CA2616271C

CA2616271C - Highly efficient absorbents for acidic gas separation

Info

Publication number: CA2616271C
Application number: CA2616271A
Authority: CA
Inventors: Jae Goo Shim; Jun Han Kim; Kyung-Ryong Jang; Cheong Kyul Ryu; Hee Moon Eum; Jae Sil Hu
Original assignee: Korea Electric Power Corp
Current assignee: Korea South East Power Co Ltd; Korea Southern Power Co Ltd
Priority date: 2007-09-27
Filing date: 2007-12-20
Publication date: 2011-05-31
Anticipated expiration: 2027-12-20
Also published as: NO20076504L; CA2616271A1; CN101396636A; KR100920116B1; KR20090032375A

Abstract

Provided is a high-efficiency, low-energy type mixed absorbent for separation of carbon dioxide, which has a rapid reaction rate with carbon dioxide and a high-carbon dioxide absorption capacity and does not require a large amount of energy for regeneration of the absorbent, in conjunction with low risk of absorbent oxidation. The absorbent comprises a mixed aqueous solution of: 100 parts by weight of a compound of Formula 1 having one alcoholic hydroxyl group and one primary amine in the molecular structure with no substituent being on the alpha carbon adjacent to the amine and both of an alkyl substituent and an alcoholic hydroxyl group being on the beta carbon, and 1 to 60 parts by weight of a heterocyclic compound of Formula 2 having at least one amine in the ring: (See formula 1) (See formula 2) wherein R1, R2, R3, R4, R5, and X are as defined in the specification.

Description

[DESCRIPTION]

[Invention Title]

HIGHLY EFFICIENT ABSORBENTS FOR ACIDIC GAS SEPARATION

[Technical Field]

The present invention relates to a mixed absorbent for separation of acidic gas. More specifically, the present invention relates to a mixed absorbent for separation of carbon dioxide, which has a rapid reaction rate with carbon dioxide and a high-carbon dioxide absorption capacity and does not require a large amount of energy for regeneration of the absorbent.

[Background Art]

As industrialization and urbanization have progressed in the early nineteenth-century, increased consumption of fossil fuels used in the energy industry, such as coal, petroleum, LNG, and the like, brought about an increased concentration of acidic gases (such as CO2, CH4, H2S and COS) in the atmosphere.
Continued industrial development and growth led to a rapid increase in the concentration of the acidic gases since the mid twentieth century. With accelerated global warming due to industrial advancement in conjunction with an increased concentration of such acidic gases, particularly an increased level of carbon dioxide in the atmosphere, many countries around the world have strictly strengthened

2 regulations on emission and disposal of acidic gases. Owing to the results of the United Nations Conference on Environment and Development (UNCED), also known as the Earth Summit, held in Rio de Janeiro, Brazil, June 1992, international concerns about global warming have gradually grown. For example, international agreements on the reduction of acidic gas emissions have been made between many advanced countries. As such an effort, industrialized countries including USA
and Japan agreed to reduce greenhouse gas emissions on average 5.2 percent below levels by 2010. In particular, capture and separation of carbon dioxide, which accounts for most proportions of the acidic gases responsible for global-warming phenomenon, becomes a more important issue. Therefore, there is an urgent need for the development of a technique to cope with such demands.

As technologies for inhibiting increasing emissions of carbon dioxide, there may be mentioned energy-saving technologies for reduction of carbon dioxide emissions, separation and recovery technologies of carbon dioxide from exhaust gas, utilization and fixing technologies of carbon dioxide, alternative energy technologies involving no emission of carbon dioxide, and the like.

As examples of the separation technologies of carbon dioxide studied until now, there have been proposed absorption, adsorption, membrane separation, and cryogenic separation as feasible alternative methods.

