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The pyrolytic behavior of wood is investigated under inert and oxidative conditions. The TGA experiment is given a temperature variation from 323 to 1173 K by setting the heating rate between 5 and 40 K/min. The results of DTG curves show that the hemicellulose shoulder peak for birch is more visible under inert atmosphere due to the higher content of reactive xylan-based hemicellulose (mannan-based for pine). When oxygen presents, thermal reactivity of biomass (especially the cellulose) is greatly enhanced due to the acceleration of mass loss in the first stage, and complex reactions occur simultaneously in the second stage when char and lignin oxidize. A new kinetic model is employed for biomass pyrolysis, namely the distributed activation energy model (DAEM). Under inert atmosphere, the distributed activation energy for the two species is found to be increased from 180 to 220 kJ/mol at the solid conversion of 10-85% with the high correlation coefficient. Under oxidative atmosphere, the distributed activation energy is about 175-235 kJ/mol at the solid conversion of 10-65% and 300-770 kJ/mol at the solid conversion of 70-95% with the low correlation coefficient (below 0.90). Comparatively, the activation energy obtained from established global kinetic model is correspondingly lower than that from DAEM under both inert and oxidative environments, giving relatively higher correlation coefficient (more than 0.96). The results imply that the DAEM is not suitable for oxidative pyrolysis of biomass (especially for the second mass loss stage in air), but it could represent the intrinsic mechanism of thermal decomposition of wood under nitrogen better than global kinetic model when it is applicable., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Lignin is a key component in the biomass with a complex polymeric structure of the phenyl-C(3) alkyl units. The kraft lignin from the wood pulping process is tested in TG-FTIR and Py-GC-MS. The samples are pyrolyzed in TGA coupled with FTIR from 30 to 900 degrees C at the heating rate of 20 and 40K/min. The evolution of phenolic compounds in the initial pyrolysis stage of lignin is determined by FTIR, while the second stage is mainly attributed to the production of the low molecular weight species. A bench-scale fast pyrolysis unit is employed to investigate the effect of temperature on the product yield and composition. It is found that the guaiacol-type and syringol-type compounds as the primary products of lignin pyrolysis are predominant in bio-oil, acting as the significant precursors for the formation of the derivatives such as the phenol-, cresol- and catechol-types. A series of free-radical chain-reactions, concerning the cracking of different side-chain structures and the methoxy groups on aromatic ring, are proposed to demonstrate the formation pathways for the typical compounds in bio-oil by closely relating lignin structure to the pyrolytic mechanisms. The methoxy group (-OCH(3)) is suggested to work as an important source for the formation of the small volatile species (CO, CO(2) and CH(4)) through the relevant free radical coupling reactions., ((c) 2010 Elsevier Ltd. All rights reserved.)

Experiment is performed to investigate the mechanism of the cellulose pyrolysis and the formation of the main products. The evolution of the gaseous products is examined by the 3-D FTIR spectrogram at the heating rate of 5-60 K/min. A pyrolysis unit, composed of fluidized bed reactor, carbon filter, vapour condensing system and gas storage, is employed to investigate the products of the cellulose pyrolysis under different temperatures (430-730 degrees C) and residence time (0.44-1.32 s). The composition in the bio-oil is characterized by GC-MS while the gases sample is analyzed by GC. The effects of temperature and residence time on the main products in bio-oil (LG, 5-HMF, FF, HAA, HA and PA) are examined thoroughly. Furthermore the possible routes for the formation of the products are developed from the direct conversion of cellulose molecules and the secondary reactions of the fragments. It is found that the formation of CO is enhanced with elevated temperature and residence time, while slight change is observed for the yield of CO(2).