Thermogravimetry Analysis for Thermally Decomposed Wood by using Superheated Water Vapor

抄録

Thermogravimetry analysis was carried out for thermally decomposed woods. The carbonizations of a wood were performed by using superheated water vapor, air, nitrogen gas, and CO₂ gas and the effects of the gases on the carbonization were examined in detail. The furnace temperature was 623 K and the pyrolysis time was 100 min with a heating time at about 30 min. Japanese Hinoki was used as a wood sample. The yield of the wood carbonized by using superheated water vapor was about 33.9 wt%, which was smaller than those of nitrogen gas carbonization; 40.2 wt% and CO₂ gas carbonization; 38.5 wt%. The decompositon rate of the wood with the superheated water vapor treatment was faster than that with the nitrogen gas or CO₂ gas treatment. Oxidation and combustion reactions took place in the air condition. The kinetic parameters of the thermal decomposition were determined from experimental thermogravimetric curves using a first-order reaction equation and the calculated activated energies of the decomposition were 62.6, 72.6, and 69.1 kJ mol-1 for the superheated water vapor, nitrogen gas, and CO₂ gas treatments, respectively. The rate constant of the superheated water treatment was found to be larger than that by nitrogen gas or CO₂ gas treatment at low temperatures below 550 K. These results suggest that hydrolysis decomposition occurred in the superheated water vapor treatment. A mathematical model of the decomposition reaction of the wood was presented using a first-order reaction equation and a nonlinear thermal conduction equation. The model showed good agreements with the experimental results of thermal decomposition of the hinoki woods.