The Role of H2:N2 Ratio on the NH3 Synthesis Rate and on Process Economics over the Co3Mo3N Catalyst
In this study, the process economics of ammonia synthesis over Co3Mo3N was investigated by searching an optimum feed stoichiometry. By ammonia synthesis rate measurements at atmospheric pressure and 400 oC over Co3Mo3N, it was found that, the rate was independent of H2:N2 stoichiometries above 0.5:1. For H2:N2 stoichiometries below 0.5:1, there was a linear dependency of ammonia synthesis rate on the H2:N2 stoichiometry. Static measurements of hydrogen adsorption isotherms measured at 25, 50, and 100 oC revealed that the adsorbed amounts of the strongly bound hydrogen over Co3Mo3N surface were saturated at around 100 Torr hydrogen pressure. This pressure corresponds to the partial pressure of hydrogen when H2:N2 stoichiometries are around 0.5:1, correlating the role of strong hydrogen in ammonia synthesis. These results were used to modify an existing kinetic expression to be used in a conceptual design, based on a lateness of mixing strategy for the hydrogen stream. This conceptual design and its economical analysis revealed that keeping low hydrogen stoichiometries can cut the investment and operating costs by a factor of 2.
- This article is part of the themed collection: Reaction mechanisms in catalysis