Title of Invention: ABSORBING SOLUTION FOR SEPARATING AND
CAPTURING CARBON DIOXIDE, AND METHOD FOR SEPARATING AND CAPTURING
CARBON DIOXIDE IN WHICH SAME IS USED
Technical Field
[0001]
The present invention relates to absorbing liquids
for separating and capturing carbon dioxide from a carbon
10 dioxide-containing gas, and methods for separating and capturing
carbon dioxide from a carbon dioxide-containing gas using the
absorbing liquids.
Background Art
15 [0002]
Recent years have seen climate changes and natural
disasters likely due to global warming significantly affecting
agricultural production, dwelling environments, and energy
consumption. Global warming is believed to be caused by increased
20 greenhouse gases in the atmosphere accompanying the expansion of
human activities, such as carbon dioxide, methane, nitrous oxide,
and chlorofluorocarbons. Among these greenhouse gases, carbon
dioxide in the atmosphere is considered to be the primary cause,
and taking measures to reduce emissions of carbon dioxide into the
25 atmosphere is a worldwide agenda.
[0003]
The sources of carbon dioxide include thermal power
plants using fuels such as coal, heavy oil, and natural gas,
ironworks blast furnaces for reducing iron oxide with coke,
30 ironworks converters for burning carbon contained in pig iron to
manufacture steel, factory boilers, and cement plant kilns, as
well as transport equipment including automobiles, marine vessels,
and aircraft using fuels such as gasoline, heavy oil, and light
oil. Except for transport equipment, the sources above are
35 stationary facilities where it is thus easy to take measures to
-2-
reduce emissions of carbon dioxide into the atmosphere.
[0004]
Several methods for separating and capturing carbon
dioxide from gases emitted from the sources listed above are
5 known.
[0005]
For example, a method for absorbing carbon dioxide by
bringing a carbon dioxide-containing gas into contact with an
aqueous solution of an alkanolamine in an absorption tower is
10 known. Examples of known alkanolamines include monoethanolamine,
diethanolamine, triethanolamine, methyl diethanolamine,
diisopropanolamine, and diglycolamine, and of these,
monoethanolamine is widely used.
15
[0006]
The use of aqueous solutions of these alkanolamines as
an absorbing liquid for carbon dioxide, however, requires the use
of expensive corrosion-resistant steel or requires lowering the
concentration of the amine in the absorbing liquids because
primary amines such as monoethanolamine severely corrode
20 materials of equipment. The absorbed carbon dioxide is typically
desorbed and regenerated by heating the absorbing liquid to about
120°C in a regeneration tower, but this method ends up consuming
a large amount of energy in capturing carbon dioxide per unit
weight because the use of the alkanolamines is unsatisfactory in
25 terms of the amount of absorbed carbon dioxide in the absorption
tower and the amount of desorbed carbon dioxide in the
regeneration tower.
[0007]
In an age in which reducing C02 emissions and saving
30 energy and natural resources are being sought, large energy
consumption in separating and capturing carbon dioxide has been a
major constraint on practical use of the technology, and
techniques for separating and capturing carbon dioxide with less
energy need to be developed.
35 [0008]
-3-
As an example of prior art techniques for separating
and capturing carbon dioxide using less energy, PTL 1, for
example, discloses a method for removing carbon dioxide from a
combustion exhaust gas by bringing an aqueous solution of a
5 specific hindered amine into contact with a combustion exhaust
gas at atmospheric pressure. The Examples of PTL 1 disclose Nmethylaminoethanol
and N-ethylaminoethanol as hindered amines,
and also other amines, such as 2-isopropylaminoethanol, which is
not used in the Examples though.
10 [0009]
PTL 2 discloses an absorbing liquid that contains a
mixture of multiple alkanolamines and that achieves the highest
performance taking advantage of the characteristics of each amine,
and a method for absorbing carbon dioxide.
15 [0010]
These absorbing liquids disclosed in PTL 1 and 2,
however, cannot sufficiently reduce the energy required for
separating and capturing carbon dioxide. In PTL 3, studies were
conducted on the use of a non-aqueous organic compound such as an
20 alcohol instead of an aqueous liquid, which uses water with a
large specific heat capacity, as a solvent. Because the use of an
alcohol, for example, instead of water lowers the specific heat,
and carbon dioxide is once converted to unstable alkyl carbonate
in the steps of separating and capturing carbon dioxide, the use
25 of an alcohol is expected to improve low-temperature desorption.
