Impact of torrefaction on chemical structure of woody biomass

Torrefaction is a thermochem. pretreatment of biomass at temps. of 200-​300 °C in an inert atm.  This method improves the final characteristics of the fuel, amongst them resistance to biodegrdn., less hydrophilicity, better grindability and higher energy d.  In spite of the available information about torrefaction, several aspects of thermal effect on wood needs further research, including the chem. changes of wood constituents during torrefaction.  In this study with birch chips torrefied in a pilot reactor at ECN, The Netherlands, cellulose and hemicellulose degrdn. was measured by sugar anal. and acetone extractable material was measured by gravimetry.  Changes in the lignin structure were measured by ^CNMR.  Pentosan's decrease by more than 50​% already at 240 °C and cellulose degrdn. is less than 50​%, while mass loss increases from 19 wt.​% to 35 wt.​%, Fig.1.  Acetone extn. shows a significant increase in total amt. of extractives by gravimetry at mild torrefaction and then a gradual decrease at higher temps.  The sharp increase at mild torrefaction is due to degrdn. of carbohydrates and lignin polymers to their monomers.  Anal. by GC-​MS shows an increase in extractives such as lignans and vanillin among others.  A better understanding of the chem. of torrefaction has implications for both its usage in the energy field, and perhaps other biorefinery applications such as fine chems.