Impact of Torrefaction on the Chemical Structure and Catalytic Fast Pyrolysis Behavior of Hemicellulose, Lignin, and Cellulose

To understand the effect of torrefaction severity on structure changes of hemicellulose, cellulose, lignin and their subsequent catalytic fast pyrolysis (CFP) behavior, torrefaction of lignin, hemicellulose, and cellulose was performed in a tubular reactor with different reaction temperatures (210-300 degrees C) and residence times (20-60 min). The experimental results show that the rank order of thermal stability during torrefaction was cellulose > lignin > hemicellulose. The torrefied hemicelulose, cellulose, and lignin were subsequently catalytic-fast-pyrolyzed over HZSM-5 in a semi-batch pyroprobe reactor. The effects of the torrefaction temperature and residence time on aromatic yields and selectivity from CFP of torrefied hemicellulose, cellulose, and lignin were investigated. The experimental results showed that torrefaction can cause the reduction in the aromatic yield and increase in benzene, toluene, and xylenes (BTX) selectivity from CFP of torrefied hemicellulose and lignin. It has little impact on CFP of torrefied cellulose. The results can be explained by Fourier transform infrared (FTIR) spectroscopy and C-13 cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) analysis of torrefied hemicellulose, cellulose, and lignin. The rank order of structure change during torrefaction was hemicellulose > lignin > cellulose. The devolatilization and polycondensation of hemicellulose and lignin during torrefaction could be mainly responsible for the yield penalties of aromatic production from CFP of torrefied hemicellulose and lignin.