close

Вход

Забыли?

вход по аккаунту

?

Sorption of carbon dioxide by ionic liquid-based sorbents.

код для вставкиСкачать
ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
Published online 27 July 2010 in Wiley Online Library
(wileyonlinelibrary.com) DOI:10.1002/apj.495
Research article
Sorption of carbon dioxide by ionic liquid-based sorbents
Wentao Bi,1 Tao Zhu,1 Dong Wha Park1,2 and Kyung Ho Row1 *
1
Department of Chemical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751, Korea
Regional Innovation Center for Environmental Technology of Thermal Plasma, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751,
Korea
2
Received 16 April 2010; Revised 11 June 2010; Accepted 14 June 2010
ABSTRACT: Ionic liquids and ionic liquid-based materials were emerging as sorbents for carbon dioxide capture.
Amino-imidazolium materials, a kind of sorbents, were synthesized and characterized for the sorption of carbon
dioxide. The ionic liquid-modified materials have higher sorption capacity of carbon dioxide than the unmodified
sorbents. The effects of pressure and temperature were investigated. The adsorbed amount of carbon dioxide increased
with the increasing pressure and the ionic liquid-based polymer show higher sorption efficiency than that of ionic
liquid-based silica.  2010 Curtin University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: sorption; carbon dioxide; silica; polymer; ionic liquid
INTRODUCTION
Carbon dioxide is the major greenhouse gas causing global warming. The increasing atmospheric
concentration of carbon dioxide resulting from increasing consumption of fossil fuel is becoming an important environmental issue.[1] In this situation, a great
deal of efforts is devoted to limiting the emissions of
greenhouse gases in the environment today.[2] Until
now, liquid alkanolamines have been the commercial technology most widely applied to CO2 capture.[3]
The reaction sequences in such systems involve
formation of ammonium carbamate species under
anhydrous conditions and their transformation to ammonium bicarbonate and carbonate species in the presence of water. However, the use of liquid amines
has several drawbacks, such as high energy consumption, solvent regeneration and flow problems caused by
viscosity.
Recently, ionic liquids, organic salts with a low
melting point (<100 ◦ C), have been emerging as nonvolatile and reversible carbon dioxide sorbents for CO2
capture.[4 – 10] Supported liquid membranes using ionic
liquids have also been developed.[11,12] Bates et al .
developed a task-specific ionic liquid for CO2 capture
by introducing an amine group to the ionic liquid, substantially increasing its CO2 solubility.[7]
*Correspondence to: Kyung Ho Row, Department of Chemical
Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku,
Incheon 402-751, Korea. E-mail: rowkho@inha.ac.kr
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Curtin University is a trademark of Curtin University of Technology
However, liquid and viscosity of ionic liquids cause
the complication of processing. In this case, poly(ionic
liquid)s were developed for the sorption of CO2 .[13] The
polymer show higher absorption capacity than the ionic
liquid monomers. But the surface area of the polymer was low and limited the application. Therefore,
the amino ionic liquids were immobilized on the conventional sorbents with relatively high surface area to
increase the adsorbed amount of carbon dioxide as well
as simplification of processing. The synthesized materials were employed to investigate the CO2 sorption
capacity with different pressures and temperatures in
this study.
EXPERIMENTAL METHODS
Materials
(3-Chloropropyl)triethoxysilane (95%) were purchased from Sigma (St Louis, MO, USA) and imidazole (99%), 3-bromopropylamine hydrobromide (98%)
were obtained from Aldrich (Milwaukee, WI, USA).
4-(Chloromethyl)styrene (90%), divinylbenzene (50%),
and polyvinylpyrrolidone (K 30) were purchased from
Tokyo Chemical Industry Co., Ltd (Tokyo, Japan). 2,2 Azobisisobutyronitrile (AIBN) was from Junsei Chemical Co., Ltd. (Tokyo, Japan). Methanol, ethanol, and
toluene were obtained from Pure Chemical Co., Ltd
(Ansan, Korea). The 15 µm Apex silica particles were
purchased from Merck Chemicals Ltd.
