most preferably at least 740 °C, particularly at least 770 °C. Preferably, the component is exposed to a temperature of at least 800 °C, more preferably at least 830 °C, even more preferably at least 860 °C, most preferably at least 890 °C, particularly at least +920 °C.

[0251] NH3 is preferably in a gaseous state in the reactor. <L

[0252] NH3 is preferably not in a supercritical state in the reactor.

[0253] Figure 1 is a schematic diagram of a preferred embodiment of the reactor 1 of the present invention, which, as an example, comprises four tubular reaction chambers 2, each containing an NH3 decomposition catalyst. The reactor 1 forms a combustion chamber 3 inside, and the four tubular reaction chambers 2 are arranged in parallel as a bundle within the combustion chamber. NH3 (reaction gas) is supplied to the reactor 1 and each reaction chamber 2 via a supply system 4, and reacts on the NH3 decomposition catalyst to produce a product gas. The product gas, containing N2 and H2, is discharged from the reaction chambers 2 and the reactor 1 via an exhaust system 5. In a flow direction parallel to the NH3, the combustion gas is guided to the combustion chamber 3 via a supply 6, where it is burned to form a flame 7. The heat of combustion generated by the combustion flows from the inside of the combustion chamber 3 through the walls of the reaction chambers 2 to the NH3 decomposition catalyst. The flue gas generated by the combustion is discharged from the combustion chamber 3 and the reactor 1 via an outlet 8. [Explanation of Symbols]

[0254] 1 Reactor 2. Reaction Chamber 3 Combustion chamber 4 NH3 supply line system 5. Emission system for generated gases 6. Supply of combustion gases 7 Flames 8. Flue gas outlet

Claims

1. NH ３ to N ２ and H ２ By catalytic decomposition, H ２ A plant for manufacturing, The aforementioned plant, NH ３ Equipped with a reactor containing a decomposition catalyst, The reactor comprises at least one component formed at least partially from a metal alloy, The metal alloy, during the operation of the reactor, in at least one region of its surface, the NH ３ and / or N ２ They made direct contact with him, A plant in which the metal alloy contains nickel and chromium, and the total content of nickel and chromium is at least 15% by weight based on the total weight of the metal alloy.

2. The plant according to claim 1, wherein the metal alloy may further contain cobalt, and the total content of nickel and optionally cobalt is at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight, even more preferably at least 35% by weight, most preferably at least 40% by weight, and in particular at least 45% by weight, based on the total weight of the metal alloy each time.

3. The plant according to claim 2, wherein the total content of nickel and optionally cobalt is at least 50% by weight, preferably at least 54% by weight, more preferably at least 58% by weight, even more preferably at least 62% by weight, most preferably at least 66% by weight, and in particular at least 70% by weight, based on the total weight of the metal alloy each time.

4. The plant according to any one of claims 1 to 3, wherein the total content of nickel and optionally cobalt is, on a case-by-case basis, up to 60% by weight, preferably up to 55% by weight, more preferably up to 50% by weight, even more preferably up to 45% by weight, most preferably up to 40% by weight, and particularly up to 35% by weight.

5. The plant according to any one of claims 1 to 4, wherein the nickel content is at least 5.0% by weight, preferably at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, most preferably at least 30% by weight, and particularly at least 35% by weight, based on the total weight of the metal alloy each time.

6. The plant according to any one of claims 1 to 5, wherein the nickel content is, each time based on the total weight of the metal alloy, a maximum of 60% by weight, preferably a maximum of 55% by weight, more preferably a maximum of 50% by weight, even more preferably a maximum of 45% by weight, most preferably a maximum of 40% by weight, and particularly a maximum of 35% by weight.

7. The plant according to any one of claims 1 to 6, wherein the metal alloy contains cobalt.

8. The plant according to any one of claims 1 to 7, wherein the metal alloy contains cobalt, and the cobalt content is at least 4.0% by weight, preferably at least 8.0% by weight, more preferably at least 12% by weight, even more preferably at least 16% by weight, most preferably at least 20% by weight, and particularly at least 24% by weight, based on the total weight of the metal alloy each time.

9. The plant according to any one of claims 1 to 8, wherein the chromium content is at least 12% by weight, preferably at least 15% by weight, more preferably at least 18% by weight, even more preferably at least 21% by weight, most preferably at least 24% by weight, and particularly at least 27% by weight, based on the total weight of the metal alloy each time.

10. The plant according to any one of claims 1 to 9, wherein the chromium content is, each time based on the total weight of the metal alloy, a maximum of 40% by weight, preferably a maximum of 38% by weight, more preferably a maximum of 36% by weight, even more preferably a maximum of 35% by weight, most preferably a maximum of 34% by weight, and particularly a maximum of 32% by weight.

11. The plant according to any one of claims 1 to 10, wherein the chromium content is, each time based on the total weight of the metal alloy, a maximum of 30% by weight, preferably a maximum of 28% by weight, more preferably a maximum of 26% by weight, even more preferably a maximum of 24% by weight, most preferably a maximum of 22% by weight, and particularly a maximum of 20% by weight.

