Lignin is a key component in the biomass with a complex polymeric structure of the phenyl-C3 alkyl<br/>units. The kraft lignin from the wood pulping process is tested in TG-FTIR and Py-GC-MS. The samples<br/>are pyrolyzed in TGA coupled with FTIR from 30 to 900 C at the heating rate of 20 and 40 K/min. The<br/>evolution of phenolic compounds in the initial pyrolysis stage of lignin is determined by FTIR, while<br/>the second stage is mainly attributed to the production of the low molecular weight species. A benchscale<br/>fast pyrolysis unit is employed to investigate the effect of temperature on the product yield and<br/>composition. It is found that the guaiacol-type and syringol-type compounds as the primary products<br/>of lignin pyrolysis are predominant in bio-oil, acting as the significant precursors for the formation of<br/>the derivatives such as the phenol-, cresol- and catechol-types. A series of free-radical chain-reactions,<br/>concerning the cracking of different side-chain structures and the methoxy groups on aromatic ring,<br/>are proposed to demonstrate the formation pathways for the typical compounds in bio-oil by closely<br/>relating lignin structure to the pyrolytic mechanisms. The methoxy group (–OCH3) is suggested to work<br/>as an important source for the formation of the small volatile species (CO, CO2 and CH4) through the relevant<br/>free radical coupling reactions
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