Fuel, thermal and surface properties of microwave-pyrolyzed biochars depend on feedstock type and pyrolysis temperature

We evaluated the fuel, thermal and surface properties of twelve biochars produced from three lignocellulosic (canola straw, sawdust, wheat straw) and one non-lignocellulosic feedstock (manure pellet) pyrolyzed at three temperatures using a microwave. Regardless of feedstock type, increasing pyrolysis temperature progressively reduced the abundance of -OH functional group and yield, but increased pH and thermal stability of biochar. Gross calorific values (GCV), carbon stability, and degree of aromaticity of biochars derived from lignocellulosic feedstocks increased with increasing temperature due to decreased elemental oxygen content. However, high ash content in the non-lignocellulosic feedstock retarded its thermal degradation, producing biochars with low GCV. The specific surface area of biochars was low, with the highest value of 43 m² g⁻¹ achieved for sawdust biochar produced at 500 °C. We conclude that the fuel, thermal, and surface properties of the biochars were dependent on the feedstock type and pyrolysis temperature.