Interplay of Temperature and Pressure on Product Distribution in the Catalytic Hydrotreatment of Biowaste Oil

The upgrading of biomass-derived oils into transportation fuels remains challenging due to their high oxygen content, chemical instability, and the presence of heteroatoms. In this study, the catalytic hydrotreatment of thermo-catalytic reforming (TCR)-derived biowaste oil was investigated in a continuous fixed-bed reactor using a sul-fided Ni–Mo catalyst, focusing on the influence of hydrogen pressure (80–120 bar) at 350–390 °C. Hydrotreatment substantially improved fuel properties, increasing the higher heating value (HHV) from 41.9 to approximately 45.6 MJ kg.¹ while strongly reducing oxygen, nitrogen, and sulfur contents. Gas chromatographic analysis revealed a pro-nounced shift from oxygenated and aromatic compounds toward predominantly saturated hydrocarbons, comprising alkanes (62–64 area%) and cyclic hydrocarbons (~30 area%). The observed transformations are consistent with hydro-deoxygenation, hydrogenation, and secondary cracking reactions. Despite increasing hydrogen availability at higher pressures, only limited improvements were observed beyond 100 bar, indicating diminishing upgrading benefits at elevated pressure. The results demonstrate that efficient upgrading of waste-derived TCR oils can be achieved through a balanced combination of hydrogen availability and reaction severity, highlighting the importance of pressure optimi-zation for economically viable hydrotreatment processes.