Adsorptive denitrogenation and desulfurization of diesel using activated carbons oxidized by (NH₄)₂S₂O₈ under mild conditions

(NH₄)₂S₂O₈ solutions were applied to oxidize a wood-based activated carbon (AC) under different conditions. Oxidation decreases the specific surface area of AC samples but increases the oxygen functional groups. Carboxylic acid groups and ketone groups may facilitate the adsorption of nitrogen (N) and sulfur (S) compounds in light cycled oil (LCO). An appropriate adsorbent was determined as the oxidized carbon which shows high N removal from LCO. The resultant adsorbent, AC-(NH₄)₂S₂O₈-15%-1.5, exhibits higher adsorption capacities for N and S compounds than the original carbon in dynamic adsorption of a model diesel fuel. Carboxylic acid groups and lactone groups might favour quinoline adsorption. Carboxylic anhydride groups and phenolic groups are likely to improve the adsorption of indole, carbazole and dibenzothiophene (DBT). The thermodynamic and kinetic behaviours of AC-(NH₄)₂S₂O₈-15%-1.5 were investigated. The adsorption of carbazole on AC-(NH₄)₂S₂O₈-15%-1.5 follows the Langmuir model, while that of quinoline, indole and DBT follows the Freundlich model. All the adsorption processes are spontaneous, with the nature of adsorption for indole and carbazole endothermic, and that for quinoline and DBT exothermic. The adsorption of the N and S compounds in this study follows a pseudo second-order model. Intra-particle diffusion is one of the rate-controlled steps for N compounds.