Secondary waste to highly efficient nanoporous carbon: The role of acidic minerals in diesel fuel desulfurization

Adsorptive desulfurization of liquid fuels with cost-effective adsorbents, like waste-derived carbons, has been extensively researched. In this work a (bio)char from gasification of waste mixed biomass was chemically treated with H₃PO₄ and pyrolyzed at 600 °C. The obtained nanoporous carbon (CERAF) was used for the deep adsorptive desulfurization of model diesel fuels, at ambient conditions. CERAF had a specific surface area of 795 m²/g with a micro- and meso-pore structure, and rich surface chemistry. Desulfurization efficiency reached 74 % (5.2 ppmwS of treated solution) starting with low initial concentration of 4,6-dimethyldibenzothiophene (4,6-DMDBT, 20 ppmwS) in hexadecane and relatively low amount of carbon (2.5 g/L). Two commercial nanoporous carbons exhibited lower desulfurization efficiencies than CERAF, despite their higher surface area and pore volumes. CERAF also showed the highest efficiency for complex model fuel (mimicking real diesel), containing 4,6-DMDBT and high concentrations of mono- and di-aromatics. Detailed physicochemical characterization suggested that the chemical composition of the adsorbent, especially the presence of silicates provide weak acidic sites promoting specific interactions with DMDBT, enhancing the desulfurization efficiency. In addition, the inorganic matter might play an important role in the carbonization and/or activation of the biochar to the nanoporous carbon CERAF. Overall, the main novelty of this work is in the utilization of a secondary char/waste of mixed biomass to produce nanoporous carbon and in highlighting the effect of specific mineral matter on adsorptive desulfurization.