The pyrolysis of lignin: Pathway and interaction studies

Three different lignin samples (alkali lignin, THF separated lignin) and hemicellulose removed biomass samples were pyrolyzed at various temperatures and heating rate in a wire mesh reactor (WMR). The product distribution and characterisation of liquid product were analyzed and compared to obtain the pyrolysis behavior of lignin and the possible interaction. Different reactivities were observed for the studied components. The pathway of lignin pyrolysis was proposed. Heating rate and temperature played a significant role on the lignin and biomass pyrolysis. At intermediate temperatures of 450–525 °C, the phenols in liquid products were at maximum, while lower and higher temperatures promoted to the formation of dimer compounds in liquid product·THF soluble lignin favored the production of liquid, while THF insoluble lignin mainly formed solid residues. The interaction between THF separated lignin can promote the formation of phenols through the cracking of carboxylic acid, ketone and aldehyde and inhibit the coupling reaction of free radicals into dimer compounds. An interaction between lignin and cellulose was also observed leading to a lower solid residue but a higher yield of liquid. The interaction between lignin and cellulose also promoted the secondary decomposition of guaiacol derivates forming new compounds such as benzene, phenol and p-xylene and inhibited the condensation reaction of lignin.