Molecular transformation of heavy oil during slurry phase hydrocracking process: A comparison between thermal cracking and hydrocracking

To systematically investigate the reaction mechanism of heavy oil in the slurry phase hydrocracking process, comparative experiments of thermal cracking and slurry phase hydrocracking of a residual oil were carried out. The molecular composition of sulfur and nitrogen compounds in the feedstock and their products was comprehensively characterized by gas chromatography and electrospray ionization Orbitrap mass spectrometry. The participation of hydrogen makes the apparent cracking rate in hydrocracking process significantly lower than that in the thermal cracking process, leading to a more controllable cracking degree and higher liquid yield. Nitrogen- and sulfur-containing aromatics with high molecular condensation degree are the key refractory heteroatoms because of large steric hindrance. Aromatics with ring number over 4 have high saturation reactivity, as well as the exposed five-membered heteroaromatic rings. The mutual influence of cracking, aromatic saturation, and hydrodeheteroatom during hydrocracking were also discussed according to bulk properties and molecular composition. The results deepen the understanding of the complex reaction network and mechanism of heavy oil hydrocracking process from both thermal reaction and hydrogenation perspectives, which will be instructive for the catalyst design and the process optimization.