Comparative Study on Pyrolysis of Wet and Dry Torrefied Beech Wood and Wheat Straw

This study compares the influences of wet and dry torrefaction on pyrolysis behaviors of beech wood and wheat straw. These two types of torrefaction were compared at similar mass loss of samples. Fourier transform infrared and nuclear magnetic resonance were employed to investigate the chemical evolution during torrefaction pretreatment. Meanwhile, thermogravimetric analysis (TGA) and pyroprobe analyzer coupled with gas chromatography/mass spectrometry were used for studying the kinetic features and the product distribution of the subsequent pyrolysis. Analysis of the chemical composition indicated the disparate evolution direction of wet and dry torrefied biomass, leading to increased and decreased oxygen containing functional groups, respectively. And, the chemical change of the wheat straw was more significant than that of beech wood. TGA results showed that the wet torrefaction increased, whereas the dry torrefaction decreased the volatile content, resulting in lower and higher char yield, respectively. Bio-oil quality was improved by both types of torrefaction despite some divergences in product distribution.