Cyano-Containing Protic Ionic Liquids for Highly Selective
Absorption of SO<sub>2</sub> from CO<sub>2</sub>: Experimental Study
and Theoretical Analysis
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Abstract
The
solubility of SO<sub>2</sub> and CO<sub>2</sub> in four cyano-containing
protic ionic liquids (PILs) was experimentally measured at temperatures
from 303.2 to 333.2 K and pressures up to 3.0 bar. Their physical
properties, such as density, viscosity, and decomposition temperature,
were also determined. It is found that [DMPANH][MOAc] and [DMAPNH][EOAc]
have the best selective absorption of SO<sub>2</sub> from CO<sub>2</sub> at 303.2 K and 1.0 bar among the investigated PILs, and the ideal
selectivities (119 and 107, respectively) of SO<sub>2</sub>/CO<sub>2</sub> are significantly higher than those reported in literature
for other ILs. The temperature-dependent Krichevsky–Kasarnovsky
(K–K equation) and PR-NRTL equations are used to calculate
the solubility data of SO<sub>2</sub> and CO<sub>2</sub>, and the
interactions between PILs and acid gases are analyzed thermodynamically.
Quantum chemical calculations are also done to obtain the interaction
configurations and energies. It is shown from the themodynamic analysis
and the quantum chemical calculations that the interaction between
SO<sub>2</sub> and PILs is more energy favorable than that between
CO<sub>2</sub> and PILs, primarily due to the existence of the cyano
group on the cation of PILs. The protic ionic liquids were reused
for five absorption–desorption cycles without obvious loss
in the absorption capacity, showing their potential as selective absorbents
of SO<sub>2</sub>