Characterization of Products from Torrefaction of Sprucewood and Bagasse in an Auger Reactor

Torrefaction experiments of sprucewood and bagasse were performed in an auger reactor at 260 °C, 280 °C, and 300 °C. The chemical composition and pyrolysis behavior of the resulting torrefied biomass were examined in detail. A number of water and lightweight organic compounds were removed from biomass through torrefaction treatment. Chemical component analysis showed that more acid insoluble fibers were formed in torrefied bagasses obtained at 280 and 300 °C, which suggested cross-linking and carbonization of carbohydrates probably took place in bagasse torrefaction. FTIR (Fourier transform infrared) analysis indicated that thermal decomposition of carbohydrate (mainly hemicellulose) predominated over lignin decomposition and the cross-linking of cellulose in torrefaction. XRD analysis revealed that the degradation of amorphous hemicellulose and amorphous regions of cellulose resulted in increases of crystallinity of torrefied biomass obtained below 300 °C. Thermogravimetric analysis revealed that the decomposition of cellulose in torrefied biomass was accelerated by torrefaction treatment. Py-GC/MS analysis exhibited that the yields of acetic acid and other lightweight compounds were lower in pyrolysis of torrefied sprucewood obtained at 300 °C and all torrefied bagasses than those in raw biomass pyrolysis, while the yields of levoglucosan in torrefied biomass pyrolysis were obviously higher. This implied that more stable pyrolysis oil with higher content of levoglucosan could be obtained from torrefied biomass.