Extraction–oxidation desulfurization by pyridinium-based task-specific ionic liquids

The Brönsted acidic ionic liquids N-carboxymethylpyridine hydrosulphate ([CH 2 COOHPy][HSO 4 ]) and N-carboxyethylpyridine hydrosulphate ([(CH 2 ) 2 COOHPy][HSO 4 ]) were synthesized and used as the extractant and catalyst for the extraction–oxidation desulfurization of model oil. The structures of the ILs were confirmed by 1 H NMR and 13 C NMR. The density, viscosity and acid strength of the ILs were also investigated. The acid strength was in order of H 2 SO 4 (98%) > [CH 2 COOHPy][HSO 4 ] > [(CH 2 ) 2 COOHPy][HSO 4 ]. The [CH 2 COOHPy][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 2 O 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 2 COOHPy][HSO 4 ] reached 82.5% and 89.1%, respectively. Ionic liquid [CH 2 COOHPy][HSO 4 ] can be recycled 9 times without a significant decrease in the sulfur removal.