Maximizing aromatic hydrogenation of bitumen-derived light gas oil: Statistical approach and kinetic studies

Bitumen-derived light gas oil (LGO) was hydrotreated over commercial NiMO/Al2O3 catalysts in a trickle bed reactor. Statistical design of experiments was used to develop response surface models for predicting percentage conversions of aromatics, sulfur, and nitrogen in the LGO feed from Athabasca oil sands. The statistical approach was also used to study the effect of process variables and their interaction on aromatic hydrogenation (AHYD), hydrodesulfurization (HDS), and hydrodenitrogenation (HDN) activities. The two-level interaction between temperature and pressure was determined to affect AHYD significantly, whereas the interaction between temperature and the liquid hourly space velocity (LHSV) was the most important parameter affecting both HDS and HDN activities. Optimal conditions for the conversion of aromatics were observed at a temperature of 379 degrees C, a pressure of 11.0 MPa, and an LHSV of 0.6 h(-1). Under these conditions, a maximum conversion of 63% can be attained. The cetane index of the diesel fraction was affected by changes in the aromatic compounds, as well as by the temperature and pressure of hydrotreating. Product distribution and gasoline yield of the liquid products were also greatly influenced by the reaction temperature, with a slight impact from pressure and LHSV. The kinetics of AHYD was modeled using a singe-site mechanism form of the Langmuir-Hinshelwood rate of reaction, whereas HDS and HDN were best described by an irreversible pseudo-first-order power-law reaction. Results of the kinetic studies showed significant inhibition of hydrogenation by hydrogen sulfide (H2S) gas produced during the HDS process.