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CO2 absorption capacity using aqueous potassium carbonate with 2-methylpiperazine and piperazine
Journal of Industrial and Engineering Chemistry 18 (2012) 105–110
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
CO2 absorption capacity using aqueous potassium carbonate with 2-methylpiperazine and piperazine Young Eun Kim, Jeong Ho Choi, Sung Chan Nam, Yeo Il Yoon * Greenhouse Gas Research Center, Korea Institute of Energy Research, 102, Gajeong-ro, Yuseong-gu, Daejeon 305-343, South Korea
A R T I C L E I N F O
Article history: Received 1 December 2010 Accepted 27 January 2011 Available online 9 November 2011 Keywords: Absorption CO2 capture Cyclic amine Phase equilibrium Potassium carbonate
A B S T R A C T
Various amines as a promoter have been added to the K2CO3 solution in order to improve the performance of the CO2 absorption process. Piperazine (PZ) and 2-methylpiperazine (2-MPZ), cyclic Þ and diamines were used as promoters in this study. The equilibrium partial pressure of CO2 ðPCO 2 pressure changes were measured at 313, 333 and 353 K condition of flue gas using VLE (vapor–liquid equilibrium) equipment. The results show that 2-MPZ possesses the ability to promote CO2 absorption capacity. The K2CO3/2-MPZ solution had an equilibrium partial pressure of CO2 that was lower than that of the MEA solution at 333 K. ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The absorption of acid gas by chemical absorbents is a commercially available method that is suitable for treating large quantities of gas. Absorption is an effective process for treatment of gases, including low partial pressure of CO2. However, chemical absorption process needs high energy consumption to strip CO2 from absorbent. Therefore many researchers tried to development the absorbent that has a low regeneration heat is required to develop cost-effective absorption process. Recently, alkanolamine solutions have been widely adopted in CO2 recovery plants because of satisfaction to use in large processes. Numerous researchers have investigated the thermodynamics and kinetics between CO2 and aqueous amine solutions, such as monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP) and methyldiethanolamine (MDEA). MEA has been used extensively due to its advantages over the other commercial amines, such as high absorption rate, high equilibrium capacity on a mass basis, and low solvent cost. However, MEA has a high enthalpy of reaction with CO2 because of the formation of a stable carbamate. Furthermore, solvent loss is greater than other amines and requires corrosion inhibitors when used in higher concentration [1–4]. Blends of primary and tertiary amines, or secondary and tertiary amines, combine the higher absorption rate of the primary or secondary amine with the higher equilibrium capacity of the tertiary amine. Glasscock et al. [5] and Hagewiesche et al. [6]
* Corresponding author. E-mail address: [email protected] (Y.I. Yoon).
studied the CO2 absorption rate of aqueous MDEA/MEA solutions. Xiao et al. [7] and Mandal and Bandyopadhyay [8] investigated CO2 absorption of aqueous AMP/MEA solutions. Potassium carbonate (K2CO3) is effective for treating CO2 from synthesis gas at high temperature and pressure. Benson et al. [9,10] tested the performance of K2CO3 40 wt% solution in a pilot plant in order to determine the steam consumption for regeneration at various operating conditions. The high temperature increases the solubility of K2CO3, thus permitting operation with high concentration. The estimated cost for removing CO2 of the process using the pot potassium carbonate was lower than that of amine. The Benfield process is an example of a commercial process that uses a K2CO3 20– 30 wt% solution. Several researchers have found the benefits of adding amine promoters to K2CO3 aqueous solution to enhance the absorption rate at a lower temperature and reduce the regeneration energy of the solvent. Various amines have been added to aqueous K2CO3 solution to improve its CO2 absorption capacity. Yih and Sun [11], for example, used DEA and DIPA as a promoter. The absorption rate of CO2 into K2CO3 20 wt% was increased approximately 1.6 times by addition of only DEA 2 wt% at 353 K. Cullinane and Rochelle [12,13] studied thermodynamics and kinetics of the aqueous K2CO3 solution promoted by piperazine (PZ). PZ has two amino groups that have favorable effects on absorption rates. K2CO3 1.8 m/PZ 1.8 m solution have absorption rate that is higher than 7 m MEA at 333 K, by a factor of 1.5. Oexmann et al. [14] simulated of the full CO2-capture process for K2CO3/PZ solution. The absorption process, using K2CO3/PZ solution with subsequent CO2-compression to 110 bar, had energetic advantages over the reference which used MEA.
