Method for recovery of CO2 from gas streams

• US 7,056,482 B2
• Filed: 06/12/2003
• Issued: 06/06/2006
• Est. Priority Date: 06/12/2003
• Status: Expired due to Fees

• Current Assignee: Cansolv Technologies Inc. (Shell Plc)
• Original Assignee: Cansolv Technologies Inc. (Shell Plc)
• Inventors: Hakka, Leo E., Ouimet, Michel A.
• Primary Examiner(s): Johnson, Edward M.
• Application Number:
  US10/459,519
• Publication Number:
  US 20040253159A1
• Time in Patent Office: 1,090 Days
• Field of Search: 423/228, 423/230, 423/242.7
• US Class Current: 423/230
• CPC Class Codes: B01D 53/1406 Multiple stage absorption
• CPC Class Codes: B01D 53/1475 Removing carbon dioxide
• CPC Class Codes: B01D 53/1493 Selection of liquid materials for use as absorbents
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

A process for recovering CO₂ from a feed gas stream comprises treating the feed gas stream with a regenerated absorbent comprising at least one tertiary amine absorbent having a pK_a for the amino function of from about 6.5 to about 9 in the presence of an oxidation inhibitor to obtain a CO₂ rich stream and subsequently treating the CO₂ rich stream to obtain the regenerated absorbent and a CO₂ rich product stream. The feed gas stream may also include SO₂ and/or NO_x.

Claims

1. A process for recovering CO₂ from a feed gas stream comprising treating the feed gas stream with a regenerated absorbent comprising at least one tertiary amine absorbent having a pK_a for the amino function of from about 6.5 to about 9 in the presence of an oxidation inhibitor to obtain a CO₂ rich stream, maintaining a sufficient oxidation inhibitor concentration in the absorbent to essentially prevent the oxidation of the absorbent by molecular oxygen and subsequently treating the CO₂ rich stream to obtain the regenerated absorbent and a CO₂ rich product stream.

2. The process as claimed in claim 1 wherein the process further comprises selecting the at least one tertiary amine absorbent from the group consisting of methyldiethanolamine, triethanolamine, N,N′

-di-(hydroxyalkyl)piperazine, N,N,N′

,N′

-tetrakis(hydroxyalkyl)-1,6-hexanediamine, tertiary alkylamine sulfonic acids and mixtures thereof.

3. The process as claimed in claim 1 wherein the process further comprises selecting the at least one tertiary amine absorbent from the group consisting of methyldiethanolamine, N,N′

-di-(2-hydroxyethyl)piperazine, N,N′

-di-(3-hydroxypropyl)piperazine, N,N,N′

,N′

-tetrakis(2-hydroxyethly)-1,6-hexanediamine, N,N,N′

,N′

-tetrakis(2-hydroxypropyl)-1,6-hexanediamine, tertiary alkylamine sulfonic acids, triethanolamine, and mixtures thereof.

4. The process as claimed in claim 3 wherein the tertiary alkylamine sulfonic acid is selected from the group consisting of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazinebutanesulfonic acid, 4-(2-hydroxyethyl)piperazine-1-(2-hydroxypropanesulfonic acid), 1,4-piperazinedi(ethanesulfonic acid) and mixtures thereof.

5. The process as claimed in claim 1 wherein the process further comprises selecting the tertiary amine absorbent such that it has a vapour pressure less than about 1 mm Hg at 120°

C. as the pure compound.

6. The process as claimed in claim 1 wherein the absorbent further comprises at least one secondary amine.

7. The process as claimed in claim 6 further comprising selecting at least one piperazine as the secondary amine.

8. The process as claimed in claim 6 wherein the at least one secondary amine is selected from the group consisting of piperazine, N-(2-hydroxyethyl)piperazine and an N-(hydroxypropyl)piperazine and mixtures thereof.

9. The process as claimed in claim 6 wherein the at least one secondary amine is selected from the group consisting of piperazine, N-(2-hydroxyethyl)piperazine and mixtures thereof.

10. The process as claimed in claim 6 wherein the absorbent comprises an aqueous solution comprising 10-50 wt % of the tertiary amine and 1-40 wt % of a secondary amine.