12. The plant according to any one of claims 1 to 11, wherein the chromium content is in the range of 15 ± 12.5% ​​by weight, 15 ± 10% by weight, 15 ± 7.5% by weight, 15 ± 5.0% by weight, or 15 ± 2.5% by weight, in ascending order of preference, based on the total weight of the metal alloy each time.

13. The plant according to any one of claims 1 to 12, wherein the chromium content is in the range of 20 ± 17.5% by weight, 20 ± 15% by weight, 20 ± 12.5% ​​by weight, 20 ± 10% by weight, 20 ± 7.5% by weight, 20 ± 5.0% by weight, or 20 ± 2.5% by weight, based on the total weight of the metal alloy, in ascending order of preference.

14. The plant according to any one of claims 1 to 13, wherein the chromium content is in the range of 25 ± 22.5% by weight, 25 ± 20% by weight, 25 ± 17.5% by weight, 25 ± 15% by weight, 25 ± 12.5% ​​by weight, 25 ± 10% by weight, 25 ± 7.5% by weight, 25 ± 5.0% by weight, or 25 ± 2.5% by weight, based on the total weight of the metal alloy each time, in ascending order of preference.

15. The plant according to any one of claims 1 to 14, wherein the total content of nickel and chromium is at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight, even more preferably at least 35% by weight, most preferably at least 40% by weight, and in particular at least 45% by weight, based on the total weight of the metal alloy each time.

16. The plant according to any one of claims 1 to 15, wherein the total content of nickel and chromium is, on a case-by-case basis, up to 85% by weight, preferably up to 80% by weight, more preferably up to 75% by weight, even more preferably up to 70% by weight, most preferably up to 65% by weight, and particularly up to 60% by weight.

17. The plant according to any one of claims 1 to 16, wherein the metal alloy contains molybdenum.

18. The plant according to any one of claims 1 to 17, wherein the metal alloy contains molybdenum, and the molybdenum content is at least 1.0% by weight, preferably at least 2.0% by weight, more preferably at least 3.0% by weight, even more preferably at least 4.0% by weight, most preferably at least 5.0% by weight, and particularly at least 6.0% by weight, based on the total weight of the metal alloy each time.

19. The plant according to any one of claims 1 to 18, wherein the metal alloy contains molybdenum, and the total content of nickel, chromium, and molybdenum is, each time based on the total weight of the metal alloy, a maximum of 85% by weight, preferably a maximum of 80% by weight, more preferably a maximum of 75% by weight, even more preferably a maximum of 70% by weight, most preferably a maximum of 65% by weight, and particularly a maximum of 60% by weight.

20. The plant according to any one of claims 1 to 19, wherein the metal alloy contains tungsten.

21. The plant according to any one of claims 1 to 20, wherein the metal alloy contains tungsten, and the tungsten content is at least 1.0% by weight, preferably at least 2.0% by weight, more preferably at least 3.0% by weight, even more preferably at least 4.0% by weight, most preferably at least 5.0% by weight, and particularly at least 6.0% by weight, based on the total weight of the metal alloy each time.

22. The plant according to any one of claims 1 to 21, wherein the metal alloy contains tungsten, and the total content of nickel, chromium, and tungsten is, each time based on the total weight of the metal alloy, a maximum of 95% by weight, preferably a maximum of 90% by weight, more preferably a maximum of 85% by weight, even more preferably a maximum of 80% by weight, most preferably a maximum of 75% by weight, and particularly a maximum of 70% by weight.

23. The plant according to any one of claims 1 to 22, wherein the metal alloy contains molybdenum and tungsten.

24. The plant according to any one of claims 1 to 23, wherein the metal alloy contains molybdenum and tungsten, and the total content of nickel, chromium, molybdenum and tungsten is, each time based on the total weight of the metal alloy, a maximum of 95% by weight, preferably a maximum of 90% by weight, more preferably a maximum of 85% by weight, even more preferably a maximum of 80% by weight, most preferably a maximum of 75% by weight, and particularly a maximum of 70% by weight.

25. The plant according to any one of claims 1 to 24, wherein the amount of {[(molybdenum content) + 0.5 × (tungsten content)]} is less than 1.5% by weight.

26. The plant according to any one of claims 1 to 25, wherein the amount of {[(molybdenum content) + 0.5 x (tungsten content)]} is, each time based on the total weight of the metal alloy, a maximum of 1.4% by weight, preferably a maximum of 1.2% by weight, more preferably a maximum of 1.0% by weight, even more preferably a maximum of 0.8% by weight, most preferably a maximum of 0.6% by weight, and particularly a maximum of 0.4% by weight.

27. The plant according to any one of claims 1 to 26, wherein the amount of {[(molybdenum content) + 0.5 × (tungsten content)]} is greater than 8.5% by weight.

28. The plant according to any one of claims 1 to 27, wherein the amount of {[(molybdenum content) + 0.5 × (tungsten content)]} is at least 8.6% by weight, preferably at least 8.8% by weight, more preferably at least 9.0% by weight, even more preferably at least 10% by weight, most preferably at least 13% by weight, and in particular at least 16% by weight, based on the total weight of the metal alloy each time.

