Synthesis of activated carbon from oil fly ash for removal of H ₂ S from gas stream

Activated carbon (AC) is made from waste oil fly ash (OFA) which is produced in large quantities from power generation plants through combustion of heavy fuel oil. OFA contains ∼80% carbon that makes it suitable for producing AC by physicochemical treatments using a mixture of HNO ₃ , H ₂ SO ₄ , and H ₃ PO ₄ acids to remove non-carbonaceous impurities. The acid treated OFA is then activated by CO ₂ at 990°C. The physico-chemical treatments of OFA have increased the surface area from 4 to 375 m ² /g. Surface morphology and pore volume of AC are characterized by combined SEM and EDX techniques. Elemental analysis shows that sulfur content is reduced from 7.1 wt% in untreated OFA to 0.51 wt% for the treated OFA. The AC is further treated with HNO ₃ and NH ₄ OH solutions in order to attach the carboxylic and amine groups on the surface, respectively. FTIR characterization is used to confirm the presence of the functional groups on the surface of AC at different stages of its development. The performance of functionalized AC samples is tested for the removal of H ₂ S from a synthetic natural gas by carrying out breakthrough experiments. The results from these tests have shown maximum adsorption capacity of 0.3001 mg/g for NH ₄ OH functionalized activated carbon with 86.43% regeneration efficiency. The ammonium hydroxide treated AC is found to be more effective for H ₂ S removal than acid treated AC as confirmed by breakthrough experiments. The results indicate that the presence of more acidic functionalities on the surface reduces the H ₂ S adsorption efficiency from the gas mixture.