Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES
Environmental and Carbon Dioxide Issues
Investigation of CO2 absorption kinetics and desorption performance in aqueous 1-(2-aminoethyl)-3-methylimidazolium bromine solution Zaikun Wu, Weiqing Li, Tianrong Zhu, Yu Zheng, Tielin Wang, Cun-Wen Wang, and Yunbai Luo Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00954 • Publication Date (Web): 24 May 2018 Downloaded from http://pubs.acs.org on May 24, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels 1
1
Investigation of CO2 absorption kinetics and desorption
2
performance in aqueous
3
1-(2-aminoethyl)-3-methylimidazolium bromine solution
4
Zaikun Wua, b, *, Weiqing Lia, Tianrong Zhub, c, Yu Zhengb, Tielin Wanga, Cunwen
5
Wanga, Yunbai Luob,*
6
a
7
Laboratory of Novel Reactor and Green Chemical Technology of Hubei Province,
8
School of Chemical Engineering & Pharmacy, Wuhan Institute of Technology,
9
Wuhan 430073, P.R. China
Key Laboratory of Green Chemical Process of Ministry of Education, Key
10
b
11
P.R. China
12
c
13
(Jianghan University), Ministry of Education, Jianghan University, Wuhan
14
430072, P. R. China
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072,
Key Laboratory of Optoelectronic Chemical Materials and Devices of Wuhan
15 16
ABSTRACT: The absorption rate and absorption amount of CO2 were determined
17
at different 1-(2-aminoethyl)-3-methylimidazolium bromine ([Aemim][Br])
18
concentration, absorption temperature and CO2 content in order to optimize
19
operational condition in our study. Meanwhile, the effects of regeneration
20
temperature, regeneration time and regeneration circles on the regeneration
21
efficiency of CO2 saturated [Aemim][Br] solution were discussed, respectively .
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
2
1
Based on these experiments, the kinetic data (i.e., in terms of the pseudo-first-order
2
rate constant ( k ov ), the second-order reaction rate constant ( k 2 ) and heat of CO2
3
absorption was calculated at 303 K as [Aemim][Br] concentration varied from 0.1 to
4
2.0 mol.L-1. The result showed that the process of CO2 absorption was fast
5
pseudo-first-order reaction regime. According to the kinetic data at 293-323 K, the
6
activation energy of reaction was calculated by the Arrhenius equation, and the
7
second-order reaction rate constant can be expressed as follows:
8
k 2 = 1.997 × 10 10 exp(
9
DEA) and amino acid ionic liquids (i.e., 1-ethyl-3-methylimidazole glycinate,
10
1-butyl-3- methylimidazole glycinate), [Aemim][Br] has the best regeneration
11
efficiency but lower absorption rate in the same condition.
12
Keywords: carbon dioxide, absorption, kinetics, regeneration
13
1. INRTODUCTION
− 5440
T
).
By contrast to common CO2 absorbents (i.e., MEA
14
Chemical and physical absorption take a vital role in the process of carbon
15
dioxide capture. New technologies and process for capturing CO2 in the natural gas,
16
coal-fired power and acid gas industry have attracted worldwide attentions [1-6].
17
Alkanolamine is the most popupar absorbent used in gas-treating for the removal of
18
the acidic components H2S and CO2 at present, such as monoethanolamine (MEA),
19
diethanolamine (DEA), diisopropanolamine (DIPA) and methyldiethanolamine
20
(MDEA) [7-9], due to its high-capacity in the process of CO2 capture [10]. However,
21
some drawbacks are exist as classical capture technology [11], including its high
ACS Paragon Plus Environment
Page 2 of 35
Page 3 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels 3
1
fugacity, toxicity, corrosiveness and energy requirement for regeneration in industry
2
[12]. Therefore, it is very important to look for substitute absorbents for minimizing
3
anthropogenic emission of greenhouse gases (GHGs) into the atmosphere [13].
4
Ionic liquids are regarded as possible replacements to the conventional solvents
5
in the process of acid gas absorption in recent years [14, 15]. It is not only because of
6
their superior properties (low vapor pressure, high thermal stability, low energy
7
consumption etc), but also because of less effects on the environment and special
8
applications in some fields [16-21]. In addition, ionic liquids have potential
9
advantages on CO2 absorption [2]. Firstly, they are very efficient absorbent because of
10
the superiority in the way of saving energy consumption of absorption process
11
compared with alkanolamine. Secondly, it is good for decreasing the investment of
12
equipment for solvent regeneration compared with MEA process in industry.
13
Amino-functionalized ionic liquids (NH2-RTILs) were considered to have the same
14
CO2 capacity as MEA solution at atmospheric pressure. It was reported that physical
15
and chemical absorption occurred in the process of CO2 absorption [22, 23]. However,
16
the CO2 capacity of NH2-ionic liquid solvents mainly depended on the reaction of
17
CO2 and the primary amine group, which has a stoichiometry of 2:1 (NH2-RTILs:
18
CO2) [22].
