Ionic liquids for thiols desulfurization: Experimental liquid-liquid equilibrium and COSMO-RS description

Aiming at the replacement of the present inefficient and expensive desulfurization processes, ionic liquids have been considered as potential solvents to be used in extraction procedures. In this context, this work provides an experimental evaluation on the feasibility of ionic liquids for the selective extraction of a less studied class of aliphatic sulfur compounds - thiols. A mixture composed of n-dodecane and 1-hexanethiol was used, as a feed model of kerosene in “jet-fuel”, and the tie-lines of the corresponding ternary systems were experimentally determined at 298.2 K and 313.2 K for imidazolium- and pyridinium-based ionic liquids. Using the experimental data, the selectivity and distribution ratios of 1-hexanethiol were also determined. Despite the small distribution ratios, these systems display a high selectivity meaning that the co-extraction of other fuel compounds can be controlled by the ionic liquids nature and/or chemical structural characteristics. The COnductor-like Screening MOdel for Real Solvents (COSMO-RS) was used to predict the liquid-liquid equilibrium of the investigated systems. A good agreement between the experimental data and the COSMO-RS results was observed. Therefore, the extraction behavior with other ionic liquids not experimentally addressed was also predicted by COSMO-RS for the identification of the best potential candidates. The ionic liquids identified are constituted by a short alkyl side chain imidazolium, pyridinium and pyrrolidium cations, combined with the anions tosylate, diethylphosphate, ethylsulfate and triflate.