Ammonia decomposition for green hydrogen

Abstract

Residual ammonia is effectively removed from the ammonia cracked gas in the hydrogen PSA system using non-zeolitic adsorbents such as activated carbon, activated alumina, or silica gel.

Description

[Background technology]

[0001] The global interest in renewable energy, and the use of this renewable energy to generate green hydrogen, has fueled interest in converting green hydrogen to green ammonia, as ammonia is easier to transport over distances of hundreds or thousands of miles. In particular, while the transportation of liquid hydrogen is not currently commercially possible, the transportation of ammonia in liquid form is currently practiced.

[0002] For use in commercial fuel cells, ammonia must be converted reactively to hydrogen.

number

[0003] This is an endothermic process, i.e., it requires heat, and is carried out over a catalyst. This process is known as decomposition. The gas produced (or "cracked gas") is a combination of hydrogen (H2) and nitrogen (N2). Because the decomposition reaction is an equilibrium reaction, the ammonia conversion given by the reaction equation is less than 100%, and residual ammonia is present in the reactor effluent. In most applications of current crackers, the hydrogen + nitrogen mixture is utilized as is. However, because ammonia can be harmful to fuel cells, this stream can be used directly in fuel cells by suitable ammonia removal, such as by washing with water. However, when hydrogen is used in vehicle fueling, the presence of nitrogen imposes a penalty on the process. Fuel to vehicle fueling systems is compressed to significant pressures, up to 900 bar. This means that nitrogen, which is merely a diluent in the process, is also compressed, requiring power, storage, increasing anode gas purge requirements, and reducing efficiency. Therefore, when hydrogen is used in vehicle fueling, it is beneficial for the hydrogen + nitrogen to be purified.

[0004] Small-scale cracking reactors, or "crackers," typically use pressure swing adsorption ("PSA") devices to separate the cracked gases, recover hydrogen, and produce a PSA tail gas (or off-gas). However, these crackers are generally electrically heated, and the PSA tail gas is typically vented to the atmosphere.

[0005] PSA can be used to produce nitrogen plus hydrogen, as is common in hydrogen production from steam methane reforming (SMR) reactors. The cracking reaction is carried out in catalyst-packed tubes that are externally heated by a furnace (see GB1142941).

[0006] GB 1142941 discloses a process for producing city gas from ammonia. The ammonia is decomposed and the decomposed gas is washed with water to remove residual ammonia. The purified hydrogen / nitrogen mixture is then condensed with propane and / or butane vapor to produce city gas for distribution.

[0007] US6835360A discloses an endothermic catalytic reactor for converting hydrocarbon feedstocks and methanol into useful gases such as hydrogen and carbon monoxide. The reactor comprises a tubular endothermic catalytic reactor in combination with a radiative combustion chamber. The resulting cracked gases are passed through a gas conditioning system and then used directly in a fuel cell.

[0008] GB977830A discloses a process for decomposing ammonia to produce hydrogen. In this process, the hydrogen is separated from the nitrogen by passing the decomposed gas through a bed of molecular sieves that adsorb the nitrogen. The nitrogen can then be driven from the bed and stored in a holder.

[0009] JP5330802A is ammonia 10 kg / cm 2The paper discloses an ammonia decomposition process in which the nitrogen is contacted with an ammonia decomposition catalyst at a pressure of 1000 kJ / s (or about 9.8 bar) and a temperature of 300-700°C. Hydrogen is recovered from the cracked gas using a PSA device. The reference mentions that the desorbed nitrogen can be used to boost upstream processes, but no details are provided.

[0010] US2007 / 178034A discloses a process in which a mixture of ammonia and hydrocarbon feedstock is passed through a combustion steam reformer at 600°C and 3.2 MPa (or about 32 bar) and converted to synthesis gas containing about 70% by volume of hydrogen. The synthesis gas is enriched in hydrogen in a shift reaction, cooled, and condensates are removed. The resulting gas is fed to a PSA system to produce a purified hydrogen product having more than 99% by volume of hydrogen. Off-gas from the PSA system is fed to the combustion steam reformer as fuel.

[0011] CN111957270A discloses a process in which ammonia is decomposed in a tubular reactor within a furnace. The decomposed gases are separated by adsorption to produce hydrogen gas and a nitrogen-rich off-gas. The fuel needs of the furnace appear to be met using a combination of the decomposed gas, hydrogen product gas, and / or the off-gas.

[0012] The vapor phase effluent of the ammonia decomposition reactor is typically cooled to a temperature in the range of about 15°C to about 60°C, and at a pressure in the range of about 10 to 40 bar, and contains a 3:1 mixture of hydrogen and nitrogen, along with some residual (or unconverted) ammonia, usually in the range of about 0.5% to 5% by volume. In some cases, low levels of water vapor, e.g., 0 to 0.5% by volume, are also present.

[0013] Producing a usable hydrogen stream from the ammonia decomposition reactor effluent typically requires a purification step. As mentioned above, nitrogen can be removed from the effluent stream by an adsorption process such as hydrogen PSA. Ammonia can be removed to very low levels (e.g., less than 50 ppm) by washing with cold water prior to the hydrogen PSA step. After the cold water wash, the dissolved ammonia is then stripped from the water with heat and recovered for further processing. However, such washing and stripping processes are energy intensive.

[0014] US 3,111,387 discloses an alternative method for removing residual ammonia from the effluent of an ammonia cracking reactor. In this process, the effluent gas is passed through a bed of a zeolitic molecular sieve material having an apparent pore size of at least 4 Å (or 0.4 nm) to simultaneously remove nitrogen, ammonia, and moisture from the gas, and a substantially pure hydrogen product gas emerges from the bed. The reference exemplifies cooling the cracked gas to -20°F (or -29°C) at a pressure of 200 psi (or 14 bar), and then passing the cooled gas through a bed of calcium zeolite A (i.e., 5A zeolite) in a PSA system to produce hydrogen product gas. The zeolitic adsorption bed is regenerated under vacuum.

[0015] However, the inventors have recognized that ammonia is very strongly adsorbed on such zeolitic materials, making it difficult to remove all of the ammonia when regenerating the bed. The inventors predict that this is the reason why vacuum regeneration is used in US 3,111,387. Over time (and many PSA cycles), ammonia can accumulate in the bed and eventually find its way into the highly undesirable hydrogen product gas.

[0016] Thus, there is a need for improved processes for the production of hydrogen from ammonia in general, and specifically for processes that are more efficient in terms of energy consumption and / or have higher levels of hydrogen recovery and / or reduce or eliminate the need to burn fossil fuels.

[0017] Throughout the specification, including the discussion of embodiments of the present invention below, pressures given are absolute pressures unless otherwise stated. Summary of the Invention

[0018] According to a first aspect of the present invention, there is provided a method for separating hydrogen gas from effluent gas of an ammonia decomposition reactor operating at elevated pressure in a PSA system comprising at least two PSA units in parallel, comprising: cooling the effluent gas by heat exchange to produce a cooled effluent gas; feeding the cooled effluent gas at elevated pressure into a PSA system to produce a hydrogen product gas and a PSA tail gas; Each PSA unit comprises a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween, the adsorbent bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen.

[0019] The term "elevated pressure" is intended to mean a pressure substantially greater than atmospheric pressure, e.g., at least 5 bar, and is intended to include the operating pressures disclosed herein for ammonia crackers, e.g., from about 5 bar to about 50 bar.

[0020] The terms "upstream" and "downstream" are intended to identify the relative locations of the non-zeolitic and zeolitic adsorbent layers within the beds with reference to the direction of flow of cooled effluent gas through the PSA unit during the adsorption phase of the PSA cycle, such that upstream layers are closer to the feed end of the unit (but further away from the product end) than downstream layers.

[0021] The expression "selective adsorption" is intended to mean that the gas in question is more strongly adsorbed by the adsorbent material than hydrogen gas. The term "selective co-adsorption" as used herein is to be interpreted accordingly.

