# Patent

## Title
Absorbent liquid, and apparatus and method for removing CO2 or H2S from gas with use of absorbent liquid

## Abstract

An absorbent liquid according to the present invention is an absorbent liquid for absorbing CO2 or H2S or both from gas, in which the absorbent liquid includes an alkanolamine as a first compound component, and a second component including a nitrogen-containing compound having in a molecule thereof two members or more selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen or a nitrogen-containing compound having in a molecule thereof all of primary, secondary, and tertiary nitrogens. The absorbent liquid has an excellent absorption capacity performance and an excellent absorption reaction heat performance, as compared to an aqueous solution containing solely an alkanolamine and a nitrogen-containing compound in the same concentration in terms of wt %, and can recover CO2 or H2S or both from gas with smaller energy.

## Background
TECHNICAL FIELD
The present invention relates to an absorbent liquid for removing CO2 (carbon dioxide) or H2S (hydrogen sulfide) or both from gas, and an apparatus and a method for removing CO2 or H2S or both with use of the absorbent liquid.
BACKGROUND ART
In recent years, as one of the causes of global warming, greenhouse effects caused by CO2 are pointed out. From the viewpoint of protecting the earth environment, the problem of greenhouse effects needs to be rapidly solved worldwide. Sources of CO2 are encompassed in any people's fields of activity where fossil fuel is burned, and there have been increasing demands for suppressing the discharge of CO2. For meeting the demands, with respect to power generation plants which use a great amount of fossil fuel, such as thermal power stations, vigorous studies are made on a method in which combustion off-gas of a boiler is brought into contact with, for example, an aqueous solution of alkanolamine to remove and recover CO2 from gas and a method in which the CO2 recovered is stored without being released to the air. An aqueous solution of alkanolamine reacts with not only CO2 (carbon dioxide) but also acidic gas, such as H2S (hydrogen sulfide). Therefore, in chemical industries, for the purpose of removing and recovering general acidic gases, the alkanolamine solution is widely used in refining processes for various gases.
Examples of alkanolamines include monoethanolamine (MEA), ethylaminoethanol (EAE), triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine, and diglycolamine, and, generally, monoethanolamine (MEA) is preferably used.
Further, an effect of a mixture of a plurality of alkanolamines such that the mixture exhibits a performance which cannot be achieved by the individual alkanolamine is disclosed (for example, the performance of a mixture of MEA and AMP is disclosed. Patent Document 1). For improving the alkanolamine in an absorption performance, the use of a cyclic amine, such as piperazine, or a linear amine, such as ethylenediamine, as an absorption auxiliary agent has been proposed (Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5).

    Patent Document 1: Japanese Patent Application Laid-open No. H6-343858
    Patent Document 2: Specification of U.S. Pat. No. 4,336,233
    Patent Document 3: Japanese Patent Application Laid-open No. H1-231921
    Patent Document 4: Japanese Patent Publication No. S61-19286
    Patent Document 5: Specification of U.S. Pat. No. 6,436,174


DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
In recovering a great amount of CO2 in a large-scale plant, an apparatus which can recover CO2 with energy as small as possible is desired. For achieving such an apparatus, an amount of the absorbent liquid circulated and an amount of heat required for desorption of the absorbed CO2 must be reduced. For reducing the amount of the absorbent liquid circulated, it is necessary to increase the absorption capacity of the absorbent liquid per unit amount of the absorbent liquid, and hence the absorbent liquid frequently has an increased amine compound concentration.
However, with respect to the absorbent liquid having an increased amine compound concentration, problems have been pointed out in that the viscosity of the absorbent liquid is increased and in that the absorbent liquid exhibits corrosive properties (Patent Document 4). Among these, the problem of corrosive properties can be solved by the addition of a corrosion inhibitor to the absorbent liquid or appropriate selection of a material for piping, however, the problem of viscosity cannot be easily solved in the general process.
Further, a certain type of amine compound has a low solubility in a solvent so that it cannot be dissolved in an increased concentration. For example, piperazine described in Patent Document 3 has a low solubility in water, and further piperazine carbamate formed by the reaction of piperazine with CO2 has a low solubility in the liquid. Therefore, piperazine can be added only in a limited concentration of 0.8 mol/l or less.
Patent Document 5 has a description showing that an absorbent liquid using a compound containing a nitrogen atom in a ring and having a branched hydroxyl group or a branched alkyl group in a wide range of concentration (0.1 to 50%) is useful, however, this absorbent liquid has a requirement that an alcohol be added to the absorbent liquid.
A known alkanolamine, such as MEA mentioned above, and water can be mixed in an arbitrary ratio and hence, generally, an aqueous solution of an alkanolamine having an increased concentration can be easily obtained. However, with respect to the aqueous solution containing a single type of a certain alkanolamine, the absorption capacity performance is not improved proportionally even when the amine concentration is increased. Accordingly, with respect to a certain type of amine, even when the amine concentration of the absorbent liquid is increased, there cannot be obtained an expected effect such that the amount of the absorbent liquid circulated is reduced. Therefore, for reducing the energy for CO2 recovery, the development of an absorbent liquid, which is not increased in viscosity even when the nitrogen-containing compound concentration of the absorbent liquid is increased, and which has an absorption capacity performance and an absorption reaction heat performance dramatically improved, is desired.
In view of the above problems, a problem of the present invention is to provide an absorbent liquid which is advantageous not only in that, even when the nitrogen-containing compound concentration of the absorbent liquid is increased, the absorbent liquid is not increased in viscosity, but also in that both the absorption capacity performance and the absorption reaction heat performance are dramatically improved, and an apparatus and a method for removing CO2 or H2S or both with use of the absorbent liquid.
Means for Solving Problem
An absorbent liquid for absorbing CO2 or H2S or both from gas according to the present invention includes a first compound component; and a second compound component including a nitrogen-containing compound having in a molecule thereof at least two members selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen, or a nitrogen-containing compound having in a molecule thereof all of primary, secondary, and tertiary nitrogens, wherein the first compound component is any one of compounds represented by following formulae (I) to (III) or a mixture thereof:




