Amarula Waste to Activated Carbon: A Low-Cost Adsorbent for Deep Desulphurization of Model Diesel Fuel

This study aimed to address two significant environmental challenges: waste management and climate change mitigation, by converting biomass waste from Amarula liqueur production into activated carbon (AC) for adsorptive desulphurization. Biomass from Amarula fruit, seed, and shell waste was subjected to pyrolysis at 800 °C and steam activation (45 min), producing activated carbon with surface areas of 740, 437, and 245 m²/g, and pore volumes of 0.37, 0.21, and 0.17 cm³/g, respectively. Furthermore, shell-derived carbon activated for 90 min achieved a significantly higher surface area of 1194 m²/g and a pore volume of 0.98 cm³/g with commercial prospects. The activated carbons were evaluated for their ability to remove dibenzothiophene (DBT) from a model diesel fuel in a batch reactor. Desulfurization efficiencies of 65 ± 4, 54 ± 3, and 31 ± 6% were achieved for the fruit-, seed-, and shell-derived carbons, respectively. Notably, the shell-based activated carbon produced with extended steam exposure exhibited the highest adsorption efficiency of 73 ± 3% for model fuel. However, its poor activity for conventional diesel was attributed to the poor selectivity of the adsorbent. The desulfurization performance was found to be strongly influenced by the presence of surface O-functional groups and the adsorbents' textural properties. In conclusion, the study demonstrates that Amarula biomass waste can be valorised into effective activated carbons for cleaner fuel applications, though further optimization is needed to enhance selectivity and extend their applicability across a wider range of fuel systems.