Acid Dicationic Ionic Liquids as Extractants for Extractive Desulfurization

A series of imidazole- and pyridine-based dicationic ionic liquids (DILs) were synthesized and employed in extractive desulfurization (EDS) for the removal of sulfur compounds from commercial fluid catalytic cracking (FCC) gasoline. The influence parameters in the EDS process and regeneration of DILs are discussed. Under optimum operating conditions, the desulfurization efficiency can reach 79.72%. After five cycles, the sulfur content was reduced to less than 10 μg/g, and deep desulfurization was realized. The regeneration of the used DILs was performed by back-extraction, and the Fourier transform infrared and 1H nuclear magnetic resonance (NMR) spectra proved that the structure of DILs did not change. The relationship between acid strength and the desulfurization effect of DILs was studied by UV–vis spectroscopy. According to 1H NMR characterization, the main mechanism of the DILs' EDS process may be the interaction of π–π bonds. It is inferred from the chemical shift that the DILs have larger cation volume, which was conducive to increasing the aromatic π-electron density, producing stronger π–π interaction between the cations and aromatic sulfides, and thus having better EDS effect than ILs with mono-cationic. Finally, the adaptability of DILs was studied, and DILs have excellent desulfurization adaptability for different FCC gasolines.