Methods and systems for hydrogen purification

Abstract

A method comprising partially condensing and separating a feed stream comprising helium and hydrogen to produce a first medium-pressure vapor stream and a first medium-pressure liquid stream; reducing the pressure of the first medium-pressure liquid stream or a stream derived from the first medium-pressure liquid stream to produce a low-pressure vapor stream and a low-pressure liquid stream; cooling the first medium-pressure vapor stream by indirect heat exchange against the low-pressure liquid stream to produce a first partially condensed medium-pressure stream; and separating the first partially condensed medium-pressure stream to produce a second medium-pressure vapor stream and a second medium-pressure liquid stream.

Description

METHODS AND SYSTEMS FOR HYDROGEN PURIFICATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application 63 / 570,268 filed March 27, 2024, which is incorporated by reference herein.BACKGROUND OF THE INVENTION

[0002] Hydrogen can be a means to reduce carbon intensity in fields such as transportation, power production, and chemicals, if a decarbonized source of hydrogen may be found. One potential low-carbon source of hydrogen is natural hydrogen, mainly produced through geochemical processes such as serpentinization (the reaction of water with ferrous minerals). Hydrogen formed in this manner may rise through the geologic layers until it is trapped by impermeable rocks, forming a reservoir. Noble gases such as helium and argon may be formed underground by radioactive decay and similarly be trapped. Natural hydrogen sources may require new purification processes because the impurities that must be removed may be in different concentrations or entirely absent in industrial hydrogen sources such as from steam methane reforming.BRIEF DESCRIPTION OF DRAWINGS

[0003] The present invention will hereinafter be described in conjunction with the appended figures wherein like numerals denote like elements:

[0004] Fig. 1 is a schematic view depicting an embodiment of a hydrogen purification process according to one or more aspects of the present disclosure.

[0005] Fig. 2 is a schematic view depicting a further embodiment of a hydrogen purification process according to one or more aspects of the present disclosure.

[0006] Fig. 3 is a schematic view depicting a modification of Fig. 2 in which a hydrogen feed does not require upgrading in a membrane prior to purification by adsorption.

[0007] Fig. 4A is a schematic view depicting an alternative to hydrogen-helium separation in which the hydrogen-helium stream is combusted to generate power.

[0008] Fig. 4B is a schematic view depicting an alternative to hydrogen-helium separation in which the hydrogen-helium stream is catalytically oxidized to convert hydrogen to water.

[0009] Fig. 5 is a schematic view of a helium recovery process in which a hydrogen feed is first combusted to generate power and helium is recovered from the combustion products.

[0010] Fig. 6 is a schematic view of a tail gas separation process in which methane, nitrogen and / or argon are recovered from the tail gas stream, allowing the recycling of the remaining hydrogen-helium mixture.

[0011] Fig. 7 is a schematic view of a cryogenic hydrogen purifier according to one or more aspects of the present disclosure.

[0012] Fig. 8 is a schematic view of a modification of Fig. 7 which yields a liquid hydrogen product.

[0013] Fig. 9 is a schematic view of a modification of Fig. 8 in which the intermediate flash is eliminated.

[0014] Fig. 10 is a schematic view of a modification of Fig. 9 in which the first mediumpressure flash is replaced with a medium-pressure distillation column.

[0015] Fig. 1 1 is a schematic view of a modification of Fig. 8 in which the first mediumpressure flash is eliminated.

[0016] Fig. 12 is a schematic view of a process to produce ammonia from a hydrogen feed stream comprising a helium impurity.

[0017] Fig. 13 is a schematic view depicting a modification of Fig. 12 in which a hydrogen PSA is used to purify the hydrogen feed stream.

[0018] Fig. 14 is a schematic view depicting a modification of Fig. 12 in which a hydrogen feed stream is reacted with a precursor to form a hydrogen carrier.DETAILED DESCRIPTION OF THE INVENTION

[0019] The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention, as set forth in the appended claims.

[0020] The present disclosure is directed to methods and systems for purifying a hydrogen feed stream. The methods and systems may also include recovering a secondary product such as helium or argon from the hydrogen feed stream.

[0021] The articles "a" or "an" as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of"a" and "an" does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used.

[0022] The term “and / or” placed between a first entity and a second entity includes any of the meanings of (1) only the first entity, (2) only the second entity, or (3) the first entity and the second entity. The term “and / or” placed between the last two entities of a list of 3 or more entities means at least one of the entities in the list including any specific combination of entities in this list. For example, “A, B and / or C” has the same meaning as “A and / or B and / or C” and comprises the following combinations of A, B and C: (1) only A, (2) only B, (3) only C, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A and B and C.

[0023] The adjective “any” means one, some, or all, indiscriminately of quantity.

[0024] The phrase “at least a portion” means “a portion or all.” The “at least a portion of a stream” has the same composition, with the same concentration of each of the species, as the stream from which it is derived.

[0025] As used herein, “first,” “second,” “third,” etc. are used to distinguish among a plurality of steps and / or features, and is not indicative of the total number, or relative position in time and / or space, unless expressly stated as such.

[0026] The terms “depleted” or “lean” mean having a lesser mole percent concentration of the indicated component than the original stream from which it was formed. “Depleted” and “lean” do not mean that the stream is completely lacking the indicated component.

[0027] The terms “rich” or “enriched” mean having a greater mole percent concentration of the indicated component than the original stream from which it was formed.

[0028] “Downstream” and “upstream” refer to the intended flow direction of the process fluid transferred. If the intended flow direction of the process fluid is from the first device to the second device, the second device is downstream of the first device. In case of a recycle stream, downstream and upstream refer to the first pass of the process fluid.

[0029] The term “indirect heat exchange” refers to the process of transferring sensible heat and / or latent heat between two or more fluids without the fluids in question coming into physical contact with one another. The heat may be transferred through the wall of a heat exchanger or with the use of an intermediate heat transfer fluid. The term “hot stream” refers to any stream that exits the heat exchanger at a lower temperature than it entered.Conversely, a “cold stream” is one that exits the heat exchanger at a higher temperature than it entered.

[0030] The term “distillation column” includes fractionating columns, rectifying columns, and stripping columns. “Distillation column” may refer to a single column or a plurality of columns in series or parallel, where the plurality can be any combination of the above column types. Each column may comprise one or more sections of trays and / or packing.

[0031] In accordance with the present embodiments, the hydrogen feed stream may comprise impurities such as helium, argon, carbon dioxide, nitrogen, water vapor, methane, and heavier hydrocarbons. Heavier hydrocarbons may include ethane, propane, butane, pentane, and hexane. The hydrogen feed stream may comprise 7% to 99%, or 20% to 99%, or 50% to 99% hydrogen by volume. The hydrogen feed stream may comprise 0.1 % to 20%, or 1 % to 17%, or 1 % to 5% helium by volume. The hydrogen feed stream may originate in an underground reservoir.

[0032] The hydrogen feed stream may be upgraded in one or more membrane stages to produce at least one permeate stream enriched in fast gases such as hydrogen and helium and at least one retentate stream enriched in slow gases such as argon, nitrogen, and methane. Prior to upgrading in the one or more membrane stages, the hydrogen feed stream may be treated to remove heavy hydrocarbons, aromatic compounds, and or water vapor to protect the membrane material. The hydrogen feed stream may be heated before entering the one or more membrane stages to prevent water from condensing on the membranes.

[0033] The at least one permeate stream may be further purified in a pressure swing adsorption (PSA) unit. If the concentration of hydrogen in the hydrogen feed stream is high enough the hydrogen feed stream may enter the PSA directly. The PSA produces a PSA product stream enriched in hydrogen and helium and a PSA tail gas stream enriched in impurities such as methane, argon, carbon dioxide, water vapor, and nitrogen. The PSA tail gas stream may be compressed and recycled to the one or more membrane stages. Water vapor may be condensed and removed from the PSA tail gas stream during compression.

