Impact of torrefaction on the chemical structure of birch wood

Torrefaction is the thermal pretreatment of biomass at temperatures of 200-300 °C in an inert atmosphere with the objectives of improving resistance to biodegradation, reducing hydrophilicity, improving grindability and increasing energy density. In this work, we studied the effect of torrefaction temperature (240-280 °C) on the chemistry of birch wood. The samples were from a pilot plant at ECN, and in that way, they were representative of industrially produced samples. We have measured the concentration of hemicellulose and cellulose; changes in the extractives content and composition; and in the lignin structure. We used acid methanolysis and acid hydrolysis for hemicellulose and cellulose analysis, respectively; Klason lignin method, ¹³C CP-MAS NMR, Dipolar Dephasing NMR, and Py-GC-MS analysis for lignin characterization; and acetone extraction, HPSEC, GC-FID, and GC-MS analysis for extractives characterization. The results provide a more complete picture of the chemical changes in wood by torrefaction.