Effects of Pyrolysis Conditions on Structural Ingredients and Functional Groups of Hybrid Poplar

In this study, thermal behavior and the functional group distributions of structural ingredients of biomass were investigated under pyrolytic conditions. An energy-forestry tree (hybrid poplar) was used as biomass material. Macromolecular ingredients in this biomass such as holocellulose (hemicellulosics + celluloses) and lignin were isolated chemically using several analytical techniques. Thermal analysis, X-ray Diffraction (XRD), X-ray Fluorescence (XRF), BET surface area, Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) techniques were applied to specify the biomass and its ingredients. Pyrolysis of biomass was carried out in a horizontal tube furnace from ambient to 600 °C with a heating rate of 10 °C/min under nitrogen flow of 100 mL/min. In this way, biochars were produced at different temperatures, and the effects of pyrolytic conditions on the structural ingredients and the distribution of the functional groups were interpreted. It was found out that the physical and chemical analysis results as well as the thermal decomposition characteristics of holocellulose, lignin, and extracted biomass are highly different from those of the main biomass sample. In addition, the obtained biochars contain large amounts of aromatic and ether type structures. Also, it was also determined that the aromatic bands get stronger with increasing pyrolysis temperature. Besides, carbonyl bands disappeared as temperature increases. It was also revealed that the lignin contains many functional groups, of which methoxyl groups were the most apparent functionalities. On the other hand, the calorific value of the produced biochars tended to increase with increasing pyrolysis temperature.