19
In order to design the absorber for CO2 capture plants and simulate industrial
20
process, it is quite necessary to investigate the reaction kinetic of CO2 with
21
NH2-RTILS in theory [24]. The kinetic study of CO2 absorption into
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
4
1
amino-functionalized ionic liquids with closed reactor at given pressure was reported
2
in some literatures [22, 23]. However, energy consumption and equipment cost
3
increase as operating pressure increases in chemical industry. Therefore, it is more
4
beneficial to save energy that remove CO2 from flue gas at atmospheric pressure.
5
Since the process of CO2 absorption into common ionic liquids is controlled
6
exclusively by physical mechanisms, the solubility of CO2 in them can be neglected at
7
atmosphere pressure. Meanwhile, the high viscosity of pure amino-functionalized
8
ionic liquids indicated a major impediment to their applicability for CO2 capture.
9
Therefore, it is necessary that investigate the kinetic of CO2 absorption into aqueous
10
amino-functionalized ionic liquids solution at atmosphere pressure in order to explore
11
CO2 absorption process in industrial application.
12
According to the research of Jing et al. [25], aqueous tetramethylammonium
13
glycinate solution exhibited good absorption performance , the activation energy of
14
CO2 absorption into aqueous [N1111][Gly] solution was 15.431 kJ mol−1. Kumar et al.
15
[26] found that the reaction constant of CO2 with aqueous potassium salt of taurine
16
had higher value than reported in the literature for aqueous alkanolamines. The study
17
from Zhou et al. [27] showed that [N1111][Gly] promoted the absorption of CO2 in
18
0.95 mol. L-1AMP aqueous solutions. However, the kinetics of CO2 absorption into
19
aqueous functionalized imidazolium cation ionic liquid solution and the regeneration
20
performance of its saturated solution have not been studied at atmospheric pressure.
21
Meanwhile, considering functionalized imidazolium cation ionic liquids take a vital
ACS Paragon Plus Environment
Page 4 of 35
Page 5 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels 5
1
role in the process of CO2 capture [22] . Therefore,
2
1-(2-aminoethyl)-3-methylimidazolium bromine was chosen as CO2 absorbent to
3
study the kinetic and activation energy of CO2 absorption into aqueous functionalized
4
imidazolium cation ionic liquids solution, owing to its low viscosity and superior
5
stability . The effect of ionic liquid concentration, temperature, CO2 partial pressure
6
and CO2 loading were investigated in our work. Meanwhile, the regeneration
7
performance of CO2 saturated [Aemim][Br] solution was also studied.
8
2. EXPERIMENTAL SECTION
9
2.1. Chemicals. Carbon dioxide (mass fraction purity≥99.9%) and nitrogen
10
(mass fraction purity≥99.9%) were supplied by Oxygen Co., Ltd. of WISCO, China.
11
N-methylimidazole was purchased from Hubei Hongyuan Pharmaceutical Co., Ltd.
12
2-bromoethylamine hydrobromide was supplied by Shanghai Nanxiang Reagent Co.,
13
Ltd. 1-(2-aminoethyl)-3-methylimidazolium bromine was prepared using the similar
14
procedure in literature [28].
15
2.2. Experimental setups and procedures. The absorption experiments
16
were carried out in a double stirred cell absorber. A full description of the setup and
17
procedure is available in detail in our previous work [29], shown as in Figure S1 (see
18
the Supporting Information). Since CO2 absorption in above absorber is intermittent
19
reaction, the absorption rate and absorption load were calculated within first 20
20
minutes. Meanwhile, under the same conditions, 1.0 mol.L-1 aqueous solution of
21
[Aemim][Br], DEA and MEA were saturated by absorbing CO2 with double stirred
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 35
6
1
cell absorber until the flow rate of mixed gas at inlet was equal to its value at outlet,
2
respectively. After saturated absorption, the CO2 loaded solution was regenerated by
3
heating with oil bath. In order to eliminate the effect of saturated water vapor pressure,
4
the CO2 loading of solution was determined by adding dilute sulphuric acid into
5
saturated solution and lean solution, the desorption setup was described in Figure1. To
6
determine the optimal condition, the regeneration efficiency of CO2 from saturated
7
solution was calculated as:
8 9
η =
V − V1 × 100% V
(1)
In Eq. (1), η represents the regeneration efficiency (%), V represents the CO2
10
volume released by the acidolysis reaction of dilute sulphuric acid and saturated
11
solution, V1 represents the CO2 volume released by the acidolysis reaction of dilute
12
sulphuric acid and lean solution.
13
2.3. Physicochemical data measurement. 2.3.1. Density, viscosity and pH.
14
The density ,viscosity and pH of the aqueous [Aemim][Br] solutions were measured
15
using pycnometer method, Ubbelohde viscosity meter and acidity meter (PHS-3C),
16
respectively.
