Enhancing simultaneous hydrodesulfurization and hydrodenitrogenation reactions: Kinetic modeling of stacked NiMoP and CoMoP catalysts beds

Stringent environmental regulations require reducing fuel sulfur content for adequate operation of vehicle emission control systems. Deep hydrodesulfurization (HDS) removes over 99 % of sulfur compounds, including the less reactive ones like 4,6-dimethyldibenzothiophene (4,6-DMDBT). However, HDS kinetics is inhibited by compounds like H₂S, nitrogenous compounds, and aromatics. This article delves into kinetic modeling of concurrent hydrodesulfurization (HDS) of 4,6-DMDBT and hydrodenitrogenation (HDN) of quinoline (Q) reactions. It explored the use of stacked beds of CoMoP and NiMoP catalysts in two configurations. The effects of temperature and weight hourly space velocity (WHSV) on conversions and product yields were investigated. Higher reaction temperatures, in addition to the expected increase of 4,6-DMDBT and quinoline overall conversions, also led to an increased in hydrogenation selectivity. Kinetic models were developed for these reactions and catalysts, and kinetic parameters were estimated using a hybrid numerical procedure. The configuration where CoMoP was the first catalyst to encounter the reaction feedstock exhibited higher conversions for both reactions. The apparent activation energies for 4,6-DMDBT HDS were 99 and 41 kJ mol⁻¹ for NiMoP and CoMoP, respectively while for HDN, values of 62 and 68 kJ mol⁻¹ were estimated. For the adsorption enthalpy of nitrogenous compounds, values of −59 and −40 kJ mol⁻¹ were observed for NiMoP and CoMoP, respectively.