Spruce bark biorefinery

Norway spruce Picea abies is a key raw material for the forest industry in the Nordic countries. In order to improve the competitiveness of the forest industry by valorising residues and creating value from new products, we have studied the upgrading of spruce bark into transport fuels and chemicals. Different fractionation, pretreatment and enzymatic steps were carried out for industrial spruce bark to solubilize condensed tannin, purify the tannin extract, and to hydrolyse and ferment bark carbohydrates. Extracts containing over 50% of tannin were produced showing the potential of spruce bark as a promising source of renewable polyphenolic compounds. Steam explosion increased the hydrolysability of spruce bark polysaccharides as expected, but it was found that unpressurized hot water treatment alone, conducted for the extraction of tannin, may be sufficient in rendering bark amenable for enzymatic hydrolysis. The hydrolysed C6 sugars could be fermented efficiently to ethanol even in 15% solids content suggesting that no harmful inhibitors were released or produced in the process. Based on our results spruce bark is a promising feedstock for a multi­product forest biorefinery.