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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 °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 13 C crosspolarization 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.

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Biomass chemical looping gasification (BCLG) is a novel and promising technology for syngas production, in which lattice oxygen in oxygen carriers (OCs) reacts with biomass. OCs can continuously supply oxygen for biomass gasification using a redox cycle between different reactors, and the reduced OC can serve as a good catalyst for biomass tar and char cracking, improving the gasification efficiency. The notable advantages of BCLG have attracted attention around the world, particularly in China. Chinese researchers have become the major drivers of the development of BCLG technologies. The experience gained from the experimental tests of BCLG in China is valuable for the further development of BCLG. In this review, we mainly focus on the biomass feedstock, the OC, the tar yield, the reactor, and the results of the BCLG tests in Chinese studies. On the basis of those findings, we summarize the criteria for biomass and the OCs in BCLG, and potential directions for reactor development are briefly discussed. In general, the mechanism of BCLG has been investigated in many studies, and the effects of the operating conditions are relatively well-understood. However, there are still few reports on BCLG units that have potential for industrial application. The controllable composition of syngas is worthy of further investigation, and this is required for downstream utilization. Additionally, as a result of the low pollutant emission, chemical looping gasification of solid wastes might be available in the future.

Chemical looping gasification (CLG) was investigated in a 10 kW th interconnected fluidized bed reactor with Fe 2 O 3 /Al 2 O 3 as oxygen carriers (OC) and pine sawdust as fuel. The effects of the operation temperatures and sawdust feeding rate on the gas composition, cold gas efficiency, and carbon conversion rate of biomass were investigated. The fresh and used oxygen carrier particles were characterized by means of XRD, SEM, and BET. The results indicated that the sawdust was partially oxidized to syngas by lattice oxygen from the oxygen carrier. The syngas yield, cold gas efficiency, and carbon conversion increased with increasing operating temperature. Also, the concentrations of CO, H 2 , and CH 4 in the syngas increased at the elevated temperature, while the CO 2 fraction decreased. The feeding rate of biomass has a significant impact on the syngas composition and cold gas efficiency. There was an optimal value of feeding rate at 2.24 kg/h corresponding to the maximum cold gas efficiency in the tested reactor system. XRD analysis showed that the oxygen carrier particles were reduced to Fe 3 O 4 from Fe 2 O 3 in the course of the CLG reactions. BET results indicated the surface area, total pore volume, and average pore size of the oxygen carrier particles increased initially and then slightly decreased with the reaction proceeding, due to the interstice and thermal sintering. However, the OC samples were well regenerated and maintained a good crystalline state after 60 h of operation, which illustrated that the synthesized oxygen carrier had a stable reactivity and good resistance to agglomeration.

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