Asia-Pacific Journal of Chemical Engineering
SORPTION OF CARBON DIOXIDE
Synthesis of imidazolium silica
and amino-imidazolium silica
Silica was first immersed in hydrochloric acid for
24 h and then washed with deionized water and dried
at 120 ◦ C for 12 h. The activated silica (10.0 g) was
suspended in 150.0 mL of dry toluene and then an
excess of 3-chloropropyltriethoxysilane (10.0 mL) was
added. The suspension was stirred and refluxed for
24 h. After refluxing, the reaction was stopped and
the modified silica was cooled to room temperature,
and washed with toluene, ethanol–water mixture and
methanol. Chloropropyl silica (SilprCl) was dried under
vacuum at 60 ◦ C for 4 h.
The chemically bonded chloropropyl group on the
silica surface was reacted with imidazole. In brief, 5.0 g
of dry chloropropyl silica was placed in a reaction flask
containing 50.0 mL of anhydrous toluene and a large
excess of imidazole (5.0 g). The mixture was refluxed
with stirring for 24 h. After refluxing, the reaction was
stopped and the modified silica was cooled to room
temperature, transferred to a vacuum glass filter, and
washed with toluene, ethanol, and methanol in turn. The
silica chemically bonded with imidazolium was dried
at 50 ◦ C for 5 h. The silica bonded with imidazole was
named as SilprImCl.
The previous obtained SilprCl reacted with imidazole (triethylamine as a catalyst). According to the
paper,[14] 5.0 g of dry chloropropyl silica was placed
in a reaction flask containing 100 mL of toluene and
5.93 g triethylamine. The suspension was stirred for
30 min and then imidazole (4.0 g) was added over
a period of 10 min with stirring. After 10 h reflux,
the reaction was stopped and the modified silica was
cooled to room temperature, and washed with toluene,
ethanol, and methanol in turn. The silica bonded with
imidazole (SilprIm) was dried under vacuum at 50 ◦ C
for 4 h.
Same as described in previous paper,[8] 5.0 g SilprIm was placed in a 250.0 mL flask to which 100 mL
ethanol and 4.0 g 3-bromopropylamine hydrobromide
were added to the flask in succession. The suspension was then refluxed with stirring for 24 h. The
amino-imidazolium silica (named as SilprImNBr) was
obtained with washing and drying. The synthesis
scheme of ionic liquid-based silica was shown in
Fig. 1(A).
Synthesis of amino-imidazolium polymer
The amino-imidazolium polymer particles were synthesized as follows: 0.2 g of polyvinylpyrrolidone
(PVP) was dissolved in 55.0 mL of ethanol/water
(10 : 1, v/v) in a two-neck flask. Then a mixture of
4-(chloromethyl) styrene (5.0 g), divinylbenzene (0.5 g)
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 1. Synthesis steps used in the preparation of ionic
liquid-based silica (A) and polymer (B).
and AIBN (0.15 g) was added under nitrogen atmosphere and rapid stirring, and the emulsion solution
was heated to 73 ◦ C for 12 h polymerization. The
obtained dried polymer (PSCl) was reacted with imidazole using triethylamine as a catalyst. According
to the study of Pernak et al .,[14] PSCl was placed in
a reaction flask containing toluene and triethylamine.
The suspension was stirred for 30 min and then imidazole was added over a period of 10 min with stirring. After 12 h reflux, the reaction was stopped and
washed. The polymer bonded with imidazole (PSIm)
was dried. Third, following the procedure reported by
Betas et al .,[7] PSIm was placed in a flask with ethanol
and 3-bromopropylamine hydrobromide. The suspension was then refluxed with stirring for 24 h. After
washing with ethanol and drying at 70 ◦ C, the aminoimidazolium polymer (PSImN) was obtained. The synthesis scheme of ionic liquid-based polymer was shown
in Fig. 1(B).
