The variations in chemical composition and the effects of sample origin and pretreatments represent a major problem in the kinetic modeling of wood pyrolysis. This study aims to a deeper understanding of these issues by examining a species, chestnut (Castanea sativa), that contains a higher amount of extractives than the common forest hardwoods of the temperate zone. Thermogravimetric and kinetic analyses were carried out on five chestnut samples obtained from plants grown in France, Italy, and Russia. The results were compared to that of a widely used and investigated species (beech) belonging to the same plant family. Degradation takes place over a narrower range and at lower temperatures, giving higher yields of char. In all cases, hot-water washing causes a decrease in the fixed carbon content and char yield, an increase in the peak rate, a better separation between pseudo-component dynamics, and a displacement of the reaction zones toward higher temperatures. Though with some scatter and quantitatively lower, the same effects are also observed as a consequence of acetone extraction. Both pretreatments act to reduce the differences between chestnut samples and with beech, but peculiarities due to origin and species are preserved. The three parallel reaction mechanism for the hemicellulose, cellulose, and lignin, with the same activation energies previously determined for other hardwood species by Grønli et al. (Ind. Eng. Chem. Res. 2002, 41, 4201) is still acceptable for engineering applications. In contrast, predictions of the process details require single curves evaluations, resulting in kinetic data specific to sample origin, except for the activation energy of the lignin devolatilization step. Kinetic parameters also indicate that the lower char yields, associated with pretreatments, are chiefly due to alterations in the cellulose decomposition kinetics, whereas the effects on the other two components nearly compensate each other. Finally, reliable evaluations are provided of experimental uncertainties associated with repeatability of experiments and reproducibility of sample properties.

Effects of sample origin, extraction and hot water washing on the devolatilization kinetics of chestnut wood

DI BLASI, COLOMBA
2004

Abstract

The variations in chemical composition and the effects of sample origin and pretreatments represent a major problem in the kinetic modeling of wood pyrolysis. This study aims to a deeper understanding of these issues by examining a species, chestnut (Castanea sativa), that contains a higher amount of extractives than the common forest hardwoods of the temperate zone. Thermogravimetric and kinetic analyses were carried out on five chestnut samples obtained from plants grown in France, Italy, and Russia. The results were compared to that of a widely used and investigated species (beech) belonging to the same plant family. Degradation takes place over a narrower range and at lower temperatures, giving higher yields of char. In all cases, hot-water washing causes a decrease in the fixed carbon content and char yield, an increase in the peak rate, a better separation between pseudo-component dynamics, and a displacement of the reaction zones toward higher temperatures. Though with some scatter and quantitatively lower, the same effects are also observed as a consequence of acetone extraction. Both pretreatments act to reduce the differences between chestnut samples and with beech, but peculiarities due to origin and species are preserved. The three parallel reaction mechanism for the hemicellulose, cellulose, and lignin, with the same activation energies previously determined for other hardwood species by Grønli et al. (Ind. Eng. Chem. Res. 2002, 41, 4201) is still acceptable for engineering applications. In contrast, predictions of the process details require single curves evaluations, resulting in kinetic data specific to sample origin, except for the activation energy of the lignin devolatilization step. Kinetic parameters also indicate that the lower char yields, associated with pretreatments, are chiefly due to alterations in the cellulose decomposition kinetics, whereas the effects on the other two components nearly compensate each other. Finally, reliable evaluations are provided of experimental uncertainties associated with repeatability of experiments and reproducibility of sample properties.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/204527
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