CO₂ removal by applying the adsorption process to biochar from waste materials

This study evaluated lignocellulosic residues as low-cost adsorbents for CO₂ capture in a dynamic column system, focusing on spent coffee grounds biochar (SCGB) as an alternative to commercial activated carbon. Commercial activated carbon, SCGB, magnetized SCGB, KOH-activated SCGB, peanut shell pellet charcoal, sugarcane bagasse charcoal containing kaolin, and calcined SCGB samples were tested. SCGB was produced by pyrolysis and modified by chemical activation, magnetite incorporation, or post-pyrolysis calcination. CO₂ adsorption tests were performed in a column under different air and CO₂ inlet flow rates, and CO₂ concentrations were monitored at the inlet and outlet using infrared sensors. The adsorption capacity ranged from 0.43 to 7.17 mmol CO₂/g, depending on the adsorbent and operating conditions. The best performance was obtained for non-activated SCGB, which reached 7.17 mmol CO₂/g under intermediate air flow conditions. Although KOH activation improved the textural properties of SCGB, it did not lead to the highest adsorption capacity in the column. These results indicate that CO₂ capture under dynamic conditions is controlled not only by BET surface area and micropore volume, but also by pore accessibility, surface chemistry, bed behavior, and gas residence time. Spent coffee grounds biochar showed competitive CO₂ adsorption performance and may be considered a promising low-cost adsorbent for carbon capture applications. The results support the use of biomass-derived residues in column-based CO₂ mitigation processes, while highlighting the need for further studies on humidity tolerance, regeneration, and scale-up.