Extraction-Coupled Oxidative Denitrogenation of <i>N</i> -Heterocyclic Compounds from Hydrocarbon Fuel by Choline Chloride/Ascorbic Acid Natural Deep Eutectic Solvent-H ₂ O ₂ Systems

This study presents an extraction-coupled oxidative denitrogenation (ECODN) of hydrocarbon fuel using natural chloride choline/ascorbic acid (ChCl/AscH2) deep eutectic solvents (DESs) as an extratant and H2O2 as an oxidant. Unlike traditional ECODNs that require heterogeneous catalysts and organic molecular solvents, the ChCl/AscH2–H2O2 system employs AscH2 as both a hydrogen bond donor for DES extractants and an activator for oxidation reactions. This work focuses on extraction and oxidation parameters, as well as the related mechanisms. Under the optimized conditions, basic and neutral nitrogen heterocyclic impurities in simulated oil can be completely removed in an ambient environment. A denitrogenation efficiency of about 79% was achieved in actual oil products. In this system, nitrogen-containing compounds in the oil phase were extracted into the DES phase by hydrogen bonding, and then destroyed by oxidation of hydroxyl, superoxide, and ascorbic acid radicals. This study presents an innovative integrated method of fuel denitration using green solvent extraction and mild oxidation, which also contributes to the understanding of the extraction and oxidation mechanisms of nitrogen heterocyclic compounds in fuel oil.