Free radicals in lignin as the key to "green" chemicals Free radicals in the lignin probably present the key to its chemical breakdown into valuable chemicals. Should it be possible to influence the type and number of these highly chemically active molecules, this could lead to new procedures for making "green" chemicals.

Lay summary

Biomass has the potential to replace fossil oil in the near future as a starting substance for the production of chemical products. The basic components of biomass are organic carbon compounds, including so-called aromatic hydrocarbons. In lignin—the "glue" that holds plants together—the latter are cross-linked in different ways to form a large molecule (macromole-cule). In order to be able to use the aromatic hydrocarbons in lignin as chemicals, they need to be split up into individual molecules. Without an understanding of the composition of lignin and of how it reacts to chemical "pressures", it is not possible to obtain more than a little of the desired substances, alongside many substances that are similar.

The macromolecule lignin has a different composition from plant to plant. The manner in which the lignin is retrieved from the plant also changes the structure of the lignin. In this project, researchers retrieve lignin from beech, spruce, poplar and pine using recognised chemical methods and analyse its composition, structure and chemical properties. Alongside the standard analyses, the researchers apply, in particular, electron paramagnetic resonance spectroscopy in order to determine the nature and concentration of the free radicals. By changing the solvent and other parameters such as pH, temperature and the addition of catalysts, the researchers find out how the nature and concentration of the free radicals change. The new insights will be used to produce commercially exploitable phenols from lignin via thermochemical splitting (e.g. through catalytic flash pyrolisis).

The research work can generate new, fundamental knowledge about the reactivity of lignin. In the future, this may enable researchers to break down lignin and subsequently produce "green" chemicals economically.