ARTICLE pubs.acs.org/EF
Selection of Blended Solvents for CO2 Absorption from Coal-Fired Flue Gas. Part 1: Monoethanolamine (MEA)-Based Solvents Dechen Zhu, Mengxiang Fang,* Zhong Lv, Zhen Wang, and Zhongyang Luo State Key Laboratory for Clean Energy Utilization, Zhejiang University, Hangzhou 310027, People’s Republic of China ABSTRACT: Solvent selection is the potential breakthrough for the chemical absorption method to capture CO2 from coal-fired flue gas. A total of 16 kinds of selected monoethanolamine (MEA)-based solvents were assessed by absorption at 40 °C up to 12 kPa CO2 partial pressure and desorption at 100 °C down to 1.0 kPa CO2 partial pressure. Results showed that the 20% MEA + 10% diethylenetriamine (DETA) system maintains the highest average absorption rates and reaches the highest loading of 0.556 kg of CO2/kg of solute during all of the tested systems. The absorption capacity of the 20% MEA + 10% DETA system is increased to 53%, and the corresponding average removal efficiency is enhanced more than 31% compared to 30% MEA solution. Furthermore, there is only a slight difference between the regeneration performance of the 20% MEA + 10% DETA system and that of the 30% MEA solution.
1. INTRODUCTION Post-combustion capture (PCC) using chemical solvents is believed to be a good answer for CO2 capture on coal-fired flue gases, in particular, because of high capture efficiency, high selectivity, and scale-up feasibility.1 The main obstacle for the application of conventional amine scrubbing technology is the energy requirement for absorbent regeneration. Solvent selection, reactor modification, and process integration are effective routes to reduce the capital cost and energy consumption of this technology. It is widely considered that combined effects caused by the above three methods can accelerate the commercial availability of chemical absorption. Development of more efficient solvents is one of the most effective solutions to reduce the energy consumption and capital cost. Generally speaking, primary or secondary amines have a fast CO2 absorption rate while tertiary amines usually possess low absorption heat and high absorption capacity.2,3 In the overall chemical absorption process, not only is the kinetics of the reaction an important criterion but also the amount of regeneration energy. Current studies emphasize the second criterion more than the first. Unfortunately, no single solvent is discovered to possess both a good CO2 absorption performance and nice regeneration performance simultaneously until now. Hence, the application of mixed amine solvents in CO2 capture is of increasing interest today. A large number of the blended amine studies published in the literature are listed in Table 1. It can be easily classified into three categories, monoethanolamine (MEA)-based blends, N-methyldiethanolamine (MDEA)-based blends and other blends. Even though a large amount of research has already been conducted in the blended solvents, few solvents have been testified to meet the industrial requirement for CO2 capture. Furthermore, the blended solvents presented in the references had been investigated under different experimental conditions. There is no available index comparing the experimental results given by the literature. Hence, a further study on blended solvents under similar experimental conditions is still necessary. r 2011 American Chemical Society
The present work investigates the carbon dioxide absorption and regeneration performance of 29 amine-based solvents carried out under the consistent experimental conditions. The absorption/desorption performances of pure MEA and pure MDEA were chosen as the baseline, because MEA and MDEA are the frequently used amines for CO2 capture. A total of 16 kinds of MEA-based solvents are discussed in this paper.