[0034] The PSA product stream may be cooled and further purified in one or more cryogenic temperature swing adsorption (CTSA) units to further remove impurities such as methane, argon, carbon dioxide, water vapor, and nitrogen. Multiple CTSA units may be arranged with each operating at a successively colder temperature. The PSA product stream may be cooled to a temperature ranging from 20 K to 120 K, or from 50 K to 80 K, prior to feeding the CTSA. Impurities are adsorbed onto an online bed and a hydrogen-helium mixture exits the online bed. The online bed may utilize one or more high surface area adsorbents, including but not limited to zeolites, metal-organic frameworks (MOF), alumina, silica gel, silicalites, activatedcarbon, Engelhard titanosilicate (ETS), and metal oxides. During the step in which the impurities are removed from the PSA product stream the adsorbent in the online bed becomes loaded with impurities to the point that the efficiency of impurity removal falls and the impurity levels in the hydrogen-helium mixture may exceed specifications. At this point the bed may be switched to regeneration mode in which a regeneration gas is passed through the bed to remove impurities and produce a spent regeneration gas enriched in impurities. The regeneration gas may comprise a portion of the hydrogen-helium mixture, or a pure hydrogen product. The bed may be regenerated at ambient temperature and ambient pressure. The spent regeneration gas may be compressed and recycled to the one or more membrane stages. The spent regeneration gas may be combined with the PSA tail gas to be compressed in the same compressor.

[0035] The hydrogen-helium mixture may be separated in a cryogenic process comprising any combination of flash separators and distillation columns. The cryogenic process may be refrigerated by liquid nitrogen, liquid hydrogen, and / or reducing the pressure of one or more streams in the process. Pressure reduction could be achieved in a device such as a valve or an expander. The separation may be designed to produce a pure hydrogen product stream and a hydrogen-helium overhead. The hydrogen-helium overhead may have a molar ratio of helium to hydrogen of about 3:1 .

[0036] The hydrogen-helium overhead stream may be separated using a variety of methods. A voltage may be applied to an electrochemical hydrogen pump or compressor to separate the hydrogen out of the hydrogen-helium overhead stream, producing a helium product stream and a second hydrogen product stream which may be combined with the pure hydrogen product stream. The second hydrogen product stream may be produced at a higher pressure than the helium product stream. The helium product stream and / or the second hydrogen product stream may require dehydration. Alternatively, the hydrogen-helium overhead stream may be combusted to generate power and / or heat. Helium may be recovered from the combustion products, for example using membranes and / or adsorption processes. The remaining portion of the combustion products stream may be vented or recycled, for example combined with the PSA tail gas stream prior to compression. The hydrogen-helium overhead stream may be combusted with enriched oxygen or pure oxygen to reduce the amount of nitrogen that must be removed from the combustion products stream. If there is insufficient demand for power, the hydrogen-helium overhead stream may be reacted with air in the presence of a catalyst to convert hydrogen to water, with the same downstream separation process to recover helium.

[0037] The PSA product stream may be separated in a cryogenic process that yields a crude helium stream and a liquid hydrogen product. The PSA product stream may be cooled andthen purified by an adsorption process such as a CTSA. When regenerating the CTSA, a spent regen gas stream may be recycled to an upstream purification step such as a membrane or PSA. The spent regen gas stream may be recycled to a point in the process with a similar composition. The PSA product stream may be cooled and passed over an O-P catalyst that catalyzes the reaction of ortho-hydrogen to para-hydrogen. Having an ortho-hydrogen to parahydrogen ratio close to the equilibrium value for liquid hydrogen may reduce the exothermic reaction of ortho-hydrogen to para-hydrogen from occurring while liquid hydrogen is stored or transported which would increase the rate of boil-off. The PSA product stream may be cooled and reduced in pressure to produce a partially condensed hydrogen-helium mixture. Any combination of cooling, purification, O-P catalyzed reactions, and reduction in pressure may be used to produce the partially condensed hydrogen-helium mixture. The partially condensed hydrogen-helium mixture may be separated to form a first medium-pressure vapor stream and a first medium-pressure liquid stream.

[0038] The partially condensed hydrogen-helium mixture may be separated in any combination of flash vessels or distillation columns. The first medium-pressure liquid stream, or a stream derived from the first medium-pressure liquid stream, may be reduced in pressure to form a partially condensed low-pressure stream which may be separated to produce a low- pressure vapor stream and a low-pressure liquid stream. The partially condensed low- pressure stream may be separated in any combination of flash vessels or distillation columns. The low-pressure liquid stream may be greater than 97% hydrogen, or greater than 98% hydrogen, or greater than 99% hydrogen, or greater than 99.97% hydrogen, or greater than 99.9995% hydrogen. The low-pressure vapor stream may be used as a refrigerant, compressed, and cooled to produce a recycle stream. The recycle stream may be combined with the partially condensed hydrogen-helium mixture. The low-pressure vapor stream may be recycled by combining with the partially condensed hydrogen-helium mixture. At least a portion of the recycle stream may be expanded to provide refrigeration to cool the PSA product stream. The first medium-pressure vapor stream may be cooled against the low-pressure liquid stream to form a first partially condensed medium-pressure stream. The first mediumpressure vapor stream may be cooled against the low-pressure liquid stream by indirect heat exchange either integrated with the separator device for the partially condensed low-pressure stream, a separate heat exchanger, or a heat exchanger integrated with other heat exchange duties in the cryogenic process. The first partially condensed medium-pressure stream may be separated to produce a crude helium vapor stream and a second medium-pressure liquid stream. The crude helium vapor stream may comprise greater than 10% helium, or greater than 50% helium, or greater than 65% helium.. The crude helium vapor stream may be further purified to produce a pure helium product. The crude helium vapor stream may be furtherpurified by combining with an oxidant and reacting over a deoxo catalyst to react the oxidant with hydrogen; the reaction products such as water then may be removed by any suitable process such as adsorption. The oxidant may comprise oxygen, air, or oxygen-enriched air. The second medium-pressure liquid stream may be combined with the first medium-pressure liquid stream either upstream or downstream of the reduction in pressure of the first mediumpressure liquid stream. When the second medium pressure-liquid stream is combined with the first medium-pressure liquid stream downstream of the reduction in pressure of the first medium-pressure liquid stream, the second medium-pressure liquid stream may be first reduced in pressure. The second medium-pressure liquid stream may be contacted with the first medium-pressure vapor stream. In the case where the partially condensed hydrogenhelium overhead stream is separated with a distillation column, the cooling of the first mediumpressure vapor stream may act as a condenser for the distillation column and the second medium-pressure liquid stream may act to wash hydrogen from the first medium-pressure vapor stream.

[0039] Prior to being reduced in pressure to form the partially condensed low-pressure stream, the first medium-pressure liquid stream may be reduced to one or more intermediate pressures in series or parallel. At each intermediate pressure stage, the intermediate pressure stream may be partially condensed and separated to form an intermediate-pressure vapor stream and an intermediate-pressure liquid stream. The intermediate-pressure vapor stream may be warmed, compressed, cooled, and recycled. The intermediate-pressure vapor stream may be warmed by indirect heat exchange against a stream such as the helium-hydrogen overhead stream to provide refrigeration. The intermediate-pressure vapor stream may be recycled by combining with the partially condensed hydrogen-helium overhead stream. The intermediate-pressure liquid stream may be reduced in pressure to produce the partially condensed low-pressure stream.

[0040] A waste stream such as the retentate stream, the PSA tail gas, and / or the spent regen gas stream may comprise significant amounts of impurities such as argon that have a significant value, or methane that carries regulatory restrictions on emissions. In those cases, the waste stream may have water vapor and carbon dioxide removed in a TSA, be cooled to cryogenic temperatures, and successively distilled to produce a second hydrogen-helium overhead stream, a nitrogen-rich overhead stream, an argon-rich overhead stream, and / or a methane-rich bottoms stream in a series of columns as necessary. For example, if there is negligible nitrogen in the waste stream, the nitrogen-rich overhead stream may be absent. The overhead streams may be indirectly heated against the waste stream to provide cooling. The bottoms stream leaving each column may be expanded to provide refrigeration. Additional refrigeration may be used to cool the waste stream such as liquid nitrogen or aclosed loop refrigeration cycle. The same heat exchanger system may also be used to cool the hydrogen-helium mixture prior to separation in the CTSA. The nitrogen-rich overhead stream may be used to regenerate the TSA. Depending on the purity, the second hydrogenhelium overhead stream may be combined with the hydrogen-helium mixture or the hydrogenhelium overhead stream. If the second hydrogen-helium overhead stream is recovered in this manner, the one or more membrane stages may be sized to increase the slip of hydrogen to the one or more retentate streams which may reduce the size of the membranes and / or increase the concentration of hydrogen in the one or more permeate streams.

