(14e) An Integrated Reaction and Separation Process for “Green Ammonia” Production from Distributed and Intermittent Renewable Energy.

Industrial ammonia production is currently responsible for 50% of global food supply through fertilizer and 1-2% of CO₂ emissions through the conventional Haber-Bosch process. “Green ammonia” produced from water, air, and renewable electricity has garnered accelerating attention in recent years for both energy storage and sustainable fertilizer. However, the conventional Haber-Bosch process is incompatible with intermittent and isolated renewable energy because it is designed to operate continuously for months at a time using fossil fuels in centralized locations. An electric Haber-Bosch process, while benefiting from efficient electric compressors and modular electrolysers, still requires a high pressure reactor with a recycle-loop. A novel integrated process has been demonstrated at the lab scale using Ru/Cs/CeO₂ catalyst and MnCl₂/SiO₂ absorbent to synthesize and separate ammonia in a single vessel.[1] The catalyst was designed for low-temperature and high-conversion activity by removing hydrogen and ammonia inhibition, respectively. The absorbent utilized MnCl₂ rather than conventional MgCl₂ because it was resilient to decomposition after exposure to water. This unique absorbent was supported on silica to prevent sintering and improve cyclical capacity. The temperature, pressure, and N₂:H₂ ratio have been optimized with respect to the forecasted production rate of the process, and economic analyses have compared the integrated process with the conventional Haber-Bosch process.[2] Such an integrated process re-defines the Haber-Bosch process by removing the requirement for high pressures and a recycle. It is anticipated that an integrated “green ammonia” process will be the foundation for both sustainable fertilizer and long-term energy storage in the future when paired with distributed and intermittent renewable energy.

Figure | Exceeding single-pass equilibrium with a single or double layer integrated flow system. Modified from [1].

1. Smith, C. and L. Torrente-Murciano, Exceeding Single-Pass Equilibrium with Integrated Absorption Separation for Ammonia Synthesis Using Renewable Energy-Redefining the Haber-Bosch Loop. Advanced Energy Materials, 2021. 11.
2. Smith, C., A.K. Hill, and L. Torrente-Murciano, Current and future role of Haber-Bosch ammonia in a carbon-free energy landscape. Energy & Environmental Science, 2020. 13(2): p. 331-344.