Plasma efficient nitrogen fixation
Industrial scale nitrogen fixation (NF) via the Haber-Bosch process dominates artificial fertilizer production and at present, enables yield enhancements which nourish over 40 % of the world population. Owing to the exceptional stability of molecular nitrogen’s triple bond the Haber-Bosch process is an energy intensive chemical process which accounts for 1-2 % of the world's energy production, consumes 2-3 % of the global natural gas output and emits more than 300 million tonnes of CO2. In light of an increasing population (and fertilizer demand) coupled with an urgency to reduce CO2 emissions, efforts to find alternative technologies for NF that offer the potential of reduced energy usage while minimizing greenhouse gas emissions have accelerated. Electrically powered plasma processes are considered as a promising alternative for delocalized fertilizer production, based on renewable energy, and more specifically for NO production. To-date, however, plasma designs for NF have not exceeded Haber-Bosch efficiencies. Pulsed powered microwave (MW) generated plasma technology offers some promise in this regard. Pulsing of the discharge power enables strategies which direct energy to primarily heat electrons (’non-thermal’ conditions) providing a far more efficient pathway to molecular bond breakage (and resulting NO production) than thermal effects. Indeed, reports on pulsed powered MW discharges have indicated an opportunity to tune electron energies to maximize molecular vibrational excitation, identified as an optimal route for energy efficiency in NO production. In a novel advance, plasma efficient nitrogen fixation ’PENFIX', proposes to interrogate ’pulsed’ powered atmospheric microwave (MW) plasma for nitric oxide (NO) production using air. Novel reactor designs informed by validated modelling will be of particular focus. Diagnostic and modelling activities will elucidate the fundamental physics while addressing the challenges of future industrial scale deployment.