2. EXPERIMENTAL SECTION 2.1. Materials Selection. Generally speaking, a good solvent must be characterized by high cyclic capacity, low reaction energy, low stripping energy, fast kinetics, low degradation rate, and easy operation. However, these characteristics have to be deserved by experiments. Some general guidelines for choosing the additives of blends had been proposed to save time and efforts for experimental research. A two-level screening method is applied to select the appropriate chemical agent and evaluate the performance of blends. As for this method, the parameters are classified into two categories, primary parameters and validation parameters. The primary parameters, which are easily deserved from the ACS database, include molecular weight, boiling point, freezing point, density, viscosity, saturation vapor pressure, selectivity, corrosive characteristics, toxicity, foaming behavior, price, etc. Validation parameters refer to the parameters deserved by experimental tests, such as removal efficiency, mass-transfer rate, cyclic capacity, absorption heat, regeneration extent, stripping energy, degradation rate, irreversible reaction, and toxicity. More details of the screening method will be discussed in the next paper. Screening experiments were carried out for 16 solvent systems: 10 wt % MEA, 20 wt % MEA, 30 wt % MEA, 15 wt % MEA + 15 wt % MDEA, 20 wt % MEA + 10 wt % MDEA, 25 wt % MEA + 5 wt % MDEA, 20 wt % MEA + 10 wt % AMP, 25 wt % MEA + 5 wt % AMP, 20 wt % MEA + 10 wt % AEEA, Special Issue: 2011 Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies Received: July 27, 2011 Revised: November 3, 2011 Published: November 05, 2011 147
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Table 1. Blends Solvents Studied in the Literature432 solvents
research content
MEA + MDEA
MEA + 2-amino-2-methyl-1-propanol (AMP)
researcher
year
MEA-Based Blends absorption/desorption
Gary T. Rochelle
absorption
D. A. Rangawala
1992
absorption modeling of absorption
D. P. Hagewiesche B. P. Mandal
1995 2001
membrane module
Zhi Wang
2006
process integration
Amornvadee Veawb
2007
regeneration
Shuiping Yan
2008
kinetics model absorption kinetics
Raphael Idem J. Xiao
2009 2000
absorption
B. P. Mandal
2006
absorption/desorption
Kwang-Joong Oh
2008
mass transfer
Adisorn Aroonwilas
2009
reaction rate
Adisorn Aroonwilas
2009
absorption heat
H. F. Swendsen Gary T. Rochelle
2010 2003
absorption rate/solubility
1991
Ross E. Dugas
2011
corrosion
Amornvadee Veawb
2009
absorption heat equilibrium solubility/viscosity
H. F. Swendsen N. Daneshvar Saeed Mazinani
2010 2004 2011
MDEA-Based Blends absorption/desorption absorption
Gary T. Rochelle Gary T. Rochelle
2000 2000
enthalpy absorption
B. Sch€afer Gary T. Rochelle
2002 2000
Other Blends kinetics of absorption
W. C. Sun
2005
membrane contactor
S. H. Lin
2008
absorption
S. S. Bandyopadhyay
2009
TIPA + PZ ethylenediamine (EDA) + AMP N,N0 -di-(2-hydroxyethyl)piperzane (DIHEP) +
absorption heat equilibrium absorption/desorption absorption heat
H. F. Swendsen N. Daneshvar Jasmin Kemper H. F. Swendsen
2010 2004 2010 2010
N-2-hydroxyethylpiperzane (MHEP) AMP + 3-(methylamino)propylamine (MAPA) N,N-diethylethanolamine (DEEA) + MAPA
absorption heat absorption heat
H. F. Swendsen H. F. Swendsen
2010 2010
MEA + piperazine (PZ)
MEA + tri-isopropanolamine (TIPA) MEA + sodium glycinate (SG)
MDEA + diethanolamine (DEA) MDEA + PZ MDEA + diglycolamine (DGA)
AMP + PZ
Table 2. Experimental Materials Chemical
CAS
purity (%)
producer
price (CN f/ton)
monoethanolamine (MEA) N-methyldiethanolamine (MDEA) (2-amino-2-methyl-1-propanol) (AMP) piperazine (PZ) aminoethylethanolamine (AEEA) triethylenetetramine (TETA) diethylenetriamine (DETA)
