A deep eutectic solvents (DES) was synthesized by stirring mixture of 1-butyl-pyridinehydrochloride (C4pyrCl) and oxalic acid (C2H2O4) at 100°C. The C4pyrCl/C2H2O4 DES was characterized by FT-IR and 1H NMR spectroscopy. This DES is capable of extracting thiophene-type sulfides due to the similar polarity of 1-butyl-pyridine and DBT. The –COOH groups within the C4pyrCl/C2H2O4 DES are readily oxidized to ‒COOOH by H2O2, which susequently catalyzes the thiophene oxidation into sulfone in the model oil. The higher polarity of sulfone compared to that of thiophone enhances their solubility in the solvent. When the V(DES)/V(model oil) = 0.2, T = 50°C, and O/S = 6, the DBT removal rate reached 98.6% within 80 min. The catalytic activity of C4pyrCl/C2H2O4 exhibited only a slight decrease after nine regeneration cycles. The apparent activation energy for DBT removal using C4pyrCl/C2H2O4 was 33.3 kJ/mol. Experimental results indicate that the low apparent activation energy contributes to the high desulfurization efficiency.
Yu et al. (Wed,) studied this question.