Multi-scale characterization of pine wood biochar from TGA and fixed-bed reactors: Implications for two-stage hydrogen production

The pyrolysis of lignocellulosic biomass offers an effective route to produce carbon rich solids that serve as intermediates for hydrogen generation via steam gasification. This study investigates the structural and compositional evolution of pine wood biochars produced under well controlled conditions in two reactor systems: a thermogravimetric analyzer (TGA) for wood powder and a laboratory scale fixed-bed reactor for wood pellets. Pyrolysis experiments were performed at 400–900 °C with heating rates of 10–100 °C min −1 . Raman spectroscopy, SEM–EDX, and oxidation tests were employed to characterize the resulting chars. Raman analysis showed that increasing temperature promotes carbon ordering, with the D band shifting from 1378 to 1335 cm −1 and the H D / H G ratio rising from 0.60 to 0.87. SEM–EDX revealed progressive surface roughening, pore formation, and mineral enrichment (mainly K and Ca), accompanied by a decline in O/C ratio from 0.663 to 0.083. Oxidation reactivity tests indicated reduced char reactivity with increasing pyrolysis severity, consistent with enhanced structural ordering and deoxygenation. This study characterizes the pyrolysis stage char precursor rather than the gasification step itself; by linking pyrolysis parameters to carbon ordering, deoxygenation, and mineral (K, Ca) enrichment, it provides a structural basis for selecting char preparation conditions in the subsequent steam gasification route to hydrogen, which is the subject of ongoing work.