Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Reexamination Certificate
1998-11-06
2002-12-31
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
C423S229000
Reexamination Certificate
active
06500397
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method for removing CO
2
(carbon dioxide) from a combustion exhaust gas. More specifically, it relates to a method for removing CO
2
from a combustion exhaust gas under atmospheric pressure by the use of a specific mixed aqueous solution containing an amine.
In recent years, a greenhouse effect by CO
2
is indicated as one cause of the warming phenomenon of the earth, and its prompt resolution is globally required in order to protect earth circumstances. The generation sources of CO
2
extend in active fields of all humans in which fossil fuels are burned, and there is a tendency that the discharge regulation of CO
2
will be further tightened in the future. Thus, for power generation facilities such as thermoelectric power plants in which a large amount of the fossil fuel is used, there are energetically researched a method for removing and recovering CO
2
from a combustion exhaust gas by bringing the combustion exhaust gas coming from a boiler into contact with an aqueous alkanolamine solution or the like, and a method for storing the recovered CO
2
without discharging it into the atmosphere.
Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, dimethyldiethanolamine, diisopropanolamine and diglycolamine, and in general, monoethanolamine (abbreviated to “MEA”) is preferably used.
However, even if the above-mentioned aqueous alkanolamine solution typified by MEA is used as an absorbing solution for absorbing/removing CO
2
from a combustion exhaust gas, the effect of the alkanolamine is not always satisfactory in view of an amount of absorbed CO
2
per predetermined amount of the aqueous alkanolamine solution having a predetermined concentration, an amount of absorbed CO
2
per unit amine mole of the aqueous alkanolamine solution having a predetermined concentration, an absorption rate of CO
2
at a predetermined concentration, heat energy required to recover the aqueous alkanolamine solution after the absorption, and the like.
In the meantime, for the separation of an acidic gas from various mixed gases by the use of an amine compound, many techniques are known.
Japanese Patent Application Laid-open No. 100180/1978 discloses a method for removing an acidic gas which comprises bringing a usually gaseous mixture into contact with an amine-solvent liquid absorbent comprising
(1) an amine mixture comprising at least 50 mole % of a steric hindrance amine constituting a part of a ring and having at least one secondary amino group bonded to either of a secondary carbon atom or a tertiary carbon atom or a primary amino group bonded to the tertiary carbon atom, and at least about 10 mole % of the tertiary amino-alcohol, and
(2) a solvent for the above-mentioned amine mixture which functions as a physical absorbent for the acidic gas. Usable examples of the steric hindrance amine include 2-piperidine ethanol [2-(2-hydroxyethyl)-piperidine] and 3-amino-3-methyl-1-butanol, and a usable example of the tertiary amino-alcohol is 3-dimethylamino-1-propanol. Furthermore, an example of the solvent is a sulfoxide compound which may contain water in an amount of 25% by weight or less, and an example of a gas to be treated is “a usually gaseous mixture containing carbon dioxide and hydrogen sulfide at high concentrations, for example, 35% Of CO
2
and 10-12% of H
2
S” on page 1, left upper column of the same gazette. In the undermentioned examples, CO
2
itself is used.
In Japanese Patent Application Laid-open No. 71819/1986, there is described a composition for the scraping of an acidic gas which contains a non-aqueous solvent such as a steric hindrance amine or sulfolane. As an example of the primary monoamino alcohol of the steric hindrance, 2-amino-2-methyl-1-propanol (abbreviated to AMP) is exemplified and used. In examples, CO
2
and nitrogen as well as CO
2
and helium are used. Furthermore, as absorbents, an aqueous solution of an amine and potassium carbonate, and the like are used. The use of water is also referred to. In addition, this gazette describes the advantage of the steric hindrance amine in the absorption Of CO
2
by reaction formulae.
In Chemical Engineering Science, Vol. 41, No. 4, pp. 997-1,003, there is disclosed a carbon dioxide gas absorption behavior of an aqueous AMP solution which is a hindered amine. As gases to be absorbed, CO
2
and a mixture of CO
2
and nitrogen at atmospheric pressure are used.
Chemical Engineering Science, Vol. 41, No. 4, pp. 405-408 has reported absorption rates of an aqueous solution of a hindered amine such as AMP and an aqueous solution of a straight-chain amine such as MEA to CO
2
and H
2
S in the vicinity of ordinary temperature. According to this report, a large difference is not present between both the aqueous solutions, in the case that the partial pressure of CO
2
is 1 atm and the concentrations of the aqueous solutions are from 0.1-0.3 mole. However, it is apparent that when the concentrations of the aqueous solutions are 0.1 mole and the partial pressure of CO
2
is decreased to 1, 0.5 and 0.05 atm, the absorption rate of AMP deteriorates more largely than that of MEA at 0.05 atm.
U.S. Pat. No. 3,622,267 discloses a technique in which an aqueous mixture containing methyldiethanolamine and monoethylmonoethanolamine is used to purify a highpartial pressure CO
2
contained in a synthetic gas such as a partially oxidized gas of a crude oil or the like, for example, a synthetic gas containing 30% of CO
2
at 40 atm.
German Laid-open Patent No. 1,542,415 discloses a technique in which a monoalkylalkanolamine or the like is added to a physical or chemical absorbent in order to improve the absorption rate of CO
2
, H
2
S and COS. Similarly, German Laid-open Patent No. 1,904,428 discloses a technique in which monomethylethanolamine is added for the purpose of improving the absorption rate of methyldiethanolamine.
U.S. Pat. No. 4,336,233 discloses a technique in which, for the purification of a natural gas, a synthetic gas or a gasified coal gas, a 0.81-1.3 mole/liter aqueous piperazine solution is used as a wash liquid, or piperazine is used in the state of an aqueous solution together with a solvent such as methyldiethanolamine, triethanolamine, diethanolamine or monomethylethanolamine as a wash liquid;
Similarly, Japanese Patent Application Laid-open No. 63171/1977 discloses a CO
2
absorbent obtained by adding piperazine or a piperazine derivative such as hydroxyethylpiperazine as an accelerator to a tertiary alkanolamine, a monoalkylalkanolamine or the like.
OBJECT AND SUMMARY OF THE INVENTION
As described above, a method for efficiently removing CO
2
from a combustion exhaust gas has been heretofore desired. In particular, in the case that the combustion exhaust gas is treated with an aqueous solution containing a CO
2
absorbent at a certain concentration, it is an urgent serious problem to select an absorbent which is capable of absorbing a large amount of CO
2
per unit mole of the absorbent and absorbing a large amount of CO
2
per unit volume of the aqueous solution and which has a high absorption rate. Furthermore, another requirement of the absorbent is to permit the separation of CO
2
and the recovery of the absorbing solution with a small amount of heat energy, after the absorption of CO
2
. Above all, it is desired to improve the absorption rate of the absorbent having a large CO
2
absorption power but a low absorption rate.
In view of the above-mentioned problems, the present inventors have intensively investigated an absorbent for use in the removal of CO
2
from a combustion exhaust gas. As a result, they have found that the employment of a specific hindered amine is particularly effective, and thus the present invention has now been completed.
That is, the present invention is directed to a method for removing carbon dioxide from a combustion exhaust gas which comprises the step of bringing the combustion exhaust gas under atmospheric pressure into contact with an aqueous solution of
Iijima Masaki
Karasaki Mutsunori
Mimura Tomio
Mitsuoka Shigeaki
Seto Touru
Bos Steven
Reed Smith LLP
The Kansai Electrical Power Co., Inc.
Vanoy Timothy C
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