Nonetheless, .an absorbing liquid of such a composition exhibits
extremely low C02 absorption efficiency and requires absorption of
carbon dioxide to be performed at low temperatures in the range
of 20°C to 25°C, meaning that extra energy for cooling in
30 absorption is necessary.
[0011]
PTL 4 and 5 propose an absorbing liquid of a two-phase
separation system. After having absorbed an acidic compound such
as carbon dioxide, the absorbing liquid separates into a phase
35 rich in the acidic compound and a phase poor in the acidic
-4-
compound. From these phases, the phase rich in the acidic
compound is separated with, for example, a decantation equipment,
and only from the phase rich in the acidic compound, the acidic
compound is desorbed in an effort to reduce the amount of the
5 absorbing liquid to be heated and energy required in desorption.
10
15
However, a significant amount of the acidic compound also remains
in the phase poor in the acidic compound, and the capture
efficiency is in fact unsatisfactory.
Citation List
Patent Literature
[0012)
PTL 1: Patent No. 2871334
PTL 2: Patent No. 5452222
PTL 3: JP2012-236165A
PTL 4: JP2009-529420A
PTL 5: JP2010-207809A
Summary of Invention
20 Technical Problem
25
[ 0013)
An object of the present invention is to provide
absorbing liquids and methods for separating and capturing carbon
dioxide highly efficiently at lower energy costs.
Solution to Pr.oblem
[0014)
The present inventors conducted extensive research to
achieve the object, and found that an absorbing liquid comprising
30 at least one specific alkanolamine, a low-molecular-weight diol
compound and/or glycerin, and water can improve the desorption
rate and regeneration efficiency of carbon dioxide at low
temperatures, thereby efficiently separating and capturing carbon
dioxide from a carbon dioxide-containing gas. The inventors
35 conducted further research based on these findings, and completed
-5-
the present invention.
[ 0015 J
Specifically, the present invention provides the
following absorbing liquids for separating and capturing carbon
5 dioxide, and methods for separating and capturing carbon dioxide.
[0016]
Item 1.
An absorbing liquid for separating and capturing carbon
dioxide from a carbon dioxide-containing gas, the liquid
10 comprising:
at least one alkanolamine represented by formula (1)
[0017]
15 wherein R1 represents hydrogen or C1_4 alkyl, R2 and R3 are
identical or different and each represent hydrogen or C1_3 alkyl,
R1
, R2
, and R3 are not all hydrogen, and n is 1 or 2;
a low-molecular-weight dial compound and/or glycerin;
and
20 water.
Item 2.
The absorbing liquid according to Item 1, wherein R1
represents hydrogen, methyl, ethyl, n-propyl, isopropyl, or n-
25 butyl, R2 and R3 are identical or different and each represent
hydrogen or methyl, and n is 1 or 2.
Item 3.
The absorbing liquid according to Item 1 or 2, wherein
30 the alkanolamine represented by formula (1) is an amine mixture
of
-6-
(I) an alkanolarnine wherein R1 represents methyl, ethyl,
n-propyl, isopropyl, or n-butyl, R2 and R3 each represent hydrogen,
and n is 1 or 2, and
(II) an alkanolamine wherein R1 represents hydrogen, R2
5 and R3 each represent methyl, and n is 1.
Item 4.
The absorbing liquid according to Item 3, wherein the
alkanolamine represented by formula (1) is an amine mixture of N-
10 isopropy1arninoethanol and 2-arnino-2-methyl-1-propanol.
Item 5.
The absorbing liquid according to any one of Items 1 to
4, wherein the low-molecular-weight diol compound and/or glycerin
15 has a concentration of 5 to 30 wt%.
Item 6.
The absorbing liquid according to any one of Items 1 to
4, wherein the low-molecular-weight diol compound and/or glycerin
20 is ethylene glycol and has a concentration of 5 to 20 wt%.
Item 7.
A method for separating and capturing carbon dioxide
from a carbon dioxide-containing gas, the method comprising the
25 following steps A and B:
30
step A of bringing the absorbing liquid according to
any one of Items 1 to 6 into contact with a carbon dioxidecontaining
gas to obtain the absorbing liquid that has absorbed
carbon dioxide from the carbon dioxide-containing gas; and
step B of heating the absorbing liquid that has
absorbed carbon dioxide obtained in step A to desorb and
regenerate carbon dioxide from the absorbing liquid and capturing
the desorbed carbon dioxide.
35 Item 8.
-7-
The method according to Item 7, wherein the absorbing
liquid that has absorbed carbon dioxide is heated at a
temperature of 80 to 95°C in step B to desorb carbon dioxide.