in the formulae (I) to (III): x and y respectively satisfy relationship: 1≦x≦5 and 2≦y≦10; and R1, R2, R3, and R4 represent —CiHjOkNl (where i=0 to 10, j=1 to 21, k=0 to 5, and l=0 to 5).

In the absorbent liquid according to the present invention, the second compound component may be a nitrogen-containing compound having a secondary nitrogen in a ring or a nitrogen-containing compound having a tertiary nitrogen in a ring.
In the absorbent liquid according to the present invention, the second compound component may be a nitrogen-containing compound having secondary and tertiary nitrogens in a ring.
In the absorbent liquid according to the present invention, the second compound component may be a nitrogen-containing compound having a nitrogen in a substituent group branching from the ring.
In the absorbent liquid according to the present invention, the nitrogen-containing compound may be a nitrogen-containing compound having a primary nitrogen in a substituent group branching from the ring.
In the absorbent liquid according to the present invention, the second compound component may be a nitrogen-containing compound having three nitrogens or more in a molecule thereof.
In the absorbent liquid according to the present invention, the nitrogen-containing compound may be a nitrogen-containing compound having in a molecule thereof all of primary, secondary, and tertiary nitrogens.
In the absorbent liquid according to the present invention, the second compound component may be any one of nitrogen-containing compounds represented by following formulae (IV) to (XIII) or a mixture thereof:




in the formulae (IV) to (V): R5 and R6 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R7 and R8 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (VI): R9 and R11 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10 represents —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (VII): R9 and R11 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10 and R12 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (VIII): R9 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R13, R14, R15 and R16 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (IX): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10, R15 and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (X): R9 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R13, R14, R16 and R19 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XI): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R17 and R20 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XII): R9 and R21 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R16 and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XIII): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R16 and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

In the absorbent liquid according to the present invention, the second compound component may be any one of nitrogen-containing compounds represented by following formulae (XIV) to (XIX) or a mixture thereof:




in the formula (XIV): R22 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23 and R24 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XV): R25 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23 and R26 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XVI): R23, R27 and R28 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XVII): R22 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23, R24, R27 and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XVIII): R25 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23, R26 and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),





in the formula (XIX): R23, R27, R28 and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5)

In the absorbent liquid according to the present invention, the second compound component may be a nitrogen-containing compound represented by following formula (XX):




in the formula (XX): R30, R32, R33 and R34 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5), and R31 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

