Free radicals in lignin as the key to chemicals based on biomass

The aim of the project was to gain new insights into the chemical reactivity of different types of lignin in view of achieving a controlled depolymerisation, i.e. breakdown of long-chain molecules into shorter chains.

Biomass has the potential to offer an alternative to fossil oil as a starting substance for the production of chemical products in the near future. The basic components of biomass are organic carbon compounds, including so-called aromatic hydrocarbons. These hydrocarbons form large molecules in lignin, an important component of wood. If they are to be used as chemicals, they need to be broken down into smaller chains. To ensure that we can produce the right sort of molecules, we need to understand the structure of lignin and how it reacts to various catalysts.

The structure of lignin differs depending on the type of wood. The method by which the lignin is extracted is a source of further variations in lignin structures. In this project, the researchers extracted lignin from beech, spruce, poplar and pine wood using various known chemical methods. They then analysed composition, structure and chemical properties of the extracted lignin. Alongside the standard analyses, the researchers used, in particular, electron paramagnetic resonance spectroscopy in order to determine the nature and concentration of the free radicals. By altering the solvent, the temperature and other parameters, the researchers determined how the types of free radicals and their concentration changed. The new insights are expected to contribute to the economical production of phenols on the basis of lignin.

The research results offer new insights into the reactivity of lignin. Based on them, it should be possible to break down lignin in a controlled manner to produce various chemicals in an economically viable way.

The way in which the lignin is extracted has a strong impact on its structure and reactivity. Compared to this, the botanical source of the lignin is less important. The production of valuable chemicals is most promising if the lignin is extracted at low temperatures and in a water-based environment.

Understanding and manipulating free radicals in lignin for a controlled depolymerisation to chemicals