Decomposition of ammonia on nickel-based catalysts

Abstract

The invention relates to a method for the preparation of H2 from NH3. NH3 is introduced into a fixed-bed reactor at a gas temperature in the range from 550 to 850°C, in which fixed-bed reactor NH3 is decomposed on an NH3 decomposition catalyst partly into H2 and N2. The gas mixture obtained in this manner is discharged from the fixed-bed reactor at a gas temperature in the range from 300 to 700°C, is heated to a temperature in the range from 550 to 700°C and is then introduced into a tubular reactor in which further NH3 is decomposed on a nickel-based NH3 decomposition catalyst into H2 and N2. The gas mixture obtained in this manner is discharged from the tubular reactor at a gas temperature in the range from 550 to 750°C.

Description

Decomposition of ammonia on nickel-based catalysts

[0001] Priority is claimed from Luxembourg patent application No. LU 103169 of 13 July 2023.

[0002] The invention relates to a process for producing H2 from NH3. NH3 is introduced into a fixed-bed reactor at a gas temperature in the range of 550 to 850°C, in which NH3 is partially decomposed to H2 and N2 by an NH3 decomposition catalyst. The gas mixture thus obtained is discharged from the fixed-bed reactor at a gas temperature in the range of 300 to 700°C, heated to a temperature in the range of 550 to 700°C, and then introduced into a tubular reactor in which further NH3 is decomposed to H2 and N2 by a nickel-based NH3 decomposition catalyst. The gas mixture thus obtained is discharged from the tubular reactor at a gas temperature in the range of 550 to 750°C.

[0003] H2 can be extracted from H2O using renewable energy and then converted into NH3 with N2. NH3 can be stored and transported much more safely than H2. NH3 can then be decomposed back into H2 and N2. After N2 is separated, H2 finds a wide variety of industrial applications.

[0004] The decomposition of NH3 to N2 and H2 is an endothermic reaction (AH° = 45.9 kJ-mol 1 ), in which the amount of substance doubles (2 NH3 N2 + 3 H2), so that the reaction is generally favored by high temperatures and low pressures. The higher the pressure, the higher the temperature must be to achieve satisfactory reaction yields. A variety of materials have been proposed as catalysts for the decomposition, which are active at different temperatures (see, for example, II. Lucentini et al., Review of the Decomposition of Ammonia to Generate Hydrogen, Ind. Eng. Chem. Res. 2021, 60, 18560-18611).

[0005] The catalytic decomposition of NH3 produces a product gas that contains H2 mixed with N2 and possibly other gaseous components, such as unreacted NH3. However, many industrial applications require H2 of high purity, necessitating purification of the product gas before it can be used in industrial applications. While H2 can be purified using various processes, such as cryogenic or membrane processes, purification by pressure swing adsorption is particularly economical on an industrial scale.

[0006] US 4,704,267 A concerns the production of high-purity hydrogen from liquid, anhydrous ammonia. Ammonia is vaporized and then separated into its components. The resulting dissociated gas stream is fed to an adiabatic metal hydride purification unit. to absorb the hydrogen present in the stream. The adsorbed hydrogen is then recovered as a high-purity product.

[0007] US 2020 / 0123006 A1 relates to a process for producing a nitrogen and hydrogen-containing product gas from ammonia, comprising the steps of non-catalytic partial oxidation of ammonia with an oxygen-containing gas to a process gas containing nitrogen, water, amounts of nitrogen oxides and residual amounts of ammonia; cracking at least a portion of the residual amounts of ammonia to hydrogen and nitrogen in the process gas by contact with a nickel-containing catalyst and simultaneously reducing the amounts of nitrogen oxides to nitrogen and water by reaction with a portion of the hydrogen formed during the cracking of the process gas by contact of the process gas with the nickel-containing catalyst; and withdrawing the hydrogen- and nitrogen-containing product gas.

[0008] FR 1 469 045 A relates to an apparatus comprising a preheater fed with ammonia, a tube bundle enclosing a catalyst for ammonia decomposition and, optionally, a cell for hydrogen purification by diffusion, which are interconnected and located in a single housing containing heating means.

[0009] CN 111 957 270 A relates to an ammonia decomposition device comprising an ammonia decomposition unit and a combustion unit acting on the ammonia decomposition unit. Ammonia enters the ammonia decomposition unit via a first purified gas inlet to conduct an ammonia decomposition reaction. Produced mixed gas is discharged via a second purified gas outlet and then enters the combustion unit via a second purified gas inlet. The mixed gas comprises nitrogen, hydrogen, and undecomposed ammonia. The mixed gas enters the combustion unit to provide heat for the ammonia decomposition reaction of the ammonia decomposition unit, thus realizing heat self-sufficiency in the ammonia decomposition-hydrogen production system.No additional fuel is required for energy supply and the cost of the ammonia decomposition hydrogen production system is reduced.

[0010] CN 112 742 310 A relates to an ammonia decomposition reaction device and ammonia decomposition method. The device comprises a heater or a pre-reactor and a reactor, wherein the reactor is a hollow space, and a first partition plate, a plurality of pipes, a gas distributor, and a second partition plate are arranged in the reactor. By arranging the pre-reactor, the catalytic combustion reaction can be started at normal temperature, the reactor temperature is raised to 350-600 °C, and the ammonia decomposition reaction is carried out; or the reactor is heated by using a heater, the catalytic combustion reaction is started after the reactor temperature has reached 200-350 °C, the heater is closed, and the reactor temperature is further raised to 350-600 °C through use. catalytic combustion reaction releases heat and the ammonia decomposition reaction is carried out.

[0011] CN 113 896 168 A relates to a process for producing hydrogen or reducing gas by ammonia cracking using a two-stage process, comprising the following steps: The liquid ammonia of the raw material is fully gasified and heated by a heat exchange gasification system and then enters a first-stage heat exchange ammonia cracking reaction system to generate a partial ammonia cracking reaction. The reaction gas from the first-stage heat exchange ammonia cracking reaction system enters a second-stage high-temperature ammonia cracking reaction system to perform a residual ammonia cracking reaction. The second-stage high-temperature ammonia cracking reaction gas sequentially enters the first-stage heat exchange ammonia cracking reaction system and the heat exchange gasification system to gradually recover heat, thus obtaining the reducing gas.

[0012] JP 2023 073692 A relates to a process for producing hydrogen by decomposing ammonia. In an ammonia decomposition step by combustion gas, heating is carried out, comprising a step of decomposing ammonia into nitrogen and hydrogen by contacting it with a catalyst containing Ru at a temperature of 400°C or more and 550°C or less while heating by contacting ammonia with a heat exchange reactor 3 at a pressure of 1.5 MPa or more and 7 MPa or less; a step of separating hydrogen by contacting gas obtained in the preceding step with a hydrogen-permeable membrane at 300°C or more and 550°C or less; a step of decompressing gas containing unreacted ammonia after hydrogen separation to 0.3 MPa or less;a step of decomposing ammonia by adding oxygen-containing gas to the decomposed gas to bring it into contact with a catalyst containing at least one metal selected from the group consisting of Ru, Rh, and Pd; and a combustion step by adding the oxygen-containing gas to the gas obtained in the previous step;

[0013] WO 2011 / 107279 A1 relates to an ammonia-based hydrogen production reactor comprising an ammonia cracking chamber with an ammonia cracking catalyst, an inner combustion chamber with a combustion or oxidation catalyst which is in thermal contact with the ammonia cracking chamber, an ammonia gas preheating chamber and an outer shroud for heat recovery from the combustion products emerging from the combustion chamber, wherein the cracking chamber, the inner combustion chamber, the preheating chamber and the heat recovery shroud are arranged concentrically.

[0014] WO 2012 / 090739 A1 relates to a hydrogen generator comprising a decomposition device that decomposes a compound containing a hydrogen atom and a nitrogen atom and generates hydrogen; a compound supply device that supplies the compound to the decomposition device; and an oxygen supply device that supplies oxygen to the decomposition device.