1226-086X/$ – see front matter ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2011.11.078
Y.E. Kim et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 105–110
106
In this study, 2-methylpiperazine (2-MPZ) and PZ, cyclic diamines, were examined as a potential additive. The pKa values of 2-MPZ and PZ were represented as higher than MEA [15,16]. The originality of this study in comparison with previous research is obtaining the VLE data of the aqueous K2CO3/2-MPZ solution that is a new absorbent. There is no existing literature that discusses the reaction between aqueous K2CO3/2-MPZ solution and CO2. Fig. 1 shows the structures of 2-MPZ and PZ where 2-MPZ has a steric hindrance caused by a methyl functional group. Sterically hindered amines form an unstable carbamate, a large amount of bicarbonate and carbonate exist in solution. Therefore, the regeneration heat of 2-MPZ may be lower than PZ. 2. Experimental 2.1. Reaction mechanism The chemical reaction of aqueous K2CO3 solution and CO2 takes place through Eqs. (1)–(4) [17–19]. Hydrolysis of K2CO3: K2 CO3 ðsÞ þ H2 OðlÞ $ 2Kþ þ HCO3 þ OH
(1)
Ionization of water: þ
2H2 OðlÞ $ H3 O þ OH
(2)
Bicarbonate formation: OH þ CO2 ðaqÞ $ HCO3
(3)
Carbonate formation: HCO3 þ OH $ CO3 2 þ H2 O
(4)
Since the reaction of the carbonate formation is instantaneous, the overall reaction between the aqueous K2CO3 solution and CO2 is represented as follows: K2 CO3 ðsÞ þ H2 OðlÞ þ CO2 ðaqÞ $ 2KHCO3
(6)
PZ deprotonation: PZHþ þ H2 OðlÞ $ PZðlÞ þ H3 Oþ
(7)
Carbamate formation: PZðlÞ þ H2 OðlÞ þ CO2 ðaqÞ $ PZCOO þ H3 Oþ
(8)
PZHþ þ H2 OðlÞ þ CO2 ðaqÞ $ Hþ PZCOO þ H3 Oþ
(9)
PZCOO þ H2 OðlÞ þ CO2 ðaqÞ $ PZðCOO Þ2 þ H3 Oþ
K+:promoter
K2CO3/promoter (wt%) K2CO3
15
PZ 2-MPZ
20
PZ 2-MPZ
7.5 10 7.5 10 7.5 10 7.5 10
2.49:1 1.87:1 2.89:1 2.18:1 3.33:1 2.49:1 3.88:1 2.90:1
During the chemical absorption of CO2 into aqueous K2CO3/PZ solution, CO2 is absorbed as carbamate (PZCOO, H+PZCOO, PZ(COO)2) and bicarbonate (HCO3). Most of the CO2 reacts in the solution with PZ to form carbamate. The CO2 absorption mechanism of the aqueous 2-MPZ solution is similar to PZ. However, the bicarbamate (2-MPZ(COO)2) may not exist in the CO2 loaded 2MPZ solution because of the sterical hindrance of the methyl group. 2.2. Materials The reagent grade 2-MPZ (>98.0% pure) and AMP (>99% pure) were obtained from Acros organics, and the K2CO3 (>anhydrous 99.5% pure), PZ (>anhydrous 99.0% pure), MEA (>99.0% pure) were obtained from Samchun Chemicals, Korea. The aqueous solutions were prepared the concentrations of K2CO3 15, 20 wt%/2-MPZ 7.5, 10 wt%, K2CO3 15, 20 wt%/PZ 7.5, 10 wt%, respectively. Aqueous MEA and AMP solution were prepared the concentration of 30 wt%. PZ is a white solid at room temperature with solubility of 150 g/‘ in water. Therefore, the K2CO3/PZ solution had to be heated before it was used in order to obtain a solution with the preferred concentration. The CO2 (purity 99.99%) and N2 (purity 99.999%) gases were obtained from Special Gas, Korea. K+/promoter ratio of aqueous K2CO3/promoter solution at 333 K is listed in Table 1.
(5)
The chemical reaction between aqueous PZ solution and CO2 is as follows [20–22]. PZ protonation: PZðsÞ þ H2 OðlÞ $ PZHþ þ OH
Table 1 K+/promoter ratio of aqueous K2CO3/promoter solution at 333 K.
(10)
2.3. Experimental apparatus and procedure The equilibrium partial pressures of CO2 and pressure change in reactor were measured by using the VLE apparatus. The VLE apparatus (Fig. 2), consisted of a gas reservoir, reactor, pressuremeasuring instrument, and a recorder. The gas reservoir and the reactor were made of 316 stainless steel with an internal volume of 300.29 cm3 and 322.56 cm3, respectively. The differing of volumes between the gas reservoir and the reactor were corrected with N2 gas. The temperatures of the CO2 gas and solution were measured with a K-type thermocouple. Furthermore, the pressure of the gas was continuously measured using a pressure sensor that was a PTB model (range: 1 to 10 kgf/cm2) of Synsys Ltd., Korea. The gas reservoir and reactor were heated using a water bath method.
Fig. 1. Structure of PZ and 2-MPZ.
Y.E. Kim et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 105–110
107
Fig. 2. Vapor–liquid equilibrium apparatus.
In this study, VLE experiments were conducted over a broad range of temperature (313–353 K) and injection pressure of CO2 (500–800 kPa). The conditions were set up considering CO2 capture in the PFBC (pressurized fluidized bed combustion) power plant. PFBC is an advanced clean-coal power production system with low emissions such as sulfur dioxide (SO2) and nitrogen oxides (NOx). It has good efficiency compared with conventional coal fired plants [23]. The inlet CO2 gas (99.99%) was heated in the reservoir prior to entering the reactor with 313 K. The solution (100 ml) was kept in a reactor. Before starting the experiment, residual gas in reactor was removed from the reactor using a vacuum pump to prevent the contamination of reactants. In all of the experiments, stirring was performed continuously in the reactor at a speed of 170 rpm, maintaining a smooth interfacial area. As the desired temperatures of the gas reservoir and the reactor were achieved, the valve was opened to inject CO2 into the reactor. The pressure of the CO2 in the reactor was decreased over time. A state of equilibrium was obtained when the pressure and temperature values were constant. By measuring the pressure at this point, the equilibrium partial pressure of CO2 was calculated. The partial pressure of CO2 was calculated as the difference between the initial and final pressure in the reactor. The pressure change in the reactor was measured every 5 s. In this experiment, the injection of CO2 into
Fig. 3. CO2 equilibrium into aqueous AMP 30 wt% solution at 313, 333, 353 K.
the reactor was conducted again when equilibrium was reached. The injected CO2 into the closed reactor was absorbed only by the absorbent. Therefore, the absorption rate was calculated by measuring pressure change. 3. Results and discussion 3.1. Preliminary test Fig. 3 describes the reliability for the VLE apparatus and experimental procedures. The solubility of CO2 in aqueous AMP 30 wt% solution measured at 313, 333, and 353 K. This result shows an agreement between this work and other literature [24,25]. The solubility that is represented by equilibrium partial pressure of CO2 ðPCO Þ decreased increasing in temperature. 2
3.2. Effect of solution concentration Figs. 4 and 5 show the VLE curves of CO2 in aqueous K2CO3 15, 20 wt%, aqueous K2CO3 15, 20 wt%/PZ 7.5, 10 wt% and K2CO3 15, 20 wt%/2-MPZ 7.5, 10 wt% solutions. We added the result of aqueous K2CO3 15, 20 wt% to compare the additive effects. The aqueous K2CO3 solution is very low capacity and slow CO2 absorption velocity because of no transfer carbonate and
Fig. 4. CO2 equilibrium into aqueous K2CO3/PZ solution at 333 K; lines are prediction results.
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Fig. 5. CO2 equilibrium into aqueous K2CO3/2-MPZ solution at 333 K; lines are prediction results.
