Extractive desulfurization and denitrogenation of fuels using functional acidic ionic liquids

• Lewis/Brφnsted acidic ILs in this work were proved to be capable of removing S-/N-compounds effectively from fuel oils.
• More than 90% extractive efficiency was realized after a single extraction of N-compounds from fuel oils.
• Influence of temperature, IL:mass ratio, multiple extractions on efficiency were tested.
• Good recyclability showed the ideality of [Bmim]Cl/ZnCl2 in industrial application.

Due to the ineffectiveness in removing cyclic sulfur compounds (S-compounds) and nitrogen compounds (N-compounds) such as thiophene (TS), dibenzothiophene (DBT), carbazole, pyridine and their derivatives from fuel oils, the traditional hydrodesulfurization and hydrodenitrogenation processes are facing some challenges especially now in the wake of sterner regulation of S-/N-content in fuel oils. This work demonstrates that some acidic ionic liquids (ILs) are capable of extracting cyclic S-/N-compounds particularly the basic N-species from fuel oils. Both Lewis acidic ILs 1-butyl-3-methylimidazolium chloride/ZnCl2 ([Bmim]Cl/ZnCl2) and [Bmim]Cl/2ZnCl2 as well as Brφnsted acidic ILs [Bmim]HSO4 and [Hmim]HSO4 are used to extract TS, DBT, carbazole and pyridine from their hexane (model gasoline) or octane (model diesel fuel) mixtures. Typically, 93.8% TS removal (S-content drops from 500 ppm to 31 ppm) and 95.9% DBT removal (S-content from 516 ppm to 21 ppm) by [Bmim]Cl/ZnCl2 after 6-stage extraction are obtained at 25 °C, 1:1(w/w)IL:oil, 30 min; while 93.8% carbazole removal (N-content from 279 ppm to 17 ppm) and 97.8% pyridine removal (N-content from 495 ppm to 11 ppm) are realized after only one stage extraction and the N-content is undetectable after 2-stage extraction. [Bmim]Cl/ZnCl2 is selected as a representative IL to undergo a series of parallel experiments to determine the influence of extraction time, temperature, IL:oil mass ratio and multi-stage extraction on S-/N-removal efficiency. The mutual solubility of [Bmim]Cl/ZnCl2 in fuel oil as well as IL recycling is also performed.