In the absorbent liquid according to the present invention, the first compound component may be contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt % and the second compound component may be contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt %, and a total amount of the first compound component and the second compound component may be more than 30 wt % to equal to or less than 90 wt %.
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where each of R1 and R2 is H.
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where x is 2 to 4 and y is 4 to 8.
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where R1 is H and R2 is -CmHnOoNp (where m=1 to 5, n=1 to 11, o=0 to 5, and p=0 to 5).
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where x is 2 to 4, y is 4 to 8, and R2 is CH3, C2H5, C3H7, or C4H9.
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where R1 and R2 represent -CmHnOoNp (where m=1 to 5, n=1 to 11, o=0 to 5, and p=0 to 5).
In the absorbent liquid according to the present invention, the first compound component may be represented by the formula (I), where x is 2, y is 4, R1 is CH3, and R2 is C2H4OH.
An absorbent liquid for absorbing CO2 or H2S or both from gas according to the present invention includes a cyclic amine compound having one nitrogen in a ring.
In the absorbent liquid according to the present invention, the cyclic amine having one nitrogen in a ring may be a cyclic amine having one nitrogen in a 5-membered ring, 6-membered ring, or 7-membered ring.
In the absorbent liquid according to the present invention, the cyclic amine having one nitrogen in a 5-membered ring, 6-membered ring, or 7-membered ring may be pyrrolidine (PR), piperidine (PZ), or hexamethyleneimine (HMI).
In the absorbent liquid according to the present invention, the cyclic amine compound having one nitrogen in a ring may be a nitrogen-containing compound having a primary nitrogen in a substituent group branching from the ring.
In the absorbent liquid according to the present invention, the nitrogen-containing compound having a primary nitrogen in a substituent group branching from the ring may be aminomethylpiperidine (AMPZ) or aminoethylpiperidine (AEPZ).
In the absorbent liquid according to the present invention, the cyclic amine compound having one nitrogen in a ring may be a nitrogen-containing compound having a hydroxyl group in a 5-membered ring, 6-membered ring, or 7-membered ring.
In the absorbent liquid according to the present invention, the nitrogen-containing compound having a hydroxyl group in a 5-membered ring, 6-membered ring, or 7-membered ring may be piperidinol (PDN).
An absorbent liquid includes a mixture of the absorbent liquid according to the present invention, and an alkanolamine.
In the absorbent liquid according to the present invention, the alkanolamine may be monoethanolamine (MEA), ethylaminoethanol (EAE), triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine, diglycolamine, or a mixture thereof.
In the absorbent liquid according to the present invention, the cyclic amine may be contained in an amount in a range from equal to or larger than 5 wt % to equal to or less than 30 wt % and the alkanolamine may be contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt %, and a total amount of the cyclic amine and the alkanolamine may be more than 20 wt % to equal to or less than 90 wt %.
An apparatus for removing CO2 or H2S or both according to the present invention includes an absorption tower that allows gas containing CO2 or H2S or both and an absorbent liquid to be in contact with each other to remove CO2 or H2S or both from the gas; and a regeneration tower that regenerates a solution which has absorbed the CO2 or H2S or both, the absorption tower reusing the solution regenerated at the regeneration tower by removing the CO2 or H2S or both from the solution, wherein the absorbent liquid includes
a first compound component, and
a second compound component including a nitrogen-containing compound having in a molecule thereof at least two members selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen, or a nitrogen-containing compound having in a molecule thereof all of primary, secondary, and tertiary nitrogens,
the first compound component is any one of compounds represented by following formulae (I) to (III) or a mixture thereof:




in the formulae (I) to (III): x and y respectively satisfy relationship: 1≦x≦5 and 2≦y≦10; and R1, R2, R3, and R4 represent —CiHjOkNl (where i=0 to 10, j=1 to 21, k=0 to 5, and l=0 to 5).

A method for removing CO2 or H2S or both implemented in an apparatus for removing CO2 or H2S or both that provides an absorption tower and a regeneration tower, the method includes allowing gas containing CO2 or H2S or both and an absorbent liquid to be in contact with each other in the absorption tower to remove CO2 or H2S or both from the gas; and regenerating a solution which has absorbed the CO2 or H2S or both in the regeneration tower, the absorption tower reusing the solution regenerated at the regeneration tower by removing the CO2 or H2S or both from the solution, wherein the removal of the CO2 or H2S or both is performed by using the absorbent liquid, the absorbent liquid including
a first compound component, and
a second compound component including a nitrogen-containing compound having in a molecule thereof at least two members selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen, or a nitrogen-containing compound having in a molecule thereof all of primary, secondary, and tertiary nitrogens,
the first compound component is any one of compounds represented by following formulae (I) to (III) or a mixture thereof:




in the formulae (I) to (III): x and y respectively satisfy relationship: 1≦x≦5 and 2≦y≦10; and R1, R2, R3, and R4 represent —CiHjOkNl (where i=0 to 10, j=1 to 21, k=0 to 5, and l=0 to 5).

Effect of the Invention
According to the present invention, an absorbent liquid can be provided, the liquid including an alkanolamine as a first nitrogen-containing compound component for absorbing CO2 or H2S or both from gas, and a second component containing a nitrogen-containing compound having in the molecule thereof two members or more selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen or a nitrogen-containing compound having in the molecule thereof all of primary, secondary, and tertiary nitrogens, and the absorbent liquid is advantageous not only in that the absorbent liquid is not increased in viscosity even when the nitrogen-containing compound concentration of the absorbent liquid is high, but also in that the absorbent liquid has an excellent CO2 or H2S removal performance and an excellent absorption reaction heat performance, as compared to an aqueous solution containing solely an alkanolamine and a nitrogen-containing compound in the same concentration in terms of wt %.
Further, when an absorbent liquid having an amine concentration as high as 30 wt % or more is used, an absorbent liquid having an excellent absorption capacity performance and an excellent absorption reaction heat performance can be provided, as compared to an absorbent liquid using solely an amine in the same concentration. Therefore, an amount of the absorbent liquid circulated and an amount of heat required for desorption of the absorbed CO2 or H2S or both can be reduced, as compared to those of an absorbent liquid using solely an amine. When the amount of the absorbent liquid circulated can be reduced, not only can the apparatus be compact, but also only a small amount of heat is required for the desorption, and further the reduction of heat of desorption enables recovery with smaller energy.
In the present invention, the absorbent liquid including a cyclic amine compound having one nitrogen in a ring has an excellent CO2 or H2S removal performance, as compared to a known absorbent liquid including alkanolamine.



BRIEF DESCRIPTION OF DRAWING
FIG. 1 is a schematic diagram of an apparatus for removing CO2.