Fig. 7. Reaction rate for the reaction of CO2 into aqueous K2CO3/2-MPZ solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
bicarbonate, which is mentioned at introduction. The results represent the effects of the concentration on the equilibrium partial pressure of CO2. The loading (mol CO2/mol solute), absorption capacity in these graphs is represented at the specific equilibrium partial pressure of CO2. These figures show that with increasing concentrations of K2CO3 and promoter in the solution, CO2 loading decreases at a given temperature. The absorption capacity of aqueous K2CO3/2-MPZ and K2CO3/PZ solutions was affected by the concentration of the promoter rather than K2CO3. At the loading of 0.35, the absorption capacity of aqueous MEA 30 wt% began to decrease rapidly (see Fig. 12). Therefore, the absorption capacities of the aqueous K2CO3/2-MPZ and K2CO3/PZ solutions were compared with at this point. Aqueous K2CO3 20 wt%/2-MPZ 10 wt% and K2CO3 20 wt%/PZ 10 wt% solutions had the lowest equilibrium partial pressure of CO2 under the same conditions. Even at high loading, the aqueous K2CO3 20 wt%/2-MPZ and PZ 7.5, 10 wt% solutions had no crystalline at 333 K. However, at the temperature range lower than 313 K, these solutions had a large amount of KHCO3 crystalline. Therefore, these solutions have the potential to cause the absorption process to shut down. Furthermore, these solutions divided into two liquid phases before they reacted with the CO2.
The absorption rates for aqueous K2CO3/PZ and K2CO3/2-MPZ solutions are shown in Figs. 6 and 7, respectively. Theses figures represent the pressure change over time after the first injection of CO2. The absorption rate of aqueous K2CO3/PZ and K2CO3/2-MPZ was similar even though the concentrations of K2CO3 and PZ changed. In this case, the absorption rates of these solutions are not directly relevant to increasing absorbent concentrations. Therefore, the concentration of K2CO3 15 wt%/2-MPZ, PZ 10 wt% appeared to be the ideal condition. Cullinane [21] showed that maximum reactive PZ concentration occurs when the PZ concentration is maximized and K+ is added in a 2:1 ratio of K+:PZ, by model prediction. Table 2 presents the K+:promoter ratio in aqueous K2CO3/2-MPZ and K2CO3/PZ solutions, which were used in this study. The K+:PZ ratio of the K2CO3 15 wt%/PZ 10 wt% solution is 1.87:1, the closest to 2:1. Also, the K+:2-MPZ of the K2CO3 15 wt%/2-MPZ 10 wt% solution is 2.18:1. However, all of the K2CO3/PZ solutions tested in this study, have a floating crystal at room temperature due to the low solubility of PZ.
In the previous section, the concentration of K2CO3 15 wt%/ promoter 10 wt% showed an excellent CO2 absorption capacity
Fig. 6. Reaction rate for the reaction of CO2 into aqueous K2CO3/PZ solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
Fig. 8. CO2 equilibrium into aqueous K2CO3 15 wt%/PZ 10 wt% solution at various temperatures; lines are prediction results.
3.3. Effect of temperature
Y.E. Kim et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 105–110
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Table 2 Solubility of carbon dioxide in aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solutions at 333 K. K2CO3/PZ (15/10 wt%)
K2CO3/2-MPZ (15/10 wt%)
a
PCO 2
0.198 0.387 0.575 0.753 0.898 0.978 1.017 1.038
1.765 3.236 7.355 29.714 120.230 336.761 540.837 675.875
(kPa)
a
PCO 2
0.207 0.411 0.612 0.805 0.960 1.029 1.058 1.074
1.961 3.236 9.414 32.068 130.821 385.205 597.127 722.358
(kPa)
MEA (30 wt%)
AMP (30 wt%)
a
PCO 2
0.090 0.177 0.267 0.351 0.436 0.514 0.571 0.608 0.632 0.652 0.662 0.672
0.785 3.236 3.530 4.119 8.924 50.112 194.662 371.574 520.733 613.014 711.669 761.094
(kPa)
a
PCO (kPa)
0.134 0.260 0.385 0.505 0.623 0.731 0.812 0.861 0.891 0.905 0.915 0.926 0.931
1.667 4.413 9.709 22.850 41.874 91.594 217.610 394.424 550.546 676.267 756.387 782.179 819.738
2
a = loading (mol CO2/mol solute), PCO ¼ equilibrium partial pressure of CO2 : 2
with no crystalline formation. Therefore, K2CO3 15 wt%/2-MPZ, PZ 10 wt% are tested to investigate the effect of temperature on CO2 absorption capacity. The VLE curves of aqueous K2CO3 15 wt%/2MPZ 10 wt% and K2CO3 15 wt%/PZ 10 wt% were shown in Figs. 8 and 9, respectively. As shown in Fig. 9, the partial pressure of CO2 in aqueous K2CO3/PZ solution increase with increasing of temperature. Figs. 10 and 11 both show that the absorption rate of K2CO3 15 wt%/2-MPZ 10 wt% and K2CO3 15 wt%/PZ 10 wt% increased according to increasing temperature. The enhancement of the absorption rate was related to an increase in the solubility of solute at a higher temperature. The CO2 loadings of K2CO3/PZ and K2CO3/ 2-MPZ solutions were lager at 313 K. The important factor is the absorption rate as well as the loading capacity because the liquid and gas come into contact rapidly in the absorption process. Therefore, it’s necessary to consider various factors such as Henry’s constant, gas feed temperature, solution temperature and gas– liquid reaction in order to determine the optimum conditions [26]. The comparison of absorption capacities between K2CO3 15 wt%/2-MPZ, PZ 10 wt% and conventional amine solutions are shown in Figs. 12 and 13. Furthermore, Table 2 presents the equilibrium partial pressure of CO2. The loading capacity of K2CO3 15 wt%/promoter 10 wt% was higher than MEA 30 wt% or AMP 30 wt% at specific partial pressure of CO2. The VLE curve of K2CO3/ PZ and K2CO3/2-MPZ had a gentle slope throughout the whole range, whereas MEA had a steep slope over the loading of 0.35. The loading capacity of MEA is limited to approximately 0.5 mol of CO2
Fig. 9. CO2 equilibrium into aqueous K2CO3 15 wt%/2-MPZ 10 wt% solution at various temperatures; lines are prediction results.
