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Catalytic Hydrogenation and Hydrogenolysis of Lignin Model Compounds in Ionic Liquid Environment

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Title: Catalytic Hydrogenation and Hydrogenolysis of Lignin Model Compounds in Ionic Liquid Environment
Author(s): Koskinen, Outi
Contributor: University of Helsinki, Faculty of Science, Department of Chemistry
Discipline: Organic chemistry
Language: English
Acceptance year: 2017
Lignin (wood in Latin) is a natural amorphous, aromatic polymer that acts as the essential glue and support that gives vascular plants their structural rigidity and colour. It is found mostly between but also within the plant cells and in the cell walls. Lignin consists of p-coumaryl (almost exclusively in grasses), coniferyl (common in softwoods) and sinapyl alcohol (common in hardwoods) monomers that form dimers with different linkage types depending on the types of monomer radicals combined together. As the result of lignin biosynthesis is a complex aromatic network where the β – aryl ether (β-O-4) linkage type is the most abundant one between monomer units. Within each type there is a lot of variation: lignins differ from species to species, and from one tissue to the next in the same plant--even within different parts of the same cell. Pulping industry separates lignin from biomass and the lignin waste is combusted on-site as energy for steam generation. Lignin is however potentially a renewable source of aromatic platform compounds that are important in other fields of industry. Many of these platform chemicals are currently obtained from fossil fuel sources. Hence there is an environmentally friendly need to develop efficient methods to convert lignin into high-value products. Rigid molecular structure of lignin and the abundant amount of hydrogen bonds in it makes it highly recalcitrant towards conventional solvents and mild reaction conditions. In addition a considerable sulfur content from the pulping processes establishes a catalyst poison. Thus the processing methods for lignin valorization need to be optimized with proper reaction conditions and effective catalysts while keeping the costs as reasonable as possible. This thesis is divided into literature and experimental sections. The literature section discusses about the chemical structure and biosynthesis of lignin, industrial view of lignin and a short review of recently examined studies of processing methods on lignin concentrating on hydrogen-dependent methods and ionic liquids as the hydrogen source. The experimental section concentrates on a novel ionic liquid in the studies with hydrogenation and hydrogen lysis of aileron, a widely used lignin model compound.

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