5 Advantageous Effects of Invention
[0018]
The present invention enables absorbing liquids formed
of aqueous liquids of the same amine composition to desorb carbon
dioxide at lower temperatures. The present invention can also
10 capture carbon dioxide with lower energy consumption. This
reduces the energy required for separating and capturing carbon
dioxide, and captures carbon dioxide efficiently with low energy
consumption. Because of its significantly improved performance in
desorbing carbon dioxide at low temperatures, the invention
15 enables the use of "low-grade waste heat," which is normally
discarded, and can substantially reduce energy required for
separating and capturing carbon dioxide.
Description of Embodiments
20 [ 0019]
The following describes the present invention in detail.
[0020]
Absorbing Solution for Separating and Capturing Carbon Dioxide
The absorbing liquid of the present invention
25 comprises:
at least one alkanolamine represented by formula (1)
[0021]
[0022]
30 wherein R1 represents hydrogen or C1 _4 alkyl, R2 and R3 are
identical or different and each represent hydrogen or c1_3 alkyl,
-8-
R1
, R2
, and R3 are not all hydrogen, and n is 1 or 2;
a low-molecular-weight diol compound and/or glycerin;
and
water.
5 [0023]
R1 in formula (1) may be any of hydrogen or C1_4 linear
or branched alkyl, and may specifically be hydrogen, methyl,
ethyl, n-propyl, isopropyl, n-butyl, or the like. Of these,
hydrogen, ethyl, n-propyl, isopropyl, and n-butyl are preferable,
10 with isopropyl being more preferable.
[0024]
In formula (1), n is 1 or 2, and more preferably 1.
[0025]
In formula (1), R2 and R3 may be any of hydrogen or c1_3
15 linear or branched alkyl, and may specifically be hydrogen,
methyl, ethyl, n-propyl, or isopropyl. Of these, hydrogen and
methyl are preferable.
[0026]
Specific alkanolamines represented by formula (1)
20 include N-ethylaminoethanol, N-n-propylaminoethanol, Nisopropylaminoethanol,
N-n-butylaminoethanol, 2-amino-1-propanol,
N-isobutylaminoethanol, 2-amino-2-methyl-1-propanol, 3-
ethylamino-1-propanol, 3-n-propylamino-1-propanol, 3-
isopropylamino-1-propanol, 3-n-butylamino-1-propanol, and 3-
25 isobutylamino-1-propanol. These can also be used on an industrial
scale.
[0027]
The absorbing liquid of the present invention comprises
at least one alkanolamine represented by formula (1) or an amine
30 mixture containing two or more alkanolamines represented by
formula (1).
[0028]
Examples of amine mixtures include amine mixtures of
(I) an alkanolamine wherein R1 represents methyl, ethyl, n-propyl,
35 isopropyl, or n-butyl, R2 and R3 each represent hydrogen, and n is
-9-
1 or 2, and (II) an a1kanolamine wherein R1 represents hydrogen,
R2 and R3 each represent methyl, and n is 1. Of these, an amine
mixture of N-isopropylaminoethanol and 2-amino-2-methyl-1-
propanol is preferable.
5 [0029]
The following describes the total amount of
alkanolamine(s) in the absorbing liquid of the present invention.
[0030]
Typically, as the concentration of the amine component
10 increases, the absorption amount, absorption rate, desorption
amount, and desorption rate of carbon dioxide per unit volume of
the liquid increase, and from the standpoint of energy
consumption, plant equipment size, and efficiency, a higher
concentration of the amine component is preferable. However, a
15 weight concentration of the amine component exceeding 70% is
likely to cause problems such as decreases in the absorption
amount of carbon dioxide, decreases in the degree of mixedness of
the amine component, and increases in viscosity, perhaps due to
decreased surfactant action of water.
20 [0031]
In the absorbing liquid of the present invention as
well, the total amount of alkanolamine(s) is preferably 60 wt% or
less, given the problems such as decreases in the degree of
mixedness of the amine component and increases in viscosity. From
25 the standpoint of practical absorption performance and desorption
performance., the total amount of alkanolamine (s) is preferably 30
wt% or more. The total amount of the alkanolamine(s) in the
absorbing liquid of the present invention is selected from the
range of preferably 30 to 60 wt%, more preferably 30 to 55 wt%,
30 and particularly preferably 40 to 55 wt%.
[0032]
Examples of the low-molecular-weight dial compound
include C2_8 aliphatic diol compounds (e.g., ethylene glycol,
diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-
35 propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol),
-10-
and ethylene glycol is preferable.
