Phase transitions involving Ca – The most abundant ash forming element – In thermal treatment of lignocellulosic biomass

Torrefaction, pyrolysis and gasification are of interest to convert lignocellulosic biomass into fuels and chemicals. These techniques involve thermal treatment at low partial pressures of oxygen. However, little is known about the transformation of ash elements during these processes. The phase transition of the major ash element calcium (Ca) was therefore studied with powder from pine as biomass model treated at temperatures 300–800 °C under atmospheres of 100% N2, 3% O2 and 6% O2 and thermodynamic equilibrium modelling. For evaluation, X-ray powder diffraction and synchrotron Ca K-edge X-ray absorption near edge structure (XANES) spectroscopy in combination with linear combination fitting and reference compounds was used.