Fig. 10. Absorption rate of CO2 into aqueous K2CO3 15 wt%/PZ 10 wt% solution at various temperatures; lines are prediction results and the level of loading at decreasing point is 0.35.
Fig. 11. Absorption rate of CO2 into aqueous K2CO3 15 wt%/2-MPZ 10 wt% solution at various temperatures; lines are prediction results and the level of loading at decreasing point is 0.35.
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Fig. 12. CO2 Equilibrium into aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solution at 333 K; lines are prediction results.
K2CO3/PZ solutions were tested by using VLE apparatus. The equilibrium partial pressures of CO2 and pressure change were measured in order to estimate the CO2 loading capacity and absorption rate. The increasing concentration of the promoter, rather than K2CO3, affected the equilibrium partial pressures of the aqueous K2CO3/2-MPZ and K2CO3/PZ solutions. However the absorption rate of CO2 was similar through the tested concentration of K2CO3/2-MPZ of K2CO3/PZ. The equilibrium partial pressure of CO2 in aqueous K2CO3/2-MPZ and K2CO3/PZ solutions increased with the increasing temperature. Moreover, the absorption rate of these solutions also increased according to increasing temperature. The aqueous K2CO3 20 wt%/2-MPZ 10 wt% and K2CO3 20 wt%/PZ 10 wt% solutions had the lowest equilibrium partial pressure of CO2 under the same conditions. However, these solutions had a large amount of KHCO3 crystalline at the temperature range lower than 313 K. Furthermore, these solutions divided into two liquid phase before they reacted with the CO2. Therefore, the concentration of K2CO3 15 wt%/2-MPZ, PZ 10 wt% appeared to be ideal condition. The CO2 loading capacities of K2CO3 15 wt%/2-MPZ and PZ 10 wt% solutions were higher than MEA 30 wt% or AMP 30 wt% at the specific partial pressure of CO2. Additionally, the CO2 loading capacity of K2CO3/2-MPZ was similar to K2CO3/PZ. However, all of the K2CO3/PZ solutions tested in this work, had a floating crystal at room temperature due to the low solubility of PZ. 2-MPZ showed potential as a promoter of K2CO3. Acknowledgements This research was supported by a grant (2010K000126) from Carbon Dioxide Reduction & Sequestration Research Center, one of the 21st Century Frontier Programs funded by the Ministry of Science and Technology of the Korean government. References
Fig. 13. Absorption rate of CO2 into aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
per mole of amine, even at a relatively high partial pressure of CO2. This was because a MEA carbamate formed a free MEA through the hydrolysis. The difference of equilibrium partial pressure of CO2 between the K2CO3/2-MPZ, PZ and MEA solutions increased according to increasing CO2 loading. This result shows that aqueous K2CO3/2-MPZ, PZ solutions are effective at high partial pressure of CO2. Therefore, it is possible to use aqueous K2CO3/2MPZ and K2CO3/PZ solutions in the cement and steel industry as well as coal-fired power plants. 4. Conclusions In this study, 2-MPZ and PZ were added to aqueous K2CO3 solution to prevent crystalline formation and increase absorption capacity. Various concentrations of aqueous K2CO3/2-MPZ and
[1] A. Veawab, P. Tontiwachwuthikul, A. Chakma, Ind. Eng. Chem. Res. 38 (1999) 3917. [2] N. McCann, M. Maeder, M. Attalla, Ind. Eng. Chem. Res. 47 (2008) 2002. [3] I.R. Soosaiprakasam, A. Veawab, Int. J. Greenhouse Gas Control 2 (2008) 553. [4] I. Kim, K.A. Hoff, E.T. Hessen, T. Haug-Warberg, H.F. Svendsen, Chem. Eng. Sci. 64 (2009) 2027. [5] D.A. Glasscock, J.E. Critchfield, G.T. Rochelle, Chem. Eng. Sci. 46 (1991) 2829. [6] D.P. Hagewiesche, S.S. Ashour, H.A. Al-ghwas, O.C. Sandall, Chem. Eng. Sci. 50 (1995) 1071. [7] J. Xiao, C.W. Li, M.H. Li, Chem. Eng. Sci. 55 (2000) 161. [8] B.P. Mandal, S.S. Bandyopadhyay, Chem. Eng. Sci. 61 (2006) 5440. [9] H.E. Benson, J.H. Field, R.M. Jimeson, Chem. Eng. Prog. 50 (1954) 356. [10] H.E. Benson, J.H. Field, W.P. Haynes, Chem. Eng. Prog. 10 (1956) 433. [11] S.M. Yih, C.C. Sun, Chem. Eng. J. 34 (1987) 65. [12] J.T. Cullinane, G.T. Rochelle, Chem. Eng. Sci. 59 (2004) 3619. [13] J.T. Cullinane, G.T. Rochelle, Ind. Eng. Chem. Res. 45 (2006) 2531. [14] J. Oexmann, C. Hensel, A. Kather, Int. J. Greenhouse Gas Control 2 (2008) 539. [15] E.S. Hamborg, G.F. Versteeg, J. Chem. Eng. Data 54 (2009) 1318. [16] F. Khalili, A. Henni, A.L.L. East, J. Chem. Eng. Data 54 (2009) 2914. [17] G. Astarita, D.W. Savage, Chem. Eng. Sci. 36 (1981) 581. [18] M.R. Rahimpour, A.Z. Kashkooli, Chem. Eng. Process. 43 (2004) 857. [19] M. Ahmadi, V.G. Gomes, K. Ngian, Sep. Purif. Technol. 63 (2008) 107. [20] P.W.J. Derks, H.B.S. Dijkstra, J.A. Hogendoorn, G.F. Versteeg, AIChE J. 51 (2005) 2311. [21] J.T. Cullinane, G.T. Rochelle, Fluid Phase Equilib. 227 (2005) 197. [22] A. Samanta, S.S. Bandyopadhyay, Chem. Eng. Sci. 62 (2007) 7312. [23] K.H. Han, Y.S. Song, J.I. Ryu, J.E. Son, G.T. Jin, Hwahak Konhak 41 (2003) 86. [24] M.H. Li, B.C. Chang, J. Chem. Eng. Data 39 (1994) 448. [25] D.J. Seo, W.H. Hong, J. Chem. Eng. Data 41 (1996) 258. [26] P.V. Danckwerts, Gas-Liquid Reactions, McGraw-Hill, 1970.
