AU2010328990B2 - Carbon dioxide absorbent for use under high pressure, and method for absorption and collection of carbon dioxide under high pressure - Google Patents

Abstract

A water-containing liquid absorbent for absorbing and collecting carbon dioxide from a gas flow having a carbon dioxide partial pressure of 2 bar or more, the absorbent being characterized by containing 60 to 90 wt% of a tertiary aliphatic amine represented by general formula [1]; and a method for absorbing and collecting carbon dioxide using the water-containing liquid absorbent.

Description

-l1 DESCRIPTION Title of Invention: CARBON DIOXIDE ABSORBENT FOR USE UNDER HIGH PRESSURE, AND METHOD FOR ABSORPTION AND COLLECTION OF CARBON DIOXIDE UNDER HIGH 5 PRESSURE Technical Field [0001] The present invention relates to an absorbent for use to remove carbon dioxide from a gas flow having a high carbon 10 dioxide partial pressure (2 bar or more), and particularly to remove carbon dioxide from exhaust gas generated in a coal gasification process. The present invention further relates to a method for absorbing and recovering carbon dioxide to remove carbon dioxide from a gas flow having a high carbon dioxide 15 partial pressure (2 bar or more), and particularly to remove carbon dioxide from exhaust gas generated in a coal gasification process. Background Art [0002] 20 In recent years, a rapid increase in the emission of greenhouse gases, such as carbon dioxide and methane, which are associated with human social activities, has been raised as one of the causes of global warming. In particular, carbon dioxide is the most predominant among greenhouse gases, and there is thus an 25 urgent need to establish measures to reduce carbon dioxide emissions in accordance with the Kyoto Protocol which came into effect in 2005. [0003] Today, while targeting mixed gases emitted from thermal 30 power plants, boilers of iron mills, kilns of cement plants, and the like using coal, heavy oil, natural gas, etc., as fuels, which are sources of carbon dioxide, carbon dioxide capture and storage (CCS), which is technology comprising a series of operations, i.e., separation/recovery, compression, transport, 35 and injection of carbon dioxide contained in a mixed gas, has -2 been attracting attention as a bridging technique for use until an energy alternative to fossil fuels has been developed. [00041 To put this capture and storage technology into 5 practical use, all possible cost reduction is required. In the series of steps comprising carbon dioxide separation/recovery, compression, transport, and injection, costs required in separation/recovery and compression, i.e., the earliest steps, account for 70% or more of the total capture and storage cost. 10 Accordingly, developing a technology for reducing the costs of these steps is important. Further, while targeting normal pressure exhaust gas emitted from electrical power plants and iron mills, the development of a technology for separating and recovering carbon dioxide by chemical absorption using an 15 alkanolamine aqueous solution as a main component has been vigorously promoted. [0005] Patent Literature (PTL) 1 discloses a process for removing carbon dioxide from a gas flow in which the partial 20 pressure of carbon dioxide is less than 0.2 bar, the process comprising bringing the gas flow into contact with a liquid absorption agent comprising an aqueous solution of (A) an amine compound containing at least two tertiary amino groups in the molecule, and (B) an activator selected from primary and 25 secondary amines. [0006] In contrast, technology regarding CO 2 separation and recovery from high-pressure gas, such as coal gasification product gas or mined natural gas, by chemical absorption has been 30 researched less than technology regarding separation and recovery from normal-pressure exhaust gas. However, because pressure energy of gas itself can be utilized for carbon dioxide separation/recovery and compression, this technology has the possibility of drastically reducing the cost of the carbon 35 dioxide capture and storage process, in particular, the cost of -3 the separation/recovery and compression steps. Accordingly, the focal point is the development of a chemical absorption liquid that is applicable to the separation of carbon dioxide from a high-pressure gas. 5 [0007] Thus far, physical absorption has gained attention as a method for removing carbon dioxide-containing acid gas from high pressure gas. Regarding physical absorption, it is known that the higher the partial pressure of the target gas component, the 10 larger the amount of acid gas absorbed per unit amount of absorption liquid, compared to chemical absorption. Representative examples of absorbents include cyclotetramethylene sulfone (sulfolane) and derivatives thereof, aliphatic aide, methanol, and an absorbent comprising polyethylene glycol dialkyl 15 ethers ("SELEXOL," a product of Union Carbide Corp.). However, all of the above absorption liquids are required to be under the condition of reduced pressure in the step of separating carbon dioxide from the absorption liquid and regenerating the absorption liquid. Accordingly, the compression cost reduction 20 effect in the subsequent compression step is extremely low. [0008] In contrast, Patent Literature 2 is directed to an acid gas regeneration process which is performed at a pressure that exceeds 3.5 bar absolute and that does not exceed 20 bar absolute. 