Thermal characterization and pyrolysis kinetics of six types of tropical timber from Central Africa

Abstract

This paper aims to study the compositions, energetic properties, combustion behaviours and pyrolysis kinetics of six tropical hardwoods species from which significant amounts of industrial lignocellulosic wastes are generated in West African countries. The composition of the biomass was studied by determining their percentages of biopolymers (cellulose, hemicelluloses and lignin) and applying FTIR analysis, proximate analysis and ultimate analysis. From the experimental data of the higher calorific value, equations based on the ultimate analysis have been selected since they allow estimating the parameter with a low Average Absolute Error (less than 5%). As regards the behaviour in combustion based in the comprehensive combustibility index (S), the best result was reached by Aucoumea klaineana (S = 3.50 × 10–6 min−2 °C−3), while the worst values were obtained by Alstonia boonei (S = 1.46 × 10–6 min−2 °C−3) and Pterocarpus soyauxii (S = 1.78 × 10–6 min−2 °C−3) which are, in addition, the biomasses with higher ash content. By the same token, Testulea gabonensis and Pterocarpus soyauxii were the species with the highest capacity to produce biochar through pyrolysis. With the mathematical modeling of pyrolysis, maximum activation energies were determined for cellulose (201.3–215.4 kJ/mol), intermediates for hemicellulose plus extractives (191.6–214.9 kJ/mol) and minimum for lignin (63.0–77.0 kJ/mol).