[0022] A hydrogen PSA system utilizing the present invention can handle the reactor effluent at its ammonia percentage level, thereby eliminating the process steps of washing and stripping, as well as the energy required to chill and heat the water.

[0023] In addition, the inventors have discovered that non-zeolitic adsorbent materials are unexpectedly better suited to removing percentage levels of ammonia from the effluent gas of an ammonia cracking reactor during a hydrogen PSA process because such materials do not adsorb ammonia as strongly as zeolitic materials. This lower adsorption strength reduces and potentially eliminates the problem of ammonia "creep" through the adsorbent bed over time.

[0024] Suitable non-zeolitic adsorbents may have a capacity for ammonia of at least 0.01 mmol / g, and optionally no more than about 2 mmol / g, at 0.005 bar and 40° C. For example, the ammonia capacity is typically in the range of about 0.01 mmol / g to about 2 mmol / g, e.g., about 0.01 mmol / g to about 0.5 mmol / g, or about 0.01 mmol / g to about 0.3 mmol / g, under these conditions.

[0025] Suitable non-zeolitic adsorbents are capable of desorbing at least 10%, preferably at least 25%, and more preferably at least 45% of the adsorbed ammonia after 100 seconds using a 1.4 bar nitrogen purge. These percentages refer to the proportion of adsorbed molecules that are desorbed during the purge step, e.g., when the bed is regenerated.

[0026] Suitable non-zeolitic adsorbents are capable of desorbing at least 30%, preferably at least 50%, more preferably at least 90% of the adsorbed ammonia after 600 seconds using a nitrogen purge of 1.4 bar at 40°C.

[0027] The inventors note that although the adsorbent bed is typically purged with substantially pure hydrogen, nitrogen is adsorbed in the downstream bed at the beginning of the purge step, so that a mixture of hydrogen and desorbed nitrogen actually purges the ammonia bed during the process.

[0028] In some preferred embodiments, suitable non-zeolitic adsorbents also selectively co-adsorb water. In this regard, the capacity of the non-zeolitic adsorbent for water may be at least 1.8 wt. % and optionally no more than 5 wt. % at a water pressure of 0.02 bar and 40° C. (See Table 1). Table 1 [Table 1]

[0029] In these embodiments, it may be possible to reduce the size of (or avoid altogether) the additional adsorbent layer before the upstream layer at the feed end of the bed dedicated to water removal.

[0030] Additionally or alternatively, suitable non-zeolitic adsorbents may also selectively co-adsorb nitrogen. In this regard, the capacity of the non-zeolitic material for nitrogen may be at least 0.18 mmol / g, e.g., at least 0.7 mmol / g, at 5 bar and 40° C. In these embodiments, it may be possible to reduce the size of the layer of zeolitic adsorbent downstream of the upstream layer of non-zeolitic adsorbent.

[0031] Particularly suitable non-zeolitic adsorbents may have a surface acidity (measured as the zero point of charge, or ZPC) in the range of about pH 6.3 to about pH 9.8, e.g., about pH 8 to about pH 9. The ZPC is determined by adding 2 grams of adsorbent to 10 milliliters of deionized water and measuring the pH of the water after 20 hours.

[0032] In some preferred embodiments, the non-zeolitic adsorbent is an activated carbon, e.g., selected from the group consisting of synthetic (i.e., polymer-derived) carbon, petroleum pitch carbon, wood-based carbon, coal-based carbon, and coconut shell carbon. These carbons are formed by carbonization (i.e., heating at about 300°C to about 900°C in the absence of air) of precursor materials, usually particles of biological material such as petroleum pitch, wood, coal, or coconut shell. Polymer-derived carbons are typically formed by carbonization of small globules of polymers such as polystyrene, polyacrylate, polyalkylamine, phenol-formaldehyde resin, or sulfonated copolymers of divinylbenzene or acrylic acid and styrene, or mixtures thereof.

[0033] Either the activated carbon can be pretreated with an acid or base before being loaded into the bed, or can be pretreated in situ by flowing nitrogen through a bed of activated carbon at an elevated temperature of at least 100° C., e.g., about 150° C., or at least 300° C., e.g., about 340° C. In situ pretreatment in this manner has the effect of reducing the oxygen functionality and acidity of the carbon's surface (see Water Research vol. 31, p. 3414, 1998 and Carbon vol. 37, p. 1379, 1999).

[0034] Particularly suitable carbon adsorbents have an inorganic content of less than 8 wt%, e.g., less than 4 wt%, less than 1 wt%, less than 0.5 wt%, or even less than 0.2 wt%. Such adsorbents may be referred to as "low ash" adsorbents. Such materials have particularly high adsorption reversibility toward ammonia; for example, when the bed is regenerated in flowing nitrogen at 1.4 bar and 40°C, at least 50% or at least 90% of the adsorbed ammonia desorbs within 600 seconds.

[0035] In other embodiments, the non-zeolitic adsorbent is activated alumina, possibly activated alumina pretreated with a base.

[0036] In a further embodiment, the non-zeolitic adsorbent is selected from the group consisting of wide pore silica gel, narrow pore silica gel, and silicalite.

[0037] Different adsorbents are layered within a vessel to form beds to remove water vapor, ammonia, and nitrogen from a gas stream. Thus, in the direction of feed gas flow through the adsorbent layers within the vessel, water vapor, as the most strongly adsorbed molecule, is removed first, ammonia second, and nitrogen, as the second least adsorbed molecule, is removed last. Hydrogen, as the least adsorbed molecule, passes through the relatively unadsorbed adsorbent layers.

[0038] The adsorbent bed may contain one or two layers of a non-zeolitic adsorbent for removing water and ammonia, along with one or two layers of a zeolitic adsorbent for removing nitrogen.

[0039] In other embodiments, the adsorption bed can include an intermediate layer of activated carbon with an inorganic content of less than 1% positioned between the upstream and downstream layers. Examples of such activated carbons include polymer-derived carbon, petroleum pitch carbon, and wood-based carbon. Because ammonia is readily desorbed from them, these "low-ash" materials can be used as a second non-zeolitic (e.g., carbon) layer between a first non-zeolitic (e.g., carbon) layer with high ammonia adsorption capacity and a downstream layer of zeolitic adsorbent (e.g., molecular sieve) used to adsorb nitrogen in the PSA process. Due to the easy desorption from the second non-zeolitic layer during the purge step, such a layer arrangement prevents ammonia from reaching the molecular sieve.

[0040] Other adsorbents for water removal in PSA processes are well known. Commonly used materials for water adsorption are activated alumina, silica gel, and carbon. In some embodiments, the adsorbent bed has an initial layer of one of these materials at the feed end.

[0041] Zeolite-based adsorbents for nitrogen removal in PSA processes are also well known. Commonly used materials for nitrogen adsorption are zeolites or molecular sieves such as 13X, LiX, LiLSX, CaX, CaA(5A), and Ca-Chabazite. In the purification of hydrogen from an ammonia cracking reactor, one or more of these materials may be utilized for nitrogen removal.

[0042] Examples of suitable packed beds for removing water, ammonia, and nitrogen from the effluent of an ammonia decomposition reactor to produce substantially pure hydrogen include (from feed end to product end): Activated alumina / activated carbon (e.g., coal-based or coconut-based carbon) / 5A zeolite Activated alumina / narrow pore silica gel / 5A zeolite Activated alumina / narrow pore silica gel / CaX zeolite Activated alumina / narrow pore silica gel / CaX zeolite / 5A zeolite Activated carbon / "low ash" carbon (e.g., petroleum pitch carbon) / 5A zeolite The gas feed to the PSA system originates from an ammonia decomposition reactor and typically has 0% to about 0.5% by volume water and about 0.1% to about 5% by volume ammonia, with the remainder of the gas consisting essentially of a mixture of hydrogen and nitrogen in a ratio of about 3:1.

[0043] The operating temperature of an ammonia decomposition reactor is typically high, usually in the range of about 250°C to about 800°C, e.g., about 400°C to about 600°C, and therefore the effluent gas must be cooled before being fed to the PSA system. In this regard, the cooled effluent gas is typically at a temperature in the range of about 15°C to about 100°C, e.g., about 50°C.

