The synthesis of ammonia via the Haber-Bosch process is one of the most massive industrial processes worldwide [1]. Performed in traditional packed bed reactors, this large-scale operation suffers from multiple inefficiencies mostly stemming from mass and heat transfer limitations [2]. Currently, the process yields hundreds of millions of tons of ammonia [1], contributing about 1.6% of global carbon dioxide emissions [3] and relying on about 1-2% of the worldwide energy supply [1]. Thus, improving the efficiency of these reactors would have far-reaching economic and sustainability benefits. There have been numerous efforts to increase the performance of packed bed reactors, including ones used for ammonia synthesis [1, 4]. These included changes in the process itself, its operating conditions, and catalyst choices, as well as adopting entirely new technologies like photocatalytic reactors [5].
In this work, we present an innovative approach that enables exploring the potential improvements that can be made to the packed bed reactors on the pore scale. We computationally model a small portion of the reactor, discerning catalyst pellets, and the void space. We then sample numerous randomly generated pellet arrangements and use small differences in the reactor’s performance to statistically determine the routes to improved synthesis. To characterize the reactor we use two types of tessellations and elements of graph theory while the performance is assessed by tracking the yield, outlet temperature, and hydraulic permeability. By analyzing the subtle changes in the outcomes as a function of the pellet arrangements, we can identify unique mechanisms of performance optimization that are possible to be applied on the reactor’s pore scale. We have previously demonstrated the success of our approach in a two-dimensional model of an isothermal flow of fluid [6] and a two-dimensional representation of an ammonia synthesis reactor. Here we demonstrate the viability of our approach in a three-dimensional ammonia synthesis reactor and link the pore-scale findings with its macroscopic performance.
[1] Faria, J.A., 2021. Renaissance of ammonia synthesis for sustainable production of energy and fertilizers. Current Opinion in Green and Sustainable Chemistry, 29, p.100466.
[2] Andrigo, P., Bagatin, R. and Pagani, G., 1999. Fixed bed reactors. Catalysis Today, 52(2-3), pp.197-221.
[3] Cunanan, C.J., Elorza Casas, C.A., Yorke, M., Fowler, M. and Wu, X.Y., 2022. Design and analysis of an offshore wind power to ammonia production system in Nova Scotia. Energies, 15(24), p.9558.
[4] El-Shafie, M. and Kambara, S., 2023. Recent advances in ammonia synthesis technologies: Toward future zero carbon emissions. International Journal of Hydrogen Energy, 48(30), pp.11237-11273.
[5] Zhang, S., Zhao, Y., Shi, R., Waterhouse, G.I. and Zhang, T., 2019. Photocatalytic ammonia synthesis: Recent progress and future. EnergyChem, 1(2), p.100013.
[6] Geohagan, A. and Truszkowska, A., 2025. Finding the Dominant Properties of Porous Media: An Example of Fluid Flow. Multiscale Science and Engineering, pp.1-13.