One-dimensional non-isothermal modeling and parametric analysis of a hydrogen-based ammonia synthesis reactor

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Context—Ammonia synthesis is a key process in the global chemical industry, especially for fertilizer production and emerging hydrogen-based energy systems. With growing interest in green hydrogen, ammonia has gained attention as both an energy carrier and a chemical feedstock. Therefore, understanding reactor behavior under different operating conditions is essential, and mathematical modeling provides an effective tool for analyzing performance and evaluating parameter effects without extensive experimental work.Objective—The objective of this study is to develop a one-dimensional non-isothermal packed-bed reactor model for hydrogen-based ammonia synthesis and to evaluate the effects of key parameters, including inlet composition, pressure, and catalyst loading, on reactor performance.Method—The model is based on species mass balances, an energy balance, and pressure drop described by the Ergun equation. The reaction kinetics were represented using the Temkin–Pyzhev rate expression, which is widely used for ammonia synthesis systems. The governing differential equations were solved numerically in MATLAB using an ODE solver. The model predicts the axial variation of temperature, pressure, molar flow rates, mole fractions, and the conversions of nitrogen and hydrogen along the reactor length. A parametric analysis was then performed by systematically varying inlet hydrogen–nitrogen composition, inlet pressure, and catalyst amount.Results—Under the base operating conditions (Tin = 700 K, Pin = 35 bar, yH2 = 0.75, yN2 = 0.25, mcat = 3 g, ɛ = 0.40), the model predicts outlet nitrogen and hydrogen conversions of approximately 0.1161, while the ammonia molar flow rate at the reactor outlet reaches 3.84 × 10-5 mol/s. The results show that ammonia formation increases along the reactor length due to the progress of the exothermic reaction. Among the investigated parameters, inlet pressure has the most pronounced effect on ammonia production. The highest formation was observed at an inlet pressure of 100 bar, where the outlet ammonia molar flow rate reached 9.02 × 10-5 mol/s and the nitrogen and hydrogen conversions increased to approximately 0.1500. The optimal feed composition within the investigated range was found near the stoichiometric ratio (yH2 = 0.75, yN2 = 0.25). Catalyst loading in the range of 1–5 g produced only minor changes in performance, with slightly higher ammonia production observed around 2–3 g.Conclusion—In conclusion, the developed one-dimensional non-isothermal reactor model successfully describes the axial behavior of a hydrogen-based ammonia synthesis reactor and provides valuable insights into the influence of operating and bed parameters. Unlike many previous studies, the present work provides a simple integrated framework for evaluating the effects of operating and packed-bed parameters on hydrogen-based ammonia synthesis reactors.

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