[0044] The operating pressure of an ammonia decomposition reactor is also typically high, usually in the range of about 5 bar to about 50 bar, e.g., about 10 bar to about 40 bar. Therefore, because the effluent gas is already pressurized, pressure adjustment is typically not required before the gas is fed to the PSA system. Thus, the pressurization of the cooled effluent gas is usually in the range of about 5 bar to about 50 bar, e.g., about 10 bar to about 40 bar.

[0045] Typically, the PSA exhaust gas has a back pressure within the range of about 0.2% to about 20% of the effluent gas pressure boost.

[0046] According to a second aspect of the present invention, there is provided a PSA unit for separating hydrogen gas from the effluent gas of an ammonia decomposition reactor operating at elevated pressure, the PSA unit comprising a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween, the adsorbent bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen.

[0047] According to a third aspect of the present invention, there is provided a PSA system for separating hydrogen gas from the effluent gas of an ammonia decomposition reactor operating at elevated pressure, the PSA system comprising at least two PSA units according to the second aspect in parallel. The PSA system may comprise at least four of such PSA units in parallel.

[0048] Suitable non-zeolitic adsorbents for use in the PSA unit are as described above.

[0049] According to a fourth aspect of the present invention, there is provided an apparatus for producing hydrogen from ammonia, comprising: a pump for pressurizing the liquid ammonia; at least one first heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) liquid ammonia from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a reactor tube containing a catalyst in fluid communication with the first heat exchanger for decomposing the heated ammonia from the first heat exchanger to produce a first decomposed gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a fuel to heat the catalyst-containing reactor tubes and form a flue gas; a cracked gas conduit for supplying cracked gas from the reactor tube containing the catalyst to the first heat exchanger; a flue gas conduit for supplying flue gas from the furnace to the first heat exchanger; a first PSA system according to a third aspect of the present invention in fluid communication with the reactor tubes containing the catalyst for purifying the cracked gas cooled after passing through the at least one heat exchanger to produce a first hydrogen product gas and a first PSA tail gas; a first PSA exhaust gas conduit for removing the first PSA exhaust gas from the first PSA system; a first hydrogen product gas conduit for removing the first hydrogen product gas from the first PSA system.

[0050] In some embodiments, the apparatus includes a compressor in fluid communication with a first PSA system for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas, and a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA system. In these embodiments, there is typically a first PSA exhaust gas recirculation conduit for recirculating the first PSA exhaust gas from the first PSA device to the furnace, optionally after passing through a heat exchanger.

[0051] In another embodiment, the apparatus comprises a compressor in fluid communication with the first PSA system for compressing a first PSA tail gas to produce a compressed PSA tail gas, a second PSA system in fluid communication with the compressor for purifying the compressed PSA tail gas to produce a second PSA tail gas and a second hydrogen product gas, a second hydrogen gas conduit for removing a second hydrogen gas from the second PSA system, and a second PSA tail gas conduit for removing the second PSA tail gas from the second PSA device. The second PSA system may also be in accordance with the third aspect of the invention or may have a different arrangement of layers within the adsorption bed.

[0052] In these embodiments, the first and second hydrogen product gas conduits may combine to form a combined hydrogen product gas conduit. Additionally or alternatively, the second PSA exhaust gas conduit may recirculate the second PSA exhaust gas from the second PSA system to the furnace, optionally after passing through a heat exchanger.

[0053] The PSA system can operate using any suitable PSA cycle. Particularly suitable PSA cycles include any of the cycles disclosed in US9381460, US6379431, and US8778051, the disclosures of which are incorporated herein by reference.

[0054] In embodiments where at least a first PSA system comprises at least four PSA units in parallel, the PSA system may operate the PSA cycle disclosed in US8778051. The repeating cycle includes, in order, (a) a feed step, (b) a first pressure drop equalization step, (c) a provide purge step, (d) a blowdown step, (e) a purge step, (f) a first pressure increase equalization step, and (g) a repressurization step. These steps are defined as follows:

[0055] The feed step (a) comprises introducing the cooled effluent gas at a feed gas pressure in the range of about 10 bar to about 50 bar into an adsorbent bed undergoing step (a), and simultaneously adsorbing moisture, ammonia, and nitrogen within the adsorbent bed undergoing step (a) while withdrawing hydrogen product gas from the adsorbent bed undergoing step (a).

[0056] The first pressure reduction equalization step (b) comprises simultaneously withdrawing a pressure equalization gas from the adsorbent bed undergoing step (b) and passing the pressure equalization gas through the adsorbent bed undergoing step (f), thereby equalizing the pressure between the adsorbent beds undergoing steps (b) and (f).

[0057] The providing purge step (c) comprises cocurrently withdrawing a purge gas from the adsorbent bed undergoing step (c) and passing the purge gas from the adsorbent bed undergoing step (c) through the adsorbent bed undergoing step (e).

[0058] The blowdown step (d) comprises countercurrently withdrawing a blowdown gas from the adsorption bed undergoing step (d), the blowdown gas having concentrations of moisture, ammonia, and nitrogen that are higher than the concentrations of these components in the cooled effluent gas feed.

[0059] The purging step (e) comprises countercurrently introducing purge gas from the adsorbent bed undergoing step (c) into the adsorbent bed undergoing step (e) and countercurrently withdrawing a purge gas effluent from the adsorbent bed undergoing step (e), the purge gas effluent having concentrations of moisture, ammonia, and nitrogen that are higher than the concentrations of these components in the cooled effluent gas feed.

[0060] The first pressure increase equalization step (f) involves introducing pressure equalization gas from the adsorbent bed undergoing step (b) countercurrently into the adsorbent bed undergoing step (f).

[0061] The repressurization step (g) comprises increasing the pressure in the adsorbent bed undergoing step (g) until the adsorbent bed undergoing step (g) is at substantially the feed gas pressure by at least one of: cocurrently introducing the cooled effluent gas into the adsorbent bed undergoing step (g); and countercurrently introducing a portion of the product gas from the adsorbent bed undergoing step (a) into the adsorbent bed undergoing step (g).

[0062] The process includes at least one of: (i) step (b) further comprising introducing a rinse gas cocurrently with the withdrawal of the pressure equalization gas; and (ii) step (c) further comprising introducing a rinse gas cocurrently with the withdrawal of the purge gas, wherein the rinse gas is formed by compressing at least a portion of at least one of the blowdown gas from the adsorbent bed undergoing step (d) and the purge gas effluent from the adsorbent bed undergoing step (e).

[0063] The first pressure increase equalization step (f) further comprises at least one of: (i) introducing the feed gas mixture cocurrently into the adsorbent beds undergoing step (f) simultaneously with the countercurrent introduction of pressure equalization gas from the adsorbent beds undergoing step (b); and (ii) introducing product gas from at least one of the adsorbent beds undergoing step (a) countercurrently into the adsorbent beds undergoing step (f) simultaneously with the countercurrent introduction of pressure equalization gas from the adsorbent beds undergoing step (b).

[0064] The invention will now be described with reference to the embodiments depicted in the following drawings. [Brief explanation of the drawings]

[0065] [Figure 1] FIG. 1 is a process flow diagram of a first embodiment of an ammonia decomposition process for producing hydrogen in which the present invention may be utilized. [Figure 2] FIG. 2 is a process flow diagram of a second embodiment of an ammonia decomposition process to produce hydrogen in which the present invention may be utilized. [Figure 3] FIG. 1 is a process flow diagram of a third embodiment of an ammonia decomposition process to produce hydrogen in which the present invention may be utilized. DETAILED DESCRIPTION OF THE INVENTION

[0066] Described herein is a process for producing hydrogen by decomposing ammonia. The process has particular application for producing so-called "green" hydrogen, which is hydrogen produced using renewable energy instead of fossil fuels. In this case, ammonia is typically produced by electrolyzing water using electricity generated from renewable energy, such as wind and / or solar energy, to produce hydrogen, which is then catalytically reacted with nitrogen to produce ammonia, which is easier to transport than hydrogen (Haber process). After reaching its destination, the ammonia is then decomposed to regenerate hydrogen.

