High solubilities of small hydrocarbons in trihexyl tetradecylphosphonium bis (2, 4, 4-trimethylpentyl) phosphinate

Experimental solubilities are reported for methane, ethane,
ethylene, propane, and propylene in trihexyl tetradecylphosphonium bis(2,4,4-
trimethylpentyl) phosphinate [P(14)666][TMPP] from 313 to 353 K up to 6.7
MPa. A literature review on solubilities of small hydrocarbons in ionic liquids
shows that solubilities in [P(14)666][TMPP] are appreciably larger than those in
other ionic liquids. Contrary to solubilities in ionic liquids studied earlier,
solubilities of paraffins (ethane and propane) in [P(14)666][TMPP] are larger
than those of the corresponding olefins (ethylene and propylene). Because, at fixed
temperature, the vapor pressure of an olefin is larger than that of the
corresponding paraffin, the relative volatility of the olefin exceeds that of the
corresponding paraffin, contrary to the relative volatility observed in conventional
extractive distillation with polar solvents where the volatility of the paraffin exceeds
that of the corresponding olefin.