Catalytic hydrodesulfurization of a light gas oil over a NiMo catalyst: kinetics of selected sulfur components

The hydrotreating of a real light gas oil feedstock over a commercial NiMo catalyst has been investigated in a pilot plant reactor operating at industrial conditions. The sulfur containing species in the oil and hydrotreated product have been characterized using a sulfur-sensitive gas chromatography technique, and the behavior of several individual components has been followed. The slow-reacting components all belong to the class of dibenzothiophenes, like dibenzothiophene (DBT), 4-methyl-DBT (4-MDBT) and 4,6-dimethyl-DBT (4,6-DMDBT). The individual kinetic behavior of these components was analyzed, and pseudo-first-order rate constants were obtained. The relative rates of HDS decrease in the order DBT>4-MDBT>4,6-DMDBT, the ratio between the rates of these components is shown to be strongly dependent on the reaction temperature. The behavior of 4,6-DMDBT with increasing temperature indicates a limitation on the HDS rate in an agreement with a reversible reaction, suggesting this component has to be hydrogenated before the carbon–sulfur bond is broken.