Abstract: The pyrolysis of sawdust using microwaves is a potential technology for the transformation of biomass waste to high-value bio-energy. The influence of microwave cavities as multimode and single mode to the pyrolysis were investigated, moisture content and heat rate were examined for the influence of microwave processing. It was found that the pore water is the key factor to induce pyrolysis under microwave irradiation; the moisture content can highly increase the pyrolysis possibility and heating rate of the sample bulk. The pyrolysis products depend upon the treatment conditions and moisture content. The mechanism of microwave pyrolysis is quite different from conventional heating pyrolysis. In conventional method, pyrolysis develops toward a direction from the surface to the center, the escape rate of volatile products through the high temperature surface region is slow. Therefore, the pyrolysis carbon will deposit on the pores, and it is difficult to prevent the undesired secondary reactions leading to low liquid yields. On the other hand, microwave heating showed the reverse temperature distribution. Undesired secondary reactions are decreased due to higher volatile gas transfers from the high temperature core region results to clean micro-pores with more open structure and larger specific areas of char than that produced by conventional heating. The liquid product is a mixture of oxygenated aliphatic and aromatic compounds, and the main compositions of the gas product are: CO, CO₂, CH₄ and C₂H₆.

Key words: microwave heating, biomass pyrolysis, bio-energy