Thermogravimetric analysis of pretreated Turkish lignites

Abstract

The kinetics of nonisothermal pyrolysis of raw, demineralized or oxidized Turkish lignites have been investigated by thermogravimetry, differential thermal analysis and differential scanning calorimetry. The analyses were carried out in an inert atmosphere or in air atmosphere. The weight loss data indicate that pyrolysis characteristics of the lignites and the prevailing kinetic mechanism vary depending on temperature. The weight loss rates show essentially two regimes, and the major weight loss occurs in the range of 300°C–650°C. The results for the low temperature region (T<200°C) suggest that the weight loss may be represented by 1.2–1.4-th order of reaction with an activation energy of approximately 15–35kJmol−1. The differential thermal analysis and the differential scanning calorimetry data gave similar values for the overall reaction order and activation energies for this temperature region. At the higher temperature region (T>300°C), 1.2–1.8-th order of reaction shows a good fit with the weight loss data. The values of the estimated activation energies for this region vary from approximately 40 to 85kJmol−1 depending on the type of sample. However, the differential thermal analysis data suggest that the overall reaction order is around 1.0–1.2 and the effective activation energies vary approximately from 170 to 250kJmol−1.