CO2 capture by task specific ionic liquids (TSILs) and polymerized ionic liquids (PILs and AAPILs)

Article abstract of DOI:10.1016/j.molliq.2016.02.046

In the present study, new ionic liquids (ILs) such as task specific ionic liquids (TSILs), polymerized ionic liquids (PILs), and amino acid-based polymerized ionic liquids (AAPILs) were synthesized and their efficiency for capturing CO₂ was stu

Full text of DOI:10.1016/j.molliq.2016.02.046

Journal of Molecular Liquids 219 (2016) 306–312
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
CO2 capture by task specific ionic liquids (TSILs) and polymerized ionic
liquids (PILs and AAPILs)
b
Maisara Shahrom Raja Shahrom a, Cecilia Devi Wilfred a, , AboBakr Khidir Ziyada Taha
⁎
a
Center of Research in Ionic Liquids (CORIL), Universiti Teknologi PETRONAS, Tronoh, 32610 Bandar Seri Iskandar, Perak, Malaysia
Department of Applied Chemistry & Chemical Technology, Faculty of Engineering & Technology, University of Gezira, Wad Medani, Sudan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, new ionic liquids (ILs) such as task specific ionic liquids (TSILs), polymerized ionic liquids
(PILs), and amino acid-based polymerized ionic liquids (AAPILs) were synthesized and their efficiency for captur-
ing CO2 was studied. Nitrile imidazolium-based TSILs with different alkyl chain length and different anion ([DDS],
[TFMS], [SBA], [BS], [DOSS]), PILs consisting of [VBTMA], [VBTEA] and [METMA] cations and [BF4],[Cl], [NO3], [PF6]
and [TFMS] anions and AAPILs incorporating [VBTMA] as cation and [Arg], [Pro] as anions were synthesized. The
results showed that the CO2 sorption increases as alkyl chain length increased and [C2CNDim][DOSS] gave the
highest CO2 sorption among the TSILs, which reach up to 0.55 mol fraction at 10 bar, 298 K. In polymerized
ionic liquids the CO2 sorption capacity increases in polymeric forms than monomeric forms. To enhance the
efficiency of PILs for adsorbing CO2, AAPILs have been studied. The results showed that the AAPILs are capable
of capturing CO2 more than TSILs and PILs as they have functionalized amine tethered at the anion. The result
of CO2 sorption showed that even at low pressure (Peq 0.7 bar) and 298 K, the AAPILs [VBTMA][Arg] and
[VBTMA][Pro] absorbed 0.530 and 0.38 mol fractions of CO2.
Received 23 October 2015
Received in revised form 20 February 2016
Accepted 20 February 2016
Available online xxxx
Keywords:
CO2 capture
Task specific ionic liquids
Polymerized ionic liquids
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
organic solvents for capturing CO2 [9]. ILs are liquid that contains cations
(organic) and anions (organic or inorganic) which are liquid over a wide
The emissions of greenhouse gases which resulted to the global
warming have received widespread attention. CO2 contributes more
than 60% to global warming, where the concentration is now closed to
400 ppm which is higher than preindustrial level of 300 ppm. There
are several CO2 capture technologies such as chemical absorption, phys-
ical adsorption and membrane separation that have been studied.
Among the current CO2 capture technologies, chemical absorption by
alkanolamines or their mixtures such as monoethanolamine (MEA),
diethanolamine (DEA) and n-methyldiethanolamine (MDEA) are one
of the effective methods for the CO2 uptake. However, there were
some serious drawbacks such as corrosion of amines, limitation of the
concentration of amines in solution, and the degradation of amines in
high temperature during regeneration process. Thus, this would seri-
ously influence the development of green processing and environmen-
tal impact [1–7].
temperature range with low melting point (below 100 °C). ILs can be
designed by an appropriate combination of various cations (quaternary
ammonium, imidazolium, pyridinium, phosphonium ions and etc.) and
various anions ([Cl]−, [Br]−, [PF6]−, [BF4]−, [Tf2N]−, etc.) [10].
There are numerous studies on the thermal stability of ILs [11–15].
Cao et al. have investigated thermal stability on 66 of ILs by using TGA
method [11]. The investigations showed that anion type plays the
major role than the cation while cation modification has the least effect.
By varying the anions, it has a close relationship with anion coordinating
nature, nucleophilicity and hydrophilicity. The thermal stability in-
creased by using shorter alkyl chain, greater substituent number and
by replacing the C2-H with a methyl group. The functionalization such
as allyl-functionalization would decrease the thermal stability. By
studying the functionalized ILs, Liu et al. have studied the thermal stabil-
ity and decomposition mechanism of amine-functionalized ILs [12]. It
showed that amine-functionalized ILs were found to reduce the thermal
stability of [aEMMIM][BF4] compared to their non-functionalized coun-
terpart. This is due to the tether of amine NH2 to the imidazolium cation
that makes the nearby carbon atom more positively charged hence eas-
ier to be attacked by the F from the anion.
The development of a solution which could absorb high CO2 which
minimizes these disadvantages is highly recommended. Ionic liquids
(ILs), organic salt with melting point below 100 °C are an attractive re-
placement to alkanolamines because they have negligible vapor pres-
sure, high thermal stability, designable structure and wide liquids
temperature range [8]. This makes ILs the best candidate to substitute
ILs also are promising candidates as absorbents for CO2 removal
because of their high thermal stability, negligible vapor pressure and
tunable physicochemical properties [16]. Many research groups have
carried out research on solubility of CO2 in ILs [17–21]. Brennecke
⁎
Corresponding author.
