Method for absorbing CO2 from a gas mixture

Abstract

In a method of absorbing CO.sub.2 from a gas mixture the use of an absorption medium comprising water and at least one amine of formula (I) ##STR00001## where R.sup.1 is a (CH.sub.2).sub.n(XCH.sub.2CH.sub.2).sub.mYR.sup.3 radical where R.sup.3=hydrogen or an alkyl radical having from 1 to 6 carbon atoms, X and Y are each, independently of one another, NR.sup.3, oxygen, SO or SO.sub.2, where in the case of YSO and in the case of YSO.sub.2, R.sup.3 is not hydrogen, and YR.sup.3 can be an N-morpholinyl radical or an N-piperazyl radical, n=2 to 4, m=0 to 4 and R.sup.2 is hydrogen, an alkyl radical having from 1 to 6 carbon atoms or a radical R.sup.1, where m is not 0 when R.sup.2 is not a radical R.sup.1, YNR.sup.3 and YR.sup.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.sub.2 and a separation into two liquid phases during the regeneration of the absorption medium.

Claims

1. A method of absorbing CO.sub.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): ##STR00003## where R.sup.1 is a (CH.sub.2).sub.n(XCH.sub.2CH.sub.2).sub.mYR.sup.3 radical where R.sup.3=hydrogen or an alkyl radical having from 1 to 6 carbon atoms, X and Y are each, independently of one another, NR.sup.3, oxygen, SO or SO.sub.2, where in the case of YSO and in the case of YSO.sub.2, R.sup.3 is not hydrogen, and YR.sup.3 can be an N-morpholinyl radical or an N-piperazyl radical, n=2 to 4, m=0 to 4 and R.sup.2 is hydrogen, an alkyl radical having from 1 to 6 carbon atoms or a radical R.sup.1, where m is different from 0 when R.sup.2 is not a radical R.sup.1, YNR.sup.3 and YR.sup.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.sup.3 or oxygen.

3. The method of claim 2, wherein Y in formula (I) is oxygen.

4. The method of claim 3, wherein R.sup.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 YR.sup.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.sub.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.sub.2 the absorption medium is used again for absorbing CO.sub.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.

Description

EXAMPLES

(1) For determining the CO.sub.2 loading, the CO.sub.2 uptake and the relative absorption rate, 150 g of absorption medium consisting of 45 g of amine and 105 g of water were charged to a thermostatable container with a top-mounted reflux condenser cooled at 3 C. After heating to 40 C. or 100 C., a gas mixture of 14% CO.sub.2, 80% nitrogen and 6% oxygen by volume was passed at a flow rate of 59 l/h through the absorption medium, via a frit at the bottom of the container, and the CO.sub.2 concentration in the gas stream exiting the reflux condenser was determined by IR absorption using a CO.sub.2 analyser. The difference between the CO.sub.2 content in the gas stream introduced and in the exiting gas stream was integrated to give the amount of CO.sub.2 taken up, and the equilibrium CO.sub.2 loading of the absorption medium was calculated. The CO.sub.2 uptake was calculated as the difference in the amounts of CO.sub.2 taken up at 40 C. and at 100 C. From the slope of the curve of CO.sub.2 concentration in the exiting gas stream for an increase in concentration from 1% to 12% by volume, a relative absorption rate of CO.sub.2 in the absorption medium was determined. The amines tested are given in Table 1 with the equilibrium loadings determined in this way at 40 C. and 100 C., in mol CO.sub.2/mol amine, the CO.sub.2 uptake in mol CO.sub.2/mol amine, the relative absorption rate of CO.sub.2, relative to Example 1 with 100%, and the boiling point of the amine.

(2) For determining the phase separation temperatures, the absorption medium was heated slowly in a closed, pressure-rated glass container until a clouding or separation into two liquid phases was discernible. An entry marked with the symbol > means that up to that temperature there was no demixing and that the experiment was ended at the temperature indicated, for safety reasons.

(3) The abbreviations used in Table 1 have the following meanings: MEA: ethanolamine TAD: 4-amino-2,2,6,6-tetramethylpiperidine Pr-TAD: 4-(n-propylamino)-2,2,6,6-tetramethylpiperidine Bu-TAD: 4-(n-butylamino)-2,2,6,6-tetramethylpiperidine amine 1: 4-(2-hydroxyethylamino)-2,2,6,6-tetramethylpiperidine amine 2: 4-(2-methoxyethylamino)-2,2,6,6-tetramethylpiperidine amine 3: 4-(2-hydroxyethylaminoethylamino)-2,2,6,6-tetramethylpiperidine amine 4: 4-[bis(2-hydroxyethyl)amino]-2,2,6,6-tetramethylpiperidine amine 5: 4-(2-piperazinoethylamino)-2,2,6,6-tetramethylpiperidine amine 6: 4-(2-morpholinopropylamino)-2,2,6,6-tetramethylpiperidine

(4) TABLE-US-00001 TABLE 1 Phase Loading at Loading at Relative Boiling point of separation 40 C. in 100 C. in CO.sub.2 uptake absorption amine in C. at temperature Example Amine mol/mol mol/mol in mol/mol rate in % pressure (in mbar) in C. 1* MEA 0.45 0.22 0.23 100 69 (10) n.d. 2* TAD ** 0.54 ** ** 79 (10) n.d. 3* Pr-TAD 1.53 0.39 1.14 41 102 (14) 70 4* Bu-TAD 1.38 0.20 1.18 50 251 (1013) 45 5 Amine 1 1.15 0.39 0.76 27 142 (11) >90 6 Amine 2 1.13 0.33 0.80 34 117 (12) 116 7 Amine 3 1.56 0.64 0.92 52 166 (3) >120 8 Amine 4 1.14 0.37 0.77 28 194 (10) >90 9 Amine 5 1.70 0.79 0.91 75 123 (5) >145 10 Amine 6 1.26 0.29 0.97 89 113 (1) 124 *not according to the invention ** solid precipitated during introduction of gas n.d. not determined

(5) In addition, the corrosion rate of the steel C22 (material number 1.0402) in contact with the absorption medium was determined for the absorption media of Examples 1 and 8 by measurement of the potentiodynamic polarization resistance and interpretation via a Tafel plot using the method ASTM G59-97 (2009). The results are shown in Table 2.

(6) TABLE-US-00002 TABLE 2 Example Amine Corrosion rate in mm/year 1 MEA 1.99 8 Amine 4 0.19