25 Patent Literature 2 discloses that a desorbed acid gas flow emerging from a regenerator is compressed and injected into a subsurface reservoir. Patent Literature 2 mentions triethanolamine, etc., as examples of chemical solvent agents for acid gas absorption. The absorption fluid used in an Example of 30 Patent Literature 2 is composed of 43 wt% of N methyldiethanolamine and 57 wt% of water. [0009] When an aqueous solution of an amine compound containing at least two tertiary amino groups in the molecule as 35 disclosed in Patent Document 1, or aqueous solutions of N- -4 methyldiethanolamine (MDEA) and triethanolamine as disclosed in Patent Document 2 have a typical concentration of 30 to 50 wt%, such solutions exhibit poor releasing ability in a region where the partial pressure of carbon dioxide is high, such as that 5 assumed in an IGCC (integrated gasification combined cycle), which results in a low carbon dioxide recovery and low amine regeneration efficiency, thus increasing the cost and energy required of carbon dioxide recovery. Furthermore, the use of MDEA in an amount of 60 wt% or more deteriorates ease of handling and 10 lowers the absorption rate due to an increased viscosity, thus causing difficulties in practical use. [0010] In contrast, Patent Literature 3 discloses a process for the removal of an acid gas from a gaseous feed stream, 15 comprising a regeneration step of heating an acid gas-rich absorbing fluid at a pressure greater than atmospheric pressure. The absorbing fluid comprises a tertiary alkylamine selected from diamines, triamines, and tetramines. Patent Literature 3 discloses that when the amine concentration in the aqueous 20 solution is high (60 to 90% by weight), the absorbing fluid can be regenerated under high pressure. [0011] However, to design a compact separator for removing carbon dioxide from a gas flow, the use of an amine that achieves 25 high absorption and desorption rates is important. In the field of CO 2 absorption at a pressure higher than atmospheric pressure, the absorption and desorption rates have not yet been investigated. Citation List 30 Patent Literature [0012] PTL 1: Japanese Unexamined Patent Publication No. 2007-527790 PTL 2: WO 2005/009592 PTL 3: WO 2004/082809 35 Summary of Invention -5 Technical Problem [0013] An object of the present invention is to provide a highly efficient CO 2 absorbent; and a method for absorbing and 5 recovering carbon dioxide that can desorb carbon dioxide from a gas at higher carbon dioxide absorption and desorption rates than ever, in regions where the partial pressure of carbon dioxide is high. Solution to Problem 10 [0014] As described above, Patent Literature 3 discloses that when an aqueous solution containing an amine in a high concentration of 60% by weight or more is used in regions where the partial pressure of carbon dioxide is high, an increased 15 amount of carbon dioxide can be recovered. [0015] Further, the present inventors confirmed that the use of an aqueous solution of an tertiary aliphatic amine containing an ether group and not containing a hydrogen bonding group 20 increases the amount of carbon dioxide recovered, as well as the absorption and desorption rates. [0016] Accordingly, the present inventors .found that when an aqueous solution of a tertiary aliphatic amine containing an 25 ether group and not containing a hydrogen bonding group is used in a high concentration, the amine solution can achieve high absorption and desorption rates, and recover a large amount of carbon dioxide in a region having a high carbon dioxide partial pressure; and thus can achieve the above object. The present 30 invention has been accomplished based on these findings and further research; and provides the following carbon dioxide absorbent, and method for absorbing and recovering carbon dioxide. [0017] Item 1. A water-containing liquid absorbent for absorbing and 35 recovering carbon dioxide from a gas flow having a carbon dioxide -6 partial pressure of 2 bar or more, the absorbent comprising 60 to 90 wt% of a tertiary aliphatic amine represented by Formula [1]: [0018] R' R R6$N R4 1 2 L j n [ 3 R R 3 5 (wherein R1, R 2, R 3, and R4 are the same or different, and each represents an alkyl group, R 5 and R 6 are the same or different, and each represents an alkylene group, and n is 1 to 5.) [0019] Item 2. The water-containing liquid absorbent according to Item 1, 10 wherein the tertiary aliphatic amine is bis(2 dimethylaminoethyl)ether. [0020] Item 3. A method for absorbing and recovering carbon dioxide, comprising (1) bringing the water-containing liquid absorbent 15 according to Item 1 or 2 into contact with a gas flow having a carbon dioxide partial pressure of 2 bar or more to absorb carbon dioxide from the gas flow, and (2) heating the water-containing liquid absorbent having carbon dioxide absorbed therein to desorb and recover the carbon dioxide absorbed in step (1). 20 [0021] Item 4. The method for absorbing and recovering carbon dioxide according to Item 3, wherein step (1) is performed at a carbon dioxide partial pressure of 2 to 40 bar, and step (2) is performed at a carbon dioxide partial pressure of 2 bar or more. 25 [0022] Item 5. The method for absorbing and recovering carbon dioxide according to Item 3 or 4, wherein step (1) is performed at a temperature of 25 to 60 0 C, and step (2) is performed at a temperature of 70 to 120 0

