Process for removing a target gas from a mixture of gases by thermal swing adsorption

• US 20080314245A1
• Filed: 05/16/2008
• Published: 12/25/2008
• Est. Priority Date: 05/18/2007
• Status: Active Grant

• Current Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Original Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Inventors: Hershkowitz, Frank, Deckman, Harry W., Kelley, Bruce T., Northrop, Paul S.
• Granted Patent: US 7,938,886 B2
• Time in Patent Office: Days
• US Class Current: 95/115
• CPC Class Codes: B01D 2253/108 Zeolites
• CPC Class Codes: B01D 2253/308 Pore size
• CPC Class Codes: B01D 2253/311 Porosity, e.g. pore volume
• CPC Class Codes: B01D 2253/342 Monoliths
• CPC Class Codes: B01D 2256/10 Nitrogen
• CPC Class Codes: B01D 2257/102 Nitrogen
• CPC Class Codes: B01D 2257/304 Hydrogen sulfide
• CPC Class Codes: B01D 2257/504 Carbon dioxide
• CPC Class Codes: B01D 53/02 by adsorption, e.g. preparative gas chromatography solid sorbent compositions B01J20/00, preparation of inorganic compounds or elements C01
• CPC Class Codes: B01D 53/0423 Beds in columns
• CPC Class Codes: B01D 53/0462 Temperature swing adsorption
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• CPC Class Codes: C10L 3/102 of acid contaminants
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

The separation of a target gas from a mixture of gases using a thermal swing adsorption process wherein a thermal wave is used, primarily in the desorption step. The process of this invention enables one to separately remove multiple contaminants from a treated gaseous stream.

Claims

1. A process for selectively removing a first target gas component from a gas mixture containing said first target gas component and a product gas component, said process comprising:

a) providing a temperature swing adsorption gas separation unit containing at least one adsorbent contactor at an initial temperature, wherein the adsorbent contactor is comprised of a plurality of substantially parallel open flow channels, and wherein the channel surface of at least a portion of said flow channels is comprised of an adsorbent material that has a selectivity for said first target gas component over said product gas component of greater than 1;

b) passing said gas mixture through at least a fraction of said flow channels thereby resulting in the adsorption of at least a portion of said first target gas component from the gas mixture onto said adsorbent material, thereby producing a first product gas stream, that has a lower mol % of the first target gas component than said gas mixture;

c) collecting said product gas stream;

d) heating said at least one adsorbent contactor having said first target gas component adsorbed thereon with a heat transfer fluid to an effective temperature that will result in the desorption of at least a fraction of said first target gas component from said adsorbent material, thereby resulting in a first waste gas stream that has a higher mol % concentration of the first target gas component than said gas mixture;

e) collecting said first waste gas stream; and

f) cooling said least one adsorbent contactor to the initial temperature;

wherein a thermal wave is generated in the adsorbent contactor in the desorption step d) thereby creating a thermal wave temperature gradient, which thermal wave temperature gradient moves along the length of the at least one adsorbent contactor and which adsorbent contactor has a Δ

T_HT ranging from about 0 to about 50°

C. wherein Δ

T_HT=H/h wherein Δ

T_HT is the heat transfer delta-temperature, h is equal to the heat transfer coefficient, and H is the heat rate requirement.

2. The process of claim 1 wherein desorption is performed by passing the heat transfer fluid, at an effective desorption temperature, through the same flow channels as said gas mixture, thereby desorbing at least a portion the first target gas component into said heat transfer fluid.

3. The process of claim 2 wherein the heat transfer fluid is comprised of steam.

4. The process of claim 1 wherein the gas mixture is comprised of a flue gas and the first target gas component is CO₂.

5. The process of claim 2 wherein the gas mixture is comprised of a flue gas, the first target gas component is CO₂, and at least a portion of the CO₂ is separated from the heat transfer fluid after desorption.

6. The process of claim 1 wherein a thermal wave temperature gradient, which thermal wave temperature gradient moves along the length of the at least one adsorbent contactor, is produced during the cooling step f).

7. The process of claim 1 wherein the adsorbent contactor has less than about 20% of its open pore volume in pores greater than about 20 angstroms.

