Revealing low temperature microwave-assisted pyrolysis kinetic behaviors and dielectric properties of biomass components

The kinetic characteristics of microwave-assisted pyrolysis (MAP) of biomass components were investigated in a self-designed microwave thermogravimetric analysis using the KAS model and the master plot method. Compared with conventional pyrolysis, the initial decomposition temperatures of biomass components were reduced by 50-100 degrees C and the fastest weight loss regions were shifted to lower temperatures. The average apparent activation energies of cellulose, hemicellulose, and lignin were 47.82, 44.81, and 51.54 kJ/mol, respectively. Analysis with master plot method suggested the MAP of cellulose followed the 2-D diffusion reaction model, while hemicellulose and lignin could be interpreted by third order-based and 3-D diffusion model. The change of dielectric properties was consistent with the weight loss behaviors of biomass components during the pyrolysis process. The increase of dielectric properties with temperature can lead to a thermal gradient and hot spots within biomass, which accelerated the pyrolysis process at low temperatures and reduced the apparent activation energy. (c) 2018 American Institute of Chemical Engineers AIChE J, 64: 2124-2134, 2018