Propylene and Propane Solubility in Imidazolium, Pyridinium, and Tetralkylammonium Based Ionic Liquids Containing a Silver Salt

The gas solubility of propane and propylene in seven ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4 ), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMImBF 4 ), 1-octyl-3-methylimidazolium tetrafluoroborate (OMImBF 4 ), 3-methylimidazolium nitrate (BMImNO 3 ), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) (BMImTf 2 N), methyltrioctylammonium bis(trifluoromethylsulfonylimide) (MOOONTf 2 N), and butyltrimethylammonium bis(trifluoromethylsulfonylimide) (BMMMN Tf 2 N), is reported. The equilibrium isotherms of both pure gases were measured in the pure ionic liquids and in presence of a silver salt containing the same anion of the ionic liquid in a range of concentration of (0 to 0.77) mol·kg IL –1 at temperatures between (288 and 308) K and pressures ranging from (0 to 700) kPa. Henry’s law constant values for physical solubility as well as the characteristic parameters for chemical solubility such as chemical equilibrium constants and enthalpies of the chemical reactions between silver cations and propylene are reported. Based upon the experimental results, ionic liquids based on imidazolium cations with less and shorter alkyl substituents improve the selective separation of propylene from these mixtures. Regarding to the structure of the anion it was gathered that ionic liquids with the BF 4 – anion, combined with the AgBF 4 silver salt, provided the best results in terms of olefin capacity and selectivity. In this article we provide valuable data that evidence that the separation of propane/propylene gas mixtures by reactive absorption could represent an efficient alternative to the traditional separation process based on cryogenic distillation and serve for the new process design.