Towards a Norwegian Spruce Bark Biorefinery

This project explores the development of a potential biorefinery based on Norwegian spruce bark using Soxhlet, microwave pyrolysis and subcritical water extraction processes in order to yield chemicals, materials and bioenergy. Spruce bark contains 18% ethanol extractives (Soxhlet extraction) including a significant amount of phenols and condensed tannins (39 mg GAE/g) commensurate with lignocellulosic matter. Component analysis of spruce bark revealed: cellulose (25%), hemicellulose (8%), lignin (25%), ethanol extractives (18%), ash (2%), moisture (9.2%), C (47.64%), H (5.91%), N (0.23%) and HHV (17.3 MJ/kg). Depending on the processing temperature, microwave pyrolysis of spruce bark yielded bio-oil (8%-14%) and bio-char (65%-75%) depending on pyrolysis temperature. The bio-oil mainly comprised phenolic compounds, such as: phenol, guaiacol, eugenol, and 2-methoxy-4-methylphenol, whilst the biochar gave a relatively high calorific value (26.6 MJ/kg at 240℃), compared with native spruce bark (22.4 MJ/kg), thus showing energy densification. Subcritical water extraction (SWE) yielded organic extractives (3%-8%), sugars (3%-6%) and residues (60%-70%). The organic extractive comprises phenols and furfurals, and a range of sugars, notably glucose and rhamnose, demonstrating the potential of SWE as a hydrolytic process for spruce bark. The sugars can be used for downstream fermentation processes, and the residues may be converted into nanocellulose or used as fuel (bioenergy). Thus, within the context of a potential biorefinery spruce bark affords high-value chemicals (phenols, tannins etc.), fermentable sugars, bio-char and cellulosic materials.