Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Abstract

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150 µm and 500 µm) and at different heating rates (10, 15, 20, and 25 °C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150 µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500 µm, whereas 500 µm particle sizes exhibited higher peak temperatures compared to 150 µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27 kJ mol−1 and 3.84 × 105 min−1 for 150 µm particle size, whereas for 500 µm particle size were 97.12 kJ mol−1 and 3.74 × 107 min−1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35 kJ mol−1, 1.29 × 107 min−1, and 88.50 kJ mol−1, 1.32 × 107 min−1 for 150 µm particle sizes. While for 500 µm particle sizes, the E and A were 108.46 kJ mol−1, 3.14 × 109 min−1, and 113.05 kJ mol−1, 7.56 × 109 min−1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.