Thermal Degradation and Kinetic Study of Cassava Rhizome for Torrefaction Application

Abstract

Thermal decomposition kinetics of cassava rhizome (CR) is an important key in the torrefaction process. Kinetic analysis of the cassava rhizome torrefaction was investigated using a thermogravimetric analyser in which CR weight loss is measured under nitrogen atmosphere from ambient temperature to 973K at 5, 10, 20, and 30 K•min-1. Two model-free iso-conversional methods, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) have been used to determine activation energies as a function of the extent of degradation. In this work, the CR particles were separated into 3 study groups, 0.125-0.425 mm, 0.425-0.850, and 0.850-2 mm. The average activation energies calculated by using the methods are relatively similar for all three-particle size samples. The average activation energy values calculated by FWO method were 170.509, 172.593, and 130.149 kJ•mol-1, respectively. These data were comparable to KAS method in which the average activation energy numbers were 170.647, 177.276, and 128.620 kJ•mol-1. Both methods indicated that the activation energy was relatively constant until the conversion of 0.5. The pre-exponential factor values from FWO and KAS ranged 4.87E+17 s-1 and 7.28E+14 s-1, respectively. The experimental results show that kinetic parameters from both methods are suitable and effective to help describe the thermal degradation of the cassava rhizome.