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
CO2 absorption capacity using aqueous potassium carbonate with 2-methylpiperazine and piperazine Young Eun Kim, Jeong Ho Choi, Sung Chan Nam, Yeo Il Yoon * Greenhouse Gas Research Center, Korea Institute of Energy Research, 102, Gajeong-ro, Yuseong-gu, Daejeon 305-343, South Korea
A R T I C L E I N F O
Article history: Received 1 December 2010 Accepted 27 January 2011 Available online 9 November 2011 Keywords: Absorption CO2 capture Cyclic amine Phase equilibrium Potassium carbonate
A B S T R A C T
Various amines as a promoter have been added to the K2CO3 solution in order to improve the performance of the CO2 absorption process. Piperazine (PZ) and 2-methylpiperazine (2-MPZ), cyclic Þ and diamines were used as promoters in this study. The equilibrium partial pressure of CO2 ðPCO 2 pressure changes were measured at 313, 333 and 353 K condition of flue gas using VLE (vapor–liquid equilibrium) equipment. The results show that 2-MPZ possesses the ability to promote CO2 absorption capacity. The K2CO3/2-MPZ solution had an equilibrium partial pressure of CO2 that was lower than that of the MEA solution at 333 K. ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The absorption of acid gas by chemical absorbents is a commercially available method that is suitable for treating large quantities of gas. Absorption is an effective process for treatment of gases, including low partial pressure of CO2. However, chemical absorption process needs high energy consumption to strip CO2 from absorbent. Therefore many researchers tried to development the absorbent that has a low regeneration heat is required to develop cost-effective absorption process. Recently, alkanolamine solutions have been widely adopted in CO2 recovery plants because of satisfaction to use in large processes. Numerous researchers have investigated the thermodynamics and kinetics between CO2 and aqueous amine solutions, such as monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2-methyl-1-propanol (AMP) and methyldiethanolamine (MDEA). MEA has been used extensively due to its advantages over the other commercial amines, such as high absorption rate, high equilibrium capacity on a mass basis, and low solvent cost. However, MEA has a high enthalpy of reaction with CO2 because of the formation of a stable carbamate. Furthermore, solvent loss is greater than other amines and requires corrosion inhibitors when used in higher concentration [1–4]. Blends of primary and tertiary amines, or secondary and tertiary amines, combine the higher absorption rate of the primary or secondary amine with the higher equilibrium capacity of the tertiary amine. Glasscock et al. [5] and Hagewiesche et al. [6]
* Corresponding author. E-mail address: [email protected] (Y.I. Yoon).
studied the CO2 absorption rate of aqueous MDEA/MEA solutions. Xiao et al. [7] and Mandal and Bandyopadhyay [8] investigated CO2 absorption of aqueous AMP/MEA solutions. Potassium carbonate (K2CO3) is effective for treating CO2 from synthesis gas at high temperature and pressure. Benson et al. [9,10] tested the performance of K2CO3 40 wt% solution in a pilot plant in order to determine the steam consumption for regeneration at various operating conditions. The high temperature increases the solubility of K2CO3, thus permitting operation with high concentration. The estimated cost for removing CO2 of the process using the pot potassium carbonate was lower than that of amine. The Benfield process is an example of a commercial process that uses a K2CO3 20– 30 wt% solution. Several researchers have found the benefits of adding amine promoters to K2CO3 aqueous solution to enhance the absorption rate at a lower temperature and reduce the regeneration energy of the solvent. Various amines have been added to aqueous K2CO3 solution to improve its CO2 absorption capacity. Yih and Sun [11], for example, used DEA and DIPA as a promoter. The absorption rate of CO2 into K2CO3 20 wt% was increased approximately 1.6 times by addition of only DEA 2 wt% at 353 K. Cullinane and Rochelle [12,13] studied thermodynamics and kinetics of the aqueous K2CO3 solution promoted by piperazine (PZ). PZ has two amino groups that have favorable effects on absorption rates. K2CO3 1.8 m/PZ 1.8 m solution have absorption rate that is higher than 7 m MEA at 333 K, by a factor of 1.5. Oexmann et al. [14] simulated of the full CO2-capture process for K2CO3/PZ solution. The absorption process, using K2CO3/PZ solution with subsequent CO2-compression to 110 bar, had energetic advantages over the reference which used MEA.
1226-086X/$ – see front matter ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2011.11.078
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In this study, 2-methylpiperazine (2-MPZ) and PZ, cyclic diamines, were examined as a potential additive. The pKa values of 2-MPZ and PZ were represented as higher than MEA [15,16]. The originality of this study in comparison with previous research is obtaining the VLE data of the aqueous K2CO3/2-MPZ solution that is a new absorbent. There is no existing literature that discusses the reaction between aqueous K2CO3/2-MPZ solution and CO2. Fig. 1 shows the structures of 2-MPZ and PZ where 2-MPZ has a steric hindrance caused by a methyl functional group. Sterically hindered amines form an unstable carbamate, a large amount of bicarbonate and carbonate exist in solution. Therefore, the regeneration heat of 2-MPZ may be lower than PZ. 2. Experimental 2.1. Reaction mechanism The chemical reaction of aqueous K2CO3 solution and CO2 takes place through Eqs. (1)–(4) [17–19]. Hydrolysis of K2CO3: K2 CO3 ðsÞ þ H2 OðlÞ $ 2Kþ þ HCO3 þ OH
(1)
Ionization of water: þ
2H2 OðlÞ $ H3 O þ OH
(2)
Bicarbonate formation: OH þ CO2 ðaqÞ $ HCO3
(3)
Carbonate formation: HCO3 þ OH $ CO3 2 þ H2 O
