Biochar chemical-looping gasification for hydrogen-rich syngas production in solid-solid reaction: O, H and CaO of carbide slag effect NiFe2O4 oxygen carrier.

Abstract

Biomass chemical-looping gasification represents a promising technology for the production of hydrogen-rich syngas, wherein the yield of gas is contingent upon the rate of solid-solid reactions. In this study, the incorporation of carbide slag as an oxygen carrier, hydrogen carrier, and in-situ carbon capture agent, as well as the modification of the synthesis method for the NiFe₂O₄ oxygen carrier, were specifically targeted to enhance the solid-solid reaction activity. The results indicate that the reactivity can be significantly improved by synthesizing NiFe₂O₄ using the sol-gel method with varying ratios of citric acid. Specifically, a citric acid ratio of 1:3 demonstrated a substantial hydrogen gas yield of 0.032 Nm³/kg, although CO remained the predominant product. The addition of carbide slag markedly enhanced the H₂ gas yield. Notably, the incorporation of 4g of carbide slag exhibited a pronounced synergistic effect with the NiFe₂O₄ oxygen carrier, resulting in a H₂ gas yield improvement that exceeded fivefold compared to the NiFe₂O₄ sample alone. The formation of the Ca₂Fe₂O₅ phase was identified as one of the key factors contributing to the enhanced activity of hydrogen production. Regarding the reaction temperature, an optimal H₂ gas yield of 0.169 Nm³/kg was achieved at 800 °C. According to Pearson correlation coefficient analysis, both reaction temperature and the amount of carbide slag were identified as the primary parameters influencing hydrogen-rich syngas production. Additionally, the production of H₂ was attributed to reforming reactions, while the production of CO was attributed to gasification processes. Ultimately, the possible reaction mechanism involving the interaction between carbide slag and NiFe₂O₄ was elucidated.