The exploration of NiO/Ca2Fe2O5/CaO in chemical looping methane conversion for syngas and H2 production

Materials used for chemical looping can be exploited to process methane in a number of ways. Using the oxygen on the solid material leads to partial or total oxidation, whilst methane cracking to carbon on the depleted solid can produce hydrogen. Regeneration of the solid to remove the cracked carbon or restore the oxygen can produce CO, H2 or a combination if CO2 or H2O is used as the oxidant. The chemical looping material separates the conversion of methane from the addition of oxygen. Materials containing sorbents like CaO can interact with the CO2 produced to shift the equilibrium in desirable ways. These materials could be utilised to configure a cyclic process that is a linear combination of DRM, SMR, and cracking with combustive regeneration of the solid. Here, a material combining a catalyst (i.e. Ni), an oxygen carrier (i.e. Ca2Fe2O5) and CaO was investigated for converting methane to syngas or hydrogen-rich gas in a cyclic DRM process. In Stage 1, methane is converted to syngas or H2 in a fluidised bed of NiO/Ca2Fe2O5/CaO, where the solid is reduced/carbonated at, e.g., 700 °C; in Stage 2, the reduced/carbonated material is regenerated at 900 °C. The thermodynamics of the Ni-Ca-Fe-O system allows Ni to stay separate from Ca2Fe2O5, meaning that CaO inhibits the formation of any mixed oxide phase of Ni and Fe. A high rate of production of syngas or H2 (depending on different phases of Stage I) was found after the NiO/Ca2Fe2O5/CaO became activated. The activated NiO/Ca2Fe2O5/CaO gave high production of syngas or H2 for over 30 cycles without material deactivation. Carbon whiskers formed during CH4 processing, and did not cause deactivation.