Changing biomass into carbon-negative through dual-step approach: CO2-assisted pyrolysis and biochar-based CO2 adsorption

To realize carbon negativity in the valorization of biomass waste, a dual-step approach was investigated: the CO₂-assisted pyrolysis of sugarcane bagasse and CO₂ adsorption using biochar. Energy (syngas) production from CO₂-assisted pyrolysis was higher than that from conventional pyrolysis (sugarcane bagasse pyrolyzed under N₂ conditions) because of the reaction between CO₂ and the volatiles liberated from the thermolysis of sugarcane bagasse. The use of catalysts promotes the reaction, thereby enhancing syngas generation. Because of CO₂ reaction participation during pyrolysis, 97.9 mg of CO₂ was consumed (per 1 g of sugarcane bagasse) in CO₂-assisted pyrolysis, whereas conventional pyrolysis emitted 132.5 mg of CO₂. The CO₂ adsorption capacity of biochar produced from conventional/CO₂-assisted pyrolysis was evaluated to assess its potential for direct air capture. The CO₂ adsorption capacity of the biochar produced from CO₂-assisted pyrolysis (74.86 mg g⁻¹) was higher than that of the biochar produced from conventional pyrolysis (70.35 mg g⁻¹) because of enhanced micropore development under CO₂ conditions. Given the annual generation of sugarcane bagasse (526 Mt), it was estimated that 60.0 Mt of CO₂ could be treated using this dual-step approach. The results of this study will contribute to the establishment of sustainable waste management, particularly in terms of carbon management. By combining CO₂ consumption during pyrolysis and enhancing the CO₂ adsorption capabilities of biochar, this approach offers a carbon-negative solution for biomass waste valorization.