C.

-7 Advantageous Effects of Invention [0023] The absorbent according to the present invention can achieve high carbon dioxide absorption and desorption rates in an 5 environment having a high carbon dioxide partial pressure, which enables design of a more compact, economic separator. Furthermore, due to an increased amount of carbon dioxide recovered in an environment having a high carbon dioxide partial pressure, a separation with low energy consumption can be made. 10 Brief Description of Drawings [00.24] [Fig. 1] Fig. 1 is a graph showing the results of measuring the amount of carbon dioxide absorbed in Test Example 2. [Fig. 2] Fig. 2 is a graph showing the results of measuring the 15 carbon dioxide absorption and desorption rates, and the amount of carbon dioxide recovered in Test Example 3. Description of Embodiments [0025] The water-containing liquid absorbent and method for 20 absorbing and recovering carbon dioxide according to the present invention are described below in detail. [0026] Water-containing liquid absorbent for absorbing and recovering carbon dioxide 25 A feature of the water-containing liquid absorbent of the present invention is that the absorbent absorbs and recovers carbon dioxide from a gas flow having a carbon dioxide partial pressure of 2 bar or more. Another feature thereof is that the absorbent contains a tertiary aliphatic amine represented by 30 Formula [1] in an amount of 60 to 90 wt%. Formula [1]: [0027] -8 N O N 1 2 Ln [ 1 ] R2 R3 [0028] wherein R1, R 2, R 3 , and R 4 are the same or different, and each represents an alkyl group, preferably an alkyl group having 1 to 5 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. [0029] Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 10 tert-butyl, n-pentyl, isopentyl, and hexyl. [0030] Examples of alkyl groups having 1 to 3 carbon atoms include methyl, ethyl, n-propyl, and isopropyl. [00311 15 R 5 and R 6 in Formula [1] may be the same or different, and each represents an alkylene group, preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms. [0032] 20 Examples of alkylene groups having 1 to 6 carbon atoms include methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, tert-butylene, n-pentylene, isopentylene, and hexylene. [00331 25 Examples of alkylene groups having 1 to 3 carbon atoms include methylene, ethylene, n-propylene, and isopropylene. [0034] In Formula [1], n is an integer selected from 1 to 5, preferably 1 to 4, and more preferably 1 to 2. 30 [0035] -9 Examples of the tertiary aliphatic amine represented by Formula [1] include bis(2-dimethylaminoethyl)ether. [0036] The above tertiary aliphatic amine can be produced 5 according to a known method as disclosed in Documents 1 to 4 listed below, or is easily available as a commercial product. [0037] More specifically, the tertiary aliphatic amine can be produced according to the following formula: 10 Me2NH + HO-CHr(CH 2

