Environmental analysis of plasma-based nitrogen fixation powered by renewable energy

This study assesses the environmental performance of plasma-based nitric acid (HNO₃) production powered by renewable electricity using process modelling and comparative life cycle assessment. Two plasma technologies, a gliding arc plasmatron (GAP) and a rotating gliding arc (RGA), were evaluated under air-fed (N₂ : O₂ 4 : 1) and oxygen-enriched (N₂ : O₂ 1 : 1) configurations using experimental reactor data and real photovoltaic (PV) generation profiles, and were benchmarked against the conventional steam methane reforming-Haber-Bosch-Ostwald process. At atmospheric pressure and an annual electricity mix of 41.5% solar, plasma-based routes show global warming impacts of 1.82-2.25 kg CO₂ eq. per kg HNO₃, while the conventional route emits 1.93 kg CO₂ eq. per kg HNO₃ at the factory gate. When the solar share is over 60%, all plasma plant configurations emit lower carbon than the benchmark, reaching emissions as low as 0.99 kg CO₂ eq. per kg HNO₃ for the air-fed GAP reactor when the plant is powered 100% by solar PV. The results were also highly sensitive to future improvements in plasma electricity demand: a scenario reducing demand by 20% decreased climate change impacts by approximately 11-18%, with all four plasma configurations achieving lower impacts than the benchmark. Similar benefits were observed for ozone formation and terrestrial acidification. Seasonal variation in solar/grid share (18-64%) changed global warming impacts by approximately 43%. Plasma routes also showed higher toxicity and land use impacts, mainly due to electrical infrastructure and PV systems. Oxygen enrichment improved NO _x yields but required additional energy for O₂ production; it became environmentally favourable only below approximately 0.5 kWh kg^-1 O₂. Elevated-pressure RGA operation at 4 bar substantially improved performance, reducing total plant energy cost by 43% and 27% for the 4 : 1 and 1 : 1 configurations, respectively, and lowering global warming impacts to 1.19 and 1.10 kg CO₂ eq. per kg HNO₃. Overall, plasma-based HNO₃ production shows strong low-carbon potential, particularly under elevated-pressure operation.