Valorization of brewery spent grain through pyrolysis: Production of thermally stable carbon-rich biochar

Brewery spent grain (BSG) is one of the most abundant agro-industrial residues generated by the brewing industry and represents a promising lignocellulosic feedstock for the production of value-added carbonaceous materials. In this study, the effects of pyrolysis operating conditions on the conversion of BSG into carbon-rich biochar were systematically investigated. The influence of temperature, residence time, particle size, and biomass loading on product yields and biochar properties was evaluated. The resulting materials were characterized by CHN elemental analysis, FTIR, Raman spectroscopy, XRD, and TGA. The results demonstrated that pyrolysis temperature and particle size were the most influential parameters governing carbon enrichment and structural evolution. The highest carbon content (75.31 wt%) was obtained at 700 °C, 120 min, 800 μm particle size, and 8 g biomass loading, indicating effective conversion of the lignocellulosic matrix into a highly carbonized material. FTIR and Raman analyses revealed a progressive reduction of oxygen-containing functional groups and the development of aromatic carbon structures with increasing pyrolysis severity. XRD patterns indicated a predominantly amorphous carbon matrix containing residual mineral phases, while TGA confirmed the enhanced thermal stability associated with the formation of condensed carbonaceous structures. Product distribution analysis showed a strong tendency toward biochar formation, whereas bio-oil yields remained below 4 wt% under all investigated conditions. These findings demonstrate that BSG can be efficiently converted into thermally stable and carbon-rich biochar through pyrolysis. The optimized material exhibits characteristics that make it a promising precursor for the production of activated carbons and other advanced carbonaceous materials.