Effects of Torrefaction on the Physicochemical Characteristics of Sawdust and Rice Husk and Their Pyrolysis Behavior by Thermogravimetric Analysis and Pyrolysis–Gas Chromatography/Mass Spectrometry

The purpose of this research is to investigate the torrefaction behavior of sawdust and rice husk and the torrefaction influence on the thermal chemical properties of the two kinds of biomass, using three different temperature levels 200–220, 240–260, and 280–300 °C for 1 h. Results showed that the weight loss of sawdust was more significant than that of rice husk at 280–300 °C, which was 27.72% and 18.33%, respectively. The energy yields decreased with the increase of the torrefaction temperature, which were 77.63% and 89.38% for sawdust and rice husk at 280–300 °C, respectively. After torrefaction at 280–300 °C, the higher heating value (HHV) of sawdust increased from 20.84 to 22.38 MJ/kg and that of rice husk changed from 17.07 to 18.68 MJ/kg. Hemicellulose was the most reactive material in the process of devolatilization by thermogravimetric analysis (TGA). The degradation temperature of cellulose occurred at 270–360 and 250–345 °C for sawdust and rice husk, respectively. Pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) data showed that the process of torrefaction reduced the levels of alcohols, ketones, aldehydes, acids, esters, and furans of the pyrolysis products for both kinds of biomass. Phenols content in sawdust was increased from 13.84% to 15.68% after torrefaction and that for rice husk was increased from 10.94% to 13.66% after torrefaction. Systematic characterization of sawdust and rice husk in the surface morphology, energy yield, lignocellulose components composition, and thermal cracking performance before and after the torrefaction process was carried out, which enhances the practicability of using the torrefied biomass as a fuel and facilitates the application of biomass as a promising alternative clean energy