Synthesis, characterization, and adsorptive desulfurization behavior of Merrifield resin supported polymeric ionic liquids with different alkyl chain lengths

Ionic liquids (ILs) as environmental-friendly extractive solvents can remove aromatic heterocyclic sulfur compounds (S-compounds) from fuel oils, which due to their capacity for S-compounds (easy separation and higher selectivity). In this work, a series of polystyrene (PS)-supported polymeric ILs (PS-PILs or PS-6-PILs) with different alkyl side chain length were synthesized. Characterization with Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), elemental analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) demonstrated that IL monomers had been successfully loaded and polymerized on the surface of PS to form a thin polymer coating. The adsorptive desulfurization behavior of polystyrene-supported polymeric ILs was investigated by removing aromatic S-containing compound from model fuel (cyclohexane/thiophene, 2-methylthiophene, benzothiophene, and dibenzothiophene). Under the experimental conditions, the adsorption ability followed the order of PS < PS-PILs < PS-6-PILs. With the length of alkyl chain of imidazole ring increased, the desulfurization rate of thiophene was gradually increased, 2-methylthiophene was first increased and then decreased, benzothiophene and dibenzothiophene were slightly decreased. These trends were due to the different steric effect and aromatic pi-electron density of ILs with different alkyl side chain length.