In particular, the absorption method is convenient for treatment of a large volume of gases and is suitable for separation of low-concentration gas.
Therefore, this method can be easily applied to most of industrial companies and power plants.
For example, a process using monoethanolamine (MEA, produced by ABB lummus

3 Crest) as an absorbent is currently operated in Trona (CA, USA) and Shady Point (Oklahoma, USA).

Meanwhile, an absorption process employing the aforementioned monoethanolamine (hereinafter, referred to as "MEA") as an absorbent has a fast reaction rate, but suffers from problems such as consumption of large amounts of energy in the separation of carbon dioxide, the use of large amounts of an absorbent solution, and corrosion of the facility caused by the absorbent solution.
Accordingly, there is a strong need for the development of an additive or absorbent which is capable of solving such problems.

As another example of the absorption method, separation and recovery of acidic gases (such as CO?, H2S and COS), which are present in the mixed gases emitted from steel plants and thermal power plants, via the chemical reaction of the gases with an aqueous alkanolamine solution, have been actively undertaken by numerous research groups and institutions. Examples of alkanolamines that have been conventionally and widely used in the art may include primary amines such as monoethanolamine (MEA), secondary amines such as diethanolamine (DEA), and tertiary amines such as triethanolamine (TEA), N-methyl diethanolamine (MDEA), triisopropanolamine (TIPA) and the like.

The aforesaid MEA and DEA have been widely used due to a high reaction rate, but are known to suffer from various difficulties of the problems such as high corrosiveness intrinsic to those compounds, consumption of large amount of energy for regeneration of the compounds, performance degradation, and the like.
Further, the aforesaid MDEA exhibits low corrosiveness and a low energy input for regeneration of such a compound, but suffers from a low absorption rate.

4 In recent years, a great deal of research has been actively undertaken on sterically hindered amines as a novel alkanolamine absorbent. The sterically hindered amines have various advantages such as high absorption capacity, high selectivity to acidic gases and low expenditure of energy for regeneration of the amine compounds, but have a problem of a relatively low absorption rate.

Further, Korean Patent Application Publication No. 2005-0007477 Al (2005.01.18), entitled "METHOD FOR ABSORPTION OF ACID GASES", discloses a method of using an amino acid salt having a chemical composition different from that of conventional alkanol amines known in the art, as an absorbent.

However, use of potassium taurate as the absorbent in the above Korean Patent Application Publication No. 2005-0007477 Al results in problems associated with additional and expensive processes for treatment of precipitates formed after the reaction of the absorbent with carbon dioxide, thus presenting economic and environmental problems. Further, the potassium taurate exhibits a low absorption rate of carbon dioxide as compared to a conventional absorbent, and is an absorbent in the form of a primary amine salt having no steric hindrance effects, thus disadvantageously resulting in consumption of large amounts of energy in separation of carbon dioxide.

Further, U.S. Patent No. 3,622,267 discloses a technique of purifying carbon dioxide contained in the syngas under high-pressure (40 atm) conditions, using an aqueous MDEA or monoethylmonoethanolamine solution. However, the aforesaid U.S. Patent No. 3,622,267 suffers from disadvantages such as a low absorption rate of carbon dioxide as well as a need for high-pressure conditions.

Further, Japanese Patent No. 2,871,335 discloses a technique of using a secondary amine such as 2-amino-2-methylpropanol (hereinafter, referred to as "AMP") or (2-aminoethyl)ethanol exhibiting high steric hindrance due to attachment of amine to a tertiary carbon atom, in conjunction with a piperazine derivative as a

5 reaction accelerator. However, the aforesaid Japanese Patent No. 2,871,335 suffers from disadvantages associated with a sluggish reaction rate with carbon dioxide, which arises from the steric hindrance of secondary amine such as AMP or (2-aminoethyl)ethanol, used as a main absorbent.