8. The process of claim 1 wherein the adsorbent material is comprised of an 8-ring zeolite.

9. The process of claim 1 wherein the gas mixture also comprises a second target gas component, wherein following step e) and prior to step f) the process comprises the steps of:

e1) heating said at least one adsorbent contactor having said first target gas component and a said second target gas component adsorbed thereon with a heat transfer fluid to an effective temperature that will result in the desorption of at least a fraction of said second target gas component from said adsorbent material, thereby resulting in a second waste gas stream that has a higher mol % concentration of the said second target gas component than said gas mixture; and

e2) collecting said second waste gas stream.

10. The process of claim 9 wherein said first waste gas stream has a higher mol % of said first target gas component than said second waste gas stream.

11. The process of claim 9 wherein said second waste gas stream has a higher mol % of said second target gas component than said first waste gas stream.

12. The process of claim 1 wherein the plurality of substantially parallel open flow channels are divided into a first fraction of flow channels and a second fraction of flow channels, wherein said first fraction and second fraction are in thermal communication with each other but not in fluid communication;

and said gas mixture in step b) is passed through said first fraction of the plurality of substantially parallel open flow channels having channel surfaces comprised of said adsorbent material; and

said heat transfer fluid in step d) is passed through the second fraction of the plurality of substantially parallel open flow channels.

13. The process of claim 12 wherein the gas mixture is comprised of a flue gas and the first target gas component is CO₂.

14. The process of claim 13 wherein the flue gas is comprised of N₂ and said adsorbent material has a selectivity for CO₂ over N₂ of greater than 5.

15. The process of claim 12 wherein the adsorbent contactor has less than about 20% of its open pore volume in pores greater than about 20 angstroms.

16. The process of claim 12 wherein the adsorbent is comprised of an 8-ring zeolite.

17. The process of claim 16 wherein the zeolite is selected from DDR, Sigma-1 and ZSM-58.

18. The process of claim 1 wherein the adsorbent contactor is further comprised of second set of flow channels that are not substantially parallel to said substantially parallel open flow channels, wherein said gas mixture flows through said substantially parallel open flow channels and said heat transfer fluid flows through said second set of flow channels.

19. The process of claim 18 wherein the flow direction of said gas mixture in said substantially parallel open flow channels is at a substantially 90°

angle to the flow direction of said heat transfer fluid in said second set of flow channels.

20. The process of claim 1 wherein said adsorbent material is located on the inner surface of said substantially parallel open flow channels.

21. The process of claim 1 wherein said adsorbent material is located on the outer surface of said substantially parallel open flow channels.

22. The process of claim 1 wherein the adsorbent contactor is comprised of a first adsorbent material and a second adsorbent material, wherein said first adsorbent material has a selectivity of greater than 5 for said first target gas component over said product gas component and said second adsorbent material has a selectivity of greater than 5 for a second target gas component over said product gas component.

23. The process of claim 9 wherein the adsorbent contactor is comprised of a first adsorbent material and a second adsorbent material, wherein said first adsorbent material has a selectivity of greater than 5 for said first target gas component over said product gas component and said second adsorbent material has a selectivity of greater than 5 for said second target gas component over said product gas component.

24. The process of claim 1 wherein the gas mixture is comprised of a flue gas and the first target gas component is selected from the group consisting of water, CO₂, SO_x, and NO_x.

25. The process of claim 24 wherein the product gas component is N₂.

26. The process of claim 25 wherein the adsorbent material has a selectivity of greater than 5 for said first target gas component over said product gas component.

27. The process of claim 1 wherein the thermal wave during desorption moves through the adsorbent contactor counter-current to the direction that the gas mixture flowed through the adsorbent contactor.

28. The process of claim 1 wherein the thermal wave during desorption moves through the adsorbent contactor co-current to the direction that the gas mixture flowed through the adsorbent contactor.

29. The process of claim 1 wherein adsorbent contactor has a Δ

T_HT ranging from about 0 to about 10°

C.

