655
3.3.1 IL-Water
The water addition into ionic liquids greatly decreases the ionic liquid viscosity;
however, it also affects the CO 2 solubility. The presence of 1% water in the aminofunctionalized ionic liquid could absorb equimolar amount of CO 2 , and the obtained
product so formed is different from the products obtained by pure ionic liquids [73].
Experiments conducted by Ventura et al. suggest that though the viscosity of ionic
liquid decreases with the addition of water, at the same time, CO 2 absorption capacity also decreases [84]. The CO 2 absorption capacity of ILs-water blends largely
vary with the choice of ionic liquid and the amount of water present. Additionally,
the energy required for regeneration of these blends is lesser than that required for
the aqueous amine (30%) solution. The enthalpy of CO 2 absorption was measured
for the ILs-water (60 wt% IL) system which was found to be significantly lower
(41.1 ± 3.2 kJ/mol IL) as compared to the aqueous MEA-based solvent (82 kJ/mol
MEA) [85]. This suggests that addition of water reduces the regeneration energy of
the ionic liquids.
3.3.2 IL-Amine
Further improvement for the CO 2 solubility can be achieved by addition of alkanolamine to ionic liquid. Partly replacing the water from the aqueous alkanolamine
solution by ionic liquid can diminish the solvent regeneration energy and also limits
the loss of alkanolamine. Industrial CO 2 capture process uses solvents with 60 wt%
water; therefore, a large volume of water is also lost during solvent regeneration.
Ionic liquid [C 6 mim][Tf 2 N] with MEA blend showed significant increase in CO 2
absorption [86]. Four ionic liquids with tetramethylammonium and tetraethylammonium as cations and glycinate and lysinate as anions, e.g., ([N1111][Gly]),
([N2222][Gly]), ([N1111][Lys]), and ([N2222][Lys]), were blended with the
MDEA aqueous solution to study the CO 2 absorption capacity. All these blends
were found to have high CO 2 solubility capacities than the conventional ILs [87].
The experimental results of amines-IL-H 2 O, amines-H 2 O, and IL-H 2 O blends in the
temperature range of 30–70 °C suggest that amines-IL-H 2 O blends are better for
CO 2 absorption as compared to IL-H 2 O and amines-H 2 O [88]. Baj et al. reported
that CO 2 absorption follows physisorption process in [EMIM][OcSO 4 ]-MEA-water
system [89], whereas pure ionic liquid like [bmim][OAc] absorbs the CO 2 by chemical absorption process. The experiments conducted by Murugesan et al. showed
that the CO 2 uptake is more in [bmim][BF 4 ] as compared to bis(2-hydroxyethyl)
ammonium acetate (bheaa), whereas aqueous blend of bheaa-MEA showed higher
CO 2 solubility than the aqueous mixture of MEA-[bmim][BF 4 ] [90].
The MEA-based blend with three ILs [bmim][DCA], ([Bpy][BF 4 ]), and ([bmim]
[BF 4 ]) was explored for CO 2 absorption process. It was found that [Bpy][BF 4 ]-MEA
blends can reduce energy consumption by 15% as compared to conventional amine
process [91]. The techno-economical aspect for the CO 2 capture was also investigated for water-MEA-[bmim][BF 4 ] blends. The results show that solvent
Potential Application of Ionic Liquids and Deep Eutectic Solvents in Reduction…
3.3.1 IL-Water
The water addition into ionic liquids greatly decreases the ionic liquid viscosity;
however, it also affects the CO 2 solubility. The presence of 1% water in the aminofunctionalized ionic liquid could absorb equimolar amount of CO 2 , and the obtained
product so formed is different from the products obtained by pure ionic liquids [73].
Experiments conducted by Ventura et al. suggest that though the viscosity of ionic
liquid decreases with the addition of water, at the same time, CO 2 absorption capacity also decreases [84]. The CO 2 absorption capacity of ILs-water blends largely
vary with the choice of ionic liquid and the amount of water present. Additionally,
the energy required for regeneration of these blends is lesser than that required for
the aqueous amine (30%) solution. The enthalpy of CO 2 absorption was measured
for the ILs-water (60 wt% IL) system which was found to be significantly lower
(41.1 ± 3.2 kJ/mol IL) as compared to the aqueous MEA-based solvent (82 kJ/mol
MEA) [85]. This suggests that addition of water reduces the regeneration energy of
the ionic liquids.
3.3.2 IL-Amine
Further improvement for the CO 2 solubility can be achieved by addition of alkanolamine to ionic liquid. Partly replacing the water from the aqueous alkanolamine
solution by ionic liquid can diminish the solvent regeneration energy and also limits
the loss of alkanolamine. Industrial CO 2 capture process uses solvents with 60 wt%
water; therefore, a large volume of water is also lost during solvent regeneration.
Ionic liquid [C 6 mim][Tf 2 N] with MEA blend showed significant increase in CO 2
absorption [86]. Four ionic liquids with tetramethylammonium and tetraethylammonium as cations and glycinate and lysinate as anions, e.g., ([N1111][Gly]),
([N2222][Gly]), ([N1111][Lys]), and ([N2222][Lys]), were blended with the
MDEA aqueous solution to study the CO 2 absorption capacity. All these blends
were found to have high CO 2 solubility capacities than the conventional ILs [87].
The experimental results of amines-IL-H 2 O, amines-H 2 O, and IL-H 2 O blends in the
temperature range of 30–70 °C suggest that amines-IL-H 2 O blends are better for
CO 2 absorption as compared to IL-H 2 O and amines-H 2 O [88]. Baj et al. reported
that CO 2 absorption follows physisorption process in [EMIM][OcSO 4 ]-MEA-water
system [89], whereas pure ionic liquid like [bmim][OAc] absorbs the CO 2 by chemical absorption process. The experiments conducted by Murugesan et al. showed
that the CO 2 uptake is more in [bmim][BF 4 ] as compared to bis(2-hydroxyethyl)
ammonium acetate (bheaa), whereas aqueous blend of bheaa-MEA showed higher
CO 2 solubility than the aqueous mixture of MEA-[bmim][BF 4 ] [90].
The MEA-based blend with three ILs [bmim][DCA], ([Bpy][BF 4 ]), and ([bmim]
[BF 4 ]) was explored for CO 2 absorption process. It was found that [Bpy][BF 4 ]-MEA
blends can reduce energy consumption by 15% as compared to conventional amine
process [91]. The techno-economical aspect for the CO 2 capture was also investigated for water-MEA-[bmim][BF 4 ] blends. The results show that solvent
Potential Application of Ionic Liquids and Deep Eutectic Solvents in Reduction…