EXPLANATIONS OF LETTERS OR NUMERALS


    
    
        1 absorption tower
        15 regeneration tower
    
    


BEST MODE(S) FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. The invention is not limited to the embodiments. In addition, constituent elements in the embodiments and examples include those that can be easily assumed by those skilled in the art or that are substantially equivalent.
Embodiments of the Invention
A first absorbent liquid according to the present invention is an absorbent liquid for absorbing CO2 or H2S or both from gas, where the absorbent liquid includes a first compound component, and a second compound component including a nitrogen-containing compound having in the molecule thereof at least two members selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen or a nitrogen-containing compound in the molecule thereof all of primary, secondary, and tertiary nitrogens.
The first compound component is any one of compounds represented by the following [Chemical formula 21] to [Chemical formula 23] or a mixture thereof:




in the formulae (I) to (III): x and y respectively satisfy relationships: 1≦x≦5 and 2≦y≦10; and R1, R2, R3, and R4 represent —CiHjOkNl (where i=0 to 10, j=1 to 21, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (I) used in the present invention include monoethanolamine (MEA), methyldiethanolamine (MDEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), 3-amino-1-propanol (AP), 2-amino-2-methylpropanol (AMP), ethyldiethanolamine (EDEA), 2-methylaminoethanol (MAE), 2-ethylaminoethanol (EAE), 2-n-propylaminoethanol, 2-n-butylaminoethanol (n-BAE), 2-n-pentylaminoethanol, 2-isopropylaminoethanol, 2-sec-butylaminoethanol, 2-isobutylaminoethanol (IBAE), 2-dimethylaminoethanol (DMAE), and 2-diethylaminoethanol (DEAE).
Examples of compounds of the formula (II) used in the present invention include 2,3-diaminopropionic acid (DAPA) and glycine.
Examples of compounds of the formula (III) used in the present invention include 1,2-ethylenediamine.
Two or more of these nitrogen-containing compounds can be used in combination.
In the present invention, with respect to the second compound component, there can be used any one of the following nitrogen-containing compounds: 1) a nitrogen-containing compound having a secondary or tertiary nitrogen in a ring; 2) a nitrogen-containing compound having secondary and tertiary nitrogens in a ring; 3) the nitrogen-containing compound of item 1) or 2) above, which has a nitrogen in a substituent group branching from the ring; 4) the nitrogen-containing compound of item 3) above, which has a primary nitrogen in a substituent group branching from the ring; 5) a nitrogen-containing compound having at least three nitrogens in the molecule thereof; and 6) the nitrogen-containing compound of item 5) above, which has in the molecule thereof at least nitrogens of different types.
While Examples of the nitrogen-containing compounds of items 1) to 6) above are shown in the formulae (IV) to (XX) below, the nitrogen-containing compounds in the present invention are not limited thereto.
The nitrogen-containing compounds represented by the formulae (IV) and (V) are individually a linear nitrogen-containing compound as shown in each formula and have all of primary, secondary, and tertiary nitrogens.
The nitrogen-containing compounds represented by the formulae (VI) to (XIII) are individually a cyclic nitrogen-containing compound and have all of primary, secondary, and tertiary nitrogens.
The nitrogen-containing compounds represented by the formulae (XIV) to (XIX) are individually a cyclic nitrogen-containing compound and have nitrogens at a cyclic portion and a branched portion, of which types are different from each other.
The nitrogen-containing compound represented by the formula (XX) is a cyclic nitrogen-containing compound, and contains at least three nitrogens and has in the molecule thereof at least nitrogens of different types.
Examples of compounds of the formula (IV) below used in the present invention include 4,7-diazo-2-amino-2-ethyl-7-methyloctane.




in the formula (IV): R5 and R6 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R7 and R8 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (V) below used in the present invention include 4,7-diazo-2-amino-2,4-diethyloctane.




in the formula (V): R5 and R6 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R7 and R8 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (VI) below used in the present invention include 1-(2-aminoethyl)piperazine (AEPRZ).




in the formula (VI): R9 and R11 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10 represents —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (VII) below used in the present invention include 1-methyl-2-aminomethylpiperazine.




in the formula (VII): R9 and R11 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10 and R12 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (VIII) below used in the present invention include (2-amino)-(5-dimethylamino)pyrrolidine.




in the formula (VIII): R9 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R13, R14, R15, and R16 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (IX) below used in the present invention include 2-(aminoethyl(methylamino))pyrrolidine.




in the formula (IX): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10, R15, and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (X) below used in the present invention include (1-methyl)(2-amino)-(5-methylamino)pyrrolidine.




in the formula (X): R9 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R13, R14, R16, and R19 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XI) below used in the present invention include (1-methyl)(2-aminoethylamino)pyrrolidine.




in the formula (XI): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R17, and R20 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XII) below used in the present invention include (1-aminomethyl) (4-methylamino)piperidine.




in the formula (XII): R9 and R21 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R16, and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XIII) below used in the present invention include (1-methylaminoethyl)4-aminopiperidine.




in the formula (XIII): R9 and R18 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R14, R16, and R17 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XIV) below used in the present invention include 4-aminopiperidine.




in the formula (XIV): R22 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23 and R24 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XV) below used in the present invention include (1-aminomethyl)piperidine.




