Catalytic Fast Pyrolysis of Biomass Pretreated by Torrefaction with Varying Severity

Pretreatment of corncobs using torrefaction was performed in a tubular reactor with varying reaction temperature (210, 240, 270, or 300 °C) and residence time (20, 40, or 60 min). The torrefied corncobs were subsequently catalytically fast pyrolyzed over nanosized HZSM-5 in a semibatch pyroprobe reactor. The torrefied corncobs were characterized by elemental analysis, thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (FTIR), and FTIR. The aromatic production was online analyzed by gas chromatography mass spectroscopy. The effect of torrefaction severity on product distribution and aromatic selectivity from catalytic fast pyrolysis of torrefied corncobs was investigated. The experimental results show that torrefaction can serve as an effective thermal pretreatment for improving the selectivity of BTX (benzene, toluene, and xylenes). Light and mild torrefaction (torrefaction at 210 and 240 °C) has little impact on the aromatic yield. However, severe torrefaction (torrefaction at 270 or 300 °C) can lead to the sharp increase of coke yield and reduction of aromatic yield. The results could be explained by the serious cross-linking and charring of corncob under severe torrefaction conditions. The optimal torrefaction condition is 210–240 °C with residence time of 40 min.