Torrefaction of wood and bark from Eucalyptus globulus and Eucalyptus nitens: Focus on volatile evolution vs feasible temperatures

Torrefaction is a thermal pretreatment leading to the improvement of most of the fuel properties of biomass, namely energy density, HHV (higher heating value), grindability and hydrophobicity. The aim of this study is to identify the most feasible temperature to carry out torrefaction of Eucalyptus globulus and nitens, based on chemical evidences associated to the release of volatiles during thermal treatment of biomass. With that end: (i) Devolatilization kinetics, (ii) Effects of temperature and residence time and (iii) volatiles composition during torrefaction of both wood and bark were analyzed. In all cases DIG (derivative thermogravimetric curves) exhibited the typical shape of lignocellulosic materials, with three decomposition phases and two reaction zones. Values of activation energies for hemicellulose decomposition, were in agreement with those reported in the literature (121-170 kJ/mop. Carboxylic acids, water and phenolic compounds showed two peaks, which were associated to torrefaction (below 310 degrees C) and pyrolysis (310-410 degrees C) respectively. The most feasible temperatures for torrefaction were estimated as a function of these peaks, and it ranged between 295 degrees C and 310 degrees C for all samples. Main volatile species at the torrefaction peaks were distributed as Water > Acetic Acid > CO2 > Others, while Levoglucosan formation was marginal, due to the catalytic effect of inorganics. (C) 2015 Elsevier Ltd. All rights reserved.