Hydrogen-rich syngas production from straw char by chemical looping gasification: The synergistic effect of Mn and Fe on Ni-based spinel structure as oxygen carrier

Chemical looping gasification (CLG) is one of the promising ways to exploit biomass resources and produce hydrogen-rich syngas. In this work, two spinel oxygen carrier (NiMn2O4 and NiFe2O4) were studied for hydrogen-rich syngas production. A series of characterizations techniques including XRD, XPS, BET, SEM, TPR-H2 and TPD-CO2 were used to investigate the fresh and spent oxygen carriers. The result reveals that the NiMn2O4 oxygen carrier has higher reactivity and redox performance due to its higher oxygen vacancy con-centration. On the other hand, the NiMn2O4 oxygen carrier obtain greater reactivity for hydrogen generation due to its phases and structure changes. NiMn2O4 oxygen carrier was reduced form (NiO)0.25(MnO)0.75 to (NiO)0.75(MnO)0.25 to Ni + MnO phases at 650-850 degrees C. Ni generated adhere to sufure of MnO, and the structure become loose and porous. And the more oxygen vacancise was formed. However, NiFe2O4 oxygen carrier showed different reduction behavior, it reduced from Ni1.25Fe1.85O4 to Fe2O3 + Ni3Fe phases at 650-850 degrees C. The formed Ni phase for NiMn2O4 oxygen carrier promote hydrogen gas generation (2.65Nm3/kg) at 800 degrees C. Based on the charaterize analysis, the proposed reaction process was explained. For the hydrogen-rich syngas production, the optimum conditions in this works shows at temperature (800 degrees C), steam flow (80 mu L/min) and ratio of oxygen carrier with straw char (1:1).

Automated summary

This study investigated the production of hydrogen-rich syngas using two spinel oxygen carriers. NiMn2O4 showed higher reactivity and redox performance, and its phase and structure changes promoted hydrogen generation. On the other hand, NiFe2O4 exhibited different reduction behavior. The proposed reaction process and optimum conditions were also discussed.