Deep oxidative desulfurization of fuels by superbase-derived Lewis acidic ionic liquids

In this work, a kind of novel, inexpensive and stable superbase-derived Lewis acidic ionic liquids (ILs) with the protonated 1,5-diazabicyclo[4.3.0]-non-3-ene (DBN) cation and the ZnCl2-based complex anion have been synthesized for the first time and employed in the extraction combined oxidative desulfurization (ECODS) process of both model oil and real diesel with hydrogen peroxide (H2O2, 30 wt%) as an oxidant. Comparing the three ILs [HDBN] Cl/nZnCl(2) (n = 1, 2 and 3), the ECODS performance decreased with the increasing of ZnCl2 proportion, which is quite different from the previous reports. Therefore, detailed characterizations were carried out to research the resonance structures of protonated DBN and the conformation transition related to the ZnCl2 fraction was revealed. As the [HDBN] Cl/ZnCl2 performed the best by reaching complete removal of dibenzothiophene in model oil, other important factors were also investigated, including reaction temperature, molar ratio of H2O2/S, mass ratio of IL/oil and sulfur species. After reused for six cycles, no noticeable changes in both sulfur removal performance and chemical structure were observed. Under the optimal reaction conditions, the S-content of a real diesel could be decreased from 559.7 ppm to 6.5 ppm with 98.8% sulfur removal via only one-step ECODS. Neither the original heterocyclic sulfides nor the oxidation products were detected, which indicated the excellent catalytic activity and extractive capacity of the ILs. (C) 2017 Elsevier B.V. All rights reserved.