E-mail address: cecili@petronas.com.my (C.D. Wilfred).
http://dx.doi.org/10.1016/j.molliq.2016.02.046
0167-7322/© 2016 Elsevier B.V. All rights reserved.

M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
307
et al. were the first to report on carbon dioxide solubility in imidazolium
and pyridinium ionic liquids. They found out that ILs that contain
fluoroalkyl chains on either cation or anion improves CO2 solubility
when compared to less fluorinated ILs. These fluorinated ILs have high
stability and low reactivity and thus give them many excellent proper-
ties [22–25]. However, they are poorly biodegradable and persistent in
the environment and thus are less environmentally benign [23]. The
anion plays a key role in determining CO2 solubility in ILs and through
physical adsorption with CO2, less energy is needed for the regeneration
of ILs. The enthalpy required is about 20 kJ/mol to release the physically
adsorbed CO2 in regeneration step, which is only a quarter of the energy
consumed in amine-based method [6].
Bates et al. have designed a mechanism of TSILs-amine functional-
ized with CO2. The reaction mechanism results in a maximum of
0.5 mol of CO2 being captured with 1 mol of ILs. (1:2 mechanism)
[26]. Goodrich et al. suggested that 1:1 (CO2: IL) mol ratio can be
achieved when amine is tethered in anion instead of cation called
amino acids ionic liquids (AAILs) [27]. Therefore AAILs have an advan-
tage since amino acids act as anion. Since [AA]− have a structure of
[H2N–CHR–COO−], it can represented as R− NH2.
and methane, nitrogen, and helium with 99.99% purity. Amberlite IRA
402 (OH form), arginine and proline were purchased from Aldrich. All
the chemicals were used without any purification.
2.2. Experimental procedure of task specific ionic liquids (TSILs)
2.2.1. Synthesis of 1-alkyl-3-propanenitrile imidazolium bromide,
[C2CN Cnim][Br]
1-Alkyl-3-propanenitrile imidazolium bromide ILs were synthesized
by following the method shown in Fig. 1.
Imidazole (0.5 mol) was mixed with methanol and acrylonitrile
(0.6 mol) and refluxed under nitrogen atmosphere at 50–55 °C for
10 h. The volatile materials were removed from the mixture under
vacuo at 70 °C. The viscous liquid left was propanenitrile imidazole.
Then, nitrile functionalized IL was synthesized by direct quartenization
reaction of the propanenitrile imidazole with 1-bromobutane (0.5 mol).
The resulting compound was cooled to room temperature and washed
with ethyl acetate and kept in vacuo at 80 °C.
Similar procedure was repeated for the synthesis of 1-hexyl-3-
propanenitrile imidazolium bromide, [C2CN Him][Br], 1-octyl-3-
propanenitrile imidazolium bromide, [C2CN Oim][Br] and 1-decyl-3-
propanenitrile imidazolium bromide, [C2CN Dim][Br] by replacing 1-
bromobutane with 1-bromohexane, 1-bromooctane and 1-
bromodecane, respectively.
CO2 þ R−NH2↔R−NþH2COO−
ð1Þ
R−NþH2COO− þ R−NH2↔R−NHCOO− þ R−NH3þ:
ð2Þ
2.2.2. Synthesis of [C2CN Cnim][DOSS]
1-Alkyl-3-propanenitrile imidazolium dioctylsulfosuccinate, [C2CN
Cnim][DOSS] was synthesized by mixing [C2CN Cnim][Br] (0.03 mol)
and sodium dioctylsulfosuccinate (0.03 mol) in 50 ml acetone. The mix-
ture was stirred at room temperature for 48 h. The solid precipitate
formed was separated and the solvent removed in vacuo.
The theoretical calculations showed that dianion formed in the
second Eq. (2) is chemically unstable therefore the reaction would
expect to terminate at Eq. (1) upon addition of CO2 to AAILs.
Polymerized ionic liquids (PILs) also have attracted recent attention
on CO2 absorption due to their higher CO2 absorption exhibited by PILs
compared to the monomeric ILs [28–32]. PILs can be prepared by poly-
merization of the monomer or co-polymerization of the monomer with
ILs species being in repeating units indicating that PILs have higher CO2
absorption compared to the monomer [33]. Therefore, PILs would have
larger volume which in turn will theoretically trap a large amount of
CO2.
2.2.3. Synthesis of [C2CN Cnim][DDS], [C2CN Cnim][SBA], [C2CN Cnim][BS]
and [C2CN Cnim][TFMS]
1-Alkyl-3-propanenitrile imidazolium dodecylsulfate, [C2CN
Cnim][DDS] was synthesized by mixing [C2CN Cnim][Br] (0.04 mol)
and sodium dodecyl sulfate (0.04 mol) in 40 ml hot deionized water
(60 °C). The mixture was stirred at room temperature for 48 h. The
solid precipitate formed was separated and the solvent removed by
vacuum. Similar procedure was applied to [C2CN Cnim][SBA], [C2CN
Cnim][BS] and [C2CN Cnim][TFMS] by using equimolar of sodium
sulfobenzoic acids, sodium benzenesulfonate and lithium
trifluoromethanesulfonate, respectively.
In amino acid-based polymerized ionic liquids (AAPILs), the CO2
sorption increased and by using functionalized-amine anion, (amino
acids), the AAPILs showed higher absorption due to the chemical reac-
tion of amine and CO2 to form carbamate group.
