Comparison of the thermal reactivities of isolated lignin and holocellulose during pyrolysis

Woody shells of Turkish hazelnuts which are rich in lignin content offer an important potential as a renewable energy source. Hence, this study focuses on the investigation of the thermal reactivities of the real macromolecular ingredients of this biomass species. Hazelnut shells were treated with chemicals to isolate its holocellulose (hemicelluloses + cellulose) and lignin. Scanning Electron Microscopy (SEM) images revealed the significant differences between the physical features of the untreated biomass and its isolated ingredients. Thermal properties of the biomass and these ingredients were examined by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) techniques under non-isothermal pyrolysis conditions from ambient to 900 °C. It was found that unlike holocellulose, lignin slowly decomposes in a wider temperature range, and its decomposition is associated with exothermic heat flow. It was also concluded that the hemicellulosics in holocellulose have very important effects with respect to the char yield and the exothermicity of the process. Besides, inorganics in biomass play a catalytic role during pyrolysis. The activation energies calculated according to Borchardt-Daniels' kinetic model were 64.8 and 51.8 kJ/mol for the pyrolysis of holocellulose and lignin, respectively, and each of them is higher than that for the untreated biomass.