Investigation of the enhanced solubility of fluorinated methanes in CO2 by Monte Carlo simulation: Absolute free energy of solvation and structural properties of solution

The absolute free energy of solvation of methane (CH4) and its fluorinated forms (CH3F, CH2F2, CHF3 and CF4) have been computed via statistical perturbation theory (SPT) in the NPT ensemble at four thermodynamical states (whitin liquid and supercritical regions), in the context of Monte Carlo Simulations. Thermodynamical interpretation of the observed trend in the absolute free energy of solvation in different states reveals an exothermic solvation with ΔSslv < 0 (entropically unfavorable solvation) that the intermolecular interactions play an important role in the solvation process. The fluorinated methanes are confirmed to control the mutual arrangement of neighboring CO2 molecules and the axis of CO2 molecules near F atom of fluorinated solutes make a right angle with F(solute)–C(CO2) axis. Moreover, the energetic distribution along with structural and orientational distributions confirm the existence of a direct interaction between CO2 and F atom, although the extent of this interaction is not very large.