141-43-5 105-59-9 124-68-5 110-85-0 111-41-1 112-24-3 111-40-0
g99.9 g99.9 g97 99 99 99 99
Sigma-Aldrich Sigma-Aldrich Fluka Anhydrous Adama-beta Adama-beta Lingfeng Chemical
12800 15000 42000 18300 16500 26900 29000
25 wt % MEA + 5 wt % AEEA, 20 wt % MEA + 10 wt % TETA, 25 wt % MEA + 5 wt % TETA, 20 wt % MEA + 10 wt % DETA, 25 wt % MEA + 5 wt % DETA, 20 wt % MEA + 10 wt % PZ, and 25 wt % MEA + 5 wt % PZ. The weight concentration was chosen as a reference parameter in this paper because of its relatively high visuality and wide application during
the industry operation process compared to the mole concentration. The amine absorbents used, along with their purities, were obtained as provided in Table 2. 2.2. Experimental Setup and Procedures. 2.2.1. Absorption Experiments. 2.2.1.1. Experimental Setup. The experimental 148
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wire and oil bath. The temperature of the solution rapidly rises to 95 °C or more. (iv) For regeneration during the temperature stable period, the solution temperature is kept constant and only heated by the oil bath. (v) For sample analysis, during the experiments, the small dose solution of about 1 mL is extracted from the reactor each 5 min and its CO2 loading in the sample solution is analyzed. Meanwhile, the original solution before regeneration of the same volume with the sample has been made up to the system. For each sample, CO2 loading is analyzed 23 times. The average value is applied to avoid the analysis difference. The gas volume is recorded each minute. 2.2.2.2. Experimental Parameters. The volume of the glass reactor for CO2 regeneration is 800 mL, and the volume of the rich-CO2 solution is 500 mL. The temperature of the oil bath is 160 °C, and liquid agitation speed is 300 revolution/min. The heating power of plug-in heat resistance is 80 4 = 320 W. The temperature rapid rising time is 5 min. The stable temperature during the regeneration process is about 100 °C. 2.3. Parameters Involved. 2.3.1. Absorption Rate. The absorption rate refers to the amount of CO2 absorbed into the chemical agents during the unit time. It can reveal how fast the mass transfer will carry out. The wetted wall column (WWC) is currently considered as the most suitable tool to provide the relatively precise absorption rate at unit area. However, the results are still affected by the gas inlet design and the inner structure of gas flowing within WWC to some extent. It indicates that even the same chemical reaction occurs under the same experimental conditions, and the results obtained by different WWCs are not confidential. The gas/liquid contacting area in the laminar flow state is also hard to determine for the tested systems in this paper. Here, the absorption rate at unit volume is applied as the base parameter. Under this condition, there is no more consideration on the mass-transfer difference between the horizontal and vertical directions. The absorption rate of absorbents can be defined as follows:
Figure 1. Experimental apparatus for the absorption study: (1) MFC, (2) mixing tank, (3) valve, (4) thermostatic water bath, (5) acid wash, (6) desiccators, (7) gas analyzer, (8) computer, (9) vent, (10) N2 cylinder, and (11) CO2 cylinder.
Figure 2. Experimental apparatus for the regeneration study: (1) oil bath, (2) glass reactor, (3) stirring cell, (4) condenser, (5) flow meter, (6) gas flow meter by drainage, (7) sampling port, (8) condensation water inlet, (9) condensation water outlet, (10) plug-in heat resistance, and (11) thermocouple.
