Hydrogen production via Chemical Looping Ammonia Cracking: A multiscale experimental investigation

This work presents a multiscale, bottom-up experimental investigation of chemical looping ammonia cracking (CLAC) in dynamically operated packed-bed reactors. In this process, ammonia reduces the oxygen carrier while simultaneously undergoing catalytic cracking. Regeneration of the oxygen carrier is subsequently achieved either by steam (two-step process) or by sequential steam and air oxidation (three-step process). Fe-based oxygen carriers derived from killed basic oxygen waste were synthesised as pellets and tested using thermogravimetric analysis (TGA), small and large-scale laboratory reactors, up to 120 g. The process demonstrated good chemical stability (over 200 cycles in TGA) with oxygen transport capacity decay of approximately 6.4% from cycle 10. Testing at reactor scale could demonstrate a theoretical H₂:NH₃ molar ratio of 1.5 in the two-step process, whereas hydrogen yielded 1.25 H 2 :NH 3 ratio in the three-step process because of the reduction of Fe₂O₃ to Fe₃O₄. At 900 °C, steam oxidation made a significant contribution to H₂ production, accounting for 4.2 mol H2 /kg OC , 49% of the total H₂ generated in the three-step configuration. The testing in a non-isothermal reactor replicated the same H 2 yield, showing a strongly transient thermochemical behaviour, characterised by a limited temperature drop during reduction with NH 3 and a significant increase in temperature during oxidation (+200 °C).