Oxidative Desulfurization of Fuel Oil with H3PO4-based Deep Eutectic Solvents

A series of Lewis-acid deep eutectic solvents (DESs) were synthesized by stirring phosphoric acid and zinc chloride as raw materials at 80 degrees C to form H3PO4/nZnCl(2) (n = 0.1, 0.25, 0.5, 0.75, 1). The DESs were characterized by Fourier transform infrared spectrophotometry (FT-IR), thermogravimetry/differential thermogravimetry (TG/DTG), and electron spray ionization mass spectrometry (ESI-MS). The DESs were used as both extractants and catalysts to remove dibenzothiophene from fuels via oxidative desulfurization (ODS). Experiments were performed to investigated the inffuence of factors such as composition of DES, temperature, oxidant dosage (molar ratio of O:S), DES dosage (volume ratio of DES:oil), and number of cycles on desulfurization rate. The results indicated that the removal rate of dibenzothiophene (DBT) was affected by the Lewis acidic DESs, with that of H3PO4/0.25 center dot ZnCl(2)reaching 96.4% under optimal conditions (V-oil =5 mL, V-DES=1 mL, an oxidant dosage of 6, T=50 degree celsius). After six cycles, the desulfurization rate of H3PO4/0.25 center dot ZnCl2 remained above 94.1%. The apparent activation energy of dibenzothiophene (DBT) removal reaction was determined by a pseudo-ffrst order kinetic equation according to the Arrhenius equation to be 32.34 kJ/mol, as estimated. A reaction mechanism is proposed based on the experimental data and characterization results.