-O-CH

2

)-CH

2 -OH -+ Me 2

N-C-(CH

2 -0-CH 2 )n-CH 2 -NMe 2 using diethylene glycol or polyethylene glycol as a starting material as disclosed in the following Documents 1 to 4. Document 1: WO 2005/110969 Document 2: Japanese Unexamined Patent Publication No. H9-20735 15 Document 3: European Patent Publication No. 300 323 Document 4: West German Patent Publication No. 34 22 610 [0038] The heat of reaction of the tertiary aliphatic amine is preferably 40 to 70 kJ/mol-C0 2 , and particularly preferably 45 to 20 60 kJ/mol-C0 2 . As used herein, the heat of reaction refers to the amount of heat generated during absorption of 1 mol of CO 2 at 40 0 C under atmospheric pressure. [0039] Preferably, the CO 2 absorption and desorption rates of 25 the tertiary aliphatic amine are 2 to 5 times those of MDEA, and the amount of carbon dioxide recovered by the tertiary aliphatic amine is twice to three times that recovered by MEDA. [0040] The water-containing liquid absorbent of the present 30 invention contains a tertiary aliphatic amine as mentioned above in an amount of 60 to 90 wt%. When the amount of tertiary aliphatic amine is within this range, excellent carbon dioxide absorption and desorption rates can be achieved. The amount of tertiary aliphatic amine is preferably 60 to 80 wt%, and more 35 preferably 60 to 70 wt%.