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
87
88
W. BI et al.
Asia-Pacific Journal of Chemical Engineering
Figure 2. Apparatus of static volumetric method.
Characteristic analysis
Electron spectroscopy for chemical analysis (ESCA)
data were obtained with a Sigma-Probe (Thermo VG,
UK) spectrometer using Mg Kα radiation as an excitation source. Thermogravimetric measurements were
obtained on a Thermogravimetric Analysis (TGA) unit
(SCINCO thermal gravimeter S-1000) with a heating rate of 10 ◦ C/min under nitrogen. FT-IR data
were obtained by a Vertex 80V (Bruker, USA).
Brunauer–Emmett–Teller (BET) surface area was measured by ASAP2010 (Micromeritics, USA). The carbon, hydrogen, and nitrogen contents were determined
by elemental analysis performed on a 2400 Series II
CHNS/O Elemental Analyzer (PerkinElmer, USA).
Apparatus of static volumetric method
Adsorption equilibrium data were obtained using a static
volumetric method. Figure 2 shows a schematic representation of the apparatus. In this method, the amount
of gas in the system is determined using appropriate pressure, volume, and temperature measurements.
The pressure and temperature were recorded using a
mobile recorder (MV 100, Yokogawa Co.). Moreover,
the temperature in each cell was measured using K-type
thermocouple operated within an accuracy of ±0.01 K;
the pressure was measured using a pressure transducer
(Sensys, Sensor system tech.) with an accuracy of
0.133%. The adsorption cell, loading cell, and all connection tubes consisted of stainless steel. The volumes
of the adsorption and loading cells were 154.7 ± 1 mL
and 156.4 ± 1 mL, respectively, and determined from
the expansion of hydrogen gas. 1/4 in. tubes and 1/4
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
in. valves were used. During the experiments, the
adsorption and the loading cells were immersed in a
water bath (BS-21, Jeio Tech.) maintained at a given
temperature using a refrigeration circulator (MC-31,
Jeio Tech.). A vacuum pump was used to eliminate
gaseous impurities from the adsorption and loading
cells.
Procedure for determination of adsorbed
amount
The adsorbent was put into the adsorption cell. The
adsorbent was regenerated to eliminate trace impurities
under vacuum (< −1 kgf /cm2 ) for at least 12 h using
a vacuum pump. The CO2 was introduced into the
loading cell, and its pressure and temperature were
measured when the cell was stabilized. Then the valve
between the loading and adsorption cells was opened,
allowing the gas to contact the adsorbent. The pressure
and temperature were measured after equilibrium was
achieved, and the number of moles remaining in the
two cells was calculated. The adsorption equilibrium
state was considered to occur when the respective
temperature and pressure of the cells were constant.
The amount adsorbed was calculated using a mass
balance equation (Eqn (1)). This balance was derived
from generalized equation of state before and after
adsorption equilibrium.
PV PV PV PV +
=
+
+ qM
Z RT L1 Z RT A1
Z RT L2 Z RT A2
(1)
where P is pressure, T is temperature, V is volume, R
is the gas constant, M is the molecular weight, Z is the
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Figure 3. ESCA spectra of the surface of SilprCl and
SilprImCl.
SORPTION OF CARBON DIOXIDE
Figure 4. FT-IR spectra of (A) SilprCl and (B) SilprIm.
compressibility factor, and q is the amount adsorbed.
Subscripts 1 and 2 represent the state before and after
adsorption equilibrium, respectively.
RESULTS AND DISCUSSION
Characterization of SilprImCl, SilprIm
and SilprImNBr
The surface area (540 m2 /g) of silica was calculated by
BET determination. Figure 3 shows the ESCA spectra
of the surface of SilprCl and SilprImCl. The existence
of covalently bound chlorine atoms on the SilprCl silica
surface was confirmed by the Cl 2p signal at a binding
energy of 200 eV.[15] The peak at 401 eV is attributed
to N1s, indicating the linked imidazolium on the surface
of SilprImCl. These spectra prove that immobilization
is realized on the surface.
