Global Kinetics of the Thermal Decomposition of Materials

Abstract

Abstract Results on the thermal destruction behavior during the decomposition of cellulose under controlled conditions are presented. Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) tests have been carried out on the celluose samples under conditions of various heating rate and surrounding gas environment. Pyrolysis times were also measured for different size particles having different moisture contents in a controlled mixing history reactor (CMHR). The global decomposition kinetics were investigated and it was found that the decomposition process is shifts to higher temperatures at higher heating rates as a result of the competing effects of heat and mass transfer, product diffusion and the reactions kinetics. The Arrhenius parameters for pyrolysis were determined using a first order decomposition reaction of the type, dm = −km dt. It was found that the activation energy, heat of pyrolysis and char yield are a strong function of the heating rate. An increase in heating rate from 5 to 60°C/min resulted in a change of activation energy from 204.19 to 138.31 kJ/mole °C. This heating rate dependence of the kinetics is discussed. The overall decomposition process of the examined materials is generally endothermic. In general, heat transfer, mass diffusion, product evolution, heating rate, temperature and environment are the parameters that control the decomposition process. It was also shown that heat transfer and mass transport have the most effects on the decomposition process.