-10 (0041] The water-containing liquid absorbent of the present invention may contain an antioxidant, a corrosion inhibitor, a physical absorbent, etc., as components other than the tertiary 5 aliphatic amine. [0042] Examples of the antioxidant include BHT (dibutylhydroxytoluene), BHA (butylhydroxyanisol), sodium erythorbate, sodium sulfite, sulfur dioxide, and the like. 10 [0043] Examples of the physical absorbent include cyclotetramethylene sulfone (sulfolane) and derivatives thereof, aliphatic acid amide (acetyl morpholine, N-formylmorpholine), N alkylated pyrrolidones and corresponding piperidones, such as N 15 methylpyrrolidone (NMP), propylene carbonate, methanol, dialkyl ethers, such as polyethylene glycol, etc. [0044] The carbon dioxide partial pressure in the gas flow from which the water-containing liquid absorbent of the present 20 invention absorbs and recovers carbon dioxide is 2 bar or more. When the carbon dioxide partial pressure is within this range, excellent carbon dioxide .absorption and desorption rates can be achieved. The carbon dioxide partial pressure is preferably 10 bar or more, and more preferably 10 to 40 bar. 25 [0045] Examples of the gas flow include exhaust gas generated in a coal gasification process, mined natural gas, etc. The concentration of carbon dioxide in the gas is typically about 20 to 50 volume%, and particularly preferably about 30 to 40 volume%. 30 When the concentration of carbon dioxide is within the above mentioned range, the effect of the present invention is more advantageously provided. The gas flow may contain other gases such as water vapor, CO, H 2 S, COS, and H 2 , in addition to carbon dioxide. 35 [0046] -11 Method for absorbing and recovering carbon dioxide A feature of the method for absorbing and recovering carbon dioxide of the present invention is that the method comprises (1) bringing the water-containing liquid absorbent into 5 contact with a gas flow having a carbon dioxide partial pressure of 2 bar or more to absorb carbon dioxide from the gas flow, and (2) heating the water-containing liquid absorbent having carbon dioxide absorbed therein to desorb and recover carbon dioxide. [0047] 10 Step (1) In step (1), the water-containing liquid absorbent is brought into contact with a gas flow having a carbon dioxide partial pressure of 2 bar or more to absorb carbon dioxide from the gas flow. 15 [0048] The method of bringing the gas flow into contact with the water-containing liquid absorbent is not particularly limited. Examples of usable methods include a method comprising bubbling a gas flow into the absorbent; a method comprising mist-spraying 20 the absorbent over a gas flow (misting or spraying method); and a method comprising bringing a gas flow into countercurrent contact with the absorbent in an absorption column containing a ceramic or metal mesh filler. [0049] 25 Step (1) is preferably performed at a carbon dioxide partial pressure of 2 to 40 bar, and particularly preferably 2 to 20 bar. Step (1) is preferably performed at a temperature of 25 to 60 0 C, and particularly preferably at a temperature of 40 to 60 0 C. 30 [0050] Step (2) In step (2), the water-containing liquid absorbent having carbon dioxide absorbed therein obtained in step (1) is heated to desorb and recover carbon dioxide. 35 [0051] -12 The method of separating carbon dioxide from the water containing liquid absorbent having carbon dioxide absorbed therein, and recovering carbon dioxide in a pure form or in a high concentration include a desorption method comprising heating 5 and boiling the absorbent in a pot as in distillation; and a method comprising heating the absorbent in a tray column, a spray column, or a desorption column containing a ceramic or metal mesh filler to increase the liquid contact interface. Carbon dioxide is thereby liberated and desorbed from the absorbent. 10 [0052] Step (2) is preferably performed at a carbon dioxide partial pressure of 2 bar or more, and particularly preferably at 2 to 80 bar. Furthermore, step (2) is preferably performed at a temperature of 70 to 120*C, and particularly preferably 90 to 15 120 0 C. The upper temperature limit is not restricted to 120 0 C. The temperature may be higher than 120 0 C. [0053] The absorbent from which carbon dioxide has been desorbed is recycled and reused in step (1). During this process, 20 the heat added in step (2) is effectively utilized to raise the temperature of the absorbent by heat exchange with the absorbent in the recycling step, thus reducing the energy of the entire recovery process. [0054] 25 The purity of the carbon dioxide thus recovered is typically about 95 to 99.9 volume%, which is an extremely high purity. Such a pure or high concentration of carbon dioxide can be used as chemicals, starting materials for producing polymer materials, refrigerants for freezing foods, etc. It is also 30 possible to isolate and store the recovered carbon dioxide in underground facilities or the like, the technology for which is currently under development. In this case, as the pressure of carbon dioxide recovered in step (2) is higher, less energy is required for compression to 100 to 150 bar, which is required for 35 capture and storage.

