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Projeto de investigação
Lignin and phenolic-based extractives as key components for the bio-economic sustainability of biorefineries
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Chemical characterization of lignocellulosic materials by analytical pyrolysis
Publication . Lourenço, Ana; Gominho, Jorge; Pereira, Helena
Analytical pyrolysis is used to chemically study complex molecular materials
and is applied in a wide range of fields. Pyrolysis is a thermochemical process
associated to the breaking of chemical bonds using thermal energy, transforming
a nonvolatile compound into a volatile degradation mixture. This chapter
refers to analytical pyrolysis of lignocellulosic materials, i.e., when pyrolysis is
used for chemical characterization, applied to samples with small particle sizes,
at 500–650°C, and with short residence times. The reactions that occur during
pyrolysis of the structural components are discussed regarding the mechanisms
and the pyrolysis products obtained from cellulose, hemicelluloses, and lignin.
A compilation of data is made on the characterization of lignocellulosic materials
using Py-GC/FID(MS) or Py-GC/MS as analytical tools including woods and
barks of several species. The pyrogram profiles and important parameters on lignin
chemical composition such as the H:G:S relation and the S/G ratio are summarized.
Analytical pyrolysis is a versatile methodology that may be applied to characterize
the lignin directly on the lignocellulosic material or after isolation from the cell wall
matrix (e.g., as MWL or dioxane lignin) or from pulps or spent liquors. It is therefore
an excellent tool to study lignin compositional variability in different materials
and along various processing pathways.
Compositional variability of lignin in biomass
Publication . Lourenço, Ana; Pereira, Helena
The objective of this chapter is to provide a concise overview of lignin composition and
structure in different species and materials (wood, barks and nonwood plants). It includes
a brief review on the lignin precursors and their polymerization as well as of the analytical
tools used for lignin characterization from wet chemical to spectroscopic methods. Wood
of gymnosperms is characterized by high lignin content (25–35%) and a HG-type of lignin
with more guaiacyl (G) units and a small portion of p-hydroxyphenyl (H) units. Wood of
angiosperms has a lignin content of 15–28%, with a GS-lignin having different proportions
of syringyl (S) units. Nonwoody monocotyledon species have different lignin content
(9–20%) and a HGS type of lignin, characterized by a high proportion of H units. Bark
lignin content ranges from 13 to 43% and is of HGS-type with species-specific composition
and different in the bark components, phloem and cork. Lignin composition and macromolecular
structure are key issues to understand the properties of lignocellulosic materials
and to design a lignin-based pathway within biomass biorefineries. The available information
on lignin composition is still limited to a few species and plant components. This is
certainly an area where more research is needed.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
OE
Número da atribuição
SFRH/BPD/95385/2013