Fractionation of woody biomass : lignin and suberin in focus

Sammanfattning: This thesis is dedicated to the research of fractionation and valorization of different types of woody biomass. In the first part, oak (Quercus suber) and birch (Betula pendula) barks are considered. Bark is the outer layer of wood and is treated as waste in the current wood processing technologies. The main polymers which form bark are lignin (aromatic polyether) and suberin (aliphatic polyester). In the present study, these compounds have been transformed into monomeric phenols which may serve as a precursors for bio-based polyesters, and hydrocarbon bio-oil of gasoline, diesel, and heavy gas oil ranges. The bio-oil has been studied with GC-MS, 2D GC, and simulated distillation techniques.   The second part concerns birch heartwood. In contrast with bark, wood does not contain suberin but has a higher content of lignin. A variety of fractionation processes are known for wood. The major disadvantages are contamination of pulp with catalyst and irreversible recondensation of lignin which takes place in harsh pulping conditions. For the purpose of solving these problems, a flow process has been developed in which the biomass and the catalyst are separated in time and space and the lignin is stabilized and cleaved into monomers immediately after its extraction. The process has been optimized to obtain monophenolic lignin-derived compounds, while the remaining cellulose pulp was enzymatically converted into glucose. Hemicellulose serves as a hydrogen donor for the lignin reduction, and therefore no external hydrogen source is required. The experimental work was complemented with a theoretical study of the process of lignin cleavage on the Pd surface. Computations under on the ReaxFF approach were used to model the successive steps of the adsorption of the molecules on the catalyst, their fragmentation, reactions, and desorption. The products obtained in the experiment have been also observed in this simulation.