Effect of Torrefaction Temperature on Product Distribution from Two-Staged Pyrolysis of Biomass

Two-staged biomass pyrolysis process consisting of torrefaction and subsequent fast pyrolysis is proposed to obtain high quality bio-oil. The purpose of this study is to evaluate the effect of torrefaction temperature on yield, composition, and physical properties of the liquid of torrefaction and bio-oil. Torrefaction of pine was conducted on an auger reactor at 240–320 °C with a residence time of 40 min to produce liquid of torrefaction and torrefied pine. Then, the torrefied pine was fast pyrolyzed in a bubbling fluidized bed reactor at 520 °C to produce bio-oil. Torrefied pine was characterized by chemical composition analysis and Fourier transform infrared (FTIR) spectroscopy. The liquid of torrefaction was determined by gas chromatography (GC); bio-oil was characterized by gas chromatography mass spectroscopy (GC-MS) and 13C nuclear magnetic resonance spectrometry (NMR). The experimental results show that water content in liquid of torrefaction and water and acetic acid content in bio-oil decreased with elevated torrefaction temperature, while the yield of liquid of torrefaction, aromaticity, higher heating value, and density of bio-oil increased. However, the yield of total liquid (sum of liquid of torrefaction and bio-oil) decreased significantly with elevated torrefaction temperature because of the cross-linking and carbonization of torrefied pine.