[0041] The hydrogen feed stream may be used to produce ammonia. In cases where the hydrogen feed stream comprises a helium impurity, the helium impurity may accumulate in the ammonia process such that integrating a hydrogen-helium separation step becomes practical. In contrast, a typical ammonia process begins with a natural gas stream. If the natural gas stream comprises a commercially valuable amount of helium, the helium may be separated from the natural gas stream upstream of an ammonia synthesis reactor since separating helium from methane and other hydrocarbons is simpler and lower cost than separating helium from hydrogen. In contrast, in the present disclosure it may be advantageous to separate helium from hydrogen downstream of the ammonia synthesis reactor.

[0042] The hydrogen feed stream may comprise hydrogen, helium, and other impurities such as water, carbon dioxide, oxygen, argon, methane, sulfur compounds, and heavier hydrocarbons. The other impurities may be removed upstream of the ammonia synthesis reactor, for example using adsorption and / or absorption processes to produce a cleaned feed stream. Carbon dioxide and water may be removed by a TSA. Liquid nitrogen may be used to wash impurities such as methane from the hydrogen feed stream. The cleaned feed stream may be combined with nitrogen and may be compressed as needed to produce an ammonia synthesis feed stream.

[0043] The ammonia synthesis reactor may operate at a pressure ranging from 60 to 200 bar. In the ammonia synthesis reactor hydrogen and nitrogen may be reacted in the presence of a catalyst to produce ammonia. A reaction product stream may then be cooled to condense at least a portion of the ammonia to form a first ammonia product stream and an ammonia condenser overhead stream enriched in nitrogen, hydrogen and helium. The ammonia condenser overhead stream may be indirectly heated against the reaction product stream. At least a portion of the ammonia condenser overhead stream may be recycled to the feed of the ammonia synthesis reactor, and may be compressed as required. At least a portion of the ammonia condenser overhead stream may be sent to an ammonia scrubber which separates the ammonia condenser overhead stream to produce a first lights stream and a secondammonia product stream. The ammonia scrubber may use a high-pressure water stream to recover ammonia from the ammonia condenser overhead stream, then the second ammonia product stream may be stripped from the high pressure water stream. The first lights stream may comprise unreacted hydrogen and nitrogen, as well as light inert species such as helium and argon. The first lights stream may be separated to form a nitrogen-enriched lights stream and a nitrogen-depleted lights stream. The first lights stream may be separated using any combination of membranes, adsorption, cryogenic distillation, or partial condensation. At least a portion of the nitrogen-enriched lights stream may be vented to prevent buildup of inert species such as argon. If the amount of argon in the vented stream is commercially viable, it may be separated to form an argon product. At least a portion of the nitrogen-enriched lights stream may be recycled to the ammonia synthesis reactor. The nitrogen-depleted lights stream may be separated to produce a hydrogen-enriched lights stream and a helium- enriched lights stream. The nitrogen-depleted lights stream may be separated using any combination of membranes such as palladium membranes, electrochemical processes such as applying a voltage to an electrochemical hydrogen pump / compressor, and / or cryogenic distillation. The separation of the nitrogen-depleted lights stream may comprise a step in which the nitrogen-depleted lights stream ora stream derived from the nitrogen-depleted lights stream is contacted with an adsorbent at a temperature less than 30 K. Using an adsorbent at a temperature below 30 K may produce a helium enriched lights stream at with >99.999% helium purity. The adsorbent may be regenerated using an electric heater or internal coils with flowing fluid at a temperature ranging from 100 to 300 K. The rejected impurities such as hydrogen may be recycled to the ammonia synthesis reactor. The rejected impurities may be recycled to the compressor upstream of the ammonia synthesis reactor. In cases where both the first lights stream and the nitrogen-depleted lights streams are separated using cryogenic distillation and / or partial condensation, the two processes may be integrated into a single heat exchange network. The hydrogen-enriched lights stream may be recycled to the ammonia synthesis reactor, and maybe compressed as required. The hydrogen-enriched lights stream may be recycled to the cleaned feed stream, and may be compressed as required. The helium-enriched lights stream may be further purified, such as by reacting hydrogen impurities with oxygen followed by adsorption, to form a helium product. The helium-enriched lights stream may be of sufficiently high purity to form a helium product depending on the separation method used for the nitrogen-depleted lights stream and the end user specifications of the helium product.

[0044] The hydrogen feed stream may be used to react with a precursor produce a hydrogen carrier, for example by hydrogenating toluene to form methylcyclohexane (MCH). MCH may then be stored and / or transported in a dense liquid phase at lower cost compared to gaseous hydrogen, and dehydrogenated at the end point to recover hydrogen. An ammonia synthesisreactor may be considered a hydrogenation reactor in which nitrogen is the precursor and ammonia is the hydrogen carrier. The hydrogenation and / or dehydrogenation reactions may require a catalyst. Any suitable compound may be selected as a precursor that readily hydrogenates to form a hydrogen carrier that readily dehydrogenates to recover the hydrogen. Aromatic hydrocarbons and other unsaturated hydrocarbons may serve as suitable precursors. The hydrogenation reaction may take place at an elevated temperature and pressure to produce a reactor effluent comprising unreacted precursor and hydrogen, hydrogen carrier, and unreacted impurities in the hydrogen feed stream. The reactor effluent may be cooled to reduce the vapor pressure of the precursor and hydrogen carrier. The reactor effluent may be separated to produce a first hydrogen carrier-enriched liquid stream and a reactor effluent overhead stream. A second hydrogen carrier-enriched liquid stream may be recovered from the reactor effluent overhead stream by cooling and / or washing with a stream such as liquid water, yielding a first lights stream with negligible concentrations of precursor and hydrogen carrier. If helium is present in the hydrogen feed stream, a high degree of conversion of hydrogen in the hydrogen feed stream may yield a significant concentration of helium in the first lights stream. As in the case of ammonia production, separation of helium and hydrogen may employ any combination of membranes, adsorption, absorption, and cryogenic separation to form a helium product and a hydrogen recycle stream to be returned to the hydrogenation reactor.

[0045] Fig. 1 is a schematic view depicting an embodiment of a hydrogen purification process according to one or more aspects of the present disclosure. A natural hydrogen feed stream 101 enters one or more stages of membranes 110, producing a retentate stream 111 enriched in methane, argon, and nitrogen, and a permeate stream 112 enriched in helium and hydrogen. Carbon dioxide and water may be removed from the retentate stream using a TSA 120, and the resulting purified retentate stream 121 is separated in the CH4 / N2 / Ar recovery section 130 to produce methane 131 , nitrogen 132, and argon 133 products as appropriate, as well as a hydrogen-helium mixture 134 that may either be combined with the permeate stream 112 or compressed in recycle compressor 135 and recycled to the one or more stages of membranes 110. The permeate stream 112 is compressed if required to feed a hydrogen PSA 140, producing a PSA product stream 141 enriched in hydrogen and helium and a PSA tail gas stream 142 enriched in methane, argon, carbon dioxide, water vapor, and nitrogen. The PSA tail gas stream 142 may be recycled to the one or more stages of membranes 110. The PSA product stream 141 may then be cooled and fed to a cryogenic hydrogen purifier 150. Using a cryogenic separation system comprising one or more flash separators and / or distillation columns, the cryogenic hydrogen purifier 150 may produce a first hydrogen product stream 151 , a cryogenic hydrogen purifier tail gas stream 152 that may be recycled to the one or more stages of membranes 110, and a hydrogen-helium overhead stream 153. Thecryogenic hydrogen purifier 150 may be integrated with the CH4 / N2 / Ar recovery section 130 by sharing a single insulated cold box, combining into a single multiple stream heat exchanger, and / or sharing cooling utilities 154. The hydrogen-helium overhead stream 153 may then be separated in a hydrogen removal step 160 which may produce a second hydrogen product stream 161 , a hydrogen removal tail gas stream 162 that may be recycled to the one or more stages of membranes 1 10, and / or a crude helium stream 163. The crude helium stream 163 may be purified in a helium PSA 170 to produce a helium product stream 171 and a helium PSA tail gas stream 172 that may be recycled to the one or more stages of membranes 1 10.

