Chemical looping pyrolysis-gasification staged conversion of microalgae biomass with Ca-Fe composite oxygen carrier

Abstract

Chemical looping pyrolysis-gasification staged conversion (CL-PGSC) of biomass was proposed in this work, which involves the separation of chemical looping gasification into two stages: biomass pyrolysis stage and bio-char gasification stage at different temperature. Pyrolysis and gasification behavior of Nannochloropsis sp., a microalga, with Ca-Fe composite oxygen carrier was investigated in a tubular reactor at varying temperatures and Ca-Fe molar ratios. The results indicate that all Ca-Fe composite oxygen carriers are capable of catalytically upgrading the quality of bio-oils in-situ during the pyrolysis stage. The complex metal oxides calcium ferrites facilitate the formation of aromatics and ketones, while both Fe2O3 and CaO components promote the production of alcohols. As for oxygen carrier with Ca-Fe molar ratio 1:1, the total peak area percentage of hydrocarbons and ketones reaches 66.5 area% within bio-oils, with 28.7 area% being toluene and 18.8 area% being 2-heptadecanone. Moreover, at the gasification stage, clean CO-rich or H2-rich syngas were generated from bio-chars produced at various pyrolysis temperatures with or without steam as a gasifying agent. In the proposed CL-PGSC process, Ca-Fe composite oxygen carrier serves as a catalysis for in-situ upgrading pyrolytic bio-oils, then as an oxygen donor for the gasification of pyrolytic char to achieve the simultaneous production of valuable pyrolytic bio-oils and clean syngas free from tar contamination. This provides a promising strategy for the full utilization of biomass.