656
regeneration for blended solution requires 37.2% lower energy than aqueous amine
solution [92]. Haider et  al. measured CO 2 uptake in various IL-amine blends as
shown in Fig. 5. The highest CO 2 solubility and the reaction rate were observed by
the [bmim][BF 4 ]-MEA-piperazine blend [93]. The amine addition in ionic liquid
significantly increases the CO 2 uptake.
The CO 2 solubility was further enhanced using piperazine owing to its chemisorption behavior. Addition of piperazine results into the solid phase separation as
shown in Fig.  6. In general, IL-amine blends have shown significantly high CO 2
loadings, and in some cases, CO 2 loadings are more than the aqueous alkanolamine
solution [87, 94].
A comparison of CO 2 uptake in ionic liquids and aqueous amine solution has been
given in Table 3. It was found that most of the ionic liquids have lower CO 2 solubility
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
4
6
8
1 0
1 2
1 4
Pressure(bar)
bmim[BF4]
bmim[BF4]+MEA
bmim[BF4]+MDEA
bmim[BF4]+MEA+PZ
bmim[BF4]+MDEA+PZ
mole of CO
2 /mole of ILs
Fig. 5 Effect of amine and piperazine on CO 2 solubility in [bmim][BF 4 ]
Fig. 6 (a) 70%
[Bmim]
+ [BF 4 ]
−
—10%
PZ–20% MDEA before
CO 2 absorption; (b) and (c)
70% [Bmim]
+
[BF 4 ]
−
—10%
PZ–20% MDEA after CO 2
absorption
M. B. Haider et al.