[0046] Fig. 2 shows a further embodiment utilizing three stages of membranes (210A, 210B, 210C) arranged so that each successive stage accepts the retentate from the previous stage. The concentration of hydrogen in each successive permeate stream is lower, such that the first permeate stream 21 1 and second permeate stream 212 are combined and fed to the hydrogen PSA 240 and the third permeate stream 213 is compressed and recycled to the first membrane stage feed. The third retentate stream 214 may be re-injected into a suitable underground formation 215 or sent to the CH4 / N2 / Ar recovery section 230 to produce methane 231 , nitrogen 232, and argon 233 products as appropriate. The PSA product stream 241 may then be cooled and further purified in a CTSA 250 to produce a hydrogen-helium mixture 251. When the CTSA is regenerated, the spent regeneration gas 252 may be compressed in regen compressor 255 and used in the purge step of the hydrogen PSA 240 to increase hydrogen recovery prior to being combined with the third permeate stream 213, compressed in recycle compressor 235, and recycled to the first membrane stage 210A as recycle stream 236. A water stream 237 may be condensed and separated in the recycle compressor 235, for example in the coolers after stages of compression. Additional recycle streams may be compressed in recycle compressor 235, such as tail gas stream 238 from downstream purification of a helium stream. The hydrogen-helium mixture 251 may then be separated in cryogenic hydrogen purifier 260 as in Fig. 1 to produce a helium-enriched hydrogen-helium mixture 261 and a first hydrogen product stream 262. The final hydrogen- helium separation step in Fig. 2 is an electrochemical hydrogen pump / compressor 270 which produces a helium product stream 271 and a second hydrogen product stream 272. The second hydrogen product stream 272 may require dehydration in dehydration unit 280 before it may be combined with the first hydrogen product stream 262 exiting the cryogenic hydrogen purifier 260 to form a combined hydrogen product stream 273. In at least some embodiments, the hydrogen stream may be recycled to any point upstream of the hydrogen PSA 240 (not shown) to eliminate the need for dehydration unit 280.

[0047] Fig. 3 shows a modification of Fig. 2 in which the hydrogen feed stream 301 is at a sufficient hydrogen concentration to allow direct entry into the hydrogen PSA 340. A two-stage membrane (31 OA, 31 OB) in which the first retentate stream feeds the second membrane stage 31 OB may be required to recycle tail gas streams from the downstream process. First permeate stream 31 1 may be compressed in permeate compressor 315 before being combined with the hydrogen feed stream 301. Second permeate stream 312 may be compressed in recycle compressor 235 and recycled to the first stage membrane 31 OA. At least a portion of the recycle stream 236 may be reinjected to a suitable underground formation 339.

[0048] Fig. 4A shows an alternative to the hydrogen helium separation in Figs. 2 and 3 in which the helium-enriched hydrogen-helium mixture 261 is combusted with an oxidant 402 such as air, oxygen, or oxygen-enriched air to produce power and / or heat 411 in power generator 410. Flue gas 412 exiting the power generator may be cooled in heat exchanger 420 and compressed in compressor 430. Water (421 , 431) may be condensed and removed in one or both steps. The cooled and compressed flue gas 432 may then be separated in a helium PSA 440 to produce a helium product stream 441 and a helium PSA tail gas stream 238 that may be recycled to the recycle compressor 235 in Fig. 2.

[0049] Fig. 4B shows an alternative to the hydrogen helium separation in Figs. 2 and 3 in which the hydrogen-helium mixture is catalytically oxidized using a deoxo catalyst 450.

[0050] Fig. 5 shows a helium recovery process in which a hydrogen feed is first combusted to generate power and helium is recovered from the combustion products. The natural hydrogen feed stream 501 is first combusted with an oxidant 502 such as air, oxygen, or oxygen- enriched air in power generator 510 to produce power and / or heat 51 1. Flue gas 512 may then be cooled in heat exchanger 520 and compressed in compressor 530, with optional water removal (521 ,531) in one or both steps as in Figs. 4A and 4B. The cooled and compressed flue gas 532 then may enter one or more stages of membranes (540A, 540B). When two stages of membranes are used as in Fig. 5, a first permeate stream 541 enriched in helium, a second permeate stream 542 and a retentate stream 543 depleted in helium are produced. The first permeate stream 541 may then be purified in a helium PSA 550 to produce a helium product stream 551 and a helium PSA tail gas stream 552 which may be vented or compressed and recycled to the first membrane stage 540A. The second permeate stream 542 may be compressed in permeate compressor 560 and recycled to the first membrane stage 540A to improve overall helium recovery. The retentate stream 543 may be expanded in expander 560 to produce power which may be used to deliver at least a portion of the power required to compress the helium PSA tail gas stream 552. Carbon dioxide from the flue gas may be captured and utilized or sequestered.

[0051] Fig. 6 is a schematic view of a tail gas separation process in which methane, nitrogen and / or argon are recovered from the tail gas stream, allowing the recycling of the remaining hydrogen-helium mixture. The retentate stream 611 (which may be equivalent to stream 111 from Fig. 1 or stream 214 from Figs. 2 or 3) may have carbon dioxide and / or water vapor removed in a TSA 620 to prevent freezing at cryogenic temperatures. A treated retentate stream 621 may then be cooled in heat exchanger 630 against returning product streams and liquid nitrogen 623, which would exit the heat exchanger 630 as at least partially vaporized nitrogen 624, if needed. A hydrogen product stream 625 (which may be equivalent to first hydrogen product stream 151 and / or second hydrogen product stream 161 from Fig. 1 , or first hydrogen product stream 262 and / or second hydrogen product stream 272 from Figs. 2 or 3) may also be cooled in heat exchanger 630 and further purified in a cryogenic TSA 640. The cooled retentate stream 631 may be separated in a first distillation column 650 to produce a second hydrogen-helium overhead 651 that may be warmed in heat exchanger 630 and recycled to the hydrogen-helium mixture 151 from Fig. 1 or 251 from Figs. 2 or 3 orthe helium- enriched hydrogen-helium mixture 261 from Figs. 2 or 3. First bottoms stream 652 from the first distillation column 650 then may enter a second distillation column 660 to produce a nitrogen-rich second overhead stream 661 that may be warmed in heat exchanger 630 and used to regenerate the TSA 620. Second bottoms stream 662 from the second distillation column 660 then may enter a third distillation column 670 to produce an argon-rich overhead stream 671 and a methane-rich third bottoms stream 672. The nitrogen-rich second overhead stream 661 , the argon-rich third overhead stream 671 , and the methane-rich third bottoms stream 672 may then be warmed in the heat exchanger 630 and sold, vented, flared, or reinjected as desired.

