Oxidation kinetics of biochar from woody and herbaceous biomass

•Oxidation kinetics were derived for six biochars from woody and herbaceous biomass.•Inorganic content was used as predictive tools for oxidation reactivity.•Potassium content best explained difference in oxidation reactivity.•CO2 vs CO ratio among feedstocks had positive correlation with inorganic content.•Thermogravimetric analyzer and fluidized bed experiments explored attrition effects. The goal of this study was to determine oxidation kinetics for biochar produced from fast pyrolysis of various biomass feedstocks. In particular, the role of inherent ash content on the oxidation rate was evaluated. Thermogravimetric analysis (TGA) and fluidized bed combustion experiments were used to explore oxidation kinetics of six fast pyrolysis produced biochars with diverse ash content. Reaction rates varied by a factor of three under chemical kinetic-limited conditions, demonstrating inorganic content impacts oxidation rate. Chemical kinetic rate coefficients were proposed as a function of compositional parameters to determine overall fit and impact. Potassium content was found to have a positive correlation, best describing the differences in the oxidation kinetic rate coefficients. Additionally, feedstocks were subjected to a 1 M HCl acid wash mitigating the catalytic activity of the metals. Acid washed biochars had lower oxidation kinetic rates compared to their unwashed counterparts, indicating the removal of catalytically active metals reduced oxidation rate. Gas composition (CO/CO2) was measured during fluidized bed experiments for both acid-washed and unwashed biochars, which varied between the six biochars. Formation of CO2 was greatly affected by catalytic metals, finding potassium content to correlate well with a higher percentage of CO2 formation as compared to CO. Comparison of oxidation rates were made between the two experimental apparatuses to measure the effect of attrition on biochar oxidation.