An insight into the analogy between solute-solvent binding energy and solubility of acid gases in ionic liquids: Thermodynamic modeling versus molecular dynamic simulation

Ionic Liquids (ILs) have emerged as a promising generation of solvents for the absorption of acid gases (e.g., CO2 and H2S) due to their unparalleled physiochemical properties. This study focuses on thermodynamic modeling and molecular dynamic simulation approaches to estimate the solubility and interaction energies of CO2 and H2S gases in/with different frequently-used ILs. For thermodynamic modeling, the GE/EOS method was employed. This method allows for combining activity-coefficient models in the structure of the cubic equation of states. In the GE/EOS method, the modified Peng-Robinson equation of state (MPR2) together with the LCVM mixing rules was used. Excess Gibbs free energy models of Wilson, NRTL, and UNIQUAC were also applied for combination with the GE/EOS models. The prediction results of the combined models were compared with the experimental solubility data. The results demonstrated the capability of these models to predict the thermodynamic behavior of the acid gas-ILs systems. The results uncovered that the MPR2-LCVM-Wilson model can tabulate the highest correlation with the experimental data compared to the other model combinations. Results of the sensitivity analysis on the principal operational variables (temperature and pressure), showed superior effect of pressure on the gas solubility. In addition, the results of the molecular dynamic (MD) simulation disclosed an agreement between the trends of the solubility of acid gases in ILs with those of the released interaction energies of acid gases absorbed by the ILs. MD results also confirmed that the solubility of acid gases in ILs increases with an increase in the binding energy of the molecules with the ILs.