11. The process as claimed in claim 6 wherein the absorbent comprises 10-50 wt % of the tertiary amine, 0-8 wt % of piperazine, 1-30 wt % of N-(2-hydroxyethyl)piperazine with the remainder comprising water.

12. The process as claimed in claim 1 wherein the CO₂ rich stream is treated with steam to regenerate the absorbent.

13. The process as claimed in claim 1 further comprising removing only a portion of the heat stable salts from the absorbent.

14. The process as claimed in claim 1 in which the oxidation inhibitor comprises a free radical scavenger.

15. The process as claimed in claim 14 wherein the process further comprises selecting an alcohol, alkanolamine, thiosulfate and mixtures thereof as the free radical scavenger.

16. The process as claimed in claim 14 wherein the process further comprises selecting thiosulfate as the free radical scavenger.

17. The process as claimed in claim 1 wherein the process further comprises selecting at least one phenolic amine antioxidant or aromatic amine antioxidant as the free radical scavenger.

18. The process as claimed in claim 1 in which the oxidation inhibitor comprises an oxygen scavenger.

19. The process as claimed in claim 18 wherein the process further comprises selecting sulfite or bisulfite as the oxygen scavenger.

20. The process as claimed in claim 1 in which the oxidation inhibitor comprises a mixture of at least one oxygen scavenger and at least one free radical scavenger.

21. The process as claimed in claim 1 further comprising treating the regenerated absorbent to comprise greater than 0.05 wt. % thiosulfate.

22. The process as claimed in claim 1 further comprising adding a chelating agent to reduce metal ion catalyzed oxidation of the absorbent.

23. The process as claimed in claim 1 further comprising subjecting the absorbent to an ion exchange step to remove multivalent metal ions to reduce metal ion catalyzed oxidation of the absorbent.

24. The process as claimed in claim 1 wherein the absorbent is in solution and the process further comprises increasing the concentration of absorbent or salts in the solution to reduce the solubility of O₂ in the solution.

25. The process as claimed in claim 1 wherein the feed gas stream further comprises NO_x and the process further comprises treating the feed gas stream to remove at least a portion of the NO_x.

26. The process as claimed in claim 1 wherein the feed gas stream further comprises NO_x and the process further comprises providing a reagent to react with the NO_x to produce reaction products comprising molecular nitrogen, sulfonated ammonia chemicals, and sulfate and/or dithionate ions, treating the CO₂ rich stream to remove sulfate andlor dithionate ions and regenerate the reagent and adjusting the pH of the regenerated absorbent from about 7 to about 9.5.

27. The process as claimed in claim 26 further comprising selecting the reagents from the group consisting of a metal chelate, sulfite and mixtures thereof.

28. The process as claimed in claim 27 further comprising selecting the metal chelate from the group consisting of iron nitrilotriacetic acid, iron ethylenediaminetetraacetic acid, iron diethylenetriaminepentaacetic acid and mixtures thereof.

29. A process for recovering SO₂ and CO₂ from a feed gas stream comprising:

(a) treating the feed gas stream in an SO₂ scrubbing loop with a first absorbent stream to obtain a SO₂ rich stream and a SO₂ lean stream and subsequently treating the SO₂ rich stream to obtain a first regenerated absorbent stream which is used in the SO₂ scrubbing loop;

(b) treating the SO₂ lean stream in a CO₂ scrubbing loop with a second absorbent stream to obtain a CO₂ rich stream and subsequently treating the CO₂ rich stream to obtain a second regenerated absorbent stream which is used in the CO₂ scrubbing loop; and

,

(c) treating at least a potion of one or both of the first and second regenerated absorbent streams to remove heat stable salts

wherein the absorbent used in each of the scrubbing loops comprises at least one tertiary amine and at least one secondary amine as an activator.

30. The process as claimed in claim 29 further comprising selecting the tertiary amine from N,N′

-di-(2-hydroxyethyl)piperazine, N,N′

-di-(3-hydroxypropyl)piperazine, N,N,N′

,N′

-tetrakis(2-hydroxypropyl)-1,6-hexanediamine or mixtures thereof, and selecting the secondary amine from N-2-hydroxyethylpiperazine, piperazine, a N-(hydroxypropyl)piperazine or mixtures thereof as an activator.

