Molecular Simulation and SAFT Modeling of Solvation in Ionic Liquids

The solubility and other thermodynamic properties of ethanol, propanol, dimethyl formamide, and dimethyl sulfide in the ionic liquid trimethylbutylammonium bis(trifluoromethylsulfonyl)imide has been computed via Monte Carlo simulations. A united atom model (UAM) force field has been developed for both the organic solutes and the ionic liquid. The force field gives accurate vapor liquid coexistence curves and vapor pressures for the solutes and accurate liquid density and surface tension for the ionic liquid. Computed mixture properties including isotherms, activity coefficients, excess entropy, excess enthalpy, and mixing volume are all modeled accurately and agree with the experimental data of Massel et al. The experimental data are also modeled accurately using the Perturbed-Chain Induced-Polar Statistical Associating Fluid Theory (PCIP-SAFT) equation of state. Experimental results show a negative excess entropy trend for mixing of dimethyl formamide and dimethyl sulfoxide in the ionic liquid, whereas ethanol and propanol exhibit a positive enthalpy of mixing. The simulations and PCIP-SAFT capture this trend and analyses of the simulation trajectories show that this is driven by differences in hydrogen bonding tendencies of the solutes and that the entropy of solvation dominates for all four systems.