Combined production of fuels and chemicals from wood

The project team examined a special steam pretreatment that can break down the structure of wood. The process is characterised by the addition of so-called radical scavengers to stop lignin fragments from repolymerising. As a result, the subsequent enzymatic hydrolysis produces higher yields of sugar, which can then be turned into biofuels. In addition, the researchers analysed a concept to use lignin in the production of chemicals.

Biofuels from wood have economic and ecological advantages as compared to fuels from corn and sugar cane (costs, availability, no conflict with food production). But it is much more difficult to turn wood into biofuels. This is because the components of wood-cellulose, hemicelluloses and lignin are strongly interwoven. In the production of biofuels, this impedes the enzymatic degradation of lignocellulose into sugar, which can subsequently be fermented to produce, for example, bioethanol. Therefore, it is necessary to pretreat the wood in order to break up its structure and improve the enzymatic access.

Steam pretreatment is a possible pretreatment of biomass. But this approach is hampered by cross-linking reactions of emerging lignin fragments. So-called "radical scavengers" can stop these undesired reactions and make the wood much more soluble. The developed procedure is aimed at achieving, on the one hand, a cellulose fraction with improved enzymatic access and, on the other hand, a high-quality lignin fraction. The latter serves as a starting material for the production of aromatic chemicals.

The examined approach is aimed at producing fuels and aromatic chemicals which are today still gained almost exclusively from petrochemical resources. This opens up new avenues for gradually replacing some fossil oil with biomass.

The researchers showed that steam pretreatment in combination with radical scavengers leads to an increased glucose yield from conifers by up to 64 per cent.

They then transferred the process from the stirred-tank reactor of the laboratory to an industrial steam-explosion reactor and could show that the glucose yield increased by 150% per cent if steam explosion was used to pre-treat the wood.

Use of scavengers in the pretreatment of lignocellulosic biomass for improved chemicals production