Plasma-Based NH3 Cracking: A Better Insight in the Performance by Chemical Kinetics Modeling

Abstract

This study examines performance characteristics of (warm-)plasma-based NH3 cracking using a detailed plasma chemical kinetics model across a wide range of gas temperatures (Tg = 1000–6000 K) and electron temperatures (Te = 0–3.5 eV, i.e., 0–40,000 K). NH3 conversion increases with both temperatures, but the Tg-dependence flattens near full conversion. Pure thermal cracking reaches full conversion at 2300 K and 10 ms, while plasma achieves full conversion at Te > 2.75 eV for all Tg, even the lowest Tg values investigated. At Tg < 2700 K, high Te dramatically reduces the time for full conversion, for example, from thousands of years (thermal) to milliseconds (plasma) at Tg = 1100 K, while differences vanish at Tg > 2700 K. Product composition follows thermal equilibrium, showing negligible Te influence. Importantly, we also suggest strategies for performance improvement. The best energy cost for typical warm plasmas with continuous power is predicted to be 197 kJ/mol-NH3 at 2500 K, where thermal pathways dominate. Reducing vibrational energy losses suggests potential improvement at Tg ≈1500 K, predicting an energy cost of 157 kJ/mol-NH3, for so-called “plasma-initialized” thermal cracking. Further reduction in energy cost should be feasible via heat recovery. Overall, our model shows that plasma cracking offers rapid NH3 conversion with reasonable energy cost.