Characteristics and kinetic analysis of pyrolysis of forestry waste promoted by microwave-metal interaction

Highlights: • Biomass pyrolysis exploiting microwave-metal interaction has been proposed. • Kinetic analysis was conducted using a microwave thermogravimetric analyzer. • The number of metals inserted significantly influenced the pyrolysis behavior. • The maximum pyrolysis rate increased by microwave-metal interaction. • Activation energy in the presence of one metal was the lowest. In the present work, a method of pyrolyzing forestry waste (FW) under microwave-metal interaction was proposed. The kinetic analysis of the process was carried out using a microwave thermogravimetric analyzer. The mechanism of FW pyrolysis under microwave-metal interaction was discussed from the perspective of microwave-induced metal discharge and non-discharge processes. The initial pyrolysis temperature T_i reduced, and the maximum pyrolysis rate R_m and pyrolysis characteristic index S increased by employing a method where microwave and metal were coupled. The number of metals inserted also significantly affected the pyrolysis behavior. R_m in the presence of one metal was 92.3% higher than that recorded in the absence of metal. The results of kinetic analysis revealed in the presence of metal, the activation energies at 400 W and 560 W were 51.7% and 57.5% lower, respectively, than the activation energy recorded in the absence of metal. Multiple effects of light, heat, and plasma produced by microwave-induced discharge caused the local pyrolysis of FW. The promotion of FW pyrolysis in the non-discharge stage was primarily caused by the microwave absorption of carbon into heat and the conversion of current on the metal surface into Joule heat.