The FT-IR spectra of chloropropyl silica exhibited
a conspicuous peak at the wavelength of 700 cm−1 in
Fig. 4 and the finger print region of the C–Cl group was
from 704 to 690 cm−1 .[16] In the spectra of SilprIm, the
finger print peak decreased only when the imidazole
was reacted with chloropropyl silica and the chlorine
was replaced by imidazole. In comparison, the finger
print peak of N-H group was not observed from 3500
to 3300 cm−1 in the spectra of SilprCl and SilprIm.
This result showed that the SilprIm was synthesized
successfully.
Thermogravimetry can be employed to determine
the thermo stability of the chemically modified silica
because the weight loss observed between 200 and
800 ◦ C was found to be associated with the loss of
the organic groups attached to the surface.[17] Figure 5
shows the thermogravimetric curves for SilprIm and
SilprImNBr. From 200 to 750 ◦ C, it presents about
12 and 20% mass loss for SilprIm and SilprImNBr,
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 5.
TGA curves obtain for (A) SilprIm and
(B) SilprImNBr.
respectively. The SilprImNBr shows a higher mass loss
due to the extra amino group. This result showed that
the immobilization of amino group on imidazole was
successful.
Characterization of PSCl and PSImN
The surface area (5.0 m2 /g) of polymer was calculated
by BET determination. The Fourier transform infrared
(FT-IR) spectra of PSCl and PSImN are shown in
Fig. 6. The absorption bands at 723–682 cm−1 were
attributed to the stretching vibrations of C–Cl bonds.[18]
In comparison with PSCl and PSImN, the peak at
703 cm−1 was decreased in the spectra of PSImN, due
to the destruction of the C–Cl groups and their replacement with imidazole. The broad band at 3423 cm−1 was
ascribed to the symmetrical and asymmetrical stretching vibrations of NH and NH2 . The band at 1560 cm−1
was assigned to the NH2 asymmetric bending mode.[19]
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
89
90
W. BI et al.
Asia-Pacific Journal of Chemical Engineering
Figure 6. FT-IR spectrum of (A) PSCl and (B) PSImN.
Figure 7. Adsorption isotherms of CO2 on normal
silica, SilprImCl and SilprImNBr at room temperature.
Table 1. Elemental analysis and surface coverage of
SilprImNBr and PSImN.
Materials
SilprImNBr
PSImN
C%
H%
N%
Coverage (µmol/m2 )
9.35
58.43
1.75
15.18
2.02
6.20
1.13
295.23
These FT-IR results confirmed the successful synthesis
of the amino-imidazolium polymer.
Surface coverage of SilprImNBr and PSImN
The element contents and surface coverage of SilprImNBr and PSImN are listed in Table 1. The bonding densities based on the nitrogen percentages were
1.13 and 295.23 mmol/m2 for SilprImNBr and PSImN,
respectively.
Sorption of carbon dioxide
by amino-imidazolium silica
The adsorption isotherms of CO2 on normal silica,
SilprImCl and SilprImNBr at 298.15 K were plotted,
as shown in Fig. 7. The adsorbed amount of CO2
increased with increasing pressure. The SilprImNBr
adsorbed CO2 at fairly higher capacities and rate than
those of normal silica and SilprImCl. There was around
0.2 mmol/g more adsorbed CO2 on SilprImNBr. When
the pressure was increased to 5 atm, the SilprImNBr
had 0.8 mmol/g of adsorbed CO2 , nearly twice than
the others. This phenomenon was due to the amino
and imidazolium groups on the SilprImNBr, which
increased the interactions with CO2 . However, the
adsorbed amounts of SilprImCl was little more than
those of normal silica, and the increase of adsorbed
amount did not accord with the theoretically predicted
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 8. Adsorption isotherms of CO2 on SilprImNBr
at various temperatures.
amount when comparing SilprImNBr and normal silica.
