Effect of Torrefaction on the Structure and Pyrolysis Behavior of Lignin

The influences of torrefaction on the structure and pyrolysis behavior of lignin were investigated in this study. After torrefaction, the oxygen content of lignin was reduced, which led to the increase of its high heating value. The main reactions occurring during torrefaction were the cleavage of aryl ether linkages, demethoxylation, and dissociation of the aliphatic side chain, as indicated by Fourier transform infrared spectroscopy analysis. The distributed activation energy model with double combined Gaussian functions was adopted to analyze the pyrolysis kinetics of lignin. It was found that torrefaction increased the activation energy for degradation and condensation reactions. The devolatilization contribution of condensation reactions increased as well after torrefaction. Torrefaction also had a great effect on the pyrolytic product distribution of lignin. The yields of non-methoxylated phenols and phenols without a propyl side chain increased after torrefaction.