29. The plant according to any one of claims 1 to 28, wherein the amount of (1.8 x chromium / {[(molybdenum content) + 0.5 x (tungsten content)]}) is less than 3.0% by weight.

30. The plant according to any one of claims 1 to 29, wherein the amount of (1.8 x chromium / {[(molybdenum content) + 0.5 x (tungsten content)]}) is, each time based on the total weight of the metal alloy, a maximum of 2.9% by weight, preferably a maximum of 2.6% by weight, more preferably a maximum of 2.3% by weight, even more preferably a maximum of 2.0% by weight, most preferably a maximum of 1.7% by weight, and particularly a maximum of 1.4% by weight.

31. The plant according to any one of claims 1 to 30, wherein the amount of (1.8 x chromium / {[(molybdenum content) + 0.5 x (tungsten content)]}) is greater than 10% by weight.

32. The plant according to any one of claims 1 to 31, wherein the amount of (1.8 x chromium / {[(molybdenum content) + 0.5 x (tungsten content)]}) is at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 75% by weight, most preferably at least 80% by weight, and particularly at least 85% by weight, based on the total weight of the metal alloy each time.

33. - The metal alloy may further contain cobalt, and the total content of nickel and optionally cobalt is at least 40% by weight. - The chromium content is at least 20% by weight, based on the total weight of the metal alloy each time. The plant according to any one of claims 1 to 32.

34. The plant according to any one of claims 1 to 33, wherein the metal alloy contains aluminum and / or titanium.

35. The plant according to any one of claims 1 to 34, wherein the metal alloy contains aluminum and / or titanium, and the total content of aluminum and / or titanium is, on a case-by-case basis, up to 4.5% by weight, preferably up to 4.0% by weight, more preferably up to 3.5% by weight, even more preferably up to 3.0% by weight, most preferably up to 2.5% by weight, and particularly up to 2.0% by weight.

36. The plant according to any one of claims 1 to 35, wherein the aluminum content is preferably up to 3.0% by weight, preferably up to 2.5% by weight, more preferably up to 2.0% by weight, even more preferably up to 1.5% by weight, most preferably up to 1.0% by weight, and particularly up to 0.5% by weight, based on the total weight of the metal alloy each time.

37. The plant according to any one of claims 1 to 36, wherein the metal alloy of the present invention contains at most a very small amount of titanium, preferably up to 1.0% by weight, more preferably up to 0.6% by weight, even more preferably up to 0.5% by weight, and most preferably up to 0.1% by weight, and in particular, titanium is nominally absent.

38. Each time, based on the total weight of the aforementioned metal alloy, - The total content of nickel and, optionally, cobalt is at least 54% by weight. - The chromium content is up to 24% by weight. - The total content of aluminum and / or titanium is a maximum of 2.1% by weight. The plant according to any one of claims 1 to 37.

39. Each time, based on the total weight of the aforementioned metal alloy, - The total content of nickel and, optionally, cobalt is at least 57% by weight. - The chromium content is at least 26% by weight. The plant according to any one of claims 1 to 38.

40. Each time, based on the total weight of the aforementioned metal alloy, - The total content of nickel and, optionally, cobalt is at least 30% by weight. - The chromium content is in the range of 15 to 35% by weight, preferably in the range of 19 to 35% by weight. - The aluminum content is up to 2.5% by weight. - The titanium content is up to 0.6% by weight. The plant according to any one of claims 1 to 39.

41. Said NH ３ The plant according to any one of claims 1 to 40, wherein the decomposition catalyst is nickel-based.

42. NH ３ Regarding the decomposition of the said NH ３ The decomposition catalyst has an apparent activation energy E －１ of at least 50 kJ·mol ａｐｐ The plant according to any one of claims 1 to 41

43. The plant consists of one or fewer devices that are fluidly connected to each other. (i) Liquid NH ３ A device for storing (ii) the liquid NH ３ A device for heating and evaporating, (iii) The reactor, (iv) From the generated gas H ２ Apparatus for purifying, (v) Apparatus for recovering process heat A plant according to any one of claims 1 to 42, including the plant described in any one of claims 1 to 42.

44. The aforementioned metal alloy is gaseous NH ３ A plant according to any one of claims 1 to 43, which is in direct contact with the plant.

45. The aforementioned metal alloy is in a supercritical state NH ３ A plant according to any one of claims 1 to 44, which does not come into direct contact with the plant.

46. In a plant as described in any one of claims 1 to 45, NH ３ to N ２ and H ２ A catalytic decomposition method for the NH ３ A method wherein the material is introduced into the reactor at a temperature of at least 500°C, more preferably at least 530°C, even more preferably at least 560°C, most preferably at least 590°C, and in particular at least 620°C.

47. The NH in the reactor ３ The method according to claim 46, wherein is in a gaseous state.

48. The NH in the reactor ３ The method according to claim 46 or 47, wherein the substance is not in a supercritical state.

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