Experimental Investigation of Fe-Ni-Al Oxygen Carrier Derived from Hydrotalcite-like Precursors for the Chemical Looping Gasification of Biomass Char

摘要

Chemical looping gasification (CLG) of biomass uses the lattice oxygen of oxygen carriers to convert biomass into syngas with a low tar content, high heating value, and low price. It is of key importance to exploit well-dispersed and thermally stable oxygen carriers for the CLG process. In the current work, a series of oxygen carriers with varied Fe and Ni molar ratios were synthesized from hydrotalcite compound precursors (HTlcs), which made the metallic elements mix at the molecular level. Consequently, highly dispersed complex metal oxygen carriers can be achieved after precursor calcinations. CLG of biomass char was carried out in TGA and a fixed bed reactor accompanied by various physical and chemical analyses for the fresh and used oxygen carriers. The result manifested the HTlcs crystalline form, which was formed in the precursors and produced the Fe(0.99)Ni(0.6)A(1.1)O(4) compound after calcination, suggesting that a high degree dispersion of the multimetal oxygen carrier was synthesized. The main H-2 uptake and CLG reactivity of the oxygen carriers were related to its higher metal dispersion and synergistic effect between Fe and Ni. Accordingly, there was an optimum Fe/Ni ratio of 4:1 in oxygen carriers at which the oxygen carrier can achieve better CLG reactivity. Also, the oxygen carrier to biomass char mass ratio of 7:3 provided a maximum weight loss of 35.59% and a largest mass loss rate of 2.46 wt %/min, suggesting higher lattice oxygen releasing efficiency. CO exhibited a higher generating rate in the CLG reactions owing to its higher reaction activation energy with lattice oxygen [0], while H-2 was more prone.to being consumed. The morphological analysis of fresh and regenerated samples exhibited that the oxygen carrier was reduced to the Fe3Ni2 alloy phase after the CLG process, and the lattice oxygen can be fully recovered in an air atmosphere. Although the BET surface displayed a decreased trend in the regenerated oxygen carriers, serious sintering was not observed in the samples, and the main metallic crystallized phases were still maintained.