(43c) Novel Pyridinium-Based Ionic Liquids for Efficient and Reversible Capture of SO2

Novel
Pyridinium-based Ionic Liquids for Efficient
and Reversible Capture of SO₂

Shaojuan
Zeng ^{a, b}, Hongshuai Gao ^a,Xiangping
Zhang ^a,*,
Suojiang Zhang ^a,*

^aBeijing
Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of
Multiphase Complex System, Institute
of Process Engineering, Chinese Academy of Sciences, 100190, Beijing, China

^bCollege
of Chemical and Engineering, University of Chinese Academy of Sciences,
100049,  Beijing, China

*Corresponding author: sjzhang@ipe.ac.cn; xpzhang@ipe.ac.cn

 The reduction of SO₂ emission from flue gases has become one of the
most urgent environmental issues for a sustainable society. Although some
traditional methods for flue gas desulfurization (FGD) have been commercialized, there are still some inherent drawbacks. For example, limestone
scrubbing produces
a large amount of solid wastes and waste water, which may result in secondary
pollution to the environment¹. Therefore, the development of a proper absorbent
for efficient and reversible capture of SO₂ is of critical
importance.

 Recently,
ionic liquids (ILs) have drawn much attention as potential absorbents for SO₂ capture due to their unique
properties². To our knowledge, very few studies on pyridinium-based ILs
for SO₂ removal
were reported, although they
have higher thermal stability, lower cost and higher biodegradability than imidazolium-based ILs³. In this work, the
interaction between various cations, e.g. different alkyl chain length and functionalized substituent
groups on the pyridinium ring, and anions of ILs and SO₂
was firstly studied by Quantum
Chemical calculation and Molecular Dynamic simulation. Based on the calculation results,
a series of pyridinium-based
ILs were
designed and synthesized for
SO₂ capture. The results indicated that the gravimetric capacity of SO₂
decreases with increase of the length of alkyl chain. Comparing with cation of
IL, anion plays a dominant role in SO₂ absorption, which is consistent with the calculation resluts.
Among the investigted anions, the conventional IL with [SCN] shows the highest SO₂ capacity, and good selectivity for SO₂
to other gases and excellent reversibility⁴. Meanwhile, the incorporation of functionalized substituent
groups on the
cation, such as tertiary amino group, ether group and
nitrile group plays
a key role in improving SO₂
capture, which exhibited much
better absorption performances of SO₂ than the conventional IL with [SCN]. This work will provide some useful information to design more competitive absorbents for SO₂
capture.

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