2. Experimental procedure
2.3. Experimental procedure of poly(ionic liquid)s, (PILs)
2.1. Chemicals
2.3.1. Synthesis of vinylbenzyltriethylammonium chloride, [VBTEA][Cl]
4-Vinylbenzyl chloride (0.16 mol), triethylamine (0.168 mol) and
DBMP (0.4 g) were mixed and stirred at 50 °C for two days under N2
Imidazole, acrylonitrile, 1-bromohexane, 1-bromooctane, 1-
bromodecane, 1-chlorohexane, 1-chlorooctane, 1-chlorotetradecane,
sodium
dioctylsulfosuccinate,
sodium
dodecylsulfate,
sodiumbenzenesulfonate, 3-sulfobenzoic acid sodium salt and lith-
ium trifluoromethanesulfonate 98–99%, 1-chlorobutane, anhy-
drous methanol, anhydrous ethylacetate, acetone, anhydrous
diethyl ether 98–99%, α-(Vinylbenzyl)trimethylammonium chloride
99%, ([VBTMA][Cl]), dimethylformamide (DMF) 99.89%, anhydrous ace-
tonitrile 99.8%, sodium trifluoromethanesulfonate 98%, triethylamine
99.5%, [2-(methacryloyloxy)ethyl]trimethylammonium chloride
75 wt.% in H2O, ([METMA][Cl]) and sodium methyl sulfate 98%, sodium
nitrate 99%, anhydrous sodium acetate 99% and diethylamine 99.5%,
2,6-di-tert-butyl-4-methylphenol (DBMP) 99%, 4-vinylbenzyl chloride
90%, Amberlite IRA 402 (OH form), arginine and proline were pur-
chased from Aldrich. 1-Bromobutane 98% purity was purchased from
Merck. Azobisisobutyronitrile (AIBN) 98% was purchased from R&M.
Purified gases supplied by MOX-Linde Gases Sdn. Bhd were used for
the CO2 solubilities measurement. The grades of gases used are carbon
dioxide 99.99% minimum (moisture b10 ppm, hydrocarbon b1 ppm)
Fig. 1. Synthesis route of the RTILs [C2CN Cnim][X].

308
M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
atmosphere. The formed solid vinylbenzyl triethylammonium chloride
[VBTEA][Cl] was washed with diethyl ether, filtered and dried under
vacuum.
3.2. CO2 solubility in TSILs
The CO2 solubility in ILs depends primarily on the strength of inter-
action of CO2 with the anion. Five ILs with same cation ([C2CN Him]) and
five different anions ([DOSS], [DDS], [TFMS], [SBA] and [BS]) were used
to study the effect of their anions on CO2 solubility.
2.3.2. Synthesis of poly[VBTMA][BF4], poly[VBTMA][PF6], poly[VBTMA][TFMS]
and poly[VBTMA][NO3]
Poly[VBTMA][BF4], Poly[VBTMA][PF6], Poly[VBTMA][TFMS] and
Poly[VBTMA][NO3] were prepared in two steps. In the first step, metath-
esis reactions of the [VBTMA][Cl] with sodium tetrafluoroborate,
sodium hexafluorophosphate, sodium trifluoromethanesulfonate
and sodium nitrate were performed to prepare [VBTMA][BF4],
[VBTMA][PF6], [VBTMA][TFMS] and [VBTMA][NO3] respectively. In the
second step, [VBTMA][BF4], [VBTMA][PF6], [VBTMA][TFMS] and
[VBTMA][NO3] were polymerized by mixing 10 g from each with AIBN
(100 mg) and DMF (20 ml) at 60 °C for 6 h. Similar procedure was ap-
plied to synthesize Poly[VBTEA] ][NO3] and Poly[METMA][NO3].
3.2.1. Effects of the anions on CO2 solubility in TSILs
Fig. 2 shows the CO2 solubility at 10 bar, 298 K with [C2CN Him] as
cation and [DOSS], [DDS], [TFMS], [SBA] and [BS] as anion.
The results showed that the CO2 solubility depends on the anion
type as reported in literature [34]. From Fig. 2, it can be seen that ILs
with [C2CN Him][DOSS] have higher affinity for CO2 with 0.443 mol frac-
tion compared with the ILs incorporating [DDS], [TFMS], [SBA] and [BS]
as anions with 0.281, 0.340, 0.306 and 0.263 mol fraction, respectively.
The carbonyl and sulfonyl functionalities, long alkyl chains and
branched alkyl chains in [DOSS] lead to good CO2 solubility [35]. Anoth-
er major factor is the molar free volume of ILs which exerted a more
pronounced effect besides the anion basicity. The larger the molecular
size of anion, the larger the free volume in which CO2 can occupy [36].
The relatively high solubility of CO2 in the [TFMS] compared to the
[DDS], [SBA] and [BS] may be due to the greater interactions between
CO2 and the fluoroalkyl substitutents in [TFMS] anion [37,38]. There
are basically two interactions between CO2 and anion which are an
acid–base interaction between CO2 and anion and also CO2 and fluorine
in anion in ILs [39]. The fluorinated compounds have a high stability and
low reactivity which gives them many excellent properties, but these
also led them to being poorly biodegradable and persistent in environ-
ment [40]. The high solubility of CO2 in ILs with [SBA] anion compared
to [DDS] and [BS] anions is associated with the presence of carbonyl
functionality. This enhances a molecule's CO2 philicity and led to good
CO2 solubility of CO2 [41]. Moreover, the relatively high solubility capac-
ity of CO2 in [DDS] compared to [BS] anion is due to the long alkyl chain
of [DDS], which results in the increases of van der Waals-type interac-
tions between the gas and the liquids.
