in Wiley InterScience (www.interscience.wiley.com).The reaction mechanism for gas and tar evolution in the steam gasification of cellulose, lignin, xylan, and real biomass (pulverized eucalyptus) was investigated with a continuous cross-flow moving bed type differential reactor, in which tar and gases can be fractionated according to reaction time. In the steam gasification of real biomass, the evolution rates of water-soluble tar (derived from cellulose and hemicelluloses) and water-insoluble tar (derived from lignin) decrease with increasing reaction time. It was found that the evolution of water-soluble tar occurs earlier than in the gasification of pure cellulose, indicating an interaction of the three components. The predicted yield of water-insoluble tar is substantially less than that of real biomass. This implies that the evolution of tar from the lignin component of biomass is enhanced, compared with pure lignin gasification, by other components. The gas evolution rate from real biomass is similar to that predicted by the superposition of cellulose, lignin, and xylan.

We developed a drop-tube reactor with a separation unit containing a quartz glass filter that is capable of fractionating alkali and alkaline earth metals (AAEMs) released as solid particle, vapor, and combined with water-soluble and water-insoluble tar. The ratio of released AAEMs in pulverized wood chips that had been steam-gasified was examined by changing the temperatures of the reactor and the separation unit independently. We found that approximately 63-80% of the released AAEMs were combined with tar. In addition, as the gasification temperature increased, the yields of the AAEMs combined with water-soluble and water-insoluble tars remained nearly constant, even though the amount of recovered water-soluble tar decreased as a result of secondary decomposition. This finding implies that AAEMs released by the secondary decomposition of watersoluble tar are fine particles that cannot be collected in a quartz glass filter. Additionally, yields of condensed AAEMs substantially increased as the gasification temperature increased, implying that the evolution of AAEMs from char was enhanced at high gasification temperatures. Evaluation of the water-soluble and water-insoluble tar using a Fourier transform infrared spectrometer (FTIR) and an elemental analyzer indicated that AAEMs likely combine with the OH groups of carboxylic acids and phenols in water-soluble tar. This finding infers that the AAEMs recovered from water-insoluble tar are present in aromatic compounds that are derivatives of benzene, xylene, furfural, and naphthalene in the product gas.

The pyrolysis of cellulose was studied using a novel CCDR in which tar and gases can be fractionated according to the reaction time. Similar trends of evolution behavior were observed for both tar and lowmolecular-weight gases in the pyrolysis of cellulose at 673 K. The evolution of tar and low-molecular-weight gases achieve a peak at 20-30 s, converting depolymerizing cellulose to nascent char. The dehydration of nascent char produced by depolymerization and devolatilization was found to take place after the devolatilization is completed.