Ammonia synthesis rate over a wide operating range: from experiments to validated kinetic models

Abstract

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 valueable 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.