The oxidation of model sulfur compounds (thiophene derivatives, benzothiophene derivatives,
and dibenzothiophene derivatives), straight run-light gas oil (SR-LGO, S: 1.35 wt %), and vacuum
gas oil (VGO, S: 2.17 wt %) were conducted with a mixture of hydrogen peroxide and formic
acid. The thiophene derivatives with 5.696 to 5.716 electron densities on the sulfur atoms could
not be oxidized at 50 °C. Benzo[b]thiophene with 5.739 electron density and other benzothiophene
and dibenzothiophenes with higher electron densities could be oxidized. The sulfur compounds
in SR-LGO and VGO appeared to be oxidized to a detectable levels (c.a., 0.01 wt % S) by GC-FPD analysis. The IR spectra of oxidized SR-LGO and VGO showed that sulfones were formed
by oxidation. The removal of sulfur compounds by extraction became more effective for the oxidized
samples than for the original samples. Lighter sulfur compounds were preferentially extracted.
The extraction efficiencies of solvents, i.e., N,N
‘-dimethylformamide (DMF), acetonitrile (ACN),
methanol, varied greatly. The most effective solvent for the removal of sulfur compounds was
DMF. The recovery of oil was, however, lowest with DMF.
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