Oxidative desulfurization and denitrogenation of a light gas oil using an oxidation/adsorption continuous flow process Original Research Article

The oxidation of undesirable sulfur compounds present in a desulfurized light gas oil (LGO; sulfur content: 39 ppm) was performed with tert-butyl hydroperoxide (t-BuOOH) as the oxidant in the presence of a 16 wt.% MoO3/Al2O3 catalyst. The oxidation activity of the sulfur compounds in the light gas oil increased when the O/S molar ratio increased up to 15; the activity slightly decreased for higher ratios. This optimal ratio was significantly higher that the stoichiometric one (=2) due to parallel oxidation reactions of olefins, etc., in the LGO. Further, we compared the oxidation reactivity of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and trimethyldibenzothiophene (C3-DBT), which are refractory compounds present in the light gas oil. The reactivity decreased in the order DBT ≫ 4,6-DMDBT > C3-DBT, irrespective of the WHSV and the temperature. Subsequent mathematical treatment revealed that the oxidative reaction of each sulfur compound follows a first-order kinetics. We found an activation energy of 32 ± 2 kJ mol−1, whatever the compound, suggesting that the oxidation mechanism was the same for these compounds. Then, according to the proposed global process, the previously oxidized molecules in the treated light gas oil were further removed by adsorption over a silica gel at ambient temperature. As a result, the total sulfur content could be decreased after oxidation/adsorption to less than 5 ppm. Further, N-containing model compounds were also treated according to the same procedure and the denitrogenation performance decreased in the order indole > quinoline > acridine > carbazole. Subsequently, the same process allowed decreasing the N content in the LGO from an initial value of 13.5 ppm to a value of 0.8 ppm, which is a remarkable result.