Impact of Pyrolysis Temperature on Charcoal Characteristics

Charcoals were produced from spruce and beech wood under laboratory conditions at different pyrolysis temperatures (300–1300 °C). Characterization of these charcoals was conducted using eight analytical methods. Each method describes specific changes in the temperature range until 1300 °C. Therefore, the combination of these methods provides comprehensive information on different pyrolysis stages. Fourier transform infrared (FTIR) spectroscopy, NMR spectroscopy, and thermogravimetry display changes until 700 °C. A prediction model for pyrolysis temperature until 800 °C is presented based on FTIR spectra with an R2 of 0.98. He-pycnometry resolves the temperature range between 500 and 890 °C. Small angle X-ray scattering (SAXS) describes precisely the evolution of the porous structure and completes the set of techniques by a description of the physical properties of the charcoal. X-ray diffraction (XRD) reveals the crystallographic change of the lignocellulosic structure toward precursors of graphite. The formation of calcite out of CaO and CO2 becomes evident.