Coking behavior on a Ni–Mo/Al2O3 catalyst for the hydrocracking of vacuum residue

In this study, we performed the hydrocracking of vacuum residue (VR) in an autoclave reactor using a Ni–Mo/Al2O3 catalyst at 450 and 500 °C under 150 bar of pressure and characterized coke structure generated over the catalyst during the reaction in order to understand the coking behavior in the hydrocracking of vacuum residue. The insoluble coke generated during VR hydrocracking was characterized by N2 sorption, TGA, XRD, FE-SEM (EDX), EPMA, FT-IR, Raman, and 13C CP/MAS–NMR techniques. In the absence of catalyst, dominant thermal hydrocracking at 500 °C produced pregraphite coke containing sulfur compounds since sulfur components in the feed could not be removed by thermal hydrocracking. With catalyst, the coke structures generated during a reaction depended on the reaction temperature. The NMR, Raman, XRD, TPO, and FT-IR spectra showed that amorphous coke containing highly branched oligomers and polycyclic aromatics were generated during hydrocracking at 450 °C, whereas hydrocracking at 500 °C mainly produced pregraphite coke. The presence of the catalyst in hydrocracking of VR played an important role in increasing decomposition of VR and decreasing coke deposition.