Solubility of carbon dioxide, nitrous oxide, ethane, and nitrogen in 1-butyl-1-methylpyrrolidinium and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate (eFAP) ionic liquids

Abstract

The density and viscosity of the ionic liquids 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate [C1C4Pyrro][eFAP] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P66614][eFAP] were measured as a function of temperature and pressure and as a function of temperature, respectively. These two ionic liquids are more viscous than those based in the same anion associated to imidazolium cations. The effect of the addition of water on the density and viscosity of [P66614][eFAP] was studied at pressures close to atmospheric and as a function of the temperature. This ionic liquid is only partially miscible with water, its solubility being of around XH2O=0.2 in the range of (303 to 315)K. Experimental values of the solubility of carbon dioxide, nitrous oxide, ethane, and nitrogen were obtained as a function of temperature and at pressures close to atmospheric. Carbon dioxide and nitrous oxide are the more soluble gases with mole fraction solubilities up to 7·10−2. Ethane is four times and 1.3 times less soluble than carbon dioxide in [C1C4Pyrro][eFAP] and [P66614][eFAP], respectively. Nitrogen is one order of magnitude less soluble than the others gases in the two ionic liquids studied. In order to understand behavior of the different gases with these ionic liquids, the thermodynamic functions of solvation such as enthalpy and entropy were calculated from the variation of the Henry’s law constant with temperature. It is shown that the more favorable interactions of the gases with the ionic liquid explain the larger solubility of carbon dioxide and nitrous oxide in [C1C4Pyrro][eFAP]. In the case of [P66614][eFAP], it is the less favorable entropic contribution that explains the lower solubility of ethane in this ionic liquid.