A molecular-level insight into the synergistic separation of acidic and basic heteroatoms from coal tar: A strategy for fuel upgrading

The upgrading of coal-based fuels by eliminating acidic phenols and basic N-heterocyclic compounds is key to generating clean fuels, yet their simultaneous elimination is still a formidable challenge. According to this research, a tetraethylammonium chloride/oxalic acid (TEAC/OA) deep eutectic solvent (DES) realizes high simultaneous extraction efficiencies (>97 %) and a synergistic promotion: m -cresol’s extraction efficiency is increased from 90.6 % to 97.5 % by the presence of quinoline. In order to reveal the origin of this high performance, the integration between multi-scale simulations and spectroscopic analysis was conducted. The findings reveal that the high performance is caused by a complex “division-of-labor” system, where the Cl – anion anchors m -cresol while the quinoline is sequestered by the TEA + and OA. This selective capture is thermodynamically boosted, with the target molecules showing greater calculated interplay energies than the oil matrix. A near two-order-of-magnitude reduction in the diffusion parameters of the target molecules upon extraction further confirms the merit of this molecular “caging”. This research shows an effective method to purify complicated fuel oils and set up a novel principle of synergistic design for next-generation extractive separation media.