N ¼
PðVin Vout Þ VRT
ð1Þ
where N is the CO2 absorption rate of the tested solvents (kmol L1 s1), Vin and Vout are the inlet simulated gas flow rate and outlet gas flow rate, respectively (m3 s1), P is the operation pressure (0.1 MPa), V is the solution volume (L), R is the ideal gas constant (kJ kmol1 K1), and T is the operation temperature (K). 2.3.2. CO2 Removal Efficiency. CO2 removal efficiency refers to the ratio between the absorbed CO2 volume flow rate and the original CO2 volume flow rate. CO2 removal efficiency, ηCO2,R, can be calculated from the following equation:
apparatus for the absorption study is shown in Figure 1. N2 and CO2 flowing out of the compressed cylinders are mixed in the mixing tank at first and then sent to the glass reactors. The treated gas is sent to the gas analyzer after acid washing and desiccation. During the whole process, the gas flow is controlled by mass flow controllers (MFCs). 2.2.1.2. Experimental Parameters. Experimental reactors are a glass bottle with a cylinder shape, whose average inner diameter is 36.5 mm and liquid surface height/average inner diameter is 3.5. The absorbents of 120 mL are filled into the reactors. The optimization of the design parameters of the reactor, such as height/inner diameter ratio, gas inlet design, and stirring rate, has already been discussed.27 The absorption temperature was 40 °C. The gas flow of N2 was 0.8 L/ min, and the gas flow of CO2 was 109 mL/min. The CO2 concentration of the simulated gas was 12%. The operation time of the experiments will end when the outlet CO2 concentration of the simulated gas is above 11%. Generally speaking, 2 h is suitable for most of the absorption processes. The duration time is usually less than 2 h for some solutions for better absorption performance. 2.2.2. Regeneration Experiments. 2.2.2.1. Experimental Steps. The experimental apparatus for the regeneration study is shown in Figure 2. The following are the experimental procedures: (i) For rich-CO2 solution preparation, the original volume of solutions with a weight concentration of 30% is 1200 mL. Pure CO2 with a gas volume of 2 L/min is vented into the absorbent solution to make solutions saturated. The duration time is about 2 h. (ii) The temperature of the oil bath is raised to 160 °C by heating. (iii) For regeneration during the temperature rising period, in the first 5 min, the solution is heated by an electric
ηCO2 , R ¼
VCO2 , in VCO2 , out VCO2 , in
ð2Þ
CCO2 , in VN2 , in CN2 , in
ð3Þ
during which VCO2 , in ¼ VCO2 , out ¼
CCO2 , out VN2 , out CN2 , out
VN2 , in ¼ VN2 , out
ð4Þ ð5Þ
Above all, eqs 25 can be turned into the following form: ηCO2 , R ¼
CCO2 , in CCO2 , out CCO2 , in ð1 CCO2 , out Þ
ð6Þ
In the above equations, V is the gas volume flow rate (mL/min) and C is the gas volume concentration. 2.3.3. CO2 Loading. In these experiments, the solution CO2 loading data obtained by the liquid sample analysis, with its specific method 149
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Figure 4. Additive effects on the maximum CO2 loading.
Figure 4 quantitatively presents the additive effects on the maximum CO2 loading. Generally speaking, the maximum CO2 loading of the tested absorbent equals the absorption capacity. Theoretically speaking, the increase of the maximum CO2 loading affords the potential of a higher net CO2 absorption capacity. Hence, the higher CO2 loading for the absorbent is preferred. It can be observed that MEA solution added to DETA, PZ, TETA, and AEEA obtained a relatively higher absorption rate and higher capacity compared to pure MEA solution. However, MDEA and AMP have a negative effect on the absorption rate and absorption capacity for MEA solution. The structure feature of PZ with two secondary amine sites can be applied to explain the reason why PZ has a relatively higher absorption rate and capacity. AEEA has one more secondary amine site than MEA, while TETA has one more primary amine site and two more secondary amine sites compared to MEA. The poorer performance of AMP can be explained by the alkyl group increase compared to MEA. Furthermore, increasing the solute concentration can accelerate the absorption rate; however, the capacity is eventually decreased for pure MEA solution. It can be explained by the higher viscosity of the higher concentration of the MEA solution, which led to reduced diffusivity, resulting in a reduced mass-transfer contact area and, thus, a