in the formula (XV): R25 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23 and R26 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XVI) below used in the present invention include N-methyl-2-aminopiperidine.




in the formula (XVI): R23, R27, and R28 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XVII) below used in the present invention include N,N-dialkyl-4-aminopiperidine.




in the formula (XVII): R22 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23, R24, R27 and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XVIII) below used in the present invention include (N-alkylaminomethyl)piperidine.




in the formula (XVIII): R25 represents —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23, R26, and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XIX) below used in the present invention include (N-alkyl-4-aminoalkyl)piperidine.




in the formula (XIX): R23, R27, R28, and R29 represent —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

Examples of compounds of the formula (XX) below used in the present invention include (1-methyl-aminoethyl)(4-methyl)piperazine.




in the formula (XX): R30, R32, R33, and R34 represent —CiHjOkNl (where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R31 represents —CiHjOkNl (where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5).

With respect to the concentration of the amine component in the first absorbent liquid of the present invention to be brought into contact with gas, it is preferred that the first compound component is contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt % and the second compound component is contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt %, where the total amount of the first compound component and the second compound component is more than 30 wt % to equal to or less than 90 wt %. The total amount is more preferably in a range of from 40 wt % to 70 wt %.
When the amine component concentration falls outside of the above range, as shown in Examples below, the absorbent liquid is inevitably increased in viscosity. In addition, such a concentration makes no contribution to dramatic improvement of the absorption capacity performance or the absorption reaction heat performance.
With respect to the component other than the amine, water is generally used, however, other solvents and a mixture thereof can be also used. Further, a corrosion inhibitor, a deterioration preventing agent, or the like is optionally added.
In the present invention, the temperature of the first absorbent liquid being in contact with gas is generally in a range of from 30° C. to 70° C.
With respect to the conditions for gas usable in the present invention, representative conditions are such that a total pressure is approximately atmospheric pressure and a CO2 concentration is 10%, however, the conditions are not limited thereto.
Examples of gases to be treated by the present invention include coal gas, synthetic gas, coke oven gas, petroleum gas, and natural gas, however, the gas is not limited thereto, and any gas can be used as long as the gas contains acidic gas, such as CO2 or H2S.
With respect to the process which can be employed in the method for removing CO2 or H2S or both from gas in the present invention, there is no particular limitation, and an example of an apparatus for removing CO2 is described below with reference to FIG. 1.
FIG. 1 is a schematic diagram of an apparatus for removing CO2. As shown in FIG. 1, gas is led to an absorption tower 1 through a CO2-containing gas-feed inlet 4. In a packed portion 2, the gas placed in the absorption tower 1 is brought into contact in a counter flow with a CO2 absorbent liquid fed from a nozzle 7, and CO2 is absorbed and removed from the gas by the absorbent liquid, and the resultant gas is discharged through a CO2-removed gas-discharge outlet 5. The absorbent liquid fed to the absorption tower 1 absorbs CO2, and is led to a heat exchanger 14 and a heater 8 and heated and led to a regeneration tower 15. In the regeneration tower 15, the absorbent liquid flows through a nozzle 16 and a packed portion 17 toward the lower portion of the tower. During this time, CO2 is removed to regenerate the absorbent liquid. The regenerated absorbent liquid is led by a pump 9 to the heat exchanger 14 and an absorbent liquid cooler 26 and fed back to the absorption tower 1 through an absorbent liquid feed inlet 6.
On the other hand, in the upper portion of the regeneration tower 15, the CO2 removed from the absorbent liquid is brought into contact with a reflux water fed from the nozzle 18, and cooled by a regeneration tower reflux condenser 23, and, in a reflux drum 21, the CO2 is separated from the reflux water formed by condensing water vapor accompanying the CO2, and led to a CO2 recovery step through a recovered CO2 line 22. The reflux water is fed by a reflux water pump 20 to the regeneration tower 15. The present embodiment briefly describes an overview of the apparatus, and descriptions of some parts of peripheral instruments will be omitted.
By using the first absorbent liquid of the present invention as an absorbent liquid for the above-described apparatus for removing CO2, efficient absorption and removal of CO2 can be achieved.
With respect to the second absorbent liquid of the present invention, the absorbent liquid can include: the first absorbent liquid which includes a first compound component, and a second compound component including a nitrogen-containing compound having in the molecule thereof at least two members selected from a primary nitrogen, a secondary nitrogen, and a tertiary nitrogen or a nitrogen-containing compound having in the molecule thereof all of primary, secondary, and tertiary nitrogens; and a cyclic amine compound having one nitrogen in a ring.
It is preferred that the cyclic amine having one nitrogen in a ring is a cyclic amine having one nitrogen in a 5-membered ring, 6-membered ring, or 7-membered ring.
Examples of the cyclic amines having one nitrogen in a 5-membered ring, 6-membered ring, or 7-membered ring include pyrrolidine (PR) represented by [Chemical formula 41] below, piperidine (PZ) represented by [Chemical formula 42] below, and hexamethyleneimine (HMI).




