Comparison of the thermal degradation behaviors and kinetics of palm oil waste under nitrogen and air atmosphere in TGA-FTIR with a complementary use of model-free and model-fitting approaches

Abstract

Palm oil waste from palm oil industry is a promising biomass resource for bio-fuels and bio-chemicals production by biomass thermochemical conversion technology. In this paper, thermogravimetric analyzer coupled with fourier transform infrared spectrometry (TGA-FTIR) were used to investigate the difference of the thermal degradation behaviors and kinetics of palm kernel shell under nitrogen and air atmosphere. Based on the TG analysis, the weight loss in the third stage with the air atmosphere was higher than the nitrogen atmosphere, presenting as weight loss of 12.4wt.% in the carbonization stage of nitrogen atmosphere and 36.9wt.% in combustion stage of air atmosphere. Based on the 3D-FTIR analysis, the dominant components in the nitrogen atmosphere was CO2, CO bond contained organics, and CH or CO bond contained organics, while CO2 and H2O in the air atmosphere. The evolution and formation mechanism of non-condensable inorganic gaseous components (H2O, CH4, CO2 and CO) in the two atmospheres were remarkably different. The H2O and CO2 were mainly contributed by the breakage of OH group and the cracking/reforming reaction of CO and COOH groups in the nitrogen, however higher contents of H2O and CO2 were observed because of the combustion reaction in the air. The CH4 and CO were mainly contributed by the decomposition of OCH3, CH3, CH2 groups and the cracking of carboxyl group in the nitrogen, while the content of CH4 decreased by the diluting of H2O and CO2, and the CO increased by the incomplete combustion reaction in the air. The kinetic triple (mechanism function, activation energy, and pre-exponential factor) was estimated by the combined use of model-free (Ozawa and Kissinger) and model-fitting (Šatava-Šesták) method.