Abstract :
[en] Lignin is a promising molecule constituting a renewable alternative to some petrochemical industry products. Lignin is an aromatic cross-linked heteropolymer composed of three phenylpropanoids (p-hydroxyphenyl, guaiacyl and syringyl units) linked together via radical coupling reactions by specific ether or carbon-carbon bonds. With this phenylpropanoid structure, lignin is a rich resource of biobased products that could find high-valued applications in a lot of different areas like petrochemical polymer reinforcement and replacement, antioxidants, stabilizers, resins and vanillin production...
The first challenge of the valorization of lignins is their extraction from raw materials. Lignins can be found in different lignocellulosic substrates like grasses, softwood and hardwood. This extraction process needs the development of suitable biomass treatments, allowing efficient lignin recuperation without degradation. This one could lead to the loss of some interesting properties and so of some valorization possibilities.
In this study, beech wood (Fagus sylvatica L.) was collected in the region of Gaume (Belgium). Beech wood particles were delignified at atmospheric pressure by a mixture of formic acid/acetic acid/water. A central composite design and response surface methodology were used for the optimization of treatment parameters for delignification.
The optima of two independent variables, namely time (1h30, 3h, 4h30) and temperature (87°C, 97°C, 107°C), were determined on delignification yield, pulp yield, concentration of degradation products (furfural and hydroxymethylfurfural). Moreover, the impact of these two variables on the amount of residual linkages between phenylpropanoid units was evaluated by semi-quantitative bidimensional nuclear magnetic resonance spectroscopy (NMR-HSQC).
Our results highlight that the delignification yields increase when cooking time and temperature are elevated. Nevertheless, under these conditions, pulp yield decreases as hydrolysis of hemicelluloses and cellulose occurs. The hydrolysates of carbohydrates (free sugars or oligosaccharides) are contained in the black liquor. At elevated temperature and time, the amount of degradation products in the black liquor is increased.
