Compositions and methods for carbon dioxide capture

1. An aqueous composition comprising:

a) at least two nucleophilic compounds, wherein the nucleophilic compounds comprise a sterically unhindered primary amine moiety, a sterically unhindered secondary amine moiety, or a combination thereof;

b) at least one Brønsted base, wherein the Brønsted base comprises a basic nitrogen moiety and the Brønsted base does not comprise a sterically unhindered primary amine moiety and a sterically unhindered secondary amine moiety;

c) about 30% to about 50% by weight of a water-soluble organic solvent, wherein the organic solvent is a glyme; and

d) about 20% to about 40% by weight of water;

wherein the composition is a homogeneous mixture within the temperature range of 20° C. to 80° C.

2. The composition of claim 1 wherein the water-soluble organic solvent is tetraglyme, the Brønsted base is 2-ethyl-4-methylimidazole or 2-[2-(dimethylamino)ethoxy]ethanol, and the at least two nucleophilic compounds comprise piperazine and 2-methylpiperazine.

3. The composition of claim 1 wherein

the combination of the nucleophilic compounds, the Brønsted base, the organic solvent, and the water components of the composition are completely miscible within the temperature range of 20° C. to 80° C.;

the boiling points of the nucleophilic compounds, Brønsted base, and organic solvent are each at least 140° C.; and

the vapor pressures of the nucleophilic compounds, Brønsted base, and organic solvent are each about 100 Pa or below at about 20° C.

4. The composition of claim 1 wherein the composition comprises about 10% to about 35% by weight of the Brønsted base, and about 10% to about 35% by weight of the nucleophilic compounds.

5. The composition of claim 4 wherein the composition comprises 15 wt. % to 25 wt. % of the Brønsted base.

6. The composition of claim 4 wherein the composition comprises 15 wt. % to 25 wt. % of the nucleophilic compounds.

7. The composition of claim 1 wherein the Brønsted base comprises an imidazole, a piperazine, a morpholine, a piperidine, a non-alcoholic tertiary amine, a non-alcoholic sterically hindered amine, or a combination thereof; and the molecular weight of the Brønsted base is about 60 daltons to about 250 daltons.

8. The composition of claim 1 wherein the Brønsted base is 2-ethylimidazole, 2-ethyl-4-methylimidazole, 1,4-bis(2-hydroxyethyl)piperazine, 4-(2-hydroxyethyl)morpholine, 4-hydroxy-1-methylpiperidine, bis[2-(N,N-dimethylamino)ethyl] ether, N,N,N′,N″,N″-pentamethyldiethylenetriamine, N,N,N′,N″,N″-pentamethyldipropylenetriamine, triethylenediamine, 3,3′-iminobis(N,N-dimethylpropylamine), di-sec-butylamine, N-propyl-sec-butylamine, 2-[2-(dimethylamino)ethoxy]ethanol, or a combination thereof.

9. The composition of claim 1 wherein the first nucleophilic compound of the at least two nucleophilic compounds is a piperazine, a morpholine, an amino ether, a non-alcoholic polyamine, a non-alcoholic monoamine, or a combination thereof.

10. The composition of claim 1 wherein the second nucleophilic compound of the at least two nucleophilic compounds is 2 methyl-piperazine, 1-(2-hydroxyethyl)piperazine, 1-(2-aminoethyl)piperazine, 4-(2-aminoethyl)morpholine, bis(2-aminoethyl) ether, bis(3-aminopropyl)amine, 1,3-diaminopropane, 3,3′-diamino-N-methyldipropylamine, 3-(aminomethyl)pyridine, 1-(3-aminopropyl)imidazole, hexamethyleneimine, N-methylcyclohexylamine, or a combination thereof.

11. The composition of claim 10 wherein the second nucleophilic compound is 2-methyl-piperazine.

12. The composition of claim 1 wherein the viscosity of the composition is 10 cP or less at 20° C.

13. The composition of claim 12 wherein the water-soluble organic solvent comprises triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), or a combination thereof.

14. A method for capturing carbon dioxide comprising contacting carbon dioxide gas with an aqueous composition according to claim 1 ;

wherein

a) the at least two nucleophilic compounds and carbon dioxide gas form a carbamate moiety via the nitrogen atom of the sterically unhindered primary or sterically unhindered secondary amine moiety to provide carbamate compounds;

b) the Brønsted base forms a conjugate acid wherein the dissolution of carbon dioxide gas is facilitated;

c) the water in the aqueous composition becomes enriched with the carbamate compounds; and

d) the aqueous composition partitions to form a biphasic composition that has a CO 2 -rich phase and a CO 2 -lean phase, wherein the rich phase comprises the highest % weight of water, the highest % weight of the carbamate compounds, and the highest % weight of the conjugate acid; and the lean phase comprises the highest % weight of the organic solvent;

wherein carbon dioxide is thereby captured.

15. The method of claim 14 wherein the organic solvent comprises tetraglyme, the Brønsted base is 2-ethyl-4-methylimidazole, and the at least two nucleophilic compounds comprise piperazine and 2-methylpiperazine.

16. The method of claim 14 further comprising heating the CO 2 -rich phase at about 100° C. to about 160° C. to release captured carbon dioxide as molecular carbon dioxide; and optionally recovering recycled nucleophilic compounds and Brønsted bases;

wherein the amount of energy used to release molecular carbon dioxide at 100° C. to 160° C. is less compared to the release of molecular carbon dioxide from a monophasic composition comprising 30% by weight of monoethanolamine at 100° C. to 125° C.

17. A method of processing carbon dioxide comprising:

a) contacting carbon dioxide gas and the aqueous composition according to claim 1 in one or more absorption columns to form a biphasic composition comprising carbamate compounds, a CO 2 -rich phase, and a CO 2 -lean phase;

b) at least partially separating the CO 2 -rich phase from the CO 2 -lean phase in one or more liquid-liquid phase separation (LLPS) units, wherein the at least partially separated CO 2 -rich phase is dispatched from the one or more LLPS units;

c) feeding the CO 2 -rich phase to one or more thermal strippers and heating the CO 2 -rich phase to a temperature that releases an amine compound and molecular carbon dioxide from the carbamate compound;

wherein

i) the CO 2 -rich phase is optionally preheated, wherein the preheated CO 2 -rich phase is fed to the middle or lower portion of the one or more thermal strippers; or

ii) the CO 2 -rich phase is not preheated, wherein the not preheated CO 2 -rich phase is fed to the top portion of the one or more thermal strippers;

d) returning the amine compound to the one or more absorption columns;

e) compressing the molecular carbon dioxide with one or more compressors into liquid carbon dioxide; and

f) optionally at least partially separating a second CO 2 -lean phase is from a second CO 2 -rich phase in a second LLPS unit and dispatching the at least partially separated second CO 2 -lean phase from the second LLPS unit, wherein the one or more thermal strippers comprise the second LLPS unit;

wherein carbon dioxide is thereby processed from a gas to a liquid.