[0052] Fig. 7 is a schematic view of a cryogenic hydrogen purifier according to one or more aspects of the present disclosure. A first heat exchanger 710 cools a PSA product stream 707, which may be equivalent to the PSA product stream 141 in Fig. 1 or the PSA product stream 251 in Figs. 2 or 3. Cooling duty may be provided by reheating streams from the downstream process and / or liquid nitrogen 708 which may exit as at least partially vaporized nitrogen 709. Impurities may be removed in a CTSA 720 to produce a hydrogen-helium mixture 721 . When regenerating the CTSA 720, spent regeneration gas 722 may be recycled to the one or more membranes in any of Figs. 1-3 . The hydrogen-helium mixture 721 may then be cooled further and partially condensed in a second heat exchanger 730. Cooling duty may be provided by reheating streams from the downstream process and / or liquid hydrogen. Liquid hydrogen may be available from an onsite hydrogen liquefier (not shown). The partially condensed hydrogen-helium mixture 731 may then be separated in a flash drum 740, producing a helium-enriched overhead stream 741 and a hydrogen-enriched bottoms stream742. The helium-enriched overhead stream 741 may then be reheated to ambient temperature in the second heat exchanger 730 and first heat exchanger 710 to provide cooling duty. The warmed helium-enriched overhead stream 743 may have any remaining hydrogen impurity removed for example by reaction with an oxidant 744, such as air, over a deoxo catalyst 750 to produce a crude helium stream 751 . The crude helium stream 751 may enter a helium PSA 760 to produce a pure helium product 761. A helium-depleted tail gas stream 762 may be compressed and recycled to the one or more membranes in any of Figs. 1-3. At least a portion of the warmed helium-enriched overhead stream 743 may be compressed in recycle compressor 745 (if necessary), and combined with the hydrogen-helium mixture 707 to increase the concentration of helium in the stream entering the CTSA 720. The hydrogen- enriched bottoms stream 742 may be reduced in pressure and feed a stripper column 770. The reboiler for the stripper column 770 may be heated by the second heat exchanger 730. Helium may be stripped from the hydrogen-enriched bottoms stream 742 to produce a liquid hydrogen product stream 771 which may be reduced in pressure to provide more cooling duty in the second and first heat exchangers. In cases where the stripper column operates at a lower pressure, the hydrogen-enriched bottoms stream 771 may be pumped and then vaporized at a higher pressure. In at least some embodiments, the hydrogen-enriched bottoms stream 771 may be pumped to a pressure such that after being heated in second heat exchanger 730 and first heat exchanger 710, the resulting hydrogen product stream 772 is at the desired pressure for utilization, transport, or storage. In at least some embodiments, at least a portion of the hydrogen-enriched bottoms stream 771 may be divided, combined with an optional liquid hydrogen stream 773 if additional refrigeration is needed, heated in second heat exchanger 730 and first heat exchanger 710, compressed in hydrogen product compressor 775, and combined with hydrogen product stream 772. A second hydrogenhelium mixture 776 exits the top of the stripper and may be reheated in the second heat exchanger 730 and first heat exchanger 710, compressed in recycle compressor 745 (if necessary), and recycled to the PSA product stream 707. The first heat exchanger 710 and second heat exchanger 730 may be combined in a single multiple-stream heat exchanger.

[0053] Fig. 8 is a schematic view of a modification of Fig. 7 which yields a liquid hydrogen product. The partially condensed hydrogen-helium mixture 731 is passed over an O-P catalyst 840 that catalyzes the reaction of ortho-hydrogen to para-hydrogen to produce a para- hydrogen-enriched hydrogen-helium mixture 836, which in turn may be reduced in pressure and separated in a first medium-pressure flash 840 to produce a first medium-pressure vapor stream 841 and a first medium-pressure liquid stream 842. The first medium-pressure liquid stream 842 may then be reduced in pressure and separated in intermediate-pressure flash 850 to produce an intermediate-pressure vapor stream 851 and an intermediate-pressure liquid stream 852. The intermediate-pressure vapor stream 851 may be heated in secondheat exchanger 730 and first heat exchanger 710, and compressed in recycle compressor 855 to produce a recycle stream 856. The recycle stream 856 may be cooled in first heat exchanger 710 and second heat exchanger 730, reduced in pressure and fed to the first medium-pressure flash 840. At least a portion of the recycle stream 856 may be divided to form refrigeration stream 857. The refrigeration stream 857 may be expanded in expander 865 and heated in second heat exchanger 730 and / or first heat exchanger 710, then returned to recycle compressor 855. Intermediate-pressure liquid stream 852 may then be reduced in pressure and separated in low-pressure flash 860 to produce a low-pressure vapor stream 861 and a low-pressure liquid stream 862. The low-pressure vapor stream 861 may be heated in second heat exchanger 730 and first heat exchanger 710, and compressed in recycle compressor 855 to be recycled. The low-pressure liquid stream 862 may be withdrawn as a liquid hydrogen product. The first medium-pressure vapor stream 841 may be cooled by indirect heat exchange in intermediate-pressure flash 850 and low-pressure flash 860 to produce partially condensed medium-pressure stream 863. The partially condensed mediumpressure stream 863 may then be separated in second medium-pressure flash 870 to produce a second medium-pressure vapor stream 871 and a second medium-pressure liquid stream 872. The second medium-pressure vapor stream 871 is enriched in helium and may be heated in second heat exchanger 730 and first heat exchanger 710 to produce warmed helium-enriched overhead stream 843 which may be purified as in Fig. 7.

[0054] Fig. 9 is a schematic view of a modification of Fig. 8 in which the intermediate flash is eliminated. The first medium-pressure liquid stream 842 may be combined with the second medium-pressure liquid stream 872, reduced in pressure, and fed to low-pressure flash 860. In an alternative embodiment (not shown), the first medium-pressure liquid stream 842 and the second medium-pressure liquid stream 872 may be separately reduced in pressure and fed to low-pressure flash 860.

[0055] Fig. 10 is a schematic view of a modification of Fig. 9 in which the first mediumpressure flash is replaced with a medium-pressure distillation column. The para-hydrogen- enriched hydrogen-helium mixture 836 may be reduced in pressure and separated in mediumpressure distillation column 1040. Second medium-pressure liquid stream 872 may enter the medium-pressure distillation column 1040 at the same location as the para-hydrogen-enriched hydrogen-helium mixture 836, or may be fed at a higher or lower location as needed. The medium-pressure distillation column 1040 may employ trays and / or packing as required to improve the separation of helium and hydrogen. Overhead stream 1041 may be cooled by indirect heat exchange in low-pressure flash 860. Bottoms stream 1042 may be reduced in pressure and fed to low-pressure flash 860. Reboiler stream 1043 may be heated and at least partially boiled in second heat exchanger 730 and returned to the medium-pressure distillation column 1040. The distillation column may also replace the first medium-pressure flash in Fig.8 in which case the bottoms stream would feed the intermediate-pressure flash 850 and the overhead would be cooled by indirect heat exchange in the intermediate-pressure flash 850.

[0056] Fig. 1 1 is a schematic view of a modification of Fig. 8 in which the first mediumpressure flash is eliminated. The para-hydrogen-enriched hydrogen-helium mixture 836 may be cooled by indirect heat exchange in intermediate-pressure flash 850 and low-pressure flash 860 to produce subcooled liquid stream 1163. The recycle stream 856 may be cooled in first heat exchanger 710 and second heat exchanger 730, reduced in pressure and / or combined with the para-hydrogen-enriched hydrogen-helium mixture 836, the partially condensed hydrogen-helium mixture 731 (not shown), or the subcooled medium-pressure liquid stream 1163 (not shown), or separately reduced in pressure and fed to medium-pressure flash 1 170 (not shown). Subcooled liquid stream 1163 may be reduced in pressure and fed to mediumpressure flash 1 170. Medium-pressure liquid stream 1172 may then be reduced in pressure and fed to intermediate-pressure flash 850. In at least some embodiments, medium-pressure flash 1 170 may be replaced with a distillation column. The distillation column may use second heat exchanger 730 to provide reboiler heating duty as shown in Fig. 10.

