Extractive desulfurization using choline chloride-based DES/molybdate nanofluids; Experimental and theoretical investigation

Abstract Recently, greater attention is being paid for desulfurization by deep eutectic solvents as an efficient extractive desulfurization agent. Deep desulfurization is a critical process to reach fuel with an ultra-low percentage of less than 10 ppm sulfur. Deep eutectic solvents (DESs) are eutectic mixture formed of Lewis or Bronsted acids and bases and have a lower melting point than individual components. Interaction strength among molecules in the DES affects their characteristics and applications. In this work, four DESs were prepared and characterized. The extractive desulfurization affinities of the DESs were evaluated using n-octane solvent as a model fuel containing thiophene as a sulfur compound. The DES consisted of choline chloride and ethylene glycol (ChCl-EG) exhibited the highest desulfurization affinity ~37% using the low volumetric ratio of DES: model fuel (1: 2). Moreover, molybdate nanofluid (0.02 wt%) based on ChCl-EG was prepared and analyzed by XRD, TGA, DLS, and TEM. The sulfur extraction of simulated fuel consisting of thiophene was conducted by MoO3-based DES nanofluid, which exhibited a high extraction efficiency of 98.01% in a single step, so considered as a deep desulfurization process. The concentration of sulfur in the model oil reached less than 4 ppm in one cycle. Furthermore, Molecular dynamics (MD) simulation and computational chemistry were implemented to evaluate the thiophene removal and oil desulfurization by deep eutectic solvent, in addition to investigating the intermolecular interactions between the DES and thiophene. The obtained results provide insights into the desulfurization mechanism by the DES solvents.