Molecular level simulation and analysis of removal of sulfur, nitrogen and carbon residue in residual oil hydrotreating process

Residual oil hydrotreating was a deep processing technology to remove sulfur, nitrogen, heavy metals and carbon residue, which provided high quality feed oil for fluid catalytic cracking (FCC). To realize molecular level analysis of the removal laws of impurities, Structure Oriented Lumping (SOL) method was used to construct the molecular level reaction kinetics model of residual oil hydrotreating process. The residual oil and the reaction network were digitally described at the molecular level. The model was used to trace the generation paths and reaction paths of hydrocarbon and non-hydrocarbon molecules and reveal their transformation laws during the residual oil hydrotreating process. The removal rates (92.6% and 88.2%) of sulfur atoms in dibenzothiophene sulfides and polycyclic thiophene sulfides were greater than the removal rates (43.8% and 68.9%) of nitrogen atoms in carbazole nitrides and polycyclic pyrrole nitrides under industrial reaction conditions, indicating sulfur atoms were easier to be removed than nitrogen atoms when the sulfides and nitrides had the same structure. Through the calculation of the model, the effects of reaction conditions on the product distribution of residual oil hydrotreating process were studied to provide guidance for the removal of impurities. As the reaction temperatures increased from 355 degrees C to 385 degrees C, the rates of hydrogenation saturation reactions increased, which strengthened the conversion of aromatics with high ring number to aromatics with low ring number. The content of pentacyclic aromatic hydrocarbons and hexacyclic aromatic hydrocarbons decreased. The content of tetrabenzothiophene and amyl dibenzoquinoline decreased due to the strengthening of hydrodesulfurization and hydrodenitrification reactions. The SOL model could provide molecular guidance for the process optimization of the residual oil hydrotreating process.