Exploring feedstock structural components as predictors for physico-chemical biochar properties

To further improve the capabilities necessary to accurately predict biochar properties based on feedstock characteristics, a study correlating feedstock structural components with biochar properties was conducted. To produce biochar, ten different biomass feedstocks were sourced mostly from Austria. The feedstocks gathered were spruce chips; woodchips from broad-leaved forestry; wheat bran; Japanese knotweed; walnut shells; screening overflow from composting; and residues from Mary thistle, rapeseed, hemp, and poppy flower processing. These feedstocks were pyrolyzed at 500 and 700 °C under nitrogen (N₂) atmosphere in a customized muffle furnace. The feedstocks were analyzed for their lignin, hemicellulose, cellulose, fat content, and other properties. Mercury intrusion porosimetry (MIP) was performed on the biochar samples, with the highest documented intruded volume being 3.64 cm³/g. Elemental recoveries in the biochar samples were determined and correlated with feedstock structural components (FSC). Additionally, the water solubility of biochar nutrient elements was determined, with K showing the highest solubility of 35.5 ± 18.5% at 700 °C. Elemental recoveries of C/H/N/Cl showed significant correlations with FSC (e.g., Cl showed a significant and strong negative correlation with cellulose, r = - 0.874/p < 0.01). Intruded volume as well as K solubility also showed significant correlations. These results indicate that feedstock structural components can serve as predictors for more biochar properties than currently used in the literature, although the limited sample size requires further research to confirm the findings presented here.