Separation factors for [amim]Cl–CO2 biphasic systems from high pressure density and partition coefficient measurements

• Measurement of [amim]Cl densities and viscosities at atmospheric pressures.
• Measurement of [amim]Cl densities at pressures up to 200 MPa.
• Experimental partition coefficients (Kw) of benzene derivatives in [amim]Cl–CO2.
• Application of ePC-SAFT and LSER-δ models to predict and correlate Kw data.
• Nonpolar/polar solute separation factors for [amim]Cl–CO2 higher than [bmim]Cl–CO2.

In this work, densities and viscosities at atmospheric pressure and densities at high pressures of the ionic liquid, [amim]Cl (1-allyl-3-methylimidazolium chloride) were measured. The densities were evaluated by correlation with the Tait equation and the ePC-SAFT equation of state. Both relationships could describe the experimental density data over the full range of all temperatures (313–373 K) and pressures (0.1–200 MPa) within 0.007% and 0.053%, respectively. Infinite dilution partition coefficients, Kw3∞, of fundamental benzene derivatives (chlorobenzene, bromobenzene, benzaldehyde and benzyl alcohol) between [amim]Cl and supercritical carbon dioxide were measured at 313–353 K and 6–21 MPa. The ePC-SAFT applied as a predictive model for the experimental partition coefficient gave high deviations (>900%). However, when the ePC-SAFT was applied as a correlative model, average deviation in Kw3∞ were 20%. A previously proposed semi-empirical LSER-δ   model could correlate the Kw3∞ data to within 8.9%. Separation factors of solutes in [amim]Cl–CO2 system were calculated with ePC-SAFT model and compared with literature results for [bmim]Cl–CO2 since both of these ionic liquids have application to biomass processing. For each given ionic liquid, [amim]Cl and [bmim]Cl, the separation factors of non-polar or slightly polar compounds (chlorobenzene, bromobenzene and benzaldehyde) to the reference polar compound (benzyl alcohol) were always greater than 100, with [amim]Cl–CO2 always having a higher separation factor than [bmim]Cl–CO2. Thus, [amim]Cl–CO2 can probably provide better separation between non-polar and polar mixtures than [bmim]Cl–CO2.

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