Activated hydrochar from areca sheath biomass for CO₂ capture: adsorption performance and life cycle challenges

The development of sustainable CO₂ capture technologies is critical in the present global drive to combat climate change. Hydrochar, obtained from hydrothermal carbonization (HTC), has demonstrated capabilities to adsorb CO₂. This study evaluates activated hydrochar derived from areca sheath biomass for CO₂ capture, associated with a life cycle assessment (LCA) study. Hydrochars were produced at 180 °C (AS-180), 200 °C (AS-200), and 220 °C (AS-220), followed by chemical activation using KOH at a KOH : hydrochar mass ratio of 3 : 1 and carbonization at 700 °C for 2 h to enhance microporosity. AS-200 achieved the highest surface area (144 m² g^-1), outperforming AS-180 and AS-220. Life cycle assessment of sorbent production reveals pronounced differences in climate change impacts, with AS-200 exhibiting the lowest carbon footprint (235 kg CO₂-eq. per kg), followed by AS-220 (611 kg CO₂-eq. per kg) and AS-180 (941 kg CO₂-eq. per kg). Across all cases, chemical activation using KOH dominates emissions (about 67%), while fossil-derived thermal energy contributes about 16%, identifying upstream chemical manufacture and energy supply as primary hotspots. AS-200 achieves the highest measured CO₂ adsorption capacity (2.5 mmol g^-1). Under the baseline inventory with an assumed 1% sorbent makeup, its adsorption-regeneration LCA gives 2.55 kg CO₂-eq. per kg CO₂ processed, with fresh-sorbent production contributing substantially. This modelled climate burden is conditional on the replacement assumption; cyclic stability and the actual replacement requirement were not established. The baseline assessment identifies upstream sorbent manufacture as a priority for reducing emissions. Wastewater-treatment burdens are excluded from these baseline totals.