Thermochemical valorization of biomass into sustainable biomaterials and biofuels: The potential of AAEMs rich mediterranean wastes

• Co-pyrolysis of CC and PGP/PC for biochar and bio-oil production was studied. • Co-pyrolysis of lignocellulosic biomass improved bio-oil quality. • CC-PGP showed the maximum biochar and bio-oil yields. Mediterranean biomass presents distinctive features compared to the Northern lignocellulosic biomasses, which are typically exploited for thermochemical conversion. The present work addresses slow pyrolysis and co-pyrolysis of three biomass largely available in the Mediterranean regions, namely cactus cladodes (CC), pomegranate peels (PGP) and pine cones (PC) in a fixed bed batch. Notably, CC, is characterized by a large content of ashes (˃20 %), and is particularly rich in alkali and alkaline-earth metals (AAEMs), which, upon co-pyrolysis, could act as catalysts and affect the chemical composition of the bio-oil, as well as the properties and yields of the biochar. The results indicated that co-pyrolysis decreases the gas yield and increases the bio-oil and biochar yields. The bio-oils produced from either PGP or PC are complex mixtures of chemicals, including phenols, aromatics, aliphatics and anhydrosugars. Co-pyrolysis of PC with CC increases the content of phenol and aromatics in the bio-oil, while decreases the content of retene derivatives. Co-pyrolysis of PGP with CC increases the content of phenols and reduces that of furfural and anhydrosugars. The biochars produced from co-pyrolysis of CC with either PGP or PC have low O/C and H/C ratios, high alkalinity and large content of Ca, K, Mg and P.