It is preferred that the cyclic amine compound having one nitrogen in a ring is a nitrogen-containing compound having a primary nitrogen in a substituent group branching from the ring.
Examples of the nitrogen-containing compounds having a primary nitrogen in a substituent group branching from the ring include nitrogen-containing compounds having an aminomethyl group or aminoethyl group in a 5-membered ring, 6-membered ring, or 7-membered ring, represented by [Chemical formula 44] to [Chemical formula 49] below.
Particularly, aminomethylpiperidine (4-(aminomethyl)-piperidine: AMPZ) represented by [Chemical formula 46] below or aminoethylpiperidine (4-(aminoethyl)-piperidine: AEPZ) represented by [Chemical formula 47] below is preferably used, because they exhibit excellent CO2 absorption rate.




Further, it is preferred that the cyclic amine compound having one nitrogen in a ring is a nitrogen-containing compound having a hydroxyl group in a 5-membered ring, 6-membered ring, or 7-membered ring.
Examples of the nitrogen-containing compounds having a hydroxyl group in a 5-membered ring, 6-membered ring, or 7-membered ring include nitrogen-containing compounds represented by [Chemical formula 50] to [Chemical formula 52] below. Particularly, 4-piperidinol (PDN) represented by [Chemical formula 51] is preferably used, because it exhibits excellent CO2 absorption rate.




In the second absorbent liquid of the present invention, a cyclic amine or a mixture thereof can be used, and the absorbent liquid includes a mixture of the absorbent liquid including any one of the above cyclic amines and an alkanolamine which is the above-described first compound component.
Particularly, examples of the alkanolamines include monoethanolamine (MEA), ethylaminoethanol (EAE), triethanolamine, N-methyldiethanolamine (MDEA), diisopropanolamine, and diglycolamine, and, generally, examples include a monoethanolamine (MEA) and a mixture thereof.
With respect to the concentration of the amine component in the absorbent liquid of the present invention to be brought into contact with gas, it is preferred that the cyclic amine is contained in an amount in a range from equal to or larger than 5 wt % to equal to or less than 30 wt % and the alkanolamine is contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt %, where the total amount of the cyclic amine and the alkanolamine is more than 20 wt % to equal to or less than 90 wt %.
When the amine component concentration falls outside the above range, the absorbent liquid is inevitably increased in viscosity. In addition, such a concentration makes no contribution to dramatic improvement of the absorption capacity performance or the absorption reaction heat performance.
Meanwhile, with respect to the component other than the amine, water is generally used, however, solvents other than water and a mixture thereof can be also used. Further, a corrosion inhibitor, a deterioration preventing agent, or the like is optionally added.
In the present invention, the temperature of the absorbent liquid being in contact with gas is generally in a range of from 30° C. to 70° C.
With respect to the conditions for gas usable in the present invention, representative conditions are such that the total pressure is approximately atmospheric pressure and the CO2 concentration is 10%, however, the conditions are not limited thereto.
Like the first absorbent liquid, by using the second absorbent liquid of the present invention as an absorbent liquid for the above-described apparatus for removing CO2 shown in FIG. 1, efficient absorption and removal of CO2 can be achieved.
EXAMPLES
The present invention will be explained below in more detail with reference to Examples.
Examples 1 to 3 and Comparative Examples 1-1 to 4-2
In each of reaction vessels made of glass on the sample side and on the reference side of an apparatus for measuring heat of reaction (Calvet calorimeter), an aqueous solution containing monoethanolamine (MEA) having a primary amino group in an amount of 30 wt % as a first compound component and an aqueous solution containing 1-(2-aminoethyl)piperazine (AEPRZ) having primary, secondary, and tertiary amino groups in an amount of 30 wt % as a second compound component were mixed together to form an absorbent liquid (Example 1).
Further, an aqueous solution containing 2-ethylaminoethanol (EAE) having a secondary amino group in an amount of 30 wt % as a first compound component and an aqueous solution containing 1-(2-aminoethyl)piperazine (AEPRZ) in an amount of 30 wt % as a second compound component were mixed together to form an absorbent liquid (Example 2).
Further, an aqueous solution containing methyldiethanolamine (MDEA) having a tertiary amino group in an amount of 30 wt % as a first compound component and an aqueous solution containing 1-(2-aminoethyl)piperazine (AEPRZ) in an amount of 30 wt % as a second compound component were mixed together to form an absorbent liquid (Example 3).
5 grams of each of the absorbent liquids in Examples 1 to 3 was placed in the vessel, and a temperature of a thermostatic chamber was adjusted to 40° C. While maintaining the temperature at 40° C., test gases were individually brought by bubbling into contact with the respective absorbent liquids on the sample side and on the reference side under atmospheric pressure at a flow rate of 50 ml/min.
With respect to the test gases, a model gas at 40° C. having a composition of CO2: 10 mol %; N2: 90 mol % was used for the sample side, and a gas at 40° C. having a composition of N2: 100 mol % was used for the reference side.
The test gases were continuously allowed to flow, and time derivative values (W) of the amounts of heat generated on the sample side and on the reference side were individually measured, and, from a change with time of a difference between these values (heat flow), a calorific value (kJ) caused due to the CO2 absorption reaction was determined by making a calculation. A point in time when the heat flow value was lowered to 2% of the peak value or less was judged to be a completion (saturation) point of the CO2 absorption reaction, and a period of time from the start of the gas flowing to the completion of the reaction was used as a reaction time (minute). CO2 contained in the CO2 absorbent liquid after completion of the reaction was measured using a CO2 analyzer (total organic carbon analyzer), and a CO2 saturation absorption (mol CO2/kg absorbent liquid) of the absorbent liquid was determined by making a calculation.
From the calorific value, reaction time, and CO2 saturation absorption until completion of the reaction, a CO2 absorption reaction rate (mol CO2/min) and a CO2 absorption reaction heat (kJ/mol CO2) were determined by making a calculation.
In addition to the mixtures of a plurality of amines, with respect to 30 wt % or 60 wt % aqueous solutions of MEA, EAE, MDEA, or AEPRZ as Comparative Examples, similar tests were conducted.
The results of the CO2 saturation absorption amount, CO2 absorption reaction rate, and CO2 absorption reaction heat in the Examples and Comparative Examples are shown in Table 1 below.












