(2025) Thermal Science and Engineering Progress_Carbon negative pyrolysis system for the valorization of agricultural waste into syngas

Kim J.-H.; Lee T.; Lee D.; Chen W.-H.; Kwon E.E.

(Elsevier Ltd) Thermal Science and Engineering Progress ISSN: 24519049 Vol.65 Issue. Article No.103927 DOI: 10.1016/j.tsep.2025.103927

 High cost of biofuel production remains a major barrier to replacing fossil fuels, largely because of the low energy density of feedstocks. The utilization of non-edible biomass waste is a viable strategy for cost-effective biofuel production. Here, we explored the pyrolysis of walnut husk (WH) as a model non-edible biomass, employing CO₂ as a reactive gas to enhance sustainability and economic feasibility. Under CO₂-rich atmospheres, single-phase reactions involving CO₂ and volatiles released from WH resulted in distinct syngas (H₂ and CO) production trends compared to N₂ atmospheres. The introduction of a Ni/Al₂O₃ catalyst further amplified these effects, increasing CO production by 162.6% relative to the reference case. Notably, the CO₂-assisted catalytic pyrolysis of WH has been shown to generate sufficient energy to sustain the walnut industry while sequestering CO₂ at levels that could offset its emissions. Given the CO₂ consumption during the process, the resulting H₂ and CO can be classified as carbon-negative syngas, highlighting the potential of WH as a renewable feedstock in a circular bioeconomy. © 2025 Elsevier Ltd

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT) (No. RS-2023-NR077231). Jung-Hun Kim also acknowledges the financial support from the Hyundai Motor Chung Mong-Koo Foundation.