These results were due to the blockage of micropores
in the silica and decrease of the silanol groups on the
surface by modification of ionic liquids. In this case,
mesoporous materials may be preferred.
The effect of temperature was also investigated.
Figure 8 showed the adsorption isotherms of CO2 on
SilprImNBr, respectively, at various temperatures. Generally, as a consistent trend, the adsorbed amounts
of CO2 on ionic liquid-modified silica increased with
increasing pressure at various temperatures, but the
adsorbed amount decreased with increasing temperature. This can be explained by desorption of CO2 at relatively high temperature. Previous research shows that,
the π –π interaction between the imidazolium center
and CO2 decreases with increasing temperature.[20,21]
Meanwhile, physical adsorption usually has a lower
adsorbed amount at relatively high temperatures.
Besides the reasons mentioned above, there was another
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
SORPTION OF CARBON DIOXIDE
Figure 9. Adsorbed amount of CO2 on PSCl and PSImN under different temperatures. (A) 298 K, (B) 308 K, and (C) 318 K.
factor affecting SilprImNBr. Each pair of NH2 groups
can react with one CO2 molecular and ionizes, a balanced and exothermic reaction. In this situation, the
reaction preferred a relatively low temperature.
Sorption of carbon dioxide
by amino-imidazolium polymer
Figure 9 shows the CO2 sorption of the aminoimidazolium and blank polymers. Generally, the CO2
sorption of the polymers increased with the increasing
pressure. Although the trend of CO2 sorption increased,
some of the absorbed amount of CO2 was not consistent with the trend with increasing pressure. This can
be explained as follows: at high pressure, the polymer
particles huddle together with the decreasing surface
area. But the gas can penetrate the polymers with the
increasing pressure. These interactions affect the CO2
sorption of polymers and generate equilibrium between
these two factors.
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Comparing the blank and ionic liquid polymer, it
was found that the CO2 sorption capacity of ionic liquid polymer was higher than that of blank polymer.
This phenomenon was due to the interactions of the
functional groups with CO2 on the ionic liquid polymer. The cation of imidazole plays an important role
in absorption.[12] Besides the imidazolium group, the
amino group was typically used as a functional group
for CO2 sorption. A pair of amino groups can capture
a CO2 molecular.
The effect of temperatures was also investigated
(Fig. 9). The absorbed amounts of CO2 changed with
the temperatures ranging from 298 to 318 K. According
to the trends of CO2 sorption, the CO2 sorption at 308 K
was better than the others. The polymer softens with
the increasing temperature. In this case, the gas can
easily penetrate the polymer and was absorbed. But
higher temperature causes desorption of CO2 on the
surface of the polymer. By these two factors, the CO2
sorption can arrive to the highest capacity at a certain
temperature.
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
91
92
W. BI et al.
Asia-Pacific Journal of Chemical Engineering
Acknowledgement
This research was supported by Basic Science Research
Program through the National Research Foundation
(NRF) of Korea funded by the Ministry of Education,
Science and Technology (2010-0015731).
REFERENCES
Figure 10. Adsorbed amount of CO2 on PSImN and
SilprImNBr at 298 K.
Comparison of amino-imidazolium silica
and polymer
The adsorbed amount of carbon dioxide on aminoimidazolium silica and polymer at 298.15 K was shown
in Fig. 10. According to the adsorbed amount of carbon
dioxide per square meter, the sorption efficiency of
PSImN was proved to be better than that of SilprImNBr.
This phenomenon may be caused by the high-surface
coverage of functional groups on PSImN. In this case,
the increase of the surface area of the polymer sorbent
may increase the adsorbed amount of carbon dioxide
significantly.
CONCLUSION
The amino-imidazolium sorbents were synthesized and
applied for the capture of carbon dioxide. The sorption
capacity of carbon dioxide on SilprImNBr and PSImN
increased with the increasing pressure. The optimal temperature of SilprImNBr and PSImN were found to be
298 and 308 K, respectively. The sorption efficiency of
PSImN was found to be higher than that of SilprImNBr
due to the higher surface coverage of functional groups
on PSImN. Further investigation about the increase of
sorption amount of carbon dioxide is underway.
