Thermal behavior and conversion of agriculture biomass residues by torrefaction and pyrolysis

Vegetal biomass is an abundant, readily available and easy to collect resource which can be converted into energy and materials. Biomass residues from agriculture and fruit crop activities, grouped in four classes (stalks, hulls, shells, pits), were subjected to thermal analysis and valorization. Thermogravimetry revealed high homogeneity between shells, large heterogeneity of stalks, and presence of thermally sensitive compounds in hulls. The Fisher weight variable selection analysis indicates that the differences in thermal behavior of biomass residues come from the components with specific biological functions (e.g. light volatiles and oils), while the structural components (hemicelluloses, cellulose and lignin) provide the general trend. This allows sample classification prior deciding on further waste management procedures. Torrefaction at 250 °C concentrated most part of the energy content into solids, with energy yield approaching 100%. Pyrolysis at 550 °C produces biochars with calorific values above 30 kJ/g from shells and pits. Most part of the energy input is used to produce oils with various compositions. Shells can be used to obtain phenolic compounds, hulls for production of aromatics and stalks for furans and ketones. Pits, on the other hand, are suitable raw material when fatty acids are targeted as pyrolysis compounds.