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

Abstract Inexpensive N-methyl-pyrrolidone (NMP)-based ionic liquids (ILs) are synthesized by coordinating N-methyl-pyrrolidone with anhydrous FeCl 3 or ZnCl 2 . The introduction of metal chlorides lowers the solubility of NMP for actual diesel. The obtained C 5 H 9 NO·0.3FeCl 3 IL shows remarkable extraction ability for dibenzothiophene (DBT) with Nernst partition coefficients ( k N ) 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 H 2 O 2 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. FeCl 3 -based ILs show much better effects in catalyzing H 2 O 2 to generate OH than ZnCl 2 -based ILs. The process and mechanism for extraction and catalytic oxidation of DBT in an oil–ionic liquid–H 2 O 2 system are proposed. The C 5 H 9 NO·0.3FeCl 3 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 (DBTO 2 ), the main oxidation product of DBT, in the IL.