The removal degree of hydrogen is nearly two times higher than
that of carbon in both CF and PW with the exception of PW pyrolysis
at 200 and 250 C. As we know, the hydrogen and carbon in
biomass are removed mainly through dehydration and decarboxylation
reactions, respectively. Considering co-occurrence of
demethanation reaction, removal degrees of carbon and hydrogen
indicate that decarboxylation reaction has similar preference to
de-hydration under low temperature pyrolysis. In addition, the
variation in elemental composition of the biochars was also analyzed
via a van Krevelen diagram as illustrated in Fig. 3. It can be
seen that only the biochar obtained at 330 C pyrolysis has similar
atomic composition to that of the lignite. Besides low temperature