Life Cycle Assessment of CO ₂ Conversion to Single-Walled Carbon Nanotubes via Tandem Thermocatalysis

This study presents a cradle-to-gate life cycle assessment of the production of single-walled carbon nanotubes (SWCNTs), focusing on a tandem thermocatalytic CO2 conversion process. This process involves CO2 methanation over Ni/SiO2 followed by methane pyrolysis over Fe–Mo/MgO. This process enables the direct utilization of captured CO2 for synthesizing high-value carbon materials. The system was designed as a pilot-relevant continuous production framework under steady operation, with a defined SWCNTs output target of approximately 50 kg/day. Environmental impacts were assessed with a primary focus on global warming potential (GWP). The results demonstrate that the GWP of the tandem process is primarily influenced by electricity consumption in the high-temperature reaction units, particularly the methane pyrolysis reactor. Across various electricity supply scenarios, including domestic grid electricity, natural gas-based power generation, and photovoltaic power, the total GWP ranges from 46.45 to 109.6 kg CO2-eq per kg of SWCNTs produced. Overall, these findings provide valuable quantitative insights into the environmental impact of producing SWCNTs from CO2 and highlight the importance of increasing yield and decarbonizing electricity to mitigate climate impacts.