Assessing carbon negative potential in CO2-mediated pyrolysis of agricultural residue

Abstract

Wheat straw (WS), one of the most abundant agricultural residues, has garnered attention as a renewable alternative to petroleum-derived carbon resources. However, current biofuel production faces challenges in realizing efficient carbon use. To address this, pyrolysis offers a promising platform capable of converting all the carbon in WS into value-added pyrogenic products such as syngas, biocrude, and biochar. This study focused on enhancing carbon-negative potential of WS pyrolysis by incorporating carbon dioxide (CO₂) as partial oxidant and carbon resource. At temperatures ≥ 430˚C, CO₂ interacted homogeneously with volatiles pyrolyzed from WS and converted them into carbon monoxide (CO), contributing to carbon-negative character to the pyrolysis system. To accelerate the kinetics of CO₂-driven reactions, the pyrolysis setup was systematically modified by delivering an additional heat and introducing a nickel catalyst. Additionally, two process parameters (reaction temperature and CO₂ concentration) were tailored to optimize CO-rich syngas production. The energy requirements and net CO₂ emissions of CO₂-mediated catalytic pyrolysis were evaluated under optimal conditions. CO₂-mediated catalytic pyrolysis of WS demonstrated a carbon-negative potential of 1260 mg CO2 per gram of WS. Therefore, this finding offers opportunities to suppress 1235 million tons of CO₂ annually across the agricultural sector linked to wheat straw harvest.