Similarity and difference of biochar and hydrochar from leaves, bark, and wood of the same sycamore tree.

Distinct reaction network in pyrolysis and hydrothermal carbonization (HTC) forms biochar/hydrochar of varied nature, which was investigated herein by pyrolysis and HTC of leaves, bark, and wood of same sycamore tree at 500 and 240 °C, respectively. The results showed that dominant cracking/gasification in pyrolysis formed biochar with yields of 30-50 % lowered than that of hydrochar formed via main polymerization in HTC. HTC led to leaching of inorganics, forming hydrochar from leaves or bark with ash content half of that biochar or from wood with negligible ash, making hydrochar suitable as solid fuel. More CH, CO and olefinic CC but not aromatic CC in hydrochars resulted in their lower thermal stability but superior capability for adsorption of Cr. The HTC showed lower environmental impact than pyrolysis, while release of N- and P-containing pollutants from HTC/pyrolysis of leaves showed more negative influence on environment than that from conversion of wood/bark.