[0057] Fig. 12 is a schematic view of a process to produce ammonia from a hydrogen feed stream comprising a helium impurity. Pretreatment TSA 1210 may remove CO2 and H2O from hydrogen feed stream 1201 to produce partially cleaned feed stream 121 1. A liquid nitrogen wash 1220 may contact the partially cleaned feed stream 1211 with a liquid nitrogen stream 1231 to remove other impurities such as methane and produce a cleaned feed stream 1221 comprising hydrogen and nitrogen and a spent liquid wash stream 1222. Air separation unit 1230 may supply the liquid nitrogen stream 1231 . The cleaned feed stream 1221 may be combined with a nitrogen stream 1232 from the air separation unit 1230 to produce a mediumpressure ammonia synthesis feed stream 1234 which may be compressed in ammonia synthesis feed compressor 1235 as needed to produce ammonia synthesis feed stream 1237. The spent liquid wash stream 1222 may be vaporized and used to regenerate the pretreatment TSA 1210 and may be vented or flared as needed. Ammonia synthesis feed stream 1237 may then be reacted in the presence of a catalyst in ammonia synthesis reactor 1240 to produce a reaction product stream 1241 enriched in ammonia. The reaction product stream 1241 may then be cooled in heat exchanger 1245 to condense at least a portion of the ammonia. The partially condensed reaction product stream 946 may be separated in ammonia condenser 1250 to produce a first ammonia product 1251 and an ammonia condenser overhead stream 1252 which may be heated in the heat exchanger 1245 to provide at least a portion of the refrigeration needed to cool reaction product stream 1241. The warmed ammonia condenser overhead stream 1253 may be divided into a first recycle stream 1254 that may be returned to the ammonia synthesis reactor 1240 and an ammonia scrubber feed stream 1256 that may be fed to ammonia scrubber 1260. The ammonia scrubber furtherrecovers ammonia from the ammonia scrubber feed stream 1256, for example using a high- pressure water stream followed by a stripper, to produce a second ammonia product 1261 and a first lights stream 1262. First lights stream 1262 may be separated using one or more stages of membranes 1270 to produce a nitrogen-enriched lights stream 1271 and a nitrogen- depleted lights stream 1272. The nitrogen-enriched lights stream 1271 may be vented to purge the system of inert species such as argon that may otherwise accumulate. If a commercially relevant amount of argon is present in nitrogen-enriched lights stream 1271 , it may be further separated to recover argon (not shown). Nitrogen-depleted lights stream 1272 may then be separated to produce a hydrogen-enriched lights stream 1281 and a helium- enriched lights stream 1282 in hydrogen-helium separator 1280. Hydrogen-helium separator 1280 may comprise any combination of membranes, electrochemical processes, and / or cryogenic distillation. Hydrogen-enriched lights stream 1281 may be recycled to the ammonia synthesis feed compressor 1235 and / or to the first recycle stream 1254 after compression as needed. Helium-enriched lights stream 1282 may have any hydrogen impurity removed by reacting with an oxidant 1283, such as air, over a deoxo catalyst 1285 to produce a crude helium stream 1286. Crude helium stream 1286 may be purified in helium PSA 1290 to produce a pure helium product 1291 and helium PSA tail gas stream 1292. PSA tail gas stream 1292 may be recycled to the ammonia synthesis reactor 1240 (not shown).

[0058] Fig. 13 is a schematic view depicting a modification of Fig. 12 in which a hydrogen PSA is used to purify the hydrogen feed stream. In at least some embodiments, particularly when hydrogen feed stream 1201 is low in methane, hydrogen PSA 1320 may separate hydrogen feed stream 1201 to produce cleaned feed stream 1221 and hydrogen tail gas stream 1312. Air separation unit 1230 provides only gaseous nitrogen 1232 to combine with cleaned feed stream 1221 to produce medium-pressure ammonia synthesis feed stream 1234. Downstream, in at least some embodiments crude helium stream 1282 may be of sufficient purity exiting the hydrogen-helium separator 1280 to be utilized without further purification.

[0059] Fig. 14 is a schematic view depicting a modification of Fig. 12 in which a hydrogen feed stream is reacted with a precursor to form a hydrogen carrier. The hydrogen feed stream may comprise a helium impurity. In at least some embodiments, the precursor is toluene and the hydrogen carrier is methylcyclohexane (MCH). Cleaned feed stream 1421 comprising hydrogen may be compressed in hydrogenation reactor feed compressor 1435 and combined with precursor 1430 (which may be pumped if required) to form hydrogenation reactor feed stream 1437. In a hydrogenation reactor 1440 hydrogen reacts with precursor to form a hydrogen carrier, producing a hydrogenation reactor effluent stream 1441 enriched in hydrogen carrier and depleted in precursor and hydrogen. The hydrogenation reactor effluent stream 1441 may be cooled in heat exchanger 1445 to reduce the amount of precursor andhydrogen carrier in the vapor phase of cooled hydrogenation reactor effluent stream 1446. Cooled hydrogenation reactor effluent stream 1446 is then separated in hydrogenation reactor effluent separator 1450 to form hydrogen carrier-enriched liquid 1451 and hydrogen reactor effluent overhead 1452. Hydrogen reactor effluent overhead 1452 may provide cooling to heat exchanger 1445. At least a portion of warmed hydrogen reactor effluent overhead 1453 may be divided to form a first recycle stream 1454 comprising unreacted hydrogen which may be compressed and returned to the hydrogenation reactor 1440. In at least some embodiments the first recycle stream 1454 may be recycled to the hydrogenation reactor feed compressor 1435. At least a portion of warmed hydrogen reactor effluent overhead 1453 may be divided to form a scrubber feed stream 1456. Scrubber feed stream 1456 may have a second hydrogen carrier-enriched liquid 1461 recovered in scrubber 1460, for example by washing with high pressure water followed by a stripper. The remaining gases exit the scrubber 1460 as first lights stream 1472 comprising helium and hydrogen. In at least some embodiments the concentrations of precursor and hydrogen carrier in the warmed hydrogen reactor effluent overhead 1453 are sufficiently low that the scrubber may be eliminated and the scrubber feed stream 1456 may form first lights stream 1472 (not shown). First lights stream 1472 may be separated to produce a hydrogen-enriched lights stream 1281 , a helium product 1291 , and a helium PSA tail gas stream 1292 as in Fig. 12.

[0060] Aspect 1 : A method comprising partially condensing and separating a feed stream comprising helium and hydrogen to produce a first medium-pressure vapor stream and a first medium-pressure liquid stream; reducing the pressure of the first medium-pressure liquid stream or a stream derived from the first medium-pressure liquid stream to produce a low- pressure vapor stream and a low-pressure liquid stream; cooling the first medium-pressure vapor stream by indirect heat exchange against the low-pressure liquid stream to produce a first partially condensed medium-pressure stream; and separating the first partially condensed medium-pressure stream to produce a second medium-pressure vapor stream and a second medium-pressure liquid stream.

[0061] Aspect 2: A method according to Aspect 1 , wherein the low-pressure liquid stream comprises greater than 97% H2 by volume.

[0062] Aspect 3: A method according to Aspects 1 or 2, wherein the partial condensation of the feed stream comprises cooling and reducing the pressure of the feed stream.

[0063] Aspect 4: A method according to any of Aspects 1 to 3, wherein the partial condensation of the feed stream further comprises catalyzing the reaction of ortho-hydrogen to form para-hydrogen in the feed stream.

[0064] Aspect 5: A method according to any of Aspects 1 to 4, further comprising reducing the pressure of the first medium-pressure liquid stream to produce an intermediate-pressure vapor stream and an intermediate-pressure liquid stream; reducing the pressure of theintermediate-pressure liquid stream to produce the low-pressure vapor stream and the low- pressure liquid stream; and cooling the first medium-pressure vapor stream against the intermediate-pressure liquid stream.

[0065] Aspect 6: A method according to Aspect 5, further comprising compressing the intermediate-pressure vapor stream to produce a compressed intermediate-pressure vapor stream; warming the compressed intermediate-pressure vapor stream to produce an intermediate-pressure recycle stream; and combining the intermediate-pressure recycle stream with the feed stream prior to separating to form the first medium-pressure vapor stream and the first medium-pressure liquid stream.

[0066] Aspect 7: A method according to any of Aspects 1 to 6, further comprising contacting the second medium-pressure liquid stream with the first medium-pressure vapor stream.

[0067] Aspect 8: A method according to any of Aspects 1 to 7, further comprising combining the second medium-pressure liquid stream with the first medium-pressure liquid stream.

[0068] Aspect 9: A method according to any of Aspects 1 to 8, further comprising compressing the low-pressure vapor stream to produce a compressed low-pressure vapor stream; warming the compressed low-pressure vapor stream to produce a low-pressure recycle stream; and combining the low-pressure recycle stream with the feed stream prior to separating to form the first medium-pressure vapor stream and the first medium-pressure liquid stream.

