Absorption medium and method for removing carbon dioxide from combustion exhaust gas
In some embodiments, an aqueous composition for removing acid gas components from a process gas includes a first cyclic amine having a substituted carbon atom alpha to an amine atom, and a second cyclic amine having two unsubstituted carbon atoms, wherein each of the unsubstituted carbon atoms is alpha to an amine atom. The composition further includes a molar ratio of the first cyclic amine to the second cyclic amine of about 6:1 to about 2:1.
1. An aqueous composition for removing acid gas components from a process gas, the composition comprising:
a first cyclic amine having a substituted carbon atom alpha to an amine atom; and
a second cyclic amine having two unsubstituted carbon atoms, wherein each of the unsubstituted carbon atoms is alpha to an amine atom, wherein:
the composition comprises a molar ratio of the first cyclic amine to the second cyclic amine of about 6:1 to about 2:1, and
the first cyclic amine and the second cyclic amine comprise substantially all of the amine content in the aqueous composition.
2. The composition of claim 1 , wherein the first cyclic amine can be represented by Formula (I):
wherein:
R 1 is hydrogen;
each of R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , and R 9 is independently selected from the group consisting of a hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, and sec-butyl; and
Q 1 is selected from
wherein a wavy line indicates a bonding point to the remainder of the amine of Formula (I).
3. The composition of claim 1 , wherein the first cyclic amine is selected from the group consisting of 2-methylpiperazine, 2,5-dimethylpiperazine, 1,3-dimethylpiperazine, 2,3,5,6-tetramethylpiperazine, 4-hydroxy-2,6-dimethylpiperidine, 4-hydroxy-2,2-dimethylpiperidine, 4-hydroxy-2,2,6,6,-tetramethylpiperidine, and combinations thereof.
4. The composition of claim 1 , wherein the first cyclic amine is 2-methylpiperazine.
5. The composition of claim 1 , wherein the second cyclic amine can be represented by Formula (II):
wherein:
each of R 10 , R 11 , R 12 , R 15 , and R 16 is hydrogen;
each of R 13 , and R 14 is independently hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, and sec-butyl;
Q 2 is selected from
and
Q 3 is selected from
or Q 3 is a bond connecting the carbon adjacent to Q 3 with Q 2 , wherein if Q 2 is
then Q 3 is a bond or
wherein if Q 3 is
then Q 2 is
wherein if Q 2 is
then Q 3 is
and R 13 and R 14 are each hydrogen, wherein a wavy line indicates a bonding point to the remainder of the amine of Formula (II).
6. The composition of claim 1 , wherein the second cyclic amine is selected from the group consisting of piperazine, 4-hydroxypiperidine, 3-hydroxypiperidine, 4-(hydroxymethyl) piperidine, 3-(hydroxymethyl) piperidine, 3-hydroxypyrrolidine, and combinations thereof.
7. The composition of claim 1 , wherein the second cyclic amine is piperazine.
8. The composition of claim 1 , wherein the composition comprises a total amine content of about 35 wt % to about 60 wt %.
9. The composition of claim 1 , wherein the composition comprises the first cyclic amine in an amount of about 20 wt % to about 45 wt %.
10. The composition of claim 1 , wherein the composition comprises the second cyclic amine in an amount of about 5 wt % to about 15 wt %.
11. The composition of claim 1 , wherein the molar ratio of the first cyclic amine relative to the second cyclic amine is about 5:1.
12. The composition of claim 1 , wherein the composition further comprises a water miscible solvent comprising at least 4 or more —O— or —OH groups.
13. An aqueous composition for removing acid gas components from a process gas, the composition comprising:
a first cyclic amine comprising about 20 wt % to about 45 wt % of the composition, the first cyclic amine having a substituted carbon atom alpha to an amine atom;
a second cyclic amine comprising about 5 wt % to about 15 wt % of the composition, the second cyclic amine having two unsubstituted carbon atoms, wherein each of the unsubstituted carbon atoms is alpha to an amine atom, wherein:
the first cyclic amine and the second cyclic amine comprise substantially all of the amine content in the aqueous composition; and
a water miscible solvent comprising 4 or more —O— or —OH groups.
14. The composition of claim 13 , wherein the first cyclic amine is selected from the group consisting of 2-methylpiperazine, 2,5-dimethylpiperazine, 1,3-dimethylpiperazine, 2,3,5,6-tetramethylpiperazine, 4-hydroxy-2,6-dimethylpiperidine, 4-hydroxy-2,2-dimethylpiperidine, 4-hydroxy-2,2,6,6,-tetramethylpiperidine, and combinations thereof.
15. The composition of claim 13 , wherein the second amine is selected from the group consisting of piperazine, 4-hydroxypiperidine, 3-hydroxypiperidine, 4-(hydroxymethyl) piperidine, 3-(hydroxymethyl) piperidine, 3-hydroxypyrrolidine, and combinations thereof.
16. The composition of claim 13 , wherein the water miscible solvent is selected from the group consisting of triethylene glycol, tripropylene glycol methyl ether, triglyme, tetraglyme, and combinations thereof.
17. A method of treating a process gas, the method comprising:
providing a process gas and an aqueous absorption medium to an absorption tower;
contacting the process gas with the aqueous absorption medium to produce a loaded aqueous absorption medium, the aqueous absorption medium comprising:
about 20 wt % to about 45 wt % of a first cyclic amine having a substituted carbon atom alpha to an amine atom, and
about 5 wt % to about 15 wt % of a second cyclic amine having two unsubstituted carbon atoms, wherein each of the unsubstituted carbon atoms is alpha to an amine atom, wherein:
the first cyclic amine and the second cyclic amine comprise substantially all of the amine content in the aqueous composition;
providing the loaded aqueous absorption medium to a regeneration tower;
desorbing the loaded aqueous absorption medium to form a regenerated aqueous absorption medium; and
recycling the regenerated aqueous absorption medium to the absorption tower.
18. The method of claim 17 , wherein the aqueous absorption medium comprises a molar ratio of the first cyclic amine relative to the second cyclic amine of about 6:1 to about 2:1.
19. The method of claim 17 , wherein the aqueous absorption medium comprises a molar ratio of the first cyclic amine relative to the second cyclic amine of about 3:1 to about 2:1.
20. The method of claim 17 , wherein the aqueous absorption medium further comprises a water miscible solvent in an amount of about 10 wt % to about 50 wt %.