Method for absorbing CO
In a method of absorbing CO 2 from a gas mixture the use of an absorption medium comprising water and at least one amine of formula (I) where R 1 is a —(CH 2 ) n —(XCH 2 CH 2 ) m —Y—R 3 radical where R 3 =hydrogen or an alkyl radical having from 1 to 6 carbon atoms, X and Y are each, independently of one another, NR 3 , oxygen, SO or SO 2 , where in the case of Y═SO and in the case of Y═SO 2 , R 3 is not hydrogen, and Y—R 3 can be an N-morpholinyl radical or an N-piperazyl radical, n=2 to 4, m=0 to 4 and R 2 is hydrogen, an alkyl radical having from 1 to 6 carbon atoms or a radical R 1 , where m is not 0 when R 2 is not a radical R 1 , Y═NR 3 and Y—R 3 is not an N-morpholinyl radical and not an N-piperazyl radical, makes it possible to avoid precipitation of a solid during the absorption of CO 2 and a separation into two liquid phases during the regeneration of the absorption medium.
1. A method of absorbing CO 2 from a gas mixture by contacting the gas mixture with an absorption medium wherein the absorption medium comprises water and at least one amine of formula (I):
where
R 1 is a —(CH 2 ) n —(XCH 2 CH 2 ) m —Y—R 3 radical where
R 3 =hydrogen or an alkyl radical having from 1 to 6 carbon atoms,
X and Y are each, independently of one another, NR 3 , oxygen, SO or SO 2 , where in the case of Y═SO and in the case of Y═SO 2 , R 3 is not hydrogen, and Y—R 3 can be an N-morpholinyl radical or an N-piperazyl radical,
n=2 to 4,
m=0 to 4 and
R 2 is hydrogen, an alkyl radical having from 1 to 6 carbon atoms or a radical R 1 , where m is different from 0 when R 2 is not a radical R 1 , Y═NR 3 and Y—R 3 is not an N-morpholinyl radical and not an N-piperazyl radical.
2. The method of claim 1 , wherein X and Y in formula (I) are each, independently of one another, NR 3 or oxygen.
3. The method of claim 2 , wherein Y in formula (I) is oxygen.
4. The method of claim 3 , wherein R 3 in formula (I) is methyl or hydrogen.
5. The method of claim 3 , wherein m in formula (I) is 0.
6. The method of claim 1 , wherein Y—R 3 in formula (I) is an N-morpholinyl radical or an N-piperazyl radical.
7. The method of claim 6 , wherein m in formula (I) is 0.
8. The method of claim 1 , wherein n in formula (I) is 2 or 3.
9. The method of claim 8 , wherein n in formula (I) is 2.
10. The method of claim 1 , wherein the absorption medium has a content of amines of formula (I) of from 10 to 60% by weight.
11. The method of claim 10 , wherein the absorption medium has a content of amines of formula (I) of from 20 to 50% by weight.
12. The method of claim 1 , wherein the gas mixture is a combustion off-gas, a natural gas or a biogas.
13. The method of claim 1 , wherein CO 2 absorbed in the absorption medium is desorbed again by an increase in temperature, a reduction of pressure or both and after this desorption of CO 2 the absorption medium is used again for absorbing CO 2 .
14. The method of claim 13 , wherein the absorption is carried out at a temperature in the range from 0 to 80° C. and the desorption is carried out at a higher temperature in the range from 50 to 200° C.
15. The method of claim 13 , wherein the absorption is carried out at a pressure in the range from 0.8 to 90 bar and the desorption is carried out at a lower pressure in the range from 0.01 to 10 bar.
16. The method of claim 1 , wherein said amine of formula (I) is selected from the group consisting of 4-(2-hydroxyethylamino)-2,2,6,6-tetramethylpiperidine, 4-[bis(2-hydroxyethy)amino]-2,2,6,6-tetramethylpiperidine, 4-(2-methoxyethylamino)-2,2,6,6-tetramethylpiperidine, 4-(2-hydroxyethylaminoethylamino)-2,2,6,6-tetramethylpiperidine, 4-(2-piperazinoethylamino)-2,2,6,6-tetramethylpiperidine and 4-(2-morpholinopropylamino)-2,2,6,6-tetramethylpiperidine.