Carbon-negative footprint in syngas production through aquatic plant pyrolysis

초록

In the global pursuit of carbon neutrality, biofuels have gained attention as sustainable alternatives to fossil fuels. However, the large-scale deployment of biofuel remains constrained by the insecure feedstock availability, largely due to geographical limitations and climatic sensitivity. To overcome these challenges, duckweed (DW) was chosen as a pyrolysis feedstock in this study because of its high biomass productivity, and strong environmental resilience. To further improve process sustainability, CO2 was employed as a reactive gas medium. During DW pyrolysis, CO2-driven gas-phase interactions (GPIs) with volatile matters (VMs) reduced the yield of oxygen- and nitrogen- containing chemical compounds in biocrude, while simultaneously increasing CO-rich syngas production. Specifically, CO2 partially oxidizes the VMs and was reduced to CO, redirecting carbon distribution from liquid biocrude fraction toward CO-rich syngas. The partial oxidation of volatile intermediates by CO2 also improved the structural property of the resulting DW-derived biochar, favoring its functionality for air pollutant adsorption potential. The combined application of additional thermal energy and a Ni/Al2O3 catalyst further intensified CO2-driven GPIs, increasing CO-rich syngas production and establishing a favorable carbon conversion. Carbon footprint analysis demonstrated that the CO2 mitigation achieved via syngas generation and biochar utilization exceeded the process-related CO2 emissions associated with CO2-assisted pyrolysis, thereby enabling the production of carbon-negative syngas. The process achieved a net CO2 reduction of 2226.7 kt, representing 5.3 times enhancement over conventional pyrolysis. Collectively, these findings demonstrate that CO2-assisted pyrolysis of DW represents a sustainable strategy for biomass valorization, simultaneously enhancing syngas production while achieving net-negative carbon emissions.

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