Changes in chemical and physical properties of yellow poplar (Liriodendron tulipifera) during torrefaction

In this study, changes in the chemical and physical properties of yellow poplar were investigated during torrefaction. The torrefaction temperature was an important factor for changing the chemical compositions of the biomass. In particular, hemicelluloses were significantly affected by the torrefaction temperature. The torrefied biomass contained lower xylan and higher glucan and lignin concentrations than the raw material. The carbon content of the torrefied biomass increased from 44.80 to 52.96 % as the severity factor (SF), whereas the oxygen and hydrogen contents decreased from 45.08 to 36.77 and 5.89 to 5.62 %, respectively. The high carbon content in the torrefied biomass induced a decrease in the H/C and O/C ratios. The calorific value and weight loss increased proportionally to the SF. Under severe torrefaction conditions, the calorific value of the torrefied biomass was 20.84 MJ/kg, which represents an increase of 15.01 % compared to the raw material. Regarding the physical properties of the torrefied biomass, the moisture uptake capacity and specific energy consumption for grinding of biomass significantly decreased with increasing torrefaction severity. The torrefied biomass (55.1-65.6 kWh/t) required less energy than the raw material (145 kWh/t) for size reduction.