Simultaneous in-situ tar abatement and H2-enriched syngas production via heterogeneous doping of LaFeO3 during chemical looping gasification of microalgae

Abstract

Chemical looping gasification (CLG) is an emerging environment-friendly technology for efficient and clean utilization of biomass, in which oxygen carrier (OC) is one of the key issues concerning the overall performance. As a rising-star material, perovskite with a tunable crystal structure shows great potential in syngas enrichment and tar decomposition during the CLG of biomass. In this study, the newly-developed LaNi0.5Fe0.5O3 (LN5F5) and La0.3Ba0.7FeO3 (L3B7F) perovskites through heterogeneous doping of LaFeO3 (LF) were evaluated as oxygen carriers with the purpose of simultaneous tar abatement and H2-enriched syngas production from microalgae. Silica sand (SS) and iron ore (IO) were used for comparison. Results showed that the CLG performance order of several materials was L3B7F > LN5F5 > LF > IO > SS at an oxygen carrier to biomass ratio (O/B) of 0.4, water injection rate of 0.3 mL/min and gasification temperature of 800 °C. The heterogeneous doping obviously improved the cyclic stability of perovskite during redox tests. In addition, possible tar conversion routes over L3B7F oxygen carrier were proposed. Results implied that heavy PAHs (4 rings or more) were first converted to light PAHs (1–3 rings) and n-hydrocarbon, which were finally transformed into micromolecular gases. The outstanding performance of L3B7F in microalgae CLG can be ascribed to the formation of oxygen vacancies and high-valence Fe4+ stimulated by the introduction of Ba2+, which were demonstrated by the XRD, H2-TPR and XPS results. These results evidence that the heterogeneous doped L3B7F is a good alternative for improving biomass availability in the CLG process.