Ammonia Synthesis Rate Over a Wide Operating Range: From Experiments to Validated Kinetic Models

With the increasing demand for flexible operation of ammonia production, the feasibility of using reaction kinetic models to predict the performance of a Haber Bosch reactor in a wide operating range must be evaluated. This study compares the feasibility of a lumped Temkin rate expression with a more complex lumped microkinetic model in predicting turnover rates across diverse temperatures and feed compositions. Evaluation and validation were carried out through ammonia synthesis experiments on a magnetite-based industrial catalyst at temperatures ranging from 548 K to 773 K and H2 : N2 ratios between 4 : 1 to 1 : 1 at 90 bar. While excellent agreement between model predictions and experiments was observed at 648 K, significant discrepancies emerged at 548 K. These findings are valuable for both state-of-the-art ammonia synthesis reactors and green ammonia plants utilizing electrolysis-derived hydrogen, where flexible operating conditions are paramount. Moreover, integrating site density as a function of temperature and the partial pressure of H2 into the lumped microkinetic model marks a notable advancement, promising enhanced precision in addressing varied operating conditions.
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This article investigates the performance of a Haber-Bosch reactor across a wide range of operating conditions using both Temkin and microkinetic models. Experimental validation on a magnetite-based industrial catalyst reveals critical insights into ammonia synthesis, particularly for applications in green ammonia production, where flexibility in operating conditions is essential image