Selective Extractive Desulfurization of Simulated Straight-Run Diesel with Imidazole-Based Deep Eutectic Solvents

Given the current situation of excess diesel production capacity in China and the widespread adoption of renewable energy, selective desulfurization of diesel is a key method for achieving the resource utilization of its components. Based on the principle of polarity similarity and solubility, this study designed and synthesized a series of imidazole-based deep eutectic solvents (DESs) for the selective extractive desulfurization of simulated straight-run diesel. By evaluating the performance parameters of the extractants, it was determined that the deep eutectic solvent composed of 1-ethyl-3-methylimidazole chloride (EmimCl) as the hydrogen bond acceptor (HBA) and 2-imidazolidinone (IMD) as the hydrogen bond donor (HBD) is the optimal extractant. Under optimized conditions (50°C, extractant-to-oil ratio of 4:1), sulfide removal efficiency reached 61.77%, whereas aromatic removal was significantly lower at 6.87%. This disparity was largely attributed to the effective extraction of bicyclic aromatics (1-methylnaphthalene), while monocyclic aromatics (tetrahydronaphthalene and butylbenzene) remained virtually unremoved. Consequently, a high sulfide-to-aromatic selectivity of 15.44 was achieved. Quantum chemical calculations based on an implicit solvent model indicate that the solvation free energies of the various components differ due to solvation effects. The main reason for the selectivity of the various components toward sulfides and aromatic compounds lies in the differences in solvent polarity and van der Waals interactions.