[0067] In this process, the heat required for the reaction is typically provided by combustion of the PSA tail gas (which usually contains some residual hydrogen and ammonia) in a furnace. If the PSA tail gas has insufficient heating value than either the vaporized ammonia, a portion of the product hydrogen, or an alternative fuel, it can be used along with the tail gas as a trim fuel.

[0068] In practice, natural gas could be used as a trim fuel along with the PSA exhaust gas, as is practiced in SMR for hydrogen. However, there is an incentive to use a "renewable fuel," in the hope of maintaining the "green" or renewable qualities of the hydrogen so produced. This could be cracked "renewable" ammonia, ammonia itself, or another renewable energy source such as biogas, or it could actually be electrical heating, whether or not the electricity is itself from a renewable source, in which case it would be local to the cracking process, as opposed to the renewable electricity used to produce the hydrogen transported in the form of ammonia.

[0069] An example of the process is shown in Figure 1. The process takes liquid ammonia from storage (not shown). The ammonia to be decomposed (line 2) is pumped as a liquid (pump P201) to a pressure above the desired decomposition pressure (see GB 1142941). The reaction pressure is a compromise between operating pressure and conversion, according to Le Chatelier's principle. Pumping liquid ammonia requires less power and capital than compressing product hydrogen, so there is an incentive to operate the reactor (8) at a higher pressure.

[0070] The pressurized liquid ammonia (line 4) is then heated and vaporized (if it is below its critical pressure) and further heated to temperatures up to above 250° C. via heat exchanger (E101) using the heat available in the cracked gases leaving the reactor tubes and in the flue gases from the furnace. In the diagram, heat exchanger (E101) is shown as one heat exchanger, but in reality it will be a series of heat exchangers in a network.

[0071] Alternatively, initial heating and vaporization of pressurized liquid ammonia may be performed against an alternative heat source, such as cooling water or ambient air. Typical reaction temperatures are above 500°C (see US 2601221), with palladium-based systems capable of operating at 600°C and 10 bar, while RenCat's metal oxide-based systems operate at less than 300°C and 1 bar. (See https: / / www.ammoniaenergy.org / articles / ammonia-cracking-to-high-purity-hydrogen-for-pem-fuel-cells-in-denmark / ). The operating pressure of the cracker is typically an optimization of several factors. While ammonia cracking to hydrogen and nitrogen is favored by low pressure, other factors favor higher pressures, such as power consumption (minimized by pumping feed ammonia rather than compressing product hydrogen) and PSA size (smaller at higher pressures).

[0072] Hot ammonia (line 6) enters the catalyst-containing reactor tubes of reactor (8) at the desired pressure, where additional heat is provided by furnace (10) to decompose the ammonia into nitrogen and hydrogen. The resulting mixture of residual ammonia, hydrogen, and nitrogen exits the reactor tubes (8) at the reaction temperature and pressure (line 12). The reaction product is cooled in heat exchanger (E101) against a combination of feed ammonia (from line 4), furnace fuel (in this case, natural gas from line 50), and combustion air (from line 22, fan K201, and line 24) to reduce the temperature as close as possible to the required temperature for the inlet to the PSA system (26). Residual heat in the decomposed gas mixture (line 28) is removed in a water cooler (not shown) to achieve an inlet temperature to the PSA system (26) in the range of about 20°C to about 100°C, e.g., about 50°C.

[0073] The PSA system (26) includes multiple PSA units (not shown), each having an adsorbent bed according to the present invention. Thus, each PSA unit includes a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween. The adsorbent bed includes an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, such as activated carbon, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen, such as a molecular sieve. The bed may also optionally include an additional layer of water adsorbent material at the feed end of the bed, along with a second layer of zeolitic adsorbent at the product end of the bed. Finally, there may also be an intermediate layer of "low ash" carbon positioned between the so-called upstream and downstream layers.

[0074] The PSA product (line 30) is pure hydrogen conforming to ISO standard 14687 (hydrogen fuel quality) with residual ammonia <0.1 ppmv and nitrogen <300 ppmv at about the reaction pressure. The product hydrogen (line 30) can be further compressed (not shown) to be loaded into a tube trailer (not shown) for transport, or liquefied in a hydrogen liquefier (not shown) after any necessary compression. The PSA tail gas (line 18) or "purge gas" from the PSA device (26) is shown heated via heat exchanger E101 using cracked gas (line 12) or furnace flue gas (line 32) leaving the reactor (8) reaction tubes before being sent to the furnace (10) as combustion fuel (in line 36). However, the PSA tail gas (line 18) can also be fed directly to the furnace (10) without heating.

[0075] The resulting warmed natural gas fuel (line 52) is depicted as being combined with (optionally) warmed PSA exhaust gas (line 36) in mixer (42) to produce a combined fuel, which is fed (line 44) to furnace (10) for combustion to produce flue gas (line 32 and, after cooling with E101, line 48). Note, however, that one or more fuels may be fed directly to the furnace without pre-mixing. Warmed air (for combustion of the fuel) is fed to furnace (10) in line 46.

[0076] One of the objectives of the preferred embodiment of the process is to maximize the amount of hydrogen produced by cracking renewable ammonia. This means minimizing the amount of hydrogen used as fuel, or ammonia if ammonia is used directly as fuel. Therefore, heat integration is important to properly utilize the hot flue gas and cracked gas, for example, to preheat the air (line 24) and ammonia (line 4) to the cracker, thereby reducing the amount of "fuel" used in the burners of the furnace (10). This leads to higher hydrogen recovery, since less hydrogen is lost as water in the furnace flue gas (lines 32 and 48). Therefore, for example, steam generation should be minimized in favor of in-process heat integration.

[0077] Figure 2 depicts a similar process to Figure 1. All common features of the processes depicted in Figures 1 and 2 are given the same reference numerals. The following paragraphs discuss the features that distinguish Figures 1 and 2.

[0078] In Figure 2, the PSA exhaust gas from the PSA system (26) is split into two portions. The first portion (line 56) is fed as fuel to the furnace (10) with the process of Figure 1 via valve 58, line 60, and line 36, line 18 being equivalent to line 60 in Figure 2. Valve 58 can be used to control the flow rate of the PSA exhaust gas in line 60, and therefore the ratio of the amount of PSA exhaust gas to the amount of natural gas in the fuel mixture fed to the furnace (10).

[0079] Varying the amount and composition of fuel burned in the furnace 10 varies the carbon intensity of the cracking process, thereby allowing control of the overall carbon intensity of the hydrogen product. In this way, it is possible to maintain the overall carbon intensity below certain predetermined limits, such as those specified by regulatory authorities for "renewable hydrogen," in the face of variations in carbon intensity upstream of the process.

[0080] The second portion (line 54) is compressed in compressor K301 to form compressed exhaust gas, which is returned (line 62) to the PSA system (26) for further processing.

[0081] The PSA system of Figure 1 is capable of recovering about 75% to about 85% hydrogen. Returning the PSA tail gas to the PSA system improves hydrogen recovery. Recirculating the PSA tail gas in this manner can achieve an overall hydrogen recovery of about 94% to about 96%.

[0082] Figure 3 depicts a similar process to Figures 1 and 2. All common features of the processes depicted in Figures 1 and 3 are given the same reference numerals. The following paragraphs discuss the features that distinguish Figure 3 from both Figures 1 and 2.

[0083] In FIG. 3, a second portion of the compressed PSA tail gas (line 62) is fed to a second PSA system (64) and separated into a second substantially pure hydrogen product gas (line 68) and a second PSA tail gas (line 72).

