Conversion of birch bark to biofuels†
Substitution of fossil energy sources for bio-based ones will require development of efficient processes that can convert inedible and preferably low-value fractions that currently are not used into high-value products. It is desirable that such processes are developed so that both current logistics and infrastructure can be used. Bark, which is the outer layer of woody biomass, is currently burnt in a low-value process or left in the forests to decay and is therefore considered waste. In this work, birch (Betula pendula) bark was converted to hydrocarbons suitable for use in both road and aviation fuels in two efficient steps. Development of an efficient, recyclable, salt- and metal-free solvent-based system to solubilize birch bark under benign reaction conditions was a key outcome. The obtained gum was composed of organosolv lignin and suberin oligomers and was fully characterized. This gum had unique properties and could be directly processed in a conventional hydroprocessing unit set-up to afford hydrocarbons in the road and aviation fuel ranges. Life cycle assessment was applied to evaluate different scenarios for implementing this technology. When using bark generated as a forestry by-product and current infrastructure in a pulp mill, the process had a favorable low carbon dioxide footprint for biofuel generation.