Monte Carlo simulations of phase equilibria and microstructure of thiophene/[Bmim][PF6]/CO2

Monte Carlo simulations were carried out to calculate the phase behavior of thiophene in the binary and ternary mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) and carbon dioxide using a united atom model. The calculated pure ionic liquid densities and structural properties of [Bmim][PF6] as well as the vapor pressure of thiophene in the ionic liquid were compared with the available experimental data in the literatures, and a good agreement was obtained. Based on the radial distribution functions (RDFs) and spatial distribution functions (SDFs) results, thiophene molecules prefer to organize around the C10 atom of the butyl chain connected with the imidazolium ring. The concept of local composition in solutions was used to better understand the solution structure. It is shown that thiophene molecules can strongly associate with the cation. For the ternary system of CO2/thiophene/IL, CO2 can affect the solubility of thiophene in ionic liquid when the pressure is changed. CO2 molecules interact with the anion stronger than thiophene molecules. This implies that CO2 can be used as a potential recovery desorbent of thiophenic compounds in the ionic liquid by tuning the pressure.