On the Nonideality of CO2 Solutions in Ionic Liquids and Other Low Volatile Solvents

The nonideality of CO2 solutions in ionic liquids and other low volatile solvents, with which CO2 is known to form electron donor-acceptor (EDA) complexes, is here investigated. It is shown that the deviations from the ideality observed are not related with the stability of the EDA complex formed, and in most cases these deviations are small and dominated by entropic effects For this reason, when the CO2 concentration is expressed in molality, the pressure versus concentration phase diagrams of CO2 in nonvolatile solvents are within the uncertainty of the experimental data, solvent independent. Following this approach, a correlation for the solubility of CO2 in nonvolatile solvents, valid for pressures up to 5 MPa and temperatures ranging from room temperature up to 363 K, is here proposed. These results are tested with success by measuring the solubility of CO2 in [THTDP][Cl] to show that, in such heavy ionic liquid the solubility, although identical in molality units, if expressed in mol fractions, it is larger than that in [BMIM][NTf2].