[0084] The second PSA system (64) comprises a plurality of PSA units (not shown), each having an adsorbent bed according to the present invention. Thus, each PSA unit comprises a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween. The adsorbent bed comprises an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, such as activated carbon, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen, such as a molecular sieve. The bed may also optionally comprise an additional layer of water adsorbent material at the feed end of the bed, along with a second layer of zeolitic adsorbent at the product end of the bed. Finally, there may also be an intermediate layer of "low ash" carbon positioned between the so-called upstream and downstream layers.

[0085] The second hydrogen product gas may be combined with the first hydrogen product gas (line 30) to form a combined hydrogen product gas (line 70).

[0086] The second PSA off-gas (line 72) is combined with a second portion (line 60) of the PSA off-gas from the first PSA system (26), and the combined stream is supplied to the furnace (10) as fuel. Further processing in this manner can achieve an overall hydrogen recovery of about 95% to about 97%. For example, if the first PSA system achieves 83% recovery and the second PSA system achieves 80% recovery, the overall recovery is 96.6%.

[0087] Another difference between the processes of Figures 2 and 3 is that valve 58 in Figure 2 must remain somewhat open to allow some PSA exhaust gas from the first PSA system to be used as fuel in the furnace (10), whereas valve 58 in Figure 3 can completely shut off the flow of PSA exhaust gas from the first PSA system to the furnace because there is always a flow of PSA exhaust gas from the second PSA system (64) to the furnace.

[0088] The invention will now be illustrated with reference to the following drawings. [Example]

[0089] The adsorbents for ammonia removal in a hydrogen PSA process were characterized using a dynamic adsorption apparatus. The experimental system consisted of: a packed column of adsorbent; a flow control device; a pressure control device; An ammonia concentration analyzer was used.

[0090] The experimental method is as follows: First, the packed column is purged with a 50:50 mixture of hydrogen gas and nitrogen gas; Introduction of a fluidized gas of 500 ppm ammonia into a diluent gas of a 50:50 mixture of hydrogen gas and nitrogen gas at 10 bar through a packed column; monitoring the ammonia concentration at the outlet of the packed column until the ammonia concentration reaches 500 ppm; Depressurizing the packed column to 1.4 bar; Purging the packed column with flowing nitrogen gas at 1.4 bar; It consists of monitoring the ammonia concentration at the outlet of the packed column until the concentration of ammonia reaches 0 ppm.

[0091] The empty column residence times for the experiment were 3.4 seconds for the ammonia adsorption step and 1.3 seconds for the nitrogen purge step.

[0092] The adsorption rate of ammonia for these materials was relatively fast. Except for the polymer-derived carbon and the carbon made from petroleum pitch, the desorption rate of ammonia was slow. For ammonia, the Henry's law constant, which is the adsorption region where the amount adsorbed is directly proportional to the partial pressure of the adsorbate, was extracted from the experimental data.

[0093] Acid-treated coconut shell carbon was prepared by treating coconut shell carbon with hydrochloric acid by soaking 125 g of coconut shell carbon in 300 ml of 3% HCl (aqueous) for 2 hours at 25°C. The carbon was then filtered, resuspended in 300 ml of deionized water, soaked for 30 minutes, and then filtered. The deionized water wash / filtration process was repeated four times until the air-dried carbon reached a final pH of 6.2. The air-dried carbon was heated to 150°C overnight to remove adsorbed water and carbon dioxide before testing.

[0094] Base-treated coconut shell carbon was prepared by impregnating coconut shell carbon with 3% NaOH (aqueous) by incipient wetness. The impregnated carbon was air-dried and then activated at 150°C overnight before testing. At 40°C and 0.005 bar, the ammonia capacity increased, but the desorption amount at a 600 second purge was the same as the untreated sample.

[0095] Coconut shell carbon was also treated in situ in flowing nitrogen at 150°C and then 340°C.

[0096] The performance of an adsorbent for ammonia in a PSA cycle depends on how much is adsorbed during the adsorption step and how easily it desorbs during the purge step. Overall PSA performance for the purification of hydrogen from cracked gas depends on several factors, including the adsorption capacity for hydrogen, the adsorption capacity for nitrogen, and the density within the packed column. The following data pertains to these aspects.

[0097] The results obtained in the experiments are summarized in Table 2. Table 2 [Table 2]

[0098] In comparison, binderless 5A zeolite has an ammonia capacity at 40° C. of greater than 0.005 bar and 2.5 mmol / g. In addition, only 0.015 mmol / g (i.e., less than 0.5%) of the adsorbed ammonia desorbs in 100 seconds, and only 0.062 mmol / g (i.e., less than 2.5%) of the adsorbed ammonia desorbs in 600 seconds.

[0099] The results were analyzed using an in-house dynamic simulation program for adsorption processes. The dynamic simulation program numerically solves the mass and energy balance by discretizing each layer into equal-sized nodes, thereby reducing partial differential equations to ordinary differential equations. The physics of momentum transfer and equilibrium adsorption within each node are expressed by standard models for these phenomena, such as the Ergun and Langmuir equations. Model constants were extracted through simulation of dynamic ammonia adsorption / desorption experiments. The dynamic simulation program was then used to evaluate the performance of these materials in an industrial-scale hydrogen PSA process.

[0100] The effectiveness of several adsorbents for removing ammonia from ammonia decomposition reactor effluent was evaluated through dynamic simulation of a hydrogen PSA process. The feed gas to the hydrogen PSA process was 0.1 mol% water, 1.2 mol% ammonia, 24.7 mol% nitrogen, and 74.0 mol% hydrogen at 45°C and 20 bar. The simulated cycle was the cycle disclosed in Figure 22 of US 9,381,460 with a feed time (P / SP) of 150 seconds. The backpressure on the waste gas was 1.45 bar. Ammonia removal in the process was simulated using an adsorption model with parameters extracted from experimental results summarized in Table 1. The amount of ammonia adsorbent was varied so that the ammonia level at the end of the adsorbent bed was 0.1 ppm at the end of the feed (adsorption) step. Nitrogen removal in the process was simulated using an adsorption model and parameters representing a 5A molecular sieve. The amount of nitrogen adsorbent was varied to achieve a nitrogen impurity of 50 ppm in the hydrogen product.

[0101] The simulation results are summarized in Table 3, which shows the effectiveness of these adsorbents for ammonia removal, and Table 4, which shows the overall PSA performance of the ammonia absorbent and nitrogen adsorbent for the purification of hydrogen to 50 ppm nitrogen. Table 3 [Table 3] The hydrogen productivity of a system is the ratio of the flow rate of purified hydrogen from one adsorber vessel, in tons per day (or TPD), to the amount of adsorber in that vessel. Table 4 [Table 4] The effectiveness of the ammonia removal adsorbent is measured by the ammonia working capacity at cyclic steady state, which is the ratio of the amount of ammonia (mmol) introduced to the adsorbent during the feed step to the mass of adsorbent (grams) in the simulated vessel. The working capacity is the difference between the amount of ammonia in the adsorber vessel at the end of the feed (adsorption) step and the amount of ammonia in the adsorber vessel at the end of the regeneration step. The results show that carbon, activated alumina, and silica gel are all suitable for ammonia removal in a hydrogen PSA process.

[0102] The choice of one depends on several factors, including cost and stability in the presence of ammonia and water vapor. The adsorption capacity for nitrogen, also listed in Table 2, also determines the appropriate choice of ammonia adsorbent for this process. Compared to alumina and silica gel, activated carbon has a significantly higher adsorption capacity for nitrogen. Nitrogen adsorption in this first layer reduces the amount of nitrogen removal required by the second layer.

[0103] Although the ammonia capacity of polymer-derived carbons formed by carbonization of polymer beads (see US 2011 / 296990) and petroleum pitch carbons is low, nearly all of the ammonia adsorbed at 40° C. and 0.005 bar was released after a 600-second nitrogen purge at 1.4 bar and 40° C. Under the same purge conditions, much lower fractions are desorbed from coal-based and coconut shell carbons.