[0069] Aspect 10: A method comprising cooling a feed stream comprising helium and hydrogen to produce a subcooled hydrogen-helium mixture; reducing the pressure of and separating the subcooled hydrogen-helium mixture or a stream derived from the subcooled hydrogen-helium mixture to produce a medium-pressure vapor stream and a mediumpressure liquid stream; and reducing the pressure of the medium-pressure liquid stream or a stream derived from the medium-pressure liquid stream to produce a low-pressure vapor stream and a low-pressure liquid stream; wherein at least a portion of the cooling duty to cool the feed stream is derived from cooling by indirect heat exchange with the low-pressure liquid stream.

[0070] Aspect 1 1 : A method according to Aspect 10, wherein the low-pressure liquid stream comprises greater than 97% H2 by volume.

[0071] Aspect 12: A method according to Aspects 10 or 1 1 , further comprising compressing the low-pressure vapor stream to produce a compressed low-pressure vapor stream; warming the compressed low-pressure vapor stream to produce a low-pressure recycle stream; and combining the low-pressure recycle stream with the subcooled hydrogen-helium mixture prior to separating to form the medium-pressure vapor stream and the medium-pressure liquid stream.

[0072] Aspect 13: A method according to any of Aspects 10 to 12, further comprising reducing the pressure of the subcooled medium-pressure liquid stream to produce an intermediate-pressure vapor stream and an intermediate-pressure liquid stream; and reducing the pressure of the intermediate-pressure liquid stream to produce the low-pressure vapor stream and the low-pressure liquid stream; wherein at least a portion of the cooling duty to cool the feed stream is derived from cooling by indirect heat exchange with the intermediate-pressure liquid stream.

[0073] Aspect 14: A method according to Aspect 13, further comprising compressing the intermediate-pressure vapor stream to produce a compressed intermediate-pressure vapor stream; warming the compressed intermediate-pressure vapor stream to produce an intermediate-pressure recycle stream; and combining the intermediate-pressure recycle stream with the subcooled hydrogen-helium mixture prior to separating to form the mediumpressure vapor stream and the medium-pressure liquid stream.

[0074] Aspect 15: A method according to any of Aspects 10 to 14, further comprising catalyzing the reaction of ortho-hydrogen to form para-hydrogen in the feed stream prior to cooling to produce the subcooled medium-pressure stream.

[0075] Aspect 16: A method for producing ammonia from an ammonia synthesis feed stream comprising hydrogen, nitrogen, and helium, the method comprising reacting hydrogen with nitrogen in the ammonia synthesis feed stream to produce a crude ammonia stream; partially condensing and separating the crude ammonia stream to produce a first ammonia product stream and an ammonia condenser overhead stream; separating at least a portion of the ammonia condenser overhead stream to produce a second ammonia product stream and a first lights stream; separating the first lights stream to produce a nitrogen-enriched lights stream and a nitrogen-depleted lights stream; separating the nitrogen-depleted lights stream to produce a hydrogen-enriched lights stream and a helium-enriched lights stream; and combining the hydrogen-enriched lights stream with the ammonia synthesis feed stream.

[0076] Aspect 17: A method according to Aspect 16, further comprising contacting a hydrogen feed stream comprising helium, hydrogen, and one or more impurities with a liquid nitrogen stream to produce a cleaned feed stream depleted in the one or more impurities and a spent liquid nitrogen stream enriched in the one or more impurities; wherein the ammonia synthesis feed stream comprises the cleaned feed stream.

[0077] Aspect 18: A method according to Aspects 16 or 17, wherein the first lights stream is separated by selective permeation of the nitrogen-depleted lights stream across a membrane.

[0078] Aspect 19: A method according to any of Aspects 16 to 18, wherein the separation of the nitrogen-depleted lights stream comprises contacting the nitrogen-depleted lights stream or a stream derived from the nitrogen-depleted lights stream with an adsorbent at a temperature below 30K.

[0079] Aspect 20: A method according to Aspect 19, further comprising regenerating the adsorbent with a regeneration gas to produce a spent regeneration gas; and combining the spent regeneration gas with the ammonia synthesis feed stream.

[0080] Aspect 21 : A method comprising reacting a cleaned feed stream comprising hydrogen and helium with a precursor to produce a hydrogenation reactor effluent stream comprising a hydrogen carrier; separating the hydrogenation reactor effluent stream to produce a liquid stream enriched in the hydrogen carrier and a hydrogenation reactor effluent overhead stream; separating the hydrogenation reactor effluent overhead stream or a stream derived from the hydrogenation reactor effluent overhead stream to produce a hydrogen-enriched lights stream and a helium-enriched lights stream; and combining the hydrogen-enriched lights stream with the hydrogenation reactor feed stream.

[0081] Aspect 22: A method according to Aspect 21 , further comprising contacting a hydrogen feed stream comprising helium, hydrogen, and one or more impurities with a liquid nitrogen stream to produce the cleaned feed stream depleted in the one or more impurities and a spent liquid nitrogen stream enriched in the one or more impurities; wherein the hydrogenation reactor effluent overhead stream is separated to produce a nitrogen-enriched lights stream and a nitrogen-depleted lights stream prior to the nitrogen-depleted lights stream being separated to produce the hydrogen-enriched lights stream and the helium-enriched lights stream.

[0082] Aspect 23: A method according to Aspect 22, wherein the hydrogenation reactor effluent overhead stream is separated by selective permeation of the nitrogen-depleted lights stream across a membrane.

[0083] Aspect 24: A method according to Aspects 22 or 23, wherein the separation of the nitrogen-depleted lights stream comprises contacting the nitrogen-depleted lights stream or a stream derived from the nitrogen-depleted lights stream with an adsorbent at a temperature below 30K.

[0084] Aspect 25: A method according to Aspect 24, further comprising regenerating the adsorbent to produce a spent regeneration gas; and combining the spent regeneration gas with the cleaned feed stream.Example 1

[0085] A computer simulation of the process of Figure 7 was carried out using Aspen Plus® process simulation software, available from Aspen Technology Inc. A summary of selected stream data can be found in Table 1. PSA product stream 707 comprising about 99% H2 and 1% He by volume is cooled, partially condensed, and separated to produce a helium-enriched overhead stream 741 comprising over 63% He by volume. The hydrogen in the helium- enriched overhead stream 741 is consumed by reaction with air and the resulting water,nitrogen, and unreacted oxygen are removed by adsorption. The hydrogen-enriched liquid stream 742 is purified in stripper column 770 to greater than 99.99% H2 purity by volume.Table 1Example 2

[0086] A computer simulation of the process of Figure 8 was carried out using Aspen Plus® process simulation software, available from Aspen Technology Inc. A summary of selected stream data can be found in Table 2. In contrast with the process of Fig. 7, a higher purity of helium is obtained in the second medium-pressure flash 870 due to the colder temperature achieved by further cooling against intermediate-pressure and low-pressure liquid streams. The increased refrigeration in the process also allows for a liquid hydrogen product to be removed, again at a greater than 99.99% purity by volume.Table 2Example 3

[0087] A computer simulation of the process of Figure 9 was carried out using Aspen Plus® process simulation software, available from Aspen Technology Inc. A summary of selected stream data can be found in Table 3. Hydrogen feed stream 901 comprises CO2 and H2O impurities that must be removed by TSA, methane impurities that must be partially removed by liquid nitrogen wash, as well as a potentially valuable helium byproduct at 0.9% by volume. This is a higher concentration of helium than would be found in a typical hydrogen stream produced by steam methane reforming of natural gas, which would typically comprise less than about 100 ppmv helium. The ammonia synthesis feed stream 937 comprises a stoichiometric mixture of hydrogen and nitrogen as well as sub-1% by volume concentrations of methane, argon, and helium. Note that the helium content in the first lights stream 962 has been concentrated up to over 7% by volume. Argon and methane have also been concentrated in the first lights stream 962 and are partially removed in the one or more membranes 970. Partial condensation yields a helium-enriched lights stream with 65% helium by volume and a hydrogen-enriched lights stream with 99.5% hydrogen by volume. Incorporating the helium recovery downstream of the ammonia synthesis reactor takes advantage of the concentration of helium in the first lights stream to reduce the size of the helium recovery equipment that would ordinarily be placed on a natural gas stream upstream of a typical ammonia synthesis reactor.Table 3

[0088] While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.

