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
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.