Pressure–volume–temperature–composition relations for carbon dioxide + pyrrolidinium-based ionic liquid binary systems

The pressure–volume–temperature–composition relations for CO2 + pyrrolidinium-based ionic liquid systems were measured over the pressure range up to 6 MPa at T = (298.15, 313.15, 333.15) K. Three ionic liquids were studied in the present work: N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([Pyr13][TFSA]), N-methoxymethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([Pyr1,1O1][TFSA]), and N-methoxymethyl-N-methylpyrrolidinium bis(fluorosulfonyl)amide ([Pyr1,1O1][FSA]). The pressure dependence of CO2 solubility indicates that CO2 molecules are dissolved physically in the three ionic liquids. The mole fraction scaled solubility of CO2 in [Pyr1,1O1][TFSA] is almost the same as that in [Pyr13][TFSA], and [Pyr1,1O1][FSA] showed the smallest solubility at certain pressures and temperatures. On the other hand, the molarity scaled solubility of CO2 in [Pyr1,1O1][TFSA] was nearly equal to that in [Pyr1,1O1][FSA]. The CO2 solubility of [Pyr13][TFSA] was smaller than the other two ionic liquids. The molar volume and density of ionic liquid phase decrease monotonically with an increase of mole fraction of CO2. The volume expansion of liquid phase was not almost dependent of temperature but composition of CO2 under the conditions investigated.