[0015] WO 2020 / 095467 A relates to an apparatus for generating hydrogen gas, comprising: an evaporator that heats liquid ammonia to generate ammonia gas; a main thermal decomposition device that causes combustion of a fuel gas, whereby the ammonia gas generated by the evaporator is heated and decomposed into nitrogen gas and hydrogen gas; a cooler that cools a decomposition gas containing the nitrogen gas and the hydrogen gas generated by decomposition by the main thermal decomposition device; and a separator (8) that separates the hydrogen gas from the cooled decomposition gas.

[0016] WO 2021 / 257944 A1 relates to the recovery of hydrogen from an ammonia cracking process in which the cracked gas is purified in a PSA device. The use of a membrane separator for the PSA off-gas improves the recovery.

[0017] WO 2022 / 096529 A1 relates to a process for cracking ammonia, producing hydrogen and generating electric power, comprising electrolysis of water in supplied ammonia, evaporation, preheating and cracking of ammonia using ammonia synthesis catalysts at low temperatures.

[0018] WO 2022 / 189560 A1 relates to a process and system for producing a hydrogen product from ammonia, comprising: optionally at least one pre-cracking reactor, for example an adiabatic pre-cracking reactor, arranged to receive an ammonia feed stream and thereby produce a partially converted ammonia feed stream comprising ammonia, hydrogen, and nitrogen; an ammonia cracking reactor, for example an electrically heated reactor. The reactor is arranged to receive the partially converted ammonia feed stream or the ammonia feed stream to produce an off-gas stream comprising hydrogen and nitrogen and optionally also unconverted ammonia; and a hydrogen recovery unit arranged to receive the off-gas stream for producing the hydrogen product and an off-gas stream comprising hydrogen, nitrogen, and optionally unconverted ammonia.

[0019] WO 2022 / 243410 A1 relates to a process for the synthesis of hydrogen via the catalytic cracking of ammonia; wherein an ammonia-containing stream is subjected to a catalytic cracking step in the presence of heat to obtain a combusted gas and a thermally cracked stream containing nitrogen, hydrogen and possibly residual ammonia and optionally water; wherein the thermally cracked stream is subjected to a hydrogen recovery step to obtain a high-purity hydrogen stream.

[0020] WO 2022 / 265647 A1 relates to the recovery of a renewable hydrogen product from an ammonia cracking process, in which the cracked gas is purified in a first PSA device and at least a portion of the first PSA tail gas is recycled as fuel to reduce the carbon intensity of the renewable hydrogen product.

[0021] WO 2022 / 265648 A1 relates to the removal of NOx contaminants by selective catalytic reduction (SCR) from a flue gas produced in an ammonia cracking process, using an aqueous ammonia solution produced by cooling the compressed exhaust gas from a hydrogen PSA device to purify the cracked gas.

[0022] WO 2022 / 265649 A1 relates to reducing the water content of ammonia used in an ammonia cracking process, thereby enabling the use of water-incompatible cracking catalysts. The water removal process can also be used to recover and recycle ammonia from the cracking gas.

[0023] WO 2022 / 265650 A1 relates to an ammonia cracking process in which cracked gas is purified in a PSA system. Residual ammonia in a first cracked gas is converted into further hydrogen and nitrogen by feeding PSA residual gas or a gas derived therefrom to a secondary cracking reactor and further processing a second cracked gas.

[0024] WO 2022 / 265651 A1 relates to a process in which residual ammonia is removed from ammonia cracking gas in a hydrogen PSA system using a non-zeolitic adsorbent such as activated carbon, activated alumina or silica gel.

[0025] The state-of-the-art processes for the production of H2 from NH3 are not entirely satisfactory, and there is a need for improved processes that can be economically implemented on a large-scale. A suitable reactor concept must be developed for the production of H2 from NH3. For an endothermic or quasi-isothermal high-temperature reaction, a fired tubular reactor analogous to a steam reformer is generally suitable. However, the technical transfer of steam reforming to the catalytic decomposition of NH3 is associated with various obstacles.

[0026] It is an object of the invention to provide an improved process for producing H2 from NH2. The process should be economical in terms of energy balance and yield and capable of being carried out on an industrial scale. It should be possible to use NH2 decomposition catalysts that have a sufficient lifetime under the given reaction conditions at a reasonable cost.

[0027] This problem is solved by the subject matter of the patent claims.

[0028] It has been found that the purification of the product gas by pressure swing adsorption requires a product gas pressure of at least 10 bar a, preferably at least 20 bar a, to function economically. However, such a pressure is in itself insufficient for the catalytic decomposition of NH; unfavorable. Carrying out the catalytic decomposition at lower pressure and subsequent compression of the product gas before pressure swing adsorption would not be economical.

[0029] It has now surprisingly been found that a reaction procedure is possible which, on the one hand, achieves a good yield of the decomposition reaction, but on the other hand also takes place at a sufficiently high pressure so that subsequent purification by pressure swing adsorption is possible in an economical manner and without prior compression of the product gas.

[0030] It has been found that conducting the reaction in two reactors connected in series is particularly advantageous when the first reactor is a substantially adiabatically operated fixed-bed reactor without external heat input, and the second reactor is designed as a fired tubular reactor analogous to a primary reformer (steam reformer). This allows the fired tubular reactor to be made smaller. Consequently, it also limits the amount of heat contained in the combustion air, i.e., in the exhaust gas from the firing system for the tubular reactor. This heat must be returned to the process for economical operation to prevent it from being released unused into the environment.

[0031] It was found that the temperatures at the inlet (Ti) and outlet (T2) of the first reactor, the temperatures at the inlet (T3) and outlet (T4) of the second reactor, the degree of partial conversion in the first reactor and the design of the second reactor interact with each other and can be influenced in a way that enables optimization of the economic efficiency of the process.

[0032] For the upstream fixed-bed reactor, the inlet temperature (Ti) and outlet temperature (T2) are limited by the permissible preheating and the lower limit by the catalyst activity. Depending on the type of catalyst(s), the operating range is preferably between approximately 650°C and approximately 350°C.

[0033] For the downstream fired tubular reactor, a parabolic profile of the energy supply through the tube wall preferably leads to a significantly lower catalyst requirement compared to a linear profile of the energy supply. A ceiling firing with a comparatively short flame has proven to be the optimal solution for the energy supply. The downstream fired tubular reactor is preferably designed for an inlet temperature in the range of approximately 550°C to 700°C. At higher temperatures, the reaction consumes more energy than can be supplied through the tube wall as a result of the firing. In addition, special materials with a shortened service life would be required for the equipment, and there would be only a small saving in catalyst volume. The downstream fired tubular reactor is preferably designed so that its outlet temperature is higher than its inlet temperature. In this way, an approximation to the Equilibrium conversion can be achieved. Lower outlet temperatures would lead to lower conversions and thus to a higher gas load and an increase in the required reactor volume.

[0034] In particular, reaction conditions were found under which conversions of 98% and more in terms of H2 can be achieved, whereby the remaining amount of unreacted NH3 in the product gas is so low that separation of the H2 by pressure swing adsorption is possible without further measures.

[0035] A first aspect of the invention relates to a process for producing H2 from NH3 comprising the steps: (a) providing a reactant gas comprising or consisting essentially of NH3; (b) heating the reactant gas to a gas temperature Ti in the range of 550 to 850°C at a pressure pi of at least 10 bar a; (c) introducing the heated reactant gas at the gas temperature Ti and the pressure pi into at least one fixed bed reactor which contains at least one catalyst bed which comprises or consists essentially of an Nff reduction catalyst; (d) partially decomposing NH3 in the at least one fixed-bed reactor on the at least one catalyst bed to obtain an intermediate gas comprising or consisting essentially of H2, N2 and undecomposed NH3; and (e) discharging the intermediate product gas from the at least one fixed bed reactor at a gas temperature T2 in the range from 300 to 700°C and a pressure p2 of at least 10 bar a; (f) heating the intermediate gas to a gas temperature T3 in the range from 550 to 700°C at a pressure ps of at least 10 bar a; (g) introducing the heated intermediate gas at the gas temperature T3 and the pressure p3 into at least one tubular reactor comprising a plurality of parallel tubes, each containing at least one catalyst bed heated by combustion of a combustion gas and comprising or consisting essentially of a nickel-based NH3 decomposition catalyst; (h) decomposing NH3 in the at least one tubular reactor on the catalyst beds to obtain a product gas which comprises or consists essentially of H2, N2 and optionally undecomposed NH3; and (i) discharging the product gas from the at least one tubular reactor at a gas temperature T4 in the range from 550 to 750°C and a pressure p4 of at least 10 bar a.

