Process for making ammonia

Patent metadata

Field	Value
Publication number	US-10287173-B2
Application number	US-201715432236-A
Country	US
Kind code	B2
Filing date	Feb 14, 2017
Priority date	Nov 7, 2013
Publication date	May 14, 2019
Grant date	May 14, 2019

Abstract

An ammonia-producing system comprises a reactor that catalytically converts nitrogen and hydrogen feed gases to ammonia to form a reaction mixture of the ammonia, unreacted nitrogen gas, and unreacted hydrogen gas. A feed system feeds the nitrogen and hydrogen gases to the reactor at a reaction pressure of from about 9 to about 100 atmospheres. A reactor control system controls the temperature during conversion of the nitrogen and hydrogen to ammonia by maintaining a reaction temperature of from about 330° C. to about 550° C. An absorbent selectively absorbs at least a portion of the ammonia from the reaction mixture, and an absorbent control system controls one or both of a temperature and pressure at the absorbent during selective absorption of the ammonia from the reaction mixture. A recycle line downstream of the absorbent recycles the unreacted nitrogen and unreacted hydrogen to the reactor.

First claim

What is claimed is:

1. A system for producing ammonia, the system comprising: a reactor configured to receive a nitrogen feed gas (N 2 ) and a hydrogen feed gas (H 2 ), the reactor comprising a catalyst that converts at least a portion of the nitrogen gas and at least a portion of the hydrogen feed gas to ammonia (NH 3 ) to form a reaction mixture comprising the ammonia, unreacted nitrogen feed gas, and unreacted hydrogen feed gas; a feed system to feed the nitrogen feed gas and the hydrogen feed gas to the reactor at a reaction pressure of from about 9 atmospheres to about 100 atmospheres; a reactor control system to control the temperature of the reactor during conversion of the nitrogen feed gas and the hydrogen feed gas to the ammonia, wherein the reactor control system is configured to maintain a reaction temperature of the reaction mixture at from about 330° C. to about 500° C.; an absorbent that selectively absorbs at least a portion of the ammonia from the reaction mixture, wherein the absorbent comprises a porous support structure; an absorbent control system to control one or both of a temperature and a pressure at the absorbent during selective absorption of the ammonia from the reaction mixture; and a recycle line downstream of the absorbent to recycle the unreacted nitrogen feed gas and the unreacted hydrogen feed gas to the reactor.

2. The system of claim 1 , further comprising: a product line downstream of the absorbent and separate from the recycle line; and one or more flow control devices to direct gas flow to either the recycle line or the product line; wherein the absorbent control system is configured to cycle between an absorption phase and a desorption phase, wherein the absorbent control system maintains one or both of a first temperature and a first pressure at the absorbent that is conducive to absorption of ammonia into the absorbent during the absorption phase and maintains one or both of a second temperature and a second pressure at the absorbent that is conducive to desorption of ammonia form the absorbent during the desorption phase, and wherein the one or more flow control devices direct the gas flow of unreacted nitrogen feed gas and unreacted hydrogen feed gas to the recycle line during the absorption phase and direct the gas flow of desorbed ammonia to the product line during the desorption phase.

3. The system of claim 2 , wherein the absorbent control system maintains the absorbent at the first temperature to provide for absorption of ammonia into the absorbent during the absorption phase and increases a temperature at the absorbent to the second temperature to provide for desorption of ammonia from the absorbent during the desorption phase.

4. The system of claim 3 , wherein the first temperature is about 100° C. or lower, and the second temperature is from about 175° C. to about 350° C.

5. The system of claim 2 , further comprising: a first set of one or more first absorbers each comprising some of the absorbent; and a second set of one or more second absorbers each comprising some of the absorbent; wherein the absorbent control system cycles between: a first operating state wherein the absorbent control system operates the first set of one or more first absorbers in the absorption phase and the second set of one or more second absorbers in the desorption phase, and a second operating state wherein, the absorbent control system operates the second set of one or more second absorbers in the absorption phase and the first set of one or more first absorbers in the desorption phase.

