Effects of torrefaction on hemicellulose structural characteristics and pyrolysis behaviors.

The effects of torrefaction on hemicellulose characteristics and its pyrolysis behaviors were studied in detail. The oxygen content decreased significantly after torrefaction, leading to the increase of high heating value. Two-dimensional perturbation correlation analysis based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed to characterize the structural evolutions. It was found the dehydration of hydroxyls and the dissociation of branches were the main reactions at low torrefaction temperature. When the temperature further increased, the depolymerization of hemicellulose and the fragmentation of monosaccharide residues occurred. The distributed activation energy model with double Gaussian functions based on reaction-order model was used to investigate the pyrolysis kinetics. The results showed that torrefaction enhanced the activation energy for degradation reactions while lowered that for condensation reactions, and increased the devolatilization contribution of condensation reactions. Besides, torrefaction decreased the yields of typical pyrolytic products, such as acids, furans, alicyclic ketones and so on.