[0036] In step (a) of the process according to the invention, a reactant gas is provided which comprises or consists essentially of NH3.

[0037] In preferred embodiments, the NH3 is stored in liquid form at low temperatures and is therefore essentially pure, so that the reactant gas preferably consists essentially of NH3.

[0038] The NH3 is preferably synthetic NH3 produced from N2 and H2, wherein the H2 is preferably obtained by electrolysis of water, and wherein the electricity for the electrolysis is preferably obtained from renewable energies, preferably solar energy (in particular photovoltaics) and / or wind energy.

[0039] In step (b) of the process according to the invention, the reactant gas previously provided in step (a) is heated to a gas temperature Ti in the range from 550 to 850°C at a pressure pi of at least 10 bar a.

[0040] Ti is preferably in the range of 550 to 700°C.

[0041] Preferably, Ti is at least 595°C, preferably at least 600°C, more preferably at least 605°C, even more preferably at least 610°C, most preferably at least 615°C, and especially at least 620°C. Preferably, Ti is at least 625°C, preferably at least 630°C, more preferably at least 635°C, even more preferably at least 640°C, most preferably at least 645°C, and especially at least 650°C.

[0042] Preferably, Ti is at most 710°C, preferably at most 705°C, more preferably at most 700°C, even more preferably at most 695°C, most preferably at most 690°C, and especially at most 685°C. Preferably, Ti is at most 680°C, preferably at most 675°C, more preferably at most 670°C, even more preferably at most 665°C, most preferably at most 660°C, and especially at most 655°C.

[0043] Preferably, pi is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a.

[0044] Preferably, pi is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a.

[0045] In step (c) of the process according to the invention, the reactant gas previously heated in step (b) is introduced at the gas temperature Ti and the pressure pi into at least one fixed bed reactor which contains at least one catalyst bed which comprises or consists essentially of an NFh decomposition catalyst.

[0046] Preferably, at least one catalyst bed of the fixed bed reactor is not heated.

[0047] Preferably, the at least one fixed bed reactor is operated adiabatically.

[0048] Preferably, the NFF reduction catalyst of the at least one catalyst bed of the fixed bed reactor is nickel-based, preferably supported nickel.

[0049] Preferably, the nickel-based NHs decomposition catalyst of the at least one catalyst bed of the fixed bed reactor for the decomposition of NH3 has an (apparent) activation energy of at most 240 kJ-mol 1 preferably not more than 230 kJ-mol 1 , preferably not more than 220 kJ-mol 1 , more preferably not more than 210 kJ-mol 1 , most preferably not more than 200 kJ-mol 1 , and in particular not more than 190 kJ-mol 1 .

[0050] Preferably, the nickel-based NHs decomposition catalyst of the at least one catalyst bed of the fixed bed reactor for the decomposition of NH3 has an (apparent) activation energy of at most 180 kJ-mol1 preferably not more than 170 kJ-mol 1 , preferably not more than 160 kJ-mol 1 , more preferably not more than 150 kJ-mol 1 , most preferably not more than 140 kJ-mol 1 , and in particular not more than 130 kJ-mol 1 .

[0051] In preferred embodiments, the at least one fixed-bed reactor contains a first catalyst bed comprising a first NFh reduction catalyst and a second catalyst bed comprising a second NFF reduction catalyst. The second catalyst bed is arranged downstream of the first catalyst bed in the flow direction of the reactant gas or intermediate product gas.

[0052] In preferred embodiments, the first NFf decomposition catalyst and the second NH3 decomposition catalyst are the same.

[0053] In other preferred embodiments, the first NFF decomposition catalyst and the second NH3 decomposition catalyst are different.

[0054] Preferably, for the decomposition of NH3, the second NH3 decomposition catalyst has a higher (apparent) activation energy than the first NH3 decomposition catalyst.

[0055] In preferred embodiments, the at least one catalyst bed of the fixed bed reactor has a substantially cylindrical shape and is flowed through axially by the reactant gas or intermediate product gas.

[0056] In other preferred embodiments, the at least one catalyst bed of the fixed bed reactor has substantially the shape of a hollow cylinder and is radially flowed through by the reactant gas or intermediate product gas.

[0057] Preferably, the at least one catalyst bed of the fixed bed reactor has a substantially circular cross-section with a diameter of at least 80 cm, preferably at least 100 cm, more preferably at least 120 cm, even more preferably at least 140 cm, most preferably at least 160 cm, and in particular at least 180 cm.

[0058] Preferably, the at least one catalyst bed of the fixed bed reactor has a length of at least 80 cm, preferably at least 100 cm, more preferably at least 120 cm, even more preferably at least 140 cm, most preferably at least 160 cm, and in particular at least 180 cm in the flow direction of the reactant gas or intermediate gas.

[0059] Preferably, the at least one catalyst bed of the fixed bed reactor has a space velocity in the range of 5,000 to 25,000 h 1 preferably 10,000 to 20,000 h 1 , preferably 12,500 to 17,500 h 1 .

[0060] In step (d) of the process according to the invention, NH3 is partially decomposed in the at least one fixed bed reactor on the at least one catalyst bed to obtain an intermediate gas which comprises or consists essentially of FF, N2 and undecomposed NH3.

[0061] Preferably, in step (d), the conversion of the decomposed NH3 is at least 12.5%, preferably at least 15%, more preferably at least 17.5%, even more preferably at least 20%, most preferably at least 22.5%, and in particular at least 25%, in each case based on the amount of NH3 which was originally contained in the reactant gas provided in step (a).

[0062] Preferably, in step (d), the conversion of the NH3 is at most 42.5%, preferably at most 40%, more preferably at most 37.5%, even more preferably at most 35%, most preferably at most 32.5%, and in particular at most 30%, in each case based on the amount of NH3 which was originally contained in the reactant gas provided in step (a).

[0063] In step (e) of the process according to the invention, the intermediate product gas previously obtained in step (d) is discharged from the at least one fixed bed reactor at a gas temperature T2 in the range from 300 to 700°C and a pressure p2 of at least 10 bar a.

[0064] Preferably T2 is in the range of 300 to 690°C.

[0065] Preferably, T2 is at least 300°C, preferably at least 310°C, more preferably at least 320°C, even more preferably at least 330°C, most preferably at least 340°C, and especially at least 350°C. Preferably, T2 is at least 400°C, preferably at least 410°C, more preferably at least 420°C, even more preferably at least 430°C, most preferably at least 440°C, and especially at least 450°C.

[0066] Preferably, T2 is at most 510°C, preferably at most 500°C, more preferably at most 490°C, even more preferably at most 480°C, most preferably at most 470°C, and especially at most 460°C. Preferably, T2 is at most 410°C, preferably at most 400°C, more preferably at most 390°C, even more preferably at most 380°C, most preferably at most 370°C, and especially at most 360°C.

[0067] Preferably, p2 is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a.

[0068] Preferably, p2 is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a.

[0069] Preferably Ti > T2 applies.

[0070] Preferably, the magnitude of the relative temperature difference | Ti - T2 | is at least 50°C, more preferably at least 75°C, even more preferably at least 100°C, most preferably at least 125°C, and especially at least 150°C. Preferably, the magnitude of the relative temperature difference | Ti - T2 | is at least 175°C, more preferably at least 200°C, even more preferably at least 225°C, most preferably at least 250°C, and especially at least 275°C.

[0071] In preferred embodiments, - Ti in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C.

[0072] In other preferred embodiments, - Ti in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C.

[0073] Preferably pi > P2.

[0074] Preferably, the magnitude of the relative pressure difference | pi - P2 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar.

[0075] Preferably T3 > T2.

[0076] Preferably, the amount of the relative temperature difference | T3 - T2 | is at least 20°C, more preferably at least 40°C, even more preferably at least 60°C, most preferably at least 80°C, and in particular at least 100°C.

[0077] Preferably, the amount of the relative temperature difference | T3 - T2 | is at least 110°C, more preferably at least 120°C, even more preferably at least 130°C, most preferably at least 140°C, and in particular at least 150°C.

