Deep extractive denitrogenation with Cu-based ionic liquids and mechanistic insights

A major challenge in the extractive denitrogenation (EDN) of fuel oils lies in achieving high nitrogen removal efficiency with minimal extractant usage. To address this, a series of Cu-based ionic liquids (ILs) ([Bmim]Cl/CuCl₂-X) with different cation-to-anion ratios were synthesized and characterized. The cation-to-anion ratio was found to be crucial in determining the predominant anions present in the ILs. Among the synthesized Cu-based ILs, [Bmim]Cl/CuCl₂-1 exhibited outstanding EDN performance, achieving 100% nitrogen removal with minimal ionic liquid consumption. The anion [CuCl₃]⁻ was identified as playing a key role in the EDN process, where the unoccupied orbitals of Cu and the chloridion in [CuCl₃]⁻ facilitate effective coordination with nitrogen atoms in organic nitrogen compounds. This coordination forms Lewis acid–base interactions, which are essential for deep EDN. The study not only introduces an efficient Cu-based ionic liquid but also provides insights into optimizing ionic liquid design for better extraction performance.