TABLE 1








CO2
CO2
CO2




Saturation
Absorption
Absorption



Type and
absorption
reaction
reaction



concentration
amount [mol CO2/kg
rate [×10−5
heat



of amine
absorbent liquid]
mol CO2/min]
[kJ/mol CO2]




















Example 1
MEA 30 wt. % +
4.7
8.8
77.8



AEPRZ 30 wt. %


Example 2
EAE 30 wt. % +
4.1
11.3
73.5



AEPRZ 30 wt. %


Example 3
MDEA 30 wt. % +
3.8
7.6
55.1



AEPRZ 30 wt. %


Comparative
MEA 30 wt. %
2.6
10.1
77.7


Example 1-1


Comparative
MEA 60 wt. %
4.7
9.3
83.6


Example 1-2


Comparative
EAE 30 wt. %
2.2
6.2
69.7


Example 2-1


Comparative
EAE 60 wt. %
3.3
7.4
82.2


Example 2-2


Comparative
MDEA 30 wt. %
1.1
0.9
26.6


Example 3-1


Comparative
MDEA 60 wt. %
0.3
0.3
96.1


Example 3-2


Comparative
AEPRZ 30 wt. %
2.4
10.0
67.7


Example 4-1


Comparative
AEPRZ 60 wt. %
3.5
11.7
79.3


Example 4-2









As can be seen from Table 1, when the 30 wt % absorbent liquids (Comparative Examples 1-1, 2-1, 3-1, and 4-1) and 60 wt % absorbent liquids (Comparative Examples 1-2, 2-2, 3-2, and 4-2) comprised of MEA, EAE, MDEA, or AEPRZ are compared with each other in respect of the performance, the CO2 saturation absorption amount performance and the CO2 reaction heat performance are not proportional to the amine concentration. From this, it is apparent that, with respect to the aqueous solution containing a single type of amine, the increase of the amine concentration of the aqueous solution cannot be expected to satisfactorily improve the performance.
In contrast, it has been found that the mixed absorbent liquid of MEA and AEPRZ (Example 1), the mixed absorbent liquid of EAE and AEPRZ (Example 2), and the absorbent liquid of MDEA and AEPRZ (Example 3) individually have both an excellent CO2 absorption capacity performance and a CO2 absorption reaction heat performance, as compared to the aqueous solutions each containing solely an alkanolamine or amine compound (Comparative Examples 1-2, 2-2, 3-2, and 4-2) in the same concentration in terms of wt %.
For example, with respect to the absorbent liquid in Example 2 including EAE 30% by weight+AEPRZ 30% by weight, the CO2 absorption capacity was increased by 20% and the CO2 absorption reaction heat was reduced by 10%, as compared to those of the absorbent liquid in Comparative Example 2-2 including EAE 60 wt %, which is one of the constituents of the absorbent liquid in Example 2, and the CO2 absorption capacity was increased by 15% and the CO2 absorption reaction heat was reduced by 7%, as compared to those of the absorbent liquid in Comparative Example 4-2 including AEPRZ 60 wt %, which is one of the constituents of the absorbent liquid in Example 2. From this, it is found that the performance is remarkably improved by the effect of mixing.
The energy required for the recovery of CO2 is largely determined by a factor contributing to the CO2 absorption capacity performance and a factor contributing to the CO2 absorption reaction heat performance. Therefore, the improvement of the above performance by the present invention enables a great saving of energy.
Examples 5 to 10 and Comparative Examples 5 and 6
Using absorbent liquids (Examples 5 to 9) each including solely a cyclic amine of pyrrolidine (PR) represented by the [Chemical formula 41] above (Example 5), piperidine (PZ) represented by the [Chemical formula 42] above (Example 6), 4-(aminomethyl)-piperidine (AMPZ) represented by the [Chemical formula 46] above (Example 7), hexamethyleneimine (HMI) represented by the [Chemical formula 43] above (Example 8), or 4-piperidinol (PDN) represented by the [Chemical formula 51] above (Example 9), and an absorbent liquid (Example 10) including a mixture (50:3) of EAE and AMPZ as secondary amines, an absorption rate and an absorption rate ratio were determined.
As Comparative Examples, using as an alkanolamine monoethanolamine (MEA) which is primary (Comparative Example 6) and ethylaminoethanol (EAE) which is secondary (Comparative Example 5), similar evaluations were made.
An absorption rate ratio was determined using MEA in Comparative Example 6 as a reference.
The results are shown in Table 2 below. In Table 2 below, an amine concentration, a CO2 partial pressure, CO2 absorption rate, and an absorption rate ratio are shown.