2.4. Synthesis of amino acid-based polymerized ionic liquids (AAPILs)
Two amino acid ionic liquids (AAILs); [VBTMA][Arg] and
[VBTMA][Pro] were synthesized according to the following method. In
the first step, [VBTMA][Cl], was dissolved in deionized water and
underwent anion exchange by subjecting it to a Amberlite IRA 402
(OH form) resin in a column. The resulting [VBTMA][OH] was tested
for the presence of chloride by using AgNO3. In the second step, The
[VBTMA][OH] was neutralized with an equimolar of arginine [Arg] and
proline [Pro] to synthesize [VBTMA][Arg] and [VBTMA][Pro] respective-
ly. The mixtures were stirred at room temperature for 12 h then the
water was evaporated by using rotary evaporator at 50 °C with under
reduced pressure. The excess of amino acids were precipitated by
adding proportions of acetonitrile and methanol in 7:3 ratio. The prod-
ucts ([VBTMA][Arg] and [VBTMA][Pro]) were dried by using rotary
evaporator and followed by vacuum oven. In polymerization process,
the monomer ([VBTMA][Arg]) (10 g), AIBN (100 mg) and methanol
(20 ml) were mixed at 60 °C for 6 h to form poly[VBTMA][Arg]. Similar
procedure was repeated for the polymerization of [VBTMA][Pro].
3.2.2. Effects of cations on CO2 solubility in TSILs
The influence of ILs cation on CO2 solubility was studied by compar-
ing the CO2 solubility with a similar anion, [DOSS] and difference of alkyl
chain length from butyl to decyl. Fig. 3 shows the CO2 solubility at tem-
perature 298 K, 10 bar.
From Fig. 3, it can be seen that the CO2 solubility increases as the
alkyl chain length increases; [C2CN Bim] (0.412 mol fraction) b [C2CN
Him] (0.443 mol fraction) b [C2CN Oim] (0.502 mol fraction) b [C2CN
Dim] (0.548 mol fraction). As expected, CO2 is more soluble in ILs with
long alkyl chain. The alkyl groups also increases the dispersion force of
the cation for better interaction with CO2 [42]. The increasing trend
for CO2 solubility in the [C2CN Bim][DOSS], [C2CN Him][DOSS], [C2CN
2.5. Characterization of ionic liquids
All the ionic liquids (TSILs) and polymerized ionic liquids (PILs and
AAPILs) were characterized by using 1H NMR Bruker Avance 400 (9.4
Tesla magnet), 400 MHz.
The CO2 sorption measurement was performed by using Magnetic
Suspension Balance (MSB), Rubotherm GmbH (Germany) rated at
500 bar and 500 °C. The MSB consists of a sorption chamber where
the sample is exposed to a gas at the desired temperature and pressure,
and a microbalance with accuracy up to five decimals of a gram. An elec-
tromagnet is connected to the microbalance and adjusted to keep the
permanent magnet in suspension. The microbalance measures a weight
which is proportional to the electromagnetic force that keeps the rod-
rod basket assembly in suspension. A heating circulator (Julabo, model
F25ME) is used to control the temperature of the sorption chamber
with an accuracy of 0.5 °C.
FTIR spectra before and after CO2 sorption were recorded using FTIR
Shimadzu in the mid region of 4000–600 cm−1 using Diamond Attenu-
ated Total Reflactance (D-ATR) measurement mode.
3. Results and discussion
3.1. 1H NMR
The 1H NMR for all TSILs, PILs and AAPILs are provided at supple-
mentary information (ESI-1). These 1H NMR results confirm the struc-
ture of ionic liquids synthesized.
Fig. 2. Effect of anion on CO2 solubility with [C2CN Him] as cation.

M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
309
Oim][DOSS] and [C2CN Dim][DOSS] may be due to the increase of the
molar volume and the presence of the CN group in the side chain of
the ILs. This is because the presence of the CN group would change
the architecture of the hydrogen bonding network of these ILs. The
differences in the alkyl chain affects the hydrogen bond interaction
between the C-2 of the imidazolium cation, the remaining H atoms on
the cation and the anions [43].
However, these TSILs often suffer the problem of having high viscos-
ity. On the other hand, polymerized ionic liquids (PILs) have recently
attracted attention for CO2 absorption due to its solid form
and exhibiting higher CO2 sorption compared to the monomeric ILs
[28–33]. The properties of PILs also can be customized by varying the
combination of polycation-anion pair [44].
3.3. CO2 solubility in poly ionic liquids (PILs)
Fig. 4. CO2 solubility for [VBTMA][Cl] and poly[VBTMA][Cl] at 10 bar, 298 K.
3.3.1. Effects of polymerization on PILs
Fig. 4 shows the solubility of CO2 by [VBTMA][Cl] monomer and its
polymer poly[VBTMA][Cl] at 10 bar, 298 K.
From Fig. 4, it can be concluded that the polymerization increased
the sorption capacity. The polymer, poly[VBTMA][Cl] showed CO2 solu-
bility at 0.188 mol fraction higher than the monomer, [VBTMA][Cl] at
only 0.07 mol fraction.
sorption with 10.2 mol% follows with poly[VBTEA][BF4] (4.85 mol%)
and poly[VBTBA][BF4] with 3.1 mol% [46].
