Kinetic Analysis of Tropical Lignocellulosic Agrowaste Pyrolysis

The thermal behavior of three Colombian agricultural residues was studied by non-isothermal thermogravimetric analysis (TGA) at various heating rates. An approach using a combined kinetics parallel reaction model and model-free isoconversional methods proved to be suitable to determine the pyrolysis kinetic parameters of biomasses with different macromolecular composition and H/C and O/C ratios near 1.5 and 0.8, respectively. Fraser-Suzuki functions representing the derivative TGA (DTG) of hemicellulose, cellulose and lignin showed a very good agreement with the experimental data. The calculated apparent activation energy of biomass pseudo-components evidenced no dependence on the reaction extent in all the conversion range, validating the use of master plots for decomposition mechanism identification. Pseudo-hemicellulose, pseudo-cellulose, and pseudo-lignin showed to be close to a second-order kinetic model, a random scission, or an Avrami-Erofeev model and a high-order kinetic model, respectively. Comparing the three feedstocks, the apparent activation energy of the pseudo-components was in the order: bamboo guadua E-a < coconut shells E-a < oil palm shells E-a . The results show that even when sample elemental composition is very similar, macromolecular constituents, in particular lignin, could have an impact in the biomass decomposition rate and apparent activation energy. For the three studied materials, the model fitting error below 10% showed that the calculated kinetic parameters are suitable for the description and prediction of the biomass thermal decomposition.