[0033]
The absorbing liquid of the present invention comprises
at least either a low-molecular-weight diol compound or glycerin.
5 When a low-molecular-weight diol compound is added, the lowmolecular-
weight diol compound for use may be a single lowmolecular-
weight diol compound or a combination of two or more
low-molecular-weight diol compounds. Of the low-molecular-weight
diol compound and glycerin, ethylene glycol is preferable. The
10 total amount of the low-molecular-weight diol compound and
glycerin in the absorbing liquid of the present invention is
preferably 5 to 30 wt%, and more preferably 5 to 20 wt%.
[0034]
The absorbing liquid of the present invention
15 comprises water.
[0035]
The content of water in the absorbing liquid of the
present invention is not particularly limited, and the remaining
liquid may be water.
20 [0036]
The water for use in the absorbing liquid of the
present invention is not particularly limited, and distilled
water, ion-exchanged water, tap water, groundwater, etc. can be
suitably used.
25 [0037]
.The absorbing liquid of the present invention may
optionally comprise components other than the alkanolarnine
represented by formula (1), the low-molecular-weight diol,
glycerin, and water as long as the effects of the present
30 invention are not impaired. Other components include stabilizers
for ensuring chemical or physical stability of the liquid (e.g.,
side reaction inhibitors such as antioxidants), degradation
inhibitors for inhibiting the degradation of materials of devices
or equipment used with the liquid of the present invention (e.g.,
35 corrosion inhibitors), and antifoarning agents (e.g., surfactants).
-11-
The content of these components is not particularly limited as
long as the effects of the present invention are not impaired.
[0038]
Examples of the carbon dioxide-containing gas include
5 exhaust gases from thermal power plants using fuels such as heavy
oil and natural gas, factory boilers, cement plant kilns,
ironworks blast furnaces for reducing iron oxide with coke, and
ironworks converters for burning carbon contained in pig iron to
manufacture steel. The concentration of carbon dioxide in the gas
10 is not particularly limited, and may typically be about 5 to 30
val%, and particularly about 10 to 20 val%. The concentration of
carbon dioxide within these numerical ranges allows the effects
of the present invention to be suitably achieved. The carbon
dioxide-containing gas may contain impurity gases derived from
15 sources such as water vapor and CO, in addition to carbon dioxide.
[0039]
Method for Absorbing and Capturing Carbon Dioxide
The method for separating and capturing carbon dioxide
of the present invention comprises step A of bringing the
20 absorbing liquid into contact with a carbon dioxide-containing
gas to obtain the absorbing liquid that has absorbed carbon
dioxide from the carbon dioxide-containing gas, and step B of
heating the absorbing liquid that has absorbed carbon dioxide
obtained in step A to desorb and regenerate carbon dioxide from
25 the absorbing liquid, and capturing the desorbed carbon dioxide.
[0040]
Step A: Step of Absorbing Carbon Dioxide
In the present invention, the absorbing liquid is
brought into contact with a carbon dioxide-containing gas, and
30 the liquid thereby absorbs carbon dioxide. The method for
bringing the absorbing liquid into contact with a carbon dioxidecontaining
gas to absorb carbon dioxide is not particularly
limited, and examples include a method comprising bubbling a
carbon dioxide-containing gas in the absorbing liquid to absorb
35 carbon dioxide, a method comprising mist-spraying the absorbing
-12-
liquid over a carbon dioxide-containing gas stream (misting or
spraying method), and a method comprising bringing a carbon
dioxide-containing gas into countercurrent contact with the
absorbing liquid in an absorption tower containing a porcelain or
5 metal mesh filler.
[0041]
Carbon dioxide in a carbon dioxide-containing gas is
absorbed into the absorbing liquid at a temperature of typically
about 60°C or less, preferably about 50°C or less, and more
10 preferably in the range of about 20 to 45°C.
[0042]
As the temperature at which carbon dioxide in a carbon
dioxide-containing gas is absorbed into the absorbing liquid
decreases, the absorption amount of carbon dioxide increases.
15 However, how far the temperature should be lowered is determined
in accordance with the gas temperature of the carbon dioxidecontaining
gas, the heat recovery target, and the like. Because
the absorption of carbon dioxide by amines is an exothermic
reaction, increasing the absorption amount of carbon dioxide at
20 low temperatures requires energy for cooling the absorbing liquid.
Thus, the step of absorbing carbon dioxide is typically performed
at a temperature of around 40°C.
