Co3O4 and CoFe2O4 as oxygen carriers in straw char on solid-solid and gas-solid reactions behavior during chemical-looping gasification for hydrogen-rich syngas production

Biomass chemical-looping gasification is a promising technology for hydrogen-rich syngas production. The CoFe2O4 oxygen carrier exhibits favorable redox stability and synergistic performance. Herein, the gasification characteristics between biochar and CoFe2O4 were studied in solid-solid and gas-solid reactions by fixed bed reactor experiments, respectively. Compared with Co3O4, CoFe2O4 in solid-solid reaction reveals that CO is a dominant gas, and it shows higher CO gas yield due to Co3Fe7 formatted. In gas-solid reaction, the result reveals that H2 is a dominant gas, and it shows the highest H2 gas yield at 850 degrees C and 80 mu L/min (steam flow) since (Co0.62Fe1.38)FeO4 structure assist the mobility of lattice oxygen. Between solid-solid and gas-solid reactions, CoFe2O4 displays different characteristic as follows: 1) it shows compact surface in solid-solid step, while it keeps a porous structure in gas-solid step; 2) Co exhibits a higher oxidizing role in the gas-solid step than in the solidsolid step. After different steam flows (60-100 mu L/min), the maximum H2 gas yield is 1.16 Nm3/kg at 80 mu L/min with CoFe2O4. However, the formation of Fe3C hinders H2 gas production at steam flow rates exceeding 80 mu L/ min. In the chemical looping process, CoFe2O4 exhibits relative stability after three cycles.