Distinct property of biochar from pyrolysis of poplar wood, bark, and leaves of the same origin

The biochemical composition of wood, bark, and leaves is different, and this difference will inevitably project to products from the pyrolysis of different parts of a tree. In this study, different tissues of the same poplar tree (wood, bark, and leaves) were pyrolyzed to probe the characteristics of pyrolysis products of varied feedstock. The results indicated that wood tended to be pyrolyzed to form bio-oil with the highest yield (57.7% at 600 °C) while gases with the lowest yield (12.2% at 400 °C) among the three feedstocks. The high content of inorganic species in bark (5.8%) and especially leaves (10.3%) promoted the gasification of the aliphatic structures to produce a high yield of gases (18.9% of gas yield in leaves pyrolysis at 600 °C). In addition, unlike that in pyrolysis of wood, the pyrolysis of leaves produced little sugar derivatives like ketones (0%) /aldehydes (0%), but more hydrocarbons, N-containing organics, and phenolics with large fused ring structures. The organic components in leaves and bark were highly unstable, and their decomposition was further enhanced with the abundant inorganic species. This hindered the aromatization of the leaves/bark-derived biochar, resulting in their lower heating value, energy density, thermal stability, and their lower comprehensive combustion index than the biochar derived from wood. Additionally, as the pyrolysis temperature increases, the varied composition of feedstock also led to distinct patterns for the evolution of functionalities of biochar.