Effect of Fluorination and Size of the Alkyl Side-Chain on the Solubility of Carbon Dioxide in 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide Ionic Liquids

Abstract

It is proven in this work that it is possible to significantly increase the carbon dioxide uptake by an ionic liquid relying on physical interactions only. The solubility and thermodynamics of solvation of carbon dioxide in the ionic liquids 1-octyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide [C(8)mim][Ntf(2)], 1-decyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide [C(10)mim][Ntf(2)], and 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-3-methylimidazolium bis[trifluoromethylsulfonyl]amide [C(8)H(4)F(13)mim][Ntf(2)] were determined experimentally between 298 and 343 K at pressures close to atmospheric. The solubility of carbon dioxide is significantly higher in the fluorine-substituted ionic liquid with Henry's law constants at 303 K of 33.3 and 30.7 bar for [C(8)mim][Ntf(2)] and [C(10)mim][Ntf(2)], respectively, and of 28.0 bar for [C(8)H(4)F(13)mim][Ntf(2)]. Molecular simulation was used for interpreting the molecular mechanisms of solvation of carbon dioxide in the studied ionic liquids and coherent molecular mechanisms of solvation are proposed in light of the solute-solvent radial distribution functions. It is shown that the increase of the size of the hydrogenated or fluorinated alkyl chain in the imidazolium cation does not lead to a steady augmentation of the gaseous uptake by the liquid probably due to an increase of the nonpolar domains of the ionic liquid, carbon dioxide being solvated preferentially in the charged regions of the solvent.

Ionic Liquid Co-catalyzed Artificial Photosynthesis of CO

“…The high structural symmetry of Tf 2 N 2 anion is known to endow the system with a low viscosity that is favorable for reaction kinetics 35 . Both www.nature.com/scientificreports fluoroalkyl group and Tf 2 N 2 with a large ionic size are known to increase the interaction of the ILs and CO 2 36 . When the substituted alkyl chain on 1-position of the imidazolium ring was extended from ethyl to octyl, the activities for the production of CO decreased sequentially.…”

“…Obviously, the decreased yields were due to the increased length of the carbon chain, associating with the increase in van der Waals interactions and molecular weight. These cause an increased viscosity of the solvent, which together with the increased steric hindrance limits catalytic kinetics, leading to low reactivities 36 . These observations underline the fact that the promotional effect of ILs in the photochemical reduction of CO 2 are closely related to both the counterions and the organic functional groups on ILs, which determine the properties of ILs such as viscosity, conductivity, polarity, dielectric constant and acid-base chemistry.…”

The Presence of Functional Groups Key for Biodegradation in Ionic Liquids: Effect on Gas Solubility

“…As for other ionic liquids based on the 1-alkyl-3-methylimidazolium cation, hydrogen is the least soluble gas. [24][25][26][27][36][37][38] Thus, the chemical modification of the alkyl chain does not seem to cause major modification of the solvation properties of ionic liquids. For all the tested systems, the mole fraction solubility decreased with temperature.…”

CO₂ Absorption Property of Ionic Liquid and CO₂ Permselectivity for Ionic Liquid Membrane

“…It is also pointed out that this enhancement is mainly due to the Lewis acid-base interaction between the acidic carbon atom of CO2 and the basic fluorine atom. However, the fluorination sometimes increases the viscosity of ILs dramatically 8) . The worse transport property causes the depression of CO2 absorption and desorption kinetics as mentioned in introduction.…”