Ammonia and nitrogen-based fertilizer production by solar-thermochemical processes

Abstract

Ammonia is one of the most-produced chemicals in the world. It is applied in the fertilizer industry, and nitrogen fertilizers are a necessity to feed the world's growing population. Due to the high energy demand of the Haber- Bosch ammonia synthesis process, and due to the energy-intensive production of its precursors hydrogen and nitrogen, this process is associated with a significant carbon footprint. To reduce the greenhouse gas emissions of ammonia and fertilizer production, the authors develop solar-thermochemical routes for the production of nitrogen and hydrogen. Here we present an energetic optimization for combining pressure swing adsorption and thermochemical air separation to beat the energy efficiency of cryogenic air separation, and show recent results on materials development and experimental test campaigns of such two-step thermochemical redox cycles. We show that solar-thermochemical air separation is feasible and hint towards potential improvements of this technology and associated synergistic effects in fertilizer production. By this means, the CO2 emissions of fertilizer production can be significantly reduced through application of concentrated solar energy. Future challenges include reactor design and heat recovery, as well as the selection of suitable redox materials.