Synthesis and characterization of new polysubstituted pyridinium-based ionic liquids: application as solvents on desulfurization of fuel oils

Abstract

The production of transportation fuels which have a very low content of sulfur has became one of the priority challenges for the oil industry worldwide, due to by strict new regulatory requirements. Ionic liquids (ILs) have been proposed as suitable and promising solvents for this purpose due to their excellent qualities as solvents. In this work a series of ten new ILs derived from pyridinium cation substituted with different alkyl chains have been synthesized from 2-alkyl-3,5-dimethylpyridines. The starting materials were prepared by selective metalation of 2,3,5-trimethylpyridine, which allowed the introduction of different alkyl groups in pyridine position 2 with high yields. To test the ILs sulfur-removal capacity, liquid–liquid equilibrium (LLE) data for ternary systems (heptane + thiophene + IL) were determined at T = 298.15 K and atmospheric pressure. Selectivity and solute distribution ratio, calculated from tie-lines, were used to evaluate whether these new ILs could be used as solvents for the extraction of thiophene from heptane. Finally, the experimental LLE data were correlated with the NRLT thermodynamic model.