slight capacity decrease, even though the increase of the solute concentration can increase the collision probability between CO2 and MEA molecular, which caused the absorption rate to increase. Obviously, the 20% MEA + 10% DETA system can improve the absorption capacity of the tested system to the largest extent and even increase the maximum CO2 loading to 53% compared to the 30% MEA solution. Note that (1) the number listed in Figure 4 refers to the solution number, which is consistent with the number in Table 3, and (2) the value refers to the percentage of the relative maximum loading change compared to the 30% MEA solution. Table 3 lists the maximum CO2 loading, maximum absorption rate, and average absorption rate for different systems. It can be easily found from Table 3 that the 20% MEA + 10% DETA system can increase the absorption capacity to 53%, while the average absorption rates have been improved more than 15% compared to the 30% MEA solution. 3.1.2. Removal Efficiency. Removal efficiency is the most concerned parameter for industry production, which can directly reveal the absorption performance of any PCC system. The real gasliquid contacting time corresponding to the high removal efficiency above 80% for a solvent is important reference data for
Figure 3. Absorption rate versus loading curves for the solvents (313 K, 1 atm, 12% CO2, and 30% total amine concentration). shown in eq 4, can be defined as follows: α¼
44f ðV2 V1 Þ 1000 22:4FV0 msolute
ð7Þ
where V0 is the volume of the tested sample (m3), V1 is the initial volume of the gauge tube before titration (L), V2 is the ending volume of the gauge tube after titration (L), msolute is the weight concentration of solute (%), F is the density of the mixture (kg/m3), and f is the gas volume correction factor when the experimental operating conditions are converted into standard operating conditions. It is a dimensionless coefficient, and its calculation formula is as follows: f ¼
273 P0 273 þ t P
ð8Þ
3. RESULTS AND DISCUSSION 3.1. Absorption Process. 3.1.1. Absorption Rate and Absorption Capacity. The absorption rates versus loading (kilograms of
CO2 per kilogram of solute) curves for various systems tested are shown in Figure 3. It can be observed that the 20% MEA + 10% DETA system maintained the highest average absorption rate and reached the highest CO2 loading of 0.556 kg of CO2/kg of solute when compared to other systems. The high performance of MEA solution with DETA additives could be explained by the structural feature of DETA, where two primary and one secondary amine sites combine to enhance the absorption rate and capacity in DETA. The 15% MEA + 15% MDEA system maintained the lowest average absorption rate and reached the lowest loading of 0.260 kg of CO2/kg of solute. This phenomenon is quite easy to understand because MDEA usually maintains a lower absorption rate and lower capacity relative to MEA because of the secondary amine site and molecular-weight difference. Furthermore, for the additives of the same mass concentration, the enhancement effects on the absorption rate caused by the additives are listed as follows from highest to lowest: DETA > PZ > AEEA > TETA > AMP > MDEA. For the same additive, with the increase of the mass concentration, the effect on the absorption rate of pure MEA solution is enhanced, whether it is positive or negative. The 20% MEA + 10% PZ system occupies the highest initial absorption rate. 150
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Table 3. Absorption Performance Summary for Solvents number
solvent
maximum loading (kg/kg)
maximum absorption rate (mol L1 s1)
average absorption rate (mol L1 s1)
1
10% MEA
0.403
55.345
19.0425
2
20% MEA
0.373
61.311
34.55167
3
30% MEA
0.364
64.124
47.984
4
25% MEA + 5% AEEA
0.409
62.479
50.11315
5
20% MEA + 10% AEEA
0.52
63.251
52.95952
6
25% MEA + 5% AMP
0.344
61.291
44.79652
7
20% MEA + 10% AMP
0.301
61.198
40.14629
8 9
25% MEA + 5% DET 20% MEA + 10% DETA
0.462 0.556
62.952 63.566
52.37651 55.18439
10
25% MEA + 5% MDEA
0.331
62.251
43.26813
11
20% MEA + 10% MDEA
0.302
59.697
39.12327
12
15% MEA + 15% MDEA
0.26
58.459
33.07023
13
25% MEA + 5% PZ
0.488
66.043
55.05085
14
20% MEA + 10% PZ
0.428
67.584
54.37849
15
25% MEA + 5% TETA
0.437
63.863
52.09817
16
20% MEA + 10% TETA
0.452
63.22
51.38292
Figure 5. Removal efficiency versus CO2 loading for the solvents (313 K, 1 atm, 12% CO2, and 30% total amine concentration).