[0078] In preferred embodiments, - T2 in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C; and - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and

[0079] In other preferred embodiments, - T2 in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C; and - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C.

[0080] Preferably ps > P2.

[0081] Preferably, the magnitude of the relative pressure difference | ps - P2 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar.

[0082] In preferred embodiments, T3 > Ti applies.

[0083] In other preferred embodiments, T3 < Ti.

[0084] Preferably, the amount of the relative temperature difference | Ti - T3 | is at least 5°C, more preferably at least 10°C, even more preferably at least 15°C, most preferably at least 20°C, and in particular at least 25°C. Preferably, the amount of the relative temperature difference | Ti - T3 | at least 30°C, more preferably at least 35°C, even more preferably at least 40°C, most preferably at least 45°C, and in particular at least 50°C.

[0085] Preferably, the magnitude of the relative temperature difference | Ti - T3 | is at most 50°C, more preferably at most 45°C, even more preferably at most 40°C, most preferably at most 35°C, and in particular at most 30°C. Preferably, the magnitude of the relative temperature difference | Ti - T3 | is at most 25°C, more preferably at most 20°C, even more preferably at most 15°C, most preferably at most 10°C, and in particular at most 5°C.

[0086] In preferred embodiments, - Ti in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C.

[0087] Preferably ps < pi.

[0088] Preferably, the magnitude of the relative pressure difference | ps - pi | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar.

[0089] Preferably, the nickel-based NHs decomposition catalyst of each of at least one catalyst bed of the plurality of tubes of the tubular reactor is supported nickel.

[0090] Preferably, the nickel-based NHs decomposition catalyst of the at least one catalyst bed of the plurality of tubes of the tubular reactor for the decomposition of NH3 has an (apparent) activation energy of at most 240 kJ-mol 1 preferably not more than 230 kJ-mol 1 , preferably not more than 220 kJ-mol 1 , more preferably not more than 210 kJ-mol 1 , most preferably not more than 200 kJ-mol 1 , and in particular not more than 190 kJ-mol 1 .

[0091] Preferably, the nickel-based NHs decomposition catalyst of the at least one catalyst bed of the plurality of tubes of the tubular reactor for the decomposition of NH3 has an (apparent) activation energy of at most 180 kJ-mol 1 preferably not more than 170 kJ-mol 1 , preferably not more than 160 kJ-mol 1 , more preferably not more than 150 kJ-mol 1 , most preferably not more than 140 kJ-mol 1 , and in particular not more than 130 kJ-mol 1 .

[0092] Preferred support materials are selected from the group consisting of 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, NaNbCf, Nb2Os, Sm2O3, SmAlCh, SrMnCf, SrTiO2, SrZrCf. TiO2, Y2C>3, ZrO2, carbon (e.g. CNTs, SWCNTs, AX-21, MSC-30, MESO-C, GNP, activated carbon, graphene, graphene oxide), attapulgite, hydrocalumite, sepiolite, and mixtures thereof.

[0093] In step (f) of the process according to the invention, the intermediate gas is heated to a gas temperature T3 in the range of 550 to 700°C at a pressure ps of at least 10 bar a.

[0094] T3 is preferably in the range of 560 to 700°C.

[0095] Preferably, T3 is at least 590°C, preferably at least 595°C, more preferably at least 600°C, even more preferably at least 605°C, most preferably at least 610°C, and especially at least 615°C.

[0096] Preferably, T3 is at most 650°C, preferably at most 645°C, more preferably at most 640°C, even more preferably at most 635°C, most preferably at most 630°C, and in particular at most 625°C.

[0097] Preferably, ps is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a.

[0098] Preferably, ps is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a.

[0099] In step (g) of the process according to the invention, the intermediate product gas previously heated in step (f) is introduced at the gas temperature T3 and the pressure ps into at least one tubular reactor which comprises a plurality of parallel tubes, each of which contains at least one Containing a catalyst bed which is heated by combustion of a combustion gas and comprises or consists essentially of a nickel-based NFL decomposition catalyst.

[0100] Preferably, the number of parallel tubes of the tubular reactor is at least 50, preferably at least 100, more preferably at least 150, even more preferably at least 200, most preferably at least 250, and in particular at least 300.

[0101] Preferably, the plurality of parallel tubes of the tubular reactor in the flow direction of the intermediate gas or product gas each have a length LR of at least 5.5 m, preferably at least 6.0 m, more preferably at least 6.5 m, even more preferably at least 8 m, most preferably at least 7.0 m, and in particular at least 7.5 m.

[0102] Preferably, the plurality of parallel tubes of the tubular reactor in the flow direction of the intermediate product gas or product gas has a substantially circular cross-section with an inner diameter of at least 5.0 cm, preferably at least 5.5 cm, more preferably at least 6.0 cm, even more preferably at least 6.5 cm, most preferably at least 7.0 cm, and in particular at least 7.5 cm.

[0103] Preferably, the plurality of parallel tubes of the tubular reactor in the flow direction of the intermediate product gas or product gas has a substantially circular cross-section with an internal diameter of at most 12 cm, preferably at most 11 cm, more preferably at most 10 cm, even more preferably at most 9.5 cm, most preferably at most 9.0 cm, and in particular at most 8.5 cm.

[0104] Preferably, the catalyst beds of the tubular reactor have a total space velocity in the range of 500 to 15,000 h 1 preferably 1,000 to 10,000 h 1 , preferably 2,500 to 7,500 h 1 .

[0105] Preferably, the at least one catalyst bed of the fixed bed reactor has a greater space velocity than the catalyst beds of the tubular reactor as a whole.

[0106] In step (h) of the process according to the invention, NH3 is decomposed in the at least one tubular reactor on the catalyst bed to obtain a product gas which comprises or consists essentially of FE, N2 and optionally undecomposed NH3.

[0107] Preferably, in step (h), the conversion of the decomposed NH3 is at least 90%, preferably at least 92.5%, more preferably at least 95%, even more preferably at least 96%, most preferably at least 97%, and in particular at least 98%, in each case based on the amount of NH3 which was originally contained in the reactant gas provided in step (a).

[0108] In step (i) of the process according to the invention, the product gas previously obtained in step (h) is discharged from the at least one tubular reactor at a gas temperature T4 in the range from 550 to 750°C and a pressure p4 of at least 10 bar a.

[0109] Preferably, T4 is in the range of 560 to 750°C.

[0110] Preferably, T4 is at least 650°C, preferably at least 655°C, more preferably at least 660°C, even more preferably at least 665°C, most preferably at least 670°C, and especially at least 675°C.

[0111] Preferably, T4 is at most 710°C, preferably at most 705°C, more preferably at most 700°C, even more preferably at most 695°C, most preferably at most 690°C, and in particular at most 685°C.

[0112] Preferably, p4 is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a.

[0113] Preferably, p4 is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a.

[0114] T4 > T3 is preferred.

[0115] Preferably, the amount of the relative temperature difference | T3 - T4 | is at least 10°C, more preferably at least 15°C, even more preferably at least 20°C, most preferably at least 25°C, and in particular at least 30°C.

[0116] Preferably, the amount of the relative temperature difference | T3 - T4 | is at least 35°C, more preferably at least 40°C, even more preferably at least 45°C, most preferably at least 50°C, and in particular at least 55°C.

[0117] Preferably, the amount of the relative temperature difference | T3 - T4 | is at most 55°C, more preferably at most 50°C, even more preferably at most 45°C, most preferably at most 40°C, and in particular at most 35°C.

[0118] Preferably, the amount of the relative temperature difference | T3 - T4 | is at most 30°C, more preferably at most 25°C, even more preferably at most 20°C, most preferably at most 15°C, and in particular at most 10°C.

[0119] In preferred embodiments, - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C.

[0120] Preferably p4 > p3.

[0121] Preferably, the magnitude of the relative pressure difference | ps - P4 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar.

[0122] Preferably, the combustion of the combustion gas is carried out with at least one burner, generating at least one flame, with which heat energy is introduced into the tubes, wherein a heat energy flow Q introduced into the tubes w has a non-constant course over the length of the tubes LR.

[0123] Preferably, the heat energy flow Q w reaches a maximum over the length of the tubes LR.

