Oxygen donation of alkali earth metal ferrites for biomass chemical looping gasification: A comparative study

Abstract

This study objectives to compare the oxygen donation properties among a series of alkali earth metal (AEM) ferrites as oxygen carriers (OCs), including MgFe2O4, CaFe2O4, SrFe2O4 and BaFe2O4, in biomass chemical looping gasification (CLG), through fixed bed reactivity tests and several characterizations, including XRD, XPS, TPR and thermogravimetric analysis. It was found that BaFe2O4 possessed the best syngas production performance, owing to its highest reactivity with char and lowest reactivity with CO/H2. Thermogravimetry analysis and TPR tests show that heavier AEM ferrites exhibited higher reactivity with char and lower reactivity with syngas, except for the relationship between SrFe2O4 and CaFe2O4. Fixed bed tests show that the AEM ferrites could be ranked as BaFe2O4 > CaFe2O4 > SrFe2O4 > MgFe2O4 according to their syngas production performance. Other than reactivity, 20-cycle tests demonstrate that BaFe2O4 had the best stability on H2 production compared to other OCs. The advantage of BaFe2O4 may be related to its more sufficient oxygen vacancy and crystal structure. Therefore, BaFe2O4-based OCs were found the most suitable for biomass CLG. The current study filled the gap in screening of AEM ferrite OCs and provided guidance for future OC development, achieving cleaner biomass conversion and enhanced sustainability.