Quantification of cashew nut shell pyrolysis products and the effect of extractives on the product distribution

Cashew nut shell (CNS) is an abundant agro-industrial residue characterized by a high content of solvent-extractives compounds, which strongly influences its thermal conversion behavior and the nature of pyrolysis products. In this study, two complementary questions were addressed using a combined experimental strategy that integrated sequential Soxhlet extraction, multi-scale thermogravimetric analysis, and product quantification. CNS was sequentially extracted with hexane, acetone, and water to remove extractives of increasing polarity extractives and generate solid residues of increasing lignocellulosic character. The thermal behavior of raw CNS was investigated under near-intrinsic conditions by micro-TGA using small sample masses, and under macro-scale conditions using whole shells and packed beds of milled CNS to analyze heat- and mass-transfer limitations. Non-condensable gases were quantified using µ-GC, while condensable products were quantified by GC–MS/MS together with water determination. The results show that sequential extraction recovered about 69 wt.% of the initial CNS mass as extractives and altered pyrolysis pathways. Under near-intrinsic conditions, the DTG profile of raw CNS was described by eight Gaussian pseudo-components with R² > 0.988, indicating a multi-step devolatilization pattern. At the gram scale, decomposition peaks broadened, shifted to higher temperatures, and overlapped, indicating transport limitations associated with sample organization. Product quantification showed that extractive removal shifted the condensable fraction from phenolic- and aromatic-rich compositions toward higher formation of acids, furans, sugars, and water, while H₂ formation increased in the gas phase. Overall, these results establish a quantitative relationship between extractive removal, thermal decomposition behavior, and pyrolysis product distribution, and provide a basis for the valorization of CNS in integrated biorefinery applications.