Deep extractive and catalytic oxidative desulfurization of liquid fuels by using iron(iii) based dication ionic liquids

Abstract

A series of dicationic ionic liquids (DcILs) (1–5), with varying lengths of alkyl chain along with [FeCl₃Br]⁻ as the counter anion, have been synthesized and are characterized by using FT-IR, Raman spectroscopy, and mass spectrometry besides single crystal X-ray analysis. The thermal stability, chemical and elemental composition of the synthesized compounds are assessed by thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) respectively. They have been exploited as extractants and catalysts for oxidative desulfurization (ODS) of liquid fuels using H₂O₂ as an oxidizing agent. Certain parameters like the effects of reaction time, temperature, catalyst loading amount, oxidant-to-sulfur ratio, and reactivity of different sulfur substrates on desulfurization have also been surveyed comprehensively. The synthesized DcILs exhibit very efficient extractive and catalytic activity with the advantage of very mild reaction conditions, rapid reaction equilibrium, and substantial sulfur removal at room temperature with minimal amount of catalyst and oxidant. A reaction mechanism of DcILs with DBT has been proposed and its kinetics appeared to be a pseudo-first-order reaction. The extraction and catalytic oxidation (ECODS) process has been explicated and authenticated by GC-MS. The present work demonstrates that DcILs have the least contribution to the contamination of liquid fuels as they are insoluble in them and due to higher recyclability, they may be attributed as green and eco-friendly extractants as well as catalysts.