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.