Towards a room temperature oxidative desulfurization of refractory compounds over 1-octyl-3-methylimidazolium tetrachloroferrates/silica gel: The beneficial effects of immobilization

Abstract

A successful immobilization of 1-octyl-3-methylimidazolium tetrachloroferrates ([Omim][FeCl4]) thin films on a silica gel while remaining its mesoporousity, was accomplished in this work. The developed catalyst was highly active and cost-effective for deep oxidative desulfurization of refractory thiophenic compounds at room temperature utilizing H2O2 oxidation agent. The reaction products were well separated from fuel by the catalyst itself under a beneficial solvent-free condition. The catalyst was characterized applying different analyses of FT-IR, TGA, XRD, SEM, EDS, AFM, N2 adsorption desorption, BET, and BJH. A sufficiently large pore diameter (∼6.2 nm) and high surface area (∼490 m2/g) of the silica gel for supporting the Lewis acidic [Omim][FeCl4] having a proper anion and cation structure, synergistically enabled a high efficient and selective catalyst for removal of refractory thiophenes. The influences of reaction temperature and time, loading amount of ionic liquid (IL), catalyst and oxidant amount as crucial reaction factors were evaluated in order to have a maximum desulfurization yield. Impressively, only a very low IL loading of 5 wt.% on the silica gel support achieved complete elimination of dibenzothiophene at the optimal mild conditions and room temperature. In the presence of a non-sulfur aromatic hydrocarbon beside different thiophenic models, the desulfurization selectivity of [Omim][FeCl4] increased from 0.92 to 0.95 via immobilization on the silica gel support. A significant decline in the IL consumption was verified as another beneficial effect of this immobilization. The catalyst could be easily separated having a capability for 100 % removal of dibenzothiophene after recycling four times. Meanwhile, GC–MS analysis was employed for further founding of the desulfurization pathway.