Mixed amine and non-nucleophilic base CO2 scrubbing process for improved adsorption at increased temperatures

• US 8,715,397 B2
• Filed: 09/09/2011
• Issued: 05/06/2014
• Est. Priority Date: 09/09/2010
• Status: Active Grant

• Current Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Original Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Inventors: Kortunov, Pavel, Baugh, Lisa S., Calabro, David C., Siskin, Michael, Kamakoti, Preeti, Li, Quanchang
• Primary Examiner(s): Smith, Duane
• Assistant Examiner(s): GLOVER, JOUBERT
• Application Number:
  US13/228,869
• Publication Number:
  US 20120060686A1
• Time in Patent Office: 970 Days
• Field of Search: 952/36
• US Class Current: 95/199
• CPC Class Codes: B01D 2252/20415 Tri- or polyamines
• CPC Class Codes: B01D 2252/20421 Primary amines
• CPC Class Codes: B01D 2252/20426 Secondary amines
• CPC Class Codes: B01D 2252/20431 Tertiary amines
• CPC Class Codes: B01D 2252/20478 Alkanolamines
• CPC Class Codes: B01D 2252/2056 Sulfur compounds, e.g. Sulfolane, thiols
• CPC Class Codes: B01D 2252/30 Ionic liquids and zwitter-ions
• 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: B01D 53/62 Carbon oxides
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

A CO₂ amine scrubbing process uses an absorbent mixture combination of an amine CO₂ sorbent in combination with a non-nucleophilic, relatively stronger, typically nitrogenous, base. The weaker base(s) are nucleophilic and have the ability to react directly with the CO₂ in the gas stream while the relatively stronger bases act as non-nucleophilic promoters for the reaction between the CO₂ and the weaker base. The sorption and desorption temperatures can be varied by selection of the amine/base combination, permitting effective sorption temperatures of 70 to 90° C., favorable to scrubbing flue gas.

Claims

1. A cyclic process for separating CO₂ from a gas stream, which process comprises:

dehumidifying the gas stream to remove substantial quantities of water therefrom;

contacting the dehumidified gas stream with an absorbent system comprising a non-aqueous aprotic solvent, an amine CO₂ sorbent, and a non-nucleophilic base having a pK_a at least 3 units higher than that of the amine at a temperature above 50°

C. to sorb CO₂, wherein the contacting of the absorbent system with the dehumidified gas stream results in formation of a stabilized mixed carbamate in which the CO₂ forms a carbamate by reaction with the amine sorbent and in which a protonated form of the non-nucleophilic base forms a stabilizing counterion for the carbamate; and

treating the absorbent system containing the sorbed CO₂ under conditions sufficient to cause desorption of at least a portion of the CO₂.

2. The process of claim 1, wherein the amine sorbent comprises a primary amine, a secondary amine, or mixture thereof.

3. The process of claim 1, wherein the amine sorbent comprises a primary or secondary aliphatic, cycloaliphatic, or aromatic amine, or mixture thereof.

4. The process of claim 3, wherein the aliphatic amine comprises a primary amine selected from:

monoethanolamine, 2-amino-2-methyl- 1-propanol, 2-(2-aminoethylamino)ethanol, 2-amino-2-hydroxymethyl- 1,3-propanediol, diglycolamine, 2-ethoxyethylamine, 2-n-propoxyethylamine, 1,5-diamino-3-oxapentane, 3-aminopropionitrile, aminoacetonitrile, or hydroxyetliyletiediamine.

5. The process of claim 3, wherein the amine comprises a secondary amine selected from piperidine, piperazine, diethanolamine, diisopropanolamine, 1,5-bis(methylamino)-3-oxapentane, bis(2-methoxyethyl)amine, bis(2-ethoxyethyl)amine, ethoxyethanol tertiarybutylamine, or 3,3′

-iminodipropionitrile.

6. The process of claim 3, wherein the aliphatic amine comprises aniline.

7. The process of claim 1, wherein the non-nucleophilic base comprises an amine, an imine, an amidine, a guanidine, or a biguanide.

8. The process of claim 7, wherein the non-nucleophilic base has a pK_a of at least 8.5.

9. The process of claim 8, wherein the non-nucleophilic base has a pK_a of at least 9.

10. The process of claim 9, wherein the non-nucleophilic base has a pK_a of at least 10.

11. The process of claim 10, wherein the non-nucleophilic base has a pK_a of at least 13.

12. The process of claim 1, wherein the amine has a pK_a not greater than 11.5.

13. The process of claim 8, wherein the amine has a pK_a not greater than 11.5.

14. The process of claim 12, wherein the amine has a pK_a not greater than 10.

15. The process of claim 14, wherein the amine has a pK_a not greater than 9.

16. The process of claim 1, wherein the non-nucleophilic base has a pK_a of at least 7 units higher than that of the amine.

17. The process of claim 1, wherein the dehumidified gas stream is contacted with the absorbent at a temperature of at least 70°

C. but not more than 100°

C.

18. The process of claim 17, wherein the dehumidified gas stream is contacted with the absorbent at a temperature of at least 90°

C. but not more than 100°

C.

19. The process of claim 1, wherein the CO₂ is desorbed from the absorbent containing the sorbed CO₂ at a temperature of at least about 100°

C. to cause desorption of at least a portion of the sorbed CO₂.

20. The process of claim 15, wherein the CO₂ is desorbed from the absorbent containing the sorbed CO₂ at a temperature from 100 to 120°

C.

21. The process of claim 1, wherein the amine and the non-nucleophilic base are dissolved in a polar, aprotic solvent having a boiling point of at least 65°

C.

22. The process of claim 1, wherein the amine or the non-nucleophilic base is integrated onto a porous support.

23. The process of claim 1, wherein the amine and the non-nucleophilic base are integrated onto a porous support.

24. The process of claim 22, wherein the porous support is comprised of a, material selected from carbon, alumina, silica, silica-alumina, magnesia, zeolites, and solid porous polymers.

25. The process of claim 23, wherein the porous support is comprised of a material selected from carbon, alumina, silica, silica-alumina, magnesia, zeolites, and solid porous polymers.

26. The process of claim 1, wherein the amine comprises a polyamine having both primary and secondary amine groups, having both secondary and tertiary amine groups, or having each of primary, secondary, and tertiary amine groups.

27. The process of claim 21, wherein the non-aqueous polar aprotic solvent is selected from the group consisting of toluene, acetonitrile, dimethylformatnide, dimethylsulfoxide, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, amyl acetate, 1,2-orthodichlorobenzene, and combinations thereof.