Insight into physicochemical properties and carbon-silicon interaction mechanisms of biochar during gasification

Biomass gasification emerges as a potential technology for biochar production due to its carbon neutral property and independence to external energy sources. Compared to pyrolysis for producing biochar, the biomass gasification is more complex which contains pyrolysis, reduction, and oxidation stages. In this study, a series of experiment was performed to exactly control the heating rate and atmosphere in order to collect the biochars from different stages of gasification. With comprehensive characterizations, the evolution of biochar's physicochemical properties and the interaction between carbon and silicon during different stages of gasification were investigated. Biomass undergoes sequential dehydration, demethylation, decarboxylation, and secondary demethylation reactions. The graphitization of carbon begins during the pyrolysis stage, whereas the crystallization of silicon primarily occurs in the reduction and oxidation stages. The proportion of hydrogen bonding functional group rapidly declined during the oxidation stage, from 82.99 % to 14.32 %. A dense three-layer carbon-silicon-carbon structure forms. During the reduction and oxidation stages, a gradual occurrence of silicon-encapsulated carbon structures is found, and carbon is immobilized through the interactions with different types of siloxane. This work provides new insights into the preparation of biochar by gasification, which paves a way for the precise control and smart design of gasification process.