Comprehensive characterization of steam exploded woody biomass using NMR spectroscopy
Résumé
Biorefinery processes using lignocellulosic biomass (LB) are currently in full development to
fight overconsumption of fossil resources. However, LB can be difficult to transform, especially using
biological processes, due to the highly complex network formed by its constituents (cellulose,
hemicelluloses, and ligni n). A pretreatment step is usually required, among which steam explosion has
been found to be highly efficient and cost effective. Understanding LB recalcitrance and predict its
reactivity are challenges, which require a thorough characterization of pretre ated LB.
In our project, three structurally different wood species (oak, poplar, and spruce) were
pretreated with steam explosion and analyzed to assess physico chemical parameters using a
combination of NMR spectroscopy technics. This poster describes tho se techniques and their
complementarity to produce a comprehensive characterization of woody biomass samples.
The impact of steam explosion on cellulose supramolecular organization was investigated by
13 C multiCPMAS. An increase of cellulose crystallinity concomitant with an increase of aggregate
dimension was observed. Changes in the lignin structure, in relation to the decrease of β O 4 bonds,
were evidenced. To supplement these findings, polarization transfer kinetics was studied. The
dynamical parameter T 1 ρH was thus determined using the Variable Spin Lock (VSL) sequence. Steam
explosion led to the apparition of two populations within the lignocellulosic structure: one with
decreasing T 1 ρH values associated with a decrease of the molecular order, i.e. de structuring, and with
the density of water molecules in the macromolecular assembly, and the other with increasing T 1 ρ
H values meaning increased molecular order due to removing of amorphous cellulose. Furthermore, the
porosity distribution of these samples was evaluated by low field T 2 measurements at two different
water contents. Overall, we were able to evaluate the decrease in porosity of the samples and the
evolution of water accessibility during the steam explosion.
NMR spectroscopy is thus an efficient and far reaching analytical technique that allows to
investigate and better understand the effect of steam explosion of wood at molecular and
morphological levels, two key factors to predict wood reactivity for bioethanol production.