Deoxygenation-enhanced chemical looping gasification: a new pathway to produce hydrogen from biomass

Abstract

Biomass to hydrogen production has been regarded as a potential approach for green hydrogen synthesis. However, carbon dioxide and bio-tar are inevitably produced, which critically restricts the refinement of biomass-derived syngas. In this study, deoxygenation-enhanced chemical looping biomass gasification (DE-CLBG) is proposed for hydrogen-rich syngas production together with CO₂/H₂O deoxygenation and catalytic bio-tar removal using the composite Fe/CaO as the deoxidizer. The DE-CLBG process is comprised of a deoxygenated gasification stage and a regeneration stage. During the deoxygenated gasification stage, the deoxidizer is converted under steam gasification via CaO + Fe + O²⁻ → Ca₂Fe₂O₅ with biochar generation; at the regeneration stage, biochar is further gasified with the achievement of deoxidizer reduction via Ca₂Fe₂O₅ + C → CaO + Fe + CO_x. Experimental results show that the hydrogen production and maximum concentration upon applying 0.300 g of deoxidizer per g of biomass are 6.70 mmol and 89.61 vol%, which was increased by 287% and 27%, respectively, compared with the non-deoxygenated process. Results from the Mössbauer spectrum show that Fe⁰ is finally transformed into Fe³⁺ in the form of Ca₂Fe₂O₅ and a small amount of Fe₃O₄, corresponding to the deoxygenation efficiency of 99.21%. The NMR results imply that aromatic carbon is the main form in biochar whether introducing deoxidizer or not, and deoxygenation can promote the removal of O-alkyl C.