TABLE 2









CO2




Amine
CO2
Absorption



concen-
Partial
rate



tration
pressure
(kmol/s · m2) ×
Absorption



mol/L
kPa
106
rate ratio





















Example 5
PR
1.4
1.0
2.5
2.6


Example 6
PZ
1.4
1.0
1.9
1.9


Example 7
AMPZ
1.4
1.0
1.8
1.9


Example 8
HMI
1.4
1.0
1.8
1.8


Example 9
PDN
1.4
1.0
1.6
1.6


Example 10
EAE +
1.4
1.0
1.2
1.2



AMPZ


Comparative
EAE
1.4
1.0
1.1
1.1


Example 5


Comparative
MEA
1.4
1.0
0.98
1.0


Example 6









As can be seen from Table 2, each of the absorbent liquids in Examples 5 to 10 has more excellent absorption rate than those of MEA and EAE in the Comparative Examples.
Examples 11 and 12 and Comparative Example 7
Among the above amines, using AMPZ (Example 11) or PDN (Example 12), gas-liquid equilibrium was measured. As a Comparative Example, a similar evaluation was made using MEA (Comparative Example 7).
Conditions for measurement are as follows. Absorption conditions were such that, at the bottom of the absorption tower, the temperature was 40° C. and the CO2 partial pressure was 9.8 kPa. On the other hand, regeneration conditions were such that, at the bottom of the regeneration tower, the temperature was 120° C. and the CO2 partial pressure was 9.8 kPa.
The results are shown in Table 3 below.











TABLE 3










CO2 Loading
CO2



Amine
molCO2/mol amine
Loading












concentration
Absorption
Absorption
difference



mol/L
condition *1
condition *2
(molCO2/mol amine)
















Example 11
AMPZ
1.0
1.15
0.65
0.5


Example 12
PDN
1.0
0.74
0.27
0.47


Comparative
MEA
1.0
0.61
0.2
0.4


Example 7





*1 Absorption conditions: At bottom of absorption tower, temperature: 40° C.; CO2 partial pressure: 9.8 kPa


*2 Regeneration conditions: At bottom of regeneration tower, temperature: 120° C.; CO2 partial pressure: 9.8 kPa






As can be seen from Table 3, in the gas-liquid equilibrium, AMPZ and PDN are individually more excellent in the CO2 loading than MEA (Comparative Example 7), which confirms that they achieve excellent absorption and regeneration of CO2.
INDUSTRIAL APPLICABILITY
As described above, the absorbent liquid of the present invention achieves both the reduction of the amount of the absorbent liquid circulated and the reduction of the amount of heat required for dissociation of the absorbed CO2, and therefore is advantageously used in removal and recovery of CO2 (carbon dioxide) or H2S (hydrogen sulfide) from gas discharged from plant facilities including various boilers.

## Claims

1. An absorbent liquid for removing CO2 or H2S or both from a gas, comprising:
a first compound component including at least one member selected from the group consisting of 2-methylaminoethanol, 2-ethylaminoethanol, 2-n-propylaminoethanol, 2-n-butylaminoethanol, 2-n-pentylaminoethanol, 2-isopropylaminoethanol, 2-sec-butylaminoethanol, or 2-isobutylaminoethanol, and
a second compound component including at least one member selected from the group consisting of 1-(2-aminoethyl)piperazine and (1-methylaminoethyl)-4-methylpiperazine,
wherein
the first compound component is contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt % and the second compound component is contained in an amount in a range from equal to or larger than 15 wt % to equal to or less than 45 wt %, and
a total amount of the first compound component and the second compound component is more than 30 wt % to equal to or less than 90 wt %.

2. An apparatus for removing CO2 or H2S or both from a gas, comprising:
an absorption tower that allows gas containing CO2 or H2S or both and an absorbent liquid to be in contact with each other to remove CO2 or H2S or both from the gas; and
a regeneration tower that regenerates a solution which has absorbed the CO2 or H2S or both, the absorption tower reusing the solution regenerated at the regeneration tower by removing the CO2 or H2S or both from the solution,

wherein said absorbent liquid is an absorbent liquid according to claim 1.

3. A method for removing CO2 or H2S or both from a gas, comprising:
contacting gas containing CO2 or H2S or both with an absorbent liquid according to claim 1 in an absorption tower to remove CO2 or H2S or both from the gas, thereby producing a solution which has absorbed the CO2 or H2S or both; and
regenerating the solution which has absorbed the CO2 or H2S or both in a regeneration tower, and
causing said absorption tower to reuse the solution, regenerated at the regeneration tower by removing the CO2 or H2S or both from the solution, to remove CO2 or H2S or both from gas containing CO2 or H2S or both.