Removal of Hydrogen Sulfide from Biogas by Adsorption on Activated Carbon Derived from Cashew Tree Branches

Abstract

In the context of the energy transition, Côte d'Ivoire aims to increase the share of renewable energies in its energy mix, particularly by utilizing biogas. However, the presence of hydrogen sulfide (H₂S) in biogas poses technical and environmental challenges, necessitating its removal. This study explores the use of activated carbon derived from cashew tree branches as an adsorbent for biogas desulfurization. Cashew tree branches, an abundant byproduct of the cashew nut industry, were used as a precursor to produce activated carbon. The process involved chemical impregnation with different activating agents (H₃PO₄, NaOH, KOH), followed by carbonization at 500-550°C. The obtained activated carbon was characterized by determining its ash content, yield, pH at the point of zero charge, and iodine index. The results show that activation with KOH produced activated carbon with the highest adsorption capacity, achieving an iodine index of 923 mg/g and an average yield of 35.28%. The H₂S filtration test revealed an initial near-total removal of the gas (≈100%), with an efficiency maintained at 90.9% after 8 hours. The activated carbon did not reach its breakthrough time during the experiment, confirming its prolonged effectiveness. In conclusion, this study demonstrates that activated carbon derived from cashew tree branches is an effective adsorbent for biogas desulfurization. Its use could enable the local valorization of agricultural waste while contributing to the reduction of greenhouse gas emissions and the improvement of biogas quality.