-13 Examples [0055] The present invention is described below in detail with reference to Examples. However, it should be understood that the 5 scope of the present invention is not limited to these Examples, etc. [0056] Reagents The types of reagents and gases used in Examples and 10 Comparative Examples are shown below. [0057] [Table 1] Type of amine Abbreviation Purchased from Model No. Bis(2-dimethylaminoethyl)ether Bis(2DMAE)ER Tokyo Chemical Industry, Co., Ltd. B1291 N-methyldiethanolamine MDEA Aldrich 471828 N,N,MN',N"- . PMDETA Aldrich 369497 pentamethyldiethylenetriamine [0058] [Table 2] Type of gas Purity (%) Purchased from Carbon dioxide bottle 99.9 Ueno Gas Co., Ld. Nitrogen gas bottle 99.99 Ueno Gas Co., ld. 15 [0059] Experimental method The carbon dioxide absorption and desorption rates and the amount recovered by the water-containing liquid absorbent were measured using an apparatus produced by sequentially 20 connecting a carbon dioxide bottle, a nitrogen gas bottle, a carbon dioxide flow rate controller, a nitrogen gas flow rate controller, a high-pressure vessel (600 cc), a condenser, a pressure-regulating valve, a flowmeter, and a CO 2 monitor. Two oil baths whose temperatures were controlled to 40 0 C and 120 0 C, 25 respectively, were connected to the perimeter of the high pressure vessel. [0060] After a water-containing liquid absorbent (300 cc) was -14 added to the high pressure vessel, air in the high pressure vessel was replaced with nitrogen at atmospheric pressure. [0061] The pressure-regulating valve was adjusted to control 5 the pressure within the high-pressure vessel to a predetermined pressure (0.2 to 40 bar), and the nitrogen gas flow rate controller was set to 3 L/min to start the pressure increase. The 40 0 C oil bath was circulated around the high-pressure vessel to maintain the temperature of the high-pressure vessel at 40 0 C. The 10 condenser was maintained at a temperature of 5 0 C, and its role is to return the volatilized water-containing liquid absorbent into the high-pressure vessel. [0062] After the temperature and pressure were stabilized, the 15 carbon dioxide flow rate controller was set to 0.3 to 2.7 L/min, and the nitrogen gas flow rate controller was set to 0.3 to 2.7 L/min to absorb carbon dioxide. The amount of carbon dioxide absorbed by the water-containing liquid absorbent was calculated from the difference in value between the inlet flow rate and gas 20 composition, and the outlet flowmeter and CO 2 monitor. [0063] After the carbon dioxide absorption step was completed, the 40 0 C oil bath circulated around the high-pressure vessel was switched to the 120 0 C oil bath to raise the temperature of the 25 high pressure vessel to 120*C, thereby releasing carbon dioxide. The amount of carbon dioxide desorbed from the water-containing liquid absorbent was calculated from the difference in value between the inlet flow rate and gas composition, and the outlet flowmeter and CO 2 monitor. 30 [0064] The rate of carbon dioxide absorption by the water containing liquid absorbent was defined as the absorbed amount per time unit from the commencement of carbon dioxide absorption. [0065] 35 The rate of carbon dioxide desorption from the water- -15 containing liquid absorbent was assessed based on the absorbed amount per time unit from the commencement of carbon dioxide desorption. [0066] 5 The amount of carbon dioxide recovered from the water containing liquid absorbent was defined as the value obtained by subtracting the amount of carbon dioxide absorbed at 120*C from the amount of carbon dioxide absorbed at 40 0 C. [0067] 10 Test Example 1 A carbon dioxide absorption/desorption test was performed using an absorber (not shown). The water-containing liquid absorbents used in Test Example 1 had the following compositions: Bis(2DMAE)ER: 30 wt% or 60 wt%; or MDEA: 35 wt%. 15 The absorption and desorption conditions used in this test example were as follows: absorption conditions: 40 0 C, 16 bar (CO 2 partial pressure), desorption conditions: 120 0 C, 16 bar (CO 2 partial pressure); absorption conditions: 40 0 C, 0.2 bar (CO 2 partial pressure), 20 desorption conditions: 120 0 C, 0.2 bar (CO 2 Partial Pressure). [0068] Table 3 shows the results of measuring the carbon dioxide absorption and desorption rates and the amount of CO 2 recovered in Test Example 1. 25 [0069] As shown in Table 3, when Bis(2DMAE)ER was used at a

CO

2 partial pressure of 0.2 bar, absorption and desorption rates were slow, and the amount of carbon dioxide recovered was also small. However, when Bis(2DMAE)ER was used at a CO 2 partial 30 pressure of 16 bar, increased absorption and desorption rates were achieved. Further, when the amine concentration was 60 wt%, the absorption and desorption rates were increased, and a large amount of CO 2 was recovered. When using MDEA, the higher the CO 2 partial pressure, the higher the absorption and desorption rates 35 and the larger the amount of CO 2 recovered; however, no remarkable -16 increase as high as that achieved by 60 wt% of Bis(2DMAE)ER was observed. [0070] [Table 3]

