Extractive/catalytic oxidative mechanisms over [Hnmp]Cl·xFeCl3 ionic liquids towards the desulfurization of model oils

Abstract

In this work, N-methyl-2-pyrrolidonium (NMP) was acidized using hydrochloric acid to obtain [Hnmp]Cl first, which was then reacted with FeCl₃ to prepare a series of inexpensive tunable [Hnmp]Cl·xFeCl₃ (x = 0.2–2.0) ionic liquids (ILs) for the extractive and oxidative desulfurization of model oils. The Lewis acidities of these ILs were tested by the Fourier transform infrared (FT-IR) method, which indicated that when the x value of [Hnmp]Cl·xFeCl₃ was above 1.0, the ILs exhibited Lewis acidity. The extraction results showed that the acidification of NMP reduced its dissolubility ability toward dibenzothiophene (DBT) and its Lewis acidity played a determining role in extractive desulfurization. In the catalytic oxidation removal process of the DBT model oil in the presence of H₂O₂, electron paramagnetic resonance (EPR) and scavenger experiments showed that the hydroxyl radical (˙OH) plays a key role and the superoxide anion radical (O₂˙⁻) has a minor function. [Hnmp]Cl·1.5FeCl₃ IL showed excellent recycling performance, which was due to its high dissolving capacity (23 700 ppm) for dibenzothiophene-sulfone (DBTO₂).