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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