Further, most of compounds known as a carbon dioxide absorbent, including the compounds of the aforesaid Patent publications, are significantly susceptible to performance degradation resulting from oxidation of the absorbent.
That is, the alkanolamine absorbent, which accounts for the most parts of the already granted patents, does not contain other substituents (such as alkyl) on the alcoholic hydroxyl-substituted carbon atom. Accordingly, oxidation of the alcoholic group with the passage of time leads to degradation into zwitterions in the form of aldehydes, carboxylic acids, and ammonium salts, thus resulting in loss of a function of the compound as the carbon dioxide absorbent, and the presence of the resulting degradation product also accelerates corrosion of the apparatus.

Reaction Scheme 1 /~ OH /H OH + 0' HyN/ `~ H2N ' -r H2NZ H3N~

6 An oxidation-induced degradation process of a typical carbon dioxide absorbent MEA and 1-amino-2-propanol as an example of a main absorbent developed in the present invention is as follows.

Due to no substituents on the carbon atom which is directly attached to the alcoholic hydroxyl group, MEA is easily oxidized with the passage of time into aldehydes by oxygen contained in the exhaust gas during an absorption process of carbon dioxide. The aldehyde can be further oxidized to carboxylic acids, thus forming glycine. Then, glycine is converted into a zwitterion in the form of an ammonium salt, via the intramolecular deprotonation. The zwitterion, which is a final degradation product, no longer serves as the absorbent because amine has a positive charge, thus failing to absorb carbon dioxide (see Reaction Scheme 1).
Therefore, the loss of the alkanolamine absorbent, i.e., MEA, occurs in the practical process, which consequently requires periodic replenishment of the absorbent, and the thus-produced degradation product also accelerates corrosion of the facility in conjunction with a decreased efficiency of the absorbent compound.

[Disclosure]
[Technical Problem]

Therefore, the present invention has been made in view of the above problems, and provides for a high-efficiency absorbent for separation of carbon dioxide, which has a rapid reaction rate with carbon dioxide and a high-carbon dioxide absorption capacity and does not require a

7 large amount of energy for regeneration of the absorbent, in conjunction with low risk of absorbent oxidation.

[Technical Solution]

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a mixed absorbent for separation of acidic gas, comprising a mixed aqueous solution of:

100 parts by weight of a compound of Formula 1 having one alcoholic hydroxyl group and one primary amine in the molecular structure with no substituent being on the alpha carbon adjacent to the amine and both of an alkyl substituent and an alcoholic hydroxyl group being on the beta carbon, and 1 to 60 parts by weight of a heterocyclic compound of Formula 2 having at least one amine in the ring:

Ot RSOH

RI (Formula 1) ::x:x:
H (Formula 2) wherein Ri is -(CH2)a-H (a = 1 to 3) or -CH-(CH3)2;

R2, R3, R4 and R5, which may be identical or different, are independently H, or CI-C4 alkyl optionally substituted with amine or an alcoholic hydroxyl; and

8 X is -CH2, 0, NH or SH.

In the compound of Formula 1, the alpha-carbon atom directly attached to the amine contains no substituent, whereas the beta-carbon atom is substituted with alcoholic hydroxyl and alkyl. Since there is no substituent on the alpha-carbon atom attached to the amine, less steric hindrance of the compound in the reaction with carbon dioxide leads to a rapid absorption reaction. On the other hand, the presence of the alkyl substituent on the beta-carbon atom prevents performance degradation of the compound which may be caused by oxidation of the alcoholic hydroxyl group, thereby increasing a lifespan of the absorbent. Further, the presence of the alkyl substituent increases a degree of steric hindrance of the compound upon removing out of carbon dioxide which was reacted with the amine, advantageously facilitating carbon dioxide removal. Further, the number of the carbon atom contained in R1 of Formula I is preferably in a range of 1 to 3. As the compound of Formula 2, one or more heterocyclic compounds having at least one secondary or tertiary amine in the molecular structure may be employed in combination with the compound of Formula 1.