[0104] Polymer-derived carbons and petroleum pitch carbons have much lower inorganic ash contents than coal-based and coconut shell carbons (Table 4). These low-ash carbons are formed by heating polymer beads composed of polystyrene (co)polymers or petroleum pitch, a petroleum-derived viscoelastic polymer, to 300-900°C in the absence of oxygen. Table 5 [Table 5]

[0105] Because ammonia readily desorbs, polymer-derived carbon or petroleum pitch carbon can be used as a second carbon layer between a first carbon layer with high ammonia adsorption capacity and a molecular sieve layer used for nitrogen adsorption in a PSA process. Due to the easy desorption from the polymer-derived carbon during the purge step, such layering prevents ammonia from reaching the molecular sieve. Due to the very high capacity of ammonia at low pressure, ammonia does not readily desorb from the molecular sieve. Ammonia continues to accumulate in the molecular sieve layer, reducing the nitrogen capacity.

[0106] The percentage of ammonia desorbed at 100 seconds compared to the ZPC for different non-zeolitic adsorbents is plotted below. These data show that non-zeolitic adsorbents having ZPC values ​​in the range of about pH 6.3 to about pH 9.8, and particularly in the range of about pH 8 to about pH 9, are suitable for removing ammonia in the adsorption bed of a hydrogen PSA tasked with purifying the effluent gas of an ammonia cracking reactor. [Table 6]

[0107] Example 1 A dynamic simulation program using models and parameters for the adsorption of ammonia and nitrogen on coal-based carbon, as well as parameters for the adsorption of nitrogen on 5A molecular sieves, was used to demonstrate the process to provide a purified hydrogen stream.

[0108] The adsorption cycle was that shown in Table 5 of US6379431.

[0109] The feed gas to the hydrogen PSA system was 3 mol% ammonia, 24.2 mol% nitrogen, and 72.8 mol% hydrogen at 34 bar and 40°C. The adsorbent was regenerated at 1.4 bar backpressure during the blowdown and purge steps. Each adsorber vessel was 6 feet (1.8 m) in diameter. 10 feet (3.0 m) of coal-based carbon was used to reduce ammonia to 0.1 ppm. 20.5 feet (6.2 m) of 5A molecular sieves were used to reduce nitrogen levels to 50 ppm. The adsorption time was 100 seconds. The hydrogen recovery from the first PSA system was 83.3%.

[0110] The waste gas from the first PSA system contained 7.6 mol% ammonia, 61.5 mol% nitrogen, and 30.9 mol% hydrogen. The flow rate was 988 kmol / hr. A dynamic simulation program was used to adsorb the ammonia and nitrogen from this stream after compressing it to 34 bar and cooling it to 40°C. Six feet (1.8 m) of coal-based carbon was used to reduce the ammonia to 0.1 ppm. 24.5 feet (7.5 m) of 5A molecular sieves were used to reduce the nitrogen level to 50 ppm. Hydrogen recovery from the second PSA operating on the waste gas from the first PSA was 78.5%.

[0111] The overall hydrogen recovery from the two PSA systems operating in series (as depicted in Figure 3) was 96.4%. The hydrogen flow rate was 85 tonnes / day.

[0112] Example 2 A dynamic simulation program using models and parameters for the adsorption of ammonia and nitrogen on coal-based carbon, as well as parameters for the adsorption of nitrogen on 5A molecular sieves, was used to demonstrate a process that provides a substantially pure hydrogen stream.

[0113] The adsorption cycle was that shown in Figure 13 of US8778051. A portion of the exhaust gas was compressed and introduced into an adsorber vessel which was simultaneously subjected to reduced pressures eq1d and eq2d. The flow rate to the adsorber vessel during Eq1d and eq2d was 594 kmol / hr.

[0114] The feed gas to the hydrogen PSA system was 3 mol% ammonia, 24.2 mol% nitrogen, and 72.8 mol% hydrogen at 34 bar and 40°C. The adsorbent was regenerated at 1.4 bar pressure during the blowdown and purge steps. Each adsorber vessel was 7 feet (2.1 m) in diameter. 10 feet (3.0 m) of coal-based carbon was used to reduce ammonia to 0.1 ppm. 19.5 feet (5.9 m) of 5A molecular sieves were used to reduce the nitrogen level to 50 ppm. The adsorption time was 100 seconds.

[0115] The hydrogen recovery from this PSA system (as depicted in Figure 2) was 94.3%. The pure hydrogen flow rate was 85 tonnes / day.

