The Challenge of Lignin as a Chemical Resource

Bio based platform chemicals can be provided through lignin, especially aromatic compounds. Lignin is a 3D- macromolecule which contains phenolic structures and a variety of functional groups. The ecological point of view of the exchange of crude oil production strains with biomass like lignin should be held high. Nevertheless, on the one hand lignin is a natural molecule which is built to resists environmental influences, so the use as a starting material held a lot of challenges. On the other hand, lignin could be a source of bifunctional molecules, like the monocyclic compounds catechol or guaiacol, which can be used as monomeric compounds for polymers. However, no method for aromatics production from lignin has been established by now.Hence, the focus of the presented work is to get a better knowledge of lignin as a starting material to produce chemicals. Therefore, the different influences of temperature and reaction times, the reaction pathways and the therefore necessary analytics need to be understood. But lignin brings a lot of challenges with it. The first is that every lignin has a different composition, depending on the wood source and the degradation method applied to gain the lignin which has a significant influence on the lignin structure. And with this, a lot of changes come e.g. in the handling of the biomass. To liquefy lignin towards high functional molecules, hydrothermal conditions are used. Water is already a main component of biomass and an ecological friendly solvent. It further proved to increase the yield and selectivity towards bifunctional molecules like catechol. The combination of fast hydrolysis, thermal degradation reactions, and hydrogenation drives the hydrothermal liquefaction; this gives the possibility to narrow down the product spectrum in comparison to other "dry" methods, towards a higher yield of e.g. catechols.