New exploitation strategies of the by-products deriving from the hazelnut supply chain

Hazelnut processing industry generates significant waste streams, in particular cuticles and shells. Extractives are the main components of the cuticle fraction (~36 wt%), mainly including polyphenols and fatty acids, which can be advantageously used in the pharmaceutical and cosmetic industry. Focusing on the shell fraction, this represents ~50 % of the total nut weight (about 273 thousand metric tons, based on the 2021-2022 worldwide data on hazelnut production). Differently from cuticles, shells are rich in recalcitrant lignin (~38 wt%), in addition to cellulose and hemicellulose (each component accounting for ~23 wt%). Up to now, this waste, which is preponderantly produced in Italy and Turkey, is mostly underutilized, being limitedly used as a boiler fuel for domestic heating and for landscaping. On the other hand, these both fractions of hazelnut shells can be successfully valorized and, in this perspective, we have proposed a new cascade approach, converting its cellulosic fraction into levulinic acid (∼9-12 wt%), and recovering an abundant carbonaceous hydrochar as the final waste (∼45 wt%), mainly composed of aromatic and furanic units. In this work, the exploitation of this waste biomass-derived hydrochar for environmental applications has been investigated, after its pyrolysis and chemical activation treatments (H3PO4, ZnCl2, KOH, NaOH). The synthesized new active carbons (ACs) have been properly characterized and used as adsorbents for CO2 and methylene blue removal. This proposed integrated approach makes possible to fully exploit the hazelnut shell feedstock, smartly closing the biorefinery cycle of the hazelnut wastes, in a sustainable and circular perspective.