[0116] The present invention is not to be limited in scope by the specific aspects or embodiments disclosed in the examples, which are intended as illustrations of some aspects of the invention; any embodiments that are functionally equivalent are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art and are intended to be within the scope of the appended claims. The following embodiments can be given as examples of the present invention. (Appendix 1) 1. A method for separating hydrogen gas from an effluent gas of an ammonia decomposition reactor operating at elevated pressure in a pressure swing adsorption (PSA) system comprising at least two PSA units in parallel, comprising: The method comprises: cooling the effluent gas by heat exchange to produce a cooled effluent gas; supplying the cooled effluent gas at the elevated pressure to the PSA system to produce a hydrogen product gas and a PSA tail gas; 1. A process according to claim 1, wherein each PSA unit comprises a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween, the adsorbent bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen. (Appendix 2) 2. The method of claim 1, wherein the non-zeolitic adsorbent has a capacity for ammonia of at least 0.01 mmol / g at 0.005 bar and 40°C. (Appendix 3) 3. The method of claim 1 or 2, wherein the non-zeolitic adsorbent desorbs at least 10% of the adsorbed ammonia after 100 seconds at 1.4 bar and 40° C. using a nitrogen purge. (Appendix 4) 4. The method of any one of claims 1 to 3, wherein the non-zeolitic adsorbent desorbs at least 30% of the adsorbed ammonia after 600 seconds using a 1.4 bar nitrogen purge. (Appendix 5) 5. The method according to any one of claims 1 to 4, wherein the non-zeolitic adsorbent selectively co-adsorbs water. (Appendix 6) 6. The method according to any one of claims 1 to 5, wherein the non-zeolitic adsorbent selectively co-adsorbs nitrogen. (Appendix 7) 7. The method of claim 6, wherein the non-zeolitic adsorbent has a nitrogen capacity of at least 0.18 mmol / g at 5 bar and 40°C. (Appendix 8) 8. The method according to any one of claims 1 to 7, wherein the non-zeolitic adsorbent has a surface acidity in the range of about pH 6.3 to about pH 9.8. (Appendix 9) 9. The method according to any one of claims 1 to 8, wherein the non-zeolitic adsorbent is activated carbon. (Appendix 10) 10. The method of claim 9, wherein the activated carbon is selected from the group consisting of polymer-derived carbon, petroleum pitch carbon, wood-based carbon, coal-based carbon, and coconut shell carbon. (Appendix 11) 11. The method of claim 10, wherein the activated carbon is pretreated with an acid. (Appendix 12) 11. The method of claim 10, wherein the activated carbon is pretreated in situ by flowing nitrogen through the layer of coconut shells at an elevated temperature of at least 150°C. (Appendix 13) 11. The method of claim 10, wherein the activated carbon is pretreated with a base. (Appendix 14) 14. The method of any one of claims 9 to 13, wherein the activated carbon has an inorganic content of less than 1% by weight. (Appendix 15) 9. The method according to any one of claims 1 to 8, wherein the non-zeolitic adsorbent is activated alumina. (Appendix 16) 16. The method of claim 15, wherein the activated alumina is pretreated with a base. (Appendix 17) 9. The method according to any one of claims 1 to 8, wherein the non-zeolitic adsorbent is selected from the group consisting of wide pore silica gel, narrow pore silica gel, and silicalite. (Appendix 18) 18. The method of any one of claims 1 to 17, wherein the adsorption bed comprises an intermediate layer of activated carbon having an inorganic content of less than 1% positioned between the upstream and downstream layers. (Appendix 19) 19. The method of any one of claims 1 to 18, wherein the activated carbon of the intermediate layer is selected from the group consisting of polymer-derived carbon and petroleum pitch carbon. (Appendix 20) 20. The method of any one of claims 1-19, wherein the effluent gas has 0% to about 0.5% by volume water and about 0.1% to about 5% by volume ammonia, with the remainder of the gas consisting of a mixture of hydrogen and nitrogen in a ratio of about 3:1. (Appendix 21) 21. The method of any one of claims 1 to 20, wherein the cooled effluent gas has a temperature in the range of about 15°C to about 100°C. (Appendix 22) 22. The method of any one of claims 1 to 21, wherein the pressurization of the cooled effluent gas is in the range of about 5 bar to about 40 bar. (Appendix 23) 23. The method of any one of claims 1 to 22, wherein the PSA exhaust gas has a backpressure in the range of about 0.2% to about 20% of the pressurization of the effluent gas. (Appendix 24) 1. A PSA unit for separating hydrogen gas from the effluent gas of an ammonia decomposition reactor operating at elevated pressure, the PSA unit comprising: a feed end; a product end downstream from the feed end; and an adsorption bed positioned therebetween, the adsorption bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen. (Appendix 25) 25. The PSA unit of claim 24, wherein the non-zeolitic adsorbent has a capacity for ammonia of at least 0.01 mmol / g at 0.005 bar and 40°C. (Appendix 26) 26. The PSA unit of claim 24 or 25, wherein the non-zeolitic adsorbent desorbs at least 10% of the desorbed ammonia after 100 seconds using a 1.4 bar nitrogen purge. (Appendix 27) 27. A PSA unit according to any one of claims 24 to 26, wherein the non-zeolitic adsorbent desorbs at least 30% of the adsorbed ammonia after 600 seconds using a 1.4 bar nitrogen purge. (Appendix 28) 28. A PSA unit according to any one of claims 24 to 27, wherein the non-zeolitic adsorbent selectively co-adsorbs water. (Appendix 29) 29. A PSA unit according to any one of claims 24 to 28, wherein the non-zeolitic adsorbent selectively co-adsorbs nitrogen. (Appendix 30) 30. The PSA unit of claim 29, wherein the non-zeolitic adsorbent has a capacity for nitrogen of at least 0.18 mmol / g at 5 bar and 40°C. (Appendix 31) 31. A PSA unit according to any one of claims 24 to 30, wherein the non-zeolitic adsorbent has a surface acidity in the range of about pH 6.3 to about pH 9.8. (Appendix 32) 32. A PSA unit according to any one of claims 24 to 31, wherein the non-zeolitic adsorbent is activated carbon. (Appendix 33) 33. The PSA unit of claim 32, wherein the activated carbon is selected from the group consisting of polymer-derived carbon, petroleum pitch carbon, wood-based carbon, coal-based carbon, and coconut shell carbon. (Appendix 34) 33. The PSA unit of claim 32, wherein the activated carbon has been pretreated with an acid. (Appendix 35) 33. The PSA unit of claim 32, wherein the activated carbon has been pretreated in situ by flowing nitrogen through the layer of coconut shells at an elevated temperature of at least 150°C. (Appendix 36) 33. The PSA unit of claim 32, wherein the activated carbon has been pretreated with a base. (Appendix 37) 37. A PSA unit according to any one of claims 32 to 36, wherein the activated carbon has an inorganic content of less than 1% by weight. (Appendix 38) 32. A PSA unit according to any one of claims 24 to 31, wherein the non-zeolitic adsorbent is activated alumina. (Appendix 39) 39. The PSA unit of claim 38, wherein the activated alumina is pretreated with a base. (Appendix 40) 32. A PSA unit according to any one of claims 24 to 31, wherein the non-zeolitic adsorbent is selected from the group consisting of wide pore silica gel, narrow pore silica gel, and silicalite. (Appendix 41) 41. A PSA unit according to any one of claims 24 to 40, wherein the adsorption bed comprises an intermediate layer of activated carbon having an inorganic content of less than 1% positioned between the upstream and downstream layers. (Appendix 42) 42. A PSA unit according to any one of claims 24 to 41, wherein the activated carbon of the intermediate layer is selected from the group consisting of polymer-derived carbon and petroleum pitch carbon. (Appendix 43) 43. A PSA system for separating hydrogen gas from the effluent gas of an ammonia decomposition reactor operating at elevated pressure, the PSA system comprising at least two PSA units according to any one of claims 24 to 42 in parallel. (Appendix 44) 1. An apparatus for producing hydrogen from ammonia, comprising: a pump for pressurizing the liquid ammonia; at least one first heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) the liquid ammonia from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a catalyst-containing reactor tube in fluid communication with the first heat exchanger for decomposing the heated ammonia from the first heat exchanger to produce a first cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a fuel to heat the catalyst-containing reactor tubes and form a flue gas; a cracked gas conduit for supplying cracked gas from the catalyst-containing reactor tube to the first heat exchanger; a flue gas conduit for supplying flue gas from the furnace to the first heat exchanger; 44. A first PSA system of claim 43 in fluid communication with the catalyst-containing reactor tube for purifying cracked gas that is cooled after passing through the at least one heat exchanger to produce a first hydrogen product gas and a first PSA tail gas. a first PSA exhaust gas conduit for removing a first PSA exhaust gas from the first PSA system; a first hydrogen product gas conduit for removing a first hydrogen product gas from the first PSA system. (Appendix 45) a compressor in fluid communication with the first PSA system for compressing the first PSA exhaust to produce a compressed PSA exhaust; 45. The apparatus of claim 44, further comprising: a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA system. (Appendix 46) 46. ​​The apparatus of claim 45, optionally comprising a first PSA exhaust gas recirculation conduit for recirculating a first PSA exhaust gas from the first PSA device to the furnace after passing through the heat exchanger. (Appendix 47) a compressor in fluid communication with the first PSA system for compressing the first PSA exhaust to produce a compressed PSA exhaust; a second PSA system in fluid communication with the compressor for purifying the compressed PSA exhaust gas to produce a second PSA exhaust gas and a second hydrogen product gas; a second hydrogen product gas conduit for removing the second hydrogen gas from the second PSA system; 45. The apparatus of claim 44, further comprising: a second PSA exhaust conduit for removing the second PSA exhaust gas from the second PSA device. (Appendix 48) 48. The apparatus of claim 47, wherein the first and second hydrogen product gas conduits combine to form a combined hydrogen product gas conduit. (Appendix 49) 49. The apparatus of claim 47 or 48, wherein the second PSA exhaust gas conduit optionally recirculates the second PSA exhaust gas from the second PSA system to the furnace after passing through the heat exchanger.

Claims

1. 1. A method for separating hydrogen gas from an effluent gas of an ammonia decomposition reactor operating at elevated pressure in a pressure swing adsorption (PSA) system comprising at least two PSA units in parallel, comprising: The method comprises: cooling the effluent gas by heat exchange to produce a cooled effluent gas; feeding the cooled effluent gas at the elevated pressure into the PSA system to produce a hydrogen product gas and a PSA tail gas; each PSA unit comprising a feed end, a product end downstream from the feed end, and an adsorbent bed positioned therebetween, the adsorbent bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia, and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen; A process wherein the non-zeolitic adsorbent has a capacity for ammonia of at least 0.01 mmol / g at 0.005 bar and 40°C.

2. 10. The method of claim 1, wherein the non-zeolitic adsorbent desorbs at least 10% of the adsorbed ammonia after 100 seconds at 1.4 bar and 40°C using a nitrogen purge.

3. 3. The method of claim 1 or 2, wherein the non-zeolitic adsorbent desorbs at least 30% of the adsorbed ammonia after 600 seconds using a 1.4 bar nitrogen purge.

4. 4. The method of claim 1, wherein the non-zeolitic adsorbent selectively co-adsorbs water.

5. 5. The method of claim 1, wherein the non-zeolitic adsorbent selectively co-adsorbs nitrogen.

6. 6. The method of claim 5, wherein the non-zeolitic adsorbent has a capacity for nitrogen of at least 0.18 mmol / g at 5 bar and 40°C.

