Kinetic Characterization of the Residues from the Pruning of Apple Trees for their Use as Energy Vectors

Abstract

The residues from the pruning of apple trees were evaluated for their use as feedstock in thermochemical processes with energy recovery purposes. With the aim to better understand their thermal and thermo- oxidative behavior, these residues were tested at the laboratories of the Free University of Bolzano by multi- rate linear non-isothermal thermogravimetric experiments under inert (nitrogen) and oxidant (oxygen) atmosphere conditions. They were tested at 2, 5, 10 and 20 °C/min as heating rates under a constant flow of 20 mL/min of gas of analysis. Their decomposition profiles and kinetic parameters were evaluated and compared for all samples. The thermogravimetric profiles showed four different decomposition stages for inert conditions that correspond to the main degradation processes (drying and cellulose, hemicellulose and lignin decomposition), whereas five different decomposition stages were found under oxidant conditions(the extra peak assigned to the combustion of char). The major loss was obtained in the range of T = 200°C – 400°C, regardless the atmosphere of work and the values of residue were higher when using nitrogen (N2) as a result of a lower reactive atmosphere. The characteristic peak temperatures of all decomposition processes increased when increasing the heating rate and when inert conditions were applied. A kinetic methodology based on the combination of iso-conversional methods /Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Vyazovkin) and the use of Master Plots assessed by Coats-Redfern criterion permitted to mathematically describe the thermo-chemical reactions under study.