[0124] Preferably, the tubes can be divided into two equal halves along their length LR, with the intermediate product gas or product gas flowing first through the first half and then through the second half, with the maximum of the heat energy flow Q w is achieved in the first half.

[0125] Preferably, the tubes can each be divided into four equal segments over their length LR, with the intermediate product gas or product gas first flowing through the first segment, then the second segment, finally the third segment and then the fourth segment, with the maximum of the heat energy flow Q w in the second segment.

[0126] Preferably, the combustion of the combustion gas is carried out with at least one burner to generate at least one flame whose length LF in the flow direction of the burning combustion gas runs substantially parallel to the length of the tubes LR.

[0127] Preferably, the burning combustion gas flows essentially in the same direction as the intermediate product gas or product gas (ceiling firing).

[0128] Preferably LR > LF applies.

[0129] Preferably, the length ratio LR:LF is in the range of 10:1 to 1.1:1, preferably 7:1 to 1.5:1, more preferably 4:1 to 2:1.

[0130] Preferably, in step (h), when intermediate product gas or product gas flows through the tubes, the amount of heat consumed by the endothermic decomposition of NH; is initially greater than the amount of heat which is released by the combustion of the combustion gas as heat energy flow Q wis introduced into the tubes so that the intermediate gas or product gas initially reaches a minimum gas temperature T m in cools down (T m in < T3).

[0131] Preferably, the relative temperature difference | T3 - T m in | at least 10°C, more preferably at least 20°C, even more preferably at least 30°C, most preferably at least 30°C, and especially at least 40°C.

[0132] Preferably T m in the range of 560 to 600°C, preferably 570 to 590°C.

[0133] Preferably, after reaching the minimum gas temperature T m in the amount of heat consumed by the endothermic decomposition of NH3 is subsequently smaller than the amount of heat which is released by the combustion of the combustion gas as heat energy flow Q wis introduced into the tubes so that the intermediate gas or product gas is subsequently heated as it flows through the tubes (T m in < T4).

[0134] Preferably, the relative temperature difference | T4 - T m in | at least 50°C, more preferably at least 55°C, even more preferably at least 60°C, most preferably at least 65°C, and especially at least 70°C.

[0135] Preferably, the tubes can be divided into two equal halves along their length LR, with the intermediate product gas or product gas flowing first through the first half and then through the second half, with the minimum gas temperature T m when flowing through the first half.

[0136] Preferably, the tubes can each be divided into four equal segments over their length LR, with the intermediate gas or product gas first flowing through the first segment, then the second segment, finally the third segment and then the fourth segment, with the minimum gas temperature T m when flowing through the first segment.

[0137] In preferred embodiments, - Ti in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; - T2 in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C; - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C.

[0138] In other preferred embodiments, - Ti in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; - T2 in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C; - T3 in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and T4 is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C

[0139] Preferably, the combustion gas comprises NH3; preferably, the reactant gas provided in step (a) is divided into (i) a first fraction, which is fed to step (b), and (ii) a second fraction, which serves as combustion gas.

[0140] Preferably, the second fraction makes up at most 8.0 mol% of the reactant gas provided in step (a), more preferably at most 7.5 mol%, even more preferably at most 7.0 mol%, most preferably at most 6.5 mol%, and in particular at most 5 mol%.

[0141] Preferably, the method comprises the additional step (j) purifying the product gas by pressure swing adsorption to obtain a product gas enriched in H2 and an exhaust gas depleted in H2; preferably, the exhaust gas depleted in H2 is recycled and introduced into the combustion gas.

[0142] A further aspect of the invention relates to a device for carrying out the method according to the invention described above.

