Anion-Functionalized Task-Specific Ionic Liquids: Molecular Origin of Change in Viscosity upon CO2 Capture

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• 作者：Ailin Li ; Ziqi Tian ; Tianying Yan ; De-en Jiang ; Sheng Dai
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：December 26, 2014
• 年：2014
• 卷：118
• 期：51
• 页码：14880-14887
• 全文大小：370K
• ISSN：1520-5207

文摘

The structure and dynamics of a task-specific ionic liquid (TSIL), trihexyl(tetradecyl)phosphonium imidazolate, before and after absorbing CO₂ were studied with a molecular dynamics (MD) simulation. This particular ionic liquid is one of several newly discovered azole-based TSILs for equimolar CO₂ capture. Unlike other TSILs whose viscosity increases drastically upon reaction with CO₂, its viscosity decreases after CO₂ absorption. This unique behavior was confirmed in our MD simulation. We find that after CO₂ absorption the translational dynamics of the whole system is accelerated, accompanied by an accelerated rotational dynamics of the cations. Radial distribution function and spatial distribution function analyses show that the anions become asymmetric after reaction with CO₂, and this causes the imbalance of the interaction between the positive and negative regions of the ions. The interaction between the phosphorus atom of the cation and oxygen atoms of the carboxyl group on the anion is enhanced, while that between the phosphorus atom and the naked nitrogen atom of the anion is weakened. The ion-pair correlation functions further support that the weakened interaction leads to faster dissociation of cation鈥揳nion pairs, thereby causing an accelerated dynamics. Hence, the asymmetry of anions influences the dynamics of the system and affects the viscosity. This insight may help design better TSILs with decreased viscosity for CO₂ capture.