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
[1] C.M. White, B.R. Strazisar, E.J. Granite, J.S. Hoffman,
H.W.J. Pennline. Air Waste Manage. Assoc., 2003; 53, 645.
[2] K. Takahshi, S. Nii, F. Kawaizumi. Asia-Pac. J. Chem. Eng.,
2005; 13, 159–176.
[3] D. Camper, J.E. Bara, D.L. Gin, R.D. Noble. Ind. Eng. Chem.
Res., 2008; 47, 8496–8498.
[4] C. Cadena, J.L. Anthony, J.K. Shah, T.I. Morrow, J.F.
Brennecke, E.J. Maginn. J. Am. Chem. Soc., 2004; 126,
5300–5308.
[5] L.A. Blanchard, Z. Gu, J.F. Brennecke. J. Phys. Chem. B,
2001; 105, 2437–2444.
[6] J.L. Anthony, E.J. Maginn, J.F. Brennecke. J. Phys. Chem. B,
2002; 106, 7315–7320.
[7] E.D. Bates, R.D. Mayton, I. Ntai, J.H. Davis. J. Am. Chem.
Soc., 2002; 124, 926–927.
[8] A.P.S. Kamps, D. Tuma, J. Xia, G. Maurer. J. Chem. Eng.
Data, 2003; 48, 746.
[9] D. Camper, P. Scovazzo, C. Koval, R. Noble. Ind. Eng. Chem.
Res., 2004; 43, 3049–3054.
[10] P. Scovazzo, D. Camper, J. Kieft, J. Poshusta, C. Koval,
R. Noble. Ind. Eng. Chem. Res., 2004; 43, 6855–6860.
[11] P. Scovazzo, A.E. Visser, J.H. Davis, R.D. Rogers, C. Koval,
D.L. DuBois, R. Noble. ACS Symp. Ser, 2002; 818, 69.
[12] P. Scovazzo, J. Kieft, D.A. Finan, C. Koval, D.L. DuBois,
R. Noble. J. Membr. Sci., 2004; 238, 57–63.
[13] J. Tang, W. Sun, H. Tang, M. Radosz, Y. Shen. Macromolecules, 2005; 38, 2037–2039.
[14] J. Pernak, A. Czepukowicz, R. Poniak. Ind. Eng. Chem. Res.,
2001; 40, 2379–2383.
[15] P. Hemström, M. Szumski, K. Irgum. Anal. Chem., 2006; 78,
7098–7103.
[16] K.S. Khachatryan, S.V. Smirnova, I.I. Torocheshnikova, N.V.
Shvedene, A.A. Formanovsky, I.V. Pletnev. Anal. Bioanal.
Chem., 2005; 381, 464–470.
[17] B. Lumley, T.M. Khong, D. Perrett. Chromatographia, 2004;
60, 59–62.
[18] J.H. Hong, D. Li, H. Wang. J. Membr. Sci., 2008; 318,
441–444.
[19] D. Chira, S.S. Seo. J. Sens., 2009; 2009, 1–6.
[20] S. Hanioka, T. Maruyamaa, T. Sotani, M. Teramoto,
H. Matsuyamaa, K. Nakashima, M. Hanaki, F. Kubota,
M. Goto. J. Membr. Sci., 2008; 314, 1–4.
[21] L.M. Galán Sánchez, G.W. Meindersma, A.B. de Haan.
Chem. Eng. Res. Des., 2007; 85, 31–39.
Asia-Pac. J. Chem. Eng. 2012; 7: 86–92
DOI: 10.1002/apj
Документ
Категория
Без категории
Просмотров
32
Размер файла
287 Кб
Теги
base, dioxide, sorbent, ioni, sorption, liquid, carbon
1/--страниц
Пожаловаться на содержимое документа