Nutshell waste to carbon strategy for sustainable model diesel fuel desulfurization: Role of surface chemistry and aromatic interference

Within the framework of circular-economy materials design strategies aimed at turning wastes into solutions, this study addresses the challenge of ultradeep desulfurization of transportation fuels at ultralow sulfur concentrations under realistic conditions, a critical requirement for environmental compliance and catalyst protection. To this end, cashew nutshell waste was sustainably converted into activated nanoporous carbons (ACs) and evaluated as adsorbents for sulfur removal. The novelty of this work lies in performing ultradeep desulfurization tests (at an initial sulfur concentration of 20 ppmwS) in the presence of ultra-high mono- and bi-aromatic contents, thereby closely mimicking the competitive adsorption environment of real fuels. Unlike most previous studies, the experiments were conducted under mild conditions (25 °C, 1 atm) and using a low adsorbent-to-fuel ratio (2.5 g L −1 ), under which the carbons showed the highest desulfurization efficiency. To elucidate the influence of carbonization temperature on desulfurization performance and its correlation with surface chemistry and microporosity, a series of nutshell-derived activated carbons was synthesized by varying the activation/carbonization temperature between 400 and 700 °C. The AC obtained at 600 °C exhibited superior adsorption capacities (up to 21.1 mg S g −1 ) and removals (up to 53%) of thiophenic sulfur compounds (4,6-DMDBT and DBT) at an ultralow initial sulfur concentration (20 ppmwS), outperforming many biomass-derived adsorbents reported in the literature and exceeding the performance of a commercial benchmark carbon (BAX) by 22%. The presence of benzene and naphthalene had a negative impact on adsorption performance, confirming their antagonistic effects. The carbons obtained at 600 and 700 °C showed greater declines in sulfur uptake compared with those prepared at 400 and 500 °C, suggesting possible differences in adsorption mechanisms or active sites. Physicochemical characterization revealed that the surface chemical heterogeneity decreases with increasing treatment temperature, while the highest porosity was obtained at 600 °C. Overall, it was concluded that microporosity and surface functional group density should be balanced towards high desulfurization, since the micropores with sizes comparable to thiophenic molecules play a key role, whereas high surface chemical heterogeneity can hinder sulfur removal. These findings demonstrate that nutshell-derived activated carbons, particularly the material carbonized at 600 °C, combine high desulfurization efficiency with sustainable feedstock utilization, offering a promising and scalable pathway for industrially relevant ultradeep desulfurization of fuel streams.