An inexpensive N-methyl-2-pyrrolidone-based ionic liquid as efficient extractant and catalyst for desulfurization of dibenzothiophene

• Inexpensive C5H9NO·MCln (M = Fe, Zn) ionic liquids are prepared.
• The ILs show highly efficient extractive performance for dibenzothiophene.
• The low viscosity and bifunctional groups of ILs are responsible for the extraction.
• C5H9NO·FeCl3 have the ability of catalyzing the decomposition of H2O2 to form OH.
• The IL exhibit excellent recycling performance due to the high solubility for DBTO2.

Inexpensive N-methyl-pyrrolidone (NMP)-based ionic liquids (ILs) are synthesized by coordinating N-methyl-pyrrolidone with anhydrous FeCl3 or ZnCl2. The introduction of metal chlorides lowers the solubility of NMP for actual diesel. The obtained C5H9NO·0.3FeCl3 IL shows remarkable extraction ability for dibenzothiophene (DBT) with Nernst partition coefficients (kN) above 7.5, which can be attributed to its low viscosity and bifunctional extractive groups of five-membered ring of NMP and unoccupied orbitals of Fe ion. The oxidative desulfurization of DBT using H2O2 as oxidant and ILs as extractants are investigated. The scavenger experiments and electron paramagnetic resonance (EPR) measurement verify the active species is hydroxyl radical (OH) responsible for the oxidation of DBT. FeCl3-based ILs show much better effects in catalyzing H2O2 to generate OH than ZnCl2-based ILs. The process and mechanism for extraction and catalytic oxidation of DBT in an oil–ionic liquid–H2O2 system are proposed. The C5H9NO·0.3FeCl3 IL shows excellent recycling performance. After six-run experiment, there is only little loss in activity, which can be ascribed to the high solubility (18,190 ppm) of dibenzothiophene-sulfone (DBTO2), the main oxidation product of DBT, in the IL.

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