absorber design. Furthermore, the optimal CO2 loading control for CO2-rich solution and CO2-lean solution also relates to the removal efficiency. The relationships among the removal efficiency, CO2 loading, and reaction time for various systems are shown in Figure 5. In this figure, the lines with a hollow tag refer to the CO2 loading curves, while the other lines stand for removal efficiency. It can be easily observed that the additive effect on removal efficiency is similar to the additive effect on the maximum loading, which means that the effect caused by DETA, PZ, TETA, and AEEA is positive, whereas the effect caused by AMP and MDEA is negative. During the first 20 min, the 20% MEA + 10% PZ system maintained the highest removal efficiency, with an average removal efficiency of 98.93%. However, for the whole absorption process, which lasts more than 110 min, the 20% MEA + 10% DETA system maintained the highest average removal efficiency of 72.50%, while the average removal efficiency for the 30% MEA solution is only 55.37%. The 10% MEA
solution maintained the highest CO2 loading increasing rate during the first 20 min, while the 20% MEA + 10% DETA system eventually reached the highest CO2 loading. Table 4 shows the detailed parameters that may be helpful for industry design. These parameters include the corresponding time when the CO2 loading reaches 0.4 mol of CO2/mol of solute or when the average removal efficiency is above 80%. The operational state of the tested systems at 60 min has also been presented. As seen from Table 4, the corresponding time when the CO2 loading reaches 0.4 mol of CO2/mol of solute of all of the blended systems is shorter than that of the 30% MEA solution, except for those systems with added MDEA or AMP. It indicates that the improved blended systems are much easier to load CO2 from flue gas. Furthermore, the corresponding time decreases with the increase of the additive concentration. It can also be observed that the maintained time when the average removal efficiency is above 80% of improved systems is longer than that of the 30% MEA solution. The maintained time of the 151
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Table 4. Parameter Summary for the Whole Absorption Processa time = 60 min number
a
type
L = 0.4 corresponding time
Re = 80% corresponding time
L > 0.4
Re > 80%
1
10% MEA
24
8
Y
N
2
20% MEA
43
33
Y
N
3
30% MEA
61
62
Y
Y
4
25% MEA + 5% MDEA
60
51
Y
N
5
20% MEA + 10% MDEA
60
30
Y
N
6
15% MEA + 15% MDEA
68
13
N
N
7
25% MEA + 5% AMP
62
46
N
N
8 9
20% MEA + 10% AMP 25% MEA + 5% DETA
63 54
37 73
N Y
N Y
10
20% MEA + 10% DETA
48
87
Y
Y
11
25% MEA + 5% AEEA
55
64
Y
Y
12
20% MEA + 10% AEEA
49
76
Y
Y
13
25% MEA + 5% PZ
51
85
Y
Y
14
20% MEA + 10% PZ
47
81
Y
Y
15
25% MEA + 5% TETA
51
74
Y
Y
16
20% MEA + 10% TETA
46
69
Y
Y
Note that L is CO2 loading (mol of CO2/mol of solute) and Re is removal efficiency.
Figure 7. Desorption extent versus time curves for the solvent systems at 100 °C.
Figure 6. Desorption rate versus loading curves for the solvent systems at 100 °C.
