The influence of inorganic species content on the slow pyrolysis of thermally thick wood particles has been investigated with the application of laser-based spectroscopic techniques. Infrared laser absorption and laser-induced fluorescence were used to characterize, on-line and in situ, the release of permanent gases (CO and CH4) and of species emitting fluorescence, respectively. These advanced methods were combined with the continuous monitoring of mass and temperature and with off-line GC–MS analysis of the liquid fraction. The experiments were performed using spherical particles of beech, H2O- and HCl-washed beech, KCl-doped beech, and pine. The pyrolytic behavior of washed beech (with lower content in inorganic species) was found to resemble much closely the one of pine, rather than the one of beech, probably due to the pine low content in K. Both washed beech and pine showed a more clear separation between cellulose and lignin decomposition, being lignin decomposition, and potentially the presence of heterogeneous secondary reactions, shifted to higher temperatures. The release of species emitting fluorescence was also affected by the removal/addition of inorganic species. K was observed to catalyze the pyrolysis reaction. A strong exothermic behavior, coincident with the maximum of the TFI (tracking the release of fluorescence-emitting species -e.g. PAHs-), was observed, attributed to the presence of heterogeneous secondary (charring) reactions. Moreover, at the end of the pyrolysis process, reactions in the char matrix, enhanced by the presence of K, were detected, with no further significant mass loss or temperature gradient, leading also to the formation of fluorescence-emitting species (e.g. PAHs). Higher content in inorganic species (beech versus washed beech) resulted also in lower major carbohydrates yields and slightly higher guaiacols, syringols, and phenols yields. This indicates an enhancement of charring reactions, in good agreement with the higher exothermicity, as well as in fragmentation reactions and in lignin reactivity with higher presence of inorganic species.
- Heterogeneous secondary reactions
- Infrared laser absorption spectroscopy
- Laser-induced fluorescence spectroscopy
ASJC Scopus subject areas
- Analytical Chemistry
- Fuel Technology