Systematic investigation of Iranian Vacuum Bottom hydrodenitrogenation to produce clean fuel oil for marine transportation

Recent environmental regulations have urged refiners to decrease NO_x emissions related to fuels particularly used in marine transportation. To this, hydrodenitrogenation (HDN) of Iranian Vacuum Bottom (IVB), as one of the most abundant but problematic effluents of Iranian refineries used for marine applications, was evaluated for the very first time via batch hydrotreating procedure over a commercial NiMo catalyst. First, the feed material's physicochemical properties were fully analyzed using several analytic techniques such as CHNS, micro-carbon residue, and TGA. Process chemistry of the HDN and mild hydrocracking (MHC) processes was studied systematically following an L₉-assisted design of experiment (Taguchi method) whereby temperature (350–410 °C), reaction time (1–3 h), oil content:catalyst ratio (1.5–2.5), and H₂ initial pressure (3.0–7.0 MPa) were considered as control factors. Adding to the highly pre-pressurized medium (H₂ initial pressure of 7.0 MPa) at elevated temperature (410 °C) as the most favorable condition for HDN and MHC reactions, results also highlighted a few critical interactions between the operating variables. The key was simultaneous saturation and decomposition of the highly aromatic nature of IVB, under which 65.3% of nitrogen impurities were taken out of the feed’s recalcitrant network. Notably, we took advantage of some well-known analytic techniques like Sim Dis and GC–MS to shed light on the origin of the N-containing compounds in the feed material and physicochemical characteristics of liquid products. These fuel-related analyses provided us a deeper look into the process chemistry using thermodynamic and kinetic backgrounds.