Environmental Impacts and Adsorption Isotherms of Coconut Shell Activated Carbon: Effect of Acids Activation, Water, and Fuel

Abstract

Activated biomass has gained interest as an alternative to coal-based activated carbon (AC). This study investigates the potential of coconut shell (CS)-derived AC as a substitute for non-renewable coal-based AC, using tandem acid activation and pyrolysis with two activation pathways: sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄). This work has the following merits: (i) evaluating environmental impact (EI) based on actual experimental data and its comparison with commercial coal-based AC; (ii) providing dye adsorption isotherms for acid-activation pathways; and (iii) emphasizing the role of activation-route, fuel source and water used in the process in reducing the EIs. The evaluation focuses on six key impacts: climate change, fossil depletion, freshwater ecotoxicity, freshwater eutrophication, land use, and energy net. The H₂SO₄ activation pathway is more favorable in terms of EI due to its lower net energy requirement (27.2 MJ) and reduced carbon emissions (1.18 kg CO₂ eq.). However, it requires 4.7 kg of AC to adsorb 1 kg of dye, whereas the H₃PO₄ pathway requires only 4.3 kg. Therefore, while the H₃PO₄ pathway may be preferred for applications needing higher adsorption capacities, the H₂SO₄ pathway offers a more environmentally benign option, highlighting the trade-offs in selecting an activation method for AC production. Additionally, the study highlights that CS-derived AC offers substantial energy savings of 78%, alongside a 75% reduction in carbon emissions and an 80% decrease in fossil depletion compared to coal-based AC. Overall, the synthesized AC shows promise as a sustainable alternative to coal-based counterparts.

Keywords: biomass, Coconut Shell, activated carbon, adsorption isotherm, Climate Change, Net Energy