Chemical composition, morphology, antioxidant, and fuel properties of pine nut shells within a biorefinery perspective

Pine nut shells are waste lignocellulosic residues from the production of edible pine nut kernels that are generally only used for energy production by combustion. Lignocellulosic feedstocks, such as pine nut shells, may be valorized namely by their integration into biorefinery schemes. This article set out to analyze the chemical composition, morphology, antioxidant, and fuel properties of pine nut shells from Pinus pinea obtained from two different locations in Turkey. Pine nut shells have a rough surface with small intercellular pores. Lignin (50–56%) and potassium (1486–1833 mg kg⁻¹) are the principal organic and inorganic components of pine nut shells. The hydrophilic extracts (72.9–80.6% of pine nut shell extractives) contain a high amount of phenolics (up to 455.5–288.4 mg GAE g⁻¹ extract for ethanol and water solvents, respectively) and have good antioxidant properties. The calorific value was 20.6–20.7 MJ kg⁻¹, and pyrolysis activation energy of pine nut shells ranges between 122 and 222 kJ mol⁻¹. The pine nut shells are potential feedstocks for biomass biorefineries integrating thermochemical and chemical platforms, for applications ranging from adsorbents and chemicals to advanced functional materials. Graphical Abstract: [Figure not available: see fulltext.].