Oxidative desulfurization of fuels promoted by choline chloride-based deep eutectic solvents

In this study, a new type of "green solvents" named deep eutectic solvents (DESs) has been synthesized by combining hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). Choline chloride (ChCl) was chosen as typical HBA, and polyethylene glycol (PEG), 1,3-butyleneglycol (BG), ethylene glycol (EG), glycerol (Gl), propionate (Pr), malonic acid (MA) and urea (U) were chosen as HBDs. The extraction and catalytic oxidative desulfurization (ECODS) system was evaluated with phosphotungstic acid (HPW) as catalyst and 30 wt% H2O2 as oxidant. Among all the neutral, acid and basic DESs, choline chloride/2polyethylene glycol (ChCl/2PEG) showed the best performance and 99.1% of dibenzothiophene (DBT) could be eliminated from model oil at 50 °C within 3 h. Interestingly, the volume ratio of DES to model oil was just 1:10, which was much less than the amount of extractant in the literature. The gas chromatography–mass spectrometer (GC–MS) analysis demonstrated that DBT sulfoxide (DBTO) and sulfone (DBTO2) were the products of oxidation of DBT. The desulfurization efficiency of the five sulfides in ECODS system occured in the following order: DBT > 4-MDBT > 4,6-DMDBT > 3-MBT >BT.