[0143] Preferred embodiments of the invention are summarized below as sentences 1 to 103: Sentence 1: A process for producing H2 from NH3 comprising the steps: (a) providing a reactant gas which comprises or consists essentially of NH3; (b) heating the reactant gas to a gas temperature Ti in the range from 550 to 850°C at a pressure pi of at least 10 bar a; (c) introducing the heated reactant gas at the gas temperature Ti and the pressure pi into at least one fixed bed reactor which contains at least one catalyst bed which comprises or consists essentially of an NH3 decomposition catalyst; (d) partially decomposing NH3 in the at least one fixed bed reactor on the at least one catalyst bed to obtain an intermediate product gas which comprises or consists essentially of H2, N2 and undecomposed NH3; (e) discharging the intermediate product gas from the at least one fixed bed reactor at a gas temperature T2 in the range from 300 to 700°C and a pressure p2 of at least 10 bar a;(f) heating the intermediate product gas to a gas temperature Tj in the range from 550 to 700°C at a pressure ps of at least 10 bar a; (g) introducing the heated intermediate product gas at the gas temperature T3 and the pressure ps into at least one tubular reactor comprising a plurality of parallel tubes, each containing at least one catalyst bed heated by combustion of a combustion gas and comprising or consisting essentially of a nickel-based NFh decomposition catalyst; (h) decomposing NH3 in the at least one tubular reactor on the catalyst beds to obtain a product gas comprising or consisting essentially of H2, N2 and optionally undecomposed NH3; and (i) discharging the product gas from the at least one; Tubular reactor at a gas temperature T4 in the range of 550 to 750°C and a pressure p4 of at least 10 bar a. Sentence 2: The process according to sentence 1, wherein the at least one catalyst bed of the fixed bed reactor is not heated. Sentence 3: The process according to sentence 1 or 2, wherein the at least one fixed-bed reactor is operated adiabatically. Sentence 4: The process according to one of the preceding sentences, wherein the NH3 decomposition catalyst of the at least one catalyst bed of the fixed-bed reactor is nickel-based, preferably supported nickel. Sentence 5: The process according to one of the preceding sentences, wherein the nickel-based NH3 decomposition catalyst of the at least one catalyst bed of the fixed-bed reactor has an (apparent) activation energy of at most 240 kJ-mol for the decomposition of NH3. 1 preferably at most 230 kJ-mol 1 , preferably not more than 220 kJ-mol 1 , more preferably not more than 210 kJ-mol 1 , most preferably not more than 200 kJ-mol 1 , and in particular not more than 190 kJ-mol 1 . Sentence 6: The process according to one of the preceding sentences, wherein the nickel-based NFF decomposition catalyst of the at least one catalyst bed of the fixed bed reactor has an (apparent) activation energy of at most 180 kJ-mol for the decomposition of NH3 1 preferably at most 170 kJ-mol 1 , preferably not more than 160 kJ-mol 1 , more preferably not more than 150 kJ-mol 1 , most preferably not more than 140 kJ-mol 1 , and in particular not more than 130 kJ-mol 1 . Sentence 7: The process according to any one of the preceding sentences, wherein the at least one fixed bed reactor contains a first catalyst bed comprising a first NFF reduction catalyst and a second catalyst bed comprising a second NFF reduction catalyst, wherein the second catalyst bed is arranged downstream of the first catalyst bed in the flow direction of the reactant gas or intermediate product gas. Sentence 8: The process according to Sentence 7, wherein the first NFF decomposition catalyst and the second NH3 decomposition catalyst are the same. Sentence 9: The process according to Sentence 7, wherein the first NFF decomposition catalyst and the second NH3 decomposition catalyst are different. Sentence 10: The process according to sentence 9, wherein for the decomposition of NH3 the second NFF reduction catalyst has a higher (apparent) activation energy than the first NFF reduction catalyst. Sentence 11: The process according to one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has a substantially cylindrical shape and is flowed through axially by the reactant gas or intermediate product gas. Sentence 12: The process according to one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has substantially the shape of a hollow cylinder and is radially flowed through by the reactant gas or intermediate product gas. Sentence 13: The process according to any one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has a substantially circular cross-section with a diameter of at least 80 cm, preferably at least 100 cm, more preferably at least 120 cm, even more preferably at least 140 cm, most preferably at least 160 cm, and in particular at least 180 cm. Sentence 14: The process according to any one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has a length of at least 80 cm, preferably at least 100 cm, more preferably at least 120 cm, even more preferably at least 140 cm, most preferably at least 160 cm, and in particular at least 180 cm in the flow direction of the reactant gas or intermediate gas. Sentence 15: The process according to any one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has a space velocity in the range of 5,000 to 25,000 h 1 preferably 10,000 to 20,000 h 1 , preferably 12,500 to 17,500 h 1 . Sentence 16: The process according to any one of the preceding sentences, wherein Ti is in the range of 550 to 700°C. Sentence 17: The process according to any one of the preceding sentences, wherein Ti is at least 595°C, preferably at least 600°C, more preferably at least 605°C, even more preferably at least 610°C, most preferably at least 615°C, and especially at least 620°C. Sentence 18: The process according to any one of the preceding sentences, wherein Ti is at least 625°C, preferably at least 630°C, more preferably at least 635°C, even more preferably at least 640°C, most preferably at least 645°C, and especially at least 650°C. Sentence 19: The process according to any one of the preceding sentences, wherein Ti is at most 710°C, preferably at most 705°C, more preferably at most 700°C, even more preferably at most 695°C, most preferably at most 690°C, and especially at most 685°C. Sentence 20: The process according to any one of the preceding sentences, wherein Ti is at most 680°C, preferably at most 675°C, more preferably at most 670°C, even more preferably at most 665°C, most preferably at most 660°C, and especially at most 655°C. Sentence 21: The process according to any one of the preceding sentences, wherein pi is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a. Sentence 22: The process according to any one of the preceding sentences, wherein pi is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a. Clause 23: The process according to any one of the preceding clauses, wherein T2 is in the range of 300 to 690°C. Sentence 24: The process according to any one of the preceding sentences, wherein T2 is at least 300°C, preferably at least 310°C, more preferably at least 320°C, even more preferably at least 330°C, most preferably at least 340°C, and especially at least 350°C. Sentence 25: The process according to any one of the preceding sentences, wherein T2 is at least 400°C, preferably at least 410°C, more preferably at least 420°C, even more preferably at least 430°C, most preferably at least 440°C, and especially at least 450°C. Sentence 26: The process according to any one of the preceding sentences, wherein T2 is at most 510°C, preferably at most 500°C, more preferably at most 490°C, even more preferably at most 480°C, most preferably at most 470°C, and in particular at most 460°C. Sentence 27: The process according to any one of the preceding sentences, wherein T2 is at most 410°C, preferably at most 400°C, more preferably at most 390°C, even more preferably at most 380°C, most preferably at most 370°C, and in particular at most 360°C. Sentence 28: The process according to any one of the preceding sentences, wherein P2 is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a. Sentence 29: The process according to any one of the preceding sentences, wherein P2 is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a. Theorem 30: The method according to any of the preceding theorems, where Ti > T2. Sentence 31: The process according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - T2 | is at least 50°C, more preferably at least 75°C, even more preferably at least 100°C, most preferably at least 125°C, and in particular at least 150°C. Sentence 32: The process according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - T2 | is at least 175°C, more preferably at least 200°C, even more preferably at least 225°C, most preferably at least 250°C, and in particular at least 275°C. Sentence 33: The process according to any one of the preceding sentences, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 is in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C. Sentence 34: The process according to any one of Sentences 1 to 32, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 is in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C. Theorem 35: The method according to one of the preceding theorems, where pi > P2. Sentence 36: The method according to any one of the preceding sentences, wherein the magnitude of the relative pressure difference | pi - P2 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar. Sentence 37: The process according to any one of the preceding sentences, wherein in step (d) the conversion of the decomposed NH; is at least 12.5%, preferably at least 15%, more preferably at least 17.5%, even more preferably at least 20%, most preferably at least 22.5%, and in particular at least 25%, in each case based on the amount of NHs which was originally contained in the reactant gas provided in step (a). Sentence 38: The process according to any one of the preceding sentences, wherein in step (d) the conversion of the NH; is at most 42.5%, preferably at most 40%, more preferably at most 37.5%, even more preferably at most 35%, most preferably at most 32.5%, and in particular at most 30%, in each case based on the amount of NEE which was originally contained in the reactant gas provided in step (a). Theorem 39: The method according to any of the preceding theorems, where T3 > T2. Sentence 40: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T2 | is at least 20°C, more preferably at least 40°C, even more preferably at least 60°C, most preferably at least 80°C, and in particular at least 100°C. Sentence 41: The process according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T2 | is at least 110°C, more preferably at least 120°C, even more preferably at least 130°C, most preferably at least 140°C, and in particular at least 150°C. Sentence 42: The process according to any one of the preceding sentences, wherein - T2 is in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C; and - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C. Sentence 43: The process according to any one of sentences 1 to 41, wherein - T2 is in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C; and - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C. Theorem 44: The method according to any of the preceding theorems, where p3 > P2. Sentence 45: The method according to any one of the preceding sentences, wherein the magnitude of the relative pressure difference | P3 - P2 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar. Theorem 46: The method according to any one of the preceding theorems, where T3 > Ti. Theorem 47: The method according to any one of the preceding theorems, where T3 < Ti. Sentence 48: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - Ts | is at least 5°C, more preferably at least 10°C, even more preferably at least 15°C, most preferably at least 20°C, and in particular at least 25°C. Sentence 49: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - Ts | is at least 30°C, more preferably at least 35°C, even more preferably at least 40°C, most preferably at least 45°C, and in particular at least 50°C. Sentence 50: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - Ts | is at most 50°C, more preferably at most 45°C, even more preferably at most 40°C, most preferably at most 35°C, and in particular at most 30°C. Sentence 51: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | Ti - Ts | is at most 25°C, more preferably at most 20°C, even more preferably at most 15°C, most preferably at most 10°C, and in particular at most 5°C. Sentence 52: The process according to any one of the preceding sentences, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C. Theorem 53: The method according to any of the preceding theorems, where ps < pi. Sentence 54: The method according to any one of the preceding sentences, wherein the magnitude of the relative pressure difference | P3 - pi | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar. Sentence 55: The process according to any one of the preceding sentences, wherein