Effect of Water on the Carbon Dioxide Absorption by 1-Alkyl-3-methylimidazolium Acetate Ionic Liquids

Abstract

The absorption of carbon dioxide by the pure ionic liquids 1-ethyl-3-methylimidazolium acetate ([C(1)C(2)Im][OAc]) and 1-butyl-3-methylimidazolium acetate ([C(1)C(4)Im][OAc]) was studied experimentally from 303 to 343 K. As expected, the mole fraction of absorbed carbon dioxide is high (0.16 at 303 K and 5.5 kPa and 0.19 at 303 and 9.6 KPa for [C(1)C(2)Im][OAc] and [C(1)C(4)Im][OAc], respectively), does not obey Henry's law, and is compatible with the chemisorption of the gas by the liquid. Evidence of a chemical reaction between the gas and the liquid was found both by NMR and by molecular simulation. In the presence of water, the properties of the liquid absorber significantly change, especially the viscosity that decreases by as much as 25% (to 78 mPa s) and 30% (to 262 mPa s) in the presence of 0.2 mol fraction of water for [C(1)C(2)Im][OAc] and [C(1)C(2)Im][OAc] at 303 K, respectively. The absorption of carbon dioxide decreases when the water concentration increases: a decrease of 83% in CO(2) absorption is found for [C(1)C(4)Im][OAc] with 0.6 mol fraction of water at 303 K. It is proved in this work, by combining experimental data with molecular simulation, that the presence of water not only renders the chemical reaction between the gas and the ionic liquid less favorable but also lowers the (physical) solubility of the gas as it competes by the same solvation sites of the ionic liquid. The lowering of the viscosity of the liquid absorbent largely compensates these apparent drawbacks and the mixtures of [C(1)C(2)Im][OAc] and [C(1)C(2)Im][OAc] with water seem promising to be used for carbon dioxide capture.

Carbon dioxide uptake from natural gas by binary ionic liquid–water mixtures

“…43 The authors concluded that "the overall tendency is that adding a certain amount of water into the pure ionic liquids will slightly decrease the absorption capacity of CO 2 , but the lower viscosity of the mixture is favourable as it can promote gas diffusion in the solvent and reduce operational constrains on the use of ionic liquids fluids". 62,64 Of the multitude of papers on carbon dioxide solubility in ionic liquids, those that mention water content, with very few exceptions, state that the ionic liquids must be as dry as possible. 62,64 Of the multitude of papers on carbon dioxide solubility in ionic liquids, those that mention water content, with very few exceptions, state that the ionic liquids must be as dry as possible.…”

CO2 Capture Efficiency, Corrosion Properties, and Ecotoxicity Evaluation of Amine Solutions Involving Newly Synthesized Ionic Liquids

“…Indeed, a recent study that combined experimental data with a molecular simulation for the system [EMIM][OAc]/H 2 O indicated that the presence of water not only reduced the (physical) solubility of the gas as it competed for the same solvation sites of the IL but also rendered the chemical reaction between the gas and the IL less favorable. 34 Investigations with Raman analysis at several water contents, CO 2 pressures, and temperatures are currently underway to [TCM] ILs, the almost 4-fold increase of the CO 2 absorption capacity along with the 10-fold increase of the CO 2 absorption rate when mixed with water makes them very promising materials for CO 2 capture. For that reason they were thoroughly investigated as potential solvents in the laboratory-scale device involving a mass transfer column.…”

Densities at Pressures up to 200 MPa and Atmospheric Pressure Viscosities of Ionic Liquids 1-Ethyl-3-methylimidazolium Methylphosphate, 1-Ethyl-3-methylimidazolium Diethylphosphate, 1-Butyl-3-methylimidazolium Acetate, and 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide

“…High pressure densities have been reported for [bmim][Ac] by Stevanovic et al 48 and Safarov et al 49 Supporting Information, Figure S12 shows the relative deviations of those data. From the figure, both deviations were larger than the uncertainties of this work.…”