3.3.3. Effect of anions with CO2 in PILs
Fig. 6 shows the CO2 sorption on different of anion with [VBTMA] as
cation at 10 bar, 298 K. The anions studied were [Cl], [BF4], [NO3], [PF6]
and [TFMS].
3.3.2. Effects of cations with CO2 in PILs
From Fig. 6 can be seen that poly[VBTMA][BF4] shows the highest CO2
sorption capacity with 0.209 mol fraction. The sorption capacity is in the
order of poly[VBTMA][BF4] (0.209 mol fraction) N poly[VBTMA][Cl]
(0.188 mol fraction) N poly[VBTMA][PF6] (0.180 mol fraction) N
The type of cation for PILs with [NO3] showed a significant effect on
sorption capacity. Fig. 5 shows the CO2 sorption for different cations
with [NO3] as anion at 10 bar, 298 K.
The results showed that the sorption trend is in the order of
poly[VBTMA][NO3] 0.177 mol fraction N poly[VBTEA][NO3] 0.133 mol
fraction N poly[METMA][NO3] 0.066 mol fraction. This is agreed by Tang
et al. where the [VBTMA] cation shows higher CO2 sorption than
[VBTEA] and [METMA] cation [45]. The result shows that, polycation
with longer alkyl side chain may pose a stearic hindrance that hinders
CO2 sorption thus results in a decrease of microvoid volume with fewer
interaction between CO2 and cation [44]. Therefore, long alkyl substitu-
ents on the cation and cross-linking would decrease the CO2 sorption ca-
pacity [45]. This explains the highest sorption rate of poly[VBTMA][NO3]
compared to poly[VBTEA][NO3]. The difference between [VBTMA] and
[METMA] is the structure of backbone. PILs with [VBTMA] have
vinylbenzyl backbone and this would enhance the sorption rate and
CO2 capacity compared to methacryloyloxyethtyl backbone poly ionic
liquids [44].
poly[VBTMA][NO3] (0.177 mol fraction)
N poly[VBTMA][TFMS]
(0.164 mol fraction). Contrary to RTILs, in PILs the presence of fluorine
atom in anion is not a decisive factor to enhance the CO2 sorption
which explains the lower of CO2 sorption in PF6 and TFMS anions. This
is agreed by Tang et al. that poly[VBTMA][Tf2N] (2.85 mol%) had a sorp-
tion capacity much lower than [BF4] and [PF6] anions and similar to
non-fluorinated PILs which is poly[VBTMA][Sac] with 2.67 mol% [46].
This indicates that in PILs, fluorine atom is not a decisive factor for CO2
sorption. The bulky anion on [TFMS], may decrease the spare volume
and would prevent CO2 penetration towards the polycation which is re-
sponsible for CO2 capture [44].
From these results, it can be concluded that by polymerizing the
ionic liquids, the CO2 sorption increases than in monomeric forms. How-
ever, this PILs CO2 solubility results are much lower than in reported
TSILs. Therefore, we synthesized amino acid-based polymerized ionic
liquids (AAPILs) where it has amine tethered in the anions, so the chem-
isorptions of CO2 can be achieved.
This trend was agreeable at low pressure (592.3 mmHg, 22 °C) as
reported by Tang et al. where poly[VBTMA][BF4] shows higher CO2
Fig. 3. Effects of cations in ILs on CO2 solubility with [C2CNCnim] cation (butyl,octyl, hexyl,
decyl) and [DOSS] as anion.
Fig. 5. CO2 sorption for different poly cations with [NO3] as anion at 10 bar.

310
M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
anion. The absorption capacity of CO2 reaches 0.9 mol CO2 per mol ILs
at 303 K, 1 bar [49]. The absorption mechanism shows chemical process
and it confirms by NMR and FTIR. This CO2 can easily desorb at higher
temperature and under vacuum therefore, it can be reuse.
These results support the idea that the CO2 sorptions of PILs were af-
fected by anion types. From these results, we have showed that AAPILs
with polymerized amino acids-anion showed much higher CO2 sorption
compared to other PILs.
3.4.1. Effect of pressure
The CO2 sorption for poly[VBTMA][Arg] was measured in the range
0.7 to 10 bar in 25 °C. Fig. 8 shows the effect of pressure on CO2 sorption
to poly[VBTMA][Arg].
The plot indicates that the CO2 absorption increases with increasing
pressure. At 7.7 bar, the CO2 absorbed was 0.742 mol ratio which, was
higher compared to 0.530 mol ratio at 0.7 bar. It can be seen that the
CO2 molar uptake increases continuously with increasing pressure
under studied conditions. At low pressure, a large uptake of CO2 can
be expected to be due to the chemical absorption process and the fur-
ther increase at higher pressure is in part because of physical adsorption
[27]. This is especially relevant at high pressures whereas they reach
their absorption limits at low pressure. This is agreed by Chen et al.
where there are both physical and chemical interactions between
amine-functionalized ionic liquids with CO2 [50]. In general, this
arginate AAPILs might have an absorption capacity as high as 2 mol
CO2/mol ILs if all of the amine nitrogens are active towards CO2. This
shows how the absorption performances of AAILs merge the character-
istics of physical solvents with the attractive features of chemical
solvents [51]. The time required in high pressure for the system to attain
equilibrium increases because of the chemical complexation by
forming carbamate species as well with physical adsorption on
poly[VBTMA][Arg].
