• Energy Research

AbstractLignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E. globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p‐hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in β‐ether linkages (83 %), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of ≈5:50:45), with a predominance of β‐ethers (73–75 %) and lower amounts of condensed carbon–carbon linkages; the lignin from A. dealbata bark also includes some resorcinol‐related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P. abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in β‐O‐4′ alkyl–aryl ether linkages (44 %) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorization.

AbstractPine nut shells, a biomass residue from the Mediterranean Pinus pinea pine nut industrial processing, were treated by microwave-assisted autohydrolysis to produce xylo-oligosaccharides. Microwave-assisted processes provide alternative heating that may reduce energy input and increase overall process efficiency. The autohydrolysis treatments were performed under isothermal and non-isothermal operations within a wide range of operational conditions (temperature/reaction times) covering several severity regimes (as measured by the log R0 severity factor). The composition of the autohydrolysis liquors was determined in terms of oligo- and monosaccharides, aliphatic acids and degradation compounds. The process was highly selective towards hemicelluloses hydrolysis and liquid streams containing a mixture of oligomeric compounds (mainly xylo-oligosaccharides) could be obtained under relatively mild operation conditions (190 °C, 30 min) with a maximal oligosaccharides’ concentration of 18.48 g/L. The average polymerization degree of the obtained oligosaccharides was characterised by HPLC, showing that for the optimal conditions a mixture of oligomers with DPs from 2 to 6.

AbstractClimate change induces in the Mediterranean region more frequent and extreme events, namely, heat waves and droughts, disturbing forest species and affecting their productivity and product quality. The cork oak (Quercus suber) is present along the western Mediterranean basin and its outer bark (cork) is sustainably collected and used for several products, mainly wine bottle stoppers. Since most cork properties arise from its chemical composition, this research studies the effect of drought on cork chemical composition (suberin, lignin, polysaccharides and extractives) and on polysaccharide and suberin monomeric composition. Three sets of cork samples, from the same site, were examined: in one set the cork grew without drought; in another two drought events occurred during cork growth and in the third one drought event happened. The results show that, in general, drought does not affect the proportion of the main components of cork, the monomers of suberin or of polysaccharides, with few exceptions e.g. drought increased ethanol extractives and xylose in polysaccharides and decreased arabinose in polysaccharides. The variability associated to the tree is much more relevant than the effect of drought conditions and affects all the parameters analyzed. Therefore, our research suggests that the tree genetic information, or its expression, plays a much more important role on the chemical composition of cork than the drought conditions occurring during cork growth. In practical terms, the potential increased occurrence of droughts arising from climatic changes will not compromise the performance of cork as a sealant for wine bottles.

AbstractThe torrefaction is a thermal pre-treatment to improve biomass quality for biofuel applications. In this study, the effects of a mild torrefaction (T) on eight eucalypt species (Eucalyptus botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. salignaandE. viminalis) have been compared. Namely, the mass loss (ML), the equilibrium moisture content (EMC), density and chemical composition were determined and FTIR spectra were recorded of the initial and torrefied woods (TWs). The average ML was 11% and the heat-treated woods had an overall 10% density decrement. All the TW had 50% lower EMC compared to untreated wood samples (W). Elemental composition showed that carbon content increased from 48% to 53% and the oxygen/carbon ratio decreased from 0.80 to 0.65. The chemical changes induced by T included an increment of extractives, a 20% higher lignin content and a 16% lower holocellulose content in relation to W. The hemicelluloses modification is manifested by a decrease of xylose, galactose, and acetyl groups in TWs. The fourier transform infrared (FTIR) spectra of the different wood species were very similar, and reflected in a uniform manner the chemical changes upon T. Because of the similar reaction of the eucalypt species, they can also be used in form of mixed eucalypt feedstock as biofuel.

Ring width and wood density variation were studied from pith-to-bark and along the stem in two naturally regenerated stands of Quercus faginea Lam. in Portugal. Ring width was significantly different between sites, in both heartwood and sapwood rings, ranging from 1.83 mm to 2.52 mm and from 0.77 mm to 2.11 mm, respectively. Wood density was significantly different between sites only in the heartwood, i.e., 914 kg m−3 and 1037 kg m−3. Site effects were the main source of variation for ring width and wood density within the heartwood as well as for sapwood ring width, while the between-tree effects explained more the density variation within the sapwood. Wood density showed within-tree uniformity that was not affected by site. The stand characteristics such as basal area and tree age may override the environmental growth conditions. There was also a weak correlation between wood density and ring width components therefore suggesting the possibility of forestry management for both fast tree growth and high wood density.

Forest residues have been gaining interest as a source of renewable fuels due to their availability and the risks they represent for increasing forest fires. A major drawback for their removal and processing is the cost of transportation, which can be overcome through densification procedures, e.g., torrefaction. To optimize the torrefaction parameters, Cistus ladanifer residues from the Portuguese forest were torrefied for 30 min in a lab-scale reactor at 250 and 350 °C. The quality of the torrefied material was assessed, and its energy and mass yields were determined through thermal analysis. The changes in morphological structure occurring during torrefaction were analysed through scanning electron microscopy. When compared to the original biomass, the charcoal obtained at 350 °C had a substantial increase in energy density accompanied by a significant mass reduction. Increasing the mass in the reactor had a positive effect on the energy yield. For the highest mass tested, a mass reduction of around 30% was obtained and a char with no loss in energy content (with a cumulative heat flow (CHF) of 9.0 MJ/kg compared to 5.8 MJ/kg of the original biomass). Modelling of the reactor allowed the analysis of the heat profile required for torrefaction.

Four Cynara cardunculus clones, two from Portugal and two from Spain were studied for biomass production and their lignin was characterized. The clones differed in biomass partitioning: Spanish clones produced more capitula (54.5% vs. 43.9%), and Portuguese clones more stalks (37.2% vs. 25.6%). The heating values (HHV0) of the stalks were similar, ranging from 17.1 to 18.4 MJ/kg. Lignin was studied by analytical pyrolysis (Py-GC/MS(FID)), separately in depithed stalks (stalksDP) and pith. StalksDP had in average higher relative proportions of lignin derived compounds than pith (23.9% vs. 21.8%) with slightly different lignin monomeric composition: pith samples were richer in syringyl units as compared to stalksDP (64% vs. 53%), with S/G ratios of 2.1 and 1.3, respectively. The H:G:S composition was 7:40:53 in stalksDP and 7:29:64 in pith. The lignin content ranged from 18.8% to 25.5%, enabling a differentiation between clones and provenances. © 2015 Published by Elsevier Ltd.