The absorbent prepared according to the present invention, for example 1-amino-2-propanol, has a structural characteristic that is highly resistant to oxidation-induced degradation. That is, in the case of 1-amino-2-propanol, oxidation of alcohol into ketone is very difficult to occur, due to steric hindrance of the alkyl substituent present on the carbon atom which is directly attached to the alcoholic hydroxyl group. Further, since the oxidation process no longer proceeds even when the ketone structure may be formed over a long period of time, 1-amino-2-propanol

9 can continuously maintain the function of the absorbent, unlike the above-exemplified alkanolamine absorbents (see Reaction Scheme 2).

Reaction Scheme 2 oH
H2N ...... H2N 1*'~f The compound of Formula I may be at least one selected from the group consisting of I -amino-2-propanol, 1-amino-2-butanol, I -amino-2-pentanol, 1-amino-3-methyl -2-butanoI and any combination thereof.

The compound of Formula 2 that can be used in the present invention may include piperazine, morpholine, thiomorpholine, piperidine and derivatives thereof, such as piperazine, morpholine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,3-dimethylpiperazine, 2,4-dimethylpiperazine, 2-ethanolpiperazine, 2,5-diethanolpiperazine, 2-aminoethylpiperazine, thiomorpholine, and piperidine.

The compound of Formula 2, which is used in admixture with the compound of Formula 1, may be at least one.

Preferably, the absorbent of the present invention may be used in the form of a 5 to 50% (w/v) aqueous solution of a mixed absorbent containing one or more compounds selected from a group of compounds of Formula 1 and a group of compounds of Formula 2. If a concentration of the mixed absorbent is lower than 5%, the carbon dioxide-absorption capacity of the absorbent may be maintained, but a reaction rate is sluggish, thus resulting in a decrease in an absolute amount of carbon dioxide to be absorbed. On the other hand, if a concentration of the mixed absorbent is higher than 50%, the carbon dioxide-absorption capacity and absorption rate of the absorbent may be excellent, but a large amount of the absorbent is used and therefore the process is not efficient from an economic point of view.

Further, the compound of Formula I and the compound of Formula 2 may 5 be preferably used in a weight ratio of 100: 1-60. If the compound of Formula 2 is added in a weight ratio of less than 1, an increase in the reaction rate is insignificant.
On the other hand, if the compound of Formula 2 is added in a weight ratio of more than 60, an increase in the reaction rate relative to an addition amount of the compound is not significant.

10 The absorbent of the present invention refers to a mixed absorbent of one or more compounds selected from compounds of Formula 1 and compounds of Formula 2, and not only enhances the carbon dioxide-absorption rate and absorption capacity but also enables easy removal of carbon dioxide at a high temperature.

The carbon dioxide absorption/separation process basically involves absorbing carbon dioxide at a low temperature, separating the thus-absorbed carbon dioxide from the absorbent by application of heat energy at a high temperature, and recycling the absorbent to the absorption/separation process. Preferably, an acidic gas-absorption temperature of the mixed absorbent is in a range of 0 to 60 C, whereas a gas- removal temperature of the mixed absorbent is in a range of 70 to 200 C C. Therefore, the highest consumption of energy in the carbon dioxide absorption/separation process takes place upon separation of the absorbed carbon dioxide from the absorbent at a high temperature and regeneration (removal) of the absorbent, which consumes about 50 to 80% of energy necessary for the overall process. In conclusion, economic efficiency of the absorbent and the overall carbon

11 dioxide separation process is determined by the degree of energy reduction in the regeneration (removal) process of the absorbent. Thus, it is preferred to separate the absorbed carbon dioxide from the absorbent at a low temperature.

The absorbent of the present invention exhibits a significant carbon dioxide absorption reaction at a low temperature while showing a relatively insignificant absorption reaction of carbon dioxide at a high temperature.
Therefore, the difference in a unit absorption rate of carbon dioxide due to such a temperature difference is very significant as compared to a conventional absorbent. This result means that use of the absorbent developed according to the present invention leads to reduction of energy to be used upon separation of carbon dioxide, i.e.
regeneration of the absorbent, as compared to a conventional absorbent, for example MEA. That is, no reaction of the absorbent with carbon dioxide at a high temperature represents that the absorbent can be easily regenerated, so it is possible to secure economic efficiency of the reaction in the overall carbon dioxide removal process using the absorbent.

