No abstract

Pyrolytic reactions of Japanese cedar (Cryptomeria japonica, a softwood) and Japanese beech (Fagus crenata, a hardwood) milled wood lignins (MWLs) were studied with thermogravimetry (TG) and by pyrolysis in a closed ampoule reactor (N 2 / 600 °C). The data were compared with those of guaiacol/syringol as simple lignin model aromatic nuclei. Several DTG peaks were observed around 300-350, 450, 590 and 650 °C. The first DTG peak temperature (326 °C) of beech was lower than that (353 °C) of cedar. This indicates that the volatile formation from cedar MWL is slightly delayed in heating at 600 °C. The gas-phase reactions via GC/MS-detectable low MW products were explainable with the temperature-dependent reactions observed for guaiacol/syringol in our previous paper. The methoxyl groups became reactive at ~450 °C, giving O-CH 3 homolysis products (catechols/pyrogallols) and OCH 3 rearrangement products (cresols/xylenols). The former homolysis products were effectively converted into gaseous products (mainly CO) at >550-600 °C. However, the GC/MS-detectable tar yields, especially syringyl unit-characteristic products, were much lower than those from guaiacol/syringol. Thus, contributions of higher MW intermediates and solid/liquidphase reactions are more important in lignin pyrolysis. From the results of stepwise pyrolysis of char+coke fractions at 450 and 600 °C, the methoxyl group-related reactions (450 °C) and intermediates gasification (600 °C) were suggested to occur also in the solid/liquid phase. This was consistent with the DTG peaks observed around these temperatures. These solid/liquid-phase reactions reduced the tar formation, especially catechols/pyrogallols and PAHs. Different features observed between these two MWLs are also focused.

a b s t r a c tThermal reactivities of lignin pyrolysis intermediates, catechols/pyrogallols (O-CH 3 homolysis products) and cresols/xylenols (OCH 3 rearrangement products), were studied in a closed ampoule reactor (N 2 /600 • C/40-600 s) to understand their roles in the secondary reactions step. Reactivity tends to be enhanced by increasing the number of substituent groups on phenol and this effect was greater for -OH than for -CH 3 . Thus, catechols/pyrogallols were more reactive than cresols/xylenols and syringol-derived products were more reactive than corresponding guaiacol-derived products. Catechols/pyrogallols were effectively converted into CO (additionally CO 2 in the case of pyrogallols) in the early stage of pyrolysis. In contrast, cresols/xylenols were comparatively stable and produced H 2 , CH 4 and demethylation products (cresols and phenol) after prolonged heating. All intermediates except phenol and 2-ethylphenol formed coke during a long heating time of 600 s (second stage coking). Based on the present results, the roles of intermediates in tar, coke and gas formation from guaiacol and syringol are discussed at the molecular level, focusing on their differences. Molecular mechanisms of gas formation from pyrogallols and demethylation of cresols/xylenols are also discussed.

No abstract

Chemical structures of hemicellulose and lignin are different for two distinct types of wood species, i.e. softwood and hardwood. Such differences are expected to affect the pyrolysis behaviors. In this paper, they were discussed for Japanese cedar wood (a softwood) and Japanese beech wood (a hardwood) pyrolyzed in a closed ampoule reactor (N 2 / 600 o C/ 40-600 s). The oven-dried samples were used for the purpose of eliminating the influence of initial water. Their demineralized samples (prepared by acid washing) were also used to understand the influence of the minerals contained in the wood samples. As a result, some features were disclosed for secondary char (coke) formation, char reactivity, tar formation and subsequent decomposition and so on.