Slurry-phase hydrotreating of vacuum gas oil with Mo-based dispersed catalyst in semi-batch and continuous reactors

Abstract

In this study, we investigate the use of Mo-based dispersed catalyst, using oleo-soluble Mo-octoate as precursor, for the slurry hydrocracking of VGO as model feedstock in both semi-batch and continuous slurry reactors. The in-situ formation of the catalyst from the corresponding precursor investigated under reaction conditions with Light Cycle Oil (LCO) as feed demonstrates that Mo sulfidation occurs rapidly between 300 and 350 °C, leading to the formation of MoS₂ nanoparticles of hexagonal structure with laminar morphology. Thermal and catalytic semi-batch tests at varying Mo concentration and reaction time indicate that the hydrodesulfurization reactions are catalytically-driven, while cracking follows the thermal free-radical reaction mechanism. At Mo concentrations ≤ 2000 wppm, the active hydrogen formed by the catalyst quenches the free radicals thereby restricting the cracking reactions, while at loadings > 2000 wppm Mo, MoS₂ partially contributes to cracking via CC bond hydrogenolysis. Continuous pilot-scale tests for over 60 h showed no operability issues, achieving high liquid yields (> 98 wt.%). Variation of the sulfur removal and cracking extent with time-on-stream suggests partial catalyst accumulation in the slurry reactor during operation.