Hydrodesulphurization of dibenzothiophene on NiMoS catalysts: Impact of the carbon support on the reaction kinetics

Abstract

The hydrodesulphurization (HDS) activity of nickel molybdenum sulphided catalysts supported on activated carbon (NiMoS/AC), activated petroleum coke (NiMoS/APC), and conventional alumina (NiMo/γ-Al2O3) have been compared using dibenzothiophene (DBT) as a model reactant. The reactions were carried out in a slurry-phase batch microreactor at different reaction times (30–120 min) and temperatures (588–638 K) and a fixed H2 pressure (4.8 MPa). The NiMoS/APC catalyst had higher dispersion than the NiMoS/AC catalyst, resulting in a higher DBT conversion activity per gram of catalyst on the NiMoS/APC catalyst. However, similar activities were obtained on both catalysts when accounting for the NiMoS dispersion. The NiMoS/APC activity was marginally lower than the NiMoS/γ-Al2O3 commercial catalyst, suggesting that activated petcoke is a promising support for NiMoS catalysts. The pseudo 1st order rate constants for both the direct desulphurization (DDS) and hydrogenation (HYD) reaction pathways were of similar magnitude on the NiMoS/APC catalyst, as were the apparent activation energies. Hence the selectivities for HYD versus DDS were favoured equally on the NiMoS/APC, unlike on NiMoS/Al2O3 where the DDS of DBT is favoured, or the NiMoS/AC where the DDS of DBT is favoured at higher temperatures (> 603 K). The results of this study demonstrate that raw petcoke derived from Canadian oilsands can be converted to a useful catalyst support for hydrotreating catalysts that have high NiMoS dispersion and HDS activity, comparable to that of a commercial NiMoS/Al2O3 catalyst.