Ammonia Production via a Two-Step Al₂O₃/AlN Thermochemical Cycle. 1. Thermodynamic, Environmental, and Economic Analyses

The production of ammonia via a two-step cyclic process is proposed as an alternative to its conventional production by the Haber−Bosch process. The first endothermic step is the production of AlN by carbothermal reduction of Al2O3 in a N2 atmosphere at above 1500 °C. The second exothermic step is the steam-hydrolysis of AlN to produce NH3 and reform Al2O3; the latter is recycled to the first step. Both reaction steps proceed at 1 bar, without added catalysts, and bypass the energy-intensive production of hydrogen, resulting in significant fuel and cost savings. Furthermore, the endothermic reduction step could be carried out using concentrated solar energy as the source of high-temperature process heat, eliminating concomitant CO2 emissions derived from fossil-fuelled processes.