The absorbent of the present invention can also be applied to a variety of acidic gases such as H2S, SO2, NO2, and COS, in addition to the above-exemplified carbon dioxide.

[Advantageous Effects]

As apparent from the above description, the present invention provides an absorbent which exhibits a very high removal rate of carbon dioxide while having a rapid reaction rate with carbon dioxide and a high absorption capacity of carbon

12 dioxide and is therefore capable of achieving great reduction of energy necessary for regeneration of the absorbent. Further, the absorbent of the present invention has a boiling point higher than that of MEA, thus presenting no risk of evaporation, and is also stable against oxidation and degradation of the absorbent, thereby resulting in reduced corrosion of the apparatus, which is very advantageous for practical application of the present invention.

[Description of Drawings]

FIG. I is a graph showing gas-liquid equilibrium characteristics of absorbents of Example I and Comparative Example 1 at 35 C and 120 C, respectively.

[Best Mode]

Now, preferred embodiments of the present invention will be described in more detail, such that those skilled in the art can easily practice the present invention. These and other objects, advantages and features of the present invention will become apparent from the detailed embodiments given below which are made in conjunction with the following Examples.

The present invention may be embodied in different forms and should not be misconstrued as being limited to the embodiments set forth herein, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the

13 invention as disclosed in the accompanying claims. Therefore, it should be understood that the embodiments disclosed herein are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.

EXAMPLES
Hereinafter, the present invention will be described in more detail with reference to the following examples.

Example I

100 mL of a 2.00 M mixed aqueous solution of 1-arnino-2-propanol:piperazine (9:1) as an absorbent was filled in a 700 mL stainless steel pressure-resistant reaction vessel equipped with a stirrer. Carbon dioxide gas was transferred to the reaction vessel from a carbon dioxide storage tank, and a saturated absorption amount of carbon dioxide was measured at partial pressure of carbon dioxide ranging from 0.0 kPa to about 150 to 200 kPa. The reaction vessel and the carbon dioxide storage vessel were preheated to a desired temperature in an oven, and gas-liquid equilibrium curves at 35 C and 120 C were measured respectively.
The results thus obtained are shown in FIG. 1.

Example 2 A glass reaction vessel was soaked in a water bath at 40 C, and was then filled with 300 mL of a 2.00 M mixed aqueous solution of 1-amino-2-

14 propanol:piperazine (9:1). A gas composed of 15% carbon dioxide and 85%
nitrogen at a flow rate of 3.0 L/min was dispersed and absorbed into this absorbent via a glass tube under atmospheric pressure. A concentration of carbon dioxide in gases at an outlet of the absorption solution was continuously determined in an infrared carbon dioxide analyzer to thereby calculate an absorption rate, an absorption amount and an absorption load of carbon dioxide. At a given time point (about 90 min) when the absorbent was saturated with carbon dioxide, the reaction vessel was transferred to a water bath previously warmed to 80 C, and a removal amount and a removal rate of carbon dioxide from the absorbent were measured for 30 min. The results thus obtained are given in Table 1 below.

Example 3 In the same plant as in Example 2, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.45 M mixed aqueous solution of 1-amino-2-propanol:piperazine (100:1) as an absorbent. The results thus obtained are given in Table 1 below.

Example 4 In the same plant as in Example 2, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.45 M mixed aqueous solution of 1-amino-2-propanol:piperazine (100:5) as an absorbent. The results thus obtained are given in Table 1 below.

Example 5 In the same plant as in Example 2, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.00 M mixed aqueous solution of I-amino-2-propanol:piperazine (100:20) as an 5 absorbent. The results thus obtained are given in Table 1 below.

