Extraction-oxidation desulfurization bypyridinium-based task-specific ionic liquids

The Brönsted acidic ionic liquids N-carboxymethylpyridine hydrosulphate ([CH ₂COOHPy][HSO ₄]) and N- carboxyethylpyridine hydrosulphate ([(CH ₂) ₂COOHPy] [HSO ₄]) were synthesized and used as the extractant and catalyst for the extractionoxidation desulfurization of model oil. The structures of the ILs were confirmed by ¹H NMR and ¹³C NMR. The density, viscosity and acid strength of the ILs were also investigated. The acid strength was in order of H ₂SO ₄ (98%) [CH ₂COOHPy] [HSO ₄] > [(CH ₂) ₂COOHPy][ HSO ₄]. The [CH ₂COOHPy][HSO ₄] showed better activity during the removal of dibenzothiophene (DBT) in n-octane by a combination of extraction and oxidation, and the sulfur removal reached 99.9% under the conditions of V _{model oil} = 20 mL, V _IL = 1.2 mL, T= 30 °C and H ₂O ₂/S molar ratio (O/S) = 6. In the same conditions, the removal of benzothiophene (BT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) by using [CH ₂COOHPy][HSO ₄] reached 82.5% and 89.1%, respectively. Ionic liquid [CH ₂COOHPy][HSO ₄] can be recycled 9 times without a significant decrease in the sulfur removal.