Claims

CLAIMS1. A method comprising: partially condensing and separating a feed stream comprising helium and hydrogen to produce a first medium-pressure vapor stream and a first medium-pressure liquid stream; reducing the pressure of the first medium-pressure liquid stream or a stream derived from the first medium-pressure liquid stream to produce a low-pressure vapor stream and a low-pressure liquid stream; cooling the first medium-pressure vapor stream by indirect heat exchange against the low-pressure liquid stream to produce a first partially condensed medium-pressure stream; and separating the first partially condensed medium-pressure stream to produce a second medium-pressure vapor stream and a second medium-pressure liquid stream.

2. The method of claim 1 , wherein the low-pressure liquid stream comprises greater than 97% H2 by volume.

3. The method of claim 1 , wherein the partial condensation of the feed stream comprises cooling and reducing the pressure of the feed stream.

4. The method of claim 1 , wherein the partial condensation of the feed stream further comprises catalyzing the reaction of ortho-hydrogen to form para-hydrogen in the feed stream.

5. The method of claim 1 , further comprising reducing the pressure of the first mediumpressure liquid stream to produce an intermediate-pressure vapor stream and an intermediate-pressure liquid stream; reducing the pressure of the intermediate-pressure liquid stream to produce the low- pressure vapor stream and the low-pressure liquid stream; and cooling the first medium-pressure vapor stream against the intermediate-pressure liquid stream.

6. The method of claim 5, further comprising compressing the intermediate-pressure vapor stream to produce a compressed intermediate-pressure vapor stream; warming the compressed intermediate-pressure vapor stream to produce an intermediate-pressure recycle stream; andcombining the intermediate-pressure recycle stream with the feed stream prior to separating to form the first medium-pressure vapor stream and the first mediumpressure liquid stream.

7. The method of claim 1 , further comprising contacting the second medium-pressure liquid stream with the first medium-pressure vapor stream.

8. The method of claim 1 , further comprising combining the second medium-pressure liquid stream with the first medium-pressure liquid stream.

9. The method of claim 1 , further comprising compressing the low-pressure vapor stream to produce a compressed low-pressure vapor stream; warming the compressed low-pressure vapor stream to produce a low-pressure recycle stream; and combining the low-pressure recycle stream with the feed stream prior to separating to form the first medium-pressure vapor stream and the first medium-pressure liquid stream.

10. A method comprising: cooling a feed stream comprising helium and hydrogen to produce a subcooled hydrogen-helium mixture; reducing the pressure of and separating the subcooled hydrogen-helium mixture or a stream derived from the subcooled hydrogen-helium mixture to produce a mediumpressure vapor stream and a medium-pressure liquid stream; and reducing the pressure of the medium-pressure liquid stream or a stream derived from the medium-pressure liquid stream to produce a low-pressure vapor stream and a low- pressure liquid stream; wherein at least a portion of the cooling duty to cool the feed stream is derived from cooling by indirect heat exchange with the low-pressure liquid stream.1 1. The method of claim 10, wherein the low-pressure liquid stream comprises greater than 97% H2 by volume.

12. The method of claim 10, further comprising compressing the low-pressure vapor stream to produce a compressed low-pressure vapor stream; warming the compressed low-pressure vapor stream to produce a low-pressure recycle stream; andcombining the low-pressure recycle stream with the subcooled hydrogen-helium mixture prior to separating to form the medium-pressure vapor stream and the medium-pressure liquid stream.

13. The method of claim 10, further comprising reducing the pressure of the subcooled medium-pressure liquid stream to produce an intermediate-pressure vapor stream and an intermediate-pressure liquid stream; and reducing the pressure of the intermediate-pressure liquid stream to produce the low- pressure vapor stream and the low-pressure liquid stream; wherein at least a portion of the cooling duty to cool the feed stream is derived from cooling by indirect heat exchange with the intermediate-pressure liquid stream.

14. The method of claim 13, further comprising compressing the intermediate-pressure vapor stream to produce a compressed intermediate-pressure vapor stream; warming the compressed intermediate-pressure vapor stream to produce an intermediate-pressure recycle stream; and combining the intermediate-pressure recycle stream with the subcooled hydrogenhelium mixture prior to separating to form the medium-pressure vapor stream and the medium-pressure liquid stream.

15. The method of claim 10, further comprising catalyzing the reaction of ortho-hydrogen to form para-hydrogen in the feed stream prior to cooling to produce the subcooled medium-pressure stream.

16. A method for producing ammonia from an ammonia synthesis feed stream comprising hydrogen, nitrogen, and helium, the method comprising: reacting hydrogen with nitrogen in the ammonia synthesis feed stream to produce a crude ammonia stream; partially condensing and separating the crude ammonia stream to produce a first ammonia product stream and an ammonia condenser overhead stream; separating at least a portion of the ammonia condenser overhead stream to produce a second ammonia product stream and a first lights stream; separating the first lights stream to produce a nitrogen-enriched lights stream and a nitrogen-depleted lights stream;separating the nitrogen-depleted lights stream to produce a hydrogen-enriched lights stream and a helium-enriched lights stream; and combining the hydrogen-enriched lights stream with the ammonia synthesis feed stream.

17. The method of claim 16, further comprising contacting a hydrogen feed stream comprising helium, hydrogen, and one or more impurities with a liquid nitrogen stream to produce a cleaned feed stream depleted in the one or more impurities and a spent liquid nitrogen stream enriched in the one or more impurities; wherein the ammonia synthesis feed stream comprises the cleaned feed stream.

18. The method of claim 16, wherein the first lights stream is separated by selective permeation of the nitrogen-depleted lights stream across a membrane.

19. The method of claim 16, wherein the separation of the nitrogen-depleted lights stream comprises contacting the nitrogen-depleted lights stream or a stream derived from the nitrogen-depleted lights stream with an adsorbent at a temperature below 30K.

20. The method of claim 19, further comprising regenerating the adsorbent with a regeneration gas to produce a spent regeneration gas; and combining the spent regeneration gas with the ammonia synthesis feed stream.21 . A method comprising: reacting a cleaned feed stream comprising hydrogen and helium with a precursor to produce a hydrogenation reactor effluent stream comprising a hydrogen carrier; separating the hydrogenation reactor effluent stream to produce a liquid stream enriched in the hydrogen carrier and a hydrogenation reactor effluent overhead stream; separating the hydrogenation reactor effluent overhead stream or a stream derived from the hydrogenation reactor effluent overhead stream to produce a hydrogen- enriched lights stream and a helium-enriched lights stream; and combining the hydrogen-enriched lights stream with the hydrogenation reactor feed stream.

22. The method of claim 21 , further comprising contacting a hydrogen feed stream comprising helium, hydrogen, and one or more impurities with a liquid nitrogen streamto produce the cleaned feed stream depleted in the one or more impurities and a spent liquid nitrogen stream enriched in the one or more impurities; wherein the hydrogenation reactor effluent overhead stream is separated to produce a nitrogen-enriched lights stream and a nitrogen-depleted lights stream prior to the nitrogen-depleted lights stream being separated to produce the hydrogen-enriched lights stream and the helium-enriched lights stream.

23. The method of claim 22, wherein the hydrogenation reactor effluent overhead stream is separated by selective permeation of the nitrogen-depleted lights stream across a membrane.

24. The method of claim 22, wherein the separation of the nitrogen-depleted lights stream comprises contacting the nitrogen-depleted lights stream or a stream derived from the nitrogen-depleted lights stream with an adsorbent at a temperature below 30K.

25. The method of claim 24, further comprising regenerating the adsorbent to produce a spent regeneration gas; and combining the spent regeneration gas with the cleaned feed stream.

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