This study reports on the synthesis, characterization,
and application
of two acidic ionic liquids, namely, N-carboxymethylpyridinium
acetate ([HO2CCH2Py][CH3CO2] or AIL1) and N-carboxyethylpyridinium
acetate ([HO2C(CH2)2Py][CH3CO2] or AIL2), as both extractants and catalysts
for the oxidative and extractive desulfurization (OEDS) of model fuel
oils containing heteroaromatic sulfur compounds. The structural properties
of the synthesized acidic ionic liquids (ILs) were confirmed by 1H NMR, 13C NMR, and FT-IR spectroscopic analysis.
To optimize the performance of the acidic AILs in the desulfurization
process, the effects of different parameters, such as H2O2 dosage, reaction time, and temperatures, were investigated.
The experimental results showed that AIL1 has exceptionally
high desulfurization–extraction rates, with values of 99.8%,
97.8%, and 95.4%, for DBT, BT, and 4,6-DMDBT, respectively, under
the optimum conditions established. Under the same conditions, the
desulfurization-extraction rates using AIL2 reached 91.6%,
87.3%, and 82.4%, respectively, for DBT, 4, 6-DMDBT, and BT. Both
ionic liquids can be recycled up to 9 times without a significant
decrease in their sulfur removal efficiencies. Furthermore, density
functional theory (DFT) calculations were conducted to evaluate the
electronic interaction energies (ΔIE) between the AILs with
each of the sulfur-containing compounds and their putative oxidized
products. The computational findings strongly supported the experimental
outcomes.