SO2-Induced Variations in the Viscosity of Ionic Liquids Investigated by in Situ Fourier Transform Infrared Spectroscopy and Simulation Calculations

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• 作者：Shaojuan Zeng ; Xiaochun Zhang ; Hongshuai Gao ; Hongyan He ; Xiangping Zhang ; Suojiang Zhang
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2015
• 出版时间：November 4, 2015
• 年：2015
• 卷：54
• 期：43
• 页码：10854-10862
• 全文大小：484K
• ISSN：1520-5045

文摘

In this work, the effect of SO₂ on the densities and viscosities during absorption processes of pyridinium-based ionic liquids (ILs), such as the conventional ILs [C₄Py][BF₄] and [C₄Py][SCN] and the tertiary amino-functionalized IL [NEt₂C₂Py][SCN], was investigated. The mechanism of the variations in these two physical properties was also explained in detail through a combination of experimental methods and simulation calculations. The results indicated that the densities of the conventional and functionalized ILs increased gradually with increasing amounts of SO₂. However, the viscosities of two kinds of ILs during SO₂ absorption showed different variation trends according to different mechanisms of SO₂ absorption, i.e., physical absorption and chemical absorption, which was proven by the in situ Fourier transform infrared results. The viscosity changes of the functionalized IL [NEt₂C₂Py][SCN] during SO₂ absorption experienced two stages. First, the viscosity increased sharply because of chemical interaction, forming a charge-transfer complex, and then decreased drastically because of the physical interaction between the anion and SO₂. However, there was a monotonous and sharp decline in the viscosity of the conventional ILs with an increase of the SO₂ capacity, which showed the same trend as that of [NEt₂C₂Py][SCN] in the SO₂ physical absorption stage. Furthermore, the ionic interaction and microstructures of the conventional ILs before and after SO₂ absorption were further studied by molecular dynamics simulation and quantum-chemical calculation. It was demonstrated that viscosity reduction may mainly originate from a decrease of the electrostatic interaction between the cation and anion of the ILs because of the presence of SO₂.