(209f) Sustainable High-Purity Nitrogen Production Via a Coupled PSA-Thermochemical Process for the Ammonia Industry

In order to achieve the Paris agreement's target of maximum global warming of 1.5 °C, a sustainable and CO₂ lean production, not only of fuels, but also of key commodities like ammonia, is necessary. Ammonia is a fundamental chemical commodity for fertilizer production, and becomes increasingly important as an energy vector, especially considered as fuel for maritime applications. Since not only the production of H₂, but also the production of the feedstock N₂ itself causes high CO₂ emissions, its sustainable production is mandatory. Economic analysis reveals that the combination of a solar-energy-powered pressure-swing absorption (PSA) and a redox-oxide-based, solar thermochemical cycle decreases the thermal energy input of high-purity N₂-production significantly. The viability of thermochemical air separation and the benefit of using pre-purified air has already been proven in laboratory scale experiments, but the approach of coupling PSA with such a thermochemical cycle has not yet been demonstrated.

In this contribution we present an overall approach including both the redox oxide material selection as well as the solar reactor design. The characteristics of the selected redox materials are analyzed by in-situ high-temperature x-ray diffraction (XRD) in a temperature range of 500-1100°C and thermogravimetric analysis (TGA). Various oxygen partial pressures (0-83 % O₂) are applied in both characterization methods.

The proposed air separation process is demonstrated with a PSA unit coupled to an indirectly heated, pressurized packed bed reactor (Fig. 1). The influence of the process parameters such as pressure, reduction and oxidation temperatures on the performance criteria are shown and compared to results gained by simulations. Moreover, we illustrate how the process parameters can be influenced by tuning the composition of a representative redox material Ca_1-xSr_xMnO₃. Therefore, the impact of the Sr-amount on the structure, structural changes and the enthalpy are presented. The performance of the overall system is evaluated on the basis of the achieved purity of the outlet gases, the volume flow rates and the efficiency.