[0043]
The step of absorbing carbon dioxide is typically
25 performed under substantially atmospheric pressure. Although the
absorption step can be performed under increased pressure to
increase the performance in absorbing carbon dioxide, the step is
preferably performed under atmospheric pressure to save energy
consumption for increasing pressure.
30 [0044]
Step B: Step of Desorbing and Regenerating Carbon Dioxide
In the present invention, the absorbing liquid that has
absorbed carbon dioxide obtained in step A is heated to desorb
carbon dioxide, and the desorbed pure or high-concentration
35 carbon dioxide is captured.
-13-
[0045]
Examples of the method for desorbing and regenerating
carbon dioxide from the absorbing liquid that has absorbed carbon
dioxide include a method comprising heating and boiling the
5 absorbing liquid in a vessel to desorb carbon dioxide, and a
method comprising heating the absorbing liquid in a tray
distillation tower, spray tower, or regeneration tower containing
a porcelain or metal mesh filler to increase the liquid contact
interface. These methods desorb carbon dioxide present in the
10 form of bicarbonate ions in the absorbing liquid and regenerate
the carbon dioxide as molecular carbon dioxide.
[0046]
When carbon dioxide is desorbed and regenerated from an
absorbing liquid, and the absorbing liquid is a conventional
15 aqueous liquid, the absorbing liquid is set to about 100 to 120°C.
As the temperature of the absorbing liquid rises, the amount of
desorbed carbon dioxide increases. However, raising the
temperature requires additional energy to heat the absorbing
liquid. The temperature is thus determined depending on the gas
20 temperature, heat recovery target, and the like in the process of
exhausting carbon dioxide-containing gases.
[0047]
In the present invention, when carbon dioxide is
desorbed and regenerated from the absorbing liquid, the absorbing
25 liquid may be about 70 to 120°C, or 70 to 95°C. For example, by
optimizing .the design of the regeneration tower to use "low-grade
waste heat," a sufficient amount of carbon dioxide can be
desorded at a low temperature in the range of 80 to 95°C.
30
35
[0048]
The absorbing liquid from which carbon dioxide has been
desorbed and captured in step B can be sent back to step A, and
recycled.
[0049]
Action
While substantially maintaining a high capture amount
-14-
of carbon dioxide captured from a carbon dioxide-containing gas,
the present invention can improve the amount of carbon dioxide
desorbed at low temperatures from the absorbing liquid that has
absorbed carbon dioxide. In particular, the present invention can
5 achieve a sufficient desorption amount at temperatures within the
range of 80 to 95°C, which is significantly lower than in the
prior art.
[0050]
In addition, the present invention increases the
10 desorption rate of carbon dioxide and the desorption amount of
carbon dioxide relative to the absorption amount of carbon
dioxide (which hereinafter may be referred to as ~regeneration
efficiency" in this specification), meaning that carbon dioxide
can be captured at lower energy costs. The thus-captured carbon
15 dioxide is highly pure (typically 99 vol% or more), and has
applications in chemical and food industries. The carbon dioxide
can also be sequestered underground in EOR (enhanced oil
recovery) or CCS (carbon dioxide capture and storage), the
commercial viability of which is currently being studied.
20
Examples
[0051]
The following Examples describe the present invention
in more detail. However, the present invention is not limited to
25 the Examples.
[0052]
In the Examples, alkanolamines, low-molecular-weight
diol compounds, and glycerin for use are denoted as below.
EGL: ethylene glycol
30 Gly: glycerin
1,2-PD: 1,2-propanediol
1,3-PD: 1,3-propanediol
1,2-BD: 1,2-butanediol
1,4-BD: 1,4-butanediol
35 TEG: triethylene glycol
-15-
IPAE: N-isopropylaminoethanol
AMP: 2-amino-2-methyl-1-propanol
EAE: N-ethylaminoethanol
NBAE: N-n-butylaminoethanol
5 2AlP: 2-amino-1-propanol
[0053]
Example 1
Ethylene glycol, water, and IPAE were mixed at a weight
ratio of 10:35:55, thereby obtaining an absorbing liquid.
10 [0054]
Example 2
Ethylene glycol, water, and IPAE were mixed at a weight
ratio of 20:25:55, thereby obtaining an absorbing liquid.
[ 0055]
15 Example 3
Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 10:30:45:15, thereby obtaining an absorbing
liquid.
[0056]
20 Example 4
Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 10:35:47.5:7.5, thereby obtaining an absorbing
liquid.
[0057]
25 Example 5
.Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 20:25:45:10, thereby obtaining an absorbing
liquid.