showed the highest desorption ability of these solvents. On the other hand, the 20% MEA + 10% DETA system has the highest lean loading of 0.23, indicating its low desorption potential, but it should be noted that it occupied the highest change in loading. Furthermore, the 15% MEA + 15% MDEA system has the highest average desorption rate. The solvents with a poorer absorption performance have a relatively higher desorption rate than the 30% MEA solution, while the other solvents have the opposite performance in this field. A slightly different behavior is observed in Figure 7. The 15% MEA + 15% MDEA system still possesses the highest average regeneration extent under the tested experimental conditions; however, that which followed is not the 20% MEA + 10% MDEA system but the 10% MEA solution. The other orders of average regeneration extent also have a slight difference with the orders of the average absorption rate, but the relative average regeneration extent difference among them is rather slight. Hence, all of the
20% MEA + 10% DETA system even reaches 87 min, which increases more than 40% compared to the maintained time of the 30% MEA solution. When the reaction lasts for 60 min, all of the systems have a good absorption performance, except the systems with added AMP or MDEA. 3.2. Regeneration Process. Solvents attained different loadings and absorbed different amounts of CO2 in solution. Desorption tests at 100 °C give an indication of the true CO2 carrying capacity for these solvent systems under these experimental conditions. Figures 6 and 7 show curves for the stripping rate versus loading in kilograms of CO2 per kilogram of solute and regeneration extent versus time, respectively. It can be observed from Figure 6 that the lowest lean loading of 0.05 was attained by the 15% MEA + 15% MDEA system and the 20% MEA + 10% DETA system 152
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solvents of bad stripping performance possess the average regeneration extent compatible with the 30% MEA solution.
(10) Edali, M.; Aboudheir, A.; Idem, R. Int. J. Greenhouse Gas Control 2009, 3, 550–560. (11) Xiao, J.; Li, C. W.; Li, M. H. Chem. Eng. Sci. 2000, 55, 161–175. (12) Mandal, B. P.; Bandyopadhyayb, S. S. Chem. Eng. Sci. 2006, 61, 5440–5447. (13) Choi, W. J.; Seo, J. B.; Jang, S. Y.; Jung, J. H.; Oh, K. J. J. Environ. Sci. 2009, 21, 907–913. (14) Dey, A.; Aroonwilas, A. Energy Procedia 2009, 1, 211–215. (15) Sakwattanapong, R.; Aroonwilas, A.; Veawab, A. Energy Procedia 2009, 1, 217–224. (16) Dang, H.; Rochelle, G. T. Sep. Sci. Technol. 2003, 38 (2), 337–357. (17) Nainar, M.; Veawab, A. Energy Procedia 2009, 1, 231–235. (18) Daneshvar, N.; Zaafarani Moattar, M. T.; Abedinzadegan Abdi, M.; Aber, S. Sep. Purif. Technol. 2004, 37, 135–147. (19) Sch€afer, B.; Mather, A. E.; Marsh, K. N. Fluid Phase Equilib. 2002, 929–935. (20) Critchfield, J. E.; Rochelle, G. T. CO2 desorption from DEA and DEA-promoted MDEA solution. Proceedings of the American Institute of Chemical Engineers (AIChE) Spring Meeting; New Orleans, LA, 1988. (21) Mshewa, M. M.; Rochelle, G. T. CO2 absorption/desorption in mixtures of aqueous MDEA and DEA at 313393 K. Proceedings of the American Institute of Chemical Engineers (AIChE) Spring Meeting; Houston, TX, 1995. (22) Ma, P.; Kaganoi, S.; Rochelle, G. T. Chem. Eng. Sci. 2000, 55, 5125–5140. (23) Sun, W. C.; Yong, C. B.; Li, M. H. Chem. Eng. Sci. 2005, 60, 503–516. (24) Samanta, A.; Bandyopadhyay, S. S. Chem. Eng. Sci. 2009, 64, 1185–1194. (25) Lin, S. H.; Chiang, P. C.; Hsieh, C. F.; Li, M. H.; Tung, K. L. J. Chin. Inst. Chem. Eng. 2008, 39, 13–21. (26) Kemper, J.; Ewert, G.; Gr€unewald, M. Energy Procedia 2010, 1, 231–235. (27) Zhu, D. C.; Fang, M. X.; Lv, Z.; Xiang, Q. Y. Semi-batch reactor studies for CO2 capture by aqueous ammonia. Proceedings of the International Conference on Computer Distributed Control and Intelligent Environmental Monitoring, 2010; pp 13031309. (28) Mazinani, S.; Samsami, A.; Jahanmiri, A. J. Chem. Eng. Data 2011, 56, 3163–3168. (29) Dugas, R. E.; Rochelle, G. T. J. Chem. Eng. Data 2011, 56, 2187–2195. (30) Han, B.; Zhou, C. G.; Wu, J. P.; Tempel, D. J.; Cheng, H. S. J. Phys. Chem. Lett. 2011, 2, 522–526. (31) Xie, H. B.; Zhou, Y. Z.; Zhang, Y. K.; Johnson, J. K. J. Phys. Chem. A 2010, 114, 11844–11852. (32) Zhang, Y.; Chen, H.; Chen, C. C.; Plaza, J. M.; Dugas, R.; Rochelle, G. T. Ind. Eng. Chem. Res. 2009, 48, 9233–9246.