Example 6 In the same plant as in Example 2, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 10 2.00 M mixed aqueous solution of 1-amino -2-prop anol:piperazine (100:60) as an absorbent. The results thus obtained are given in Table 1 below.

Example 7 In a continuous pilot-scale plant equipped with an absorption column, a

15 removal column, a heat exchanger and a condenser and having a throughput capacity of CO2 of 2 tons per a day, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.00 M mixed aqueous solution of 1-amino-2-propanol:piperazine (9:1) as an absorbent. The carbon dioxide absorption was carried out at 40 C, and the carbon dioxide removal was carried out at 120 C. The results thus obtained are given in Table 2 below.

Example 8

16 In the same plant as in Example 7, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.45 M mixed aqueous solution of 1-amino-2-propanol:piperazine (9:1) as an absorbent. The results thus obtained are given in Table 2 below.

Comparative Example I

Using the same plant as in Example 1 under the same conditions, gas-liquid equilibrium curves at 35 C and 120 C were calculated using a 2.45 M
aqueous solution of monoethanolamine (MEA) as an absorbent. The results thus obtained are shown in FIG. 1.

Comparative Example 2 300 mL of a 2.45 M aqueous solution of monoethanolamine (MEA) as an absorbent was filled in the same plant as in Example 2 under the same conditions.
The results thus obtained are given in Table 1 below.

Comparative Example 3 In the same plant as in Example 3, a removal rate of carbon dioxide in the exhaust gas and a loading amount of CO2 on an absorbent were measured using a 2.45 M aqueous solution of monoethanolamine (MEA) as an absorbent. The results thus obtained are given in Table 2 below.

Table 1 ----~ bsorbent CO2 loaded Absorption rate emoval rate

17 (CO2 mole/absorbent mole) 1MEA = 1) (MEA = 1) AbsorptionRemoval ~ Initial 10 Initial 10 at 40 C fat 80 C A loading 1 min 5 min min 1 min 5 min in Ex.2 0.7051 0.3382 0.3669 1.04 1.06 1.07 1.22 1.12 1.07 Ex.3 10.6382 0.3272 10.3110 1.01 1.02 11.02 ,1.01 0.90 10.98 Ex. 4 0.65 76 0.3413 10.3163 11.01 1.04 1.05 1.00 1.09 1.07 Ex.5 10.7128 0.3383 '0.3745 11.01 1.04 11.06 1.09 0.95 11.00 Ex.6 0.8025 0.3827 '0.4198 1.04 1.07 1.10 1.02 1.27 1.20 Comp. j632813l66 0.3162 1 1 1 1 1 ~1 Ex.2 Table 2 low ratemoval CO2 loaded (CO2 mole/Absorb newt.
bsorbent of "column CO2 hole) internal removal absorption emovalT-a bs ~~ nt Temp (%) (Rich) (Lean) loading ( C) loading loading Ex. 3.0 111 73.3 0.5784 0.2605 0.3179 x.7 .0 113 85.0 0.6121 0.1052 0.5069 x.8 .0 113 100 .5778 0.1502 0.4276 Comp. Ex. 3.0 111 73.1 0.5717 0.3318 0.2399 3 ompEx' .0 113 81.0 0.6011 0.1718 .4293 FIG. 1 is a graph showing gas-liquid equilibrium characteristics of absorbents of Example 1 and Comparative Example 1 at 35 C and 120 C, respectively. As is well known in the art, a conventional carbon dioxide separation/regeneration (removal) process including Comparative Example I
using