[0058]
30 Example 6
Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 10:35:42.5:12.5, thereby obtaining an absorbing
liquid.
[0059]
35 Example 7
5
-16-
Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 5:40:40:15, thereby obtaining an absorbing liquid.
[0060]
Example 8
ratio of
[0061]
Examples
Glycerin,
5:40:40:15,
9 and 10
Ethylene
water, IPAE, and AMP were mixed at a weight
thereby obtaining an absorbing liquid.
glycol, water, IPAE, and AMP were mixed at a
10 weight ratio of 10:35:40:15, thereby obtaining an absorbing
liquid.
[0062]
Examples 11 to 14
Ethylene glycol, water, IPAE, and AMP were mixed at a
15 weight ratio of 20:25:40:15, thereby obtaining an absorbing
liquid.
[ 0063]
Example 15
Ethylene glycol, water, IPAE, and AMP were mixed at a
20 weight ratio of 25:20:40:15, thereby obtaining an absorbing
liquid.
[0064]
Example 16
1,2-Propanediol, water, IPAE, and AMP were mixed at a
25 weight ratio of 10:35:40:15, thereby obtaining an absorbing
liquid.
[0065]
Example 17
1,2-Butanediol, water, IPAE, and AMP were mixed at a
30 weight ratio of 10:35:40:15, thereby obtaining an absorbing
liquid.
[0066]
Example 18
Glycerin, water, IPAE, and AMP were mixed at a weight
35 ratio of 10:35:40:15, thereby obtaining an absorbing liquid.
[ 00 67]
Example 19
-17-
1,2-Butanediol, water, IPAE, and AMP were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
5 liquid.
[0068]
Example 20
1,3-Propanediol, water, IPAE, and AMP were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
10 liquid.
[0069]
Example 21
1,4-Butanediol, water, IPAE, and AMP were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
15 liquid.
[0070]
Example 22
Triethylene glycol, water, IPAE, and AMP were mixed at
a weight ratio of 20:25:40:15, thereby obtaining an absorbing
20 liquid.
[ 0071]
Example 23
Ethylene glycol, water, IPAE, and AMP were mixed at a
weight ratio of 20:35:35:10, thereby obtaining an absorbing
25 liquid.
[ 0072]
Example 24
Ethylene glycol, water, IPAE, and EAE were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
30 liquid.
[0073]
Example 25
Ethylene glycol, water, IPAE, and NBAE were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
35 liquid.
[0074]
Example 26
-18-
Ethylene glycol, water, IPAE, and 2AlP were mixed at a
weight ratio of 20:25:40:15, thereby obtaining an absorbing
5 liquid.
[0075]
Comparative Example 1
Water and IPAE were mixed at a weight ratio of 45:55,
thereby obtaining an absorbing liquid.
10 [0076]
Comparative Example 2
Water, IPAE, and AMP were mixed at a weight ratio of
45:40:15, thereby obtaining an absorbing liquid.
[0077]
15 Comparative Example 3
Water, IPAE, and AMP were mixed at a weight ratio of
45:40:15, thereby obtaining an absorbing liquid.
[0078]
Comparative Example 4
20 Water, IPAE, and EAE were mixed at a weight ratio of
45:40:15, thereby obtaining an absorbing liquid.
[0079]
Comparative Example 5
Water, IPAE, and NBAE were mixed at a weight ratio of
25 45:40:15, thereby obtaining an absorbing liquid.
[ 0080]
Comparative Example 6
Water, IPAE, and 2AlP were mixed at a weight ratio of
45:40:15, thereby obtaining an absorbing liquid.
30 [0081]
The alkanolamines, low-molecular-weight diol compounds,
and glycerin used in the Examples and Comparative Examples above
are brand-name reagent products from Tokyo Chemical Industry Co.,
Ltd., and other companies, and products of general purity were
35 used. For IPAE, a product with a purity of 99% or more
5
-19-
manufactured by Koei Chemical Co., Ltd., was used. The water for
use was ion-exchanged water.
[0082]
Test Example 1
The absorbing liquids of Examples and Comparative
Examples were measured for the absorption amount, desorption
amount, and desorption rate of carbon dioxide. The measurement
was performed with a carbon dioxide absorption and desorption
apparatus to which a carbon dioxide gas cylinder (purity: 99.9%)
10 and a nitrogen gas bottle (purity: 99.9%), a carbon dioxide gas
flow rate controller and a nitrogen gas flow rate controller, a
glass reactor (0.5 L), a mechanical stirrer and a temperature
controller, a gas flowmeter, a chiller, and a carbon dioxide
analyzer (Yokogawa, IR100) were sequentially connected.