Fig. 6. CO2 sorption on different anions and poly [VBTMA] as cation.
3.4. CO2 solubility in amino acid-based polymerized ionic liquids (AAPILs)
In AAPILs, the anion used was amino acids where it has functional-
ized amine tethered at the anion. Fig. 7 shows the CO2 sorption of the
monomer, amino acids ionic liquids (AAILs) and the polymer, amino
acid-based polymerized ionic liquids (AAPILs). The CO2 sorption was
carried out in low pressure (Peq 0.7 bar) at 298 K. From these results,
it can be observed that poly[VBTMA][Arg] gave higher CO2 sorption at
0.530 mol fraction compared to poly[VBTMA][pro] at 0.380 mol fraction.
These AAPILs also showed higher CO2 sorption compared with the
monomers, [VBTMA][Arg], 0.454 mol fraction and [VBTMA][Pro],
0.274 mol fraction. This indicates that polymerization increases the
CO2 sorption of the monomer [47]. Arginine, [Arg] shows higher CO2
sorption than proline, [Pro] anion. This is mainly because of arginine,
[Arg], comprises of two primary amines and two secondary amines.
Thus, the accessibility of CO2 to react with one or more of these four
amine sites is an advantage compared to the [Pro] anion; has one sec-
ondary amine in a ring [48].
These results are similar with those reported in the literature that
AAILs with more than one amine site have shown higher CO2 absorption
capacity than the AAILs with only one primary amine group. Sistla et al.
reported that [bmim][Arg] has shown higher CO2 sorption with
0.62 mol/mol due to the availability of more accessible amine groups
[48]. Saravanamurugan et al. reported that [N66614][Arg] shows higher
CO2 sorption with 1.0 mol CO2/mol ILs with arginine containing several
additions of amine groups [16]. Xue et al. have synthesized dual amine
ILs, [aemmim][Tau], where the amine tethered to the cation and
3.4.2. Characterization of AAPILs after CO2 sorption
The characterization of poly[VBTMA][Arg] after CO2 absorption can
be characterized by using FTIR before and after CO2 absorption as
shown in Fig. 9. The reaction CO2 and amine shows a broad peak in
the range 3280–3350 cm−1 which corresponds to –NH in secondary
amides that resulted from CO2 reacting with NH2. New peak with high
intensity at 1639 cm−1 indicate the carbamate species. The reaction of
CO2 and NH2 was confirmed in poly[VBTMA][Arg]. The increasing of in-
tensity after CO2 sorption also can be seen. This confirmed that the
chemical and physical sorption occurred in poly[VBTMA][Arg].
4. Conclusion
The development of ionic liquids for CO2 sorptions have been stud-
ied from TSILs followed with PILs and AAPILs. Poly[VBTMA][Arg]
Fig. 7. CO2 sorption of AAPILs and AAILs in 0.7 bar, 298 K.
Fig. 8. CO2 sorption of poly[VBTMA][Arg] with increasing pressure.

M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
311
[10] Y. Zhang, S. Zhang, X. Lu, Q. Zhou, W. Fan, X. Zhang, Dual amino-functionalised phos-
phonium ionic liquids for CO2 capture, Chem. A Eur. J. 15 (2009) 3003–3011.
[11] Y. Cao, T. Mu, Comprehensive investigation on the thermal stability of 66 ionic liq-
uids by thermogravimetric analysis, Ind. Eng. Chem. Res. 53 (2014) 8651–8664.
[12] S. Liu, Y. Chen, Y. Shi, H. Sun, Z. Zhou, T. Mu, Investigations on the thermal stability
and decomposition mechanism of an amine-functionalized ionic liquid by TGA,
NMR, TG-MS experiments and DFT calculations, J. Mol. Liq. 206 (2015) 95–102.
[13] Y. Zhang, T. Li, Z. Wu, P. Yu, Y. Luo, Synthesis and thermophysical properties of
imidazolate-based ionic liquids: influences of cations and anions, J. Chem.
Thermodyn. (2013).
[14] Z. Xue, Y. Zhang, X.-q. Zhou, Y. Cao, T. Mu, Thermal stabilities and decomposition
mechanism of amino- and hydroxyl-functionalized ionic liquids, Thermochim.
Acta 578 (2014) 59–67.
[15] M. Villanueva, A. Coronas, J. García, J. Salgado, Thermal stability of ionic liquids for
their application as new absorbents, Ind. Eng. Chem. Res. 52 (2013) 15718–15727.
[16] S. Saravanamurugan, A.J. Kunov-Kruse, R. Fehrmann, A. Riisager, Amine-
functionalized amino acid-based ionic liquids as efficient and high-capacity absor-
bents for CO2, ChemSusChem 7 (Mar 2014) 897–902.
[17] Y. Zhang, P. Yu, Y. Luo, Absorption of CO2 by amino acid-functionalized and tradi-
tional dicationic, Chem. Eng. J. 214 (2013) 355–363.
[18] P. Sharma, S.D. Park, K.T. Park, S.C. Nam, S.K. Jeong, Y.I. Yoon, Solubility of carbon di-
oxide in amine-functionalized ionic liquids role of the anions, Chem. Eng. J. 193-194
(2012) 267–275.
[19] N.M. Yunus, M.I.A. Mutalib, Z. Man, M.A. Bustam, T. Murugesan, Solubility of CO2 in
pyridinium based ionic liquids, Chem. Eng. J. 189-190 (2012) 94–100.