6. The system of claim 1 , wherein the absorbent comprises one or more of magnesium chloride (MgCl 2 ), calcium chloride (CaCl 2 )), strontium chloride (SrCl 2 ), zinc chloride (ZnCl 2 ), or zinc nitrate (Zn(NO 3 ) 2 ).

7. The system of claim 1 , wherein the absorbent comprises primarily calcium chloride (CaCl 2 )).

8. The system of claim 1 , wherein overall conversion of the nitrogen feed gas and the hydrogen feed gas to ammonia for the system is at least about 40%.

9. The system of claim 1 , wherein overall conversion of the nitrogen feed gas and the hydrogen feed gas to ammonia for the system is at least about 90%.

10. A method for producing ammonia, the method comprising:
reacting at least a portion of a nitrogen feed gas (N 2 ) and at least a portion of a hydrogen feed gas (H 2 ) in the presence of a catalyst in a reactor while maintaining a reaction pressure of from about 9 atmospheres to about 100 atmospheres and a reaction temperature of from about 330° C. to about 500° C. to form ammonia (NH 3 ), wherein unreacted nitrogen gas (N 2 ), unreacted hydrogen gas (H 2 ), and the ammonia (NH 3 ) form a reaction mixture; cycling between an absorption phase and a desorption phase, wherein the absorption phase comprises: flowing at least a portion of the reaction mixture to an absorbent comprising a porous support structure while maintaining one or both of an absorption pressure and an absorption temperature at the absorbent to selectively absorb at least a portion of the ammonia from the reaction mixture into the absorbent; and following the selective absorbing, recycling unreacted nitrogen gas and unreacted hydrogen to the reactor; and wherein the desorption phase comprises: changing one or both of the pressure at the absorbent to a desorption pressure or the temperature at the absorbent to a desorption temperature so that at least a portion of ammonia absorbed in the absorbent is desorbed from the absorbent; and withdrawing at least a portion of the ammonia desorbed from the absorbent as an ammonia product stream.

11. The method of claim 10 , wherein the absorption temperature is maintained at about 100° C. or lower during the absorption phase.

12. The method of claim 11 , wherein the desorption temperature is maintained at about 175° C. or more during the desorption phase.

13. The method of claim 11 , wherein the desorption temperature is maintained about 200° C. are more during the desorption phase.

14. The method of claim 10 , wherein the desorption temperature is maintained at about 250° C. or more during the desorption phase.

15. The method of claim 10 , wherein the absorbent comprises primarily calcium chloride (CaCl 2 )).

16. The method of claim 10 , wherein overall conversion of the nitrogen feed gas and the hydrogen feed gas to ammonia in the ammonia product stream is at least about 40%.

17. The method of claim 10 , wherein overall conversion of the nitrogen feed gas and the hydrogen feed gas to ammonia in the ammonia product stream is at least about 90%.

18. The method of claim 10 , wherein the absorbent is at least partially contained in a first set of one or more first absorbers each comprising some of the absorbent and in a second set of one or more second absorbers each comprising some of the absorbent; and wherein the cycling between the absorption phase and the desorption phase comprises cycling between a first operation state and a second operation state, wherein the first operation state includes: feeding the reaction mixture to the one or more first absorbers of the first set, controlling the temperature at the absorbent in the one or more first absorbers to be at the absorption temperature or controlling the pressure in the one or more first absorbers to be at the absorption pressure, or both, controlling the temperature at the absorbent in the one or more second absorbers to be at the desorption temperature or controlling the pressure in the one or more second absorbers to be at the desorption pressure, or both, so that at least a portion of ammon

Assignees

• Univ Minnesota

Inventors

• Malmali Mohammadmahdi
• Mccormick Alon V
• Cussler Edward L

Classifications

• B01J8/0005

  Catalytic processes under superatmospheric pressure (non-catalytic processes B01J3/00) · CPC title

• Y02P20/52

  using catalysts, e.g. selective catalysts · CPC title

• B01D53/047

  Pressure swing adsorption · CPC title

• C01C1/006

  making use of solid ammonia storage materials, e.g. complex ammine salts · CPC title

• B01D2259/402

  using two beds · CPC title