15 [0083]
The glass reactor outside was surrounded by an inbuilt
electric heater, so that the temperature of the absorbing liquid
in the glass reactor could be freely controlled with the
temperature controller.
20 [0084]
0.1 L of an absorbing liquid was added to the glass
reactor, and the gas in the upper part of the glass reactor was
replaced by nitrogen gas. The absorbing liquid in the glass
reactor was maintained at 40°C. While the liquid was fully
25 stirred at a rotation frequency of 700 rpm, carbon dioxide gas at
a flow rate of 0.14 L/min and nitrogen gas at a flow rate of 0.56
L/min were blown into the absorbing liquid in the glass reactor
to start step A, and step A continued for 2 hours.
30
[0085]
After completion of step A, the absorbing liquid in the
glass reactor was subsequently heated to 80°C to 95°C to start
step B, and step B continued for 2 hours.
[0086]
In steps A and B, the exhaust gas from the glass
35 reactor was analyzed with the carbon dioxide analyzer. The amount
-20-
of carbon dioxide dissolved in the absorbing liquid (i.e., the
absorption amount) was determined from a change in carbon dioxide
concentration over time measured with the carbon dioxide analyzer.
The amount of carbon dioxide desorbed from the absorbing liquid
5 by heating was defined as a value determined by deducting the
amount of desorbed carbon dioxide after 2 hours from the start of
step B from the amount of absorbed carbon dioxide after 2 hours
from the start of step A. The desorption rate of carbon dioxide
desorbed from the absorbing liquid was defined as a change in the
10 absorption amount of carbon dioxide per unit time during 10
minutes after the start of desorption of carbon dioxide in step B.
[0087]
Table 1 shows the compositions and measurement results
of the absorbing liquids of the Examples and Comparative Examples.
15 [0088]
Absorbing liquids of the Examples exhibited
significantly higher performance in the desorption rate and
regeneration efficiency of carbon dioxide than the absorbing
liquids of the Comparative Examples.
20 [0089]
The results reveal that absorbing liquids that comprise
at least one alkanolamine represented by formula (1), a lowmolecular-
weight dial compound and/or glycerin, and water for
separating and capturing carbon dioxide from a carbon dioxide-
25 containing gas have excellent performance in the desorption rate
and regeneration efficiency of carbon dioxide, as compared with
conventional aqueous solutions, and that the absorbing liquids
show promise for their excellent desorption performance
particularly at low temperatures.
30 [0090]
I
'"'
Table 1-1
Example 1
Example 2
Example 3
Example 4
Example 5
Example 6
Example 7
Example 8
Example 9
Example 10
Example 11
Example 12
Example 13
Example 14
Example 15
Example 16
Example 17
Example 18
Example 19
Example 20
Amount of Amount
Dial and of
Others Water
lwt%) lwt%)
EGL_10 35
EGL 20 25
EGL_10 30
EGL_10 35
EGL_20 25
EGL_10 35
EGL_5 40
G1y_5 40
EGL_10 35
EGL_10 35
EGL 20 25
EGL_20 25
EGL_20 25
EGL_20 25
EGL 25 20
1,2-PD_10 35
1,2-80_10 35
G1y_10 35
1,2-PD 20 25
1,3-PD 20 25
Amine Composition
lwt%)
IPAE 55
IPAE 55
IPAE_45+AMP_15
IPAE_47.5+AMP 7.5
IPAE 45+AMP 10
IPAE 42.5+AMP 12.5
IPAE_40+AMP_l5
IPAE_40+A.MP_l5
IPAE 40+AMP 15
IPAE 40+AMP 15
IPAE 40+AMP 15
IPAE 40+AMP 15
IPAE_40+AMP_15
IPAE 40+AMP 15
IPAE 40+AMP 15
IPAE_40+AMP_15
IPAE_40+AMP_15
IPAE 40+AMP 15
IPAE 40+AMP 15
IPAE 40+AMP 15
Absorption
TemperatureDesorption
Temperature
I OC)
40-90
40-90
40-90
40-90
40-90
40-90
40-90
40-90
40-95
40-90
40-95
40-90
40-85
40-80
40-90
40-90
40-90
40-90
40-90
40-90
Absorption
Amount
I g-C02/kgAbsorbing