4. CONCLUSION A relative comparison of the CO2 absorption potentials of selected solvent systems was performed using a rapid screening apparatus under the same experimental conditions. Test results showed the following: (1) The maximum CO2 loading, which relates to cyclic capacity, of MEA in kilograms of CO2 per kilogram of MEA, was found to decrease with an increase in the weight concentration, while its CO2 removal efficiency increases with the weight concentration. (2) The 20% MEA + 10% DETA system maintained the highest average absorption rates and reached the highest loading of 0.556 kg of CO2/kg of solute when compared to other systems. The absorption capacity of the 20% MEA + 10% DETA system was increased to 53%, while the average absorption rates have been improved slightly compared to the 30% MEA solution. The corresponding average removal efficiency was enhanced more than 31% relative to the 30% MEA solution. Furthermore, there is only a slight difference between the regeneration performance of the 20% MEA + 10% DETA system and that of the 30% MEA solution. (3) Additives such as DETA, PZ, TETA, and AEEA have a positive effect on the absorption performance of pure MEA solution, while the additive effect on the absorption performance caused by MDEA and AMP is negative. Additive effects on the regeneration performance are the opposite. However, it should be noted that the additive effects on the absorption performance are much stronger than those on the regeneration performance. (4) A more considered standard for evaluation of the overall performance for solvents should be erected. More factors should be considered, such as the viscosity, volatility, toxicity, degradation, and market price. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT Support from the National Nature Science Foundation, through Grant 51076139, is gratefully acknowledged. The authors also give thanks for the help from GE Global Research. ’ REFERENCES (1) Steeneveldt, R.; Berger, B.; Torp, T. A. Chem. Eng. Res. Des. 2006, 84, 739–763. (2) Tan, Y. H. Study of CO2 absorption into thermomorphic lipophilic amine solvents. Ph.D. Dissertation, Technical University of Dortmund, Dortmund, Germany, 2010. (3) Kim, I.; Svendsen, H. F. Int. J. Greenhouse Gas Control 2010, 5, 390–395. (4) Glasscock, D. A.; Critcheld, J. E.; Rochelle, G. T. Chem. Eng. Sci. 1991, 46, 2829–2845. (5) Rangawala, H. A.; Morrell, B. R.; Mather, A. E.; Otto, F. D. Can. J. Chem. Eng. 1992, 70, 482–490. (6) Hagewiesche, D. P.; Ashour, S. S.; AlGhawas, H. A.; Sandall, O. C. Chem. Eng. Sci. 1995, 50, 1071–1079. (7) Mandal, B. P. Chem. Eng. Sci. 2001, 56, 6217–6224. (8) Gong, Y. W.; Wang, Z.; Wang, S. C. Chem. Eng. Process. 2006, 45, 652–660. (9) Yan, S. P.; Fang, M. X.; Luo, Z. Y.; Cen, K. F. Chem. Eng. Process. 2009, 48, 515–523. 153
dx.doi.org/10.1021/ef2011113 |Energy Fuels 2012, 26, 147–153
