Numbering up and sizing up gliding arc reactors to enhance the plasma-based synthesis of NOx†

Non-thermal plasma-based NO_x synthesis from ambient air is receiving an increasing amount of interest for its potential in small-scale, sustainable fertilizer production. Nevertheless, most reported research focuses on lab-scale systems and a single reactor with limited production. In this work, two gliding arc reactors (GARs) with 2 mm discharge gaps were connected in series or in parallel to explore strategies for scaling up the productivity. A single GAR with an enlarged discharge gap of 4 mm was also investigated for comparison. Operation parameters such as flow rate, discharge power & mode, and effective residence time were tested. The NO_x concentration increased for all configurations with an increase in specific energy input (SEI), and effective residence time. The case of reactors connected in series outperformed all other configurations. The energy consumptions and NO_x productions achieved were 2.29–2.42 MJ mol_N⁻¹ and 124.6–158.3 mmol_N h⁻¹, respectively. The NO₂ selectivity could be enhanced by prolonging the post-plasma oxidation time while consuming the excess O₂ in the feed and utilizing the low temperatures at the reactor(s) outlet. By using this connection strategy, NO_x production can be doubled with a 20.9% improvement in energy consumption compared to a single reactor.