Thermogravimetric and kinetic analyses of oil palm empty fruit bunch (OPEFB) pellets using the distributed activation energy model

Abstract

The thermal degradation behaviour and decomposition kinetics of oil palm empty fruit bunch (OPEFB) pellets were investigated using a thermogravimetric analyser and the distributed activation energy model (DAEM). The OPEFB pellets were heated from 30°C to 1000°C at three different heating rates (5, 10, 20°C min-1) under a nitrogen atmosphere. The thermogravimetric-derivative thermogravimetric (TG-DTG) curves revealed that the non-isothermal decomposition of OPEFB pellets occurred in the following three stages: drying (35°C-175°C), active pyrolysis (200°C-370°C) and passive pyrolysis (370°C-1000°C), which resulted in the loss of moisture, volatile matter and char, respectively. The distributed activation energy model was subsequently used to determine the apparent activation energies (E) and pre-exponential factors (A), which ranged from 37.89 kJ mol-1 to 234.05 kJ mol-1 and from 2.05 × 102 min-1 to 3.54 × 1018 min-1, respectively, for conversions of α = 0.05-0.70 during the thermal degradation. The wide E and A distributions obtained from the kinetic analysis are attributed to the complex chemical reactions of pyrolysis. The kinetic analysis revealed the kinetic compensation effect (KCE), with the highest E and A values occurring in the range of α = 0.2-0.4. This result indicates that the active pyrolysis stage is the rate-determining step during the thermal decomposition of OPEFB pellets.