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Abstract: We have focused on a protic ionic liquid, ethylimidazolium bis(trifluoromethanesulfonyl)amide ([eimH][Tf2N]), and the analogous aprotic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([emim][Tf2N]). Densities, viscosities, and electrical conductivities of the two ionic liquids have been measured over the temperature range T =(273.15–363.15)K at atmospheric pressure. The densities of [eimH][Tf2N] and [emim][Tf2N] decrease with increasing temperature. The protic ionic liquid has the higher density (the smaller molar volume) than the aprotic one. The transport properties of the two ionic liquids show ordinary temperature dependencies. [eimH][Tf2N] has the higher viscosities (smaller electrical conductivities) than [emim][Tf2N]. Empirical Walden products indicate that [eimH][Tf2N] shows smaller conductivities than [emim][Tf2N] at certain viscosities. To investigate CO2 absorption properties of the ionic liquids, binary phase equilibria in CO2 +ionic liquid systems have been investigated under high pressures up to 6MPa at T =(298.15, 313.15, 333.15)K. The solubilities of CO2 in [eimH][Tf2N] and [emim][Tf2N] show typical pressure dependencies in both mole fraction and molarity scales as physical absorbents. The mole fraction of CO2 in [eimH][Tf2N] is slightly smaller than that in [emim][Tf2N] under the conditions investigated, while the molarity of CO2 in [eimH][Tf2N] is comparable to that in [emim][Tf2N]. The molar volumes in ionic liquid phase almost linearly decrease with the mole fraction of CO2 in the present systems. The partial molar volume of CO2 in [eimH][Tf2N] at infinite dilution is almost same as that in [emim][Tf2N]. [Copyright &y& Elsevier]

Abstract: We have determined the electrical conductivity in CO2-saturated 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) at 298.1, 313.1 and 333.1K as a function of CO2 pressure. Moreover, self-diffusion coefficients of cation and anion in CO2-saturated [C4mim][PF6] have been measured at high pressures up to ∼15MPa and at a fixed temperature of 333.2K by 1H and 19F NMR using the pulsed field gradient spin-echo method. As CO2 dissolves in [C4mim][PF6], marked increases in all the three transport quantities were observed at lower pressure, and then they showed very slight changes at higher pressure. The correlation between the conductivity and the ionic diffusion coefficients has been discussed. [Copyright &y& Elsevier]