CO2 Absorption Properties and Mechanisms for 1-Ethyl-3-methylimidazolium Ether-Functionalized Carboxylates

We measured the atmospheric and high-pressure CO2 solubilities in 1-ethyl-3-methylimidatolium ([emimr) ionic liquids (ILs) with acetate ([Ac0]-), 2-methoxyethoxyacetate ([C1OC2-OC1CO2]), and 3-(2-methoxyethoxy)propionate ([C-1(OC2)(2)CO2](-)) to investigate the effect of ether modification on the CO2 physical and chemical absorptions. The NMR spectra of the CO2 saturated ILs indicated that each IL absorbed CO2 chemically, resulting in the formation of 1-ethyl-3-methylimidazolium-2-carboxylate, and desorbed CO2 reversibly by heating.,The CO2 solubilities per mole of ionic liquid in [emim][C1OC2OC1CO2], [emim][C-1(OC2)(2)CO2], and [emim] [AcO] increased in this".order, and the effect of the ether modification was discussed on the bais of the results of NMR and calorimetry. Further, we successfully deconvoluted the high-pressure CO2 solubility into the contributions of physical and chemical absorptions, taking into consideration the following two equilibria: (I) the purely physical dissolution and (2) the formation of 1-ethyl-3-i-nethylimidazolium-2-carboxylate and the dimer species between the IL anion and the corresponding carboxylic acid. The validity of this numerical analysis was quantitatively confirmed by the NMR spectra for the [emim] [AcO] + CO2 mixtures at high pressures, which can separately identify the chemical and physical species. According to the deconvolution results, the 2-methoxyethoxy group on acetate ([C1OC2OC1CO2](-)) improved the physisorption (in thole fraction based solubility) and worsened the chemisorption compared to the unmodified acetate ([AcO](-)), whereas the negative effects on both the absorptions (in liable fraction based solubility)" were observed by the 2-methoxyethoxymethyl modification ([C-1(OC2)(2)CO2](-)). The thermodynamic parameters of solution were calculated to discuss, the influences of functionalitation on the CO, physisorption.