17
2.3.2. Diffusivity of CO2 in aqueous [Aemim][Br] solutions. The diffusion
18
coefficient of CO2 in aqueous [Aemim][Br] solutions was calculated by contrast to
19
their values in water at the same condition. According to the values of viscosity, the
20
diffusion coefficient of CO2 in [Aemim][Br] solutions was calculated. This method
21
was the same as reported in the previous literatures [29].
ACS Paragon Plus Environment
Page 7 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels 7
1
2.3.3. Solubility of CO2 in aqueous [Aemim][Br] solutions. The regular solution
2
theory (RST) was used to estimate the solubility of CO2 in [Aemim][Br] solutions.
3
Referred to the calculating procedure in our previous work [29], the solubility of CO2
4
in aqueous [Aemim][Br] solutions can be obtained with the similar method.
5
3. THEORY
6
3.1. CO2 absorption in aqueous [Aemim][Br] solutions. Apart from the
7
backbone of the molecules, the functional groups of amino-imidazole ionic liquids are
8
the same as those of primary amine and the reaction mechanism is expected to be
9
similar. Therefore, the reaction mechanism can be explained by zwitterion theory
10
reported in many literatures [25, 26, 30]. According to zwitterion theory, a zwitterion
11
was formed by the reaction of CO2 and [Aemim][Br] firstly, then it was deprotonated
12
by a base (RNH2) present in solution and formed carbamate that has higher stability.
13
This process can be expressed by Eq.(2) and Eq.(3), where
14
from aqueous [Aemim][Br] solution. So it can be inferred that carbamate was formed
15
in the process of CO2 absoprion into aqueous [Aemim][Br] solutions.
16
RNH2 + CO2
represents the base
+
OOC H2N R
17
(2) (3)
18
Based on CO2 absorption into [APmim][BF4] solution reported by Galán Sánchez
19
[22], the reaction mechanism of CO2 absorption into aqueous [Aemim][Br] solution
20
can be known as the first order reaction with respect to the concentration of both
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 35
8
1
[Aemim][Br] and CO2. This process can be described by the overall reaction, shown
2
as Eq. (4).
3
RNHCOO + RNH3
CO2 + 2RNH2
(4)
4
3.2. mass transfer. The studies on kinetics of the reaction between CO2 and
5
solutions were based on the two-film theory of gas-liquid mass transfer. Since the
6
physical absorption of CO2 in [Aemim][Br] solutions can be neglected at atmospheric
7
pressure [23], absorption rate can be expressed as follows:
8
N CO = k 2[CO 2 ][RNH 2 ]
9
As CO2 absorption into a thin film occurs according to a pseudo first-order
10
regime, the absorption rate can be also given by Eq. (6), where D CO 2 is diffusivity of
11
CO2 in the liquid phase [31].
12
(5)
2
N CO = C CO ,i D CO k 2C ILS 2
2
2
(6)
13
According to the two-film model, the relationships between the absorption rate
14
( N CO 2 ) and the gas-side mass transfer coefficient ( kG ) is connected via the driving
15
force as Eq. (7).
N CO = kG(PCO − PCO16i ) 2
17
2
2,
(7)
Where PCO 2 and PCO 2 ,i are CO2 partial pressure and equilibrium CO2 partial
18
pressure in the gas-liquid interface, respectively. Meanwhile, the absorption rate can
19
be calculated by the product of enhancement factors ( E ), liquid-side mass transfer
20
coefficients ( k L ) and CO2 concentration in the gas-liquid interface ( CCO 2 ,i ) [3, 12, 25]，
21
expressed as Eq. (8).
ACS Paragon Plus Environment
Page 9 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels 9
N CO = Ek LC CO1,i 2
(8)
2
2
C CO
2 ,i
= PCO 2 ,i H CO 32
(9)
4 5
In Eqs. (7)–(8), the gas-side mass transfer coefficients and liquid-side mass
6
transfer coefficients ( k L ) can be calculated by the following equation [25, 32].
k L = kW ,CO (D CO 2
2 ,L
D CO ,W )72 3
(10)
2
8
kG = kG ,SO (DCO 2
10
2
−N 2
D SO
In this equation, D CO
2
−N 2
2, − N 2
)92 3
(11)
and D SO
2,− N 2
can be calculated by Maxwell-Gilliland
11
equation [33]. k W ,CO 2 is the mass transfer coefficients of CO2 in pure water that has
12
been reported in literature [32]. According to the values of µILs calculated from
13
preceding procedure, the diffusion coefficient of CO2 in aqueous [Aemim][Br]
14
solutions can be calculated by Eqs. (12)–(13). So based on Eqs. (9)–(12), the values of
15
k L and k G can be calculated, respectively.
16
log D CO 2 ,W = −8.1764 +
17
(D
18
CO 2 ,ILs
µILs
0.8
) = (D T
712.5
T CO 2 ,W
µW
− 0.8
2.591 × 105
T2
)
T
(12) (13)
Danckwerts [31] reported the relation among hatta number ( H a ) and other kinetic
19
parameters, expressed as Eq. (14). In case of a 1-1 reaction, the region
20
( 2 < Ha
