Monte Carlo simulation and SAFT modeling study of the solvation thermodynamics of dimethylformamide, dimethylsulfoxide, ethanol and 1-propanol in the ionic liquid trimethylbutylammonium bis(trifluoromethylsulfonyl)imide

Abstract

Understanding fundamental solvation phenomena and mixture thermodynamic properties for organic molecules in ionic liquids is essential to the development of ionic liquids in many application areas. In the present work, molecular simulations were used to compute a wide range of properties for the pure ionic liquid trimethylbutylammonium bis(trifluoromethylsulfonyl)imide as well as mixtures of this ionic liquid with ethanol, 1-propanol, dimethylformamide, and dimethylsulfoxide. A new force field for the ionic liquid was developed and validated by computing ionic liquid surface tension and density as a function of temperature. Force fields for ethanol and propanol were taken from the literature, while new force fields were developed for dimethylformamide and dimethylsulfoxide. These force fields were shown to yield vapor–liquid coexistence curves, vapor pressure curves and critical points in excellent agreement with experimental data. Absorption isotherms, enthalpies of mixing and mixture volumes were then computed and shown to agree well with available literature. The simulations help rationalize the observed trends in solubility and enthalpy of mixing in terms of the relative strength of hydrogen bonding between the solutes and the ionic liquid. It was found that the entropy of absorption plays a very important role in the solvation process. The PCIP-SAFT equation of state was able to fit the experimental data (or simulation results when experiments were unavailable) very accurately with only small adjustable binary interaction parameters.