CO

2 Type of amine Amine Absorption Desorption Amount partial concentration rate rate of CO2 pressure (wt%) (g/Lhr) (g/Lhr) recovered (bar) 1(g/L) Example 1 16 (high) Bis(2DMAE)ER 60 (high) 403 498 213 Com. Ex. 1 16 (high) Bis(2DMAE)ER 30 (low) 160 117 66 Com. Ex. 2 0.2 (low) Bis(2DMAE)ER 60 (high) <100 <100 55 Com. Ex. 3 0.2 (low) Bis(2DMAE)ER 30 (low) <100 <100 89 Com. Ex. 4 16 (high) MDEA 35 (low) 144 155 71 Com.Ex.5 0.2(low) IMDEA 35 (low) <100 <100 53 5 [0071) Test Example 2 A carbon dioxide absorption/ desorption test was performed using an absorber (not shown). The water-containing liquid absorbents used in Test Example 2 had the following 10 composition: Bis(2DMAE)ER: 30 wt% or 60 wt%; MDEA: 35 wt% or 60 wt%; or PMDETA: 30 wt% or 60 wt%. The absorption and desorption conditions used in this test example were as follows: absorption conditions: 40 0 C, 16 bar (CO 2 partial pressure), desorption conditions: 120 0 C, 16 bar (CO 2 partial pressure). 15 [0072] MDEA corresponds to the absorbent disclosed in Patent Literature 2 (WO 2005/009692), and PMDETA corresponds to the absorbent disclosed in Patent Literature 3 (WO 2004/082809). [0073] 20 Fig. 1 shows the results of measuring the amount of carbon dioxide absorbed in Test Example 2. Table 4 shows the results of measuring the carbon dioxide absorption and desorption rates, and the amount of CO 2 recovered in Test Example 2. [0074] 25 In Fig. 1, the value obtained by subtracting the CO 2 concentration in the 120 0 C liquid from the CO 2 concentration in the 40 0 C liquid indicates the amount of carbon dioxide recovered. [0075] -17 As shown in Fig. 1, whether the concentration of MDEA was 35 wt% or 60 wt% made little difference in the amount of carbon dioxide recovered. However, when the concentration of Bis(2DMAE)ER was 60 wt%, a larger amount of carbon dioxide was 5 recovered than when the concentration of Bis(2DMAE)ER was 30 wt%. [0076] Further, as shown in Table 4, compared to PMDETA and MDEA, Bis(2DMAE)ER exhibited better absorption and desorption rates, as well as a larger amount of carbon dioxide recovered, 10 when used in a concentration of 60 wt%. These results clearly indicate that the absorbent of the present invention achieves particularly high absorption and desorption rates, compared to the absorbents disclosed in Patent Literature 2 and 3. [0077] 15 [Table 4]

CO

2 partial Type of amine Amine Absorption Desorption Amount pressure concentration rate rate of CO2 (bar) (wt%) (g/Lhr) (g/Lhr) recovered Example 1 16 (high) Bis(2DMAE)ER 60 (high) 403 498 213 Com. Ex. 1 16 (high) Bis(2DMAE)ER 30 (low) 160 117 66 Com. Ex. 6 16 (high) MDEA 60 (high) 118 190 95 Com. Ex. 4 16 (high) MDEA 35 (low) 144 155 71 Corn. Ex. 7 16 (high) PMDETA 60 (high) 281 414 170 Corn. Ex.8 16 (high) PMDETA 30 (low) 151 116 63 [0078] Test Example 3 A carbon dioxide absorption/desorption test was performed using an absorber (not shown). The water-containing 20 liquid absorbents used in Test Example 3 had the following composition: Bis(2DMAE)ER: 30, 50, 60, 70, 80, or 90 wt%. The absorption and desorption conditions used in this test example were as follows: absorption conditions: 40 0 C, 16 bar (CO 2 partial pressure), desorption conditions: 120 0 C, 16 bar (CO 2 partial 25 pressure). [0079] Table 5 and Fig. 2 show the results of measuring the carbon dioxide absorption and desorption rates, and the amount of -18

