Sustainability assessment of plasma-based and electrolytic CO2 conversion to CO

Decarbonization technologies play a crucial role in addressing the global challenge of climate change by reducing the concentration of greenhouse gases, particularly carbon dioxide (CO2), in the atmosphere. Electrolysis- and plasma-based technologies have emerged as alternatives to partial combustion of fossil fuels for carbon monoxide (CO) production. A holistic sustainability assessment is required for decision-making from an environmental perspective from the early design. In this paper, Green Chemistry and circularity metrics together with life cycle assessment are used to identify hotspots and opportunities for both plasma-based and electrolytic CO2 conversion into CO, as compared with conventional procedures, such as incomplete fossil fuel combustion. In terms of environmental impacts, plasma- and electrolysis-based CO production exhibit reductions in 7 over 10 environmental impact categories when compared with the equivalent conventional process of partial combustion of fossil fuels, while electrolytic improvements are more modest. Particularly significant are the benefits in terms of acidification, freshwater ecotoxicity, and the use of fossil resources, with 86, 91, and 83 % impact reductions respectively for plasma, while 85, 87 and 77 % are the respective impact reductions for electrolysis. Sustainability metrics indicate a 40 % energy savings in plasma-based production compared to electrolysis. The essential recycling loop operation of unreacted CO2 increases the process circularity to material circularity indicator (MCI) values above 0.8, with the plasma process exhibiting 10 % higher MCI than electrolysis, in contrast to the partial combustion of fossil fuels, which is linear and non-restorative. In terms of Green Chemistry metrics, plasma-based CO production outperforms globally the electrolysis metrics by around 10–30 %.