(4)
Since the reaction of the carbonate formation is instantaneous, the overall reaction between the aqueous K2CO3 solution and CO2 is represented as follows: K2 CO3 ðsÞ þ H2 OðlÞ þ CO2 ðaqÞ $ 2KHCO3
(6)
PZ deprotonation: PZHþ þ H2 OðlÞ $ PZðlÞ þ H3 Oþ
(7)
Carbamate formation: PZðlÞ þ H2 OðlÞ þ CO2 ðaqÞ $ PZCOO þ H3 Oþ
(8)
PZHþ þ H2 OðlÞ þ CO2 ðaqÞ $ Hþ PZCOO þ H3 Oþ
(9)
PZCOO þ H2 OðlÞ þ CO2 ðaqÞ $ PZðCOO Þ2 þ H3 Oþ
K+:promoter
K2CO3/promoter (wt%) K2CO3
15
PZ 2-MPZ
20
PZ 2-MPZ
7.5 10 7.5 10 7.5 10 7.5 10
2.49:1 1.87:1 2.89:1 2.18:1 3.33:1 2.49:1 3.88:1 2.90:1
During the chemical absorption of CO2 into aqueous K2CO3/PZ solution, CO2 is absorbed as carbamate (PZCOO, H+PZCOO, PZ(COO)2) and bicarbonate (HCO3). Most of the CO2 reacts in the solution with PZ to form carbamate. The CO2 absorption mechanism of the aqueous 2-MPZ solution is similar to PZ. However, the bicarbamate (2-MPZ(COO)2) may not exist in the CO2 loaded 2MPZ solution because of the sterical hindrance of the methyl group. 2.2. Materials The reagent grade 2-MPZ (>98.0% pure) and AMP (>99% pure) were obtained from Acros organics, and the K2CO3 (>anhydrous 99.5% pure), PZ (>anhydrous 99.0% pure), MEA (>99.0% pure) were obtained from Samchun Chemicals, Korea. The aqueous solutions were prepared the concentrations of K2CO3 15, 20 wt%/2-MPZ 7.5, 10 wt%, K2CO3 15, 20 wt%/PZ 7.5, 10 wt%, respectively. Aqueous MEA and AMP solution were prepared the concentration of 30 wt%. PZ is a white solid at room temperature with solubility of 150 g/‘ in water. Therefore, the K2CO3/PZ solution had to be heated before it was used in order to obtain a solution with the preferred concentration. The CO2 (purity 99.99%) and N2 (purity 99.999%) gases were obtained from Special Gas, Korea. K+/promoter ratio of aqueous K2CO3/promoter solution at 333 K is listed in Table 1.
(5)
The chemical reaction between aqueous PZ solution and CO2 is as follows [20–22]. PZ protonation: PZðsÞ þ H2 OðlÞ $ PZHþ þ OH
Table 1 K+/promoter ratio of aqueous K2CO3/promoter solution at 333 K.
(10)
2.3. Experimental apparatus and procedure The equilibrium partial pressures of CO2 and pressure change in reactor were measured by using the VLE apparatus. The VLE apparatus (Fig. 2), consisted of a gas reservoir, reactor, pressuremeasuring instrument, and a recorder. The gas reservoir and the reactor were made of 316 stainless steel with an internal volume of 300.29 cm3 and 322.56 cm3, respectively. The differing of volumes between the gas reservoir and the reactor were corrected with N2 gas. The temperatures of the CO2 gas and solution were measured with a K-type thermocouple. Furthermore, the pressure of the gas was continuously measured using a pressure sensor that was a PTB model (range: 1 to 10 kgf/cm2) of Synsys Ltd., Korea. The gas reservoir and reactor were heated using a water bath method.
Fig. 1. Structure of PZ and 2-MPZ.
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Fig. 2. Vapor–liquid equilibrium apparatus.
In this study, VLE experiments were conducted over a broad range of temperature (313–353 K) and injection pressure of CO2 (500–800 kPa). The conditions were set up considering CO2 capture in the PFBC (pressurized fluidized bed combustion) power plant. PFBC is an advanced clean-coal power production system with low emissions such as sulfur dioxide (SO2) and nitrogen oxides (NOx). It has good efficiency compared with conventional coal fired plants [23]. The inlet CO2 gas (99.99%) was heated in the reservoir prior to entering the reactor with 313 K. The solution (100 ml) was kept in a reactor. Before starting the experiment, residual gas in reactor was removed from the reactor using a vacuum pump to prevent the contamination of reactants. In all of the experiments, stirring was performed continuously in the reactor at a speed of 170 rpm, maintaining a smooth interfacial area. As the desired temperatures of the gas reservoir and the reactor were achieved, the valve was opened to inject CO2 into the reactor. The pressure of the CO2 in the reactor was decreased over time. A state of equilibrium was obtained when the pressure and temperature values were constant. By measuring the pressure at this point, the equilibrium partial pressure of CO2 was calculated. The partial pressure of CO2 was calculated as the difference between the initial and final pressure in the reactor. The pressure change in the reactor was measured every 5 s. In this experiment, the injection of CO2 into
Fig. 3. CO2 equilibrium into aqueous AMP 30 wt% solution at 313, 333, 353 K.
the reactor was conducted again when equilibrium was reached. The injected CO2 into the closed reactor was absorbed only by the absorbent. Therefore, the absorption rate was calculated by measuring pressure change. 3. Results and discussion 3.1. Preliminary test Fig. 3 describes the reliability for the VLE apparatus and experimental procedures. The solubility of CO2 in aqueous AMP 30 wt% solution measured at 313, 333, and 353 K. This result shows an agreement between this work and other literature [24,25]. The solubility that is represented by equilibrium partial pressure of CO2 ðPCO Þ decreased increasing in temperature. 2
3.2. Effect of solution concentration Figs. 4 and 5 show the VLE curves of CO2 in aqueous K2CO3 15, 20 wt%, aqueous K2CO3 15, 20 wt%/PZ 7.5, 10 wt% and K2CO3 15, 20 wt%/2-MPZ 7.5, 10 wt% solutions. We added the result of aqueous K2CO3 15, 20 wt% to compare the additive effects. The aqueous K2CO3 solution is very low capacity and slow CO2 absorption velocity because of no transfer carbonate and
Fig. 4. CO2 equilibrium into aqueous K2CO3/PZ solution at 333 K; lines are prediction results.
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Fig. 5. CO2 equilibrium into aqueous K2CO3/2-MPZ solution at 333 K; lines are prediction results.
