Effects of Potassium on the Decomposition of Wood and Lignocellulosic Components During Torrefaction

Potassium (K) is among the most abundant minerals in plants and is responsible for their growth. It has a major role on the degradation of lignocellulosic biomass. However, there are some questions about the behavior of potassium during torrefaction. To fully understand the role of this mineral in torrefaction, a thermogravimetric analysis was performed on beech wood and its components: cellulose, hemicelluloses and lignin. The samples were impregnated with different potassium carbonate K₂CO₃ concentrations (0.004 M, 0.008 M, and 0.012 M). The results showed that the effect potassium depends on the temperature and the residence time. The TG curves of wood with different potassium concentrations intersected at the same mass loss percentage. After the intersection point, K switched from degrading the biomass to favoring char formation. The potassium was found to act mostly on cellulose and hemicelluloses. After carbohydrate degradation, the relative lignin content increases, which could potentially be the reason behind the increased char production with potassium. The obtained results provide a novel insight on the role of potassium in thermal treatment of biomass. This information could be conductive to a reduction of the process time and/or temperature, thus rendering the torrefaction an advantageous pretreatment for wood used for combustion.