Process for hydrogen recovery from ammonia purge gases
First Claim
1. In a process for synthesizing ammonia from hydrogen and nitrogen comprising introducing a synthesis feed gas comprising nitrogen, hydrogen and at least one of methane and argon as an inert contaminant at substantially a superatmospheric synthesis pressure into an ammonia synthesis loop, reacting hydrogen and nitrogen in the ammonia synthesis loop at a superatmospheric synthesis pressure to produce ammonia in an ammonia synthesis reaction zone, removing ammonia from the ammonia synthesis loop, and removing a purge stream from the ammonia synthesis loop in an amount sufficient to maintain the concentration of inert contaminants less than about 25 percent wherein the purge stream is passed to a permeator comprising a separation membrane having a feed side and a permeate exit side and exhibiting selectivity to the permeability of hydrogen as compared to the permeability of each of methane and argon, a permeating gas is recovered at the permeate exit side of the separation membrane and is recycled to the ammonia synthesis reaction zone, the improvement wherein the permeator comprises at least two permeator stages in series, each permeator stage having a feed side and a permeate exit side in which the permeate exit side is at a lower total pressure than the total pressure on the feed side, wherein between permeator stages, the non-permeating gas from the feed side of one permeator stage is passed to the feed side of the next permeator stage;
- wherein at least one permeator stage has a lower ratio of total pressure on the feed side to total pressure on the permeate exit side than the ratio of total pressure on the feed side to total pressure on the permeate exit side of at least one subsequent permeator stage; and
wherein the permeating gas from at least one permeator stage is recycled to the ammonia synthesis reaction zone.
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Abstract
Ammonia synthesis processes are disclosed which provide enhanced recovery of hydrogen from ammonia synthesis purge streams by selective permeation. The enhanced recovery of hydrogen can provide increased conversion of hydrogen values to ammonia. In the processes, a purge stream from an ammonia synthesis loop at a superatmospheric pressure is passed to at least two permeator stages in series. Each permeator stage contains a separation membrane which exhibits selective permeation of hydrogen as compared to the permeation of each of methane and argon. A total pressure differential is maintained across the thickness of the separation membrane to provide a driving force for the permeation of hydrogen across the separation membrane of each of the permeator stages. Hydrogen permeates through the membrane, and a hydrogen-rich permeating gas is obtained on a permeate exit side of each of the permeator stages. The permeating gas from each of the permeator stages is recycled to the ammonia synthesis reaction zone. Between permeator stages, the non-permeating gas from one permeator stage is passed to the feed side of the next permeator stage.
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Citations
17 Claims
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1. In a process for synthesizing ammonia from hydrogen and nitrogen comprising introducing a synthesis feed gas comprising nitrogen, hydrogen and at least one of methane and argon as an inert contaminant at substantially a superatmospheric synthesis pressure into an ammonia synthesis loop, reacting hydrogen and nitrogen in the ammonia synthesis loop at a superatmospheric synthesis pressure to produce ammonia in an ammonia synthesis reaction zone, removing ammonia from the ammonia synthesis loop, and removing a purge stream from the ammonia synthesis loop in an amount sufficient to maintain the concentration of inert contaminants less than about 25 percent wherein the purge stream is passed to a permeator comprising a separation membrane having a feed side and a permeate exit side and exhibiting selectivity to the permeability of hydrogen as compared to the permeability of each of methane and argon, a permeating gas is recovered at the permeate exit side of the separation membrane and is recycled to the ammonia synthesis reaction zone, the improvement wherein the permeator comprises at least two permeator stages in series, each permeator stage having a feed side and a permeate exit side in which the permeate exit side is at a lower total pressure than the total pressure on the feed side, wherein between permeator stages, the non-permeating gas from the feed side of one permeator stage is passed to the feed side of the next permeator stage;
- wherein at least one permeator stage has a lower ratio of total pressure on the feed side to total pressure on the permeate exit side than the ratio of total pressure on the feed side to total pressure on the permeate exit side of at least one subsequent permeator stage; and
wherein the permeating gas from at least one permeator stage is recycled to the ammonia synthesis reaction zone. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
- wherein at least one permeator stage has a lower ratio of total pressure on the feed side to total pressure on the permeate exit side than the ratio of total pressure on the feed side to total pressure on the permeate exit side of at least one subsequent permeator stage; and
Specification
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- Resources
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Current AssigneePermea Incorporated (Linde Plc)
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Original AssigneeMonsanto Company (Bayer AG)
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InventorsMacLean, Donald L., Graham, Tommy E.
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Primary Examiner(s)Vertiz, O. R.
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Assistant Examiner(s)Roy, Thomas W.
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Application NumberUS05/888,103Time in Patent Office645 DaysField of Search423/359, 423/360, 423/361, 423/362, 423/363, 55/16, 55/158US Class Current423/359CPC Class CodesB01D 53/226 in serial connexionC01C 1/0476 Purge gas treatment, e.g. f...Y02P 20/129 Energy recovery, e.g. by co...Y02P 20/52 using catalysts, e.g. selec...
