Enhanced stability of iron-nickel oxygen carriers in biomass chemical looping gasification by core-shell structure

Abstract

The chemical cycle provides a novel platform for biomass tar gasification to produce fuels and oxidizers cleanly and efficiently. In this work, core-shell structured oxygen carriers were synthesized with FeNi-based oxides as the core and TiO2 as the shell. And the reaction performance with oxygen migration behavior was investigated by coupled pine sawdust chemical looping gasification. Due to the presence of Ni and Fe, high-density and well-dispersed NiFe2O4 and NiO nanoparticles were formed in the oxygen carriers as active sites to promote tar cracking. The active component, protected by the TiO2, has an increased content of lattice oxygen (OⅠ) and chemisorbed oxygen (OII), which is more likely to bind to C in the tar molecule to promote tar cracking. Compared to pyrolysis without oxygen carriers produced only 504.8 ml/g of syngas, the gas yield was significantly increased to 870.87 ml/g at 800 °C. In the water vapor atmosphere, the formation of hydrogen was promoted to a large extent by the reoxidation of iron by steam, resulting in a gas yield of up to 1100 ml/g and a carbon conversion efficiency of up to 93 % at 800 °C. And steady performance in 50 cycles of experiments with 2500 min was kept. It was found by the characterization that the structure of spent FNO@TiO2 oxygen carriers after 50 cycles was unchanged, which indicates that the core-shell structure oxygen carrier is a promising material for chemical looping gasification.