7. A method according to any one of claims 1 to 6, wherein the non-zeolitic adsorbent has a surface acidity in the range of pH 6.3 to pH 9.

8.

8. The method of any one of claims 1 to 7, wherein the non-zeolitic adsorbent is activated carbon.

9. 9. The method of claim 8, wherein the activated carbon is selected from the group consisting of polymer-derived carbon, petroleum pitch carbon, wood-based carbon, coal-based carbon, and coconut shell carbon.

10. 10. The method of claim 9, wherein the activated carbon is pretreated with an acid.

11. 10. The method of claim 9, wherein the activated carbon is pretreated in situ by flowing nitrogen through the layer of coconut shells at an elevated temperature of at least 150°C.

12. 10. The method of claim 9, wherein the activated carbon is pretreated with a base.

13. 13. The method of any one of claims 8 to 12, wherein the activated carbon has an inorganic content of less than 1% by weight.

14. The method of any one of claims 1 to 7, wherein the non-zeolitic adsorbent is activated alumina.

15. 15. The method of claim 14, wherein the activated alumina is pretreated with a base.

16. The method of any one of claims 1 to 7, wherein the non-zeolitic adsorbent is selected from the group consisting of wide pore silica gel, narrow pore silica gel, and silicalite.

17. 17. The method of any one of claims 1 to 16, wherein the adsorption bed comprises an intermediate layer of activated carbon having an inorganic content of less than 1% positioned between the upstream and downstream layers.

18. 18. The method of claim 17, wherein the activated carbon of the intermediate layer is selected from the group consisting of polymer-derived carbon and petroleum pitch carbon.

19. 19. The method of any one of claims 1 to 18, wherein the effluent gas has 0% to 0.5% by volume water and 0.1% to 5% by volume ammonia, with the remainder of the gas consisting of a mixture of hydrogen and nitrogen in a ratio of about 3:

1.

20. A process according to any preceding claim, wherein the cooled effluent gas is at a temperature in the range of from 15°C to 100°C.

21. A method according to any one of the preceding claims, wherein the pressurisation of the cooled effluent gas is in the range of from 5 bar to 40 bar.

22. The method of any one of claims 1 to 21, wherein the PSA tail gas has a back pressure in the range of 0.2% to 20% of the pressure boost of the effluent gas.

23. 1. A PSA unit for separating hydrogen gas from an effluent gas of an ammonia decomposition reactor operating at elevated pressure, said PSA unit comprising: a feed end; a product end downstream from said feed end; and an adsorbent bed positioned therebetween, said adsorbent bed including an upstream layer of a non-zeolitic adsorbent selectively adsorbing at least ammonia; and a downstream layer of a zeolitic adsorbent selectively adsorbing nitrogen; A PSA unit wherein the non-zeolitic adsorbent has a capacity for ammonia of at least 0.01 mmol / g at 0.005 bar and 40°C.

24. 24. A PSA unit according to claim 23, wherein the non-zeolitic adsorbent desorbs at least 10% of the desorbed ammonia after 100 seconds using a 1.4 bar nitrogen purge.

25. 25. A PSA unit according to claim 23 or 24, wherein the non-zeolitic adsorbent desorbs at least 30% of the adsorbed ammonia after 600 seconds using a 1.4 bar nitrogen purge.

26. A PSA unit according to any one of claims 23 to 25, wherein the non-zeolitic adsorbent selectively co-adsorbs water.

27. A PSA unit according to any one of claims 23 to 26, wherein the non-zeolitic adsorbent selectively co-adsorbs nitrogen.

28. 28. A PSA unit according to claim 27 wherein the non-zeolitic adsorbent has a capacity for nitrogen of at least 0.18 mmol / g at 5 bar and 40°C.

29. A PSA unit according to any one of claims 23 to 28, wherein the non-zeolitic adsorbent has a surface acidity in the range of pH 6.3 to pH 9.

8.

30. A PSA unit according to any one of claims 23 to 29, wherein the non-zeolitic adsorbent is activated carbon.

31. 31. The PSA unit of claim 30, wherein the activated carbon is selected from the group consisting of polymer-derived carbon, petroleum pitch carbon, wood-based carbon, coal-based carbon, and coconut shell carbon.

32. 31. The PSA unit of claim 30, wherein the activated carbon is pretreated with an acid.

33. 32. A PSA unit according to claim 31, wherein said activated carbon has been pretreated in situ by flowing nitrogen through said bed of coconut shells at an elevated temperature of at least 150°C.

34. 31. The PSA unit of claim 30, wherein the activated carbon is pretreated with a base.

35. A PSA unit according to any one of claims 30 to 34, wherein the activated carbon has an inorganic content of less than 1% by weight.

36. A PSA unit according to any one of claims 23 to 29, wherein the non-zeolitic adsorbent is activated alumina.

37. 37. A PSA unit according to claim 36, wherein the activated alumina is pretreated with a base.

38. A PSA unit according to any one of claims 23 to 29, wherein the non-zeolitic adsorbent is selected from the group consisting of wide pore silica gel, narrow pore silica gel, and silicalite.

39. 39. A PSA unit according to any one of claims 23 to 38, wherein the adsorption bed comprises an intermediate layer of activated carbon having an inorganic content of less than 1% positioned between the upstream and downstream layers.

40. 40. A PSA unit according to claim 39 wherein said activated carbon of said intermediate layer is selected from the group consisting of polymer-derived carbon and petroleum pitch carbon.

41. 41. A PSA system for separating hydrogen gas from the effluent gas of an ammonia decomposition reactor operating at elevated pressure, said PSA system comprising at least two PSA units according to any one of claims 23 to 40 in parallel.

42. 1. An apparatus for producing hydrogen from ammonia, comprising: a pump for pressurizing the liquid ammonia; at least one first heat exchanger in fluid communication with the pump for heating (and optionally vaporizing) the liquid ammonia from the pump by heat exchange with one or more hot fluids to produce heated ammonia; a catalyst-containing reactor tube in fluid communication with the first heat exchanger for decomposing heated ammonia from the first heat exchanger to produce a first cracked gas comprising hydrogen gas, nitrogen gas, and residual ammonia; a furnace in thermal communication with the catalyst-containing reactor tubes for combusting a fuel to heat the catalyst-containing reactor tubes and form a flue gas; a cracked gas conduit for supplying cracked gas from the catalyst-containing reactor tube to the first heat exchanger; a flue gas conduit for supplying flue gas from the furnace to the first heat exchanger; 42. A first PSA system as defined in claim 41, in fluid communication with the catalyst-containing reactor tubes for purifying cracked gas cooled after passing through the at least one heat exchanger to produce a first hydrogen product gas and a first PSA tail gas; a first PSA exhaust gas conduit for removing a first PSA exhaust gas from the first PSA system; a first hydrogen product gas conduit for removing a first hydrogen product gas from said first PSA system.

43. a compressor in fluid communication with the first PSA system for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; 43. The apparatus of claim 42, comprising: a recirculation conduit for recirculating the compressed PSA exhaust gas to the first PSA system.

44. 44. The apparatus of claim 43, optionally comprising a first PSA exhaust gas recirculation conduit for recirculating a first PSA exhaust gas from said first PSA device to said furnace after passing through said heat exchanger.

45. a compressor in fluid communication with the first PSA system for compressing the first PSA exhaust gas to produce a compressed PSA exhaust gas; a second PSA system in fluid communication with the compressor for purifying the compressed PSA exhaust gas to produce a second PSA exhaust gas and a second hydrogen product gas; a second hydrogen product gas conduit for removing the second hydrogen gas from the second PSA system; a second PSA exhaust gas conduit for removing the second PSA exhaust gas from the second PSA device.

46. 46. ​​The apparatus of claim 45, wherein the first and second hydrogen product gas conduits combine to form a combined hydrogen product gas conduit.

47. 47. The apparatus of claim 45 or 46, wherein the second PSA exhaust gas conduit optionally recirculates the second PSA exhaust gas from the second PSA system to the furnace after passing through the heat exchanger.

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