Steam carbon gasification of a nickel based oxygen carrier

Ni-based oxygen carriers are promising candidates for Chemical Looping applications due to a combination of excellent methane conversion performance, mechanical stability, oxygen transfer capacity. However, experiments conducted on NiO/NiAl2O4 in a micro-fluidized bed reactor show that methane forms coke on active nickel sites. In subsequent tests, water vapour was fed to the coked Ni oxygen carrier producing a highly concentrated stream of CO/H2 (1/1). In the absence of water vapour, production of hydrogen dropped with time while a methane/argon mixture was fed to the reactor. Co-feeding water together with methane improves stability – both H2 production and carbon deposition were constant for over 1 h. Despite the tremendous lay down of carbon, catalytic activity remained stable at levels as low as 3 vol.% water vapour (and 10% methane). Water vapour is an effective oxidant for Ni(0) but is insufficient to entirely re-oxidize the oxygen carrier from Ni to NiO.

► Methane decomposes to form coke on NiO/NiAl2O4 oxygen carrier.
► Steam was fed to the coked carrier producing a highly concentrated stream of CO/H2.
► The water treatment is efficient to remove all deposited coke at 800 °C.
► Water vapour is an effective oxidant for metallic Ni.