Fig. 7. Reaction rate for the reaction of CO2 into aqueous K2CO3/2-MPZ solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
bicarbonate, which is mentioned at introduction. The results represent the effects of the concentration on the equilibrium partial pressure of CO2. The loading (mol CO2/mol solute), absorption capacity in these graphs is represented at the specific equilibrium partial pressure of CO2. These figures show that with increasing concentrations of K2CO3 and promoter in the solution, CO2 loading decreases at a given temperature. The absorption capacity of aqueous K2CO3/2-MPZ and K2CO3/PZ solutions was affected by the concentration of the promoter rather than K2CO3. At the loading of 0.35, the absorption capacity of aqueous MEA 30 wt% began to decrease rapidly (see Fig. 12). Therefore, the absorption capacities of the aqueous K2CO3/2-MPZ and K2CO3/PZ solutions were compared with at this point. Aqueous K2CO3 20 wt%/2-MPZ 10 wt% and K2CO3 20 wt%/PZ 10 wt% solutions had the lowest equilibrium partial pressure of CO2 under the same conditions. Even at high loading, the aqueous K2CO3 20 wt%/2-MPZ and PZ 7.5, 10 wt% solutions had no crystalline at 333 K. However, at the temperature range lower than 313 K, these solutions had a large amount of KHCO3 crystalline. Therefore, these solutions have the potential to cause the absorption process to shut down. Furthermore, these solutions divided into two liquid phases before they reacted with the CO2.
The absorption rates for aqueous K2CO3/PZ and K2CO3/2-MPZ solutions are shown in Figs. 6 and 7, respectively. Theses figures represent the pressure change over time after the first injection of CO2. The absorption rate of aqueous K2CO3/PZ and K2CO3/2-MPZ was similar even though the concentrations of K2CO3 and PZ changed. In this case, the absorption rates of these solutions are not directly relevant to increasing absorbent concentrations. Therefore, the concentration of K2CO3 15 wt%/2-MPZ, PZ 10 wt% appeared to be the ideal condition. Cullinane [21] showed that maximum reactive PZ concentration occurs when the PZ concentration is maximized and K+ is added in a 2:1 ratio of K+:PZ, by model prediction. Table 2 presents the K+:promoter ratio in aqueous K2CO3/2-MPZ and K2CO3/PZ solutions, which were used in this study. The K+:PZ ratio of the K2CO3 15 wt%/PZ 10 wt% solution is 1.87:1, the closest to 2:1. Also, the K+:2-MPZ of the K2CO3 15 wt%/2-MPZ 10 wt% solution is 2.18:1. However, all of the K2CO3/PZ solutions tested in this study, have a floating crystal at room temperature due to the low solubility of PZ.
In the previous section, the concentration of K2CO3 15 wt%/ promoter 10 wt% showed an excellent CO2 absorption capacity
Fig. 6. Reaction rate for the reaction of CO2 into aqueous K2CO3/PZ solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
Fig. 8. CO2 equilibrium into aqueous K2CO3 15 wt%/PZ 10 wt% solution at various temperatures; lines are prediction results.
3.3. Effect of temperature
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Table 2 Solubility of carbon dioxide in aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solutions at 333 K. K2CO3/PZ (15/10 wt%)
K2CO3/2-MPZ (15/10 wt%)
a
PCO 2
0.198 0.387 0.575 0.753 0.898 0.978 1.017 1.038
1.765 3.236 7.355 29.714 120.230 336.761 540.837 675.875
(kPa)
a
PCO 2
0.207 0.411 0.612 0.805 0.960 1.029 1.058 1.074
1.961 3.236 9.414 32.068 130.821 385.205 597.127 722.358
(kPa)
MEA (30 wt%)
AMP (30 wt%)
a
PCO 2
0.090 0.177 0.267 0.351 0.436 0.514 0.571 0.608 0.632 0.652 0.662 0.672
0.785 3.236 3.530 4.119 8.924 50.112 194.662 371.574 520.733 613.014 711.669 761.094
(kPa)
a
PCO (kPa)
0.134 0.260 0.385 0.505 0.623 0.731 0.812 0.861 0.891 0.905 0.915 0.926 0.931
1.667 4.413 9.709 22.850 41.874 91.594 217.610 394.424 550.546 676.267 756.387 782.179 819.738
2
a = loading (mol CO2/mol solute), PCO ¼ equilibrium partial pressure of CO2 : 2
with no crystalline formation. Therefore, K2CO3 15 wt%/2-MPZ, PZ 10 wt% are tested to investigate the effect of temperature on CO2 absorption capacity. The VLE curves of aqueous K2CO3 15 wt%/2MPZ 10 wt% and K2CO3 15 wt%/PZ 10 wt% were shown in Figs. 8 and 9, respectively. As shown in Fig. 9, the partial pressure of CO2 in aqueous K2CO3/PZ solution increase with increasing of temperature. Figs. 10 and 11 both show that the absorption rate of K2CO3 15 wt%/2-MPZ 10 wt% and K2CO3 15 wt%/PZ 10 wt% increased according to increasing temperature. The enhancement of the absorption rate was related to an increase in the solubility of solute at a higher temperature. The CO2 loadings of K2CO3/PZ and K2CO3/ 2-MPZ solutions were lager at 313 K. The important factor is the absorption rate as well as the loading capacity because the liquid and gas come into contact rapidly in the absorption process. Therefore, it’s necessary to consider various factors such as Henry’s constant, gas feed temperature, solution temperature and gas– liquid reaction in order to determine the optimum conditions [26]. The comparison of absorption capacities between K2CO3 15 wt%/2-MPZ, PZ 10 wt% and conventional amine solutions are shown in Figs. 12 and 13. Furthermore, Table 2 presents the equilibrium partial pressure of CO2. The loading capacity of K2CO3 15 wt%/promoter 10 wt% was higher than MEA 30 wt% or AMP 30 wt% at specific partial pressure of CO2. The VLE curve of K2CO3/ PZ and K2CO3/2-MPZ had a gentle slope throughout the whole range, whereas MEA had a steep slope over the loading of 0.35. The loading capacity of MEA is limited to approximately 0.5 mol of CO2
Fig. 9. CO2 equilibrium into aqueous K2CO3 15 wt%/2-MPZ 10 wt% solution at various temperatures; lines are prediction results.
Fig. 10. Absorption rate of CO2 into aqueous K2CO3 15 wt%/PZ 10 wt% solution at various temperatures; lines are prediction results and the level of loading at decreasing point is 0.35.
