Study of a gliding arc discharge for sustainable nitrogen fixation into NOx

With the growth of the world population, the agricultural sector is required to meet an increasing demand for nutrients.In order to achieve this, since decades the sector has relied on industrially produced fertilizers to increase its production yield.Among them, nitrogen-based fertilizers are the most common choice, although their production requires inert N 2 to be converted into more reactive molecules, such as nitric oxides NO x or ammonia NH 3 , in a process called "nitrogen fixation".Today, this is mainly performed in industry through the well-known Haber-Bosch process.Despite being the dominant choice for industrial nitrogen fixation for over a century because of an almost perfect optimization, the Haber-Bosch process is not ideal since it requires large-scale facilities to be economical and is associated with a high energy cost and high CO 2 emissions, thus, resulting in an environmental impact that is pushing for the study of different, greener, alternatives.Among several options, plasma-based nitrogen fixation to NO x is considered a promising alternative to Haber-Bosch, thanks to (i) the possibility of implementing the technology at lower scales, (ii) its compatibility with intermittent, renewable energy sources, and (iii) the absence of direct CO 2 emissions.In this context, a type of plasma reactor that proved to be particularly suitable for nitrogen fixation is the gliding arc plasma, as it operates at atmospheric pressure and of NO and NO 2 produced are discussed revealing how the conversion into NO 2 is already significant in the plasma afterglow region and the input gas flow rate is a crucial parameter affecting the temperature gradients in the afterglow region.From a technological point of view, the conventional approach of introducing external resistors to stabilize the arc is challenged by studying both the performance and the stability of the plasma replacing the external resistor with an inductor.From this work, we conclude that similar stabilization results can be obtained while significantly lowering the overall energy cost, which decreased from up to a maximum of 7.9 MJ/mol N to 3 MJ/mol N.Finally, this thesis studies whether a hypothetical small-scale fertilizer production facility based on a rotating gliding arc plasma for nitrogen fixation can be a local competitive alternative for the Haber-Bosch process.This is done by proposing a comparative model to understand how capital expenditures, gas price, CO 2 allowances, levelized cost of energy, and transport costs affect the fertilizer production costs.The model highlights how, with the current best available technology, plasma-based nitrogen fixation, while being an interesting alternative for the synthesis of NO x , still requires a more efficient use of H 2 for a direct production of NH 3 .Four years may seem a long period when you are in your 20s, but, as it happens for all the enjoyable things in life, my Ph.D. years felt as fast as a blink of an eye.Since the very beginning, I've been welcomed in a warm, friendly, and fertile environment that made me quickly grow both professionally and personally.I've felt at home and, for this reason, I would like to express my deepest gratitude to the many people who made this journey as special as it turned out to be.First of all, I want to thank Rony and Annemie.This thesis would not have been possible without your help and mentoring.Whenever I was in need I always found kindness, support, and brilliant advice from you.I honestly feel extremely lucky to have had the pleasure to work with you, and I hope you can say "he was my student" as proudly as I can say that you two were my promoters!This journey wouldn't have been as fulfilling and fun without the friends and colleagues I've met along the way.I must, of course, mention my "international" friends and colleagues Abhyuday, Omid, Kseniia, Anastasiya, Mariam, and, more generally, all the Ph.D. students and postdocs I've had the pleasure to meet in these four years.Your help has been invaluable and wide, ranging from jokes to scientific expertise.It is inevitable: our paths may diverge and separate us by hundreds or thousands of kilometers, but I will never forget you and what we went through together.A special thank goes to the "équipe d'intégration accélérée": Nathan,