(214f) Deep Desulfurization of Fuels Using Imidazolium Anion-Based Ionic Liquids

An extractive desulfurization method was developed using the imidazolium anion (Im)-based ionic liquids (ILs), 1,8-diazabicyclo[5.4.0]undec-7-ene Im ([DBU][Im]) and 1,1,3,3-tetramethylguanidine Im ([TMG][Im]), as extractants. The DBU and TMG cations with strong alkaline and Im anion which is a weak proton donor show high affinities for sulfur compounds. Effects of extraction time, initial sulfur content in model oil, the mass ratio of IL to model oil and extraction temperature on the removal efficiencies of sulfur compounds were investigated. The removal efficiencies of DBT, 4,6-DMDBT and BT with [DBU][Im]/[TMG][Im] as extractants under the selected conditions (IL:model oil (w/w) = 1:1, room temperature) were 79.2%/69.4%, 68.4%/57.7% and 61.2%/54.4%, respectively. The extra heterocyclic aromatic ring in [DBU] cation and the imidazolium ring in [Im] anion could enhance the Ï€-Ï€ interaction between [DBU][Im] and sulfur compounds, resulting in obtaining higher removal efficiency of sulfur compounds with [DBU][Im] as extractant than that with [TMG][Im]. Both the extraction processes with these two extractants were fast (extraction equilibrium was reached within 10 min). After five multi-stage cross-current extraction processes under the selected conditions ([DBU][Im]:model oil (w/w) = 1:3, room temperature), the sulfur content (DBT) in the model oil decreased from 500 ppm to 5 ppm. The reusability of [DBU][Im] and [TMG][Im] and reactive extraction model for desulfurization were studied too. Moreover, the characterization methods of ¹H NMR and FT-IR spectra and the calculation methods of optimized geometry and interaction energy between sulfur compounds and extractants by Gaussian 09 software were used for the study of extraction mechanism. Furthermore, the oxidation-extraction two-step deep desulfurization method was applied in model oil system and real diesel fuel. The results showed that the removal efficiencies of DBT and 4,6-DMDBT in model oil reached up to 98.2% and 99.9%, respectively. Meanwhile, the sulfur removal efficiency of real diesel fuel reached up to 97.0% by one-stage oxidation and three-stage cross-current extraction processes with the mass ratio of IL to real diesel fuel as 1:2.