New ways for utilisation of willow biomass: Willow wood as a novel source of lignocellulosic sugars and green aromatics

Due to the escalating global demand for energy, diminishing petroleum reserves, and the concern over rising CO₂ emissions, new non-food plant sources are needed for production of renewable chemicals and fuels. Willow (Salix sp.) represents such currently under-utilised biomass source that has a high potential to serve as a raw material for fractions with higher value than the baseline energy value. In addition, willow is fast growing and able to grow on lands not optimal for forest or agricultural use (e.g. lands with low productivity and peatlands after peat harvesting) and it can efficiently bind nutrients from runoff or waste water. Willow has been comprehensively studied as an energy crop, but the high contents of water and bark in willow biomass have been considered to be challenges for combined heat and power production. Willow wood fibres are short and therefore not favourable for pulp production. Thus, new biorefinery concepts need to be developed for the more efficient and economically feasible use of willow biomass. In the project conducted as a cooperation of VTT and Aalto, the valorisation of willow wood resulted in lignocellulosic sugars for production of green chemicals as well as a lignin residue that could be depolymerized for the production of aromatics needed in chemical industry. This concept would benefit forest owners by more efficient use of land, biofuel producers by giving a novel source of lignocellulosic sugar and chemical manufacturers by serving a sustainable source of green aromatics. The suitability of willow wood for sugar platform was characterised both with bark and as debarked. The microstructure and enzymatic hydrolysability of pre-treated willow wood were analysed and evaluated. In addition, structural features of willow lignin were characterised before and after steam pretreatment to evaluate its potential as biobased aromatic raw material.