30. The process of claim 4 wherein the first waste gas stream has a CO₂ concentration of at least 80 mol %

31. The process of claim 1 wherein the gas mixture is comprised of a natural gas, the first target component is CO₂, and the product gas component is CH4;

wherein the product gas stream contains at least 80 mol % of the CH₄ present in the gas mixture.

32. The process of claim 1 wherein in the adsorbent contactor there is a local t_delay/t_rise ratio of greater than 2.

33. The process of claim 1 wherein at least a portion of step b) and at least a portion of step f) occur simultaneously in said adsorbent contactor,

34. The process of claim 1 further comprising wherein:

said temperature swing adsorption unit contains at least a first adsorbent contactor and a second adsorbent contactor wherein the gas mixture flows through a first set of substantially parallel channels located in said first adsorbent contactor from a process gas inlet of said first adsorbent contactor to a process gas outlet of said first adsorbent contactor from which a first adsorbent contactor product outlet stream is retrieved; and

at least a portion of first adsorbent contactor product outlet stream flows through a second set of substantially parallel channels located in said second adsorbent contactor from a process gas inlet of said second adsorbent contactor to a process gas outlet of said second adsorbent contactor from which a second adsorbent contactor product outlet stream is retrieved; and

wherein

a heat transfer fluid flows through a third set of flow channels located in said first adsorbent contactor which said third set of flow channels are in thermal communication with, but not in fluid communication with, said first set of substantially parallel channels, from a heat transfer fluid inlet of said first adsorbent contactor to a heat transfer fluid outlet of said first adsorbent contactor wherein a first adsorbent contactor heat transfer fluid outlet stream is retrieved; and

at least a portion of said first adsorbent contactor heat transfer fluid outlet stream flows through a fourth set of channels located in said second adsorbent contactor which said fourth set of flow channels are in thermal communication with, but not in fluid communication with, said second set of substantially parallel channels, from a heat transfer fluid inlet of said second adsorbent contactor to a heat transfer fluid outlet of said second adsorbent contactor wherein a second adsorbent contactor heat transfer fluid outlet stream is retrieved; and

wherein

the flow of the first adsorbent contactor product outlet stream from the first adsorbent contactor to the second adsorbent contactor is substantially in co-current flow with the flow of the first adsorbent contactor heat transfer fluid outlet stream from the first adsorbent contactor to the second adsorbent contactor.

35. The process of claim 1 further comprising wherein:

said temperature swing adsorption unit contains at least a first adsorbent contactor and a second adsorbent contactor wherein the gas mixture flows through a first set of substantially parallel channels located in said first adsorbent contactor from a process gas inlet of said first adsorbent contactor to a process gas outlet of said first adsorbent contactor from which a first adsorbent contactor product outlet stream is retrieved; and

at least a portion of first adsorbent contactor product outlet stream flows through a second set of substantially parallel channels located in said second adsorbent contactor from a process gas inlet of said second adsorbent contactor to a process gas outlet of said second adsorbent contactor from which a second adsorbent contactor product outlet stream is retrieved; and

wherein

a heat transfer fluid flows through a third set of flow channels located in said second adsorbent contactor which third set of flow channels are in thermal communication with, but not in fluid communication with, said second set of substantially parallel channels, from a heat transfer fluid inlet of said second adsorbent contactor to a heat transfer fluid outlet of said second adsorbent contactor wherein a second adsorbent contactor heat transfer fluid outlet stream is retrieved; and

at least a portion of said second adsorbent contactor heat transfer fluid outlet stream flows through a fourth set of channels located in said first adsorbent contactor which fourth set of flow channels are in thermal communication with, but not in fluid communication with, said first set of substantially parallel channels from a heat transfer fluid inlet of said first adsorbent contactor to a heat transfer fluid outlet of said first adsorbent contactor wherein a first adsorbent contactor heat transfer fluid outlet stream is retrieved; and

wherein

the flow of the first adsorbent contactor product outlet stream from the first adsorbent contactor to the second adsorbent contactor is substantially in counter-current flow with the flow of the second adsorbent contactor heat transfer fluid outlet stream from the second adsorbent contactor to the first adsorbent contactor.