Rapid pyrolysis of wood block by microwave heating

Pyrolysis of cylindrical wood blocks (diameter: 60-300 mm; weight: 80-12 000 g) by microwave irradiation has been studied using two microwave ovens (1.5 and 3 kW). The pyrolysis of wood can be performed within approximate to15 min for wood of 100 min in diameter. It was demonstrated that temperature distribution, heat transfer and mass transfer are quite different from a conventional heating method. The char prepared by the microwave heating has a large specific surface area (approximate to450 m(2) g(-1)). Scanning electron microscopy shows that there are few pyrolysis carbon-particles in the micropores of the char. The char yields from cylindrical wood blocks with different diameters can be correlated by an equation. in which the electric power consumption per weight is inversely proportional to the square of the wood block diameter. In other words, a larger wood block can be pyrolyzed with less electric power consumption per unit weight than a smaller wood block. The yields of tar were 15-30 wt.%. The tar contained levolucosan. The concentration of levoglucosan in the tar was 5-9 wt.%. (C) 2003 Elsevier B.V. All rights reserved.