The heat of reaction during the pyrolysis of wood

Abstract

Published estimates of the overall heat of reaction, during the pyrolysis of wood range from q = 370 J/g (endothermic) to q = −1700 J/g (exothermic). Data from differential thermal analyses show that the pyrolysis of lignin is more strongly exothermic than that of cellulose; this is consistent with the data from two sets of experiments with bulk samples of wood which suggest that q = −800 J/g for lignin and q = −80 J/g for cellulose, and that lignin contributes 65% of the exothermic heat of reaction of pyrolyzing wood. Data from other experiments in which bulk samples of wood are heated to temperatures greater than 320°C give reasonably consistent values of q = −(160–240) J/g. Where the maximum temperature achieved is less than 320°C, the value obtained for the heat of reaction is highly dependent on conditions and may rise to −1700 J/g. The role of primary and secondary pyrolysis reactions in determining the overall heat of reaction and the influence of the physical structure of the wood are discussed.