Thermochemical and elemental characterization of aromatic seed residues for solid biofuel applications in a circular economy context

• Aromatic seed waste (ASW) has high valorisation potential due to its rich composition. • FTIR analysis is a robust tool for spectral fingerprinting and biomass classification. • ASW's calorific value ranges from 13.55–20.31 MJ/kg, similar to woody biomass. • ASW moisture is below 10 %, but ash content varies between 4–20 % (w/w). • TGA analysis revealed key thermal differences for biomass energy valorisation. Aromatic seed waste (ASW) has high valorisation potential due to their rich composition. Biorefineries can optimize ASW by extracting valuable aromatic compounds through pyrolysis and gasification, reducing waste and promoting sustainability. This study explores the thermal valorisation of 16 different aromatic seed residues, assessing their potential as a solid fuel and in pyrolysis. Characterization following ISO 18,122 standards showed a moisture content below 10 % (w/w), while ash content varied between 3.13 % and 18.80 % (w/w), exceeding normative limits in some cases. The higher heating value (HHV) ranged from 13.55 to 20.31 MJ/kg, similar to woody and other herbaceous biomass, with higher-density benefits for handling and storage. Thermogravimetric analysis (TGA) identified two main degradation stages: 30–250 °C, linked to simple carbohydrate decomposition, and 250–500 °C, associated with lignocellulose breakdown. These variations impact combustion and pyrolysis performance. Elemental analysis revealed an H/C ratio between 1.58 and 1.90, when this is greater than 1.7, it indicates better heating value in combustion processes and better bio-oil quality in pyrolysis processes. Volatile content of about 70 % (w/w), these results show a sufficiently high volatile matter content, similar to that of other biomasses, which would improve ignition at low temperatures, making combustion more efficient. This property favours bio-oil production, yielding a product rich in aromatics. The results highlight ASW’s potential as a renewable energy source and its suitability for thermal conversion processes.