18 MEA is carried out at a temperature of 100 to 120 C. As shown in FIG. 1, the absorbent of Example 1 exhibited poor absorption of carbon dioxide at 120 C in conjunction with higher absorption of carbon dioxide at 35 C, as compared to the absorbent of Comparative Example 1. These results represent that since a temperature of 120 C is a removal condition for discharging the absorbed carbon dioxide, use of the absorbent of Example 1 achieves efficient separation of carbon dioxide and easy regeneration of the absorbent, as compared to the absorbent MEA
of Comparative Example 1. Further, it can also be seen that the absorbent of Example 1 absorbs a larger amount of carbon dioxide under the absorption condition of 35 C, as compared to the absorbent MEA of Comparative Example 1.
Table 1 shows the carbon dioxide absorption and removal temperatures, and absorption and removal amounts for absorbents of Examples 2 to 6 and Comparative Example 2 at an absorption temperature of 40 C and a removal temperature of 80 C. As shown in Table 1, it can be seen that the absorbents of Examples 2, 5 and 6 exhibit higher carbon dioxide absorption and removal amounts due to a large difference of the carbon dioxide loading (A loading) under absorption and removal conditions, as compared to the absorbent of Comparative Example 2.
Further, it can be seen that the initial absorption and removal rates are higher in Examples 2, 5 and 6 than Comparative Example 2. Accordingly, it can be seen through the results of Table 1 that the absorbents of Examples 2, 5 and 6 exhibit larger absorption and removal amounts in the reaction with carbon dioxide as well as higher absorption and removal rates, as compared to that of Comparative Example 2, thus representing that the absorbents of Examples 2, 5 and 6 are a highly efficient absorbent. Meanwhile, it can be seen from the above results that in

19 case of the absorbents of the Examples 3 and 4, the differences of carbon dioxide loading (A loading) are similar to that of the Comparative Example 2 but the absorption rate and the removing rate thereof are more than that of the Comparative Example 2.

Table 2 shows results of experiments carried out in a continuous pilot-scale plant, based on the results obtained in FIG. I and Table 1.

Therefore, the absorbent of the present invention can rapidly absorb carbon dioxide due to a high-carbon dioxide absorption rate and then remove the absorbed carbon dioxide at relatively low temperature conditions, so it is possible to greatly reduce the energy consumed for removal of carbon dioxide (corresponding to about 50 to 80% of energy necessary for the overall process). Accordingly, the present invention is highly advantageous for securing of economic efficiency and practical application (commercialization).

Claims

1. A mixed absorbent for separation of acidic gas, comprising a mixed aqueous solution of:

100 parts by weight of a compound of Formula 1 having one alcoholic hydroxyl group and one primary amine in the molecular structure with no substituent being on the alpha carbon adjacent to the amine and both of an alkyl substituent and the alcoholic hydroxyl group being on the beta carbon, and 1 to 60 parts by weight of a heterocyclic compound of Formula 2 having at least one amine in the ring:

wherein R1 is -(CH2)a-H (a = 1 to 3) or -CH-(CH3)2;

R2, R3, R4 and R5, which may be identical or different, are independently H, or C1-Ca alkyl optionally substituted with amine or an alcoholic hydroxyl; and X is -CH2, 0, NH or SH.

2. The absorbent according to claim 1, wherein the compound of Formula 1 is 1-amino-2-propanol, 1-amino-2-butanol, 1-amino-2-pentanol, 1-amino-3 -methy 1-2-butanol, or any combination thereof.

3. The absorbent according to claim 1, wherein the compound of Formula 2 is piperazine, morpholine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,3-dimethylpiperazine, 2,4-dimethylpiperazine, 2-ethanolpiperazine, 2,5-diethanolpiperazine, 2-aminoethylpiperazine, thiomorpholine, piperidine, or any combination thereof.

4. The absorbent according to claim 1, wherein the absorbent is used as a 5 to 50% (w/v) aqueous solution.

5. The absorbent according to claim 1, wherein at least one compound of Formula 2 is added in a weight ratio of 100:1-60 relative to the compound of Formula 1.

6. The absorbent according to claim 1, wherein the acidic gas-absorption temperature of the mixed absorbent is in the range of 0 to 60°, and the gas-removal temperature of the mixed absorbent is in the range of 70 to 200°

7. The absorbent according to claim 1, wherein the acidic gas is CO2, H2S, SO2, NO2, COS, or any combination thereof.