A comparative study on the ex situ and in situ presulfurization of hydrotreating catalysts

An improved ex situ presulfurization (EPRES) technique is developed for transforming metal oxides of hydrotreating catalyst to the corresponding metal oxy-sulfides/sulfides. The process involves preliminarily dispersing an organo-nitrogen substance onto the oxide catalyst, introducing elemental sulfur together with an organic solvent, and a subsequent multi-step heat treatment. The physicochemical properties of the obtained EPRES catalyst with respect to the in situ presulfurization (IPRES) counterpart are studied by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and high pressure differential thermal analysis (HPDTA). XRD analysis indicates that the organo-nitrogen substance facilitates metal oxy-sulfide to disperse uniformly on γ-Al2O3 and the resulting metal oxy-sulfide species turn to be rather structurally amorphous. XPS together with TEM investigations reveal that higher content of active surface NiMoS/MoS2 species, less metallic Ni fraction, and uniformly dispersed surface S species are the features of EPRES catalyst, well correlated with its higher catalytic activity. HPDTA study indicates that the concentrative exothermic effect can be effectively minimized by adopting mixed sulfurizing agents and appropriate introducing manner. The degree of sulfurization can also be obviously enhanced by tuning thermo-treatment. The EPRES process can considerably shorten the start-up procedure in pilot plant test and a wide range of commercial practices, exhibiting its economical advantage and low environmental impact.