Liquid)
120
109
125
123
122
124
133
131
126
125
126
123
125
123
110
125
121
120
120
118
Desorption
Rate
I g-C02 /kgAbsorbing
Liquid/min)
11.2
10.4
8.7
10.6
11.2
10.8
10.4
10.4
11.2
10.8
12.8
11. 6
10.5
7. 8
9.7
9.8
9.7
9. 5
10.0
8. 6
Desorption
Amount
I g-CO,/kgAbsorbing
Liquid)
115
100
104
110
113
120
115
109
111
114
124
122
118
101
97
105
108
105
107
110
Regeneration
Efficiency
I %1
(Desorption
Amount/
Absorption
Amount)
96
92
83
89
92
97
87
84
89
91
99
99
95
82
88
84
89
88
89
94
I
N
5
[ 0091]
Table 1-2
Example 21
Example 22
Example 23
Example 24
Example 25
Example 26
Comparative
Example 1
Comparative
Example 2
Comparative
Example 3
Comparative
Example 4
Comparative
Example 5
Comparative
Example 6
1, 4-BD 20
TEG 20
EGL_20
EGL_20
EGL_20
EGL_20
0
0
0
0
0
0
25 IPAE_40+AMP 15
25 IPAE 40+AMP 15
35 IPAE_35+AMP_10
25 IPAE_40+EAE_15
25 IPAE_40+NBAE 15
25 IPAE - 40+2A1P- 15
45 IPAE 55
45 IPAE_40+AMP_15
45 IPAE_40+AMP_l5
45 IPAE_40+EAE_15
45 IPAE_40+NBAE_l5
45 IPAE_40+2A1P_15
40-90 117 9.1 112 96
40-90 112 9.5 101 90
40-90 113 9.3 97 86
40-90 126 9. 6 107 85
40-90 111 7. 6 99 89
40-90 134 9. 4 106 79
40-90 140 9.4 122 87
40-90 137 6.5 117 85
40-80 139 5.1 99 71
40-90 150 4. 8 100 67
40-90 136 5. 2 96 71
40-90 143 5.2 95 66

CLAIMS
[Claim 1]
An absorbing liquid for separating and capturing carbon
dioxide from a carbon dioxide-containing gas, the liquid
5 comprising:
at least one alkanolamine represented by formula (1)
wherein R1 represents hydrogen or C1 _4 alkyl, R2 and R3 are
10 identical or different and each represent hydrogen or Cl-3 alkyl,
R1
, R2
, and R3 are not all hydrogen, and n is 1 or 2;
a low-molecular-weight diol compound and/or glycerin;
and
water.
15
[Claim 2]
The absorbing liquid according to claim 1, wherein R1
represents hydrogen, methyl, ethyl, n-propyl, isopropyl, or nbutyl,
R2 and R3 are identical or different and each represent
20 hydrogen or methyl, and n is 1 or 2.
[Claim 3]
The absorbing liquid according to claim 1 or 2, wherein
the alkanolamine represented by formula (1) is an amine mixture
25 of
(I) an alkanolamine wherein R1 represents methyl, ethyl,
n-propyl, isopropyl, or n-butyl, R2 and R3 each represent hydrogen,
and n is 1 or 2, and
(II) an alkanolamine wherein R1 represents hydrogen, R2
30 and R3 each represent methyl, and n is 1.
5
10
-24-
[Claim 4]
The absorbing liquid according to claim 3, wherein the
alkanolamine represented by formula (1) is an amine mixture of Nisopropylaminoethanol
and 2-amino-2-metnyl-1-propanol.
[Claim 5]
The absorbing liquid according to any one of claims 1
to 4, wherein the low-molecular-weight diol compound and/or
glycerin has a concentration of 5 to 30 wt%.
[Claim 6]
The absorbing liquid according to any one of claims 1
to 4, wherein the low-molecular-weight diol compound and/or
glycerin is ethylene glycol and has a concentration of 5 to 20
15 wt%.
[Claim 7]
A method for separating and capturing carbon dioxide
from a carbon dioxide-containing gas, the method comprising the
20 following steps A and B:
25
30
step A of bringing the absorbing liquid according to
any one of claims 1 to 6 into contact with a carbon dioxidecontaining
gas to obtain the absorbing liquid that has absorbed
carbon dioxide from the carbon dioxide-containing gas; and
step B of heating the absorbing liquid that has
absorbed carbon dioxide obtained in step A to desorb and
regenerate carbon dioxide from the absorbing liquid and capturing
the desorbed carbon dioxide.
[Claim 8]
The method according to claim 7, wherein the absorbing
liquid that has absorbed carbon dioxide is heated at a
temperature of 80 to 95°C in step B to desorb carbon dioxide.