Fig. 11. Absorption rate of CO2 into aqueous K2CO3 15 wt%/2-MPZ 10 wt% solution at various temperatures; lines are prediction results and the level of loading at decreasing point is 0.35.
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Fig. 12. CO2 Equilibrium into aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solution at 333 K; lines are prediction results.
K2CO3/PZ solutions were tested by using VLE apparatus. The equilibrium partial pressures of CO2 and pressure change were measured in order to estimate the CO2 loading capacity and absorption rate. The increasing concentration of the promoter, rather than K2CO3, affected the equilibrium partial pressures of the aqueous K2CO3/2-MPZ and K2CO3/PZ solutions. However the absorption rate of CO2 was similar through the tested concentration of K2CO3/2-MPZ of K2CO3/PZ. The equilibrium partial pressure of CO2 in aqueous K2CO3/2-MPZ and K2CO3/PZ solutions increased with the increasing temperature. Moreover, the absorption rate of these solutions also increased according to increasing temperature. The aqueous K2CO3 20 wt%/2-MPZ 10 wt% and K2CO3 20 wt%/PZ 10 wt% solutions had the lowest equilibrium partial pressure of CO2 under the same conditions. However, these solutions had a large amount of KHCO3 crystalline at the temperature range lower than 313 K. Furthermore, these solutions divided into two liquid phase before they reacted with the CO2. Therefore, the concentration of K2CO3 15 wt%/2-MPZ, PZ 10 wt% appeared to be ideal condition. The CO2 loading capacities of K2CO3 15 wt%/2-MPZ and PZ 10 wt% solutions were higher than MEA 30 wt% or AMP 30 wt% at the specific partial pressure of CO2. Additionally, the CO2 loading capacity of K2CO3/2-MPZ was similar to K2CO3/PZ. However, all of the K2CO3/PZ solutions tested in this work, had a floating crystal at room temperature due to the low solubility of PZ. 2-MPZ showed potential as a promoter of K2CO3. Acknowledgements This research was supported by a grant (2010K000126) from Carbon Dioxide Reduction & Sequestration Research Center, one of the 21st Century Frontier Programs funded by the Ministry of Science and Technology of the Korean government. References
Fig. 13. Absorption rate of CO2 into aqueous K2CO3/PZ, K2CO3/2-MPZ, MEA, AMP solution at 333 K; lines are prediction results and the level of loading at decreasing point is 0.35.
per mole of amine, even at a relatively high partial pressure of CO2. This was because a MEA carbamate formed a free MEA through the hydrolysis. The difference of equilibrium partial pressure of CO2 between the K2CO3/2-MPZ, PZ and MEA solutions increased according to increasing CO2 loading. This result shows that aqueous K2CO3/2-MPZ, PZ solutions are effective at high partial pressure of CO2. Therefore, it is possible to use aqueous K2CO3/2MPZ and K2CO3/PZ solutions in the cement and steel industry as well as coal-fired power plants. 4. Conclusions In this study, 2-MPZ and PZ were added to aqueous K2CO3 solution to prevent crystalline formation and increase absorption capacity. Various concentrations of aqueous K2CO3/2-MPZ and
[1] A. Veawab, P. Tontiwachwuthikul, A. Chakma, Ind. Eng. Chem. Res. 38 (1999) 3917. [2] N. McCann, M. Maeder, M. Attalla, Ind. Eng. Chem. Res. 47 (2008) 2002. [3] I.R. Soosaiprakasam, A. Veawab, Int. J. Greenhouse Gas Control 2 (2008) 553. [4] I. Kim, K.A. Hoff, E.T. Hessen, T. Haug-Warberg, H.F. Svendsen, Chem. Eng. Sci. 64 (2009) 2027. [5] D.A. Glasscock, J.E. Critchfield, G.T. Rochelle, Chem. Eng. Sci. 46 (1991) 2829. [6] D.P. Hagewiesche, S.S. Ashour, H.A. Al-ghwas, O.C. Sandall, Chem. Eng. Sci. 50 (1995) 1071. [7] J. Xiao, C.W. Li, M.H. Li, Chem. Eng. Sci. 55 (2000) 161. [8] B.P. Mandal, S.S. Bandyopadhyay, Chem. Eng. Sci. 61 (2006) 5440. [9] H.E. Benson, J.H. Field, R.M. Jimeson, Chem. Eng. Prog. 50 (1954) 356. [10] H.E. Benson, J.H. Field, W.P. Haynes, Chem. Eng. Prog. 10 (1956) 433. [11] S.M. Yih, C.C. Sun, Chem. Eng. J. 34 (1987) 65. [12] J.T. Cullinane, G.T. Rochelle, Chem. Eng. Sci. 59 (2004) 3619. [13] J.T. Cullinane, G.T. Rochelle, Ind. Eng. Chem. Res. 45 (2006) 2531. [14] J. Oexmann, C. Hensel, A. Kather, Int. J. Greenhouse Gas Control 2 (2008) 539. [15] E.S. Hamborg, G.F. Versteeg, J. Chem. Eng. Data 54 (2009) 1318. [16] F. Khalili, A. Henni, A.L.L. East, J. Chem. Eng. Data 54 (2009) 2914. [17] G. Astarita, D.W. Savage, Chem. Eng. Sci. 36 (1981) 581. [18] M.R. Rahimpour, A.Z. Kashkooli, Chem. Eng. Process. 43 (2004) 857. [19] M. Ahmadi, V.G. Gomes, K. Ngian, Sep. Purif. Technol. 63 (2008) 107. [20] P.W.J. Derks, H.B.S. Dijkstra, J.A. Hogendoorn, G.F. Versteeg, AIChE J. 51 (2005) 2311. [21] J.T. Cullinane, G.T. Rochelle, Fluid Phase Equilib. 227 (2005) 197. [22] A. Samanta, S.S. Bandyopadhyay, Chem. Eng. Sci. 62 (2007) 7312. [23] K.H. Han, Y.S. Song, J.I. Ryu, J.E. Son, G.T. Jin, Hwahak Konhak 41 (2003) 86. [24] M.H. Li, B.C. Chang, J. Chem. Eng. Data 39 (1994) 448. [25] D.J. Seo, W.H. Hong, J. Chem. Eng. Data 41 (1996) 258. [26] P.V. Danckwerts, Gas-Liquid Reactions, McGraw-Hill, 1970.