Kinetic Study for Plasma Assisted Cracking of NH₃: Approaches and Challenges

Abstract

Ammonia is considered as one of the promising hydrogen carriers toward a sustainable world. Plasma assisted decomposition of NH 3 could provide cost-and energy-effective, lowtemperature, on-demand (partial) cracking of NH 3 into H 2 . Here, we presented a temperature-dependent plasma-chemical kinetic study to investigate the role of both electron-induced reactions and thermally induced reactions on the decomposition of NH 3 . We employed a plasma-chemical kinetic model (KAUSTKin), developed a plasmachemical reaction mechanism for the numerical analysis, and introduced a temperature-controlled dielectric barrier discharge reactor for the experimental investigation using 1 mol % NH 3 diluted in N 2 . As a result, we observed the plasma significantly lowered the cracking temperature and found that the plasma-chemical mechanism should be further improved to better predict the experiment. The commonly used rates for the key NH 3 pyrolysis reaction (NH 3 + M ↔ NH 2 + H + M) significantly overpredicted the recombination rate at temperatures below 600 K. Furthermore, the other identified shortcomings in the available data are (i) thermal hydrazine chemistry, (ii) electron-scattering cross-section data of N x H y , (iii) electron-impact dissociation of N 2 , and (iv) dissociative quenching of excited states of N 2 . We believe that the present study will spark fundamental interest to address these shortcomings and contribute to technical advancements in plasma assisted NH 3 cracking technology.

Ammonia as a Carbon-Free Energy Carrier: NH3 Cracking to H2

“…In cold plasma, ammonia is dissociated at modest temperature, exploiting the high-energy electrons, with a consequently low H 2 generation rate. Examples of cold plasma applications include dielectric barrier discharge (DBD) , and microhollow cathode discharge (MHCD). , A DBD reactor was used by Bang and coauthors with the aim of developing a plasma-chemical kinetic mechanism for the NH 3 decomposition …”

“…94,95 A DBD reactor was used by Bang and coauthors with the aim of developing a plasma-chemical kinetic mechanism for the NH 3 decomposition. 96 Warm plasma can maintain a moderate gas temperature for ammonia decomposition, with nonthermal arc plasma (NTAP) as one of the fundamental methods for warm plasma generation. In 2014, Zhao et al 97 designed a NTAP reactor using two tube electrodes driven by alternating current.…”

Combustion in a Sustainable World: From Molecules to Processes

“…For the technical application of ammonia as a combustion fuel, its low reactivity must be enhanced by the addition of promoters in the fuel mixture. , The reactivity and oxidation reactions of ammonia have been analyzed in the presence of such blending compounds as hydrogen, methane, methanol, and ozone in jet-stirred and flow reactor as well as shock tube experiments, providing valuable data sets for model improvement. , Efficient use of ammonia as a hydrogen carrier requires effective cracking procedures to release hydrogen on demand. Bang et al investigated a plasma-assisted process to lower the cracking temperature and performed kinetics experiments using a temperature-controlled dielectric barrier discharge reactor . From the comparison of the reaction behavior without and with plasma and the analysis of available reaction mechanisms, they derived targets for further research, including reactions of N 2 H x species, electron scattering cross sections for a number of species, and rate expressions for reactions of excited species …”

“…Bang et al investigated a plasma-assisted process to lower the cracking temperature and performed kinetics experiments using a temperature-controlled dielectric barrier discharge reactor. 38 From the comparison of the reaction behavior without and with plasma and the analysis of available reaction mechanisms, they derived targets for further research, including reactions of N 2 H x species, electron scattering cross sections for a number of species, and rate expressions for reactions of excited species. 38 Organic nitrate propellants, energetic compounds that can decompose by exothermic reactions without additional oxygen, are used, for example, for spacecraft to generate thrust or for underwater applications.…”

“…38 From the comparison of the reaction behavior without and with plasma and the analysis of available reaction mechanisms, they derived targets for further research, including reactions of N 2 H x species, electron scattering cross sections for a number of species, and rate expressions for reactions of excited species. 38 Organic nitrate propellants, energetic compounds that can decompose by exothermic reactions without additional oxygen, are used, for example, for spacecraft to generate thrust or for underwater applications. 39,40 The pyrolysis kinetics of isopropyl nitrate as a nontoxic, noncorrosive compound with potentially superior properties compared to hydrazine and its derivatives has been studied both numerically and experimentally by Vin et al 39 Such studies are also important for understanding the destruction behavior of explosives, for which isopropyl nitrate can serve as a surrogate.…”