the nickel-based NHs decomposition catalyst of each of at least one catalyst bed of the plurality of tubes of the tubular reactor is supported nickel. Sentence 56: The process according to any one of the preceding sentences, wherein the nickel-based NH3 decomposition catalyst of the at least one catalyst bed of the plurality of tubes of the tubular reactor has an (apparent) activation energy of at most 240 kJ-mol for the decomposition of NH3 1 preferably at most 230 kJ-mol 1 , preferably not more than 220 kJ-mol 1 , more preferably not more than 210 kJ-mol1 , most preferably not more than 200 kJ-mol 1 , and in particular not more than 190 kJ-mol 1 . Sentence 57: The process according to any one of the preceding sentences, wherein the nickel-based NH3 decomposition catalyst of the at least one catalyst bed of the plurality of tubes of the tubular reactor has an (apparent) activation energy of at most 180 kJ-mol for the decomposition of NH3 1 preferably at most 170 kJ-mol 1 , preferably not more than 160 kJ-mol 1 , more preferably not more than 150 kJ-mol 1 , most preferably not more than 140 kJ-mol 1 , and in particular not more than 130 kJ-mol 1 . Sentence 58: The process according to any one of the preceding sentences, wherein the number of parallel tubes of the tubular reactor is at least 50, preferably at least 100, more preferably at least 150, even more preferably at least 200, most preferably at least 250, and especially at least 300. Sentence 59: The process according to any one of the preceding sentences, wherein the plurality of parallel tubes of the tubular reactor in the flow direction of the intermediate product gas or product gas each have a length LR of at least 5.5 m, preferably at least 6.0 m, more preferably at least 6.5 m, even more preferably at least 8 m, most preferably at least 7.0 m, and in particular at least 7.5 m. Sentence 60: The process according to any one of the preceding sentences, wherein the plurality of parallel tubes of the tubular reactor have, in the flow direction of the intermediate product gas or product gas, a substantially circular cross-section with an inner diameter of at least 5.0 cm, preferably at least 5.5 cm, more preferably at least 6.0 cm, even more preferably at least 6.5 cm, most preferably at least 7.0 cm, and in particular at least 7.5 cm. Sentence 61: The process according to any one of the preceding sentences, wherein the plurality of parallel tubes of the tubular reactor have, in the flow direction of the intermediate product gas or product gas, a substantially circular cross-section with an inner diameter of at most 12 cm, preferably at most 11 cm, more preferably at most 10 cm, even more preferably at most 9.5 cm, most preferably at most 9.0 cm, and in particular at most 8.5 cm. Sentence 62: The process according to any one of the preceding sentences, wherein the catalyst beds of the tubular reactor have a total space velocity in the range of 500 to 15,000 h 1 preferably 1,000 to 10,000 h 1 , preferably 2,500 to 7,500 h 1 . Sentence 63: The process according to any one of the preceding sentences, wherein the at least one catalyst bed of the fixed bed reactor has a greater space velocity than the catalyst beds of the tubular reactor as a whole. Clause 64: The process according to any one of the preceding clauses, wherein T3 is in the range of 560 to 700°C. Sentence 65: The process according to any one of the preceding sentences, wherein T3 is at least 590°C, preferably at least 595°C, more preferably at least 600°C, even more preferably at least 605°C, most preferably at least 610°C, and especially at least 615°C. Sentence 66: The process according to any one of the preceding sentences, wherein T3 is at most 650°C, preferably at most 645°C, more preferably at most 640°C, even more preferably at most 635°C, most preferably at most 630°C, and especially at most 625°C. Sentence 67: The process according to any one of the preceding sentences, wherein p3 is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a. Sentence 68: The process according to any one of the preceding sentences, wherein ps is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a. Clause 69: The process according to any one of the preceding clauses, wherein T4 is in the range of 560 to 750°C. Sentence 70: The process according to any one of the preceding sentences, wherein T4 is at least 650°C, preferably at least 655°C, more preferably at least 660°C, even more preferably at least 665°C, most preferably at least 670°C, and especially at least 675°C. Sentence 71: The process according to any one of the preceding sentences, wherein T4 is at most 710°C, preferably at most 705°C, more preferably at most 700°C, even more preferably at most 695°C, most preferably at most 690°C, and especially at most 685°C. Sentence 72: The process according to any one of the preceding sentences, wherein p4 is at least 12 bar a, preferably at least 14 bar a, more preferably at least 16 bar a, even more preferably at least 18 bar a, most preferably at least 20 bar a, and in particular at least 22 bar a. Sentence 73: The process according to any one of the preceding sentences, wherein p4 is at most 80 bar a, preferably at most 70 bar a, more preferably at most 60 bar a, even more preferably at most 50 bar a, most preferably at most 40 bar a, and in particular at most 30 bar a. Theorem 74: The method according to any of the preceding theorems, where T4 > T3. Sentence 75: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T4 | is at least 10°C, more preferably at least 15°C, even more preferably at least 20°C, most preferably at least 25°C, and in particular at least 30°C. Sentence 76: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T4 | is at least 35°C, more preferably at least 40°C, even more preferably at least 45°C, most preferably at least 50°C, and in particular at least 55°C. Sentence 77: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T4 | is at most 55°C, more preferably at most 50°C, even more preferably at most 45°C, most preferably at most 40°C, and in particular at most 35°C. Sentence 78: The method according to any one of the preceding sentences, wherein the magnitude of the relative temperature difference | T3 - T4 | is at most 30°C, more preferably at most 25°C, even more preferably at most 20°C, most preferably at most 15°C, and in particular at most 10°C. Sentence 79: The process according to any one of the preceding sentences, wherein - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C. Theorem 80: The method according to any of the preceding theorems, where p4 > ps. Sentence 81: The method according to any one of the preceding sentences, wherein the magnitude of the relative pressure difference | P3 - P4 | is at most 6 bar, preferably at most 5 bar, more preferably at most 4 bar, even more preferably at most 3 bar, most preferably at most 2 bar, and in particular at most 1 bar. Sentence 82: The process according to any one of the preceding sentences, wherein in step (h) the conversion of the decomposed NH is at least 90%, preferably at least 92.5%, more preferably at least 95%, even more preferably at least 96%, most preferably at least 97%, and in particular at least 98%, in each case based on the amount of NH;, which was originally contained in the reactant gas provided in step (a). Sentence 83: The method according to one of the preceding sentences, wherein the combustion of the combustion gas is carried out with at least one burner to generate at least one flame with which heat energy is introduced into the tubes, wherein a heat energy flow Q introduced into the tubes w has a non-constant course over the length of the tubes LR. Theorem 84: The method according to theorem 83, where the heat energy flow Q w has a maximum over the length of the tubes LR. Theorem 85: The process according to Theorem 84, wherein the tubes can each be divided into two equal halves over their length LR, wherein the intermediate product gas or product gas first flows through the first half and then the second half, wherein the maximum of the heat energy flow Qw is reached in the first half. Theorem 86: The method according to theorem 83 or 84, wherein the tubes can each be divided into four equal segments over their length LR, wherein the intermediate product gas or product gas first flows through the first segment, then the second segment, finally the third segment and then the fourth segment, wherein the maximum of the heat energy flow Q w in the second segment. Sentence 87: The method according to any one of the preceding sentences, wherein the combustion of the combustion gas is carried out with at least one burner to produce at least one flame, the length LF of which runs in the flow direction of the burning combustion gas substantially parallel to the length of the tubes LR. Clause 88: The process according to any one of the preceding clauses, wherein the combustion gas being burned flows in substantially the same direction as the intermediate product gas or product gas (ceiling combustion). Theorem 89: The procedure according to Theorem 87 or 88, where LR > LF. Clause 90: The process according to any one of clauses 87 to 89, wherein the length ratio LR:LF is in the range from 10:1 to 1.1:1, preferably 7:1 to 1.5:1, more preferably 4:1 to 2:1. Sentence 91: The process according to any one of the preceding sentences, wherein in step (h) when intermediate product gas or product gas flows through the tubes, the amount of heat consumed by the endothermic decomposition of NH; is initially greater than the amount of heat which is produced by the combustion of the Combustion gas as heat energy flow Q w is introduced into the tubes so that the intermediate gas or product gas initially reaches a minimum gas temperature T m m cools down (T m m < T3). Theorem 92: The method according to Theorem 91, where the amount of the relative temperature difference | T3 - T min | is at least 10°C, more preferably at least 20°C, even more preferably at least 30°C, most preferably at least 30°C, and in particular at least 40°C. Sentence 93: The procedure according to Sentence 91 or 92, where T m m in the range of 560 to 600°C, preferably 570 to 590°C. Clause 94: The process according to one of clauses 91 to 93, wherein after reaching the minimum gas temperature Tmin, the amount of heat consumed by the endothermic decomposition of NH3 is subsequently smaller than the amount of heat which is released by the combustion of the combustion gas as heat energy flow Q w is introduced into the tubes so that the intermediate gas or product gas is subsequently heated as it flows through the tubes (T m in < T4). Theorem 95: The method according to Theorem 94, where the amount of the relative temperature difference | T4 - T min | is at least 50°C, more preferably at least 55°C, even more preferably at least 60°C, most preferably at least 65°C, and in particular at least 70°C. Clause 96: The method according to any one of clauses 91 to 95, wherein the tubes can each be divided into two equal halves over their length LR, wherein the intermediate product gas or product gas flows first through the first half and then through the second half, wherein the minimum gas temperature T m when flowing through the first half. Clause 97: The method according to any one of clauses 91 to 96, wherein the tubes can each be divided into four equal segments over their length LR, wherein the intermediate product gas or product gas first flows through the first segment, then the second segment, finally the third segment and then the fourth segment, wherein the minimum gas temperature T m when flowing through the first segment. Sentence 98: The process according to any one of the preceding sentences, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; - T2 is in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C; - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C. Sentence 99: The process according to any one of Sentences 1 to 97, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; - T2 is in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C; - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C. Sentence 100: The process according to any one of the preceding sentences, wherein the combustion gas comprises NH3; preferably wherein the reactant gas provided in step (a) is divided into (i) a first fraction which is fed to step (b), and (ii) a second fraction which serves as combustion gas. Sentence 101: The process according to sentence 96, wherein the second fraction constitutes at most 8.0 mol% of the reactant gas provided in step (a), more preferably at most 7.5 mol%, even more preferably at most 7.0 mol%, most preferably at most 6.5 mol%, and in particular at most 5 mol%. Sentence 102: The process according to any one of the preceding sentences, comprising the additional step (j) purifying the product gas by pressure swing adsorption to obtain a product gas enriched in H2 and an exhaust gas depleted in H2; preferably wherein the exhaust gas depleted in H2 is recycled and introduced into the combustion gas. Sentence 103: A device for carrying out the method according to one of the preceding sentences.