CO

2 recovered in Test Example 3. [0080] As shown in Fig. 2, much higher absorption rates were achieved at an amine concentration of 60 to 90 wt% than at an 5 amino concentration of 30 to 50 wt%. Both the desorption rate and the amount of carbon dioxide recovered achieved maximum values at an amine concentration of 60 wt%. These results clearly indicate that when the concentration of Bis(2DMAE)ER is 60 to 90 wt%, the absorbent can achieve high performance. 10 [0081] [Table 5]

CO

2 partial Type of amine Amine Absorption Desorption Amount pressure concentration rate rate of CO2 (bar) (wt%) (g/Lhr) (g/Lhr) recovered Com. Ex. 1 16 (high) Bis(2DMAE)ER 30 160 117 66 Com. Ex. 9 16 (high) Bis(2DMAE)ER 50 204 287 131 Example 1 16 (high) Bis(2DMAE)ER 60 403 498 213 Example 2 16 (high) Bis(2DMAE)ER 70 510 459 175 Example 3 16 (high) Bis(2DMAE)ER 80 513 390 142 Example 4 16 (high) Bis(2DMAE)ER 90 512 263 100 [0082] Test Example 4 A carbon dioxide absorption/desorption test was 15 performed using an absorber (not shown). The water-containing liquid absorbent used in Test Example 4 had the following composition: Bis(2DMAE)ER: 60 wt%. The absorption and desorption conditions used in this test example are as follows: absorption conditions: 40 0 C; desorption conditions: 120*C; 20 pressure during the absorption and desorption: 0.2, 2, 16, or 40 bar (CO 2 partial pressure). [0083] Table 6 shows the results of measuring the carbon dioxide absorption and desorption rates, and the amount of CO 2 25 recovered in Test Example 4. [0084] As shown in Table 6, the absorption and desorption rates were 100 g/L hr or more at a CO 2 pressure of 2 bar or more.

-19 The higher the CO 2 partial pressure, the higher the absorption and desorption rates. Carbon dioxide was recovered in an amount of 100 g/L or more at a CO 2 partial pressure of 2 bar or higher. These results clearly indicate that the absorbent achieves high 5 performance at a CO 2 partial pressure of 2 bar or more. It was also confirmed that when the absorption conditions are a temperature of 40 0 C and a CO 2 partial pressure of 40 bar, and the desorption conditions are a temperature of 120 0 C and a CO 2 partial pressure of 80 bar, carbon dioxide is recovered in an amount of 10 100 g/L or more. [0085] [Table 61

CO

2 partial Type of amine Amine Absorption Desorption Amount pressure concentration rate rate of CO2 (bar) (wt%) (g/Lhr) (g/Lhr) recovered Example 5 40 Bis(2DMAE)ER 60 (high) 728 309 363 Example 1 16 Bis(2DMAE)ER 60 (high) 403 498 213 Example 6 2 Bis(2DMAE)ER 60 (high) 173 107 116 Com. Ex. 2 0.2 Bis(2DMAE)ER 60 (high) <100 <100 55 [00861 These results clearly indicate that when a water 15 containing liquid absorbent containing 60 to 90 wt% of Bis(2DMAE)ER is used to remove carbon dioxide from a gas flow having a carbon dioxide partial pressure of 2 bar or more, carbon dioxide in the gas can be more efficiently absorbed and desorbed with a lower energy consumption than ever. 20 [00871 Further, although the water-containing liquid absorbent containing two or more ether groups is not different from bis(2 dimethylaminoethyl)ether in terms of the CO 2 absorption and desorption rates, and the amount of CO 2 recovered, the volatilized 25 amount can be reduced due to reduced vapor pressure.