[20] Z. Zhao, H. Dong, X. Zhang, The research progress of CO2 capture with ionic liquids,
Chin. J. Chem. Eng. 20 (2012).
[21] K.A. Kurnia, F. Harris, C.D. Wilfred, M.I.A. Mutalib, T. Murugesan, Thermodynamic
properties of CO2 absorption in hydroxyl ammonium ionic liquids at pressure of
(100–1600)kPa, J. Chem. Thermodyn. 41 (2009) 1069–1073.
Fig. 9. FTIR spectrum before and after CO2 sorption on poly[VBTMA][Arg].
[22] L.A. Blanchard, J.F. Brennecke, Recovery of organic products from ionic liquids using
supercritical carbon dioxide, Ind. Eng. Chem. Res. 40 (2001) 287–292.
[23] M.J. Muldoon, S.N.V.K. Aki, J.L. Anderson, J.K. Dixon, J.F. Brennecke, Improving carbon
dioxide solubility in ionic liquids, J. Phys. Chem. B 111 (2007) 9001–9009.
[24] L.A. Blanchard, D. Hancu, E.J. Beckman, J.F. Brennecke, Green processing using ionic
liquids and CO2, Nature 399 (1999) 28–29 (05/06/print).
showed higher CO2 sorption with 0.530 mol fraction in 0.7 bar, because
the structure [Arg] has greater numbers of amines to react with CO2. By
comparing the data on the best TSILs, PILs and AAPILs synthesized, at
10 bar [C2CNDim][DOSS] gave the CO2 sorption up to 0.55 mol fraction.
For PILs, Poly[VBTMA][BF4] with 0.209 mol fraction and for AAPILs,
poly[VBTMA][Arg] gave the highest CO2 sorption at 0.742 mol fraction.
This is confirmed that by polymerized the ionic liquids and with
anions-amine functionalized would enhances the CO2 sorption.
[25] J.L. Anthony, J.L. Anderson, E.J. Maginn, J.F. Brennecke, Anion effects on gas solubility
in ionic liquids, J. Phys. Chem. B 109 (2005) 6366–6374.
[26] Y.S. Sistla, A. Khanna, Carbon dioxide absorption studies using amine-functionalized
ionic, J. Ind. Eng. Chem. 20 (2014) 2497.
[27] B.F. Goodrich, J.C. De la Fuente, B.E. Gurkan, D.J. Zadigian, E.A. Price, Y. Huang, et al.,
Experimental measurements of amine-functionalized anion-tethered ionic with
carbon dioxide, Ind. Eng. Chem. Res. 2011 (2011) 111.
[28] R.S. Bhavsar, S.C. Kumbharkar, U.K. Kharul, Polymeric ionic liquids (PILs): effect of
anion variation on their CO2 sorption, J. Membr. Sci. 389 (2012) 305–315.
[29] A. Blasig, J. Tang, X. Hu, Y. Shen, M. Radosz, Magnetic suspension balance study of
carbon dioxide solubility in ammonium-based polymerized ionic liquids:
poly(p-vinylbenzyltrimethyl ammonium tetrafluoroborate) and poly([2-
(methacryloyloxy)ethyl] trimethyl ammonium tetrafluoroborate), Fluid Phase
Equilib. 256 (2007) 75–80.
[30] O. Green, S. Grubjesic, S. Lee, M.A. Firestone, The design of polymeric ionic liquids for
the preparation of functional materials, Polym. Rev. 49 (2009) 339–360.
[31] Y.-B. Xiong, H. Wang, Y.-J. Wang, R.-M. Wang, Novel imidazolium-based poly(ionic
liquid)s: preparation, characterization, and absorption of CO2, Polym. Adv. Technol.
23 (2012) 835–840.
Acknowledgment
The authors would like to acknowledge the work of the late
Mohamed Osman Hussien Ahmed Ali on the polymerized ionic liquids
and the Center of Research in Ionic Liquids (CORIL), Universiti Teknologi
PETRONAS for their lab facilities.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.molliq.2016.02.046.
[32] J. Yuan, M. Antonietti, Poly(ionic liquid)s: polymers expanding classical property
profiles, Polymer 52 (2011) 1469–1482.
[33] G. Yu, Z. Man, Q. Li, N. Li, X. Wu, C. Asumana, et al., New crosslinked-porous poly-
ammonium microparticles as CO2 adsorbents, React. Funct. Polym. 73 (2013)
1058–1064.
[34] S.N.V.L. Aki, B.R. Mellein, E.M. Saurer, J.F. Brennecke, High pressure phase behaviour
of carbon dioxide with imidazolium-based ionic liquids, J. Phys. Chem. B 108 (2004)
20355–20365.
References
[1] F. Zhang, C.-G. Fang, Y.-T. Wu, Y.-T. Wang, A.-M. Li, Z.-B. Zhang, Absorption of CO2 in
the aqueous solutions of functionalized ionic liquids and MDEA, Chem. Eng. J. 160
(2010) 691–697.
[35] M. Muldoon, S. Aki, J. Anderson, J. Dixon, J. Brennecke, Improving carbon dioxide sol-
[2] G. Jing, L. Zhou, Z. Zhou, Characterization and kinetics of carbon dioxide absorption
into aqueous tetramethylammonium glycinate solution, Chem. Eng. J. 181-182
(2012) 85–92.
ubility in ionic liquids, J. Phys. Chem. B 111 (2007) 9001–9009.
