Oxidative desulfurization of fuel oil catalyzed by a carbon nitride supported phosphotungstic acid based dicationic ionic liquid

Abstract

In this study, a novel phosphotungstic acid based dicationic ionic liquid [C₂(MIM)₂]PW₁₂O₄₀ was successfully prepared and immobilized on graphitic carbon nitride (g-C₃N₄). The supported catalysts x% [C₂(MIM)₂]PW₁₂O₄₀/g-C₃N₄ (x = 3, 10, 30, and 50 (wt%)) were characterized and applied in a bi-phase system composed of model oil (n-octane) and aqueous 30 wt% H₂O₂ to achieve deep desulfurization. Under the optimized reaction conditions (i.e., m(catalyst) = 0.05 g, T = 60 °C, t = 60 min, O/S = 4), 10% [C₂(MIM)₂]PW₁₂O₄₀/g-C₃N₄ exhibited excellent catalytic performance for dibenzothiophene (DBT) in fuel oil. The conversion rate of DBT could reach more than 99% due to the good dispersion in the oxidation desulfurization system and the electron-rich W of the catalyst. The catalytic activity of the catalyst for different sulfides was in the following order: DBT > 4,6-dimethyldibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The only oxidation product of DBT was determined to be dibenzothiophene sulfone (DBTO₂) by gas chromatography–mass spectrometry (GC-MS), and the possible mechanism was also discussed. In addition, the supported catalyst could be reused six times without a significant decrease in activity.