[0144] Preferred embodiments of the process according to the invention are illustrated by Figures 1 to 3.

[0145] Figure 1 schematically shows a preferred embodiment, wherein a stream of intermediate product gas 2 is introduced into tubular reactor 1 from top to bottom. Tubular reactor 1 contains nickel-based NFL decomposition catalyst 3. Streams of combustion gas 4 are directed into combustion chambers 5a and 5b and combusted therein, generating flames 6a and 6b in the flow direction of the combusting combustion gas. Tubular reactor 1 has a length LR, while flames 6a and 6b each have a length LF. Tubular reactor 1 is heated by the heat generated during the combustion of combustion gas 4. A stream of product gas 7 obtained by the catalytic decomposition is discharged from tubular reactor 1. The combustion exhaust gas 8 obtained during the combustion of combustion gas 7 is discharged from combustion chambers 5a and 5b.

[0146] Figure 2 shows a schematic of the change in gas temperature during the chemical reaction of the intermediate gas to form product gas over the nickel-based NH3 decomposition catalyst. Two reaction regimes, A (dashed line) and B (solid line), are distinguished, which differ in the gas temperature T3 upon introduction into the reactor, i.e. upon first contact with the NFF decomposition catalyst. In reaction regime A, the gas temperature TJA is comparatively high. Since the decomposition of NH3 is endothermic, the reaction is favored by the comparatively high temperature and proceeds rapidly, whereby the gas temperature initially drops significantly due to the amount of heat consumed, before it can rise again downstream as a result of the heating of the reactor. Finally, the product gas exits the reactor at a gas temperature T4A, with the highest possible decomposition yield.The gas temperature passes through a minimum along the path in the reactor, which also affects the rate of the decomposition reaction. passes through a minimum. In this reaction regime, the rate of the decomposition reaction is initially very fast (left of the minimum), but subsequently comparatively slow due to the associated significant temperature drop (right of the minimum). With this reaction regime, a comparatively large amount of nickel-based NH3 decomposition catalyst is required to produce a high yield. In reaction regime B, the gas temperature T3B is comparatively low. In this case, although the rate of the decomposition reaction is initially not as fast, the gas temperature does not drop as drastically either. With this reaction regime, the gas temperature downstream can rise to higher gas temperatures sooner due to the heating of the reactor.

[0147] Figure 3 schematically shows the change in gas temperature during the chemical reaction of the intermediate gas to product gas on the nickel-based NFL decomposition catalyst as a function of the length LR of the tubular reactor. In reaction mode A, the length of the tubular reactor LRA is comparatively short, and the product gas leaves the tubular reactor with a comparatively low gas temperature T4A and a comparatively low conversion of decomposed NH3. In reaction mode B, the length of the tubular reactor LRB is comparatively long, and the product gas leaves the tubular reactor with a comparatively high gas temperature T4B and a comparatively high conversion of decomposed NH3.

[0148] List of reference symbols: 1 tube reactor 2 Intermediate gas 3 Nickel-based NFL decomposition catalyst 4 Combustion gas 5a / 5b combustion chamber 6a / 6b Flame 7 Product gas 8 Combustion exhaust gas

Claims

Patent claims:

1. A process for producing H2 from NH3 comprising the steps: (a) providing a reactant gas comprising or consisting essentially of NH3; (b) heating the reactant gas to a gas temperature Ti in the range of 550 to 850°C at a pressure pi of at least 10 bar a; (c) introducing the heated reactant gas at the gas temperature Ti and the pressure pi into at least one fixed bed reactor containing at least one catalyst bed comprising or consisting essentially of an NH3 decomposition catalyst; (d) partially decomposing NH3 in the at least one fixed bed reactor on the at least one catalyst bed to obtain an intermediate gas comprising or consisting essentially of H2, N2 and undecomposed NH3; (e) discharging the intermediate product gas from the at least one fixed bed reactor at a gas temperature T2 in the range from 300 to 700°C and a pressure p2 of at least 10 bar a; (f) heating the intermediate gas to a gas temperature T3 in the range from 550 to 700°C at a pressure ps of at least 10 bar a; (g) introducing the heated intermediate gas at the gas temperature T3 and the pressure p3 into at least one tubular reactor comprising a plurality of parallel tubes, each containing at least one catalyst bed heated by combustion of a combustion gas and comprising or consisting essentially of a nickel-based NFh decomposition catalyst; (h) decomposing NH3 in the at least one tubular reactor on the catalyst beds to obtain a product gas which comprises or consists essentially of H2, N2 and optionally undecomposed NH3; and (i) discharging the product gas from the at least one tubular reactor at a gas temperature T4 in the range from 550 to 750°C and a pressure p4 of at least 10 bar a.

2. The method of claim 1, wherein T4 > T3.

3. The process according to any one of the preceding claims, wherein the at least one fixed bed reactor is operated adiabatically.

4. The process according to any one of the preceding claims, wherein the NH3 decomposition catalyst of the at least one catalyst bed of the fixed bed reactor is nickel-based, preferably supported nickel.

5. The method according to any one of the preceding claims, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 is in the range of 450±50°C, preferably 450±40°C, more preferably 450±30°C, even more preferably 450±20°C, most preferably 450±10°C.

6. The method according to any one of claims 1 to 4, wherein - Ti is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C; and - T2 is in the range of 350±50°C, preferably 350±40°C, more preferably 350±30°C, even more preferably 350±20°C, most preferably 350±10°C.

7. The process according to any one of the preceding claims, wherein in step (d) the conversion of the decomposed NH3 is at least 12.5%, preferably at least 15%, more preferably at least 17.5%, even more preferably at least 20%, most preferably at least 22.5%, and in particular at least 25%, in each case based on the amount of NH3 which was originally contained in the reactant gas provided in step (a).

8. The process according to any one of the preceding claims, wherein the plurality of parallel tubes of the tubular reactor in the flow direction of the intermediate product gas or product gas each have a length LR of at least 5.5 m, preferably at least 6.0 m, more preferably at least 6.5 m, even more preferably at least 8 m, most preferably at least 7.0 m, and in particular at least 7.5 m.

9. The method according to any one of the preceding claims, wherein - T3 is in the range of 620±50°C, preferably 620±40°C, more preferably 620±30°C, even more preferably 620±20°C, most preferably 620±10°C; and - T4 is in the range of 650±50°C, preferably 650±40°C, more preferably 650±30°C, even more preferably 650±20°C, most preferably 650±10°C.

10. The process according to any one of the preceding claims, wherein in step (h) the conversion of the decomposed NH3 is at least 90%, preferably at least 92.5%, more preferably at least 95%, more preferably at least 96%, most preferably at least 97%, and in particular at least 98%, in each case based on the amount of NH3 which was originally contained in the reactant gas provided in step (a).

11. The method according to any one of the preceding claims, wherein the combustion of the combustion gas is carried out with at least one burner to generate at least one flame whose length LF in the flow direction of the burning combustion gas is substantially parallel to the length of the tubes LR.

12. The method according to claim 11, wherein the length ratio LR:LF is in the range of 10:1 to 1.1:1, preferably 7:1 to 1.5:1, more preferably 4:1 to 2:

1.

13. The method according to any one of the preceding claims, wherein in step (h) when intermediate product gas or product gas flows through the tubes, the amount of heat consumed by the endothermic decomposition of NH; is initially greater than the amount of heat which is released by the combustion of the combustion gas as heat energy flow Q w is introduced into the tubes so that the intermediate gas or product gas initially reaches a minimum gas temperature T m m cools down (T m m < T3).

14. The method according to claim 13, wherein after reaching the minimum gas temperature T m the amount of heat consumed by the endothermic decomposition of NH3 is subsequently smaller than the amount of heat released by the combustion of the combustion gas as heat energy flow Q wis introduced into the tubes so that the intermediate gas or product gas is subsequently heated as it flows through the tubes (T m in < T4).

15. The method according to claim 13 or 14, wherein the tubes can each be divided into two equal halves over their length LR, wherein the intermediate product gas or product gas first flows through the first half and then the second half, wherein the minimum gas temperature T m when flowing through the first half.

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