The effect of temperature and heating rate on char properties obtained from solar pyrolysis of beech wood

• Char was obtained during solar pyrolysis at various temperatures and heating rates.
• “Solar chars” up to 2000 °C and up to 450 °C/s have been produced.
• Temperature and heating rate jointly affected char yield, structure and reactivity.
• Reactivity evolution with temperature and heating rate were related to structure.

Char samples were produced from pyrolysis in a lab-scale solar reactor. The pyrolysis of beech wood was carried out at temperatures ranging from 600 to 2000 °C, with heating rates from 5 to 450 °C/s. CHNS, scanning electron microscopy analysis, X-ray diffractometry, Brunauer–Emmett–Teller adsorption were employed to investigate the effect of temperature and heating rate on char composition and structure. The results indicated that char structure was more and more ordered with temperature increase and heating rate decrease (higher than 50 °C/s). The surface area and pore volume firstly increased with temperature and reached maximum at 1200 °C then reduced significantly at 2000 °C. Besides, they firstly increased with heating rate and then decreased slightly at heating rate of 450 °C/s when final temperature was no lower than 1200 °C. Char reactivity measured by TGA analysis was found to correlate with the evolution of char surface area and pore volume with temperature and heating rate.