Liquid-phase adsorption of nitrogen compounds from model diesel fuel on activated carbons

Abstract

One of the great challenges in deep hydrodesulfurization (HDS) to produce ultra-low-sulfur diesel (ULSD) is the coexisting heterocyclic nitrogen-containing compounds in middle distillates, which significantly inhibit the HDS reactions. This study investigates various activated carbon (AC) samples for selectively removing nitrogen compounds from a model diesel fuel through adsorption. The physical and chemical properties of the AC samples were characterized using low-temperature N2 adsorption–desorption, SEM–EDS, and FT-IR to explore their impact on the adsorption performance. The results indicate that the adsorption performance is influenced not only by the surface area and by the number of oxygen-containing functional groups on the surface but also by the pore diameter distribution. Among all AC samples tested, AC-W exhibited the highest adsorption capacity, achieving a nitrogen removal rate of 97.8% with the addition of 10 wt.% of AC-W. The adsorption capacity was approximately 24.0 mg-N/g-A at a nitrogen equilibrium concentration of 200 ppmw. The adsorption isotherms for total nitrogen and individual nitrogen compounds in the fuel over AC can be described well by the Freundlich isotherm model. An approach for improving the ADN performance of AC is discussed based on the findings in this study.