Absorption and separation of CO₂/C₃H₈ and C₃H₆/C₃H₈ by ionic liquid: Effect of molar volume

Ionic liquid is promising solvent for capturing carbon dioxide (CO₂) from natural gas and separation of olefin/paraffin. In this work, the solubilities of propane (C₃H₈) and propylene (C₃H₆) in two ionic liquids 1-hexyl-3-methylimidazolium trifluoromethanesulfonate and 1-hexyl-3-methylimidazolium hexafluorophosphate from 293 K to 343 K at pressures up to 990 kPa were determined using the isochoric saturation method with relative expanded uncertainty of 4%. The experimental results were correlated successfully by the NRTL equation with AAD less than 1.35%. Based on the solubility data in this work and from literature, the Henry's constants and the ideal selectivities of CO₂/C₃H₈ and C₃H₆/C₃H₈ in ionic liquids with different molar volumes were compared so as to investigate the effect of the free volume in ionic liquid. The results show that ionic liquid with very large molar volume (large free volume) has good separation performance for CO₂/C₃H₈ and C₃H₆/C₃H₈.