[36] L.A. Blanchard, Z. Gu, J.F. Brennecke, High pressure phase behaviour of ionic liquids/
CO2 systems, J. Phys. Chem. B 105 (2001) 2437–2444.
[3] P. Sharma, S.D. Park, I.H. Baek, K.T. Park, Y.I. Yoon, S.K. Jeong, Effects of anions on ab-
sorption capacity of carbon dioxide in acid functionalized ionic liquids, Fuel Process.
Technol. 100 (2012) 55–62.
[37] J.M. Pringle, J. Golding, K. Baranyai, C.M. Forsyth, G.B. Deacon, J.L. Scott, et al., The ef-
fects of anion fluorination in ionic liquids—physical properties of a range of
bis(methanesulfonyl)amide salts, New J. Chem. 27 (2003) 1504–1510.
[38] W. Xu, E.I. Cooper, C.A. Angell, Ionic liquids: ion mobilities, glass temperatures and
frangilities, J. Phys. Chem. B 107 (2003) 6170–6178.
[39] H. Lee, M. Choo, B. Lee, J. Palgunadi, H. Kim, Alkyl-fluoroalkylimidazolium-based
ionic liquids as efficient CO2 absorbents, Energy Fuel (2010) 525–541.
[40] T. Sarbu, T.J. Styranec, E.J. Beckman, Design and synthesis of low cost sustainable CO2
philes, Ind. Eng. Chem. Res. 39 (2000) 4678–4683.
[4] C.-H. Yu, C.-H. Huang, C.-S. Tan, A review of CO2 capture by absorption and adsorp-
tion, Aerosol Air Qual. Res. 12 (2012) 745–769.
[5] F. Karadas, M. Atilhan, S. Aparicio, Review on the use of ionic liquids (ILs) as alterna-
tive fluids for CO2 capture and natural gas sweetening, Energy Fuel 24 (2010)
5817–5828.
[6] C. Wang, X. Luo, X. Zhu, G. Cui, D.-e. Jiang, D. Deng, et al., The strategies for improv-
ing carbon dioxide chemisorption by functionalized ionic liquids, RSC Adv. 3 (2013)
15518.
[41] J. Huang, T. Ruther, Why are ionic liquids attractive for CO2 absorption? Aust. J.
Chem. 62 (2009) 298.
[7] J. Huang, T. Ruther, Why are ionic liquids attractive for CO2 absorption? An over-
[42] W. Ren, B. Sensenich, A. Scurto, High pressure phase equilibria of carbon
dioxide + n-alkyl-imidazolium bis (trifluoromethylsulfonyl amide) ionic liquids, J.
Chem. Thermodyn. 42 (2010) 305–311.
[43] D. Zhao, Z. Fei, R. Scopelliti, P.J. Dyson, Synthesis and characterization of ionic liquids
incorporating the nitrile functionality, Inorg. Chem. 43 (2004) 2197–2205.
[44] E.I. Privalova, E. Karjalainen, M. Nurmi, P. Maki-Arvela, K. Eranen, H. Tenhu, et al.,
Imidazolium-based poly(ionic liquid)s as new alternatives for CO2 capture,
ChemSusChem 6 (Aug 2013) 1500–1509.
view, Aust. J. Chem. 62 (2009) 298–308.
[8] Y. Gao, F. Zhang, K. Huang, J.-W. Ma, Y.-T. Wu, Z.-B. Zhang, Absorption of CO2 in
amino acid ionic liquid (AAIL) activated MDEA solutions, Int. J. Greenh. Gas Control
19 (2013) 379–386.
[9] B. Jiang, X. Wang, M.L. Gray, Y. Duan, D. Luebke, B. Li, Development of amino acid
and amino acid-complex based solid sorbents for CO2 capture, Appl. Energy 109
(2013) 112–118.

312
M.S. Raja Shahrom et al. / Journal of Molecular Liquids 219 (2016) 306–312
[45] J. Tang, Y. Shen, M. Radosz, W. Sun, Isothermal carbon dioxide sorption in poly(ionic
liquid)s, Ind. Eng. Chem. Res. 48 (2009) 9113–9118.
[46] J. Tang, H. Tang, W. Sun, M. Radosz, Y. Shen, Low pressure CO2 sorption in
ammonium-based poly(ionic liquid)s, Polymer 46 (2005) 12460–12467.
[47] J. Tang, W. Sun, H. Tang, M. Radosz, Y. Shen, Enhanced CO2 absorption of poly(ionic
liquid)s, Macromolecules 38 (2005) 2037–2039.
[49] Z. Xue, Z. Zhang, J. Han, Y. Chen, T. Mu, Carbon dioxide capture by a dual amino ionic
liquid with amino-functionalized imidazolium cation and taurine anion, Int. J.
Greenh. Gas Control 5 (2011) 628.
[50] Y. Chen, X.-q. Zhou, Y. Cao, Z. Xue, T. Mu, Quantitative investigation on the physical
and chemical interactions between CO2 and amine-functionalized ionic liquid
[aEMMIM][BF4] by NMR, Chem. Phys. Lett. 574 (2013) 124–128.
[48] Y.S. Sistla, A. Khanna, CO2 absorption studies in amino acid-anion based ionic liq-
[51] E. Torralba-Calleja, J. Skinner, D. Gutierrez-Tauste, CO2 capture in ionic liquids: a re-
uids, Chem. Eng. J. (2014).
view of solubilities and experimental methods, J. Chem. 2013 (2013) 16.