Modelling mixtures of ammonium and pyridinium-based ionic liquids and carbon dioxide with the Cubic Plus Association Equation of state

In the absence of a specific thermodynamic model to describe the behavior of ionic liquids (ILs) and their mixtures with CO2, the Cubic Plus Association Equation of state (CPA EoS) can be a viable engineering option in separation applications. The findings demonstrate that the 1A association scheme outperformed the 2B association scheme for the majority of ammonium and pyridinium-based ILs. The van der Waals volumes (& psi;) and the Kier mass connectivity index (& lambda;) can allow the prediction of CPA pure parameters for ILs in cases of lack of experimental data. For binary mixtures, the CPA EoS coupled to Lorentz-Berthelot (LB) and Huron-Vidal (HV) mixing rules were used to correlate the solubility of CO2 in ammonium and pyridinium-based ILs. For comparison, the Soave-Redlich-Kwong (SRK) EoS with HV mixture rule was also used. The results showed that the performance of CPA-HV(1A) (deviations lower than 5.46%) was slightly better than CPA-HV(2B), CPA-LB (1A and 2B) and SRK-HV for ammonium-based ILs. In the case of pyridinium-based LIs, the performance of CPA-LB (1A) (deviations lower than 4.27%) was slightly better than CPA-LB (2B), CPA-HV (1A and 2B) and better than SRK-HV. These results suggest that the CPA-LB model (with 1A scheme) can be used for both ammonium and pyridinium-based ILs with few adjustable parameters. The inclusion of speed of sound in the objective function for obtaining new CPA parameters does not improve the representation of liquid density and speed of sound data of pure ammonium and pyridinium-based ILs. The vapor pressure and enthalpy of vaporization related with volatility were predicted and compared with empirical correlations, with deviations ranging from 11 to 47%.