Sequential pyrolysis of spirulina and sawdust: Interactions of volatiles from upper-bed feedstock to lower-bed biochar

Abstract

Co-pyrolysis of mixed feedstocks is a common practice in research and industrial operation. Cross-interactions of volatiles of varied origins have been well documented in many existing studies. However, it remains a challenge to understand the transfer of volatiles from feedstock A to biochar of feedstock B during co-pyrolysis, due to the complexity of the reaction network. To examine this issue, sequential pyrolysis of spirulina and sawdust with up-down configured dual beds was conducted to probe specifically how volatiles from one feedstock could impact the biochar from another feedstock. The results confirmed the interactions of volatiles with biochar of the other feedstock, which diminished oxygen/nitrogen-containing compounds and heavy π-conjugated components in the bio-oils. Carbonaceous deposits were also observed, enhancing yields of biochar but at the expense of bio-oil. The transfer of inorganic species and N-containing species from spirulina to sawdust-biochar as well as the carbon-rich coating of the spirulina-biochar from the deposition of sawdust volatiles were observed, making the biochars more hydrophobic. Additionally, these interactions also remarkably enhanced the thermal stability of the sawdust-biochar. The transfer of organics and inorganics during sequential pyrolysis also resulted in the coarse surface of biochars dotted with many small particulate matters with an average particle size of 2.0–3.8 µm.