31. The process as claimed in claim 29 wherein only the first regenerated absorbent stream is treated to remove heat stable salts and a bleed stream of the treated amine is bled into the CO₂ removal loop and a bleed steam from the CO₂ scrubbing loop is provided to the SO2 scrubbing loop.

32. The process as claimed in claim 29 further comprising adjusting the treatment of the feed gas stream in the SO₂ scrubbing loop such that the SO₂ lean gas stream has a concentration of SO₂ so as to maintain a concentration of sulfite in the CO₂ scrubbing loop sufficient to essentially prevent the oxidation of the absorbent by molecular oxygen.

33. The process as claimed in claim 29 wherein the feed gas stream further comprises NO_x and the process further comprises providing a metal chelate to react with the NO_x to produce sulfate and/or dithionate ions, treating the CO₂ rich stream to remove sulfate and/or dithionate ions and regenerate the reagent and adjusting the pH of the second regenerated absorbent from about 7 to about 9.5.

34. The process as claimed in claim 33 further comprising selecting the metal chelate from the group consisting of iron nitrilotriacetic acid, iron ethylenediaminetetraacetic acid, iron diethylenetriaminepentaacetic acid and mixtures thereof.

35. The process as claimed in claim 29 further comprising conducting steps (a) and (b) in a single adsorption column.

36. The process as claimed in claim 29 further comprising selecting the same amines for each loop.

37. The process as claimed in claim 29 further comprising conducting step (a) at a pH in the range of about 3-6 and step (b) at a pH in the range of about 6-9.

38. A process for removal of CO₂ and NO_x from a gas stream containing SO₂ at a mole ratio <

5 times the NO_x content, comprising treating the feed gas stream to obtain a CO₂ rich stream by exposing the feed gas stream to a regenerated absorbent comprising at least one tertiary amine absorbent having a pK_a for the amino function of from about 6.5 to about 9, an oxidation inhibitor, a metal chelate and sulfite and or other reactants and reducing agents to react with the NO_x to produce reaction products comprising molecular nitrogen, sulfonated ammonia chemicals, and sulfate and/or dithionate ions, treating the CO₂ rich stream to remove heat stable salts including sulfate and/or dithionate ions and adjusting the pH of the regenerated absorbent from about 7 to about 9.5 and subsequently treating the CO₂ rich stream to obtain the regenerated absorbent.

39. The process as claimed in claim 38 wherein the regenerated absorbent comprises greater than 0.5 wt. % sulfite, greater than 0.05 wt. % thiosulfate and greater than 0.005 molar FeEDTA.

40. The process as claimed in claim 39 wherein the regenerated absorbent has a pH in the range 6-9.5.

41. The process as claimed in claim 40 wherein the regenerated absorbent has a pH in the range 7-9.5 and the maximum concentrations of the metal chelate and sulfite and/or other reactants and reducing agents are each equal to their solubility limit at 20°

C.

42. A process for recovering SO₂ and CO₂ from a feed gas stream comprising:

(a) subjecting the feed gas stream to a SO₂ removal step using a SO₂ absorbent and recovering a SO₂ lean stream and a SO₂ rich absorbent stream;

(b) regenerating the SO₂ absorbent at a first temperature to obtain a regenerated SO₂ absorbent stream and a first vapour stream;

(c) subjecting the SO₂ lean stream to a CO₂ removal step using a CO₂ absorbent and recovering a CO₂ lean stream and a CO₂ rich absorbent stream;

(d) regenerating the CO₂ absorbent at a second temperature to obtain a regenerated CO₂ absorbent stream and a second vapour stream

wherein the first temperature is lower than the second temperature so that at least a portion of the second vapour stream is used to regenerate the SO₂ absorbent.

43. The process as claimed in claim 42 wherein the SO₂ absorbent is regenerated by steam produced in a reboiler and at least a portion of the second vapour stream is used to provide heat to the reboiler.

44. The process as claimed in claim 43 wherein the second vapour stream is used to indirectly heat to the reboiler and is subsequently returned to be used in the regeneration of the CO₂ absorbent.