Pyrolysis kinetics and mechanism study of walnut shell via Asym2sig deconvolution, Sestak-Berggren reconstruction,...

Understanding the kinetics of pyrolysis and the mechanisms behind product formation from walnut shell (WS) is crucial for enhancing the thermochemical conversion processes of biomass and promoting the sustainable utilization of agricultural by-products. Based on thermogravimetric data, by applying the Asym2sig function to deconvolute asymmetric pyrolysis curves, this study accurately identified three independent component reactions with divergent thermal behaviors, providing a robust methodology to reveal the staged and intricate nature of WS pyrolysis. Consequently, four isoconversional methods were leveraged to rigorously derive the kinetic and thermodynamic properties of the pyrolysis process. This provides a basis for a deeper understanding of the mechanism involved in the pyrolysis of WS. To address the limitations of standard idealized models in capturing the complexity, the Sestak-Berggren model was adopted to analyze reaction mechanisms, yielding reliable kinetic descriptions. The optimal models for hemicellulose, cellulose, and lignin were established as: f₁(α₁) = α₁^2.0201(1-α₁)^1.1289[-ln(1-α₁)]^-2; f₂(α₂) = α₂^0.5786(1-α₂)¹[-ln(1-α₂)]^-0.4321; f₃(α₃) = α₃^-2.4701(1-α₃)³[-ln(1-α₃)]^0.0693. Furthermore, the connection between product distribution and the pyrolysis process was further clarified from three distinct viewpoints by utilizing TG-MS, Py-GC/MS, and XPS, including gaseous product evolution, liquid-phase product composition, and the surface functional groups of the resulting char. On this basis, an integrated mechanistic framework of WS pyrolysis was constructed, offering robust data support for the valorization of waste WS into high value chemicals..