High calorific value of lignin derived from Turkey oak wood: Combined effect of steaming and thermal treatment

Turkey oak (Quercus cerris L.) is a deciduous species characterized by high morphological variability and a widespread distribution range along South-East Europe. The wood of Turkey oak is scarcely considered as industrial lumber and is mainly used as firewood. Biomass pre-processing by heating improves feedstock consistency (mainly loss of water) and thereby improves its energetic efficiency. The main goal of this research was to evaluate how different hydro-thermal treatments effect the high calorific values and the relative ash content of lignin derived from Turkey oak wood differentially treated by combining temperature, time and steaming parameters. Sapwood and heartwood were distinguished for each treatment. Twelve different treatments were performed by using samples randomly selected. Samples were treated in a small heating unit with ± 1 °C accuracy under atmospheric pressure, according to two different heating cycles namely 120 and 180 °C. The Klason lignin content was assessed by a modified TAPPI method. High calorific value (HCV) was calculated by the fire testing technology bomb calorimeter method. Thermal treatment and the steaming processes significantly increased the HCV in examined wood samples. The strongest effect was highlighted when steaming was associated to the highest temperature. The combined effect of steaming and heating was shown to be effective in the process improvement in order to obtain both a higher content of lignin and a corresponding improvement of HCV.