Process Parameters and Intensification Effects of a Microwave Exposure Applied for the Extractive Oxidation of Diesel: An Optimization Using Response Surface Methodology

Extractive oxidation of diesel via microwave processing using sulfuric acid and two synthesized pyridinium- or methylpyridinium-based ionic liquids has been studied as a sustainable and clean technology. The Central Composite Design (CCD) representing one of the response surface methods was applied for the experimental design, mathematical modeling, optimization, and factor-influence study, which covered the 0.75–1.75 [CH₂COOHmPy][HSO₄]/[H₂SO₄] volumetric range, 40–80°C temperature range, and 120–300 s radiation exposure time. The developed model properly fitted experimental results, with a coefficient of determination (R²) equal to 0.9832 that indicated its accuracy. The highest predicted sulfur removal (93.338%) as well as a significant removal of nitrogen and aromatic compounds was obtained for [CH₂COOHmPy][HSO₄]/[H₂SO₄] = 1.57, T = 71.7°C, and exposure time equal to 208 s. Microwave-assisted extractive oxidation demonstrated a considerable potential as the energy-saving technology, which meets the future need for producing clean fuels with low content of heteroatoms and polyaromatic hydrocarbons.