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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In the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), the effects of H2S on catalytic activity and selectivity were investigated under deep desulfurization conditions (sulfur concentration<0.05wt%) using a commercial Co-Mo/Al2O3 catalyst. The conversions of DBTs decreased with increasing partial pressure of H2S. The formations of both biphenyls (BPs) and cyclohexylbenzenes (CHBs) were inhibited by H2S, but the former was inhibited more significantly.The HDS reactions of DBTs were described using Langmuir-Hinshelwood rate equation.

Hydrodesulfurization (HDS) of light gas oil was investigated using sulfided Co-Mo/Al 2 O 3 catalyst. The behavior of dibenzothiophene, monomethyldibenzothiophenes (C1-DBTs) and dimethyldibenzothiophenes (C2-DBTs) in HDS was traced under the following conditions: temperature, 280-400 °C; LHSV, 2-10 h -1 ; and gas/oil, 1000 and 125 NL (L-(NTP))/L. The HDS of these compounds was treated as a pseudo-first-order reaction. The ratio of the rate constants of 4-methyldibenzothiophene (4-MDBT) and DBT to that of 4,6-dimethyldibenzothiophene (4,6-DMDBT) diminished relative to those of the model reactions. The activation energies of DBTs increased in the order DBT < 4-MDBT < 4,6-DMDBT, while the differences between values diminished relative to those of HDS reactions using a single component among DBT, 4-MDBT, and 4,6-DMDBT. The retarding effect of H 2 S on HDS decreased in the order DBT > 4-MDBT, and further, 4,6-DMDBT was not inhibited. The results indicated that the selectivity for biphenyls in the HDS of DBT was higher than in the HDS of 4-MDBT or 4,6-DMDBT and that DBT and 4-MDBT were adsorbed by the catalyst more weakly than 4,6-DMDBT. An aromatic hydrocarbon of larger ring number has a stronger retarding effect on the HDS rate. The addition of phenanthrene decreased the HDS rate of DBTs in the order DBT > 4-MDBT > 4,6-DMDBT, while 1-methylnaphthalene did not affect the HDS rate. The effect of phenanthrene on the HDS rate appeared to be related to the differences in the adsorption ability of DBTs. To the contrary, the addition of acridine decreased HDS rate in the order 4,6-DMDBT > 4-MDBT > DBT. The results indicate that the retarding effect of acridine is different from that of phenanthrene.