Global kinetics of the thermal decomposition of waste materials

Abstract

Results on the thermal behavior characteristics during the decomposition of cellulose under controlled conditions are presented. Controlled pyrolysis of cellulose is examined using thermogravimetric (TGA) and differential scanning calorimetry (DSC). The tests were carried out under various heating rate conditions and surrounding gas environments. The global decomposition kinetics have been investigated and it was found that the decomposition process is shifted 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=-kmdt. 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/spl deg/C/min resulted in a change of activation energy from 204.19 to 138.31 kJ/mole/spl deg/C. The heating rate dependence of the kinetics is discussed. The overall decomposition process of these 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 is also shown that heat transfer and mass transport have the most effects on the decomposition process.